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Inhaltsverzeichnis

Frontmatter

Advanced Analysis

Aberration-Corrected STEM Study of Precipitates in an Al-Mg-Si-Ge-Cu Alloy

Precipitation in a Mg-rich Al-Mg-Si-Ge-Cu alloy was investigated using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy. The precipitates were needle or lath shaped with the longest dimension parallel to <001>Al. The precipitates had no repeating unit cell when viewed along this direction. However, the precipitate structure in projection consisted of a hexagonal network of mixed Si and Ge columns, with Mg, Al, and Cu columns occupying specific sites in between the network columns. The Cu columns appeared with the same local arrangement of atomic columns as in Al-Mg-Si-Cu precipitates, and the Cu-free regions consisted of structural units with Mg and Al at specific sites. The proposed atomic model is supported by image simulations.

Ruben Bjørge, Sigmund J. Andersen, Calin D. Marioara, Joanne Etheridge, Randi Holmestad

Diffraction-Amalgamated Grain-boundary Tracking (DAGT) technique and its application to an aluminum alloy

A novel method which provides accurate analysis of individual grains during deformation has been developed by amalgamating X-Ray diffraction (XRD) microscopy with grain boundary tracking (GBT). XRD and GBT are both non-destructive in-situ analysis techniques for characterizing bulk materials, which can be carried close to the point of fracture of metals. DAGT provides accurate information about individual grain orientations from near field XRD analysis, whilst the GBT accesses 1 micron level analysis of grain morphologies in 3-dimensions. XRD employed an X-ray pencil beam to analyze a specimen of Al-3mass%Cu before and after deformation. The morphology of the grains were determined by computer tomography (CT) imaging and liquid metal wetting, after which GBT provided an accurate description of the position and morphology of the grains. The integrated technique, DAGT, identified which diffraction spots were related to which grain, making it possible to describe misorientation between grains.

Darren J. LeClere, Takanobu Kamiko, Yasuharu Mizuseki, Yoshio Suzuki, Akihisa Takeuchi, Kentaro Uesugi, Masakazu Kobayashi, Hiroyuki Toda

Effect of Composition and Pre-Ageing on the Natural Ageing and Paint-Baking Behaviour of Al-Mg-Si Alloys

Two 6xxx series aluminium alloys were designed to have the same total solute content but very different Mg/Si ratios. An excess Mg alloy (Al-1.2Mg-0.5Si) and an excess Si alloy (Al-0.5Mg-1.2Si) were cast and rolled to 1 mm thick sheet. Both were naturally aged for 30 days and then artificially aged for 0.5 h at 170°C to simulate an automotive body panel paint-baking cycle. In order to improve the paint-bake response, pre-ageing treatments of 20 s at 200°C and 2 h at 100°C were tested and evaluated using atom probe tomography, transmission electron microscopy and hardness testing. The results show that the excess Mg alloy tends to have coarser clusters/precipitates than the excess Si alloy, and that the Mg/Si ratio of the smaller clusters is closer to the alloy composition than that of the larger clusters and precipitates. Depending on the pre-ageing treatment, both alloys can give good paint-baking responses.

Paul A. Rometsch, Sam X. Gao, Malcolm J. Couper

Improvement in the Characterization of the 2099 Al-Li Alloy by FE-SEM

This paper describes how state-of-the-art Field-Emission Scanning Electron Microscopy (FE-SEM) can contribute to the characterization of the 2099 aluminum-lithium alloy, and metallic alloys in general. Investigations were carried out on bulk and thinned samples. BSE imaging at 3kV and STEM imaging at 30kV along with highly efficient microanalysis permitted to correlate experimental and expected structures. Although our results confirm previous studies, this work points out possible substitutions of Mg and Zn with Li, Al and Cu in the T1 precipitates. Zinc and magnesium are also present in “rice grain” shaped precipitates at the grain boundaries. The versatility of the FE-SEM is highlighted in that it can provide information at the macro and micro scales with relevant details. Its ability to probe the distribution of precipitates from nano-to micro-sizes throughout the matrix makes Field-Emission Scanning Electron Microscopy a suitable technique for the characterization of metallic alloys.

Nicolas Brodusch, Michel L. Trudeau, Pierre Michaud, Mathieu Brochu, Lisa Rodrigue, Julien Boselli, Raynald Gauvin

Towards new aluminium alloys through advances in atom probe microscopy

The development of Al alloys has through the years significantly relied on advances in materials characterization techniques to allow deeper understanding of microstructural properties. Today, alloy development has reached a level where many of these properties are no longer discussed on micrometre or even nanometre scale, but rather on atomic scale. Consequently, atom probe microscopy (APM) has received greatly increased attention. APM is a powerful characterization technique with unmatched capability of three dimensional (3D) atomic scale studies of the structure and chemistry of materials. This presentation focusses on our on-going development of APM analysis techniques for studies of Al alloys and also demonstrates why APM has earned a vital position in the development road-maps for new alloys. Key aspects of the enabling science (emphasized in this abstract) are presented and applied to studies of Al alloys. Importantly, it is also shown how the insight gained can be used to explain and improve the alloys’ engineering properties.

L. Viskari, G. Sha, S. P. Ringer

Nano-Scale Characterization of Al-Mg Nanocrystalline Alloys

Materials with nano-scale microstructure have become increasingly popular due to their benefit of substantially increased strengths. The increase in strength as a result of decreasing grain size is defined by the Hall-Petch equation. With increased interest in miniaturization of components, methods of mechanical characterization of small volumes of material are necessary because traditional means such as tensile testing becomes increasingly difficult with such small test specimens. This study seeks to characterize elastic-plastic properties of nanocrystalline Al-5083 through nanoindentation and related data analysis techniques. By using nanoindentation, accurate predictions of the elastic modulus and hardness of the alloy were attained. Also, the employed data analysis model provided reasonable estimates of the plastic properties (strain-hardening exponent and yield stress) lending credibility to this procedure as an accurate, full mechanical characterization method.

Evan Harvey, Leila Ladani

Muon Spin Relaxation and Positron Annihilation Spectroscopy Studies of Natural Aging in Al-Mg-Si Alloys

Muon spin relaxation (µSR) is sensitive to magnetic fields from atomic nuclei, making it suitable for studying vacancies and solute clustering inside aluminium alloys. Positron annihilation spectroscopy (PAS) gives complimentary information about the electron density. We have conducted µSR and PAS experiments on an Al alloy with 1.07 at.% Mg and 0.53 at.% Si during natural aging after solution heat treatment. Three stages of positron lifetime change are visible, while the muon depolarization shows a decrease through the first two of these. This is explained on the basis of vacancy migration, vacancy-solute binding and solute clustering.

Sigurd Wenner, Kenji Matsuda, Katsuhiko Nishimura, John Banhart, Teiichiro Matsuzaki, Dai Tomono, Francis L. Pratt, Meng Liu, Yong Yan, Calin D. Marioara, Randi Holmestad

Monitoring Precipitation during Rapid Quenching of Aluminium Alloys by Calorimetric Reheating Experiments

Several age hardening aluminium alloys, like high alloyed 2XXX, 6XXX and 7XXX alloys require high critical quenching rates of some 100 K/s from solution annealing to suppress premature precipitation and achieve maximum strength after aging. Knowledge of the precipitation behaviour during quenching is crucial for the design of quenching processes of aluminium alloys. For monitoring the precipitation behaviour during moderate quenching, a calorimetric method (0.01 to 5 K/s) has already been successfully developed. New Differential Fast Scanning Calorimeters (DFSC, up to some 106 K/s) allow rapid quenching of aluminium alloys, but due to weak precipitation reactions the quenching results can hardly be evaluated. Hence, a new method has been developed, to monitor precipitation during rapid quenching of aluminium alloys by calorimetric reheating experiments. Quenching and reheating experiments of high alloyed, quench sensitive aluminium alloys, like 7049A will be presented.

Olaf Kessler, Davit Zohrabyan, Benjamin Milkereit, Christoph Schick

Hydrogen Depth-Profiling and Desorption Kinetics in Rapidly Solidified Al-Fe Alloys

Hydrogen surface segregation and trapping in rapidly solidified Al-0.2; 0.5 at % Fe alloys has been studied through elastic recoil detection technique, Rutherford backscattering spectroscopy and thermal desorption spectroscopy. It was detected that most hydrogen was localized in the subsurface regions (400 nm) and estimated to be 3.6 at % in Al-0.2 Fe alloy. Strong hydrogen segregation on air-side surface in alloy showed increase in its content up to 9.6 at % after heat treatment at 500°C. Our results indicated that solute-vacancy interactions and microstructural features affect hydrogen behaviour in Al-Fe alloys. The hydrogen trapping at iron atoms in the substitutional sites was concluded to be predominant.

Iya I. Tashlykova-Bushkevich, Goroh Itoh

Three-Dimensional Analysis of Microstructure in Cast Aluminium Piston Alloys

The 3D architecture of intermetallics distribution in two model cast aluminium piston alloys is examined using synchrotron X-ray microtomography and advanced image analysis tools. The highly complex morphology and 3D interconnectivity of intermetallics is delineated using advanced 3D image analysis tools. A novel technique which circumvents quantification difficulties associated with the high interconnectivity is employed for quantifying intermetallic particles. The intermetallic particle size distribution is then analysed using extreme value statistics to predict the maximum particle size in a sample of S-N fatigue specimens and subsequently, the lower bound fatigue life in the given sample.

T. O. Mbuya, I. Sinclair, K. A. Soady, P. A. S. Reed

Dislocation Density Changes in Ultrafine-grain Aluminum during Tensile Deformation

It has been reported that the tensile strength of UFG aluminum is several times higher than that of coarse-grain aluminum, and that UFG aluminum exhibits unique mechanical phenomena under tensile deformation. This implies that dislocation behavior in UFG aluminum differs from that in coarse-grain aluminum. In this research, changes in dislocation density during tensile deformation were examined by in-situ X-ray diffraction, and the effect of grain size on dislocation multiplication behavior was investigated. In samples with smaller grains, the increase in dislocation density during tensile deformation was larger and the decrease in dislocation density after unloading via fracture was also larger.

Hiroki Adachi, Yoji Miyajima, Akinobu Shibata, Daisuke Terada, Nobuhiro Tsuji

Casting

Study on DC Casting Process of Three-Layer Composite Ingots of 4045/3004/4045 Aluminum Alloys

In this study, experiments are combined with numerical simulation to study the temperature field and flow field during the casting process of 4045/3004/4045 three-layer composite ingots with section of 500mm×420mm. The effects of casting temperature, casting speed, contacting height and cooling intensity of cooling plate on the casting process were discussed. The macromorphologies and microstructures of the composite ingots, the temperature distribution and the element distribution in the interface zone were investigated, also the interface bonding strength was measured. The optimal parameters for casting composite ingots were obtained. Results show that the solid supporting layer formed on the cooling plates plays a key role in the casting process of composite ingots. The solid supporting layer can prevent the blending of two melts by resisting the impact of alloy melt, which ensures the stable casting process and casting high quality composite ingots.

Jianzhong Cui, Haitao Zhang, Ke Qin, Huixue Jiang

Study on Electromagnet-Air Knife DC Casting Process of Large-Size AA 7055 Aluminum Alloys

In this paper, Low frequency electromagnetic field and air knife are applied simultaneously to produce large-size AA 7055 aluminum alloy ingots during DC casting. Moreover, the effects of low frequency electromagnetic field and air knife on macro-physical fields during DC casting as well as microstructure and crack in the ingots are studied and analyzed by the numerical and experimental methods. Comparison of the calculated results indicates that applying electromagnetic field can modify the flow direction and increase the velocity of melt flow and homogenize the distribution of temperature in the sump, and applying air knife can homogenize the distribution of temperature and decrease the stress and strain in the solidified ingots. Further, the microstructure of the billet is refined remarkably and the crack is eliminated by applying electromagnetic field and air knife during DC casting because of modification of the macro-physical fields

Haitao Zhang, Jianzhong Cui, Hiromi Nagaumi

Development of Large-size Ultrasonic Sonotrodes for Cavitation Treatment of Molten Metals

This work presents results of the development of large-size high-amplitude ceramic sonotrodes destined for use in cavitation treatment of molten metals. The sonotrodes were characterized for their vibration amplitude, erosion resistance and cavitation-producing ability in aluminum melts. The ability of the sonotrodes to refine the grain structure was examined by applying them to the DC casting of Al-Si hypereutectic alloys. The results showed that the sonotrodes have excellent performance characteristics, and they possess far superior erosion resistance and endurance than those made of such high-resistance refractory metals as Nb alloys.

Sergey Komarov, Yasuo Ishiwata

Microstructural Evolution in Intensively Melt Sheared Direct Chill Cast Al-Alloys

The work presented here introduces the novel melt conditioned direct chill casting (MC-DC) technology, where intensive melt shearing is applied to the conventional direct-chill casting process. MC-DC casting can successfully produce high quality Al-alloy billets. The results obtained from 80 mm diameter billets cast at speed of 200 mm/min show that MC-DC casting of Al-alloys, substantially refines the microstructure and reduces macro-segregation. In this paper, we present the preliminary results and discuss microstructural evolution during MC-DC casting of Al-alloys.

S. Jones, A. K. Prasada Rao, J. B. Patel, G. M. Scamans, Z. Fan

The grain refinement of 7050 alloy using al-5ti-1b and al-3ti-0.15c grain refiners

The morphologies of particles in commercial Al-3Ti-0.2C and Al-5Ti-1B alloy used in the refining experiments were investigated and the grain refining response to 7050 alloy was studied in this paper. The results show that Al-3Ti-0.2C master alloy failed to produce an adequate grain refinement at an equal addition level to that which sufficed with the Al-5Ti-1B alloy. With increasing the holding time, settlement phenomena of TiC particles and TiB2 particles in 7050 melt were both investigated and the settling time of the particles did not match with the results calculated by Stoke’s law. Based on the experimental results, the efficiency of grain refinement for 7050 casting using Al-3Ti-0.2C grain refiners seems weaker than those using Al-5Ti-1B grain refiners.

Guo Shi-jie, Xue Guan-xia, Ma ke, Nagaumi Hiromi

Grain refining potency of LaB6 on aluminum alloy

Al-LaB6 alloy was successfully prepared by aluminum melt reaction method in this study. Microstructure analysis of the alloy was carried out by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It is found cubic LaB6 particles are highly dispersed in aluminum matrix with a uniform edge length of about 4.0 µm. The grain refining potency of LaB6 on commercial pure aluminum has also been investigated. It shows that LaB6 can act as an effective and stable nucleation substrate for α-Al during the solidification process, due to their crystallographic similarity. The coarse grains of aluminum are obviously refined to small equiaxed ones by addition of 0.5% Al-5LaB6 alloy at 720 °C.

Pengting Li, Wenjie Tian, Dong Wang, Xiangfa Liu

The good grain refining performance of a new kind of Al-Ti-C-B master alloy

A new kind of Al-Ti-C-B master alloy with a uniform microstructure was prepared using a melt reaction method to overcome the problems associated with borides agglomeration in Al-Ti-B and the obvious fading behavior of Al-Ti-C master alloys in the refining process of α-Al. The grain refining tests were carried on the commercial pure aluminum (99.7 wt. %). It is found that the average grain size of α-Al can be reduced to below 200 µm from about 3500 µm by adding 0.2 wt. % the Al-Ti-C-B master alloy and the refining efficiency does not fade obviously within 60 min. It is considered that the TiCxBy (x+y < 1) and TiB2-mCn (m+n < 2) particles found at the center of α-Al grain are the effective and stable nucleating substrates during solidification, which accounts for the good grain refining performance.

Jinfeng Nie, Xiaoguang Ma, Haimin Ding, Xiangfa Liu

Assestment of the Al-Ni-Mn-Fe-Si-Zr Phase Diagram for New Generation Heat Resistant Casting Aluminum Alloys

The phase composition of the Al-Ni-Mn-Fe-Si-Zr system was analyzed with respect to new-generation heat resistant casting aluminum alloys based on a Ni-containing eutectic. The presence of iron and silicon significantly complicates the phase composition as compared with quaternary (Al-Ni-Mn-Zr) alloys. The admissible concentration of iron, at which no primary aluminides form and a high dispersivity of the eutectic is provided for, went up (to approximately 0.5–0.7%) as the concentration of nickel was decreased from 4 to 2%. Herewith, the solidification range did not exceed 10°C, which enabled higher casting properties. Silicon strongly expands the solidification range (being ~60°C already at 0.1%), which increases the aptitude of the alloy to form hot cracks in castings.

N. A. Belov, A. N. Alabin

The Influence of Heat Treatment Parameters on the Electrical Conductivity of AlSi7Mg and AlSi10Mg Aluminum Cast Alloys

Aluminum alloy casts are widely used in industry as elements for heat exchangers. In this case, the main requirements are the thermal conductivity and the mechanical properties of the alloy. According to the Wiedemann-Franz law, the thermal conductivity of the alloy can be expressed by its electrical conductivity. The paper presents the results of the research on the effect of the heat treatment parameters on the electrical conductivity of cast aluminum alloys, type AlSi7Mg and AlSi10Mg. The aim of the work is to determine the possibilities of obtaining the electrical conductivity of an alloy, while maintaining the required level of mechanical properties. The tests include the Brinell hardness measurements and the electrical conductivity evaluation by means of the eddy current method, on samples after artificial ageing. On the basis of the studies determining a range of heat treatments, it is possible to obtain 23.5 MS/m, in the case of AlSi10Mg, and 27 MS/m, in the case of AlSi7Mg.

Piotr Uliasz, Tadeusz Knych, Marzena Piwowarska, Justyna Wiecheć

The Effect of Nickel on the Thermal Conductivity of Al-Si Cast Alloys

In this study the effect of Ni on the thermal conductivity of hypoeutectic Al-Si cast alloys is described. The Ni-containing alloys are considered as a two-phase system, which consists of a ‘matrix’, composed of α-solid solution, eutectic Si, primary Al12(Fe,Mn)3Si2 phases and secondary Mg2Si-precipitates, and Ni-containing intermetallic phases incorporated in this ‘matrix’. With increasing Ni-content the volume fraction of second phases increases, whereby the characteristics of the material change from a ‘homogeneous matrix’ to a ‘particle-reinforced’ two-phase composite. The thermal conductivity data are discussed on a systematic basis of thermodynamic calculations and compared to data for the electrical conductivity as well as theoretical models for the thermal conductivity of heterogeneous solids.

Florian Stadler, Helmut Antrekowitsch, Werner Fragner, Helmut Kaufmann, Peter J. Uggowitzer

Production of Single Cylinder Engine Piston through Vacuum Die Casting in Sedi Enugu.

This research work looked into the fundamental properties of molten metal as well as the casting processes, especially the principle of operation of vacuum die casting used in the production of single cylinder engine piston.In addition, the factors that lead to the selection of vacuum die casting method for the project were enumerated. The main structure and working principles of vacuum die casting machine was explained. Furthermore, this paper treated mould design and mould materials requirement. And in conclusion, this paper discussed the alloy design of aluminum alloys used in the production of the piston. Although all the tests have not been carried out on components to ascertain their strength and durability but a functional test has been carried out by coupling the component on an engine and test running same for a while.

E. I. Nwonye, C. O. Nwajagu

Fatigue behavior in rheocast aluminum 357 suspension arms using the SEED process

Extensive studies have been devoted to the use of aluminum alloys in the automotive industry, by virtue of the favourable mechanical properties that can be attained. Moreover, the aluminum casting method employed has also been the subject of scrutiny, given the multitude of casting options available. The present work serves to illustrate the advancements made in the area of rheocasting, using the SEED method, as carried out at the National Research Council Canada — Aluminum Technology Centre. The SEED (Swirled Enthalpy Equilibration Device) process, which relies on heat extraction of the liquid aluminum alloy via mechanical agitation in a confined cylinder to form the semi-solid billet, has already proven successful in producing sound aluminum castings having an excellent combination of strength and ductility. Moreover, fatigue testing on the cast alloy parts has shown enormous potential for this emerging technology.

Ehab Samuel, Chang-Qing Zheng, Amine Bouaicha, Mohamed Bouazara

Single Roll Caster to Cast Aluminum Alloy Strip

A scraper was developed and attached to a single roll caster to improve the free solidified surface of the as-cast strip. AA5182 aluminum alloy of thickness approximately from 1.5mm to 4 mm was cast at speeds up to 60 m/min. With the scraper, semisolid metal on the free solidified surface was flattened. The pressure of the unit width of the scraper ranged from 0.1 N/mm to 1.0 N/mm and was sufficient to make the free solidified surface flat. Because the strip was solidified on a single side by the single roll caster, center line segregation did not occur. The roll cast strip could be cold rolled down to 1 mm. Visual examination after cold rolling showed no difference between the roll contact surface and the free solidified surface of the strip. The results of tension tests of roll cast and cold rolled strips with the scraper were the same as those of direct chill (DC) cast and rolled strips. A deep drawing test was conducted under two conditions: the roll contact surface was on the outer side, and the free solidified surface was on the outer side. The limited drawing ratio of 1.8 was the same for both conditions. The thickness of the strip was controlled by the roll speed, solidification length (length of the melt pool), and the scraper pressure. The utility of the scraper was shown by the casting of 600 mm width strip. This single roll caster could cast the strip of Al-10mass%Mg which is seemed to be difficult to cast strip without the center segregation by the twin roll caster. The single roll caster is simpler than a twin roll caster. The rigidity for rolling is not a significant concern for the single roll caster. In addition, since the cost of the roll is half that of a twin roll caster, the equipment cost of the single roll caster is more economical.

Toshio Haga, Kazuya Akitsu, Keisuke Kamakura, Shinji Kumai, Hisaki Watari

Roll Caster to Cast Clad Strips

A tandem-type roll caster that can cast a three-layered clad strip was developed by mounting one twin roll caster on another twin roll caster. In this caster, the base strip is cast by the upper twin roll caster, and the overlay strips are cast by the lower caster. The three strips are metallurgically bonded by the lower caster. This study investigated three aspects of this caster. First, the clad ratio could be controlled by the solidification lengths of strips from the upper and lower twin roll casters, and a clad ratio of 1:8:1 was attained. Second, although it is known that fabrication of clad strips from Al-Mg alloy and other Al alloys is very difficult, the clad strip with the Al-Mg alloy as the base strip or the overlay strip could be cast. Finally, by adding scrapers, the caster could cast the clad strip with a base strip having a lower melting point than the overlay strip

Toshio Haga, Hiroshi Tsuge, Takuya Ishihar, Shinji Kumai, Hisaki Watari

Tests of Heat Treatment Conditions of AlZr0.22 Alloy, Produced using the Continuous Casting Method

Over the recent years, heat resistant aluminium alloys have enjoyed a lot of interest in the power engineering industry. Among these, the most popular are alloys with the addition of zirconium. These materials are used mainly in the production of overground wires with the increased current load-carrying capacity of the HTLS type (High Temperature Low Sag). These alloys are characterised by complex properties. In the article we present the results of tests of a new AlZr alloy production technology which is based on the process of continuous casting of the semi-finished products later used in the drawing process. The aim of this paper is to determine the effect of heat treatment conditions on the value of the resistivity of aluminum with the addition of 0.22% mass. Zr, and on that basis determine the optimum range of annealing process parameters of the alloy.

M. Piwowarska, T. Knych, P. Uliasz

Investigation on the evolution of the microstructure during homogenization in thin Al sheets

Excellent surface quality, low-porosity, good mechanical properties represent the most important characteristics for thin Al sheets, being it largely used in a large number of different applications. Since the aforementioned characteristics strongly depend on the structure of the material, the present paper aims to discuss the results on the investigation on the effect of homogenization treatment on the microstructure of AA 8006 alloy sheets. Some thin sheets in AA 8006 alloy have been prepared by continuous casting (CC) process with some economical and metallurgical advantages over a traditionally manufactured direct chill (DC) product. Due to the rapid solidification of the metal, the microstructure develops into a strongly supersaturated aluminium solid solution and into an increased part of fine units made up mostly of intermetallic phases. All these factors have a dangerous effect on the materials formability and on the mechanical behaviour of the final product. The microstructure and the strengthening behaviour can be modified in different ways.

I. Peter, M. Rosso

Investigation of Acoustic Streaming in Aluminum Melts Exposed to High-Intensity Ultrasonic Irradiation

The purpose of the present work is to investigate characteristics of acoustic streaming in aluminum melts experimentally and by numerical simulation. In ultrasonic casting of aluminum alloys, the acoustic streaming is of considerable importance because it can affect the metal flow causing both positive and negative influences on the alloy solidification structure.High-amplitude ultrasonic vibrations were introduced in a water or molten aluminum bath through titanium or ceramic sonotrodes. Velocity of acoustic streaming was measured by a particle image velocimetry (case of water) and dynamic pressure technique. Based on the results obtained, a mathematical model of acoustic streaming was developed and incorporated into a commercial CFD code to characterize the mixing and flow pattern in the molten aluminum bath.

Yasuo Ishiwata, Sergey Komarov, Yoshihiro Takeda

Fabrication of Aluminum Alloy-Based Diamond Grinding Wheel by the Centrifugal Mixed-Powder Method For Novel Machining Technology of CFRP

The aim of this study is to investigate the fabrication process of aluminum alloy-based diamond grinding wheels for drilling carbon fiber reinforced plastic (CFRP) by the centrifugal mixed-powder method (CMPM). An Al-5.6mass%Zn-2.5mass%Mg-1.6mass%Cu alloy and an Al-4mass%Cu alloy have been chosen as base materials. Al-Zn-Mg-Cu alloyed-powder has been mixed with diamond powder. Afterwards, the mixed powder has been placed into the mold, and then molten Al-Cu alloy has been cast into the mold by the centrifugal force at various temperatures in vacuum. The microstructural observations of the fabricated aluminum alloy-based diamond composites have been carried out with a scanning electron microscope (SEM). Effects of fabrication conditions such as casting temperature on microstructure of the fabricated composites have been investigated. As a result, aluminum alloy-based diamond grinding wheels have been successfully fabricated by CMPM.

Takahiro Kunimine, Motoko Yamada, Hisashi Sato, Yoshimi Watanabe

Preparation of Al-Sc Master Alloy by Aluminothermic Reaction with Special Molten Salt

Al-Sc master alloy is prepared by aluminothermic reaction with a kind of special molten salt under the normal atmospheric condition. To achieve larger Sc recovery rate, the composition and pretreatment of the molten salt are studied. The optimum molten salt is obtained by melting together Sc2O3, NaF, KCl, NaCl, ScF3 and Na3AlF6 mixture under a mass ratio of 3:5:10:10:2:30, followed by solidifying and crushing. The pretreated salt is added to the Aluminum melt with a mass ratio of 60:100 to prepare Al-Sc master alloy. When the residue of molten salt is reused for three times, the Sc recovery rate can reach 91%. The structure and composition of the residue are examined using X-ray diffraction (XRD) analyzer and differential scanning calorimetry (DSC) analyzer. Based on the analysis of the residue, mechanism of the aluminothermic reaction to achieve larger Sc recovery rate with this special molten salt is discussed.

Cong Xu, Xinxin Liu, Fengmei Ma, Zhiwei Wang, Wenhong Wang, Chaoli Ma

In situ Synthesis of Al/TiC Composites by Combustion Reaction in an Aluminium Melt

In situ Al/TiC composites with a homogeneous distribution of TiC reinforcements were prepared by adding a reactant mixture of Al-Ti-C to an Al melt. A certain amount of CuO addition to the Al-Ti-C system dramatically increases the adiabatic temperature and thereby enables to form in situ TiC in an Al melt at a temperature range of 750~920 °C. TiC particles with a size of 1~2 urn synthesised by self-propagating high-temperature synthesis (SHS) are present in an Al matrix along with Al3Ti. Increase in the melt temperature up to 920 °C with CuO addition promotes the synthesis of TiC with increasing its volume fraction while less Al3Ti phases are observed.

Young-Hee Cho, Jung-Moo Lee, Hwa-Jung Kim, Jong-Jin Kim, Su-Hyeon Kim

Effects of Electroslag Refining on Removal of Iron Impurity and Alumina Inclusions from Aluminum

Effects of electroslag refining on removal of iron impurity and alumina inclusions from aluminum were studied on a laboratory-scale apparatus. The electroslag refining experiments were carried out using KCl-NaCl-Na3AlF6 slag. In the experiments, the electrodes of 40 mm diameter and 80 cm length were fed into the molten slag to obtain ingots of 70 mm diameter and 20–25 cm length under a voltage of 10–12 V, a current of 600–700 A and a descending speed of 26–106 mm•min−1. In the experiment, the 10wt%Na2B4O7 was added to the slag for the removal of iron. The purification efficiency of electroslag refining for aluminum increases with the decrement of the melt rate. The iron content can decrease from 0.42% to 0.20wt%(more than a 50% reduction in iron content) after electroslag refining under the melt rate of 180 g•min−1, and the removal efficiency of electroslag refining for alumina inclusions can exceed 97% under the melt rate of 108 g•min−1.

Jun Wang, Chong Chen, Baode Sun

Aging Behavior of Flexcast® Al-Mg Alloys with Sc and Zr Additions

The Flexcaster® is a strip casting technology that transforms liquid aluminum into a directly reliable cast ingot that is not subject to scalping or homogenization processing. This technology is characterized by relatively high solidification and cooling rates and was used to lab-produce AlMg-based alloys with minor additions of Sc and/or Zr. The presence of these is known to develop strengthening phases that also influence other metallurgical phenomena such as recovery and recrystallization. Aging experiments were performed on as-cast and cold-rolled samples to study the evolution of strengthening precipitates and their impact on recovery and recrystallization. Two Al- 3%Mg alloys were cast, one Sc-free and the other containing 0.4% Sc. Both alloys were artificially aged following casting at 300 and 400°C for times ranging from 30s to 72h. The samples were characterized by hardness and electrical resistivity measurements. Results show enhanced strengthening in the Sc-containing alloy and superior high temperature microstructural stability.

M. Sohi, N. Singh, C. W. Sinclair, W. J. Poole, M. Gallerneault

Electromagnetic Continuous Casting of Free-Shaped Aluminum Billet

A free-shaped aluminum alloy billet, not round or squared shaped, was usally manufactued by the conventional direct chill casting. A new method and apparatus for the fabrication of high-quality, free-shaped aluminum billets is developed by the combination of continuous casting and electromagnetic casting/stirring technique(EMC & EMS). A new proposed process for the fabrication of free-shaped aluminum billets offers some advantages: the process of extrusion and forging is simplified and the cost of plastic working can be greatly reduced. In order to reduce the paticular problems such as the surface crack and internal defect due to the inhomogeneous cooling of billets during solidification, the electromagnetic casting and stirring technique were adopted in this paper. Sectional cooling system improves the homogeneity of microstructure. The effect of electromagnetic field was compared by observing the microstructure of billets. Grain refinement of aluminum billet was clearly observed by applying electromagnetic field to continuous casting process.

Myoung-Gyun Kim, Jong-Ho Kim, Joon-Pyo Park, Gyu-Chang Lee

Effect of Mn on the Interaction between Die Casting Steel and Al Alloy

The formation of intermetallic reaction layers was investigated for die soldering between a STD61 steel and aluminum alloy. It is generally well known that Mn contents have advantageous effect on decreasing die soldering especially with aluminum alloys containing substantial amount of Si. However, die soldering has not widely studied for the low Si aluminum (1~2wt.%) alloys. Each aluminum alloy had melted then STD61 substrate was dipped in the melt for 2hr. The result from dipping soldering test showed the Al-Fe intermetallic layer in the microstructure. In Al-1wt.%Si alloy, additional content Mn also increased the thickness of the intermetallic layer compare to the alloy without Mn.

Se-Weon Choi, Young-Chan Kim, Cheol-Woo Kim, Jae-Ik Cho, Chang-Seog Kang, Yu-Mi Kim, Sung-Kil Hong

Limitation of Shrinkage Porosity in Aluminum Rotor Die Casting

Aluminum rotor prone to have many casting defects especially large amount of air and shrinkage porosity, which caused eccentricity, loss and noise during motor operation. Many attempts have been made to develop methods of shrinkage porosity control, but still there are some problems to solve. In this research, the process of vacuum squeeze die casting is proposed for limitation of defects. The 6 pin point gated dies which were in capable of local squeeze at the end ring were used. Influences of filling patterns on HPDC were evaluated and the important process control parameters were high injection speed, squeeze length, venting and process conditions. By using local squeeze and vacuum during filling and solidification, air and shrinkage porosity were significantly reduced and the feeding efficiency at the upper end ring was improved 10%. As a result of controlling the defects, the dynamometer test showed improved motor efficiency by more than 4%.

Young-Chan Kim, Se-Weon Choi, Cheol-Woo Kim, Jae-Ik Cho, Sung-Ho Lee, Chang-Seog Kang

The Effect of Alloying Elements on Thermal Conductivity and Casting Characteristic in High Pressure Die Casting of Aluminum Alloy

Recently, demand of aluminum alloys for use in high thermal conductivity application is increases but the most aluminum die casting alloys exhibit very lower thermal properties because of their high concentrations of alloying elements. However, those alloying elements are essential to obtain sufficient fluidity and mechanical strength. Therefore, the purpose of this study is to analyze the effect of alloying elements in die casting alloys, Si, Cu, Mg, Fe and Mn, in thermal conductivity, die casting characteristics and mechanical properties and find out the appropriate amount of each alloying element for development of heat sink component. The results showed that Mn had the most deleterious effect in thermal conductivity and Si and Fe contents were important to improve strength and limit casting defects, such as hot tearing and die soldering. The alloy with 0.2~1.0wt%Cu, 0.3~0.6wt%Fe and 1.0~2.0wt%Si showed very good combination of high thermal conductivity and good casting characteristics.

Cheol-Woo Kim, Jae-Ik Cho, Se-Weon Choi, Young-Chan Kim, Chang-Seog Kang

Coating and Surfaces

Initial Studies of 6082 Aluminium Thin Films

The microstructure of thin aluminium 6082 films, with a thickness from 0.1 μm to 1.7 μm, has been investigated. The films were deposited by sputtering on Si <100> substrates. The resulting microstructure was studied using Scanning and Transmission Electron Microscopy. The grains grew columnarly and, depending on the growth conditions, the diameter varied from 20 to 100 nm. Heat treatment at 500°C for 4 h was performed in an attempt to increase the grain size, but no subsequent grain growth was observed, indicating that the grain boundaries are stable. After deposition, several different ageing temperatures ranging from 150°C to 300°C and varying ageing times from 0.5 h to 10 h were performed. No precipitation was observed in the films, which could be due to the small grain size which is in the order of the precipitation free zone dimensions in bulk alloys.

Jon Holmestad, Øystein Dahl, Sigmund J. Andersen, Oddvin Reiso, Randi Holmestad, John C. Walmsley

Finite Element Simulation of Shot Peening: Prediction of Residual Stresses and Surface Roughness

Shot peening is a surface treatment that consists of bombarding a ductile surface with numerous small and hard particles. Each impact creates localized plastic strains that permanently stretch the surface. Since the underlying material constrains this stretching, compressive residual stresses are generated near the surface. This process is commonly used in the automotive and aerospace industries to improve fatigue life. Finite element analyses can be used to predict residual stress profiles and surface roughness created by shot peening. This study investigates further the parameters and capabilities of a random impact model by evaluating the representative volume element and the calculated stress distribution. Using an isotropic-kinematic hardening constitutive law to describe the behaviour of AA2024-T351 aluminium alloy, promising results were achieved in terms of residual stresses.

Alexandre Gariépy, Claude Perron, Philippe Bocher, Martin Lévesque

The Potential of the Cold Spray Process for the Repair and Manufacture of Aluminium Alloy Parts

Being capable of producing deposits up to several centimetres thick, the cold spray process is emerging as an attractive technology for the manufacture and repair of high value aluminium and magnesium components. During the cold spray process fine aluminium or aluminium alloy powders are propelled at high velocities in the solid state at the target substrate. Due to the high velocity particle impacts, strong bonds are formed between the coating and the substrate and between particles within the deposited layer. Metallographic sections of cold sprayed coatings reveal microstructures characterised by very low porosity. With the objective of improving the abrasive wear and erosion resistance of cold sprayed coatings, ceramic reinforcements such as SiC, B4C and Al2O3 have been introduced in the feedstock to produce composite coatings, and these composite materials have been deposited with thicknesses in excess of 25mm. Several applications employing commercially available equipment have achieved industrialisation.

David Harvey, Tiziana Marrocco

Computational Metallurgy: ICME

Utilisation of Atom Probe Data to Model Precipitation and Strengthening in an Al-Mg-Si-Cu Alloy During Natural Ageing and Early-Stage Artificial Ageing

An Al-Mg-Si-Cu alloy was artificially aged for 0.13, 0.5 or 2 hours at 170°C after natural ageing times of 0.03, 3 or 168 hours. Three dimensional atom probe (3DAP) analysis and tensile testing were performed in the artificially aged and naturally aged conditions. The experimental data were used to determine model inputs such as particle size distributions and volume fractions of particles. The principle of the model is to numerically simulate the isothermal transformation of clusters, zones and/or precipitates by dividing the starting particle distribution into a series of discrete size classes and control volumes. Standard physically-based equations are used to simulate particle growth and/or dissolution by adjusting enthalpy, entropy and interfacial energy values to obtain a good fit between model predictions and 3DAP results. The predicted particle size distributions and volume fractions are then used to model yield strengths in a wide range of naturally aged and under-aged conditions.

Dacian Tomus, Paul A. Rometsch, Lingfei Cao, Malcolm J. Couper, Chris H. J. Davies

Ab initio simulations of vacancy-solute clusters in Al-Mg-Si and Al-Zn-Mg alloys

The coherent fcc (face-centred-cubic) based cluster stability of Al-Mg-Si and Al-Zn-Mg alloys is studied theoretically using augmented plane wave density functional theory calculations of a periodically repeated supercell containing 32 atoms. In particular, the presence of vacancies within the structure of Mga-Sib±Vac and Znd-Mge±Vaf clusters is investigated in detail. These fcc type arrays of solutes are considered to bind with vacancies.The binding energies between two substitutional elements, Mg and Si as well as Zn and Mg, and same arrangements bound to one vacancy in a fcc aluminium matrix are calculated. The binding energies of the co-clusters are taken as reference energies to compare the binding energies of two atom co-clusters to a vacancy in different constellations. These energies are used to predict formations of very early clusters containing single vacancies. Energetically more favourable structures are obtained and discussed.

Peter Lang, Peter Mohn, Ahmad Falahati, Ernst Kozeschnik

The Role of the Si Network to the Stabilization of Hardening Precipitates in the Al-Mg-Si(-Cu) Alloy System

Al-Mg-Si(-Cu) alloys are an important group of age hardening materials and possess some of the more complex precipitation sequences: In Al-Mg-Si, none of the metastable hardening precipitates can be described as weakly distorted versions of equilibrium phases, while in Al-Mg-Si-Cu, one of the main hardening precipitates is not associated with a unit cell. For both sequences, however, more than a decade of experimental work has revealed that a Si substructure with projected hexagonal symmetry when viewed in precipitate main growth axis projection is shared among all metastable phases. The present work seeks to clarify theoretically the significance of the Si network to phase stabilization while also quantifying the level of similarities among the various phases possessing this structure. Based on these results, very clear suggestions for a common precipitate nucleation mechanism emerge.

Flemming J. H. Ehlers, Sigurd Wenner, Sigmund J. Andersen, Calin D. Marioara, R. Holmestad

Residual Stress Analysis in AA7449 As-Quenched Thick Plates Using Neutrons and Fe Modelling

In the current trend toward thicker aluminium plates, a major concern is the generation of high internal stresses during quenching, which can cause distortions during machining and pose serious safety concerns. Although the material is stretched after quench, substantially reducing residual stresses, they are not fully suppressed. In addition, the cooling rate is not large enough at the core of such thick plates to prevent any precipitation. This has a great impact on the efficiency of ageing. In this work, residual stress distributions in a heat-treatable aluminium alloy AA7449 thick plate in the as-quenched state measured by neutron diffraction are presented. A comparison between single (311) diffraction peak and multiple peaks analysis using Pawley algorithm is shown. The variation of the stress free reference value through the plate thickness is discussed and measured stresses are compared with residual stresses predicted by a thermo-mechanical finite element model of quenching.

N. Chobaut, J. Repper, T. Pirling, D. Carron, J-M. Drezet

A Through Process Model for Extruded AA3xxx Aluminum Alloys

The application of extruded AA3xxx aluminum tubing in automotive heat exchanger systems is a growth area. This work involves the development of a series of linked mathematical models which describe microstructure evolution as a function of processing conditions including homogenization, hot extrusion and the final brazing heat treatment. It is necessary to link the processes and track microstructure through the processes in order to predict final microstructure and properties of the aluminum in heat exchanger applications. For example, the homogenization step is critical to control the morphology, shape and spatial distribution of second phase particles, i.e. dispersoids and constituent particles. The results of i) a chemistry dependent finite difference model for homogenization, ii)a finite element based hot extrusion model and iii) a model for cold work and annealing model will be described with emphasis on the successes of the model but the challenges for future work will also be addressed.

W. J. Poole, M. A. Wells, N. C. Parson

Modeling the Recrystallization Textures in Particle Containing Al Alloys after Various Rolling Reductions

Various degrees of rolling reductions account for diverse recrystallization mechanisms and thus different microstructural and texture features. The development of deformation and recrystallization textures is discussed based on experimental data and results of finite element and crystal plasticity simulations. A recrystallization model is presented that incorporates the microstructural heterogeneities and changes in local stored energy. The experimental observations and results of crystal plasticity calculations testify that orientation selection during recrystallization is controlled by low stored energy nucleation which is incorporated in the recrystallization model. Results of texture simulations show that the evolution of {100}<13> and {011}<233> components is related to a particle stimulated nucleation mechanism.

Jurij J. Sidor, Roumen H. Petrov, Koen Decroos, Leo A. I. Kestens

TCAL1 and MOBAL2 — The Development and Validation of New Thermodynamic and Mobility Databases for Aluminium Alloys

The CALPHAD technique is a powerful tool for materials process optimization and alloy design. The quality of CALPHAD-type calculations/simulations is strongly dependent on the quality of the thermodynamic and atomic mobility databases used. In the present paper the development of a new thermodynamic database, TCAL1, and an atomic mobility database, MOBAL2, is described. Examples of thermodynamic calculations and kinetic simulations for different kinds of aluminum alloys are shown using the databases and comparing where possible against experimental data, thereby validating its accuracy.

L. J. Zhang, A. Markström, P. Mason, Y. Du, S. Liu, L. Kjellqvist, J. Bratberg, Q. Chen, A. Engström

Advances in Integrated Computational Materials Engineering “ICME”

The methods of Integrated Computational Materials Engineering that were developed and successfully applied for Aluminium have been constantly improved. The main aspects and recent advances of integrated material and process modeling are simulations of material properties like strength and forming properties and for the specific microstructure evolution during processing (rolling, extrusion, annealing) under the influence of material constitution and process variations through the production process down to the final application. Examples are discussed for the through-process simulation of microstructures and related properties of Aluminium sheet, including DC ingot casting, pre-heating and homogenization, hot and cold rolling, final annealing. New results are included of simulation solution annealing and age hardening of 6xxx alloys for automotive applications. Physically based quantitative descriptions and computer assisted evaluation methods are new ICME methods of integrating new simulation tools also for customer applications, like heat affected zones in welding of age hardening alloys. The aspects of estimating the effect of specific elements due to growing recycling volumes requested also for high end Aluminium products are also discussed, being of special interest in the Aluminium producing industries.

Jürgen Hirsch

Numerical Simulation of Flat Rolling Practices

The hot rolling process with tapered ingot is simulated by finite element analysis. An in-house material model has been developed and implemented into ABAQUS finite element analysis software through a user material subroutine (UMAT). The rolling load, torque, deformed shapes are found to be in a good agreement with measurements. It has been demonstrated that this FE model is able to accurately describe the coupled thermal-mechanical behaviour for flat rolling processes at elevated temperatures under various strain rates. This model also provides a useful tool for the further product and process optimization.

Y. Shi, P. D. Wu, M. Gallerneault

Modelling the Effect of Room Temperature Storage and Deformation on the Age-hardening Behaviour of Al-Mg-Si alloys

The present investigation deals with modelling of the age-hardening behaviour of 6XXX series automotive sheet alloys. The basis for the work is a precipitation model developed for coupled nucleation, growth, dissolution and coarsening in Al-Mg-Si extrusion alloys. It has been advanced to incorporate the important effects of room temperature (RT) storage and deformation prior to the final age-hardening. The model predicts the evolution of the precipitate structure and the corresponding RT yield strength for non-isothermal heat treatments. The model validation is based on both a comprehensive set of tensile tests and TEM measurements on selected samples. A comparison between model predictions and measurements shows reasonable agreement, and it is concluded that after some further development, the model can be used as an industrial tool for process chain simulations of the yield strength response following complex heat treatments and deformation schedules.

C. Schäfer, O. R. Myhr, Z. Liang, H. J. Brinkman, O. Engler, J. Hirsch, C. Chang, J. Banhart

Evaluation Of The Quenching Sensitivity Of Al-Zn-Mg-Cu-Zr Aluminum Alloys By Mole Fraction Of Equilibrium Phases

The effect of composition on the quenching sensitivity of Al-Zn-Mg-Cu-Zr aluminum alloys was investigated through hardness test, microstructure analysis and thermodynamic calculations. The materials involved are 7085, 7050, 7150 and 7055 aluminum alloys. The quenching sensitivity of the alloys has been evaluated by the percentage of hardness reduction after aging process. The results show that the aging hardness reductions for the alloys by air quenching are up to 8.6%, 18.4%, 21%) and 21.7%, respectively, in comparison with that by water quenching. The precipitation of 7050 and 7055 aluminum alloys is much more compared to that of 7085 aluminum alloy during air quenching process, which decreases the capability of aging hardening and causes quenching sensitivity of 7050 and 7055 aluminum alloys. The interrelation of composition, equilibrium phase and quenching sensitivity is investigated from perspective of thermodynamic calculations, and the total mole fraction of equilibrium phase during quenching process is proposed to be a criterion for evaluating the quenching sensitivity of Al-Zn-Mg-Cu-Zr series aluminum alloys.

Baohua Nie, Peiying Liu, Tietao Zhou, Yanjun Xie

Modelling Grain Deformation during Extrusion of AA3003 using the Finite Element Method

A combination of numerical simulation using the finite element method (FEM), extrusion plant trials and experimental characterization was used to study microstructure changes, specifically geometric dynamic recrystallization, during the hot extrusion process for an AA3003 aluminum alloy. Extrusion plant trials were conducted at the Rio Tinto Alcan Research and Development facility in Jonquiere, Quebec in order to measure load and temperature and obtain samples for microstructure analysis. A 2D FEM based on the commercial code DEFORM was developed for the thermo-mechanical simulation of the extrusion. Load and temperature predictions resulting from this model agree well with the measured values during the pilot plat trials. Using the FEM model, it was estimated that near the surface of the extrudate the thickness of the deformed grains drops below the subgrain size which may cause the deformed grains to pinch-off and geometric dynamic recrystallization. Optical microscopy observations show that in all unrecrystallized extradates there is a transition from a fibrous to a granular structure near the surface that suggests the occurrence of Geometric Dynamic Recrystallization. The effect of extrusion conditions on grain thickness distribution was investigated using the FEM model.

Yahya Mahmoodkhani, Mary A. Wells, Lina M. Grajales, W. J. Poole, Nick Parson

Experience of Developing and Introduction in Industry New Primary and Secondary Al-Alloys with Given Properties for Shape Casting

There was created data base which includes phase diagrams, results of structure and properties investigation of thousands Al-alloys, mathematical models of composition and structure influence on mechanical and casting properties. There was developed the methodology of developing casting alloys which consists from the next steps: development of alloying principles and selection of perspective alloying systems to allow the complex of given properties by using our data base; thermodynamic calculations of phase diagrams perspective alloying systems; experimental structure investigations of perspective alloys; mathematical modeling of composition and structure influence on mechanical and casting properties; experimental investigation of all properties complex and choice the best alloys; optimization of composition and technological regimes of production best alloys for receiving needing properties, final choice the best alloy. By using that methodology there were developed tens new alloys with different complex of properties. Some of new alloys will be present in the paper.

V. S. Zolotorevskiy

Corrosion

Application of Microelectrochemical Methods for Understanding Localized Corrosion Behavior of Aluminum Alloys

Nearly all forms of localized corrosion in high strength aluminum alloys are affected by the heterogeneous microstructures these alloys posses. Alloying and thermomechanical processing result in the formation of constituent, precipitate and dispersoid particles. These particles are always enriched in one or more alloying elements causing their electrochemical behavior to differ from the surrounding matrix phase. Experimental approaches based on microelectrochemical methods have enabled characterization of alloy electrochemistry on a phase-by-phase basis, and the results derived have contributed to a better understanding of localized corrosion and corrosion inhibition. These results have also led to the development of frameworks for modeling localized corrosion damage accumulation. In this presentation, the use microelectrochemical approaches in aluminum alloys will be described and examples will be used to illustrate how the results can be used to characterize and model localized corrosion damage accumulation.

R. G. Buchheit, N. Birbilis

Precipitation of the β-phase and Corrosion Behavior of an Al-6.8 wt.% Mg Alloy

This study was performed on the Al-Mg alloy with the chemical composition: Al-Mg6.8-Mn0.51-Fe0.2-Si0.1. As-received cold rolled material (O-temper) was subjected to (i) cold rolling and annealing at 265°C and 320°C, followed by (ii) sensitization treatment at 100°C. Microstructure characterization showed that the preferential sites for β-phase precipitation were grain boundaries and preexisting Mn-rich particles. The annealing temperature had significant effect on the β-phase morphology: microstructure of sensitized specimens annealed at 265°C was characterized by formation of discontinuous particles, while annealing at 320°C resulted in the formation of the thin film at grain boundaries. Presence of the thin film induced corrosion resistance degradation and also affected grain boundary morphology: initially smooth, curved grain boundaries became strongly faceted.

Miljana Popović, Tamara Radetić, Endre Romhanji

Testing the Corrosion Behaviour of Plated Aluminum Strips for Heat Exchangers Operating in the Automotive Industry

The automotive industry uses heat exchangers made of aluminum alloys. The radiators for an engine cooling system comprise elements (tubes) in which the coolant flows. These elements are made of AlMn alloys (e.g. AlMn or AlMnCu), while ribs are made from the sheet metal plated with AlSi alloys. While in service, the heat exchangers are exposed to harsh weather conditions, hence the need to ensure that the individual elements of the design are adequately protected from corrosion. One of the ways to obtain this protection is by modification of the chemical composition of aluminum alloys used in the manufacture of radiators. In this study, corrosion tests were carried out to characterise the investigated materials in terms of their corrosive behavior. The experiments included measurements of corrosion potential, testing of corrosion resistance in neutral salt spray, and electrochemical studies of selected plated AlMn alloy strips with different chemical composition.

Marek Nowak, Mieczysław Opyrchał, Andrzej Kłyszewski, Janusz Żelechowski

Corrosion Protection of Light Alloys using Low Pressure Cold Spray

Corrosion attack of aluminum- based alloys is a major issue worldwide. This study provides a report on the electrochemical behavior of several types of protective metal coatings obtained by low pressure cold spray and describes the performance of the latter’s corrosion resistance properties. In this manner several metal feedstock compositions were cold sprayed on AA2024-T3 Alclad substrate. Electrochemical methods, such as OCP and DC polarization, were used in combination with materials characterization techniques to assess the performance of protective coating layers. All sprayed samples were tested in the accelerated corrosion chamber for a time period of up to 500 hours to obtain corrosion kinetics data, and with specific attention being focused on the characterization of the coating’s properties. The overall conclusion of this study is that the LPCS process could be utilized to deposit corrosion protection coatings and as to repair aluminum structures during overhaul maintenance schedule in an industry.

Dmitry Dzhurinskiy, Roman Gr. Maev, Volf Leshchynsky, Emil Strumban

Crystallographic Orientation Dependence of Corrosion Behabior of 5N Purity Aluminum in Different Concentrations of HCl Aqueous Solutions

The dependence of corrosion behavior of 99.999% (5N) purity aluminum on crystallographic orientation has been investigated in four concentrations of hydrochloric acid aqueous solutions. Before corrosion test the surface of specimen was analyzed to examine crystallographic orientation distribution, and then using SEM/EBSD technique the same area was observed by optical microscopy to detect corrosion behavior. Steps formed during the corrosion test at grain boundaries were precisely measured using geometrical calculation based on SEM observation and laser microscopy. It was confirmed that the corrosion behavior depended strongly on the crystallographic orientation of the planes parallel to the surface. Moreover, the orientation dependence was varied with the concentration of the solution. While {101} and {111} plane have corrosion resistance in low concentrations of 1.5 mol/L and 2.9 mol/L HCl, the pitting rate on {111} plane was highest in high concentrations of 5.8 mol/L and 11.6 mol/L HCl.

Yoshimasa Takayama, Masayuki Sato, Hideo Watanabe

Corrosion Fatigue Mechanism on Hot-Forged AA6082 Aluminum Alloy

An attempt has been made to understand the corrosion fatigue phenomenon in AA6082 aluminum hot-forged parts. Fatigue and corrosion fatigue experiments of forged parts produced by two different feedstock materials have been performed in the lab air and in a corrosive 3.5% NaCl solution under different stress levels. The scanning electron microscopy was used to study the rupture and to identify failure modes. With corrosion and mechanical stress working together, the failure occurred earlier in the specimens subjected to a 3.5% NaCl solution as compared to those subjected to the lab air irrespective of the material forms (cast-forged or extruded-forged). The corrosion fatigue performance of these specimens with different stress levels as well as the crack initiation and propagation were elaborated. It was found that there is no significant variation in corrosion fatigue resistance for final cast-forged and extruded-forged products.

N. Saleema, P. Gauthier, X.-G. Chen

Corrosion Inhibition of Stress Corrosion Cracking and Localized Corrosion of Turbo-Expander Materials

Stress corrosion cracking of 7050 aluminum alloy in the turbo expander and steam/gas turbine industry can cause catastrophic failures, especially for turbo machinery systems performing in hostile, corrosive environments. Commercially available inhibitors were investigated for their effectiveness in reducing and controlling the corrosion susceptibility. Inhibitor effectiveness was confirmed with electrochemical corrosion techniques. Polarization resistance increased with concentration of corrosion inhibitor due to film formation and displacement of water molecules. Cyclic polarization behavior for samples in the 1.0% to 10.0% inhibitor concentration showed a shift in the passive film breakdown potential. The substantial increase in the passive range has positive consequences for neutralizing pitting and crevice corrosion cell chemistry. The strain to failure and tensile strength determined from slow strain rate studies for the aluminum alloy showed pronounced improvement resulting from the inhibitors ability to mitigate SCC. Additionally, the fractographic analysis showed a changed morphology with ductile overload as the primary failure mode instead of transgranular or intergranular cracking.

Behzad Bavarian, Jia Zhang, Lisa Reiner

Corrosion Characteristics of an Al-1.78%Si-13.29%Mg Alloy in Chloride Solutions

Samples of the alloy Al-1.78%Si-13.29%Mg were immersed in aqueous 0.1M NaCl solutions up to 4 days at open circuit conditions. Morphological analysis with scanning electron microscopy (SEM) showed that the main intermetallic Al3Fe played the role of local cathode producing dissolution of the adjacent aluminum matrix. The other intermetallic, Mg2Si underwent selective dissolution of Mg but exhibited little morphological damage. Results with the scanning Kelvin probe force microscopy (SKPFM) technique showed a clear contrast in Volta potential between these two intermetallics and the matrix. For freshly prepared samples the Volta potential difference with respect to the matrix was about 600 mV for Al3Fe and −300 mV for Mg2Si. After a 19 h immersion in the chloride solution the potential difference decreased. In the case of the Mg2Si intermetallic the Volta potential contrast to the surrounding aluminum matrix disappeared.

M. A. Pech-Canul, R. Giridharagopal, M. I. Pech-Canul, E. E. Coral-Escobar

Corrosion Performance of New Generation Aluminum-Lithium Alloys for Aerospace Applications

Over the past several years, a new generation of aluminum-lithium alloys has been developed. These alloys are characterized by excellent strength, low density, and high modulus of elasticity and are therefore of interest for lightweight structural materials applications particularly for construction of current and future aircraft. These new alloys have also demonstrated significant improvements in corrosion resistance when compared with the legacy and incumbent alloys. This paper documents the superior corrosion resistance of the current commercial tempers of these materials and also discusses the corrosion performance as a function of the degree of artificial aging. Results from laboratory corrosion tests are compared with results from exposures in a seacoast atmosphere to assess the predictive capability of the laboratory tests. The correlations that have been developed between the laboratory tests and the seacoast exposures provide confidence that a set of available methods can provide an accurate assessment of the corrosion performance of this new generation of alloys.

James P. Moran, Francine S. Bovard, James D. Chrzan, Peter Vandenburgh

Comparison of corrosion performance and mechanisms of Al-Cu alloys with and without Li addition

The corrosion behaviour (intergranular corrosion, exfoliation and SCC) of alloy 2050 (AlCuLi) has been evaluated as a function of tempering and compared with some 2xxx Li free alloys. They show a similar qualitative behaviour: sensitivity to corrosion in underaged conditions, desensitization near peak age and re-sensitization in overaged conditions. The desentization can be rationalized on the basis of microstructural investigations and electrochemical measurements: preferential dissolution in underaged conditions is attributed to a Cu depleted zone near grain boundary. The re-sensitization in an overaged temper needs further investigations.

Christine Henon, Sacha Rouault

The effect of stress in age-forming on corrosion behavior of high-strength aluminum alloy

Age-forming is a form of stress ageing that is widely used in modern aerospace industry. In this paper we investigated the effect of stress in the age-forming process on corrosion behavior of AA7050 in 3.5% NaCl solution and compared it to traditional ageing. Morphology analysis through optical profilometry and electrochemical impedance spectroscopy (EIS) measurement suggest that the age-formed samples exhibit more corroded attack. Stress in age-forming induced the precipitation (MgZn2) and precipitate free zone growth, which are anodic to the matrix. The bigger precipitates and wider precipitate free zone caused by age-forming result in decreased corrosion resistance of AA7050 in 3.5% NaCl solution. Additionally, stress during age-forming increases the grain aspect ratio, which is harmful to intergranular corrosion resistance. Therefore, the stress in age-forming reduces corrosion resistance of AA7050 in 3.5%) NaCl solution.

J. F. Chen, G. S. Frankel, C. Y. Xu, G. A. Li, Z. Lu, L. Zhen

Corrosion and Potentiostatic Polarization of an Al-Cu-Li Alloy under Tensile Stress

The stress corrosion cracking (SCC) of an Al-3.8Cu-1.5Li-0.5Zn-0.5Mg-0.3Mn alloy in 3.5% NaCl solution was studied through using slow strain rate tension(SSRT). The potentiodynamic polarization and anodic potentiostastic polarization of the stressed and stress free alloy with T6 temper were investigated. The tensile stress decreased the break down potential. The alloy was sensitive to intergranular SCC (IGSCC), due to the continuous distribution of anodic phase of T2(Al6CuLi3) along the grain boundary. During the potentiostastic polarization, the current-time curve of the stressed alloy displayed a repeated transient feature that the current increased suddenly followed by a slower recovery, and corrosion crack appeared along the grain boundary. While the stress free alloy did not show this current feature and corrosion crack along the grain boundary. The repeated current transient was associated with the crack tip propagation and crack wall passivation. This feature may be used to analyze the SCC process.

Jin-feng Li, Zi-qiao Zheng

The Effect of Chemical Composition and Structure on the Corrosion Resistance of Plated Aluminium Alloy Strips

Thin 3003 alloy strips plated with 4343 alloy were subjected to microstructure examinations, X-ray phase analysis, corrosion testing, and measurement of basic mechanical properties. In a similar manner, the properties of heat exchangers made from the plated strip were characterised, watching the long-term consequences of their use in vehicles. The results of investigations were applied in the manufacturing technology of thin plated strips for heat exchangers used by the automotive industry.

Andrzej Klyszewski, Janusz Zelechowski, Mieczyslaw Opyrchal, Marek Nowak, Andrzej Frontczak, Pawel Rutecki

Fatigue and Fracture Toughness

Effect of Fatigue and Damage Tolerance Material Properties on the Efficiency of Aircraft Structures

Current aircraft structures have to meet the static, fatigue and damage tolerance (F&DT) criteria according to the actual FAA/EASA regulations. Furthermore, the structures consider common industry design standards, e.g. redundant structure, large damage capability, etc.The most efficient structure in fatigue sensitive areas will be achieved by combining materials with excellent fatigue, crack growth and fracture toughness properties, a good design practice and a reliable manufacturing process. Examples for materials with excellent F&DT properties are advanced Aluminum alloys and Fiber Metal Laminates, e.g. GLARE and CENTRAL.The overall result of the above described combination is a lightweight structure, which has an adequate fatigue life, a slow crack growth behavior not requiring penalizing in-service inspections and providing a large damage capability. Certainly this structure ensures compliance with the regulations and sufficient structural integrity during the operational life of the aircraft.The paper describes the above mentioned aspects with emphasis on the effect of the fatigue and damage tolerance properties on the allowable stresses and the weight of the structure. Three design solutions for a panel of the pressurized fuselage are presented.

Hans-Juergen Schmidt, Bianka Schmidt-Brandecker

About the Challenge in Determining the Cyclic Material Behavior of Aluminum Alloys for Numerical Fatigue Analyses

Knowledge of the cyclic material behavior is needed for a proper estimation of fatigue life. Depending on the design concept, different equations are required to describe the fatigue behavior. For the local strain concept, the cyclic material properties, according to the rules of Manson-Coffin-Basquin and Ramberg-Osgood, are very popular. For the stress concept, High Cycle and Very High Cycle Fatigue modifications of the Basquin’s rule are used. Basically, these rules were not developed for aluminum alloys and are limited to a small range of fatigue life. Since the 1970s, several ongoing investigations had shown that these rules do not fit the experimental results in a proper way for materials other than standard steels. For this reason, a new method for describing the strain S-N curve and new testing facilities for the experimental investigation of the cyclic material behavior of aluminum alloys, for the whole range of fatigue life, will be presented.

R. Wagener, C. Fischer, A. Frohm, H. Kaufmann

A Microstructure Based Multi-Site Crack Growth Model

A simple computational method to simulate component failures in engineered structures based on microstructure characteristics has been developed. The computational model deals directly with a large set of cracks in a defined geometrical region, and is capable of tracking the simultaneous growth and interaction of those cracks, including crack-tip shielding and link-up, until final failure. The Multi-Site Crack Growth (MSCG) tool is designed to start from either an initial uncracked state where cracks may nucleate from cracked particles or other microstructural features, or from an initial cracked state such as might be expected at a percentage of fatigue life expended. Alternatively, the input can be expected crack nucleation sites from microstructure simulations. The MSCG tool is designed based on microstructural origins of fatigue cracks, and the statistical distributions of microstructural parameters. Thus it is possible to extend this framework to corrosion-fatigue. The computational algorithms used enable rapid calculation of the complete crack growth geometry for the current loading cycle, including the current number of cracks, the maximum crack length, the average crack length, and the total cracked area. This makes application to life predictions possible as crack length, area, and number distribution are predicted for given number of load cycles. Example simulations of crack nucleation from large second phase particles will be given.

J. R. Brockenbrough, J. M. Fridy, H. Weiland

Short Fatigue Crack Growth Micromechanisms in a Cast Aluminium Piston Alloy

The short fatigue crack growth behaviour of a model cast aluminium piston alloy has been investigated. This has been achieved using a combination of fatigue crack replication methods at various intervals during fatigue testing and post-mortem analysis of fracture surfaces and crack profiles. Crack-microstructure interactions have been clearly delineated using a combination of optical microscopy (OM), scanning electron microscopy (SEM) and three dimensional (3D) X-ray microtomography (SRCT). Results show that intermetallic particles play a significant role in determining the crack path and growth rate of short fatigue cracks. It is observed that the growth of short cracks is often retarded or even arrested at intermetallic particles and grain boundaries. Crack deflection at intermetallics and grain boundaries is also frequently observed. These results have been compared with the long crack growth behaviour of the alloy

T. O. Mbuya, J. Crump, I. Sinclair, K. A. Soady, R. C. Thomson, P. A. S. Reed

Fatigue Life of Ablation Cast 6061-T6 Components

The fatigue life of 6061-T6 alloy, normally used in its wrought form, was investigated in this study in cast form from parts produced by the new ablation casting process. Specimens excised from military castings were first tested in unidirectional tensile test yielding elongation values comparable to forgings. Fatigue specimens tested by rotating cantilever beam revealed that the fatigue life of these castings is superior to the data from the 6061 forgings published in the literature.

M. Tiryakioğlu, P. D. Eason, J. Campbell

Mechanical Properties of Heat Exchanger Tube Materials at Elevated Temperatures

Since automotive heat exchangers are operated at elevated temperatures and under varying pressures, both static and dynamic mechanical properties should be known at the relevant temperatures. We have collected elevated-temperature tensile test data, elevated-temperature stress amplitude-fatigue life data, and creep-rupture data in a systematic fashion over the past years. For thin, soft, and braze-simulated heat exchanger tube materials tested inside closed furnaces, none of the well-established methods for crack detection and observation can be applied. In our contribution, we present a simple statistical method to estimate the time required for crack initiation.

Sören Kahl, Jozefa Zajac, Hans-Erik Ekström

Fatigue Behavior and Damage Monitoring of Ultrasonic Welded Hybrid Joints

The need of hybrid joints especially for joints between light metals and CFRP-composites is strongly increased in the last years. Ultrasonic metal welding is one promising technology to join aluminum alloys to carbon fiber reinforced polymers (CFRP). These hybrid joints can be realized by thermal softening and mechanical replacing the polymer out of the welding zone as a result of the ultrasonic shear oscillation. This allows a direct contact between the aluminum and the carbon fibers. Due to the electrical conductivity of the carbon fibers and the realized metal/fiber contact it is possible to use the hybrid joints as their own fatigue damage sensor and to describe the actual fatigue state of the welds. Additionally to standard experimental data, the change in the electrical resistivity can be monitored during the fatigue tests. Load-increase as well as constant amplitude tests of ultrasonically welded aluminum/CFRP-joints will be presented and discussed.

Stefan Huxhold, Frank Balle, Guntram Wagner, Dietmar Eifler

Fatigue Resistance of Al-Cu-Li and Comparison with 7xxx Aerospace Alloys

Al-Cu-Li alloys are of great interest for aerospace applications due to their good mechanical property balance, excellent corrosion resistance and reduced density. These alloys exhibit an increased resistance to fatigue in particular when compared to 7xxx alloys.The metallurgical parameters affecting the fatigue resistance of alloys AIR WARE™ 2050-T8 and 7050-T74 alloys are studied.Crack initiation and propagation is characterized by FEG-SEM and optical microscopy on open hole fatigue specimens. Initiation on different constituent particles or on slip bands is observed, depending on the stress level, in alloy 2050-T8, whereas only initiation on constituents is observed for alloy 7050-T74. The Paris law is obtained from crack growth rate measurements of long and microscopic fatigue cracks, as well as from inter-striation distance. The fatigue crack growth rate of alloy 7050-T74 is twice that obtained for alloy 2050-T8.The relative contribution of initiation versus propagation time in the fatigue life is analyzed.

A. Daniélou, J. P. Ronxin, C. Nardin, J. C. Ehrström

Fatigue Crack Growth Behavior of 2099-T83 Extrusions in two Different Environments

Aluminum-lithium alloy 2099-T83 is an advanced material with superior mechanical properties, as compared to traditional alloys used in structural applications, and has been selected for use in the latest generation of airplanes. While this alloy exhibits improved fatigue crack growth (FCG) performance over non-Li alloys, it is of interest to simulate the impact of fluctuating loads under variable temperature during airplane service, particularly in terms of the potential effects of material processing history. In the present paper, the FCG behavior in an Integrally Stiffened Panel (ISP) has been investigated both at room temperature and at 243 K. It has been shown that the resistance to crack growth in a cold environment was higher than in ambient laboratory air. Results of this investigation are discussed from the microfractographic point of view, with regard to the variation of the local extrusion aspect ratio, a parameter which correlates with both the crystallographic texture and the grain structure.

Franck Armel Tchitembo Goma, Daniel Larouche, Alexandre Bois-Brochu, Carls Blais, Julien Boselli, Mathieu Brochu

Influence of microstructure on the fretting resistance of Al-Cu-Li alloys

The resistance of two Al-Cu-Li alloys (2050 and 2196) to fretting has been investigated. For each material two heat treatments have been studied (T8 and low temperature ageing). Fretting tests with a cylinder-plane configuration have been performed in the partial slip regime. The results obtained show that the low temperature temper gives a better resistance to fretting crack initiation and propagation than the T8 temper for both alloys. The 3D shape of the fretting cracks has been observed by high resolution synchrotron X-ray tomography. Multiple initiation sites were observed below the contact. In their early stages of development, the fretting cracks grow approximately radially within the material leading to thumb nail cracks which eventually merge laterally. The difference in fretting resistance is analysed with respect to the 3D fracture surface of the fretting cracks in relation with the alloys precipitation state.

Jessica Delacroix, Sophie Cazottes, Armelle Daniélou, Siegfried Fouvry, Jean-Yves Buffiere

Al-Li-Cu-Mg-(Ag) Products for Lower Wing Skin Applications

Al-Li-Cu-Mg alloy products, with and without Ag additions provide substantial performance advantages over conventional 2xxx products. For lower wing applications, the combination of specific ultimate tensile strength and damage tolerance is of particular importance and this is an area in which the Al-Li alloys can excel. Since Al-Li products have historically suffered with issues surrounding high property gradients through the plate thickness and high degrees of tensile in-plane anisotropy, a great deal of attention has been paid to the thermo-mechanical processing routes used in the fabrication of the current generation of alloy products. In addition, corrosion resistance is an area that has received greater attention recently since it can impact inspection intervals. In this presentation, the microstructures and properties of two new alloy products aimed for lower wing applications, 2199-T86 and 2060-T8E86, will be reviewed and compared with non-Li 2xxx products. It is concluded that the performance improvements of Al-Li alloys/products in addition to their lower density will enable significant weight savings in modern aircraft.

L. M. Karabin, G. H. Bray, R. J. Rioja, G. Venema

Development of High Toughness Sheet and Extruded Products for Airplane Fuselage Structures

High specific ultimate strength and high plane stress fracture toughness are primary requirements of aircraft fuselage skins. The performance of alloys/products used in high performance fuselage applications is first reviewed. The specific fracture toughness for products such as 2017-T3, 2024-T3, 2524-T3 and 6013-T6, is discussed as a function of their composition and microstructure. Then the performance of modern Al-Li alloys/products such as 2199 and 2060 sheet and 2099 and 2055 extrusions is examined. It is concluded that the performance of Li containing alloys/products offer significant improvements over non-Li containing conventional fuselage products because of the optimization of strengthening precipitates and grain microstructures. The role of chemical composition on resulting microstructures is discussed.

P. E. Magnusen, D. C. Mooy, L. A. Yocum, R. J. Rioja

Expanding the Availability of Lightweight Aluminum Alloy Armor Plate Procured from Detailed Military Specifications

For many years, the range of aluminum alloys for armor plate applications obtainable in accordance with detailed military specifications was very limited. However, the development of improved aluminum alloys for aerospace and other applications has provided an opportunity to modernize the Army portfolio for ground vehicle armor applications. While the benefits of offering additional alloy choices to vehicle designers is obvious, the process of creating detailed military specifications for armor plate applications is not trivial. A significant amount of material and testing is required to develop the details required by an armor plate specification. Due to the vast number of material programs that require standardization and with a limited amount of manpower and funds as a result of Standardization Reform in 1995, one typically requires a need statement from a vehicle program office to justify and sponsor the work. This presentation will focus on recent aluminum alloy armor plate specifications that have added capability to vehicle designers’ selection of armor materials that offer possible benefits such as lower cost, higher strength, better ballistic and corrosion resistance, improved weldability, etc.

Kevin Doherty, Richard Squillacioti, Bryan Cheeseman, Brian Placzankis, Denver Gallardy

Threshold stress of A3003 alloy

The threshold stress of a commercially available A3 003 alloy was investigated. The A3003 alloy was hot- and cold-rolled into 1-mm-thick plates, and annealed in the fully recrystallized condition. This material was subjected to high-temperature tensile testing and creep testing at temperatures of 160, 200, and 240°C, and the threshold stress was evaluated at the respective temperatures. The threshold stress, which was standardized by the testing temperature, was about 10 percent higher than the Orowan stress, which was calculated from the dispersion density. Further creep-testing experiments at 200°C using the binary solid solution Al-0.6%Mn alloy exhibited threshold stress despite the absence of dispersed particles. These results indicated that the solid solution of Mn increased the threshold strength of the A3003 alloy.

Makoto Ando, Yoshikazu Suzuki, Goroh Itoh

Ultrasonic fatigue of SiC particle reinforced aluminum in the VHCF-regime

At the WKK ultrasonic testing facilities (UTF) are used to perform fatigue experiments in the VHCF regime with a frequency of 20 kHz. These systems allow an on-line characterization of the actual fatigue state by changes of different process parameters such as generator power, displacement, temperature or frequency-response characteristic. Moreover the experiments can be interrupted at user defined events in order to investigate variations of the surface microstructure or changes in the electrical resistance of the specimens. The fatigue tests were realized as load increase tests as well as constant amplitude tests.The investigated MMC was an AA2124 matrix alloy reinforced with 25 vol. % SiC particles with an average diameter of 0.7 microns. An adequate geometry of the ultrasonic fatigue specimens was found by FE-simulations using ABAQUS CAE. The microstructure of the MMC and the AA2124 matrix material were described by SEM images and EDX analysis. Furthermore the monotonic properties were determined and additional hardness measurements were carried out.

M. Wolf, G. Wagner, D. Eifler

Influence of Strain Hardening on Rheological Properties of AlMgSi Wires

Elimination of inactive Theologically supporting steel cores in overhead line conductors and replacing them with highly resistant AlMgSi alloy conductors is forced by the need to constantly increase current-carrying capacity of power lines. This solution incorporates a series of potential benefits (lower weight of conductors, ease of assembly, no corrosive contact with the steel core, favorable resistance). However, removing the steel core may result in rheological lengthening of a conductor, in effect lowering of the tension stress and increasing sag. The article contains experimental test results of low-temperature creep and stress relaxation of various diameter wires made of AlMgSi (6201) and analysis of influence of strain hardening on wire rheological behavior.

Beata Smyrak, Tadeusz Knych, Kinga Korzeń

Origin of Ductile Fracture in Aluminum Alloys

It is well known that metallic materials usually exhibit microvoid nucleation induced by particle fracture, followed by its growth and coalescence. Recently the present authors have revealed that hydrogen micropores play significant role in ductile fracture in AA2024 and AA5056 aluminum alloys, whereas the particle fracture mechanism operates only incidentally. The pre-existing hydrogen micropores exhibit premature growth under external loading before the maximum load, while particle fracture occurs after the maximum load. This tendency was accelerated in notched and cracked materials, because tri-axial stress state, which is necessary for isotropic growth of pores/voids, is generated ahead of a notch. According to the estimation on the areal fraction of dimple patterns originating from the pre-existing hydrogen micro pores, it has been concluded that the hydrogen micro pores make significant contributions to ordinary ductile fracture.

Hiroyuki Toda, Hideyuki Oogo, Hideki Tsuruta, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Masakazu Kobayashi

Damage Tolerance Applied to Design of Mid-Size Aircraft

Most of the mid-size aircraft are certified according to FAA Part 25 requirements, and in order to comply with these requirements the majority of the aircraft structure must be damage tolerant. To assure damage tolerance, despite the overall structural behavior, one should look at the details. There is a great amount of analysis tasks and tests that must be carried out in order to guarantee the aircraft structural integrity. This paper presents an overview of Embraer experience with design and analysis for damage tolerance during the last 30 years. Aspects like DT analysis for metallic and composite structures, selection of appropriate materials, loads, definition of limits of validity and definition of inspection intervals will be addressed along this work. Selected structural tests that have been performed for validation of modeling predictions will be presented. Some aspects to be discussed are related to the design differences between commercial jets, which are usually subjected to high usage conditions, business jets and military aircraft. Further, the application of future technologies, such as structural health monitoring, and also of new materials and manufacturing processes that have been evaluated in order to improve the damage tolerance capability of the aircraft structures will be discussed.

Carlos Eduardo Chaves

The Metallurgy of High Fracture Toughness Aluminum-Based Plate Products for Aircraft Internal Structure

A significant volume of “thick” aluminum plate products is used in the manufacture of an aircraft’s internal structure in applications such as ribs, spars, frames, bulkheads, etc. With the recent launch of more fuel efficient and primarily metallic single aisle aircraft as well as the introduction of composite-intensive twin-aisle aircraft, a number of opportunities exist for upgrading alloys developed more than 30 years ago with a new generation of thick plate products. These include 7xxx aluminum alloys that show significant improvements in both strength and toughness along with Al-Li alloys that show high strength, low density and very high corrosion resistance with significantly improved toughness over previous generation Al-Li. This paper will review these improvements and provide insights into the metallurgy behind better fracture toughness, particularly in the short transverse direction, by considering the impact of composition and processing on quench sensitivity.

J. Boselli, G. Bray, R. J. Rioja, D. Mooy, G. Venema, G. Feyen, W. Wang

The Evolution of Plate and Extruded Products with High Strength and Fracture Toughness

From the first use of 2017-T74 on the Junkers F13, improvements have been made to plate and extruded products for applications requiring the highest attainable strength and adequate fracture toughness. One such application is the upper wing of large aircraft. The progression of these product improvements achieved through the development of alloys that include 7075-(T6 & T76), 7150-(T6 & T77) and 7055-(T77 & T79) and most recently 7255-(T77 & T79) is reviewed. The most current advancements include aluminum-copper-lithium, alloy 2055 plate and extruded products that can attain strength equivalent to that of 7055-T77 with higher modulus, similar fracture toughness and improved fatigue, fatigue crack growth and corrosion performance. The achievement of these properties is explained in terms of the several alloy design principles. The highly desired and balanced characteristics make these products ideal for upper wing applications.

D. K. Denzer, R. J. Rioja, G. H. Bray, G. B. Venema, E. L. Colvin

Lighter and Stiffer Materials for Use in Space Vehicles

Materials for use in cryo-tanks need high specific strength, to reduce weight and high KIe fracture toughness, to avoid crack propagation through the thickness and prevent leakage. This paper presents the evolution of Aluminum alloys and products for use in rockets from the beginning of the space age to the Space Shuttle. The specific strength of alloys used in Juno, Saturn, Delta rockets and the external tank of the Space Shuttle are discussed. The microstructure and properties of 2195 plate and 2090 sheet products are reviewed. Finally, based on improved specific strength, use of 2099 and next generation upper wing 2055 Al-Li plate products is proposed for next generation rockets.

R. J. Rioja, D. K. Denzer, D. Mooy, G. Venema

Research on the High-cycle Fatigue and Crack Initiation Behavior of AA7449 Alloy

This study mainly focused on the high-cycle fatigue and crack initiation behavior of AA7449-T7951 alloy. The fatigue-life tests were carried out over a range of stress amplitudes with the stress ratio (R) of 0.5 and −1.0 at room temperature for both smooth and notch specimens,. Further evaluations were performed with the help of optical microscopy, scanning electron microscopy and transmission electron microscopy, in order to reveal the relationships between microstructure and fatigue crack initiation behavior of this alloy. The results showed that AA7449-T791 alloy had excellent fatigue properties. The fatigue limit (σN) of smooth specimens was 349 MPa for R=0.5 and 134 MPa for R= −1.0. while it was 138 MPa for R=0.5 and 70 MPa for R=−1.0 in notched specimens with the notch factor (Kt)of 3.0. The crack initiation behavior of this alloy can be related to the joint influence of inclusions, precipitates, grain structure and their interactions with dislocations or persistent slip bands.

Zi-qiao Zheng, Shen Zhong, Jing-feng Li, Shi-chen Li

Forming and Joining

Vehicle Lightweighting: Challenges and Opportunities with Aluminum

Rising energy costs, consumer preferences and regulations drive requirements for fuel economy, performance, comfort, safety and cost of future automobiles. These conflicting situations offer challenges for vehicle lightweighting, for which aluminum applications are key. This paper describes product design needs and materials and process development opportunities driven by theoretical, experimental and modeling tools in the area of sheet and castings. Computational tools and novel experimental techniques used in their development are described. The paper concludes with challenges that lie ahead for pervasive use of aluminum and the necessary fundamental R&D that is still needed.

Anil K. Sachdev, Raja K. Mishra, Anirban Mahato, Ahmet Alpas

Correlation of Fracture Behavior with Microstructure in Friction Stir Welded, and Spin-Formed Al-Li 2195 Domes

Single-piece, spin-formed domes manufactured from friction stir welded (FSW) plates of Al-Li alloy 2195 have the potential to reduce the cost of fabricating cryogenic propellant tanks. Mechanical properties in the completed domes can be related directly to the final material condition and the microstructures developed. However, these new fabrication techniques have resulted in unexpected material challenges, such as abnormal grain growth in the weld nugget and the propensity for fracture in the adjacent thermo-mechanically affected zone (TMAZ). In this study, the microstructure and texture transformations within the TMAZ are related to fracture location in the vicinity of the weldment. The texture variations in the TMAZ are caused primarily by the varying amounts of shear deformation introduced during the FSW process. Grain morphology and microtexture characteristics are examined as a function of location in the TMAZ via electron backscatter diffraction (EBSD). A strong correlation between fracture location and the presence of texture banding in the TMAZ is observed. The fracture path tends to follow a distinct region of low Taylor Factor (TF) grains.

Wesley A. Tayon, Marcia S. Domack, Stephen J. Hales

Effect of Process Parameters on Microstructure Stability of FSW Butt Joints after Thermal Treatments

Friction Stir Welding process introduces a degree of deformation in the material that is related to process parameters. Rotational and transversal speeds directly regulate the heat input of welding process and then the morphology and microstructure characteristics. In the present work, mechanical properties and microstructure stability of FSW 6082T6 butt joints were investigated after exposure to high temperature or aging. The thermal stability of fine recrystallized grains in the nugget zone depends on process parameters and post-welding heat treatment. Ductility of post-welding heat treated FSW joints substantially increases with no loss in tensile strength. The micro hardness values of the whole joint are comparable. The effect of aging after cold deformation is also examined in FSW butt joints.

E. Cerri, P. Leo

Microhardness Profile and Microstructure Characterization in Friction Stir Processing Zone of the Aged and Solid Solution Treated 7075 Aluminum Alloys

In this study significant difference on the micro-hardness profile and the microstructures evolution after friction stir processing of the aged and solution treated state 7075 alloys sheet are observed. A comparsion of results between these two initial microstructures indicate that the solution-treated state alloy exhibit lesser variation of mechanical property, and the HAZ scale and the range of micro-hardness variation of the aged state are wider than that of the solution-treated state across the transverse cross section. Besides traditional softened bands around the processing zone, an apparent additional softened band is observed at the HAZ of the mid-plane in the aged state sheet while the traditional softened band around the processing zone is only found in the solution-treated state sheet. The effects of microstructures such as grain size and precipitate behavior on the hardness profile are also investigated.

Zheng ZHOU, Sheng CHEN, Qing LIU

Microstructure and mechanical properties of dissimilar friction stir welds using AA6061-T6 and AZ31 plates

This study was performed to investigate microstructure and mechanical properties of dissimilar friction stir welds using AA6061-T6 and AZ31 plates. Tensile strengths of AA6061-T6 and AZ31 plates were 314MPa and 242MPa, respectively. Tensile strengths of the joints by condition I and condition II were 182MPa and 219MPa, respectively. These are about 75%, 90% of AZ31 tensile strength. During tensile test, fracture was occurred at the weld region. Impact absorption energy of the joint by condition II was about 2 times compared to that of AZ31 base metal. Crack propagation energy dramatically increased at the weld region. This may be due to both grain refinement and homogeneous dispersion of particle by strong plastic deformation.

Kwang-Jin Lee, Sang-Hyuk Kim, Hyeon-Taek Son, Kee-Do Woo

Microstructure and Mechanical Properties of Friction Stir Welded Aluminum Alloy/Stainless Steel Lap Joints

The mechanical properties and interfacial microstructure of an aluminum alloy/stainless steel dissimilar lap joint using friction stir welding (FSW) were characterized. In an FSWed A3003 aluminum alloy-SUS304 steel lap joint, the strength on the advancing side was larger than that at the retreating side. TEM observation indicated that a sound joint can be obtained from the stage of the formation of the amorphous layer owing to the mechanical alloying effects before the formation of intermetallic compounds. This lap joining technique was also successfully applied to A6061-T6 aluminum alloy-grooved SUS304 plates. The maximum tensile strength of the lap joint was approximately the same as that of the base alloy, however, the proof stress of the joint decreased with the dissolution of the β″ phase in the A6061 aluminium alloy, which is caused by the generation of heat during friction stir welding.

Tomo Ogura, Taichi Nishida, Hidehito Nishida, Syuhei Yoshikawa, Takumi Yoshida, Noriko Omichi, Mitsuo Fujimoto, Akio Hirose

The Effect of the Variation of Microstructure in the Friction Stir Welded Zone on the Strain and Tensile Properties of Al2139

The friction stir welding process creates three distinct zones; the weld nugget, themomechanically affected zone, and the heat affected zone. These zones have varying microstructure, texture, amounts of plastic deformation and dynamic recrystallization. The elevated local stresses and non-uniform strains under tension are attributed to the inhomogeneity in the weld. The ultimate tensile strength (UTS), yield stress, and elastic modulus were determined by tensile tests of samples in three orthogonal orientations from inside and outside the weld. The samples from inside the weld showed lower UTS and yield strength, but longer elongation than those from outside the weld. Digital image correlation was used to map the strain variations of the samples during the tensile tests. In addition, electron backscattered diffraction was used to determine the grain size and texture variation of the grains in the weld zones. The correlation of the microstructure variation on the tensile properties will be discussed.

Tomoko Sano, Jian Yu, Richard Chen, Chian-Fong Yen

Hardening Potential of an Al-Cu-Li Friction Stir Weld

The evolution of the microstructure during friction stir welding of a third generation AA2199 Al-Li alloy has been described and related to the mechanical properties of welds. The coupling of electron microscopy and micro-hardness have helped generate an understanding of the relationship between grain structure, precipitate density and morphology behind the observed changes in mechanical properties during post weld artificial ageing. The ability of welds to recover hardness and strength during post weld heat treatment was linked to the limited formation of large scale precipitates which act as sinks for alloying elements. Welds obtained with high tool rotation speed (within parameters studied) showed ultimate tensile strength levels of about 93% of the base metal, an elongation of 6% at fracture, and hardness values ranging between 120–140 HV in the stir zone, thermo-mechanically affected zone, and heat affected zone upon post weld heat treatment.

Rosen Ivanov, Julien Boselli, Diana Denzer, Daniel Larouche, Raynald Gauvin, Mathieu Brochu

Material Testing and Modeling of Aluminum Alloy Sheet in Support of Forming Simulations

This lecture emphasizes the usefulness of material modeling to improve the predictive accuracy in the forming simulations of aluminum alloy sheets, and consists of part I and II. In part I, we present a numerical simulation of sheet necking on the basis of an elastic-viscoplastic crystal plasticity model. In this model, a sheet possessing an initial imperfection in the form of a reduced thickness band is postulated, and the growth of the band caused by the strain localization is analyzed. Our attention is focused on the impact of the r-value for the stretchability of aluminum alloy sheet. In part II, we demonstrate the effect of phenomenological material modeling on the predictive accuracy of finite element analysis (FEA). It is concluded that the biaxial tensile testing method using a cruciform specimen is an effective material testing method for accurately detecting and modeling the deformation behavior of sheet metals under biaxial tension.

Toshihiko Kuwabara, Kengo Yoshida, Daisaku Yanaga

Evaluation of the Ring Compression Test for the Parameter Determination of Extended Friction Models

In the development of optimal forming processes FE-based process simulation is more and more integrated. For these process simulations it is crucial to provide appropriate models and the according parameters of mechanisms relevant for forming processes. Friction between the tool and the workpiece is one of those mechanisms. Based on the basic friction models extended models have been developed to introduce the influence of local contact conditions. It would thus be beneficial if existing friction testing methods could allow the determination of the required parameters. The ring compression test is a commonly used standard friction test. In this work standard and treated samples of a modified ring geometry made of AA1050 are investigated with confocal microscopy after applying the ring compression test supported by FE analysis. The experimental and further theoretical results reveal the limits of applicability of this test on the determination of parameters for extended friction models.

Dieter Horwatitsch, Andreas Merstallinger, Kurt Steinhoff

Finite Element Peen Forming Simulation

Shot peening consists of projecting multiple small particles onto a ductile part in order to induce compressive residual stresses near the surface. Peen forming, a derivative of shot peening, is a process that creates an unbalanced stress state which in turn leads to a deformation to shape thin parts. This versatile and cost-effective process is commonly used to manufacture aluminum wing skins and rocket panels. This paper presents the finite element modelling approach that was developed by the authors to simulate the process. The method relies on shell elements and calculated stress profiles and uses an approximation equation to take into account the incremental nature of the process. Finite element predictions were in good agreement with experimental results for small-scale tests. The method was extended to a hypothetical wing skin model to show its potential applications.

Alexandre Gariépy, Simon Larose, Claude Perron, Philippe Bocher, Martin Lévesque

The Influence of Alloy Composition on the Microstructure, Tensile Ductility and Formability of 6xxx Alloys

In this study, the effect of Si and Mg content on the microstructure, tensile ductility, and formability of naturally aged Al-Mg-Si alloys of the 6xxx series has been investigated using optical microscopy, scanning electron microscopy, tensile testing and forming limit diagram tests. The results show that by raising the Si content the work hardening capacity and the strain rate sensitivity of the alloys can be enhanced. Increase in the Si concentration also promotes a more homogeneous distribution of dispersoids. Collectively, these effects act to improve the tensile ductility and formability of these sheet materials. By contrast, an increase of the Mg content has little influence on the tensile ductility and formability due to reduced strain rate sensitivity and a more heterogeneous distribution of dispersoids.

Hao Zhong, Paul A. Rometsch, Yuri Estrin

Accelerated Post-Weld Natural Ageing in Ultrasonic Welding Aluminium 6111-T4 Automotive Sheet

In contrast to previously published reports, it is shown that there is an observable HAZ when ultrasonic spot welding (USW) automotive alloys, like AA6111-T4, the severity of which depends on the welding energy. Immediately after welding, softening is seen relative to the T4 condition, but this is rapidly recovered by natural ageing, which masks the presence of a HAZ, and the weld strength eventually exceeds that of the parent material. This behaviour is caused by dissolution of the solute clusters/GPZs in the T4 sheet, due to the high weld temperatures (> 400 °C), combined with accelerated post-weld natural ageing to a more advanced state than in the parent material. Modelling has demonstrated that this accelerated natural ageing behaviour can be attributed to an excess vacancy concentration generated by the USW process.

Ying-Chun Chen, Phil Prangnell

Limitations of the M-K Based Forming Limit Diagrams

Using a rate dependent Taylor type crystal plasticity formulation, the limitations of Marciniak-Kuczynski (M-K) approach to numerically simulate the Forming Limit Diagrams (FLDs) were studied. Three uniaxial stress-strain curves with three different post-necking hardening behaviors were generated using crystal plasticity formulation. These curves were constructed based on the real tension test data available for AA5754 aluminum. In the first one the true stress strain curve continued as saturated after the necking and in the other two the post-necking hardening behaviors experienced slopes larger than zero. The result showed that the stress-strain curves dictated different imperfections for the localized necking hence the FLDs generated by them were different. The predicted FLD resulted from the saturated hardening behavior was closer to the experimental data in the biaxial region.

Mohsen Mohammadi, Kaan Inal, Raja k. Mishra

Influence of Forming Conditions on Springback in V-bending Process Using Servo Press

To improve fuel efficiency, aluminum alloys and high tensile steel sheets are increasingly being applied to automotive body parts. However, it is difficult to obtain accurate dimensions of formed parts. Therefore, technologies for reducing springback for the part formed by press are strongly demanded. It is said that the die holding time at the bottom dead center of a servo press slide can affect springback. To clarify the forming mechanisms of this phenomenon, a V bending test with a servo press was performed. Aluminum alloys sheets are applied as specimens. The location of press slide was measured by linear scales. It was found that the movement of the slide in a slide motion program differs from the actual movement of the slide. It is important to confirm if the slide is located in the position specified in the program. In addition, a springback angle measurement system is proposed that uses laser displacement measurement apparatus. Because it avoids human error, the proposed measurement system is more accurate than the image processing method.

Shinya Abe, Susumu Takahashi

Anisotropy and Forming Limit Diagram Comparison of DC and CC 5xxx O Temper Aluminum Alloy Sheets

The microstructures of the aluminum alloy sheets were studied by using optical and scanning electronic microscopes. Textures of DC and CC 5xxx aluminum alloy sheets at O-temper were measured by X-ray diffraction method and Forming Limit Diagrams (FLD) along different angles with rolling direction were obtained. The relationship between anisotropy (crystallographic texture) and FLDs was discussed. It was found that movement and changes in shape of FLDs of two Al alloys were caused by rotations of Cube, S, Copper and Brass textures.

Xiyu Wen, Yansheng Liu, Shridas Ningileri, T. Zhai

Comparison of Localized Deformation in Crystal Plasticity Based Finite Element Simulations between Experimentally Measured and Statistically Generated Three-Dimensional Microstructures for the Aluminum Alloy 5754

This paper presents three dimensional (3D) grain structure of AA5754-O aluminum sheet collected by serial sectioning using a Dual Beam Focused Ion Beam equipped with Electron Backscatter Diffraction (EBSD) to enable an evaluation of the necessity for obtaining real 3D microstructures instead of generating 3D microstructures from 2D data using statistically equivalent microstructure generation techniques. A volume of 45.5x51x33μm material is sampled to construct the 3D microstructure and the corresponding equivalent 3D microstructure is generated using M-builder. These data sets are processed to build FE meshes containing real grain morphology and orientation. FE simulations of deformation fields using rate dependant crystal plasticity theory are conducted on both the real and generated microstructures and the predicted Forming Limit Diagrams (FLD’s) for the two microstructures are compared with the experimental FLD from the same alloy AA5754. Significant differences are observed between the two microstructures.

Jonathan Rossiter, Abhijit Brahme, Kaan Inal, Raj K. Mishra

Path Independent Polar Effective Plastic Strain (PEPS) Diagram for Sheet Forming

This paper reviews a pre-strain effect on necking limit of sheet metal, and discusses the importance of this phenomenon to industrial applications. The paper also discusses a solution to this challenge including adaption of the stress diagram. A new type of forming limit diagram, based on a Polar plot of the Effective Plastic Strain (PEPS) is proposed that appears to be an effective solution to the problem of nonlinear effects, with advantages of the familiar strain-based diagram for linear loading, and without the strain-hardening limitations of the stress diagram, or non-intuitive aspects of the alternate Cartesian diagrams based on effective plastic strain. The benefits and limitations of each method are discussed.

Jeong Whan Yoon, Thomas B. Stoughton

Effect of Impact Compression on the Age-Hardening of Rapidly Solidified Al-Zn-Mg Base Alloys

Effect of impact compression on the age-hardening behavior and the mechanical properties of Mesoalite aluminum alloy was examined by means of the high-velocity plane collision between a projectile and Mesoalite by using a single powder gun. By imposing the impact compression to the Meso10 and Meso20 alloys in the state of quenching after the solution heat treatment, the following age-hardening at 110 °C was highly increased, comparing with the Mesoalite without the impact compression. XRD results revealed that high plastic strain was introduced on the specimen inside after the impact compression. Compression test results also clarified that both Meso10 and Meso20 alloy specimens imposed the impact compressive stresses more than 5 GPa after the peak-aging at 110°C showed higher yield stresses, comparing with the alloys without the impact compression. It was also shown that the Meso10 and Meso20 specimens after the solution heat treatment, followed by the high-velocity impact compression (12 GPa) and the peak-aging treatment indicated the highest compressive yield stresses such as 994 GPa in Meso10 and 1091 GPa in Meso20.

Keitaro Horikawa, Hidetoshi Kobayashi

Fatigue and Creep Properties of Al-Si Brazing Filler Metals

The manufacturing process for automotive heat exchangers involves brazing using an aluminum brazing sheet. To ensure structural strength and improve durability, it is necessary to acquire mechanical properties for each of the materials. Al-Si alloys are most commonly used as the filler metal; however, the properties of the fillets formed by the solidification of the Al-Si filler melt have scarcely been reported previously.In this study, fatigue and creep properties of Al-10mass%Si cast alloy, which is considered to have the same chemical composition and metallic structure as those of the filler metal after brazing, were investigated. From the measured results of samples at various cooling rates during solidification, it was found the eutectic silicon particle size of the Al-Si alloy strongly related to these properties. These results showed that the finer silicon particles improved the fatigue and creep properties of fillets, even those with the same composition.

Masakazu Edo, Masatoshi Enomoto, Yoshimasa Takayama

Effect of Additional Elements of Al-Si Filler Alloy on Flowability and Clearance Fillability

Aluminum alloys are widely used for automotive heat exchangers manufactured by brazing processes. All joint gaps must be filled with Al-Si filler metal to prevent the leak of refrigerant. Recently, brazing of heat exchanger components has become difficult due to the decrease in the thickness of the brazing sheets. Since the fluidity of Al-Si molten metal is very high, the flow of molten filler metal sometimes causes dissolution of the base metal or defect of joints. In this study, we investigated the effect of additional elements (such as Mn, Fe, Ti and Zr) of Al-Si filler metal on the flowability and clearance fillability using our original evaluation model. The results indicated that the addition of Mn or Ti improved the clearance fillability significantly. We clarified the mechanism that additional elements change the properties of molten filler metal, by measuring the viscosity of each filler metal and observing the solidified microstructure.

Masakazu Edo, Michihide Yoshino, Shuu Kuroda

Influence of Erosion Phenomenon on Flow Behavior of Liquid Al-Si Filler Between Brazed Components

Automotive heat exchangers are predominantly composed of plates, tubes and fins. Each component is brazed by using Al-Si filler. In the plate/tube/fin brazed-structures, the flow of the liquid filler between the components affects the fillet size at each joint. In this study, the influence of the erosion phenomenon, i.e., silicon diffusion from the braze cladding into the core alloy, in the tube on the flow behavior of the liquid filler flowing on the tube from the plate to the fin has been investigated. As a result, the area of the liquid filler not flowing but existing around α phases on the tube during brazing, which is defined as filler flow channel, can change depending on the erosion degree. The flow ability of the liquid filler flowing from the plate to the fin increases as the area increases.

Takahiro Izumi, Toshiki Ueda

Effects of Plate Thickness and Projection Shape on the Microstructure and Strength of High-Speed Solid-State Joined 2024 Alloy Studs and 5052 Alloy Plates

An advanced stud joining method was developed that produces a strong joint without mechanical property degradation of the base materials. Specially designed 2024-T3 aluminum alloy studs with a circular ridge projection were pressed against 5052-H34 aluminum alloy plates of 1 to 4 mm in thickness. A high-density discharge current was run through the stud, and flowed through the projection and plate surface for several milliseconds, prompting local heating, plastic deformation, and atomic diffusion at the contact point. The projection crushed and spread along the plate surface. Asymmetrical deformation occurred on both the inner side and the outer side of the projection. For thin plates, joining mainly occurred at the outer side. For thick plates, in contrast, the deformation was largely symmetrical. Effects of discharge voltage and the projection shape were also investigated in an attempt to optimize joining strength.

Shinji Kumai, Keisuke Hayashida, Kento Takaya

Interfacial Reaction During Dissimilar Joining of Aluminum Alloy to Magnesium and Titanium Alloys

Ultrasonic welding (USW), a solid state joining process, has been used to produce welds between AA6111 aluminum alloy and AZ31 magnesium alloys or titanium alloy Ti-6Al-4V. The mechanical properties of the welds have been assessed and it has been shown that it is the nature and thickness of the intermetallic compounds (IMCs) at the joint line that are critical in determining joint strength and particularly fracture energy. Al-Mg welds suffer from a very low fracture energy, even when strength is comparable with that of similar metal Mg-Mg welds, due to a thick IMC layer always being formed. It is demonstrated that in USW of Al-Ti alloy the slow interdiffusion kinetics means that an IMC layer does not form during welding, and fracture energy is greater. A model has been developed to predict IMC formation during welding and provide an understanding of the critical factors that determine the IMC thickness. It is predicted that in Al-Mg welds, most of the lMC thickening occurs whilst the IMC regions grow as separate islands, prior to the formation of a continuous layer.

J. D. Robson, A. Panteli, C. Q. Zhang, D. Baptiste, E. Cai, P. B. Prangnell

Joining of 2024 Aluminum Alloy Stud to AZ80 Magnesium Alloy Extruded Plate by Advanced High-Speed Solid-State Method

For its potential usefulness for weight reduction, an advanced high-speed solid-state joining method was tested for its applicability to the joining of 2024 aluminum alloy studs to AZ80 magnesium alloy extruded plates. In this method, a stud having a circular projection at its bottom is pressed against a plate surface, whereupon a discharge current applied to the upper part of the stud flows through a contact point between the projection and the plate to form a joint between them. Observations of the joint area reveal a projection structure sticking into the plate and bending toward the outside, in line with the predominant path of current flow. Refined grains of AZ80 magnesium alloy were observed in the vicinity of the joint interface. This reveals that local plastic deformation and heating induced dynamic recrystallization within the plate. Tensile fracture strength was not found to increase with increasing discharge voltage. To maximize that strength, it was instead found necessary to select an appropriate discharge voltage.

Yohei Harada, Yutaro Sada, Shinji Kumai

Interface Structure and Bonding in Rapid Dissimilar FSSW of Al to Steel Automotive Sheet

Producing robust friction stir spot welds (FSSW) between Al and steel sheet, with a cycle time short enough for industrial application, is extremely challenging. The problems with the conventional FSSW approach are discussed and a possible solution presented, termed “Abrasion Circle Friction Spot Welding” (ABC-FSSW). In ABC-FSW a probe tool is translated through a slight orbital path to abrade the steel surface over a swept circular area. It is shown that successful welds can be produced between Al-61111 and DC04 steel 1 mm sheets with a cycle time of less than one second, that exhibit very high failure loads and a nugget pullout fracture mode. No intermetallic reaction layer was formed at the joint interface. The mechanisms of weld formation are discussed.

Ying-Chun Chen, Phil Prangnell

Effect of Additional Element on Hybrid Laser Weldability in Al-Mn Alloys

Hybrid laser welding have been carried out, with bead-on-plate and butt welding setting, on Al-Mn and Al-Mn-Mg alloys, to evaluate the welding defects morphology. On bead-on-plate welding, keyhole mode was achieved without the welding defects at 60mm/s traveling speed with 2.12kW pulsed laser in Al-Mn alloy. The increase of maximum power of pulsed laser and Mg content caused a rise of welding defects, that is, porosities and cracks. Simultaneously, both penetration depth and bead width became larger, and aspect ratio of fusion zone (depth to width) also increased. X ray tomography clearly evaluated internal welding defects such as porosity. Morphology of fusion zone and welding defects were influenced by an incorrect root gap in butt welding. An increase in the root gap tended to reduce the porosity, and achieved higher aspect ratio of fusion zone, which was deeper penetration depth and wider bead width. On the other hand, underfill, as superficial welding defect, was clearly formed in both alloys. The root gap in butt welding was one of sensitive factors on the laser weldability besides Mg content and pulsed laser power.

Kenta Suzuki, Hisashi Hori, Keiji Kanamori, Kazumitsu Mizushima, Junichi Kinoshita, Tooru Murata

Experimental and Numerical Analysis of Formation Manner of Characteristic Wavy Morphology in Impact Welded Similar- and Dissimilar-Metal Plates

The characteristic wavy interface was observed in the impact welded similar- and dissimilar-aluminum lap joints. In the present study, effects of impact conditions such as collision velocity, collision angle and materials combination on the interface morphology were investigated. The numerical simulations of the oblique collision between metal plates were performed by using smoothed particle hydrodynamic (SPH) method. The simulation could visualize the formation process of the wavy interface successfully. The wave size increased with increasing collision velocity. The interface of similar-metal joint exhibited the well-proportioned sinusoidal morphology. On the other hand, that of dissimilar joint was asymmetric wave with vortices. Occurrence of two different interface instabilities at the collision point is plausible, and the density difference is considered to control which one of them is dominant. Various joints were also fabricated by magnetic pulse welding and explosive welding. Their interface morphology agreed well with the simulation results.

Yuya Sawa, Shougo Kakizaki, Shinji Kumai

Influences on ARC Stability in Welding of Aluminum Pin-Structures

Pin structures offer an innovative way of joining dissimilar materials such as metals and plastics based on an additional geometric link. Therefore pins are placed on a metal sheet substrate by use of a special arc welding technique called cold metal transfer (CMT), developed by Fronius International. The key element of the CMT process is moving the wire back and forth during the welding process. This controlled movement combined with proper welding parameters allows a defined shaping of the pin.This concept has been applied successfully on stainless steel structures, both experimentally and in simulations. A major problem occurring in the framework of aluminum was the arc stability during the warm up phase originating from the oxide layer at the base material’s surface.In this work we describe how the concept of pin welding was extended on aluminum, which obstacles occurred and how they were surmounted successfully.

Lukas Wittwer, Nasrin Jank, Almedin Bećirović, Andreas Waldhör, Norbert Enzinger

Multiscale characterization and mechanical modeling of an Al-Zn-Mg electron beam weld

Welding of precipitation hardening alloys results in multi-scale microstructural heterogeneities, from the hardening nano-scale precipitates to the micron-scale solidification structures and to the component geometry. This heterogeneity results in a complex mechanical response, with gradients in strength, stress triaxiality and damage initiation sites.We describe the microstructure and mechanical behavior of an electron-beam welded Al-Zn-Mg alloy (7020) by combining a multi-scale quantitative characterization of the microstructure and of the mechanical properties. The microstructure is evaluated by Small-Angle X-ray Scattering and Scanning Electron Microscopy, and the mechanical properties includes local tests on micro-samples of each of the relevant weld zones, and macroscopic tests where the distribution of plastic strain is followed by Digital Image Correlation.

Quentin Puydt, Sylvain Flouriot, Sylvain Ringeval, Guillaume Parry, Frédéric De Geuser, Alexis Deschamps

High Temperature Deformation Behavior of a 6N01 Aluminum Alloy Extrusion with a Seam Weld

An aluminum alloy hollow extrusion made with a porthole-die has a few seam welds. It is known that the deformation behavior of a weld region is different from that of a non-weld region at room temperature. In the present study, the influence of a seam weld on the high temperature deformation of a 6N01 aluminum alloy extrusion bar was investigated. The elongation of the alloy with the seam weld was significantly lower than that of the alloy without it. This was because the alloy with the seam weld started localized deformation at a very early stage of deformation. An orientation analysis with an electron backscatter diffraction suggested that a difference in recrystallization texture between weld and non-weld regions would accelerate the start of localized deformation.

Shinya Yasuda, Ken Atsuta, Satoshi Wakaguri, Koji Ichitani, Akira Hibino

Simulation of Local Material Properties during Laser Beam Welding of Aluminum-Titanium Compounds

Combinations of aluminum and titanium by firmly bonding via laser beam welding enable the production of customized hybrid designs with enhanced properties. A novel approach of coupling process, microstructure and mechanical simulation, considering the development of weld geometry and local material conditions, is intended to deliver a fast and reliable method for evaluating the quasi-static strength of laser beam welded hybrid compounds. For microstructure and mechanical simulations a comprehensive data set of material specific mechanical properties is required to reach simulation results. This includes hot tensile tests, tensile tests concerning the heat affected zone (by means of micro flat specimens) and metallographic examinations to determine the microstructure and hardness. The data set was implemented into a simulation model in order to validate the simulation results including microstructure evolution and resulting local mechanical properties. These results provide the basis for refining and advancing the coupled simulation model.

Annika Barr, Martin Hunkel, Axel von Hehl

Changes in Microstructure during High Strain Rate Superplastic Deformation of an Al-Zn-Mg-Cu-Zr Alloy Containing Sc

The changes in microstructure with respect to the variation in morphology of Al3ScxZr1-x dispersoids and evolution of recrystallized grains during superplastic deformation (SPD) (at a temperature and strain rate combination of 475°C, 1.9×10−2s−1) of a suitably thermo-mechanically processed (TMP) Al alloy 7010 containing Sc have been examined. It is observed that the morphology of Al3ScxZr1-x dispersoids present in the homogenized condition continually changes during subsequent TMP through different stages of SPD process. The number density of the dispersoids is minimal in the TMP condition, whilst the number density of the dispersoids significantly increases with strain during the subsequent SPD process. A simultaneous change in the microstructure during SPD is the gradual increase in the percentage recrystallization with strain. Recrystallization occurred by continuous recrystallization process except at the very early stages of SPD wherein the maximum ODF (orientation distribution functions) intensity (MOI) showed a significant increase coincident with the presence of a reduced number density of the dispersoids in the microstructure.

A. K. Mukhopadhyay, K. S. Prasad, A. Kumar, S. Raveendra, I. Samajdar

Investigation of Superplasticity in Aluminum Alloy 5083

The superplastic response of commercial 5083 alloy (Al-4.42Mg) under uniaxial tension at strain rates ranging from 5×10−5 to 10−2s−1 in the temperature interval 400~550°C was systematically studied in this paper. The tensile test was conducted on samples of rolling direction. The maximum elongation-to-failure of 486% was found at the temperature of 500 °C and strain rate of 10−4s−1. To identify the main charecteristics of superplastic deformation of the alloy, the microstructure and fracture of the alloy are analyzed as a function of strain, strain rate and temperature using optical microscopy (OM) and electron microscopy (SEM). The strain rate sensitivity (m) of the alloy was also studied.

Shasha Zhao, Rehan Qayyume, Haoyan Diao, Chaoli Ma, Xiaowei Wu, Yong Wang

Microstructure Evolution and Tensile Property of Al-4.35Cu-1.53Mg Alloy during Creep Age Forming Process

Creep age forming (CAF) is an effective technology to manufacture large aircraft panel components of aluminum alloys. CAF has attracted much attention in the past few years, however, the evolution of microstructure and performances during the process remains unclear.In the present work, microstructure evolution and relevant variation of tensile property of the Al-Cu-Mg alloy during CAF process was investigated by combination of TEM, tensile tests and electrical conductivity tests. It was found that the presence of external stress had performed a slight but clear influence on the precipitations and the related age-hardening behavior. The precipitation process of S phases was accelerated. Compared with stress-free-aged ones, stress-aged samples achieved peak strength within shorter ageing time and they also exhibited higher yield strength at under-aged condition, but lower yield strength at over-aged stage. The electrical conductivity of stress-aged samples was higher than those of stress-free-aged ones. The effect of stress on microstructure and tensile property of Al alloy was discussed.

S. S. Wang, J. T. Jiang, K. Zhang, J. Z. Chen, L. Zhen

New Analysis of Solute Drag in AA5754 by Precise Determination of Point Defect Generation and the Orowan Relation

Serrated deformation in Al-Mg alloys creates problems that affect consumer product acceptability. This effect is usually attributed to the Portevin-LeChâtelier effect. In this study the inverse PLC effect due to solute drag on moving dislocations is examined in AA5754. The drag mechanism is dependent on the diffusivity of the solute which is in-turn dependent on the point defect evolution during deformation. Experimental determination of the parabolic James-Barnett drag profile by strain rate change experiments indicates the peak stress is centered at 1.5×10−9m/s, which requires a mechanical formation energy for vacancies of 0.4eV/at. A new slip-based constitutive relation was used to determine the evolution of vacancy volume fraction with deformation with strain, which is greater than the volume fraction of vacancies predicted by the solute drag profile.

Brad J. Diak, Alex Penlington, Shig Saimoto

The Influence of Microstructure and Composition on the Machinability of Al-Si Alloys

The motivation to replace steel and cast iron with Al-Si alloys in automotive components stems from an on-going attempt to improve fuel economy and reduce emissions. In the light of these objectives, a study was carried out to determine the influence of metallurgical parameters such as chemical composition, microstructure and morphology of second phase particles formed in 396 type near-eutectic Al-Si cast alloys containing ~11% Si, on their machinability. The Mg-free alloy produces the highest number of holes, followed by the alloys containing 0.3% Mg, and 0.6% Mg, respectively. The chip breakability of the alloys containing the Al2Cu phase is superior to that of the alloys containing Mg2Si.

Y. Zedan, A. M. Samuel, F. H. Samuel, S. Alkahtani

Modeling of Transients as a Response to Changes in Strain path of Commercially Pure Aluminium

Changes in the strain path are inherently involved in metal forming operations. Metals typically show transient behavior of the stress upon the sudden or continuous change in deformation conditions. Unexpected softening, due to the strain path changes (SPC), can have an impact on forming processes, since it may promote strain localization and fracture. Hence, there is a need to accurately predict the mechanical behavior of metals due to changes in strain path. In this study, the phenomenological plasticity model proposed by Holmedal et al. [1] has been implemented into a hypoelastic-plastic formulation with an isotropic high-exponent yield criterion. The model has also been extended by introducing a new model for transient work hardening which occurs during SPC. The model was applied to capture the transient response of as-cast, commercially pure aluminium after SPCs introduced by a sequence of rolling and subsequent uniaxial tension at various angles. By this way a large range of SPCs of relevance for sheet forming operations was covered.

Tomáš Mánik, Bjørn Holmedal, Odd Sture Hopperstad

A New Crystal Plasticity Based Constitutive Model Incorporating Backstress for FCC Polycrystals

To overcome the current limitations of phenomenological models of predicting material response under complex strain path deformation a new hardening law is proposed. The model is calibrated with experimentally measured microstructural features during deformation. The new hardening law, in contrast to existing laws, can be completely determined from observations with very few free parameters. The model accounts for hardening due to interactions with forest dislocations as well as with dislocation cells. The interaction with dislocation cells is estimated by using backstress effect. The new model is calibrated with experimental uniaxial tension data for the aluminum alloy 5754. This model allows us to examine the inhomogeneous distribution of slip arising from microstructural features and provides a powerful tool to investigate formability in FCC polycrystals.

Abhijit Brahme, Raja K. Mishra, Kaan Inal

Numerical Analysis of Surface Roughening and Necking in Aluminum Alloy Tubes Under Internal Pressure

The crystal plasticity based finite element model is used to simulate surface roughening and localized necking in aluminum alloy tubes under internal pressure. A new approach for defining onset of necking is proposed. The effects of spatial orientation distribution, strain rate sensitivity, work hardening, and initial surface topography on surface roughening and necking are discussed. It is demonstrated that while localized necking is very sensitive to both the initial texture and its spatial orientation distribution, the initial surface topography on necking has only a small influence on necking.

Y. Shi, P. D. Wu, D. J. Lloyd

Polycrystal-Plasticity Simulation of Roping in AA 6xxx Automotive Sheet Alloys

The occurrence of roping in AA 6xxx series sheet for car body applications is caused by the collective deformation of band-like clusters of grains with similar crystallographic orientation. In this study large-scale orientation maps obtained by electron back-scattered diffraction (EBSD) are input into a visco-plastic self-consistent polycrystal-plasticity model to analyze the strain anisotropy caused by the topographic arrangement of the recrystallization texture orientations and, in turn, the occurrence of roping. At variance to earlier studies, the measurements were carried out in the short transverse section of the sheets so as to get information on distribution and morphology of orientation clusters through the sheet thickness. Then, narrow bands in the EBSD maps aligned parallel to the ridges on the sheet surface are considered, and the variation in macroscopic strain response from band to band is determined. For a given deformation of the sample these simulations yield quantitative information on the level of roping of Al-alloy sheet for car body applications.

O. Engler, C. Schäfer, H.-J. Brinkman

Properties of Free-Machining Aluminum Alloys at Elevated Temperatures

In areas close to the cutting tool the workpieces being dry machined could be heated up to 350°C and they may be impact loaded. Therefore it is of interest to study mechanical properties of corresponding materials at elevated temperatures. Free-machining alloys of Al-Cu and Al-Mg-Si systems containing Pb, Bi and Sn additions (AA2011, AA2111B, AA6262, and AA6023) were subjected to Charpy U notch impact test at the temperatures ranging from 20 to 350°C. The tested alloys show a sharp drop in notch impact strength KU at different temperatures. This drop of KU is caused by liquid metal embrittlement due to the melting of low-melting point dispersed phases which is documented by differential scanning calorimetry. Fracture surfaces of the specimens were observed using a scanning electron microscope. At room temperature, the fractures of all studied alloys exhibited similar ductile dimple fracture micromorphology, at elevated temperatures, numerous secondary intergranular cracks were observed.

Jiří Faltus, Miroslav Karlík, Petr Haušild

Mechanical Properties of Al-Mg-Sc-Zr Alloys at Cryogenic and Ambient Temperatures

Mechanical properties at cryogenic and ambient temperatures were examined for two alloys belonging to Al-Mg-Sc-Zr system and containing 4.5 and 6 wt% of Mg. It was shown that both aluminum alloys exhibits negative temperature dependencies of elongation-to-failure, yield stress (YS) and ultimate tensile strength (UTS) in the temperature interval 77–293K. In rolled condition, the Al-6%Mg-0.2%Sc-0.09Zr alloy exhibits slightly higher strength in comparison with the Al-4.5%Mg-0.2%Sc-0.09Zr alloy; ductility of these two alloys is essentially the same in whole temperature interval.

Darya Zhemchuzhnikova, Anna Mogucheva, Rustam Kaibyshev

Manufacturing Challenges for Aluminum Sheet in the Automotive Industry

Aluminum sheet is used in the automotive industry for body applications such as hoods, liftgates, and doors, as a way to achieve mass reduction and improve fuel economy. Aluminum sheet usage has been steadily increasing to assist in meeting new fuel economy regulations and consumer demand for improved fuel economy resulting from high fuel costs. With the accelerated need to decrease mass to support aggressive fuel economy improvements, it is expected that the volume of new applications will not only push the manufacturing restrictions, but also exceed the current capacity of automotive-grade aluminum sheet. This paper will outline the major challenges in manufacturing aluminum sheet metal components and describe new alloys and new technologies that are being explored to overcome these challenges. Suggestions for future research and development projects will be made to accelerate additional applications.

Susan E. Hartfield-Wünsch, Jody N. Hall

Thermal Modeling and Die Design Tools for Warm Forming Applications

There has been little published work on the production, die architecture and thermal stability issues of warm forming (WF) technology when scaling from the laboratory to a full-size component at production-rates. One critical area of research essential to achieving high volume warm forming is the development of engineering tools for the heating and thermal control of dies. This paper introduces the development of an analytical analysis method supporting upfront WF die design. The analysis applies conservation of energy to manage and simplify the complex boundary conditions. The outputs include heat transfer parameters for the insulated, exposed, and metal working surfaces of the die, as well as energy and heat-up time estimates. These parameters directly support the simulation and optimization of a WF die using steady-state thermal finite element analysis. The validation of the predicted heat transfer parameters for die boundary conditions has been evaluated using a simple benchmark self-heated block with differing boundary condition parameters.

N. R. Harrison, S. G. Luckey

Buckling of Aluminium Sheet Components

Wrinkling is one of the major defects in sheet metal forming processes. It may become a serious obstacle to implementing the forming process and assembling the parts, and may also play a significant role in the wear of the tool. Wrinkling is essentially a local buckling phenomenon that results from compressive stresses (compressive instability) e.g., in the hoop direction for axi-symmetric systems such as beverage cans. Modern beverage can is a highly engineered product with a complex geometry. Therefore in order to understand wrinkling in such a complex system, we have started by studying wrinkling with the Yoshida buckling test. Further, we have studied the buckling of ideal and dented beverage cans under axial loading by laboratory testing. We have modelled the laboratory tests and also the imperfection sensitivity of the two systems using finite element method and the predictions are in qualitative agreement with experimental data.

Vishwanath Hegadekatte, Yihai Shi, Dubravko Nardini

Predicting Hot Deformation of AA5182 Sheet

Aluminum 5000-series alloy sheet materials exhibit substantial ductilities at hot and warm temperatures, even when grain size is not particularly fine. The relatively high strain-rate sensitivity exhibited by these non-superplastic materials, when deforming under solute-drag creep, is a primary contributor to large tensile ductilities. This active deformation mechanism influences both plastic flow and microstructure evolution across conditions of interest for hot- and warm-forming. Data are presented from uniaxial tensile and biaxial bulge tests of AA5182 sheet material at elevated temperatures. These data are used to construct a material constitutive model for plastic flow, which is applied in finite-element-method (FEM) simulations of plastic deformation under multiaxial stress states. Simulation results are directly compared against experimental data to explore the usefulness of this constitutive model. The effects of temperature and stress state on plastic response and microstructure evolution are discussed.

John T. Lee, Alexander J. Carpenter, Jakub P. Jodlowski, Eric M. Taleff

Examination of Buckling Behavior of Thin-Walled Al-Mg-Si Alloy Extrusions

To achieve the combination of improved crash tolerance and maximum strength in aluminium automotive extrusions, a research program was carried out. The main objective was to study AA6063 alloy thin-walled square tubes’ buckling behavior under axial quasi-static load after various artificial aging treatments. Variables included cooling rate after solid solution treatment, duration of the 1st stage of artificial aging and time and temperature of the 2nd stage of artificial aging. Metallography and tensile testing were employed for developing deeper knowledge on the effect of the aging process parameters. FEM analysis with the computer code LS-DYNA was supplementary applied for deformation mode investigation and crashworthiness prediction. Results showed that data from actual compression tests and numerical modeling were in considerable agreement.

Athanasios Vazdirvanidis, Ioanna Koumarioti, George Pantazopoulos, Andreas Rikos, Anagnostis Toulfatzis, Protesilaos Kostazos, Dimitrios Manolakos

Crystal Plasticity Calculations of Mechanical Anisotropy of Aluminium Compared to Experiments and to Yield Criterion Fittings

Mechanical anisotropy of a sheet was studied by experiments as well as crystal plasticity calculations. The material is a 99.999% high purity Aluminum with additions of 0.066%Fe and 0.068%Si. Uniaxial tensile tests at every 15° from the rolling to the transverse direction were conducted. Yield stresses were measured and also the r-values for the uniaxial tensile tests. The anisotropic Yld2004-18p yield function for fully three-dimensional stress state was fitted to the experiments. Crystallographic orientation data were measured by EBSD and used as input for the full-constraint Taylor model. The yield locus was calculated by the Taylor model and compared to the Yld2004-18p criterion fitted to the experiments. Since the number of possible mechanical tests is limited and the experimental errors can be challenged, it would be desirable to replace the mechanical tests by one texture measurement and virtual experiments by crystal plasticity calculations. The reliability of this approach is discussed for the case of pure aluminium.

Kai Zhang, Bjørn Holmedal, Tomas Manik, Qinglong Zhao

Microstructure and mechanical properties of an electron beam welds in a spray-deposited Al-Zn-Mg-Cu alloy

In this study, an electron beam welds produced in a spray-deposited Al-8.6Zn-2.6Mg-2.2Cu (wt,%) alloy were characterized by optical microscope (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and tensile tests. It is found that the joint of the alloy contained three distinctive regions, i.e. fusion zone, heat affected zone and base metal region. Tensile properties of the joints were obtained by testing flat transverse tensile specimens, and the results indicated that tensile strength of these welds approached 82.3~85.3% of the base metal.

Wang Feng, Xiong Baiqing, Zhang yongan, Zuo Yuting, Liu Hongwei, Li ZHihui, Li Xiwu

Characterization of Damage Mechanisms During Bending of 6xxx Aluminum Automotive Sheets

Bendability is a key property of aluminum automotive panels. Previous work showed that the bendability may not be characterized by macroscopic parameters. In the present work, the kinetics of damage development during bending of 6016 sheet was first characterized experimentally. Then, a mechanical model analyzing independently the influence of the microstructure, the flow stress distribution, the hardening behavior of the material and the sheet thickness on the bendability was developed.The experimental analysis showed that suppressing surface roughness does not lead to an improvement in bendability and that through thickness strain localization controls damage development. Shear bands have been characterized thanks to EBSD map analysis. The observed shear bands extend over 2–3 grains and can concentrate strains of about unity. The mechanical model reproduced the experimental observations and allowed quantifying the influence of microstructure, material behavior and sheet thickness on the bendability. The spatial distribution of the flow stress and the strain hardening at large strains control the sheet bendability.

Laurent Mattei, Dominique Daniel, Gilles Guiglionda, Helmut Klöcker

Heat treatment of welded joints made on 7020 alloy with the AlMg5 alloy

The basic problem of joints welded from the high strength aluminium alloys hardened by heat treatment is a significant drop of the welded material properties in HAZ (Heat Affected Zone). To improve the mechanical properties of welded joints and to prevent crack formation in HAZ, a multi-stage heat treatment can be used.The study examines changes in the properties and structure of HAZ in a welded joint deposited with the Al5Mg alloy on a 7020 alloy (AlZn4, 5Mg1) in the T6 condition. The impact of a two-stage heat treatment (solutioning at 470°C and aging at 90°C/8h +145°C/16h) on structure and properties of HAZ was examined. Considerable degree of elimination of the HAZ effect on structure and properties of a welded joint was observed. For the 7020/Al5Mg welded joint, the mechanical properties (Rm = 348MPa, Rp0.2=301MPa and A50=11,4%) comparable with the properties of 7020 alloy in T6 condition were obtained. Structure examinations were carried out by light microscopy and transmission electron microscopy, while mechanical properties were determined by hardness measurements and a static tensile test. An attempt was made to measure the residual stresses in an around-weld area.

Wojciech Szymański, Marzena Lech-Grega, Sonia Boczkal, Andrzej Kłyszewski

Development of Age-Hardening Technology for Ultrafine-Grained Al-Li-Cu Alloys Fabricated by High-Pressure Torsion

The age-hardening behavior and precipitation microstructures with high dislocation density and ultrafine grains have been studied for cold-rolled and severely deformed 2091 Al-Li-Cu alloy. The age-hardenability at 463K was reduced by high-pressure torsion (HPT) due to the accelerated formation of larger 8-AlLi precipitates at grain boundaries, in place of transgranular precipitation of refined δ’-Al3Li particles that are predominantly observable in the no-deformed and 10%-rolled specimens. When aged at 373K, however, it was successfully achieved for the HPT specimen to increase the hardness up to ~290HV, the highest level of hardness among conventional wrought aluminum alloys. The corresponding TEM microstructures confirmed that refined δ’ particles precipitate within ultrafine grains while keeping the grain size at ~206nm. This result suggests that the combined processing of severe plastic deformation with age-hardening technique enables the fabrication of novel aluminum alloys concurrently strengthened by ultrafine-grained and precipitation hardenings.

Hiroaki Motoshima, Shoichi Hirosawa, Seungwon Lee, Zenji Horita, Kenji Matsuda, Daisuke Terada

Tailored Welding Technique for High Strength Al-Cu Alloy for Higher Mechanical Properties

AA2014 aluminum alloy, with 4.5% Cu as major alloying element, offers highest strength and hardness values in T6 temper and finds extensive use in aircraft primary structures. However, this alloy is difficult to weld by fusion welding because the dendritic structure formed can affect weld properties seriously. Among the welding processes, AC-TIG technique is largely used for welding. As welded yield strength was in the range of 190–195 MPa, using conventional TIG technique. Welding metallurgy of AA2014 was critically reviewed and factors responsible for lower properties were identified. Square-wave AC TIG with Transverse mechanical arc oscillation (TMAO) was postulated to improve the weld strength. A systematic experimentation using 4 mm thick plates produced YS in the range of 230–240 MPa, has been achieved. Through characterization including optical and SEM/EDX was conducted to validate the metallurgical phenomena attributable to improvement in weld properties.

N. S. Biradar, R. Raman

Distinguishing Dynamic Recrystallization (DRX) in Aluminum and Single-Phase Alloys

Dynamic recovery (DRV) during hot working occurs to a decreasing degree, with lower stacking-fault energy (SFE) in Al, Ni, Cu, γ-Fe. With rising strain, the dislocations form dynamically stable boundaries (SIB). Between deformation bands, transition boundaries TD composed of at least 4 different Burgers vectors, develop to exceed 15 degrees (HAB), producing different texture components. In cold working, the presence of SIB-HAB or (TD-HAB) are not considered recrystallization until in annealing, HAB regions convert to mobile boundaries (free of dislocations within nuclei) in discontinuous static recrystallization dSRX. In hot working of Al and solute alloys, there is a critical strain for dSRX when straining is stopped. The TD are permanent and are athermal unlike the subgrain boundaries (SGB) that continually rearrange and change with temperature. In multi-directional straining, micro-shear bands that are also athermal form and become HAB possible giving rise to cDRX. In hot working of low SFE metals, the critical strain for discontinuous dDRX is higher than for dSRX that is only considered to have occurred after straining stopped. For same test condition, it is not logical to claim continuous cDRX has occurred because SIB-HAB are observed when quenched to inhibit dSRX at insufficient strain for dDRX.

H. J. McQueen

Novel Materials

Strain Hardening, Strain Softening and the Portevin-Le Chatelier Effect in Cryomilled, Ultrafine Grained AA 5083

Aluminum alloys consolidated from cryomilled (ball milled in a cryogenic liquid nitrogen or liquid argon slurry) precursor powders show promising increases in strength, commonly >30% over conventionally processed alloys, and acceptable levels of tensile ductility, typically 3 – 15 %. Mechanical behavior is governed by the microstructural features dependent on the alloy and thermomechanical processing (TMP) route chosen for primary, secondary and tertiary forming. In an effort to improve understanding of the alloying and processing parameters influencing mechanical behavior, numerous studies have been performed with various Al-Mg compositions and TMP routes. Here we focus on cryomilled and consolidated AA 5083 to characterize differences in the tensile stress-strain behavior specific to strain hardening, strain softening and Portevin-Le Chatelier (PLC) effects that have been observed. Using stress-strain data from multiple investigations, the possible contributions to these observed characteristics are discussed in terms of grain size, solute content, dislocation mechanisms and texture in the various systems.

Troy D. Topping, Enrique J. Lavernia

Fabrication of Nanostructural Aluminum Alloy Powder with Ball Milling Method

The strength of aluminum alloys can be strongly affected by addition of homogeneous dispersed strengthen particles in nanocrystalline matrix. One method to engineer nanocrystalline materials with strengthen particles is mechanical alloying. The aim of this paper is to fabricate aluminum alloy powder with nanostructure using ball milling method. The commercial Al-Mg-Cu alloy powder was milled along with a different proportion of Fe-based alloy powder (produced by argon gas atomization process) under various ball milling conditions (milling time, process control agents and rotation speed). The structure and the thermal stability of the ball milled powder were examined using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). It is revealed that the Al alloy grain size was minish to 26nm with Fe-based alloy homogeneously dispersed in it. Based on the structural observation, the formation behavior of nanostructural in ball milled powder is discussed.

Han Yang, Ruixiao Zheng, Yanbo Yuan, Xiaoning Hao, Dan Wu, Chaoli Ma

Magnetic, Structural and Mechanical Behavior of Transitional Bulk Nanostructured Al Alloy

Mechanically alloyed powders synthesized by high energy rate ball milling were consolidated to produce bulk polycrystalline Al-50 at. % Fe alloy. Consolidation was achieved by cold compaction and sintering, while annealing was done to obtain an ordered structure. Annealed samples were deformed plastically by a range of compression stresses. Combination of characterization techniques like x-ray diffraction, transmission electron microscopy, vibrating sample magnetometry and Vicker’s micro hardness measurement were utilized to examine different properties. Annealed sample exhibited ordered and non magnetic phase while deformation induced samples showed simultaneous transition to both disorder and ferromagnetism, the transitional alloy at intermediate state possessed partial disorder and low magnetization. The long range order and lattice expansion contribute to the increase in magnetism at low compression stresses while it is only due to the lattice expansion at higher stresses. The order to disorder transition can be assessed by micro hardness measurement.

M. M. Rajath Hegde, A. O. Surendranathan

Production of Al-Based Nano-Intermetallics by High-Pressure Torsion

Micro-powders of Al were mixed with 50 mol.% micro-powders of Ni and severely deformed by high-pressure torsion (HPT). Following the HPT, the powder mixtures were consolidated and their average grain size is reduced to ~28 nm. Structural analysis using high-resolution transmission electron microscopy showed that higher fractions of Al3Ni and Al3Ni2 intermetallics are formed in the Ni matrix by the HPT processing. The HPT-processed materials were transformed to a nanostructured AlNi intermetallic with an average grain size of ~50 nm by annealing at 673 K. The current findings suggest that the HPT processes can be used successfully for production of bulk nanostructured intermetallics at low temperatures.

Kaveh Edalati, Zenji Horita

Novel Cold Spray Nanostructured Aluminum

This paper discusses the introduction of a relatively new materials consolidation process, referred to as ‘Cold Spray’, which has been shown to meet the low-temperature, high velocity criteria for the production of dense, oxide-free metal-base nanostructured materials that may contribute to stronger near net-shape spray nanostructured components and as an enabling repair technology.When spraying nanostructured coatings, there are particular requirements in preserving the microstructure and functionality of the feedstock powder in the final bulk material. This is especially true when depositing temperature sensitive and readily oxidizing materials such as carbides, nitrides, and nanostructered metals. For these materials, the goal is to replace most, if not all, of the thermal energy (i.e., flame temperature) with kinetic energy (i.e., particle velocity) so as to retain the nanostructure without contributing to coating oxidation or porosity. Osmotic consolidation, pressure filtration, and tape casting have been used to produce consolidated nanostructured materials with limited thickness.The low temperature and high kinetic energy associated with the cold spray process allow for the retention of fine/nano grain structure, absence of phase change, capability for thick deposits, and promotion of compressive residual coating stress. These capabilities make the cold spray process an ideal approach to depositing nanostructured metal-base coatings, as well as nanostructured bulk materials. This paper will present data associated with the cold spray development and materials characterization of nanostructured 5083 aluminum.

Victor K. Champagne, Matthew Trexler, Yongho Sohn, George E. Kim

Self-propagating foaming process of Al-Ti reactive precursor for fabricating long scale porous materials

The authors have been investigating a novel processing route in which foam materials are made by self-propagation process. This fabrication process uses chemical reactions so called “Self-propagating high-temperature synthesis (SHS)”, which releases high heat of reaction. To make a foamable precursor, titanium and aluminum powders are blended by Al/Ti molar blending ratio of 4.0. An exothermic agent (boron carbide, B4C) powder, which releases high heat of reaction and increases the combustion temperature, was added to promote the foaming behavior. The powder blend was hot extruded and rolled to make long scale precursors. The thickness of the precursor was varied from 1mm to 4mm. The precursors were heated by both volume combustion synthesis and self-propagating high-temperature synthesis modes. In this presentation, we focus on the self-propagating and foaming behaviors of long scale Al-Ti precursors..

Makoto Kobashi, Naoyuki Kanetake

ALUHAB — The Superior Aluminium Foam

A new metal foaming technology has been developed to produce aluminum foams with controlled cell sizes, a wide range of alloy compositions, and attractive mechanical properties. ALUHAB aluminium foams are manufactured from a special foamable aluminium alloy containing ultrafine particles (80–3000 nm). The technology uses high temperature ultrasonication to homogeneously disperse the particles and thus create a stable, foamable aluminum melt. Oscillating gas injector (loud-nozzle) technology permits the injection of optimally sized bubbles into the melt that are independent of the injector orifice diameter. Using this direct gas injection method, bubble size is regulated by the frequency and the power of the ultrasound, producing uniform bubble sizes in the sub-millimeter range. The technology results in extremely stable metal foams which can be cast into complex forms and re-melted without loss of foam integrity. Processing methods and properties of the ALUHAB foams will be discussed.

N. Babcsan, S. Beke, P. Makk, P. Soki, Gy Számel, H. P. Degischer, R. Mokso

Microstructures and Mechanical properties of Al-Al2O3 Composites Processed by Disk-HPT and Ring-HPT

Al-Al2O3 composites were produced through consolidation of Al micrometer powders and Al2O3 nano-powders using high-pressure torsion (HPT) with disk-type samples (Disk-HPT) and ring-type samples (Ring-HPT). Pure Al powders were mixed with a 30% volume fraction of Al2O3 powders by ball milling (BM). HPT was conducted at room temperature with a rotation speed of 1 rpm under a pressure of 6 GPa for disk samples and 3 GPa for ring samples. The composites were also processed by HPT without BM for comparison. Agglomeration of Al2O3 particles became diminished and the dispersion of nano-sized Al2O3 particles became finer and more uniform by combination of BM and Ring-HPT. This combined use is more effective than Disk-HPT with BM to obtain a uniform Al2O3 dispersion in the Al-Al2O3 nanocomposites and thus to improve mechanical properties.

Maki Ashida, Zenji Horita

Powder metallurgy of high-strength Al90.4Y4.4Ni4.3Co0.9 gas-atomized powder

Al90.4Y4.4Ni4.3Co0.9 gas-atomized powder was hot pressed (HP) to produce highly dense bulk samples through combined devitrification and consolidation. The microstructure of the as-atomized powder is a mixture of amorphous phase with nanocrystalline fcc Al, whereas the consolidated samples consists of fcc Al and a series of intermetallic phases with or without residual amorphous phase depending on the hot pressing temperature (673 or 723 K). The HP samples exhibit a remarkable high strength of ~ 925 MPa (HP at 673 K) and ~ 820 MPa (HP at 723 K) combined with a plastic strain ranging between 14 and 30%. The reduction in strength for the sample HP at 723 K is linked to the complete crystallization of the powder with no residual amorphous phase.

K. G. Prashanth, K. B. Surreddi, S. Scudino, M. Samadi Khoshkhoo, Z. Wang, D. J. Sordelet, J. Eckert

Advanced Class of FML on the Base Al-Li Alloy 1441 with Lower Density

Structure, composition, properties combination of specimens and components, a number of technological parameters for production of advanced FML based on high-modulus Al-Li 1441 alloy (E ~ 79 GPa) with reduced density (d ~ 2.6 g/m3) and optimized adhesive prepreg reinforced with high-strength high-modulus VMP glass fibres are described. Service life 1441 alloy provides the possibility of manufacture of thin sheets (up to 0.3 mm), clad and unclad. Moreover, some experience on the usage of 1441 T1, T11 sheets and shapes in Be 200 and Be 103 aircraft was accumulated. The class of FML materials based on Al-Li alloy provide an ~5% improvement in weight efficiency and stiffness of skin structures as compared with those made from FML with conventional Al-Cu-Mg (2024T3 a.o.) and Al-Zn-Mg-Cu (7475T76 a.o.) alloys.

V. V. Antipov, O. G. Senatorova, N. F. Lukina

Solute Distribution and Mechanical Properties of Ultra-Fine-Grained Al-Mg Alloys

Ultra-fine-grained (d~200 nm) Al-Mg alloys exhibit outstanding strength due to both Hall-Petch grain-size strengthening and solid-solution strengthening. When the solubility limit is exceeded, some Mg segregates to grain boundaries. This impacts both thermal stability and mechanical properties. In this study, alloys with between 0 wt.% Mg (pure Al) and 10.5 wt.% Mg are made by ball milling powders in liquid nitrogen, and consolidated by hot isostatic pressing and extrusion. The alloys are exposed to temperatures up to 500 deg. C. Microhardness and tensile behavior are measured and correlated with the microstructure, as measured by local-electrode atom-probe tomography, X-ray diffraction, and electron microscopy.

Richard A. Karnesky, Nancy Y. C. Yang, Chris San Marchi, Troy D. Topping, Zhiui Zhang, Ying Li, Enrique J. Lavernia

Age-hardening Behavior of MgB2 Particle Dispersed Al Alloy Composite Materials

In this work, aging behavior of MgB2 particle dispersed Al-1 mass%Mg2Si alloy composite material which including 4, 8 and 50 vol. % MgB2, was investigated by hardness test and TEM observation to know their age-hardenability. The age-hardenability was observed for the composite materials with 4 and 8 vol. % MgB2 but not for that with 50 vol. % MgB2. The precipitates in these composite materials were also investigated using TEM.

Chihaya Kawamoto, Kenji Matsuda, Satoshi Murakami, Daisuke Tokai, Tokimasa Kawabata, Yasuhiro Uetani, Susumu Ikeno

Production of the Al3Ti foam by microwave heating

Al-Ti foams were produced by the combustion synthesis of blended powder compacts consisting of titanium and aluminum using microwave heating. Aiming at promoting the foaming behavior, the exothermic powder (titanium and B4C powders) was added to the blended powder to increase the combustion temperature. We examined the possibility of a microwave heating as the igniting method of a precursor. The effects of the exothermic powder addition and powder compacting pressure on the combustion foaming process were investigated. The microwave heating experiments were conducted by using a 500W, 2.45 GHz single-mode cavity. The precursors were heated in a maximum of magnetic field in the cavity. When the amount of the exothermic powder was 0 and 5vol%, combustion synthesis was identified, although the expansion of the precursor was not achieved. When the amount of the exothermic powder was 10vol%, the compacting pressure (25MPa ~ 200MPa) did not affect the porosity.

Tsuyoshi Yamamoto, Makoto Kobashi, Naoyuki Kanetake

Phase Transformations

Nanocluster Formation Behavior in Al-Zn-Mg Alloys with Microalloying Elements and Improved Mechanical Properties

The formation behavior of nanoclusters and precipitates in Al-Zn-Mg alloys containing microalloying elements was investigated using TEM and 3DAP techniques. The grain size of the alloys was controlled to investigate its influence on the nanocluster formation. In the Al-Zn-Mg alloys, small amount of Mn is effective to refine grains. The age-hardening behavior and precipitate microstructures in the alloys with refined grains were complicated. In the grain refined alloy the age-hardening is markedly decreased and precipitation is greatly suppressed. It is found that the microalloying elements of Ag and Sn are effective to increase age-hardening and to produce refined precipitates in the refined grain alloy. The behavior is similar to the phenomenon of the reduced width of PFZs. The important feature of microalloying elements is the interactions with vacancies and solute atoms. The alloys with refined grains and reduced PFZs exhibit high strength and high ductility.

Tatsuo Sato, Tomo Ogura

Effects of Microalloying Elements (Cu, Ag) on Nanocluster Formation and Age-Hardening Behavior in Al-Mg-Si Alloys

Two types of nanoclusters playing an important role in the age-hardening behavior of Al-Mg-Si alloys are detected through differential scanning calorimetry measurements in the Base, Cu-added, Ag-added and Cu-Ag added alloys. The formation of Cluster (2) during aging at 100 °C suppresses the formation of Cluster (1) during a subsequent natural aging resulting in an enhancement of the age-hardening behavior during a final aging at 170 °C. Furthermore, low additions of Cu and Ag clearly enhance the precipitation hardening, as demonstrated by the hardness measurements. Higher precipitate numbers in the pre-aged specimens as compared with the naturally-aged ones were confirmed using transmission electron microscopy (TEM). The effects of low Cu and Ag additions on the nanocluster formation during the low temperature aging and the age-hardening behavior during the multi-step aging are discussed based on the age-hardening phenomena.

JaeHwang Kim, Calin Daniel Marioara, Randi Holmestad, Equo Kobayashi, Tatsuo Sato

Effect of Low Cu Amounts and Pre-Deformation on the Precipitation in Al-Mg-Si Alloys

Transmission electron microscopy (TEM) studies were performed on two Al-Mg-Si alloys with low Cu additions (0.01 and 0.10 wt%) in order to investigate the effect of Cu and 10% pre-deformation on precipitate microstructure and its connection to mechanical properties. After 300 minutes aging at 190°C, fine microstructures associated with high hardness were observed in the alloy with 0.10% Cu. Pre-deformation led to heterogeneous distributions of precipitates along dislocations, causing microstructure coarsening. This effect was less pronounced in the alloy with the higher Cu amount.

Takeshi Saito, Shinji Muraishi, Calin D. Marioara, Randi Holmestad

High Resolution Characterization of the Precipitation Behavior of an Al-Zn-Mg-Cu alloy

This work addresses the unresolved issues regarding the structure and precipitation evolution of the metastable particles in an Al-Zn-Mg-Cu alloy using high-angle annular dark field imaging under atomic-resolution level, η’ plates were found to be composed of 7 atomic planes parallel to the {111}Al planes with five inner planes alternatively enriched in Mg and Zn and two outer Zn-rich interfacial planes. The smallest η phase has a minimum 11-planes thick structure. In rare instances, particles less than 7 planes were found indicating a very early preference for 7-layer particle formation. Throughout the aging, the plate thickness appears constant, while the plate radius increases and no particles between 7 and 11 planes were observed. Based on the HAADF contrast, our observations do not support the η’ models previously set forth by other authors. Clear structural similarities between η’ and η were also observed.

Yi-Yun Li, Libor Kovarik, Patrick J. Phillips, Yung-Fu Hsu, Wen-Hsiung Wang, Michael J. Mills

Precipitation Process in a High Mg to Cu Ratio Al-Mg-Cu-Ge Alloy

Precipitation process of Al-4.0Mg-1.5Cu-0.25Ge (wt.%) alloy ageing at 200 °C was investigated using conventional and high-resolution transmission electron microscopy techniques. For the peak-aged condition at 25 hours, the strengthening mainly derived from homogeneously formed GPB zones (2–4 nm in size) and fine S-phase precipitates (~10 nm in size). Simultaneously, small amount of coarse S-phase precipitates and cube-shaped Z′-phase precipitates were also formed. Z-phase was transformed into more stable Z-phase with prolonged ageing. The microstructural evolution among those precipitates was preliminarily discussed.

J. H. Xia, G. Sha, Z. G. Chen, S. P. Ringer

Investigations on the Precipitation in Monocrystalline Al-Mg-Si Model Alloy by Small Angle Neutron Scattering

The aim of this work is to clarify the difference in anisotropic precipitate growth in an Al-Mg-Si single crystal during artificial ageing (AA) after different natural pre-ageing (NA) conditions. In one experimental series, in-situ small angle neutron scattering (SANS) experiments were performed at 180°C right after solution heat treatment and quenching. In another series, the crystal was first naturally aged at ‘room temperature’ for 1 week before AA, after which SANS experiment was carried out. The measurements were performed at D22 of the Institut Laue-Langevin with the single crystal mounted so that the neutron beam was parallel to one of the {001}Al directions. Anisotropic scattering from the needle-like precipitates growing along {001}Al was observed. The size evolution of the precipitates is compared for the crystal aged with and without NA. For this crystal without NA, the length of the precipitates increases significantly in the first 2h of AA. After this both the length and radius increase with AA time. With NA before AA, the number density of the precipitates is lower comparing to the directly AA crystal. The rate of increase in length of ß” is lower and the mean size of β” is smaller.

Cynthia Sin Ting Chang, André Heinemann, Charles Dewhurst, Zeqin Liang, John Banhart

Prediction of the Influence of Si Content on the Ageing Behavior of Al-Mg-Si-Cu Alloys by Thermodynamic Modeling

In this study, the influence of Si content on the ageing behavior of Al-Mg-Si-Cu alloys has been predicted by thermodynamic modeling. Experiments including hardness tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were carried out to verify the predictions. It is shown that experimental results are consistent with the predictions. Moreover the Mg and Si content in the as-quenched supersaturated solution have been found to have critical influence on the resulting hardening in the alloys.

Yanli Ji, Hao Zhong, Ping Hu, Fuan Guo, Hiromi Nagaumi

Continuous Heating Dissolution Diagrams of Aluminum Alloys

To describe dissolution processes and also possible precipitation processes during continuous heating of aluminum alloys over a wide range of heating rates new methods have to be developed. According to common continuous heating transformation diagrams of steels, continuous heating dissolution diagrams can provide information about the dissolution and precipitation behavior of aluminum alloys depending on heating rate. The method developed by Milkereit et al. for quenching experiments can be used, to establish continuous heating dissolution diagrams. Heating of aluminum alloys EN AW-6082 and 6005A has been investigated in the heating rate range from 0.01 to 5 K/s up to temperatures of about 580 °C in two different types of differential scanning calorimeters. The dissolution and precipitation behavior strongly depend on initial microstructure, e.g. T4 or T6, and on heating rate. The start temperatures of dissolution and precipitation reactions increased with increasing heating rate.

Benjamin Milkereit, Julia Osten, Christoph Schick, Olaf Kessler

Dynamic room temperature precipitation during cyclic deformation of an Al-Zn-Mg-Cu alloy

The effect of pre-straining on a precipitation heat treatment is a well-chartered area and is relevant to a number of Al alloy manufacturing processes. When straining and precipitation occur concurrently, the situation is less clear. This may arise during creep, fatigue or elevated temperature forming operations. Straining introduces dislocations and strain-induced vacancies that may enhance nucleation and growth processes but the dislocations may also shear and/or cause precipitate dissolution. This study reports a systematic characterization of precipitation during room temperature cyclic deformation of the AA7050 (Al-Zn-Mg-Cu) alloy. The mechanical response is monitored using plastic strain controlled cyclic deformation tests and the precipitation state is characterized using small angle x-ray scattering. It is shown that the precipitate volume fraction increases with the number of deformation cycles and is well correlated with the hardening increment observed but the mean precipitate radii remains relatively constant during cycling at ~4–5A.

C. R. Hutchinson, F. de Geuser, A. Deschamps

Effects of Pre-Aging Condition on Multi-Step Aging Behavior in Al-Mg-Si Alloys

The effects of pre-aging temperature on natural aging and following final aging (bake hardening) behavior in the Al-0.6mass%Mg-0.6mass%Si alloy were investigated by means of hardness test, tensile test, differential scanning calorimetry analysis (DSC) and transmission electron microscopy (TEM). As the results of hardness change, lower pre-aging temperature increase the natural age hardening, and decrease the bake harden-ability with natural aging time. By comparing DSC measurements and TEM observations, it is found that Cluster(1) formed during natural aging after the pre-aging, and the β” decomposition temperature is moved higher with natural aging time. The relationship of natural age hardening and bake hardening response suggested that the Cluster(1) suppressed the β” formation even if Cluster(2) coexistent condition.

Yasuo Takaki, Tetsuya Masuda, Equo Kobayashi, Tatsuo Sato

Hardening Response to Rapid Aging Processes and Precipitation in Al-7%Si-0.3%Mg Alloy

An orthogonal test was designed to obtain a optimized rapid aging process in order to shorten aging time. Hardness and tensile tests and TEM observation were used to evaluate the hardening response to the rapid aging process. An optimized rapid aging process, 160°C2h+200°C2h, is obtained. Under this process, the alloy has an approximately equal hardness and strength to the conventional single stage peak aging process, but the aging time of the rapid aging process is remarkably shortened, only 16.7% of the conventional process. Compared with the conventional aging process, the number density of β″ precipitates formed during the rapid aging course is reduced, however, the amount of β′ precipitates is remarkably increased. Though the contribution of the β″ precipitates to hardening is reduced, that of the high density of β′ rod precipitates is considerably increased, thus the rapid aging process produces an approximately equal hardening effect to the conventional peak aging process.

Hengcheng Liao, Yuna Wu, Ke Ding

Thermodynamics of Al3Li nano-clusters in an Aluminum solid solution

An accurate thermodynamic description of nano-clusters in a solid solution is a pre-requisite for a reliable predictive homogeneous nucleation model. Unfortunately, the classical textbook description which consists in describing the free energy as a sum of a volume energy part and a surface energy parts with constant interface energy fails to capture the thermodynamic of small clusters at high enough temperatures.Equilibrium Monte Carlo (MC) calculations have been performed to study the free energy of Al3Li clusters as a function of size and temperature. Constant first and second nearest neighbor interactions were used as input. Calculations show that for a temperature range between 0°C and 200°C, the simplistic textbook description fails to reproduce the free energy of Al3Li nano-clusters and that a more complex description is required to reproduce MC results and to capture the cluster conformation entropy.This study is part of a modeling project on the simulation of the microstructure of AIR WARE™ alloys.

Christophe Sigli, Joël Lépinoux

The Effect of Cu and Cr on Clustering and Precipitation in Al-Mg-Si Alloys

A group of alloys based on pure ternary Al-0.4 wt.%Mg-1.0 wt.%Si are used to study the effect of Cu and Cr on clustering and precipitation in Al-Mg-Si alloys. Differential Scanning Calorimetry (DSC) is performed for samples naturally aged for different times after solution heat treatment and ice water quenching. Three clustering processes are observed in all the alloys. The fundamental clustering sequence does not change by additional elements. However, the Cu containing alloy shows less clustering and the first clustering event is hindered. Kissinger analysis reveals that the 2nd and 3rd processes have very similar effective activation energies. Therefore, a model incorporating only two independent reactions is used to obtain kinetic parameters. It is found that the first clustering process starts with a low effective activation energy of 50 kJ/mol and has a mechanism similar to mixed nucleation while the latter two processes are governed by a higher activation energy of 79 kJ/mol and have a mechanism similar to particle growth. During precipitation, the Cr containing alloy shows a similar precipitation heat signal in DSC as the pure ternary, thus having negligible effect on precipitation. On the other hand, the formation of β″ is less dominant in the Cu-containing alloy while precipitation of other phases before reaching the peak-aged condition is possible.

Zeqin Liang, Cynthia Sin Ting Chang, John Banhart, Jürgen Hirsch

Influence of Mg and Si on Cluster Formation in Al-Mg-Si Alloys Studied by Positron Annihilation Lifetime Spectroscopy

The change of positron lifetimes during natural ageing of binary Al-Mg and Al-Si alloys was characterized. The experiments show that for dilute alloys, the average lifetimes in Al-Si alloys decrease faster to a stable value during natural aging (NA) than in Al-Mg alloys and the vacancy-related lifetime components of Al-Si are also significantly higher than in Al-Mg alloys for equal solute content. For alloys with higher solute contents, the decrease of the lifetime becomes insignificant. This indicates that Si enhances the jump frequency of vacancy while Mg can trap vacancy and slow down the jump frequency of vacancy.

M. Liu, Y. Yan, Z. Liang, C. S. T. Chang, J. Banhart

Microstructural Characterization of Flexcast® Al-Mg Alloys with Scandium and Zirconium Additions

This contribution focuses on the microstructural characterization work performed on two Flexcast® Al-Mg alloys with Sc and Zr additions: one with and the other without Sc. In the as-cast state, both alloys showed fine Al- Fe intermetallic compounds along the solidification cell boundaries due to the high solidification rate in the belt caster. After heat treatment at 300°C, fine Al-Mn dispersoids were observed in both alloys. When the alloys were cold-rolled and aged at 300°C, the Sc-free alloy gradually recrystallized adjacent to constituents, while the Sc-containing alloy started to precipitate thermally stable L12 structured Al3(Sc,Zr) particles. After heat treatment at 400°C, the Sc-free alloy exhibited Al-Mn dispersoids only and the cold-rolled alloy was fully recrystallized in less than 30 seconds. On the other hand, the Sc-containing alloy showed more enhanced precipitation of coherent Al3(Sc,Zr) particles after aging at 400°C (1 minute) without recrystallizing. The highest strength of Flexcast® Al-Mg alloys was obtained in the Sc-containing alloy cold-rolled and aged at 300°C (4 hours) and this was ascribed to the combined effects of residual dislocations and coherent precipitates.

D. H. Kang, M. Sohi, S. H. Mousavi, M. Gallerneault

Precipitation in Al-Cu-Li alloys: from the kinetics of T1 phase precipitation to microstructure development in friction stir welds

Al-Cu-Li based alloys are experiencing a rapid development for aerospace applications. The main hardening phase of this system (T1-Al2CuLi) forms as thin platelets (1 nm) that can reach diameters of 50 to 100 nm with remarkable stability in temperature. The nucleation, growth and thickening mechanisms of this phase are of crucial importance for the understanding of the microstructures resulting from simple to complex thermo-mechanical treatments, including friction stir welding of such alloys.In this contribution, we present in-situ synchrotron small angle scattering X-ray experiments that enable to better understand the precipitation kinetics and morphology evolution of T1 precipitates. In a second part, this knowledge is applied to the understanding of the development of FSW microstructures.

A. Deschamps, F. de Geuser, B. Decreus, B. Malard

Quantitative description of the T1 morphology and strengthening mechanisms in an age-hardenable Al-Li-Cu alloy

In the Al-Cu-Li system, the main strengthening precipitate is the T1 phase (Al2CuLi). In order to understand the strengthening related to the formation of this phase, we first present an investigation of the morphology of the T1 phase in an AA2198 alloy using Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) in relation with the evolution of micro-hardness. In parallel, we present an investigation of the interaction between T1 precipitates and dislocations using High Angle Annular Dark Field (HAADF) imaging in an atomic resolution Scanning Transmission Electron Microscope (STEM). The atomic scale imaging of precipitates makes it possible to quantify the density of shearing events, which turns out to be insufficient to account for the imposed plastic strain. We discuss the implications of this result in terms of precipitate-dislocation interactions.

Thomas Dorin, Alexis Deschamps, Frédéric De Geuser, Matthew Weyland

Orientation Relationship of Dispersoids Precipitated in an AA3XXX Alloy during Annealing at Low Temperatures

In this study a DC-cast 3xxx alloy containing 0.497 wt.% Fe, 0.480 wt.% Si and 0.992 wt.% Mn has been isothermally annealed at 450°C with different holding times from 0 to 24 hours. A systematic study of the precipitation behaviour of dispersoids has been performed by using Transmission Electron Microscopy. An orientation relationship (OR) for a cubic α-Al(Mn,Fe)Si dispersoid has been determined to be approximately <601>al // <101>α, with habit planes of {010}al// {010}α. The habit planes have been confirmed by a further investigation of the electron diffraction pattern by using the ∆g approach.

Astrid Marie F. Muggerud, Yanjun Li, Randi Holmestad

Hf-Containing Precipitates in Al-Si-Mg-Hf Alloy during Heat Treatments at 400°C-560°C

Hf-containing precipitates with nanobelt-like morphology were found in Al-Si-Mg-Hf-Y alloy in the previous work, however, the precipitation behaviour of such precipitate was not understood completely. In the present work, an Al-Si-Mg-Hf alloy was cast and subsequently heat treated in the temperature range 400–560°C, in order to investigate the evolution of Hf-containing precipitates. It was found that the heat treatment temperature is a critical factor on the formation and type of the Hf-containing precipitates. Heat treatment temperatures in the range 400 to 475°C resulted in elongated Al-Hf precipitates for a holding time up to 45 h while temperature above 500°C resulted in Si2Hf nanobelt-like precipitates. A heat treatment temperature of 560°C gave a high density of belt-like precipitates with large aspect ratio.

Z. H. Jia, Z. J. Chen, L. Arnberg, P. Åsholt, Q. Liu, G. J. Huang

Ageing Hardning and Precipitationg of the 7A60 Alloy during Cooling Aging

Effect of non-isothermal aging treatment on microstructure and properties of 7A60 aluminum alloys was in present work. Hardness is decided by the start cooling temperature and cooling rate, high initial cooling temperature and fast cooling rate will improve the hardness of the alloy. The electrical conductivity of the alloy is mainly determined by the initial temperature, the higher the initial temperature, the higher the conductivity. Hardness and electronic conductivity were improved greatly during initial cooling stage. Afterward, hardness and conductivity was slightly affected. Transmission electron microscopy (TEM) and high-resolution transmission electron microscope (HRTEM) analysis showed that the main strengthen precipitate of the 7A60 alloy by cooling aging is plate-like η′ phase, which precipitating along the {111}Al. There are great different in the size of η′ phase, which dispersed in Al grains, and the PFZ is narrow by high temperature rapid cooling aging.

Liu Yan, Jiang Daming, Wu Gaohui

Precipitation Morphology in Al-Mg-Si-Sc-Zr Hot-Rolled Sheet

In order to clarify the morphology and the elemental distribution of particles in an Al-Mg-Si-Sc-Zr alloy, microstructural observations and elemental analyses were carried out by transmission electron microscopy (TEM), scanning TEM, three-dimensional electron tomography and energy dispersive X-ray spectroscopy. The Al-Mg-Si-Sc-Zr alloy was cast, homogenized and hot-rolled. Two types of Al3(Sc, Zr) particles with L12 structure were observed in the hot-rolled sheet: spherical particles about 50 nm in diameter, and rod-like particles about 50 nm in diameter and 200nm in length. All particles have the core-shell structure with the core enriched with Sc and the shell enriched with Zr atoms. One type of spherical particles have a semi-coherent relationship with the matrix, while another type of spherical particles shows a cylindrical core morphology and have an incoherent relationship with the matrix. In summary, it is concluded that the rod-like particles, the coherent spherical particles and the incoherent particles are formed during casting, homogenized treatment and hot-rolling, respectively.

Ken-ichi Ikeda, Ryutaro Akiyoshi, Takuya Takashita, Masatoshi Mitsuhara, Satoshi Hata, Hideharu Nakashima, Kazuhiro Yamada, Kenji Kaneko

The Effect of Natural Ageing on Quench Sensitivity in Al-Mg-Si Alloys

Quench sensitivity in age hardenable aluminum alloys has been attributed to solute loss on heterogeneous nucleation sites during slow cooling after extrusion. However, recent work on the influence of natural ageing at room temperature on the artificial ageing response suggests that quenched-in vacancies play a significant role in clustering and precipitation behavior of strengthening precipitates. Two different high-strength Al-Mg-Si alloys were cooled at different rates and artificially aged at 175ºC after 30 min or 24 h natural ageing at 18ºC. While natural ageing was confirmed to have a negative effect on the age-hardening response of fast cooled samples, the ageing response of slow cooled samples was independent of natural ageing time. Therefore the effects of quench sensitivity are less apparent after prolonged natural ageing. It is concluded that quench sensitivity is also affected by changes in ageing kinetics due to loss of quenched-in vacancies during slow cooling.

Katharina Strobel, Mark A. Easton, Lisa Sweet, Nick C. Parson

An Isothermal Calorimetry Technique for Measurement of C-Curves in AA6XXX Alloys

Quantitative description of precipitation processes is of importance for alloy development and process optimization in AA6xxx alloys. An isothermal calorimetry technique was used to measure the exothermic heat evolution of an AA6xxx alloy during artificial ageing following various interrupted quench experiments in the temperature range 300–450°C. Subsequently, the total heat measured in the calorimeter was used to estimate the amount of solute present in the alloy at room temperature following quenching and to construct c-curves for precipitation during the hold time of the interrupted quench. The microstructure predictions made using the c-curves compared well with resistivity and microhardness measurements in the peak-aged condition.

Leo Colley, Nitin Singh, Cyrille Bezençon

Influence of chemical composition on aging property of 7204 aluminum alloy

The influence of the room temperature pre-aging (RTPA) conditions on the strength of the AA7204 aluminum alloy in T6 temper was changed by the zinc and magnesium contents. When both the zinc and magnesium contents were the lowest and the RTPA was omitted, the strength became the lowest because the aging rate during artificial aging decreased and a nonhomogeneous precipitation of the η′-phase occurred. On the other hand, the η′-phase became finer and the strength of the T6 temper increased as the RTPA was longer and higher. Also, the two-step artificial aging resulted in a higher strength. Furthermore, the RTPA influence on the strength of the T6 temper decreased with the increasing zinc and magnesium contents, and it almost disappeared when both the zinc and magnesium contents were maximum values.

Tadashi Minoda, Hideo Yoshida

Transforming of the Morphology of Iron Phases in Aluminum Alloys

Iron containing phases with unfavorable morphology almost always exist in commercial aluminum alloys. The attempt to change morphology of the iron containing phase by addition of different alloying elements was made in present work. Experimental and thermodynamic studies of multicomponent phase diagrams with additions of refining elements were carried using ThermoCalc software and analysis of microstructures of the alloys in as-cast and annealed states. The possibility to obtain iron containing phases with almost spherical morphology, which allows to neutralize negative influence of iron on ductility and fracture strength of alloy, was presented in the work.

V. V. Cheverikin, A. V. Khvan, V. S. Zolotorevskiy

Effects of microalloying with Sn on the precipitation process of Al-3.5Cu-0.4Mg (wt%) alloy

The hardness test and transmission electron microscopy (TEM) have been used to investigate the effect of additions of Sn on precipitation processes in Al-3.5Cu-0.4Mg(wt%) alloy. It’s shown that a higher peak hardness can be obtained in the Sn-containing alloys. Additions of Sn into Al-Cu-Mg alloy stimulate the precipitation of θ′(Al2Cu). Many fine and uniform θ′ can be precipitated in underaged(15h), while the σ phase (Al5Cu6Mg2) and Ω(Al2Cu) have been inhibited in Al-Cu-Mg-Sn alloy. The Sn microalloy effects can be attributed to the formation of insoluble Mg2Sn particles in AQ condition, which remove Mg atom from matrix. The removal of Mg leaves an insufficient of Mg so that precipitation of the σ and Ω is inhibited. It also shifts the alloy matrix composition toward the (a+0+S) phase field to promote θ′ precipitate. In addition, θ′ and S phase in Sn-containing alloy exhibit a lower rate of coarsening at over-aged condition.

Jun Shu, Zhi-guo Chen, Ji-shuai Zhang

Effect of Fe Content on the Transformation of Ferrous Phases in 6XXX Alloys during Homogenizing Annealing

This work is devoted to studying the effect of Fe content on the processes of ferrous phase transformations in dilute Al-Mg-Si-Fe alloys by methods of quantitative metallography. The change of morphology of ferrous phases during homogenizing annealing is quantitative estimated. It is established that increasing of iron content to 0.4 % in dilute Al-Mg-Si-Fe alloys accelerates the phase transformation.

P. Bryantsev, M. Samoshina

Evolution of nanometer precipitates in AA7050 alloy subjected to overaging treatment and warm deformation

The aim of this work was to develop a new processing method that can be utilized to refine grain structures. In order to produce sufficiently large dispersed precipitates to obstruct the dislocation sliding, the precipitation behaviors of AA7050 alloy during overaging and warm deformation were investigated. The results show that the size and quantity of the needle-like precipitates increased with increasing aging temperatures and times during overaging. The strain can induce the dissolution of needle-like precipitates and the re-precipitation of the spherical and refined precipitates, which were wrapped around by high density dislocation cells. The size and distribution of the precipitates and dislocation density were stable during the stress relaxation processing at 300 °C with a strain rate of 10 s-1. The sub-grains and fine-grained structures were obtained owing to the pinning effect of the precipitates, resulting in both improved strength and ductility.

Lang Yujing, Cui Hua, Cai Yuanhua, Zhang Jishan

Precipitation morphology and tensile properties of Al-0.62Mg-0.32Si alloy aged at low temperature

The influence of aging precipitates on tensile properties and dislocation substructure in Al-0.62Mg-0.32Si (mass %) alloy has been investigated by tensile tests and microstructural observations. Cold-rolled sheets of the alloy were aged under the following conditions: 453 K for 20 h (sample A), 373 K for 120 h (sample Bl), 373 K for 7200 h (sample Bh) and 323 K for 14688 h (sample C). Values of Vickers hardness of samples A, Bl and C were about 75 HV. However, characters of precipitates were different among the samples: needle-like β′′ precipitates about 50 nm in length and 4 nm in diameter were observed in sample A using transmission electron microscopy (TEM), and Mg-Si clusters below 2 nm in size were observed in samples Bl and C by three-dimensional atom probe (3DAP). In sample Bh showing the maximum hardness (103HV) after 373 K aging, fine β′′ particles about 5 nm in length were observed. Samples A and Bh with the β′′ precipitation exhibited higher values of yield stress than those for samples Bl and C, and the β′′ precipitates pinned dislocations. On the other hand, samples Bl and C with the cluster formation had excellent ductility and showed different dislocation substructure from each other. Electron tomography observations revealed that dislocations in sample Bl was wavy in three dimensions, while dislocations in sample C tended to be linear in shape. These results suggested that the tensile properties and dislocation motion were dependent on the aging products, such as clusters and β′′ precipitates.

Ryutaro Akiyoshi, Ken-ichi Ikeda, Masatoshi Mitsuhara, Satoshi Hata, Hideharu Nakashima, Ken Takata, Makoto Saga, Kohsaku Ushioda, Kenji Kaneko, Masao Kikuchi

Microstructural Change and Mechanical Properties with Isochronal Aging in Al-Ni-Gd Metallic Glasses

The changes of precipitation microstructures and mechanical properties during isochronal aging have been studied for melt-spun metallic glasses of Al-Ni-Gd ternary system. The fabricated Al90Ni3Gd7, Al87Ni7Gd6 and Al85Ni7Gd8 ribbons were isochronally aged up to 400°C and then examined by X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectrometry (EDX). It was found that two different intermetallic compounds of Al23Ni6Gd4 and Al19Ni5Gd3 as well as primary crystallized α-Al are formed by the isochronal aging in good agreement with the fact that three exothermic peaks are detected in the differential scanning calorimetry (DSC) curves. The highest nanoindentation hardness and Young’s modulus were obtained for the isochronally-aged Al85Ni7Gd8, suggesting that not only the increase in Ni and Gd contents but also the isochronal aging is quite effective in strengthening the melt-spun Al-Ni-Gd alloys.

Hideomi Kato, Shoichi Hirosawa, Kenji Matsuda, Gary J. Shiflet

Age-Hardening Behavior of Al-Mg2Si Alloys with Different Mn and Fe Contents

Microstructure and aging hardness variation of Al-Mg-Si alloys with different Mn or Fe content were investigated to reveal the effect of Mn or Fe on the age hardening behavior of Al-Mg-Si alloy using transmission electron microscopy. The peak hardness of the alloys with small content of Mn or Fe is higher than that of the base alloy; the peak hardness of the alloy with 0.2at.%Fe is similar to that of the base alloy but the peak hardness of the alloy with 0.25at.%Mn is lower than that of the base alloy. Si is expensed to form the dispersoid of AlMnSi or AlFeSi in the alloy with 0.25at.%Mn or 0.2at.%Fe.

Shumei Wang, Shanshan Chen, Tokimasa Kawabata, Susumu Ikeno, Hidetoshi Takagi, Koji Kawakita, Kenji Matsuda

The Features of Phase Composition and Microstructure of Eutectic Piston Alloys AlSi12CuMgNi and AlSi12Cu2MgNi

The systematic analysis of phase composition for piston alloys AlSi12CuMgNi and AlSi12Cu2MgNi based on the thermodynamic calculations of multicomponent phase diagrams was performed. A difference in the character of crystallization due to addition of manganese and higher copper content in AlSi12Cu2MgNi was found. The microstructure of castings obtained with different solidification rates and effect of annealing at various temperatures were investigated.

M. Samoshina, N. Belov

Tem Observation of Precipitates in Ag-Added Al-Mg-Si Alloys

The influence of addition of the small amount of transition metals to Al-Mg-Si alloy had reported by many researchers. In the previous our work, β′ phase in alloys Al — 1.0 mass% Mg2Si -0.5 mass% Ag (Ag-addition) and Al -1.0 mass% Mg2Si (base) were investigated by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED), in order to understand the effect of Ag. In addition, the distribution of Ag was investigated by energy filtered mapping and high annular angular dark field scanning transmission electron microscopy (HAADF-STEM). One Ag-containing atomic column was observed per β’ unit cell, and the unit cell symmetry is slightly changed as compared with the Ag-free β’. In this work, the microstructure of G.P. zone and β’’ phase was investigated by TEM observation, which were formed before β’ phase. The deformed sample by high pressure torsion (HPT) technique before aging was also investigated to understand its effect for aging in this alloy.

Takeshi Nagai, Kenji Matsuda, Junya Nakamura, Tokimasa Kawabata, Calin Marioara, Sigmund J. Andersen, Randi Holmestad, Shoichi Hirosawa, Zenji Horita, Daisuke Terada, Susumu Ikeno

Effect of Ag and Cu Contents on the Age Hardning Behavior of Al-Zn-Mg Alloys

Al-Zn-Mg alloy has been known as one of the aluminum alloys with the good age-hardening ability and the high strength among commercial aluminum alloys. The mechanical property of the limited ductility, however, is required to further improvement. In this work, three alloys, which were added Cu or Ag into the Al-Zn-Mg-Si alloy, were prepared to compare the effect of the additional elements on the aging behavior. The content of Ag and Cu were 0.2 at.% and 0.2at.%, respectively. The age-hardening behavior and microstructures of those alloys were investigated by hardness measurement, high resolution transmission electron microscope (HRTEM) and selected area electron diffraction (SAED) technique. Ag or Cu added alloy showed higher peak hardness than Ag or Cu free alloy. According to addition of Ag or Cu, the number density of the precipitates increased than Ag or Cu free alloy.

Katsumi Watanabe, Tokimasa Kawabata, Susumu Ikeno, Tomoo Yoshida, Satoshi Murakami, Kenji Matsuda

Effect of Cu or Ag Addition on Tensile Deformation in Al-Zn-Mg Alloys

In this work, Al-Zn-Mg alloys, which were added with Cu or Ag, were prepared to compare the effect of the additional elements on tensile deformation. Hardness measurement, tensile test, SEM observation have been performed in order to understand the relationship between tensile deformation and crystallographic orientation of Al-Zn-Mg alloys. The addition of Cu or Ag increases the tensile strength of the alloy though decreases the elongation slightly comparing with the base alloy.

Naoya Miura, Katsumi Watanabe, Tokimasa Kawabata, Yasuhiro Uetani, Susumu Ikeno, Tomoo Yoshida, Satoshi Murakami, Kenji Matsuda

Hrtem Observation of the Precipitates in Cu and Ag Added Al-Mg-Si Alloys

In this study, the aging behaviour of Al-1.0mass%Mg2Si alloys containing 0.35at.%Cu, 0.35at.%Ag, 0.2at.%Cu-0.1at.%Ag and 0.1at.%Cu-0.2at.%Ag has been investigated by hardness measurement and HRTEM observation. 0.35Cu alloy has the highest peak hardness. 0.1Cu-0.2Ag alloy has the shortest aging time to the peak hardness. 0.1Cu-0.2Ag alloy has the fastest age-hardening rate in the early period of aging. 0.35Ag alloy has the finest microstructure at the peak hardness. The precipitates were classified into random-type, parallelogram-type, β’-phase and Q’-phase using HRTEM image with different aging time. Relative frequency of all types of precipitates changed by aging times.

M. Tokuda, K. Matsuda, T. Nagai, T. Kawabata, J. Nakamura, S. Ikeno

Effect of Cu or Ag Addition on Two-Step Aging Al-Mg-Si Alloy

The effect of Cu or Ag addition on 2 step aging in Al-Mg-Si alloy has been investigated to understand precipitation for this alloy.The maximum hardness of 2 step aged alloy was higher with increasing pre-aging time for Al-Mg-Si alloy. The aging time to the maximum hardness in Al-Mg-Si-Cu and Al-Mg-Si-Ag alloy pre-aged at 343K is longer than that of the alloy only aged at 473K.

Yoshihisa Oe, Kenji Matsuda, Momoko Tokuda, Takeshi Nagai, Tokimasa Kawabata, Susumu Ikeno

Effect of Cold Rolling on Age Hardening in Excess Mg-Type Al-Mg-Si Alloys Including Some Minor Elements

It has been known that transition metals improve the mechanical property of Al-Mg-Si alloy. The thermo-mechanical treatment is also effective to improve the strength of Al-Mg-Si alloy. In this work, the aging behavior of deformed excess Mg-type Al-Mg-Si alloy including Ag,Cu,Pt was investigated by hardness test and TEM observation. The value of the maximum hardness increased and the aging time to the maximum hardness became shorter by increasing the amount of the deformation. The age-hardening ability (ΔHV) was decreased with increasing amount of the deformation. The effect of additional element on AHV was also similar to the result of the deformation described above. Comparing the value of the maximum hardness for the alloys aged at 423–523 K, the ex. Mg-Cu alloy was the highest, the ex. Mg-Ag alloy was middle, and the ex. Mg and ex. Mg-Pt alloys were the lowest because of total amounts of added elements.

Yurie Ogawa, Kenji Matsuda, Tokimasa Kawabata, Yasuhiro Uetani, Susumu Ikeno

Effect of Transition Metals on the Age-Hardening Behavior of Al-Mg-Ge Alloys

In this work, several transition metals (Au, Ag Cu and Cr) were selected and added to Al-1.0mass%Mg2Ge alloy. Tensile test and TEM observation were performed to investigate the age-hardening behavior of these alloys. We found that alloy including Ag showed a quick age-hardening rate at the initial aging stage, while Al-Mg-Ge alloy including Cu had the highest peak was improved than that of Al-Mg-Ge alloy without Cu.

K. Matsuura, K. Matsuda, T. Murakami, T. Kawabata, S. Ikeno

Tem Observation of Precipitates in Al-Mg-Ge Alloys with Different Mg2Ge Contents

It has been known that Al-Mg-Ge alloy shows the similar precipitation sequence to Al-Mg-Si alloy, and its equilibrium phase is β-Mg2Ge according to its phase diagram. In this study, the precipitation sequence of Al-Mg-Ge alloys containing different contents of Mg2Ge has been investigated by hardness test, TEM and HRTEM observation to understand the effect of Mg2Ge contents on age-hardening behavior of these alloys. The hardness of as-quenched and peak-aged samples was improved by increasing Mg2Ge contents. There was no big difference between peak hardness of the alloys with higher Mg2Ge contents aged at 423, 473 and 523 K, which was different from the result of the alloys with lower Mg2Ge contents. The precipitates in the peak-aged samples were classified as some metastable phases, i.e. the β’-phase and parallelogram-type precipitates by HRTEM observation. The relative frequency of these precipitates in the matrix changed with Mg2Ge contents.

Tomoatsu Murakami, Kenji Matsuda, Tokimasa Kawabata, Susumu Ikeno

Effect of Quenching Condition on Aging of Dilute Al-Ag Alloy

GP zones in Al-Ag alloys have been studied extensively by many workers, but little attention have been paid to the condition of quenching by which super-saturated solid solution would be obtained. In this paper, aging of dilute Al-Ag alloy at 273K after quenching under various conditions was studied by measurement of electrical resistivity. Scattering of the quasi-equilibrium value of resistivity (ρE) was not random but closely related to the as-quenched value (ρ0); ρE increased with increasing ρ0. When the quenching temperature (TQ) was lower than or equal to 773K, the state at ρE was controlled substantially by the concentration of quenched vacancy. On the other hand, when Tq > 823K, GP zones formed during quenching played an important role, instead of quenched vacancies, in determining the state.

Teruto Kanadani, Keiyu Nakagawa, Akira Sakakibara, Koji Murakami, Makoto Hino

Influence of Silicon Addition on Precipitation Behavior in an Al-Cu-Mg Alloy

Influence of silicon (Si) addition on aging precipitation behavior of an Al-4Cu-1.3Mg alloy was investigated by hardness measurements and TEM analysis. The results indicated that each of the Si-containing alloys exhibits an enhanced age-hardening response, a cubic phase, previously designated σ phase, was obtained. The σ phase was showed to be a (semi-)coherent and coplanar phase with the Al matrix, i.e.,{100}σ//{100}Al and <100>σ//<100>Al. In addition, S’ phase was observed. Si addition played an important role on the formation of σ phase. σ phases were observed in the Si containing alloy for all the aging conditions studied but was absent in Si-free alloy. The content of Si significantly influenced the volume fraction of σ phase in the alloy. Prolongation of aging time will be conducive to precipitation of a greater number of σ phases.

Xiwu Li, Baiqing Xiong, Yongan Zhang, Feng Wang, Yanqi Zeng, Zhihui Li, Baohong Zhu, Hongwei Liu

X-Ray Diffraction Study on Lattice Constant of Supersaturated Solid Solution for Al Based Binary Alloys and Selected Al-Zn-Mg-Cu Alloys

The effects of Zn, Mg, Cu content on lattice constants of the supersaturated solid solution of Al-Zn, Al-Mg, Al-Cu based binary alloys and three selected 7B04, 7050, 7B85 alloys were investigated by using X-ray diffraction pattern technique, and the effect of lattice distortion on the stability of the solid solution was attempted to describe the mechanism of quench sensitivity in age hardened Al alloys. The results show that the Cu is most sensitive to the lattice distortion of Al matrix when it was added to Al alloy to form supersaturated solid solution. The effect sequence of alloying elements to lattice constant of the 7XXX series aluminum alloy solid solution was: Cu > Mg > Zn. Evidence has been presented for the obvious expansion behavior of Al lattice in the supersaturated 7B04,7050, and 7B85 alloy. The order of the lattice distortion of solid solution of was: 7B04 > 7050 > 7B85. Compared to the 7B04 and 7050 alloy, the main alloying elements seems to be most stable in the solid solution of 7B85 alloy, and this could be used to explain the lowest quench sensitivity of 7B85 alloy among three selected 7XXX series alloys in this study.

Zhihui Li, Baiqing Xiong, Yongan Zhang, Xiwu Li, Baohong Zhu, Hongwei Liu, Feng Wang, Peiyue Li

Recycling

Exploring Property Based Aluminum Specifications

One of the limiting factors to increased use of scrap in alloys is problematic tramp elements that accumulate in the scrap stream. Currently, alloy producers make use of blending models to assist in choosing from a large number of inputs (scrap sources, primary aluminum, and alloying elements) to manufacture a portfolio of alloys within specification. Alloys are batched to specification to maximize alloy function which includes a complex set of desired properties. While AA specifications have been put in place to guide batch blending decisions, often maximum constraints result in conservative scrap utilization, thus minimizing the potential for environmental and economic savings. This work begins to quantify the trade-offs in an approach where property based constraints are substituted for compositional constraints using a linear programming aluminum blending model tracking up to twenty alloying elements. Results show that increased scrap utilization is possible for a set of specific cases.

Naitik Gada, Gabrielle Gaustad

Emerging Development in Al-Alloy Recycling for Nontraditional Aluminum Metal Matrix Composites Processing

Growing demands for new emerging materials are aimed at introducing nontraditional processes. However, Direct metal oxidation, DIMOX, as applied to Al-alloys recycling has prompted production processes to be more cost efficient. Aluminum alloy scrap is heated to different temperatures, 950°C, 1000°C, and 1050°C for various holding times (15 to 90 minutes) and then poured into metallic molds. The formation of hybrid composite is introduced by alloying elements additions (α -Fe, and Si). Ceramic alumina phase with intermetallic fibers or whiskers are established in an aluminum matrix. Functionally gradient materials, FGM, are also produced after prolonged holding time (90 min. at 1050°C). Scanning electron microscopy with energy dispersive X-ray spectroscopy EDX is utilized for microstructural characterization. 3-point tests are applied on another group of samples. The application of DIMOX on recycled Al-alloy with the addition of alloying elements has a dominant effect on composite microstructure.

Bakr Mohamed Rabeeh

Reuse of Aluminum Dross as an Engineered Product

To prevent the leaching of landfilled aluminum dross waste and save the energy consumed by recovering metallic aluminum from dross, aluminum dross is reused as an engineering product directly rather than “refurbished” ineffectively. The concept is to reduce waste and to reuse. Two kinds of aluminum dross from industrial streams were selected and characterized. We have shown that dross can be applied directly, or accompanied with a simple conditioning process, to manufacture refractory components. Dross particles below 50 mesh are most effective. Mechanical property evaluations revealed the possibility for dross waste to be utilized as filler in concrete, resulting in up to 40% higher flexural strength and 10% higher compressive strength compared to pure cement, as well as cement with sand additions. The potential usage of aluminum dross as a raw material for such engineering applications is presented and discussed.

Chen Dai, Diran Apelian

Separation of Inclusion Particles from Liquid Metal by Electromagnetic Force

The separation of non-metallic inclusion particles from liquid metal is very important not only for fabricating high-quality metal products, but also for recycling materials. Electromagnetic separation is an attractive method for removing inclusions from liquid metal. It separates particles whose electrical conductivity differs from that of the liquid metal.This study investigates electromagnetic separation in a liquid Al/SiC particle system. The applied electromagnetic force causes the SiC particles to migrate toward the side wall of the crucible, causing a layer of particles to form on the wall. The thickness of this layer is limited by the electromagnetic skin depth. The layer forms by the balance between the electromagnetic separation force and the dispersion force due to turbulent flow.

Shin-ichi Shimasaki, Koichi Takahashi, Yoshimasa Kanno, Shoji Taniguchi

The Influence of Pyrolythic Reactions on the Aluminum Dross Formation during the Twin Chamber Remelting Process

After a coated aluminum product has reached the end of life cycle it needs to be recycled in an economical way. State of the art is the thermal removal of the organic fractions by pyrolysis. In modern multi chamber furnaces this step is realized in a separate pre-heating and melting compartment of the furnace. The incidence of aluminum losses can be traced back to the contained organic components, which lead to an aluminum burn off and thus increase dross production. The influence of typical scrap package structures on the de-coating step and the impact of released organic components on the dross quantity are investigated in this work. Lab-scale experiments have shown that the average residence time is too short to complete the pyrolysis. It has to be considered that the pyrolysis continuous while the scrap bale is submerged in the aluminum melt.

B. Jaroni, B. Flerus, B. Friedrich, G. Rombach

Turbulent Coagulation of Solid Particles in Molten Aluminium—Kinetics of Cluster Formation

Removal of inclusions plays a key role in the process of aluminum recycling. Many research works focus on the behaviors of inclusions in molten metal, such as particle coagulation. To reveal its mechanism water model experiments have been performed by some researchers including the authors’ group. In the present research, experiments of particle coagulation were carried out with molten Al including SiC particles in a mechanically agitated system. Particle coagulation and formation of clusters were observed under turbulent flow of the molten Al. The number of clusters in the metal decreased with agitating time whilst the size increased. 3-D analysis of the clusters in solidified Al was implemented by X-ray micro CT in SPring-8. A 3-D image analysis was adopted to a number of sliced 2-D images, and the size and structure of the SiC cluster were analyzed.

Tao Li, Shin-ichi Shimasaki, Shoji Taniguchi, Kentaro Uesugi

Purification using high pressure molten aluminum

A novel technique has been developed to separate eutectic forming elements using a continuous supply of high pressure molten aluminum. In this continuous process, enriched liquid in the mushy zone is selectively expelled from the solidifying mold through a permeable membrane. The fraction of expelled liquid and the level of purification attained can be controlled in real time. Applications of this technique for refining smelter grade aluminum as well as recycling aluminum scrap are being explored. Unique aspects and advantages of the process will be discussed.

Vivek M. Sample, William A. Cassada

Recycling of Aluminum Alloy with Dimox and Rheocasting Functionalize High Performance Structural Foam Composite

Great efforts aiming towards the synthesis and the development of structural composite materials. Direct metal oxidation, DIMOX introduced for hybrid composite processing. However, oxidation temperatures around 1100°C lead to the formation of porous ceramic materials. To utilize this porosity intentionally for foam production, a new approach based on synergetic effect of alloying elements, DIMOX and semisolid (rheocsting) processing is developed. A semisolid reaction, rheocasting is introduced to control porosity shape and size. Aluminum alloy 6xxx (automobile scrap pistons) is recycled for this objective and DIMOX at 1100°C for 30 min, then rheocasting, at 750°C for 30 minutes. The effect of α-Fe powder, Mg powder, and Boric acid powder established for the objective of a hybrid structural metal matrix composite in bulk foam matrix. The kinetic of formation of hybrid metal matrix foam composite is introduced. Microstructural and mechanical characterization established for high performance Aluminum foam hybrid composite materials.

Bakr Mohamed Rabeeh

Solidification

It’s not Your Father’S Casthouse any More

To many people in the aluminum industry, the casthouse, where scrap or primary molten metal is transformed into ingots for subsequent processing to sheet or plate, is still perceived as an area where innovation is all but impossible. Given the very fundamental role that the casthouse plays in the overall production of aluminum sheet and plate, there are often significant challenges that must be overcome to successfully introduce advancements in either overall efficiency or improved quality of the final product. However, if new concepts are sufficiently reviewed and tested, the casthouse can be a springboard for significant innovation and creativity. This presentation provides a brief review of the current state of the Direct Chill (DC) casting process, which remains the largest process for the production of rolling stock for aluminum sheet and plate, and highlights some recent technical advances in the casthouse with particular attention to their effect(s) upon the entire production chain.

Robert B. Wagstaff, Mark T. Gallerneault

Aluminum Monolithic Alloy and Multi-Alloy Cast Using Planar Solidification Approach

Direct-Chill (DC) casting of aluminum ingots and billets for the subsequent manufacture of wrought product forms has been the established industry standard practice for the past 80 years. The through-thickness characteristics of aluminum products are well understood and are affected by the phenomena of macrosegregation which occurs during casting. In the present work, two new classes of alloy ingot were cast using a novel planar solidification approach. One class is a monolithic alloy ingot with a highly uniform composition through the thickness. The other class is multi-alloy ingot with engineered compositional gradients through the thickness. The chemical and microstructural characteristics of these cast materials are discussed and compared to conventional DC ingot.

Men G. Chu, Alvaro Giron, William A. Cassada

The Effect of Planar Solidification on Mechanical Properties of Al-Zn-Mg-Cu-Zr Alloy Plate

Direct-Chill (DC) casting of aluminum ingots and billets for the subsequent manufacture of wrought product forms has been the established industry standard practice for the past 80 years. The through-thickness characteristics of aluminum products are well understood and are affected by the chemical variability introduced during DC casting by the phenomenon known as macrosegregation. In the present work, an ingot of Al-Zn-Cu-Mg-Zr was cast using a novel planar solidification approach that avoids conventional DC macrosegregation and achieves a highly uniform composition through-thickness. This ingot was fabricated to 25 mm plate and its chemical, microstructural, and mechanical characteristics are compared to a DC cast and fabricated plate of similar composition, thickness, and temper.

T. Hosch, M. G. Chu, G. Feyen, R. J. Rioja, W. A. Cassada

Functional Gradient Products Enabled by Planar Solidification Technologies

A new class of materials with engineered compositional gradients through the thickness is introduced. Ingots with different types of composition gradients through the thickness were fabricated into plate. The composition and mechanical properties of these “Functional Gradient” plate products (metallic composites) are described, and the energy absorption performance of different architectures of functional gradient products is discussed in terms of dimensionless parameters. It is concluded that ab-initio simulations of architecture and performance are needed for the development, optimization and use of functional gradient products.

R. J. Rioja, R. R. Sawtell, M. G. Chu, M. Karabin, W. A. Cassada

Role of Solute and Transition Metals in Grain Refinement of Aluminum Alloys under Ultrasonic Melt Treatment

It is well known that several factors affect the as-cast microstructure through influencing either nucleation or growth during solidification. The effect of solute elements on grain refinement, which can be quantified by the growth restriction parameter Q, is of great importance for controlling the as-cast grain size in aluminum alloy. On the other hand, the ultrasonic melt treatment (UST) is one of potent grain refining methods in aluminum alloy. Our previous results showed that ultrasonic melt treatment results in a significant grain refining effect in an aluminum alloy when transition metals, such as Ti and Zr, are present in the melt. It was suggested that UST may increase the nucleating potency of Al3(Zr,Ti) intermetallics. In this paper, the growth restriction effect caused by segregating elements is considered in order to further study the efficiency and potency of grain refiner particles caused by ultrasonic treatment. The results show that the main effect of transition metals Zr and Ti is related to the maximum number of particles which are active nucleants under UST. With increasing Zr, the maximum number of potent particles increases, which produces a better grain refining effect.

L. Zhang, D. G. Eskin, A. Miroux, L. Katgerman

Melt Conditioned Casting of Aluminum Alloys

High shear melt conditioning of aluminum alloy melts disperses oxide films and provides potent nuclei to promote non-dendritic solidification leading to refined as cast microstructures for shape castings, semis or continuously cast product forms. A new generation of high shear melt conditioning equipment has been developed based on a dispersive mixer that can condition either a batch melt or can provide a continuous melt feed. Most significantly the melt conditioner can be used directly in the sump of a DC caster where it has a dramatic effect on the cast microstructure. The present goals are to expand the castable alloy range and to increase the tolerance of alloys used in transport applications to impurities to increase the use of recycled metal. The paper will review the current status of the melt conditioning technology across the range of casting options and will highlight development opportunities.

Geoff Scamans, Hu-Tian Li, Zhongyun Fan

Impact Toughness Enhancement of Melt Treated Al-Si-Mg Cast Alloy

The alloy toughness is influenced by the alloy composition and the melt treatments applied. The present work investigates the effects of different types of grain refiners on the impact properties of Sr-modified A356.2 alloys in as-cast and heated-treated conditions. The results show that the addition of Ti and B greatly improves the alloy toughness but only in a fully modified state, and the right type of master alloy and addition levels are used. The highest values for total absorbed energy of T6-tempered alloys are obtained after using Al-5%Ti-1%B and Al-10%Ti master alloys following upon the addition of 0.04% Ti. A significant deterioration in impact properties is observed due to the Sr-B interaction in some cases. The improvements in toughness may be attributed primarily to the change in silicon particle morphology and to the dissolution and fragmentation of a number of the intermetallics formed during the T6 temper.

A. M. A. Mohamed, F. H. Samuel, Saleh Alkahtani

Intermetallic Phase Formation in TP-1 and DC Cast Billet of an AA6063 Al Alloy

The TP-1 grain size assessment process has been widely used for simulating Al grain formation in the direct chill (DC) casting process, as it is convenient and economical. However, the effectiveness of this process for the simulation of the formation of intermetallic phases present in Al alloy microstructures has never tested. This paper investigates the microstructures of AA6063 Al alloy solidified using both TP-1 and DC casting processes. The as-solidified intermetallic phases are analyzed in order to assess the effectiveness of the TP-1 process in simulating their formation in the DC casting process. A phase extraction technique is used to allow three dimensional quantitative and qualitative analyses of intermetallic phases using SEM, EDS and XRD characterization techniques.

A. Verma, S. Kumar, P. S. Grant, K. A. Q. O’Reilly

The Interdependence Model: An Improved Predictor of Grain Size

The newly developed Interdependence Theory is described by the Interdependence equation that is able to predict grain size on a more rigorous basis than has previously been possible. In this paper the theory is briefly introduced and then the Interdependence equation is used to predict the experimentally determined grain size for a broad range of aluminium alloy compositions, each cast with a range of AlTi and AlTiB master alloy additions. It is shown that the Interdependence equation provides reasonable prediction of grain size when using literature values for the diffusion coefficient, nucleation undercooling and interface growth velocity. Insights into the effect of the distribution of the added TiB2 particle size on the efficacy of master alloys are revealed illustrating why so few added particles become successful nucleants. Implications of the Interdependence model for further research are also discussed.

David H StJohn, Mark A Easton, Ma Qian

Analysis of Dendritic Primary Al Grain Ripening and Solid Fraction Measurement in A356 Alloy Semi-Solid Slurry Using Segregation Sensitive Reagent

Ripening of dendritic primary Al grain in semi-solid state has been paid much attention to since it is the most economical way to produce semi-solid slurry containing spheroidal Al grains for thixocasting. Also, solid fraction is the key factor in all the semi-solid processes. A segregation sensitive reagent (Weck’s reagent) can help to study both the two topics, revealing the inner-primary Al grain’s optical microstructure evolution during semi-solid heat treatments (partial re-melting) of small A356 alloy samples cut from both as-DC cast and compressed ingots (Recrystallization and partial re-melting process). With the help of this etching technique, the influence of induced strain on the ripening mechanism of primary Al grains was investigated precisely. Furthermore, the peripheral part of the primary Al grain grown during water quenching was distinguished by the reagent. Therefore we could exclude this area when measuring the solid fraction and avoid overestimation by image analysis.

Li Gao, Yohei Harada, Shinji Kumai

Microstructure Development and Control in Hypereutectic Cast Al-Si Alloys Evaluated by Metallurgical Analysis and Neutron Diffraction

Presented results show individual effect of key alloying elements, i.e., 2.8%Cu, 0.7%Mg and 0.01%P on the as-cast microstructure development in the hypereutectic Al-19%Si alloy evaluated using classical metallurgical analysis as well as in-situ neutron diffraction during alloy solidification process. Neutron diffraction revealed possible Si atoms clustering above liquidus temperature i.e., 677 °C and pre-mature nucleation of α-Al crystallites below liquidus temperature i.e., 667 and 625 °C in addition to liquid-to-solid phase transformation assessment during solidification. Mechanical strength i.e., hardness and ultimate tensile strength improvement due to Cu, Mg and P additions is evidenced and linked with microstructure evolution under non-equilibrium solidification conditions. Primary Si refinement was improved with subsequent addition of Cu and Mg, and P addition alone had insignificant effect on primary Si refinement.

W. Kasprzak, D. Sediako, M. Aniolek, H. Kurita

Semi-Solid Forming of A356 Alloy by Rapid Slurry Forming Process

Rapid Slurry Forming (RSF) is a relatively new technique of semi-solid forming. RSF process has been used for A356, A356+Ti+B (grain refiner) and A356+Ti+B+Sr (grain refiner and modifier) Al alloys in the present investigation. All the three alloys were held at 597°C, at which about 30% solid fraction is obtained in the semi-solid slurry, for 0, 5, 10 and 15 minutes. After each holding time, the slurry was quenched in water to preserve the semi-solid microstructure. Microstructure of all the three alloys at each stage was examined and hardness was measured. A globular microstructure was obtained for the RSF-processed alloys. The globularity of a-grains increased but grain size also increased and hardness decreased with increase in holding time. The optimum hold time appeared to be 5 minutes. The grain refiner and modifier did not seem to have any effect on the formation of semi solid slurry. The coarsening kinetics of the globular a-grains was found to be faster than that predicted by the LSW theory.

S. Sharma, A. Sharma, S. Kumar

Influence of the Fe Content, Mn/Fe Ratio and Cooling Rate on the Modification Process of Fe Intermetallic Compounds in Hypoeutectic Al-Si Alloys

The platelet β intermetallic compound has been considered as the most common and detrimental Fe intermetallic compounds in casting aluminum alloys with impurity Fe. This compound drastically deteriorates the mechanical properties of the alloys, especially ductility. It is required to modify the β compound to other less harmful Fe compounds. This study mainly focused on the influence of the Fe content, Mn/Fe ratio and cooling rate on the modification process of Fe compounds in the cast A356 alloy with different Fe contents from 1.0 wt.% to 2.5 wt.%. The results revealed that with increasing the Fe content in the alloy without Mn addition, the size of the platelet β compound increases significantly. The Mn addition was effective to modify the platelet β compound to more compact compounds, Chinese script and/or star-like even the polyhedral shape a compound, which mainly depends on the Mn/Fe ratio and the cooling rate in a given Fe level.

Zhijun Zhang, Equo Kobayashi, Hiroyasu Tezuka, Tatsuo Sato

Effect of Oxide Level on Pore Formation in A356 Alloy by X-Ray Imaging and Directional Solidification Technology

Effect of oxide level on porosity formation in an A356 alloy was investigated using micro-focus X-ray imaging and directional solidification technology. The increase of oxide level in liquid aluminum was achieved by violently stirring molten metal at elevated temperature. During solidification, the increased oxide content in melt significantly increases the amount of active nucleation sites for porosity and thus raises the nucleation temperature of pores. The fast growth of those early formed pores further restrains the succeeding nucleation operations of new pores in local regions and results in a considerable reduction in pore density. It was also found that the melt with high oxide content shows less dependency of growth rate reduction with local temperature.

Hengcheng Liao, Wan Song, Qigui Wang, Lei Zhao, Ran Fan

Microstructure of 3003/4045 Aluminum Alloy Clad Strip Fabricated by Vertical Type Tandem Twin Roll Caster

Aluminum alloy clad sheets are generally produced by hot roll bonding, but this conventional manufacturing process involves many steps. In the present study, clad strips were produced from molten alloys in one step and their microstructural characteristics were investigated. Two sets of twin roll casters were set in tandem vertically. The base strip (3003 aluminum alloy) was produced by the upper caster, and the strip was drawn into the roll-bite of the lower caster. The molten overlay material (4045 aluminum alloy) was poured, and the base strip was sandwiched between the two overlay strips. The interface between the base strip and the overlay strip was flat and no alloyed layer was observed. Remelting of the base strip did not occur, owing to the high production rate. Microstructural observation revealed that skin-formation type solidification of the overlay alloy took place from both the roll surface and the base strip surface.

Ryoji Nakamura, Toshio Haga, Yohei Harada, Shinji Kumai

Rapid Solidification of a New Generation Aluminum-Lithium Alloy via Electrospark Deposition

Electrospark deposition (ESD) is a rapid solidification processing technique capable of depositing a metal onto a conductive substrate. The short pulse duration and high pulse frequency, combined with the small amount of material transferred during each pulse, results in high cooling rates being realized, on the order of 105–106 C/sec. This study investigates the ability to induce solute trapping behavior, for a new generation aluminum-lithium alloy, AA2199, using ESD.Time-of-Flight Secondary-Ion-Mass-Spectroscopy (TOF-SIMS) and X-Ray Photoelectron Spectroscopy (XPS) were employed to determine solute distribution. Scanning Electron Microscopy and Scanning Transmission Electron Microscopy analysis were performed to investigate the microstructure of the rapidly solidified Al-Li deposits.TOF-SIMS and XPS data displayed a homogeneous distribution of lithium throughout the deposits, while the microscopy analysis revealed the presence of copper rich cells. It was therefore possible to validate the solidification front velocity of the ESD process, through comparison with Mullins and Sekerka model for interface stability.

David W. Heard, Julien Boselli, Raynald Gauvin, Mathieu Brochu

The Influence of Cu on Eutectic Nucleation and Morphology in Hypoeutectic Al-Si Alloys

The influence of increasing additions of copper on the aluminium silicon eutectic nucleation and morphology was investigated in unmodified and Sr-modified Al-10wt%Si alloys. In unmodified alloys, increase in copper content resulted in an increase in the number of polyhedral silicon particles and thus nucleation frequency of eutectic cells. In Sr modified alloys, additions of copper resulted in an increase in the nucleation frequency of eutectic cells. Also, at high copper levels in modified alloys, a change in the eutectic interface morphology from near-planar to coral-like was observed. These observations contribute to new insight in the solidification path and morphological evolution of Al-Si eutectics, and serve to provide in-situ X-radiography observations of eutectic solidification in Al-Si alloys with a more general validity.

A. Darlapudi, M. Felberbaum, R. H. Mathiesen, A. K. Dahle

Primary Cooling Heat Transfer during the Direct-Chill Casting of Aluminum Alloy AA6111

The heat transfer coefficient (HTC) associated with primary cooling during direct-chill casting of AA6111 aluminum alloy was investigated by conducting casting experiments with an instrumented mould. Mould temperature measurements obtained at various positions were used as input in an inverse heat conduction analysis in order to calculate the heat flux between the ingot and the mould. Heat transfer coefficient profiles versus vertical position within the mould were obtained for casting speeds of 1.39 and 1.83 mm/s. Relatively low HTC values of 93 to 576 W/m2·K were attributed to the formation of an air gap between the ingot surface and the mould. The experimental heat transfer coefficients were compared to theoretical values predicted using a 3-dimensional CFD model of direct-chill casting with a simple one-dimensional density-based model of shell deformation, which calculates the air gap thickness and the HTC within the mould.

Etienne Caron, Amir Baserinia, Rosa O. Pelayo, David C. Weckman, Mary A. Wells

The Relationship between Dendrite Arm Spacing and Cooling Rate of Al-Si Casting Alloys in High Pressure Die Casting

The effects of cooling rate on the solidification behavior of Al-8.5%Si-3%Cu and Al-11%Si-3%Cu alloys were studied during high pressure die casting (HPDC). The HPDC experiment was conducted by using the dies with 3 steps for 3 different cooling rates. Because of the high in both melt temperature and pressure, it was difficult to obtain the temperature profile directly from HPDC specimen. Therefore, in this study, cylindrical bar castings with different diameter were poured to acquire the cooling curves at the solidification range of 15°C/s up to 100°C/s and then the microstructures were compared to estimate the cooling rate in HPDC. The solidification characteristics including liquidus/solidus temperature and dendrite arm spacing of each alloy and each cooling rate was analyzed and the results showed strong proportional relationship between dendrite arm spacing and cooling rate in HPDC. The results were also compared with the actual die casting specimens and MAGMA simulation.

Jae-Ik Cho, Cheol-Woo Kim, Young-Chan Kim, Se-Weon Choi, Chang-Seog Kang

Thermo-mechanical Treatment

Characterization of Metal Flow in Metals Processing by a Combined Approach using Advanced Experimental Grid Pattern Techniques Coupled with FE-analysis

Experimental grid pattern (GP) techniques have lately been developed to a very high level of sophistication. Thanks to this, the engineer now can determine the real metal flow in industrial or laboratory processes with high accuracy. Concurrently, software for FE-analysis has been developed to a very powerful tool that allows detailed observations to be made regarding metal flow on the computer in any industrial process.The advanced experimental GP-techniques currently available are described and it is shown how they can be used to analyze metal flow inside and on the surface of the workpieces subjected to metal forming. It is also shown how accurate FE-models can reproduce the deformational behavior of the metal during the processing.In this way useful information can be deduced, for instance it can be explained how typical process-related defects are created in a process, so that preventive measures can be taken to avoid the occurrence of such defects in an industrial environment.

Henry Valberg

Research and Development of High-Strength of Al-Zn-Mg-Cu Alloys

The paper is focused on high-strength alloys (UTS=600–650 MPa, specific strength (UTS/density) ~ 220–230 kN•m/kg) which will allow one to retain aluminum’s predominant position during the next 15–20 years as applied in advanced aircraft primary structures. Parameters of microstructure (dispersoids, precipitates, degree of recrystallisation, grain size) and properties of semiproducts were studied in dependence on content of base alloying elements in chemical compositions of alloys (total sum of Zn+Mg+Cu — higher than 10 % mass). Contribution of minor additions (Zr, Sc, Ag) to strengthening and creation of improved combination of service properties was investigated. Evolution of phase composition and properties was studied as a dependence of different aging treatments.

R. O. Vakhromov, V. V. Antipov, E. A. Tkachenko

Effect of Alloy Elements on Microstructures and Mechanical Properties in Al-Mg-Si Alloys

Microstructures and mechanical properties in the modified Al-Mg-Si alloys with variation in the alloy elements and their contents were investigated to enhance higher strength and ductility. Optimizing both the alloy element design and the industrial processes including heat-treatments and extrusion technology was carried out along the recent suggestion from the first principles calculation. The investigation concluded that the addition of Fe and/or Cu could recovery their lost ductility, furthermore increase their tensile strength up to 420 MPa at high elongation of 24 % after T6 condition for Al-0.8mass%Mg-1.0mass%Si-0.8mass%Cu-0.5mass%Fe alloy with excess Si content. The excellent combination between strength and ductility could be obtained by improvement to the grain boundary embitterment caused by grain boundary segregation of Si as a result from the interaction of Si with Cu or Fe with optimizing the amount of Cu and Fe contents.

Yoshikazu Kato, Koji Hisayuki, Masashi Sakaguchi, Kenji Higashi

Dispersion Hardening Effect of Dispersoids in 3xxx Al Alloys With Varying Manganese and Silicon Contents

For non-heat treatable wrought aluminium alloys the strengthening occurs from solid solution hardening and work hardening. The goal of this paper is to study the dispersion hardening effect of dispersoids precipitated during low temperature annealing. The size, number density and morphology of dispersoids in four selected AA3xxx aluminium alloys with different Si and Mn contents after annealing at different temperatures and for different times are quantitatively studied. The microstructure is correlated with the strength in terms of micro hardness. It is revealed that the dispersoids have a remarkable contribution to the strength of the alloys. The hardening effect of dispersoids increases with increasing Mn and Si content in the alloys.

E. Mørtsell, A. M. Muggerud, Y. J. Li, R. Holmestad

Effect of Hot Extrusion Conditions on the Microstructure of AA3003

There is significant interest in the microstructural development during extrusion of AA3xxx aluminum alloys, which are used in heat exchanger applications. The ability to control deformation conditions allows for the design of the microstructure so that the material properties can be tailored to the final component. A systematic study of processing conditions for AA3003 was conducted using a laboratory scale fully instrumented extrusion press. Billets previously homogenized at different conditions were extruded with a variety of extrusion ratios and ram speeds. Extrusion samples were characterized with the use of optical microscopy. A full range of microstructures from recrystallized to unrecrystallized, with a wide range of final grain sizes and spatial variation were obtained. The results have been rationalized in comparison with processing conditions from the trials. It has been found that the extent of recrystallization is related to the homogenization treatment, with regards to the dispersoids number density of the structure, and ram speed.

L. M. Grajales, W. J. Poole, Y. Mahmoodkhani, M. A. Wells, N. Parson

Effect of Iron and Silicon on Strength and Electrical Resistivity of Al-Zr Wire Alloys

We have studied the effect of iron (up to 0.27wt.%) and silicon (up to 0.23wt.%) content on the structure, electrical resistivity (p) and strength (UTS) of Al-Zr wire alloys (up to 0.49 wt.%Zr) after various annealing regimes. The phase composition of the Al-Zr-Fe-Si system was analyzed with respect to new-generation heat resistant wire aluminum alloys. By the use of Thermo-Calc software we calculated the solubility of zirconium, iron and silicon in aluminum solid solution and volume fractions of all possible phases (including Al3Zr-L12 nanoparticles) at various temperatures. It was shown that a substantial decrease of p with a sufficiently high level of UTS preserved could be achieved by intermediate annealing in the fabrication of wire. In contrast with unalloyed aluminum (AA1350) silicon addition to Al-Zr alloys allows to obtain an optimal combination of electrical and mechanical properties.

A. N. Alabin, N. A. Belov

Influence of the Chemical Composition on the Structure and Properties of Lead-Free Machinable AA6023 (Al-Mg-Si-Sn-Bi) Alloy

Microstructure and properties of extruded rods of a new machinable lead-free aluminum AA6023 (Al-Mg-Si-Sn-Bi) alloy having different levels of Mg content were characterized. In the structure of the alloy there are low-melting point particles containing Sn+Bi. During machining, the temperature generated in the cutting zone is high enough to melt these dispersed entities. This melting gives rise to a local loss of the material strength and ductility which in turn leads to the formation of short, discontinuous chips. In addition to tin and bismuth, some of the Sn+Bi particles contain also a high amount of magnesium and intermetallic compounds of Mg2Sn and Mg3Bi2 are thus formed. The presence of these stable phases increases the melting temperature of Sn+Bi containing particles and their originally positive impact on improving the machinability is therefore reduced. Hence increasing of Mg content in the Al-Mg-Si-Sn-Bi alloy reduces its machinability.

Jiří Faltus, Miroslav Karlík, Petr Haušild

Homogenization of 6xxx Alloy Ingots with an Addition of Vanadium

The selection of material for elements operating in the crumple zone should consider the mechanical properties of alloys and their ability to absorb energy. Undoubtedly, such materials include aluminium alloys with an addition of vanadium.The aim of this study was to evaluate the impact of homogenization conditions on the structure and properties of ingots cast by DC technique at different solidification rates from alloys included in the 6xxx series, such as AlMgSi and AlMgSiCu with an addition of 0.2 wt% and 0.4 wt% vanadium. The alloy structure was examined by light microscopy and scanning electron microscopy combined with an EDX analysis. Changes in mechanical properties were determined by hardness measurements and static compression test after different time/temperature variants of the homogenizing treatment. Optimum parameters of the homogenizing process were determined for the examined ingots and an extension of the homogenization time was considered justified only for ingots containing Cu.

Marzena Lech-Grega, Wojciech Szymański, Maciej Gawlik, Mariusz Bigaj

Hot Extrusion of Aluminum Chips

The process of hot extrusion is a promising approach for the direct recycling of aluminum machining chips to aluminum profiles. The presented technology is capable of saving energy, as remelting of aluminum chips can be avoided. Depending on the deformation route and process parameters, the chip-based aluminum extradates showed mechanical properties comparable or superior to cast aluminum billets extruded under the same conditions. Using different metal flow schemes utilizing different extrusion dies the mechanical properties of the profiles extruded from chips can be improved. The energy absorption capacity of the profiles the rectangular hollow profiles extruded from chips and as-cast billets were analyzed using the drop hammer test set-up. The formability of the profiles extruded from chips and as-cast material were compared using tube bending tests in a three-roller-bending machine.

A. Erman Tekkaya, Volkan Güley, Matthias Haase, Andreas Jäger

3-Dimensional Microstructure of Al-Al3Ti Alloy Severely Deformed by ECAP

Microstructure of Al-Al3Ti alloy deformed by Equal-Channel-Angular Pressing (ECAP) is 3-dimensionally investigated. Especially, distribution of Al3Ti particles is focused in this study. The Al-Al3Ti alloy has coarse Al3Ti platelet particles in α-Al matrix. When the Al-Al3Ti alloy is deformed by ECAP under route A, fine Al3Ti platelet particles are observed. These Al3Ti platelet particles are aligned along to deformation axis, and its plane normal is perpendicular to the deformation axis. On the other hand, Al-Al3Ti alloy ECAPed under route Bc forms several groups consisted of fine Al3Ti platelet particles. Moreover, longitudinal size of the Al3Ti particle groups is close to that of initial Al3Ti particles with 4-pass ECAP specimen. These distribution behaviors of the Al3Ti particle can be explained by plastic flow of α-Al matrix. Finally, it is concluded that distribution of Al3Ti particle in Al-Al3Ti alloy by ECAP is controlled by plastic deformation of α-Al matrix.

Hisashi Sato, Takahisa Hishikawa, Yuuki Makino, Takahiro Kunimine, Yoshimi Watanabe

Abnormal Recrystallization Behavior of High Purity Aluminum Foil

The influence of heating rates on recrystallization behavior of high purity aluminum foil was systematically studied in the present paper. The result shows that the recrystallized sample experienced a low heating speed (180 °C/h, holding at 180 °C for 1 hour and then heating to 500 °C) has an smaller average grain size than that of sample with a high heating speed (put the sample in the furnace at 500 °C), which greatly differs from the general recrystallization behavior of typical metals. The recovery before recrystallization is suspected to be closely related with the abnormal recrystallization behavior. Most stored energy releases during recovery of annealing with low heating speed. Our result suggests that the heating speed is an effective way to modify the grain size of high purity aluminum foil.

Guangjie Huang, Jing Zhang, Yunlei Wang, Qin Liu

Effect of Annealing Condition on Earing and Texture Formation in Cold Rolled AA5182 Aluminum Alloy

The effect of annealing condition on earing and recrystallization texture formation in cold rolled AA5182 aluminum alloy was investigated. The earing of AA5182 aluminum alloy depends strongly on the heating rate. At low heating rate (0.01~1K/s) the ears on drawn cup situated at 45 deg. to the sheet rolling direction. At high heating rate (10K/s) the ears were lower. The earing behavior was characterized by the texture components. As the heating rate increases, the intensity of cube component increases whereas the intensities of Brass, Cu and SB components decrease. The transformation kinetics of recrystallization during isothermal annealing was quantified by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. The results show that the JMAK exponent for recrystallization was determined to be 2.4 at 553K and around 4 at 573K and 593K. The apparent activation energy for recrystallization was estimated to be 203kJ/mol.

Minemitsu Okada, Seiichi Hirano

Effect of Quenching Wait Time on Microstructure and Mechanical Properties of As-Extruded AA6063 Alloy

Effect of quenching wait time after hot extrusion on microstructure and mechanical properties of AA6063 alloy was investigated by optical microscopy observation, tensile and Brinell hardness tests. Results show that the quenching wait time has an important influence on the microstructure and mechanical properties of AA6063 alloy. During hot extrusion, dynamic recrystallization occurs only in local areas suffered much larger strains, however, only within 10s’ wait time after extrusion, the static recrystallized grains have maturely developed. After subsequent T6 heat treatment, the recrystallized grains of the prompt-quenched sample are more uniform than that of the wait-quenched sample, and mechanical properties of the former are also better than that of the latter.

Yuna Wu, Hengcheng Liao, Jian Yang

Hot Deformation Behavior and Microstructural Evolution of Homogenized 7150 Aluminum Alloys Micro-Alloyed with Zr and V

Hot deformation behavior of homogenized 7150 aluminum alloys micro-alloyed with 0.12% Zr and 0.11% V was studied by compression tests conducted at various temperatures and strain rates. The microstructural evolution was investigated using an optical microscope and the electron backscattered diffraction technique. The results showed that the peak flow stress of alloy 7150 increased due to the addition of Zr or V. The hot deformation activation energy of the base alloy was determined to be 209.0 kJ/mol, which increased to 244.7 kJ/mol and 248.7 kJ/mol when alloyed with 0.12% Zr and 0.11% V respectively. The softening mechanism of the base alloy was dynamic recovery during hot deformation at low temperatures (300 °C–400 °C), which transformed to dynamic recrystallization at a high temperature (450 °C) and a low strain rate (0.001 s-1). Adding Zr or V generally displayed a retardation of the dynamic recovery and inhibition of the dynamic recrystallization, and hence resulted in the increase of flow stresses.

C.-J. Shi, X.-G. Chen

Orientation Effect in the Particle Stimulated Nucleation of Recrystallization

The second phase particles present in commercial alloys have a strong influence on the recrystallization kinetics, microstructure and texture. By varying the alloying composition and material processing, the distribution of second phase particles can be changed, making it possible to control grain size and texture. It is known that there is lattice rotation around the particles after deformation, in a so-called particle deformation zone (PDZ), which is though to be important in randomizing the texture after recrystallization though particle stimulated nucleation (PSN). Although the basics of PSN are well accepted, the role of the local distribution of stored energy and its link to local lattice rotation is not well understood, making it impossible to successfully predict PSN efficiency. In this paper, we present a new method for studying the deformation around particles at using high-resolution digital image correlation (HRDIC) and electron backscatter diffraction EBSD. Combining the two techniques makes it possible, for the first time, to relate the local deformation fields to remnant changes in local lattice orientation. Initial measurements are made on a model Al-Si alloy deformed in compression to 50%. Our analysis shows that the material deforms heterogeneously with high levels of deformation localized along slip bands. EBSD analysis shows that the lattice distortion in these bands is minimal. The HRDIC analysis clearly shows particles interrupt the shear banding. Local lattice rotation measured by EBSD is considerably less than expected from the measured deformation.

L. C. L. Ko, J. Quinta Da Fonseca

Structual Evolution in Aluminium Alloy AA6082 during HPT Deformation at Increased Temperature

In this study, ultrafine grain structure evolution during high pressure torsion (HPT) of commercial aluminium alloy AA6082 at an elevated temperature is presented. Two different initial structural states of the alloy were prepared by thermal treatment. The dependence of the progress of microstructure refinement on shear strain was investigated by TEM observation of thin foils. The impact of various amounts of strain (ɛef) was analysed with respect to the increased temperature of deformation. Microhardness data measured across the deformed discs show scatter. Observation of microstructure revealed that an ultrafine grain (UFG) structure formed in the deformed disc as early as the end of the first turn, regardless of the initial structure of alloy resulting from the prior thermal treatment. The heterogeneity of UFG deformed structure in the deformed discs is consistent with the scatter in microhardness values. By increasing the strain level through adding turns (N = 2, 4, 6), the UFG structure was homogenized in the deformed discs. The effect of the increase in deformation temperature became more evident and dynamic recrystallization modified the UFG structure locally. In the specimens prepared by two-stage thermal treatment (quenching and ageing) prior to torsion deformation, the growth of new grains was inhibited and the UFG microstructure was more stable. Tensile strength values suggest that strengthening was partially relaxed by local recrystallization. Torque vs. time plots reveal that the torque required to deform the sample was increasing until the completion of the first turn and then remained stable or even decreased slightly.

Jozef Zrnik, Libor Kraus, Stephan Scheriau, Reinhard Pippan

Advances in Aluminum Mold Block for Plastic Injection Molding Operations

Mold performance with high strength aluminum alloy QC-10® in injection molding was investigated and compared with NAK 80 steel mold. Two different shapes of molds were tooled and tested. Interfacial heat fluxes between cooling mold and solidifying polymer melt were measured using the IHCP (Inverse Heat Conduction Method) technique during the injection molding cycles. The influence of thermo-physical properties of mold materials and polymer resins on molding cycle time and internal residual stress were also investigated by injection molding control optimization and birefringence analyzer. Evaluation of the thermal energy absorbed and uniform heat extraction during injection molding revealed that aluminum mold QC-10® resulted in significant cycle time reduction and produced the part with less distortion. In addition to the benefit of reduced tooling time, it was proven that aluminum mold is a promising mold material for increasing the productivity in plastic injection molding operations.

Jinsoo Kim, Ron Smierciak, Yong Seung Shin, Leighton Cooper

Metalworking of a Spherical Particle Reinforced Aluminum Composite

Gamma Technology has developed a new reinforcement for aluminum matrix composites. The reinforcement is spheroidized-alumina that allows us to manufacture high strength composites. These composites have been extruded, forged and ring rolled in order to develop near net shape preforms for manufacture of parts. This paper will discuss the metalworking operations as well as the mechanical properties of the parts that have been made. The paper will also discuss the machining of the parts since the parts were made with coated carbide tools, not diamond tools that are required for machining other aluminum composites.

William C. Harrigan

Properties, Microstructure and Hot Deformation Behaviour of Different Al-Zn-Mg (Zr) Alloys

Two alloys based on Al-Zn-Mg (Zr), were characterized from microstructural and mechanical points of view. Hot tensile tests and torsion test on as-cast samples were performed. Deformed samples exhibit some static recrystallization (SRX) more evident in the alloy without Zr. As-cast alloys hot deformed by tension exhibits considerable cavitation that increases with temperature (T) . The analysis of this phenomena on 7000 as cast alloy has shown that cavity growth is mainly controlled by plastic strain both at 250°C and 400°C even if grain boundary sliding (GBS) contributes to enhance the fraction of cavities at the highest T . Cavitation is reduced if the alloy is solutionized before deformation.

P. Leo, H. J. McQueen, E. Cerri, S. Spigarelli

Super High Strength Aluminum Alloy Processed by Mechanical Alloying and Hot Extrusion

Nanostructure strengthened aluminum alloy was prepared by powder metallurgic technology. The rapid solidification Al-Cu-Mg alloy powder was used in this study. To obtain nanostructure, the commercial powder was intensely milled under certain ball milling conditions. The milled powder was compacted first by cold isostatic pressing (CIP) at a compressive pressure of 300MPa, and then extruded at selected temperature for several times to obtain near full density material. Microstructure and mechanical properties of the extruded alloy were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and mechanical tests. It is revealed that the compressive strength of extruded alloy is higher than 800MPa. The strengthening mechanism associated with the nanostructure is discussed.

Ruixiao Zheng, Han Yang, Zengjie Wang, Shizhen Wen, Tong Liu, Chaoli Ma

A system for Continuous Extrusion Using High Pressure Molten Metal

Extrusion technology as practiced today is a batch process in which billets are sequentially extruded one piece at a time. This results in several inherent product constraints (e.g. limited product length, undesirable coupling between extrusion ratio and product length and end crop losses).A new system1–3 has been developed to generate, supply and control high pressure molten aluminum. In this process high pressure molten aluminum is continuously feed to a mold in which solidification occurs under high hydrostatic pressure. The in situ billet thus formed is then extruded in the fully solid state to obtain a wrought structure and the desired product profile. Supply pressure can be modulated in real time to enhance process control stability. Novel aspects of this process, potential applications and challenges will be discussed.

Vivek M. Sample, Ronald Chabal, Vincent Paola, Douglas Robosky

Visualization of Material Flow in Friction Extrusion

Friction extrusion is a solid state process which can produce high quality wire or fully consolidated bulk material from metal chips or powders. In order to improve understanding of consolidation and extrusion and help to validate numerical simulations, material flow visualization experiments were conducted using a marker insert technique (MIT). Results show that marker material can be traced when it is placed in an initially consolidated charge. The deformation is consistent with the extrusion ratio at the center of the extruded wire and considerably larger away from the center.

X. Li, W. Tang, A. P. Reynolds

High-Pressure Torsion for Microstructure Control in Binary Al-Fe Alloys with Different States of Fe-Containing Phases

High-Pressure Torsion (HPT) is used to process Al-Fe alloys with different initial states of their Fe-containing phases and to study the capability to improve their overall mechanical properties. The samples used in this study include a bulk form of disks with 10 mm in diameter extracted from cast ingots and extruded rods with combinations of prior annealing. In addition, mixtures of high purity powders are processed by HPT to produce the bulk form of disks. Different fractions of Fe are added to control the initial states of the Fe-containing phases. Evolution of microstructures and mechanical properties with straining by HPT is examined using transmission electron microscopy (TEM), X-ray diffraction analysis (XRD), hardness measurements and tensile testing. It is shown that the hardness increases with increasing strain and Fe addition. Second phase particles are fragmented and some dissolution occurs with straining. Formation of intermetallic phases is also confirmed after large numbers of revolutions.

Jorge M. Cubero-Sesin, Zenji Horita

Process analysis of the co-extrusion of aluminum and titanium alloys

This document provides the results of the process analysis of the co-extrusion of aluminum and titanium alloys. The compound consists of the slave material aluminum and the core material titanium. The investigation determines the influence of the parameters billet temperature, press ratio and core length on the process. The material combinations used for the experiments were Al99,5 — Ti Grade 2, and EN AW — 6082 — TiAl6V4. The titanium core material was inserted in a drilled and machined aluminum billet. Furthermore, mechanical properties of the interface were determined by tensile tests. Additionally, the formation of the interface was characterized by scanning electron microscopy, electron probe micro analysis and electron backscatter diffraction. The aim of the presented investigations is to show the technical feasibility of the co-extrusion of aluminum-titanium-compounds and to control the growth of intermetallic phases in the interface to increase the mechanical properties.

N. Grittner, B. Striewe, D. Dietrich, A. von Hehl, C. Klose, M. Schaper, H.-W. Zoch, Fr.-W. Bach

Rheo-Extrusion of Hypoeutectic Al-Si-Mg-Fe Alloy

Improvement of poor ductility in normally processed Al-6.7%Si-0.33%Mg-1.2%Fe alloy with coarse intermetallic compound β phases was tried by the rheo-extrusion process utilizing semi-solid slurry, which had been made by a newly developed octagonal rotor process. The obtained slurry had relatively fine solid granules and considerably smaller β phases than those of the usual castings. When rheo-extrusion tests at the constant extrusion ratio of 36 and at the ram speed of 5mm/s were carried out at various semi-solid temperatures, the round bars of 6mm diameter with smooth sound surfaces were obtained except for the tip portions in the every extrusion conditions. Microstructures of the bars consisted of relatively fine equiaxed α-Al grains, indeterminate shaped eutectic silicon and β phases. If a forced-air cooling treatment was given at the adequate position under the die out-let during rheo-extrsion, the extruded bar had an excellent tensile strength and ductility even in T6 aging condition, comparable with those of the iron-free alloy.

Yasuhiro Uetani, Nanako Mori, Masayoshi Dohi, Kenji Matsuda, Susumu Ikeno

Simultaneous Improvement of Strength and Ductility in Al-Ag Alloys Processed by High-Pressure Torsion and Aging

Al-Xwt%Ag (X= 5, 11, 20) alloys are subjected to solid solution treatment at 823 K for 1 hour. High-pressure torsion (HPT) is conducted on the alloys for grain refinement under an applied pressure of 6 GPa for three different revolutions (N= 1, 5, 10) at room temperature with a rotation speed of 1 rpm. Aging treatment is carried out at temperatures of 50, 75 and 100°C for the periods up to 3.9 days. Vickers microhardness measurements and tensile tests show simultaneous improvement of strength and ductility. Observation of TEM images show that grain refinement is achieved with a grain size of ~300 nm. Spherical η-zone which is formed during an initial stage of aging treatment improves the mechanical properties without grain coarsening.

Seungwon Lee, Zenji Horita

Microstructural and mechanical evolutions during the forging step of the COBAPRESS, a casting/forging process

Aluminum casting/forging processes are used to produce parts for the automotive industry. In this study, we examined the influence of the forging step on the microstructure and the mechanical properties of an A356 aluminum alloy modified with strontium. Firstly, a design of samples which allows us to test mechanically the alloy before and after forging was created. A finite element analysis with the ABAQUS software predicts a maximum of strain in the core of the specimens. Observations with the EBSD technique confirm a more intense sub-structuration of the dendrite cells in this zone. Yield strength, ultimate tensile strength, elongation and fatigue lives were then improved for the casting/forging samples compared to the only cast specimens. The closure of the porosities and the improvement of the surface quality during the forging step enhance also the fatigue resistance of the samples.

Frédéric Perrier, Christophe Desrayaud, Véronique Bouvier

The Bonding Behavior of co-extruded Aluminum-Titanium-Compounds

The combination of aluminum and titanium enables the design of lightweight structures with tailor-made properties at global as well as local scale. In this context the co-extrusion process offers a great potential for advanced solutions for long products especially being applied in the aircraft and automobile sector. While titanium alloys show particular high mechanical strength and good corrosion resistance, aluminum alloys provide a considerable high specific bending stiffness along with lower materials costs.The co-extrusion process has been simulated using the finite element program simufact.forming. The simulation results were compared with co-extrusion experiments. The formation of the intermetallic layer during co-extrusion, the mechanism of adhesion between aluminum and titanium, and the mechanical properties of the intermetallic layer were investigated in detail. In order to understand the development of the intermetallic layer results of diffusion bonding experiments were compared with those of co-extrusions. The layers were characterized by optical microscope, scanning electron microscopy as well as electro beam micro-analysis. The mechanical properties were determined by tensile tests.

Barbara Striewe, Martin Hunkel, Axel von Hehl, Norbert Grittner

The Effect of Heat Treatment Technology on Mechanical Properties of Al/Al Alloys Multilayer Sheet Fabricated by Hot Roll Bonding

The Al/Al alloy (1100/7075) multilayer sheets were fabricated by hot ARB (Accumulative roll bonding). For laminated sheet, the different heat treatment (solution and aging) were carried out for the multilayer sheets. The aging time and number of layers and interface shape were taken into account in the experiments. The mechanical properties and microstructure of multilayer Al/Al alloy composite sheets were researched. The optimal heat treatment technology were obtained by the comparison of mechanical properties.

Chen Zejun, Chen Quanzhong, Kawunga Nyirenda, Liu Qing

Orientation Dependent Subgrain Growth During Isothermal Annealing of High-Purity Aluminum

The orientation dependence on recovery have been studied in polycrystalline high-purity aluminum (99.99 wt%). After cold-rolling to 95% reduction (s = 3.0), samples were annealed at 180, 200, 220 and 240 °C. Through detailed EBSD characterization of average subgrain size and boundary misorientation during annealing, the rate of recovery in Cube and Goss was found to be faster than in the typical deformation texture components, particularly after an incubation time when discontinuous subgrain growth occurred. Subgrains with the Bs orientation grew marginally faster than Cu and S. In Cube, Goss and Bs (240 °C) where rapid growth was observed, a slight increase in the average boundary misorientations and a transition to discontinuous growth was observed. In Cu and in most cases Bs, continuous growth was accompanied by a weak decrease of the misorientations. Although exhibiting similar growth behavior, continuous growth of subgrains with S orientations resulted in larger misorientations.

Sindre Bunkholt, Knut Marthinsen, Erik Nes

Effect of Nickel Variation and Thermomechanical Treatment on Microstructure and Properties in Aluminum Alloy Fin Stock for Heat Exchanger

Aluminum alloys are commonly used as a material for heat exchangers due to their higher thermal conductivity and specific strength among various metallic materials. Twin roll strip casting process is considered to produce the high quality and low manufacturing cost aluminum alloy fin stock for automobile heat exchangers. Thermomechamical treatment has carried out to obtain optimum processes for initial cold rolling, intermediate annealing and final cold rolling, which can meet the requirements for high strength and high thermal conductivity after brazing heat treatment. In the present study the suitable thermomechnical treatment and optimum nickel content was suggested to balance the properties of strength, thermal conductivity, brazing behaviour, corrosion resistance and sagging resistance in Al-Zn-Mn-Si-Fe-Cu-Ni based alloys produced by twin roll strip casting process.

Suk Bong Kang, Dong Bae Kim, Jaehyung Cho

A study of the influence of plastic pre strain in different directions before ageing of extruded and hydro formed material on the mechanical properties of AA6063

Alloys from the 6xxx series are often candidates in materials selection made by car industry due to their good formability and response to age hardening.In this study AA6063 was subjected to experiments were the influence of plastic deformation on the age hardening response and mechanical properties was investigated. Extruded and naturally aged material was plastically deformed in different directions and subsequently aged at two temperatures (160 and 185°C). The Hydro forming technique was also used to induce plastic deformation on tubes. The aged material was then tensile tested and the microstructure studied by using TEM.The results are presented as results of tensile tests, aging curves and TEM micrograph. The main conclusion after discussion of the results is that the time to peak strength is more affected by plastic deformation than the final strength of AA6063.

Jan Kanesund, Sten Johansson

Characterization of the Artificial Aging Behavior and Formability of a High Strength EN AW-6016 at Different Heat Treatment Conditions Used for Automotive Applications

The growing demand for more fuel-efficient vehicles has led to a demand for sheets with higher strength accompanied by good formability to achieve a further weight reduction in cars. The purpose of this work is to investigate an alloy based on the EN AW-6016 composition which shows both, higher strength and improved formability. Within the present investigation the (I) influence of the main alloying elements of EN AW-6016 on the T4 strength and formability is described. Furthermore an (II) improved heat treatment cycle with the objective to increase both strength and formability is presented. The hereby produced T4* temper is (III) analyzed in comparison to standard T4 and other high strength Cu-containing 6xxx alloys in terms of artificial aging kinetics by using differential scanning calorimeter (DSC). Finally the (IV) effect of the improved mechanical properties on the forming performance is investigated in detail.

Ramona Prillhofer, Josef Berneder, Josef Enser, Dirk Uffelmann, Peter Schulz, Carsten Melzer

Low Work Hardening and Its Mitigation in Ultra-Fine Grained Aluminum Alloys

Ultra-fine grained aluminum alloys can achieve high strengths but their ductility and formability are limited by a low work hardening capacity. In this paper the factors contributing to the work hardening behavior are examined and it is suggested that the low work hardening capacity can be mainly attributed to the influence of inhomogeneous yielding, which seems to be a characteristic of ultra-fine grained alloys. Methods of improving the work hardening are then considered in the context of sheet products.

H. Jin, M. Gallerneault, D. J. Lloyd

The Influence of Initial Microstructure on the Recrystallization Behaviour of Cold-Rolled AA3003

Due to an excellent combination of strength, formability, corrosion resistance and material cost, extruded Al-Mn alloys (e.g. AA3003) are widely used in heat exchanger applications for automotive and off road applications. Grain size control is essential, as it affects important properties such as corrosion resistance, strength and formability. The present work describes experimental observations on the microstructure resulting from different homogenization practices of AA3003 which modify the dispersoid distribution and the initial grain size. This work considers deformation by cold rolling to reductions of 10–80 pet followed by annealing at the temperature range of 350 to 600 °C. Preliminary results show that there is a critical temperature below which concurrent precipitation of Mn-bearing dispersoids retards recovery and static recrystallization giving rise to different recrystallized grain sizes. The effect of initial grain size was observed to be significant when there were almost no dispersoids with cold reductions of 10–20 pct.

Payman Babaghorbani, Warren J. Poole, Mary A. Wells, Nick C. Parson

Mechanical Properties of Multilayer 1100/7075 Aluminum Sheet Produced by Hot ARB

The five layer aluminum sheet had been processed by alternating 7075 and 1100 pure aluminum sheets of controlled volume fraction at high temperature using the ARB technique. This work established that hot roll bonding of high strength 7075 aluminum alloy is perfect when rolled with pure aluminum. The rolling work was done at the solution temperature of the 7075. The strength and elongation of the roll bonded material was found to be better than the initial five layer clad sheet. In the fifth cycle of ARB, the yield strength for the same temper was 21 and 11% higher than the clad sheet in F and T6 temper, while the UTS in the F and T6 tempers was 26 and 11.5% higher. Elongation, which is a property of toughness also increased up to the fifth cycle were it began to level down to values equal or less than the preceding cycle.

Kawunga Nyirenda, Chen Zejun, Chen Quanzhong, Liu Qing

Examining the Mechanisms of Dynamic Recrystallization (DRX) in Two-Phase Al Alloys

Second phase particles raise density and stability of strain-induced dislocation boundaries (SIB-HAB high-angle) and also markedly diminish boundary transformability and mobility at high temperature. In deformation of Al-Mg-Mn, large Al6Mn particles create surroundings of high-density cells that can nucleate particle-stimulated static or dynamic recrystallization (PSN-SRX or PSN-DRX, discontinuous with mobile boundaries, GB) that are valuable for grain refinement (if no pinning by fine Al6Mn). Particle stimulated nucleation PSN-DRX is only supported in alloys with over 2% Mg that markedly reduces the level of DRV, Hornbogen showed that fine particles in high density after cold working can markedly deter dSRX, but the SIB-HAB reorganize into boundaries that would be mobile if not particle pinned; this is continuous cSRX. After heavy thermomechanical processing (TMP: <300°C,>5s−1), Al-Cu-Mg-Zr, or Al-10Mg-Zr, when subjected to superplastic testing (>400C, <10 −2s−1) SIB-HAB rapidly rearrange into GB capable of rapid shearing, thus supporting very high elongations; a rearrangement that deserves the name continuous cDRX. The dislocation build up into very stable SIB-HAB during TMP is not reasonably classed as cDRX. Initially deformed substructures (IDS) are often present where precipitates hinder SRX. They markedly and diversely affect substructure development in hot working and could lead to a pseudo IDS-DRX that deserves careful investigation but is not a general characteristic of the alloy.

H. J. McQueen

Mechanical Characterization of Bimodal Grain Size Aluminum 5083 Under Various Test Conditions

A 5083 aluminum alloy with a bimodal grain size distribution consisting of a nanocrystalline grain matrix, created by cryomilling, and coarse grains has been produced. This material has been shown to exhibit greatly improved properties when compared to conventional Al-5083 and nanocrystalline aluminum. This work investigates how the test conditions affect the mechanical behavior of this material. A full factorial experiment is designed to investigate effects of strain rate, size, material orientation, and coarse grain volume ratios through uniaxial tensile tests. The results are found to conform well to Joshi’s model for plasticity. Strength and ductility is found to decrease with increasing strain rate and specimen thickness is found to affect the stiffness of the material. Increasing coarse grain ratio is found to increase ductility, though it appears that the effect may become saturated at some point. Furthermore, significant anisotropy effects are observed.

Andrew Magee, Leila Ladani

Microstructure and Mechanical Properties of an Al-Mg-Sc-Zr Alloy Subjected to Extensive Cold Rolling

An Al-4.5%Mg-0.2%Sc-0.09%Zr alloy was subjected to cold rolling (CR) with reductions ranging from 20 to 90%. Extensive strain hardening upon the cold rolling resulted in the significant increase in strength. After cold rolling with a total reduction of 20 and 90% the yield stress (YS) increase is 30 and 62%, respectively. These increments are attributed to an increase in the density of lattice dislocations, the formation of numerous low-angle boundaries (LAB), deformation bands and microbands within interiors of initial grains.

Anna Mogucheva, Evgeniya Babich, Rustam Kaibyshev

Microstructure, Mechanical and Electrical Properties Evolution During Cold Rolling of Different 1xxx Series Aluminium After Continuous Casting

Conventional aluminum processing involves continuous casting, hot and cold metal forming and optional heat treatment. Modern processes aim to shorten the cycle of manufacturing and consist of cold metal forming after continuous casting. A well-known example of such solutions is the twin-roll casting and cold rolling of aluminum sheets. For these reasons an analysis of the impact of cold deformation on structure and properties of materials after continuous casting and analysis of its quality becomes an important research topic. The paper shows the results of laboratory aluminum continuous casting. The effects of inoculants micro-additions which modify the structure of casts and its effect on the macroscopic properties of the material were examined. This paper also shows the results of laboratory tests of material cold rolling after continuous casting. The mechanical properties of material as a function of cold deformation evolution and a number of utility properties of finished sheets were examined.

Tadeusz Knych, Artur Kawecki, Grzegorz Kiesiewicz, Paweł Kwaśniewski, Andrzej Mamala, Beata Smyrak, Wojciech Ściężor

Modeling of Work-Hardening in an Age-Hardenable AA7108 Aluminum Alloy

To understand and predict the mechanical properties of aluminum alloys are of great importance with respect to e.g. strength requirements and forming operations. For heat-treatable alloys, the strength and work-hardening behavior is mainly attributed to the presence of hardening precipitates. In this work, a first step has been taken to further develop an already existing two internal state variable work-hardening model that has been previously validated for Al-Mg-Si alloys, to include alloys within the Al-Zn-Mg system. The input parameters are based on quantitative experimental TEM investigations of the precipitate distributions in an AA7108 aluminum alloy heat treated to different tempers. The model has been calibrated, implemented and validated with respect to data obtained by tension and compression tests. The work-hardening model shows promising results, and yields reasonable agreement between model predictions and experimental results.

Ida Westermann, Odd Sture Hopperstad, Ole Runar Myhr, Knut Marthinsen, Bjørn Holmedal

A Study of the Influence of Strain Hardening and Precipitation Hardening Sequence on Mechanical Properties of AlMgSi Conductor Alloys

Precipitation-hardenable AlMgSi alloys grade 6101 of 0.5% Mg and 0.5% Si contents, are used for the construction of homogenous wires in overhead power lines. The dominating group of alloys with increased electrical conductivity is the AlMgSi alloy group, these are HC, EHC and EEHC type materials with tensile strength at approximately 300 MPa and electrical conductivity lower than conventional wires (56,5 – 54,3 %IACS). The study presents the results of the research of AlMgSi wires heat treatment in compliance with the PN-EN 50183 standard. The shaping of heat treatable AlMgSi alloy rods and wires properties is possible through an appropriate sequence of a precipitation hardening (during ageing) and strain hardening (during drawing processes). This paper is a comprehensive analysis of the technologies for the production of wires from AlMgSi alloys.

Beata Smyrak, Tadeusz Knych, Andrzej Mamala, Kinga Korzeń, Piotr Osuch

Characterization of Pre-Aged AA6061-T6 Sheet Material for Aerospace Applications

In previous papers it was shown for alloy AA6061 that the artificial aging response is adversely affected by natural aging at room temperature. A suitable pre-aging procedure at elevated temperatures immediately after solution heat treatment is effective in reducing the detrimental effects of natural aging on the artificial aging kinetics. The hereby produced temper T4* shows an increased aging response and exhibits after artificial aging to temper T6 a much higher level of mechanical properties.In the present work pre-aged AA6061 material is produced on industrial scale and is characterized in comparison to a standard production in terms of static and dynamic material properties in the peak aged temper T6. The effects of the pre-aging on artificial aging kinetics and corrosion performance as well the fatigue crack propagation rate and fracture toughness behaviour is presented in detail and the results are discussed in view of application in the aerospace industry.

Josef Berneder, Ramona Prillhofer, Peter Schulz, Carsten Melzer

Controlled Quenching of Aluminum Alloys in Flexible Spray Fields

During heat treatment of age hardenable aluminum alloys, the resulting mechanical properties are particularly influenced by the quenching process. To achieve the required strength, a high quenching rate after solution annealing is necessary, otherwise a homogeneous distribution of quenching intensity should be realized in order to avoid distortion. Controlled quenching within the heat treatment process of aluminum components can be realized by flexible spray fields. Suitable heat transfer conditions of the component are achievable by adjusted flexible flow fields (local and/or temporal) based on simulation of heat transfer by Computational Fluid Dynamics (CFD). By the use of gas-(air), spray-(water/air) or jet-(water) flow fields, it is possible to adapt the quenching intensity to the part geometry and/or to the load profile in order to influence the mechanical properties as well as the distortion after heat treatment. For this purpose, a flexible spray nozzle field was integrated into heat treatment process for age hardening of different wrought-, cast-, and spray-formed aluminum alloys.

Andrea Rose, Sven Schuettenberg, Nils Hornig, Axel von Hehl, Udo Fritsching

Effect of Coarse Particles on Work Hardening in the Al-Mn Alloy

The effects of coarse Al6Mn particles (~3µm) on the formation of a deformed microstructure in the Al-0.66mass%Mn binary alloy have been investigated by the tensile test and the microstructure analysis. The coarse particles have less effect on the dislocation migration in the deformation range up to ε=0.002. Due to the localization of the dislocations around the coarse particles, the maximum n-value appears in the deformation range around ε=0.02. The dislocation cells are formed in the deformation range above ε=0.10. In this stage, the localized dislocations around the particles promote annihilation of the dislocations and prevent an increase in the flow stress. For a higher deformation, the subgrains with a high angle boundary form around the coarse particles. As a consequence of these results, the Mn atoms in the coarse Al6Mn particles have a greater effect on the work hardening than those in the matrix as solute atoms.

Shingo Iwamura, Kazuyo Ogawa

Precipitation behavior of dispersoids in Al-Mg-Si-Cu-Mn-Cr alloy during homogenization annealing

The precipitation behavior of dispersoids containing Mn and Cr in Al-Mg-Si-Cu-Mn-Cr alloy during homogenization annealing with different heating rate was investigated in this paper. Scanning transmission electron microscopy (STEM) was used to measure the difference in the size and number density of dispersoids after the two treatments. The effect of homogenization treatment on the recrystallization fraction and grain size was determined by examining hot forged and solution treated specimens using electron back-scatter diffraction (EBSD). It was found that the slow homogenization heating rate promotes to an increase in the average dispersoid number density and decrease in particle size. The enhanced dispersoids distribution resulting from the slow homogenization heating rate leads to a reduction in the recrystallization fraction (24~29% lower) and grain size (18~22% smaller).

Yi Han, Ke Ma, Chuyan Wang, Hiromi Nagaumi

Effect of Si Addition on Solid Solution Hardening of Al-Mn Alloys

Non-heat-treatable aluminum alloys owe their strength mainly to elements in solid solution. But the effect of the combination of multiple elements on strength is not well known. Small amounts of Si usually exist in many commercial alloys. Three high purity based Al-Mn binary alloys and one ternary alloy with addition of Si are investigated in this work. The varied solute contents are achieved by cast compositions and the grain structures are controlled by recrystallization. The strength is measured by tensile tests at room temperature. It is found that the addition of Si to Al-Mn alloys leads to a similar increase in strength as adding a similar amount of Mn.

Qinglong Zhao, Bjørn Holmedal

Effects of Deformation Texture Intensities and Precipitates on the Anisotropy of Mechanical Properties of Al-Li Alloy 2099 T83 Extrusions

The use of aluminum-lithium alloys in aerospace applications requires a thorough knowledge of how processing and product geometry impact their microstructure, texture and mechanical properties. As with other aluminum alloys, anisotropy of mechanical properties has been related to the formation of deformation textures during thermo-mechanical processes.Static mechanical properties and microstructural characteristics such as texture and precipitate distribution were analysed in two series of 2099-T83 extrusions, i.e. a cylindrical extrusion and an integrally stiffened panel (ISP). The cylindrical extrusions present <111> and <100> fiber textures while the ISP possesses the same fiber textures with lower intensities. Rolling textures such as Brass were also observed in some locations of the ISP. The levels of longitudinal strength and static anisotropy correlate well with the intensity of the fiber texture. Moreover, varying densities of T1 (Al2CuLi) precipitates were observed in the TEM.

Alexandre Bois-Brochu, Carl Blais, Franck Armel Tchitembo Goma, Daniel Larouche, Julien Boselli, Mathieu Brochu

Evolution in Microchemistry and its Effects on Deformation and Annealing Behavior of an AlMnFeSi Alloy

An Al-Mn-Fe-Si model alloy has been subjected to two homogenization treatments, to achieve materials conditions with different microstructures in terms of constituents, levels of Mn in solid solution and dispersoid density, followed by cold rolling and back-annealing. The microchemistry state and evolution has been carefully characterized and quantified during processing, with a special focus on the second phase particles (constituents and dispersoids) and their effect on the softening behavior during back-annealing.

Ning Wang, Jarl Erik Flatøy, Yanjun Li, Knut Marthinsen

Influence of Process Fluctuations on Weld Seam Properties in Aluminum Alloy Extrusion

The quality of weld seams produced during extrusion of hollow profiles is a big issue in the extrusion industry. The presented investigations deal with the characterization of extruded weld seams for the alloys AlMgSi0.5 (EN AW-6060), AlMgSi1 (EN AW-6082) and AlZn4.5Mg1 (EN AW-7020). Mictrostructural analysis and material properties have been analyzed with respect to variations in billet temperature, extrusion speed, subsequent cooling and heat treatment. The alloys show distinct differences in recrystallization behavior and microstructure of the weld seams and the surrounding base material.The AlMgSi0.5 alloy shows a fully recrystallized microstructure while the AlZn4.5Mg1 and the AlMgSi1 exhibit different degrees of a partially recrystallized structure leading to substantial differences in grain size between the three alloys. This behavior results in a different dependency of the material properties on process parameter changes. As already stated by previous investigations, this influence is especially fatal to the material properties transverse to the extrusion direction for non- or partially recrystallizing alloys.

Marcus Engelhardt, Norbert Grittner, Christian Klose, Friedrich-Wilhelm Bach

Evolution of Fragmented Fe-Intermetallic Compounds in the Semi-Solid State of Al-Mg-Si-Fe Alloys by Deformation Semi-Solid Forming Process

Fe-intermetallic compounds are commonly considered as a harmful phase in the recycled aluminum alloys. The Deformation Semi-Solid Forming (D-SSF) process has advantages to modify these harmful compounds into more favorable particles by thermo-mechanical deformation and subsequently heating to the semi-solid state. The evolution of fragmented Fe-intermetallic compounds of the Al-Mg-Si-Fe alloy was investigated during heating to various semi-solid temperatures. The fragmented Fe-intermetallic compound was transformed into the polyhedral shape in the initial stage and subsequently spheroidized shape at the low semi-solid temperatures between 580–610°C. At temperatures higher than 613°C, fragmented Fe-intermetallic compounds completely melt into the liquid phase with long holding time. The Fe-intermetallic compounds are stable as solid phase at low semi-solid temperature and metastable at high semi-solid temperature.

Chakkrist Phongphisutthinan, Hiroyasu Tezuka, Equo Kobayashi, Tatsuo Sato

Identification and Distribution of Fe Intermetallic Phases in AA 5657 DC Cast Ingots

Iron intermetallic phases and their distribution in DC cast ingots have a significant impact on the quality of final sheet products. However, accurate identification and quantification of iron intermetallic phases in the cast ingots are a great challenge due to their small size and similar chemical composition. In this study, the phase identification and quantitative analysis of the volume fraction were performed using the combination of SEM, EBSD, EDS and image analysis. The results showed that four types of iron intermetallic phases (AlmFe, α-AlFeSi, Al3Fe and Al6Fe) exist in AA 5657 cast ingots. Using the deep-etching technique, typical morphologies of iron intermetallic phases were revealed. It was found that AlmFe was the dominant phase in the region near the cast surface, while Al3Fe became predominant towards the ingot center. Between the cast surface and the ingot center, α-AlFeSi changed into the leading phase. The mechanism for the phase selection and transition in cast ingots has been discussed.

Z. Zhang, G. Li, X.-G. Chen

Microstructure and Mechanical Properties of AA2195 DC Cast Ingot Plates

DC cast ingot plates are especially suitable for large mold manufacturing in the plastic and automotive industries. The microstructures and mechanical properties of AA2195 DC cast ingot plates in the as-cast and heat-treated conditions were studied. Aging treatments were carried out at 125 and 150°C for 12 and 24 h. A microstructural analysis was conducted using optical and scanning electron microscopies as well as a differential scanning calorimetry. The results show a significant increase in yield and tensile strengths after aging at 150°C. It is suggested that the strengthening of AA2195 cast plates is largely determined by the proportion of both θ′-Al2Cu and T1-Al2CuLi precipitations. By adopting an appropriate heat treatment, AA2195 cast ingot plates can provide a range of satisfactory combinations of strength and ductility which fulfill the design requirements of large mold applications.

E. M. Elgallad, A. Hekmat-Ardakan, F. Ajersch, X-G. Chen

Threshold Deformation for Exhibiting the Hardening on Annealing Behaviour in AA3103 Alloy

Hardening on annealing is reported to occur not only in nanostructured material but also at strain levels obtained by cold rolling in AA3103 alloy. A threshold deformation limit is proposed for cold rolled AA3103 alloy for exhibiting this behaviour. Tensile tests performed on samples annealed at 225 °C for 10 minutes after cold rolling to strains of 1.5 and above revealed an increase in strength after annealing, whereas the samples annealed after cold rolling to strains up to 1.5 did not exhibit hardening on annealing. EBSD studies are used for microstructural observations and it is discussed if dislocation source limitation after annealing is causing the hardening.

Nagaraj Vinayagam Govindaraj, Bjørn Holmedal

A Study of the Microstructure, Crystallographic Texture, and Recrystallization in AA4006 Alloy Strips Produced by Twin Roll Caster and Direct Chill Processes

The aluminum alloy AA4006 belongs to the Al-Fe-Si system, with Si between 0.8 and 1.2 % mass, and Fe between 0.5 and 0.8 % mass. This alloy has been little studied despite its extensive use (patent n° US 2003/0196733 A1 from 2003). A study of the as received sheet microstructures, crystallographic texture evolution (for the as received, cold rolled, and recrystallized samples), and recrystallization after 70% cold rolling has been done for two AA4006 alloy strips produced by two industrial casting processes: twin roll caster (TRC) and direct chill (DC). Polarized optical microscopy, scanning electron microscopy have been used to characterize the microstructure and X-ray diffraction for the texture evolution characterization. It has been detected that the recrystallization of the TRC strip sample occurred at a higher temperature than that of the DC strip sample. The precipitation, in the TRC strip sample, occurs mainly before recrystallization and may occur during recrystallization. Precipitation occurs before and during recrystallization in the DC strip sample. Relevant differences in the grain morphology and in grain and intermetallic particles distribution have been detected and discussed. Through thickness (surface and center) textures of these specimens (as received, cold rolled, and recrystallized) have been analyzed and compared. Results showed significant texture changes across thickness of the as received strips. The texture results also indicated the presence of a shear texture on the surface region and β-fiber in the mid section of the cold rolled (70% area reduction) sample for the TRC strip sample. In the DC strip sample, under the same conditions, the cube component and β fiber occurred through the thickness (at the surface and in the center). A texture with random oriented grains has been detected in the two deformed and recrystallized samples of the two sheet samples (TRC and DC). It has been observed that the TRC strip sample recrystallization occurs at higher temperature than that of the DC strip sample despite the little differences in their softening curves. The absence of β fiber in the recrystallized samples (TRC and DC) has also been observed.

F. M. Souza, R. C. Fernandes, R. L. Plaut, N. B. Lima, A. F. Padilha

Effect of Extensive Rolling on Mechanical Properties of An Al-Mg-Sc Alloy

Sheets of an Al-6%Mg-0.5%Mn-0.2%Sc-0.07%Zr alloy with ultrafine-grained structure containing a high dislocation density (ρ~1015 m−2) were produced by equal channel angular pressing (ECAP) to a strain of ε~12 at a temperature of 300°C followed by cold rolling to a reduction of 90%. This material exhibited a yield stress of ~600 MPa, an ultimate strength of ~640 MPa, while elongation-to-failure decreased to ~2%. It was shown that dislocation strengthening attributed to extensive cold rolling (CR) plays a major role in achieving high strength in this alloy.

Andrii Dubyna, Anna Mogucheva, Rustam Kaibyshev

The Effects of Transition Elements on the Control of Recrystallization of Al-Zn-Mg Extrusion

The 7000 series aluminum alloy has high strength and it is expected as a material with large weight saving effect in the field of transport including automobiles. However, extrusions sometimes generate coarse recrystallized grains on their surfaces. In particular for 7000 series alloy, these coarse grains may decrease the resistance for stress-corrosion cracking, resulting in potential failure in practical use. For this reason, transition elements have generally been added to 7000 series alloy, and the dispersoids composed of these transition elements suppress the coarsening recrystallized grains.As transition elements added to practical alloys, Mn and Zr are often selected. Some papers report that the addition of transition elements sharpens quench sensitivity, and thus often decreases its strength [1–4]. Therefore, it is important for structural materials, to quantitatively investigate the effect of the addition of transition elements on the strength of extrusion.In this study, the effects of Mn and Zr on the recrystallization suppression effect and strength in 7000 series aluminum alloy have been investigated. It was found that Zr has larger effect on recrystallization suppression than Mn. In addition, it was found that as the addition of Mn increased, quench sensitivity sharpened, resulting in larger reduction in strength. On the other hand, Zr addition hardly gave effect on quench sensitivity. From these results, it became clear that Zr addition is preferable than Mn addition from the viewpoints of recrystallization suppression and strength.

Yukimasa Miyata, Shinji Yoshihara

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