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Inhaltsverzeichnis

Frontmatter

Opening Session

Frontmatter

Magnesium in North America: A Changing Landscape

The changing landscape of North American manufacturing in the context of global competition is impacting the market of all raw materials, including magnesium. Current automotive fuel economy legislation and pending legislation on the emissions of greenhouse gases are impacting magnesium’s largest consuming industries, such as aluminum, automotive components, steel and transition metals. These industries are all considering innovative ways to efficiently incorporate the needed raw materials into their processes. The North American magnesium market differs from other regions based on maturity, supply streams, changing manufacturing capabilities and trade cases, combined with the transformation of North American manufacturing.The impact of these factors on the supply/demand dynamics of the North American magnesium market in both the short and long-term will be reviewed. The influence of new applications, products, and legislative changes are considered in the equation.

Susan Slade

Global Magnesium Research: State-of-the-Art and What’s Next?

In recent years magnesium and its alloys have been successfully introduced into weight-saving applications in the transportation industries in order to reduce fuel consumption and greenhouse gas emissions as well as to increase the performance of modern cars. Besides advantages, e.g. superior specific strength and excellent processability, applications of magnesium alloys are limited due to their inferior properties at elevated temperatures, e.g. low creep resistance and reduced corrosion behavior, especially when in galvanic contact with other metallic materials.Current developments are revealing possibilities to improve these properties by using modern alloys and processing routes. While the majority of industrial applications utilize cast products, the use of wrought magnesium alloys is still at an early stage. Within the framework of ongoing research and development, the corrosion behavior of both cast and wrought magnesium materials in standalone uses or in galvanic couples with other metallic materials is gaining increasing attention. New coating systems tailored to selected applications will have to be developed in order to increase the usage of magnesium alloys in the transportation industries in the future. This work also needs to be coordinated with new processes for joining magnesium alloys with similar and dissimilar metals and alloys, to achieve a broad spectrum of materials that fulfill the requirements given by the applications.After years of intensive research in Europe, North America, Australia and Asia, an increase in these activities has taken place in recent years, in particular in China and Korea. The magnesium industry has to face new challenges with regard to market issues, the breakdown of the Western magnesium industry and finally the carbon footprint discussion of the life-cycle assessment of components for the transportation industry.This presentation will first address these issues and challenges, then discuss new developments and finally show some examples of new applications. In the conclusions, gaps and challenges will be analyzed and recommendations for sustainable research and development will be given.

Karl Ulrich Kainer

Environmental Challenges for the Magnesium Industry

The subject of environmental concerns with magnesium production and magnesium processing first started showing up in technical analysis of problems about the time of Life Cycle Analysis articles. Magnesium is produced and processed in relatively small quantities throughout the world. Annual magnesium production has been around 500–700,000 metric tons per year. This compares to aluminum which is produced in annual amounts up to 35 million metric tons.There have been some excellent review papers done, but a great amount of the work related to electrolytic magnesium production which was the predominant method of production. That situation has changed totally in the past 10 years and now 85% of the world’s magnesium is produced by thermal processes and most of that is in China.Comparison papers have been written on the environmental impacts of the two main magnesium production processes. As the measurement technology improves and as the total information references are better understood the environmental challenges can be more clearly identified. This paper reviews the situation and suggests some forward looking steps that might need to be taken.

Robert E. Brown

Predicting Mg Strength from First-Principles: Solid-Solution Strengthening, Softening, and Cross-Slip

Predictive modeling of strength from first-principles electronic structure methods offers great promise to inform Mg alloy design. Simulating the mechanical behavior for new alloys requires an understanding of mechanisms for deformation at atomic-length scales, with accurate chemistry, extended to larger length- and time-scales. To design ductile Mg alloys, we identify solutes that strengthen basal slip and increase cross-slip. First-principles modeling of dislocations predict dislocation motion under stress through a field of solutes at a finite temperature. First-principles flexible boundary conditions compute accurate core structures of basal and prismatic dislocations, and dislocation/solute interactions. We develop new models to predict the solute-strengthening for basal dislocations; cross-slip from basal- to prismatic-slip for α-type screw dislocations; and cross-slip stress with solutes. First-principles data provides insight into the response of dislocations to solutes and quantitative data to build new predictive models.

Dallas R. Trinkle, Joseph A. Yasi, Louis G. Hector

Biodegradable Magnesium Implants — How do They Corrode in-Vivo?

Biodegradable magnesium implants are currently breaking the paradigm of designing and producing only corrosion resistant metallic biomaterials. The academic and industrial interest in this novel class of biomaterials is increasing dramatically in the recent years. First biodegradable metal implants have been realized as vascular stents and bone screws. However, the knowledge of the underlying degradation mechanism of these metal implants remains mainly undiscovered.This lecture will summarize the current published knowledge and recent advances in elucidating the in-vivo corrosion processes of these novel biodegradable magnesium implants [1].

Frank Witte, Norbert Hort, Frank Feyerabend

The Next Generation of Magnesium Based Material to Sustain the Intergovernmental Panel on Climate Change Policy

Current Mg alloys have several drawbacks that limit wide and profitable utilization in the industrial sector. From an environmental point of view, lighter metals like magnesium are currently considered unclean products as they require energy-intensive. But they have been proven to be “clean” in the transport sector, as they can reduce fuel consumption. Here the potential of magnesium based materials is addressed through double-tasking: a) establish innovative lean-manufacturing processes, avoid the classic melting step to substantially reduce carbon footprint of the magnesium products; b) encourage the using of no-melt processes, realizing high-resistant ultra-fined microstructures. The “Green Metallurgy 2020”, a project funded by European Community in the LIFE+ 2009 Program, started in September 2010, coordinated by Politecnico di Milano (ITA) aims to scale to industrial route such impressive results experienced by CENIM (SPA) for some ultrafine bi-phase Mg -Zr (-Y) produced by no-melting route that achieved up to 400 MPa UTS and elongation capability of about 13%.

F. D’Errico, S. Farè, G. Garces

Fracture Mechanism and Toughness in Fine- and Coarse-Grained Magnesium Alloys

The fracture mechanisms in the extruded magnesium alloys with two different grain sizes, 2 and 50 μm, were investigated by SEM, TEM and EBSD micro structural observations. The coarse-grained alloy showed that the {10–12} type deformation twins formed at the beginning of test, and the crack was propagated into the boundaries between twins and matrix. On the other hand, the fine-grained alloy showed that the sub-grain boundaries formed instead of the deformation twins. No formation of twins at the early deformation stage causes a crack-tip blunting, and thus, the fracture toughness has a high value.

Hidetoshi Somekawa, Alok Singh, Toshiji Mukai

Primary Production; Characterization and Mechanical Performance

Frontmatter

The Development of the Multipolar Magnesium Cell: A Case History of International Cooperation in a Competitive World

The author conceived the first multipolar magnesium electrolytic cell in the late 1970s, in order to offset the impact of an 80kA monopolar cell developed in cooperation with Osaka Titanium Company (OTC) being licensed by Alcan to a major competitor of OTC. During the 1980s the commercial value of the multipolar magnesium cell technology was established. The 1990s saw significant further progress by OTC, while attempts by Alcan to commercialize it in magnesium production plants met with technical difficulties and failure, due primarily to the lack of magnesium chloride feed of adequate quality. Now the author plans to commercialize a new multipolar cell design with a target productivity of 8–10 tons/day and a unit power consumption of 8.5–10 KWHR/kg of magnesium.

Olivo G. Sivilotti

Effect of KCl on Liquidus of LiF-MgF2 Molten Salts

Liquidus temperature of KCl-LiF-MgF2 molten salts was determined based on cooling curve. The method of cooling curve was reliable and accurate. Experimental accuracy has been measured by the determined liquidus temperature of KCl. The measured value of KCl liquidus temperature of 769.27 ° C is near and comparable to the documented value 769.5 ° C. The difference value is 0.23 ° C, and the relative error was 0.03%. The results show that effect of KCl on liquidus of molten salt MgF2-LiF electrolyte was great. The liquidus temperatures lowered with increasing of content of KCl in electrolyte. The liquidus temperature could be reduced 20 ° C with content of KCl in electrolyte increased to 50wt%. The experiments showed that the compound addition of KCl into LiF-MgF2 electrolyte not only reduced the liquidus temperature of electrolyte effectively, but also decreased the aluminum-magnesium production cost and increased the economic benefits.

Shaohua Yang, Fengli Yang, Xianwei Hu, Zhaowen Wang, Zhongning Shi, Bingliang Gao

Efficiency and Stability of Solid Oxide Membrane Electrolyzers for Magnesium Production

Solid oxide membrane (SOM) process has been successfully employed for the production of magnesium directly from its oxide. The process involves dissolving MgO in a fluoride based ionic flux and electrochemically pumping out the oxygen ions from the flux via an oxygen-ion-conducting SOM to the anode where they are oxidized, while reducing magnesium ions at the cathode. Understanding the long-term stability of the SOM in the flux is critical for the commercial success of this technology. In this study long term SOM stability is investigated under potentiostatic conditions. Additionally, study utilizes electrochemical techniques such as impedance spectroscopy and linear sweep voltammetry to investigate key concepts related to MgO dissociation and current efficiency. Results show that the dissociation potential of MgO is dependent on the partial pressures at which magnesium is generated and the membrane stability is likely related to the current efficiency.

E. Gratz, S. Pati, J. Milshtein, A. Powell, U. Pal

Magnesium Production by Vacuum Aluminothermic Reduction of a Mixture of Calcined Dolomite and Calcined Magnesite

A new method of magnesium production was proposed that using a mixture of calcined dolomite and calcined magnesite as raw materials with the molar ratio of MgO to CaO was 6:1 by vacuum aluminothermic reduction. The reduction process was studied by thermodynamic analysis and X-ray diffraction analysis of reduction residue. The reaction of reduction process was CaO+6MgO+4Al=CaO•2Al2O3+6Mg. The effect of briquetting pressure, reduction temperature, time and CaF2 (MgF2) on reduction ratio of MgO was investigated. And the reduction residue that the main phase of CaO•2Al2O3 was leached in alkaline solution for producing sodium aluminateme raw material for special alumina. The results show that the reduction ratio is increased with increasing of the temperature, time, briquetting pressure in range from 40 to 100 MPa and addition of CaF2 or MgF2 in range from 0 to 3%. The alumina leaching ratio of reduction residue reached 88% at the conditions of leaching temperature 95 °C and the concentration ratio of Na2CO3 to NaOH was 100:75 in leaching solution.

Wen-xin Hu, Nai-xiang Feng, Yao-wu Wang, Zhi-hui Wang

Multiphase Diffusion Study for Mg-Al Binary Alloy System

Multiphase diffusion simulation and annealing experiments have been performed for Mg-Al binary alloys at various temperatures. Annealing experiments of Mg-3wt% Al and Mg-6wt% Al alloys were carried out at 330 and 400 °C for various times and the change of concentration profiles of Al in grains were measured by Electron Probe Micro Analyzer (EPMA). In order to simulate this annealing process and understand the diffusion of Mg-Al alloys, diffusion model was developed by using Finite Difference Method (FDM) coded in FORTRAN. In the diffusion simulations, composition-independent inter-diffusion coefficients were used and the intermetallic phases were assumed to have equilibrium compositions.

Young-Min Kim, Sazol Kumar Das, Manas Paliwal, In-Ho Jung

Experiments and Modeling of Fatigue Damage in Extruded Mg AZ61 Alloy

In this study, structure-property relations with respect to fatigue of an extruded AZ61 magnesium alloy were experimentally quantified. Strain-life experiments were conducted in the extruded and transverse orientations under low and high cycle conditions. The cyclic behavior of this alloy displayed varying degrees of cyclic hardening depending on the strain amplitude and the specimen orientation. The fracture surfaces of the fatigued specimens were analyzed using a scanning electron microscope in order to quantify structure-property relations with respect to number of cycles to failure. Intermetallic particles were found to be the source of fatigue initiation on a majority of fracture surfaces. Finally, a multistage fatigue model based on the relative microstructural sensitive features quantified in this study was employed to capture the anisotropic fatigue damage of the AZ61 magnesium alloy.

J. B. Jordon, J. B. Gibson, M. F. Horstemeyer

Low-Cycle Fatigue Behavior of Die-Cast Mg Alloy AZ91

An investigation has been conducted on the influence of microstructure and artificial aging response (T6) on the low-cycle fatigue behavior of super vacuum die-cast (SVDC) AZ91. Fatigue lifetimes were determined from total strain-controlled fatigue tests for strain amplitudes of 0.2%, 0.4% and 0.6%, under fully reversed loading at a frequency of 5 Hz. Cyclic stress-strain behavior was determined using incremental step test (IST) methods. Two locations in a prototype casting with different thicknesses and, therefore, solidification rates, microstructure and porosity, were examined. In general., at all total strain amplitudes fatigue life was unaffected by microstructure refinement and was attributed to significant levels of porosity. Cyclic softening and a subsequent increased cyclic hardening rate, compared to monotonic tests, were observed, independent of microstructure. These results, fractography and damage accumulation processes, determined from metallographic sectioning, are discussed.

Luke Rettberg, Warwick Anderson, J. Wayne Jones

Small Fatigue Crack Growth Observations in an Extruded Magnesium Alloy

The purpose of this paper is to quantify the microstructurally small/physically small crack growth behavior in an extruded AZ61 magnesium alloy, Fully-reversed, interrupted load control tests were conducted on notched specimens that were taken from a magnesium alloy extrusion, In order to measure crack growth, replicas of the notch surface were made using a two-part siliconrubber compound at periodic cyclic intervals, Scanning electron microscopy analysis of the replica surfaces revealed multi site crack initiation and subsequent crack coalescence, The crack growth behavior of the small fatigue cracks was shown to have a strong dependence on the material microstructure as the crack was submitted to a tortuous growth path along grain boundaries and crystallographic slip planes, A microstructurally dependent crack growth model that was previously developed for FCC metals was further extended here to HCP metals.

J. D. Bernard, J. B. Jordon, M. F. Horstemeyer

Applicability of Mg-Zn-(Y, Gd) Alloys for Engine Pistons

Commercial magnesium alloys have a great potential for structural applications in automotive due to their significant weight saving. However, they have poor creep resistance at temperature over 125°C, thus making them inadequate for power train applications such as engine pistons, which are operated at temperature up to 300°C. Recently, creep resistant magnesium alloys with rare-earth elements and Zn have been developed, hence the applicability of Mg-Zn-(Y, Gd) alloys for engine pistons was investigated in this paper. Gravity casting was performed with Mg-Zn-(Y, Gd)-Zr alloy, followed by T6 treatment. Effects of the amount of alloying elements on the mechanical properties of tensile strength and creep strain were evaluated. Nominal composition of Mg-2Zn-11Y-5Gd-0.5Zr was selected for the actual piston cast trial and its high cycle fatigue test was conducted comparing to the current aluminum cast alloy of A336 (JIS AC8A) for pistons. At room temperature, the fatigue strength is 27% lower than A336, while it is 35% higher at 300°C. It is suggested that Mg-2Zn-11Y-5Gd-0.5Zr alloy shows attractive high temperature mechanical properties higher than A336, hence it is promising as a candidate material for the engine piston application.

Kazutaka Okamoto, Masato Sasaki, Norikazu Takahashi, Qudong Wang, Yan Gao, Dongdi Yin, Changjiang Chen

Compressive Creep Behaviour of Extruded Mg Alloys at 150 °C

Wrought magnesium alloy bars, sections and tubes have been extensively used in the aerospace, electronics and automotive industries, where component weight is of concern. The operating temperature of these components is typically limited to below 100°C, since appreciable creep relaxation of the wrought alloys takes place above this temperature.The objective of this study was to investigate the high temperature creep performance of two wrought magnesium alloys (AE42 and EZ33) developed for elevated temperature applications. Compressive creep behavior of extruded rods was studied at room temperature and at 150°C using the nano-indentation creep technique (on the microscale) and neutron diffraction (on the macroscale). Measurements were performed in the extrusion and radial directions to observe the effect of texture on the creep resistance, hardness and elastic modulus of the alloys. Microscopic examination of the alloys revealed that the distribution of second phases along the grain boundaries was critical to the alloy’s creep resistance.

M. Fletcher, L. Bichler, D. Sediako, R. Klassen

The Effect of Thermomechanical Processing on the Creep Behavior and Fracture Toughness of Thixomolded® AM60 Alloy

Creep and fracture toughness experiments were performed on a commercially available magnesium-aluminum alloy (AM60) after three processing treatments: (1) As-Thixomolded® (as-molded), (2) Thixomolded® then thermomechanically processed (TTMP), and (3) Thixomolded® then TTMP then annealed (annealed). The conventional tensile-creep experiments were performed at applied stresses ranging between 20–75MPa and temperatures between 373–473K (100–200°C). In-situ tensile-creep tests were performed on selected samples. The as-molded material exhibited creep resistance superior to the thermomechanically processed materials. Creep experiments indicated grain boundary cracking, and grain size was expected to be an important micro structural parameter that affected the creep behavior. Fracture toughness experiments were performed at room temperature (RT) on single edge notched tension (SENT) samples. The TTMP and annealed materials exhibited fracture toughness values almost twice that of the as-molded material.

Z. Chen, J. Huang, R. Decker, S. LeBeau, C. J. Boehlert

Casting and Solidification

Frontmatter

Simulation of Porosity and Hot Tears in a Squeeze Cast Magnesium Control Arm

Simulations are performed for the squeeze casting of AM60 and AZ91 automotive control arms. Advanced feeding flow and stress models are used within commercial casting simulation software to predict shrinkage porosity and hot tears. The simulations are validated through comparisons with observations made on experimental castings. Generally good agreement is obtained between the measured and predicted defect locations and extents. Design and process changes are introduced to mitigate the shrinkage and hot tear problems in these castings. The comparisons in the present study establish considerable confidence in the ability of casting simulation to predict shrinkage and hot tears in squeeze casting of magnesium alloys.

K. D. Carlson, C. Beckermann, J. Jekl, R. Berkmortel

Dendritic Microstructure in Directional Solidification of Magnesium Alloys

We demonstrate morphological transitions in Mg-Al alloy dendritic microstructure as the cooling conditions change during steady state and transient directional solidification. The effect of temperature gradient on the transition is investigated numerically using two-dimensional phase field simulations. The six-fold symmetry of Mg alloys leads to very different dendrite morphologies than those encountered in alloys exhibiting four-fold surface tension anisotropy. In particular, we find that at high temperature gradients primary dendrites become columnar in the direction of thermal gradient. In contrast, in the regions where surface energy anisotropy is dominant, primary stalks cross at 60-degree angles that characterize hexagonal crystal structure. Our modelling observations are compared to new Mg-Al experiments.

Morteza Amoorezaei, Sebastian Gurevich, Nikolas Provatas

Microstructures and Casting Defects of Magnesium Alloy Made By A New Type of Semisolid Injection Process

We have developed a new type of semisolid injection process that allows magnesium alloys to be formed in high material yields approximating 90%. In this process, generic magnesium billets are heated into their semisolid temperature range in an injection cylinder, without cover gas, and then the material is injected into a mold.In this study, several billets were precision-heated in the cylinder to obtain a desired fraction solid. Plate specimens were produced by injecting the material at different injection speeds. Microstructures were observed by optical microscopy, and casting defects were detected on an X-ray computed tomography scanner. As injection speed was increased, the size and shape of a-Mg solid particles became smaller and more spherical., and the defect volume fraction increased. In contrast, as the fraction solid was increased, the defect volume fraction decreased. Spheroidization and miniaturization of solid particles were attributed to shear stress at the nozzle, and defects were affected by viscosity.

Yuichiro Murakami, Naoki Omura, Mingjun Li, Takuya Tamura, Shuji Tada, Kenji Miwa

Macrostructure evolution in directionally solidified Mg-RE alloys

The use of Rare-Earths (RE) to develop new cast- and wrought-magnesium alloys has acquired increased interest in recent years. The good mechanical properties of Mg-RE alloys at room temperature, and in particular their high strength at relatively high temperatures are at present well-known facts that make them very promising materials for transport applications. In this context, it is necessary to achieve a better understanding of the macro and microstructure evolution of cast Mg-metals directionally solidified. To this end, binary Mg-RE alloys (where RE = Gd, Nd and Y) were cast by permanent mould direct chill casting. This process was performed in a specially optimized laboratory-scale installation in order to ensure the obtention of “clean” ingots, with homogeneous composition and free of porosity and inclusions. A set of different processing conditions was evaluated in order to better control the final microstructure, mainly in terms of grain size, orientation and distribution. The grain selection mechanisms operating during the solidification of these specimens, namely texturization and Columnar to Equiaxed Transition (CET), were characterized and put into relation with the initial composition of the alloy and the imposed cooling conditions.

M. A. Salgado-Ordorica, W. Punessen, S. Yi, J. Bohlen, K. U. Kainer, N. Hort

Microstructure and Mechanical Behavior of Cast Mg AZ31B Alloy Produced by the Magnetic Suspension Melting Process

Magnesium is the lightest of all structural metals and offers significant weight savings compared to traditional automotive materials. This paper describes the macrostructure and the micro structure of Mg AZ31B alloy produced via the Magnetic Suspension Melting (MSM) technique at a low superheat of 5°C. It was found that casting at this low superheat produced a fine globular grain structure in comparison to a dendritic structure in conventionally cast alloys. The intermetallic phases were analyzed in detail and compared with the conventionally cast alloy. In the MSM cast alloy, the Mg17Al12 phase formed mainly at the grain boundaries, in contrast to typical dendritic entrapment of this phase within the grains in conventional castings. The formation of the Al-rich secondary-α phase during solidification was investigated. The effects of this morphology change on mechanical and fracture behavior of this material are presented. These results are discussed relative to conventionally cast Mg alloys.

N. W. Rimkus, M. L. Weaver, N. El-Kaddah

Investigations on Hot Tearing of Mg-Zn-(Al) Alloys

Mg-Zn alloys are widely used as wrought alloys such as ZM, ZK and ZE series. They are reportedly to be prone to hot tearing due to the presence of Zn. The present work first evaluates the hot tearing susceptibility (HTS) of binary Mg-Zn alloys using quantitative experimental methods and thermodynamic simulations based on Clyne’s model, and then further investigate the addition of aluminum on the HTS in the ternary alloys Mg-Zn-Al. The results show that the curve of the HTS vs. the content of Zn has a typical “λ” shape. With increasing the content of Zn, the HTS increases firstly, reaches the maximum at 1.5% Zn and then decreases again. The addition of Al in Mg-Zn alloys influences the HTS. In the Mg-Zn-Al ternary system, the HTS decreases with the increase of Al content. The curve of the HTS as a function of Zn content in the ternary Mg-Zn-Al system is a little different from that observed in the binary Mg-Zn alloys. Two peaks are obtained: one is approximately at 1.0 to 1.5 wt.% Zn, another at 3.0wt.%Zn.

Le Zhou, Yuanding Huang, Pingli Mao, Karl Ulrich Kainer, Zheng Liu, Norbert Hort

Proportional Strength-Ductility Relationship of Non-SF6 Diecast AZ91D Eco-Mg Alloys

SF6 gas has been generally used for Mg alloys during melting and casting as a cover gas. The use of SF6 gas, however, will be limited owing to its significant impact on global warming. Non-SF6 process during melting and casting in diecasting industry has been proved with Eco-Mg alloys by a simple addition of small amount of CaO into AZ91D and AM60B Mg alloys. This paper will show non-SF6 diecasting procedures for AZ91D Eco-Mg alloys. Cold-chamber and hot-chamber diecasting mass productions were performed by using a Toshiba 135-ton cold chamber and a Frech 200-ton hot chamber diecasting machines under CO2 atmosphere without SF6 gas. An emphasis will be on proportional strength and ductility relationship of Eco-Mg alloys, in part, due to a high-quality melt, refined grain size and Al2Ca second phase strengthening. Microstructures and mechanical properties of AZ91D Eco-Mg alloys will be evaluated in comparison with those of conventional AZ91D Mg alloy.

Shae K. Kim

Estimation of Heat Transfer Coefficient in Squeeze Casting of Magnesium Alloy AM60 by Experimental Polynomial Extrapolation Method

In this work, a different wall-thickness 5-step (with thicknesses as 3, 5, 8, 12, 20 mm) casting mold was designed, and squeeze casting of magnesium alloy AM60 was performed in a hydraulic press. The casting-die interfacial heat transfer coefficients (IHTC) in 5-step casting were determined based on experimental thermal histories data throughout the die and inside the casting which were recorded by fine type-K thermocouples. With measured temperatures, heat flux and IHTC were evaluated using the polynomial curve fitting method. The results show that the wall thickness affects IHTC peak values significantly. The IHTC value for the thick step is higher than that for the thin steps.

Zhizhong Sun, Xiaoping Niu, Henry Hu

Wide Strip Casting Technology of Magnesium Alloys

Extensive investigations relating to the production of high performance and low cost magnesium sheet by strip casting have been performed for the application to automotive parts and electronic devices. Research on magnesium sheet production technology started in 2004 by Research Institute of Industrial Science and Technology (RIST) with support of Pohang Iron and Steel Company (POSCO). POSCO has completed the world’s first plant to manufacture magnesium coil. Another big project in order to develop wide strip casting technology for the automotive applications of magnesium sheets was started in succession.

W.-J. Park, J. J. Kim, I. J. Kim, D. Choo

Microstructural Analysis of Segregated Area in Twin Roll Cast Magnesium Alloy Sheet

Twin roll casting process of magnesium alloy has been studied by various institutes since POSTECH started at the world first time. RIST has done the research and development program of twin roll casting and reverse warm milling of magnesium alloy sheet with 600 mm width. Presently, RIST is working on twin roll casting program of magnesium alloy sheet with 2,000 mm width. Twin roll cast magnesium alloy sheet includes segregated area which is important due to controllable quality of final product. Here we present the microstructural analysis of segregated area in twin roll cast magnesium alloy sheet to understand segregation phenomena. Especially, we studied on phase identification in segregated area, comparing the theoretically calculated simulation. Scanning electron microscopy, transmission electron microscopy and energy dispersive spectrometry were used for the phase identification. Our result shows that two kinds of segregation morphologies are observed in the segregated area, not depending upon the location in the sheet. Phase identification shows that segregated area includes densely continuous or dispersed beta and phi phase, and dispersed Al8Mn5 and Mg2Si.

Jae Joong Kim, Woo-Jin Park, D. Choo

Development of the Electromagnetic Continuous Casting Technology for of Magnesium Alloys

Currently, magnesium billets produced by ingot casting or direct chill casting process, result in low-quality surfaces and low productivity, Continuous casting technology to solve these problem has not only high-quality surface billets with fine-grained and homogeneous microstructure but also cost down. The latent heat of fusion per weight (J/g) of magnesium is similar to other metals, however, considering the heat emitted to the mold surface during continuous casting in meniscus region and converting it to the latent heat of fusion per volume, magnesium will be rapidly solidified in the mold during continuous casting, which induces subsequent surface defect formation. In this study, electromagnetic casting and stirring (EMC and EMS) techniques are proposed to control solidification process conveniently by compensating the low latent heat of solidification by volume and to fabricate magnesium billet with high-quality surface. This technique was extended to large scale billets up to 300 mm diameter and continuous casting was successfully conducted. Then magnesium billet was used for the fabrication of prototype automobile pulley.

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

Alloy Design/Development; Grain Refinement and Severe Plastic Deformation

Frontmatter

Effect of Zn/Gd Ratio on Phase Constitutions in Mg-Zn-Gd Alloys

This paper discusses the influence of Zn/Gd ratio on the phase constitutions of as-cast Mg-Zn-Gd alloys in the Mg-rich corner within the range of 0.5–3.0 at.% for Zn content and 0.5–3.0 at.% for Gd content. The critical Zn/Gd ratio for the formation of icosahedral quasicrystal phase (I phase) and long period stacking ordered (LPSO) structure in the Mg-Zn-Gd system has been confirmed. LPSO structure and (Mg,Zn)3Gd phase are formed in Mg-Zn-Gd alloys in the range of Zn/Gd ratio ≤1.0. However, only (Mg,Zn)3Gd phase is observed in the alloys in the range of 1.0< Zn/Gd ratio <1.5. And if Zn/Gd ratio is ≥1.5, I phase and (Mg,Zn)3Gd phase in the alloys begin to form gradually.

S. Zhang, G. Y. Yuan, C. Lu, W. J. Ding

Optimization of Magnesium-Aluminum-Tin Alloys for as-Cast Microstructure and Mechanical Properties

The microstructure and mechanical properties of as-cast Mg-Al-Sn alloys have been investigated using computational alloy design and experimental approaches. The as-cast microstructure of Mg-Al-Sn alloys consists of α-Mg, Mg17Al12 and Mg2Sn phases. The volume fractions of Mg17Al12 and Mg2Sn phases increase with increasing Al/Sn contents, and show good agreement between computational thermodynamics modeling and the experimental results. Generally, the yield strength of as-cast alloys increases with Al/Sn alloying contents, while the ductility decreases. This study has confirmed an earlier development of Mg-7Al-2Sn alloy and led to a promising new Mg-7Al-5Sn alloy with significantly improved strength and ductility compared to commercial alloy AZ91 (Mg-9Al-1Zn).

Xiaoyu Kang, Alan A. Luo, Penghuai Fu, Zhenzhen Li, Tianyu Zhu, Liming Peng, Wenjiang Ding

Thermodynamic Analysis of As-Cast and Heat-Treated Microstructures of Mg-Ce-Nd Alloys

The phase relationships in the Mg-rich corner of the Mg-Ce-Nd system have been investigated through the evaluation of selected compositions in the as-cast and heat-treated condition. Consistent thermodynamic CALPHAD-type assessments have also been generated for the Mg-Ce-Nd system [1].It is shown that this system reveals a significant degree of meta-stability under technologically relevant solidification conditions (i.e., permanent-mould or high pressure die casting). This is simulated in thermodynamic calculations by suppression of the RE5Mg41 phase and reasonable agreement is found with the as-cast micro structures. After heat treatment these micro structures transform, depending on alloy composition, into phase assemblies consistent with the calculated stable equilibrium phase diagram. It is the elucidation of such meta-stable phase formation and the subsequent transformation from the as-cast to the heat treated state that is a particular strength of the thermodynamic approach and which makes it a powerful tool for alloy development.The solid dots in Figure 1 indicate alloys exhibiting experimentally evidenced primary precipitation of the CeMg12 phase in the as-cast condition, whereas the stable equilibrium phase diagram suggests RE5Mg41 to be the primary phase. The thermodynamic calculation, however, reveals that a relatively small undercooling will result in the (metastable) primary CeMg12 phase precipitation in all these alloys, as observed after casting. More results and the phase transformations towards equilibrium after heat treatment are given in detail by Gröbner et al. [1].

Mark A. Easton, Suming Zhu, Mark A. Gibson, Jian-Feng Nie, Joachim Gröbner, Artem Kozlov, Rainer Schmid-Fetzer

Compressive Strength and Hot Deformation Behavior of TX32 Magnesium Alloy with 0.4% Al and 0.4% Si Additions

Mg-3Sn-2Ca (TX32) alloy has good corrosion and creep resistance although its strength is inferior to AZ31 alloy. In this paper, the influence of additions of 0.4%Al and 0.4%Si on the compressive strength and hot working characteristics of TX32 is reported. Although the room temperature compressive strength improved marginally with the alloying additions, the drop in higher-temperature strength is significant. By comparing with the alloy having only 0.4% Al, it is clear that the Si addition is responsible for this deterioration. The hot working behavior as characterized by processing maps revealed that TX32 exhibits two domains of dynamic recrystallization occurring in the temperature and strain rate ranges: (1) 300 – 350 °C and 0.0003 – 0.001 s−1 and (2) 390–500 °C and 0.005–0.6 s−1. In Al and Si containing TX32, both the domains moved to higher temperatures and the flow instability is reduced improving the hot workability. In both the domains, the apparent activation energy is higher than that for self-diffusion in magnesium implying that there is a significant contribution from the back stress generated by the hard particles present in the matrix.

K. P. Rao, Y. V. R. K. Prasad, K. Suresh, C. Dharmendra, N. Hort, K. U. Kainer

An Analysis of the Grain Refinement of Magnesium by Zirconium

A Design of Experiments approach was used to conduct a systematic study of the grain refinement of magnesium by zirconium; variables included the amount of zirconium, the pouring temperature, and the settling time prior to casting. Optical microscopy was used to measure the grain size. TEM was used to identify particles that are likely nucleation sites. The TEM results show that a range of particle sizes are likely substrates and that particles which are likely nucleation sites are faceted. Sample dissolution followed by SEM was used to characterize particle size and morphology while an AccuSizer 770 was used to measure particle size distributions, both in the master alloy and grain refined samples. While less than 2% of the total particles serve as nucleation sites, a comparison of the grain density vs. faceted particle density shows close agreement, suggesting that only faceted particles are likely nucleation sites.

P. Saha, S. Viswanathan

Study on the Grain Refinement Behavior of Mg-Zr Master Alloy and Zr Containing Compounds in Mg-10Gd-3Y Magnesium Alloy

The effects of Mg-Zr master alloy and a potassium fluozirconate (K2ZrF6) salt mixture (KSM) on the grain refinement behavior of Mg-10Gd-3Y magnesium alloy were studied. The results show that the Mg-10Gd-3Y alloy is well refined by Mg-Zr or KSM. The characteristic micro structure feature of the alloy refined by Mg-Zr master alloy is the Zr-rich cores that exist in most grains, while the Zr-rich cores are not observed in the alloy refined by KSM. It is suggested that the grain refinement mechanisms of zirconium in the two cases are different: the Zr released from Mg-Zr master alloy works by adding heterogeneous nucleants, while the Zr produced from the in-situ reaction between Mg melt and K2ZrF6 works by restricting grain growth. Compared with the Mg-30.wt%Zr master alloy, the KSM refiner shows much longer fading time during melting.

Guohua Wu, Ming Sun, Jichun Dai, Wenjiang Ding

The Effect of Rare Earth Elements on the Texture and Formability of Shear Rolled Magnesium Sheet

The lower relative formability of magnesium alloy sheet can be a restrictive factor when designing light weight engineering structures. Standard symmetric rolling introduces a strong basal texture that decreases the formability; however, asymmetric rolling has been put forward as a possible route to produce sheet with weaker basal texture and greater ductility. It has also been shown in recent work that weaker textures can be produced through the addition of rare earth elements to magnesium alloys. Therefore, this study has been carried out to investigate the effect of rare earth additions on the texture changes during asymmetric rolling. Two alloys have been studied (AZ31B and ZEK100), in which a significant difference is the presence of rare earths in the ZEK100 but not in AZ31B. The differences in texture, microstructure and mechanical properties will be discussed.

D Randman, B Davis, M L Alderman, G Muralidharan, T R Muth, W H Peter, T R Watkins, O B Cavin

Improvement of Strength and Ductility of Mg-Zn-Ca-Mn Alloy by Equal Channel Angular Pressing

An ultrafine-grained (UFG) Mg-5.25 wt.% Zn-0.6 wt.% Ca-0.3 wt.% Mn alloy was produced by subjecting the as-extruded alloy to equal channel angular pressing (ECAP) for 4 passes at 250 and 300 °C, respectively. ECAP resulted in a remarkable grain refinement. After ECAP processing at 250°C, basal planes are oriented both parallel and inclined about 45° to the extrusion direction, while most the basal planes are oriented parallel to the extrusion direction after ECAP processing at 300 °C. Both yield strength and elongation were increased after ECAP processing. The yield strength was higher in the ECAPed alloy processed at 300 °C with larger grain size, indicating that the texture strengthening effect was dominant over the strengthening from grain refinement in the ECAPed alloy. The grain refinement may lead to dislocation slip on non-basal plane and grain boundary sliding, which improved the ductility of the ECAPed Mg-Zn-Ca-Mn alloy.

L. B. Tong, M. Y. Zheng, S. W. Xu, P. Song, K. Wu, S. Kamado

Deformation Behavior of Friction Stir Processed Magnesium Alloys

The present study explores the feasibility of using friction stir processing to produce high-performance Mg alloy sheet. Deformation behavior of friction stir processed Mg alloys is addressed. Analyses of grain size and crystallographic texture are made to interpret the characteristics of strength and ductility of friction stir processed Mg. It is found that friction stir processing causes variation of texture orientation in the processed sheet. The non-uniform texture distribution leads to significant in-plane anisotropy in ductility as well as localized deformation behavior of the processed sheet. Furthermore, the inhomogeneity of high-intensity texture would not be eliminated by hot compression performed along the normal of the processed sheet.

Q. Yang, S. Mironov, Y. S. Sato, K. Okamoto

Effect of Heat Index on Microstructure and Mechanical Behavior of Friction Stir Processed AZ31

Friction stir processing modifies the micro structure and properties of metals through intense plastic deformation. The frictional heat input affects the microstructure evolution and resulting mechanical properties. 2 mm thick commercial AZ31B-H24 Mg alloy was friction stir processed under various process parameter combinations to investigate the effect of heat index on micro structure and properties. Recrystallized grain structure in the nugget region was observed for all processing conditions with decrease in hardness. Results indicate a reduced tensile yield strength and ultimate tensile strength compared to the as-received material in H-temper, but with an improved hardening capacity. The strain hardening behavior of friction stir processed material is discussed.

Wei Yuan, Rajiv S. Mishra

Strengthening Mg-Al-Zn Alloy by Repetitive Oblique Shear Strain

Grain refinement is one of the possible ways to enhance the strength of magnesium without losing the ductility and/or toughness. In this study, severe plastic working by caliber rolling has been demonstrated to refine the grain structure of a commercial AZ31 Mg-Al-Zn alloy at a commercial processing speed. As a result, ultra-fine-grain structure with sub-grains in a sub-micro-meter scale was obtained. A simultaneous operation of oblique shear strain weakened the basal texture compared to that of the initial as-extruded alloy, and resulted in tensile ductility comparable to that of the commercially extruded alloy, and showed a higher asymmetry ratio of yield stress in compression/tension than that of the as-extruded alloy.

Toshiji Mukai, Hidetoshi Somekawa, Alok Singh, Tadanobu Inoue

High-Temperature Alloys; High-Strength Alloys; Precipitation

Frontmatter

Creep and elemental partitioning behavior of Mg-Al-Ca-Sn alloys with the addition of Sr

The partitioning of elements during solidification can strongly affect precipitation and solute strengthening during creep, especially in alloys where creep is controlled by viscous glide of dislocations. Elemental partitioning during solidification and its influence on creep behavior has been examined for Mg-6.5Al-2.25Ca-0.8Sn with and without 0.25wt% Sr additions. The alloy containing Sr experienced increased partitioning of Al and Ca to the α-Mg phase. However, the creep behavior in compression at 110 MPa and 180°C was not significantly different from that of the alloy without Sr. These observations are discussed in terms of current models for solid solution and precipitation strengthening. In addition, it was determined that the elemental partitioning profiles of permanent mold cast specimens were representative of the grain interiors of die-cast specimens. The partitioning profiles may be less representative for interdendritic regions of the micro structure, however.

Jessica R. TerBush, Olivia H. Chen, J. Wayne Jones, Tresa M. Pollock

Effect of Mn Addition on Creep Property in Mg-2Al-2Ca Systems

Planar Al2Ca phase forms on the basal plane in the as-cast AX22 and AXM220 alloys. In the AXM220 alloy, Mn is detected in the Al2Ca phase. The number density of the Al2Ca phase does not alter, irrespective of the creep deformation and Mn addition. Fine and planar precipitates appear during the creep deformation. The number density increases by the addition of Mn. The size of the precipitate is reduced by the Mn addition. The Mn addition can improve the creep property.

T. Homma, S. Nakawaki, K. Oh-ishi, K. Hono, S. Kamado

The Effect of Precipitate State on the Creep Performance of Mg-Sn Alloys

The Mg-Sn system has recently received attention as a potential basis for the development of creep resistant alloys. This is an age hardenable system with the potential to form ~10 vol. % of Mg2Sn. The Mg2Sn precipitate has a high melting temperature (~770 °C) and alloys based on this system might be thought to show some promise for use in applications requiring elevated temperature creep resistance [1]. The age hardening response of the binary alloy is only modest, despite the large volume fraction of precipitates that may be formed [2]. The reason is that the precipitates form with a relatively coarse distribution, in laths parallel to the basal planes of the magnesium matrix. This configuration is relatively inefficient at impeding dislocation motion [3].

Mark Gibson, Xi-Ya Fang, Colleen Bettles, Christopher Hutchinson

Microstructure and Mechanical Properties of Mg-Zn-Y-M (M: Mixed Re) Alloys with LPSO Phase

Mg96Zn2Y1.9M0.1 (M=Monazite base mixed Rare Earth (RE) (Ce52.4La26.0Nd21.6) in at. %) alloys were prepared by high-frequency induction melting in an Ar atmosphere. The micro structure and mechanical properties of the extruded alloys were investigated. The microstructure contained very small sized RE intermetallic compound particles within the α-Mg matrix and between the LPSO intergranular phase in the Mg96Zn2Y1.9M0.1 alloys. The presence of the RE compound in the Mg96Zn2Y1.9M0.1 alloy was responsible for its improved tensile and creep properties over those of the Mg96Zn2Y2 alloy. Excellent tensile yield strength was obtained in the extruded Mg96Zn2Y1.9M0.1 alloys, with a yield strength of 379 MPa at room temperature and 312 MPa at 523K, respectively. Considerable improvement was observed in the creep behavior of the Mg96Zn2Y1.9M0.1 alloys at 473K. Extended creep life and reduced minimum creep rate were also observed.

Jonghyun Kim, Yoshihito Kawamura

Application of Neutron Diffraction in Characterization of Texture Evolution during High-Temperature Creep in Magnesium Alloys

A good combination of room-temperature and elevated temperature strength and ductility, good salt-spray corrosion resistance and excellent diecastability are frequently among the main characteristics considered when developing a new magnesium alloy. Unfortunately, much less effort has been expended developing wrought-stock alloys for high temperature applications. Extrudability and high temperature performance of wrought material becomes an important factor in an effort to develop new wrought alloys and processing technologies. This paper shows some results obtained from creep testing and studies of in-creep texture evolution, for several wrought magnesium alloys developed for use in elevated-temperature applications.

D. Sediako, S. Shook, S. Vogel, A. Sediako

Improved Processing of Mg-Zn-Y Alloys Containing Quasicrystal Phase for Isotropic High Strength and Ductility

The stable quasicrystal phase in Mg-Zn-Y alloys has been proved to be beneficial for strength and ductility and has also been shown to impart high fracture toughness. However, the strength of these alloys has been limited to 300MPa with an average grain size of about 1 µm. We show here a simple procedure in which a Mg93Zn6Y alloy was chilled cast and then extruded. Yield strengths of up to 400 MPa in tension and compression, accompanied by ductility of ~14% were obtained with grain of size of about 1 µm. Compression to tension yield anisotropy ratios were in the narrow range of 0.95 to 1.03. These alloys also showed ageing response with two peaks. The effect of precipitation ageing on the mechanical properties has been studied.

Alok Singh, Y. Osawa, H. Somekawa, T. Mukai

Precipitation hardenable Mg-Ca-Al alloys

The age-hardening responses and the corresponding microstructures of Mg-0.5Ca-xAl (x = 0, 0.1, 0.3, 0.5, 1 wt. %) alloys were investigated by hardness tests and transmission electron microscopy. For the optimum Al addition of 0.3 wt. % an enhanced age-hardening response with the highest peak hardness of HV=72 was achieved. TEM analyses confirmed that the improvement in the peak hardness is associated with the dense precipitation of ordered monolayer G.P. zones. Whereas, lower content of Al resulted in the formation of G.P. zones and Mg2Ca and the excess addition of Al causes the formation of the G.P. zones and the grain boundary Al2Ca phase.

J. Jayaraj, C. L. Mendis, T. Ohkubo, K. Oh-ishi, K. Hono

Microstructure, Phase Evolution and Precipitation Strengthening of Mg-3.1Nd-0.45Zr-0.25Zn Alloy

The microstructure of the Mg-3.1Nd-0.45Zr-0.25Zn (wt.%) alloy has been investigated after solution treatment at 540°C for 24hr, followed by isothermal aging at 175°C up to 32 days. Various electron microscopy techniques, like EDX mapping and TEM with SAED, have been used to characterize the phase composition and orientation relationships between different phases. After solution treatment, the BCT (Mg1-xZnx)12Nd phase present in the as-cast alloy dissolved, and small tetragonal Zn2Zr3 rod-like particles precipitated in the oc-Mg grain interiors. Zn2Zr3 particles are elongated along [001] direction, have an orientation relationship with the Mg matrix [−2110](0001)Mg||[001](110)Zn2Zr3 and appear to be stable in the Mg matrix. Precipitation during isothermal aging involves the formation of metastable phases β″(Mg3Nd)HCP (DO19 structure) and β′(Mg3Nd)FCC (DO3 structure). The β″ precipitates formed during the first 8 days of aging have a plate shape and are fully coherent with the Mg matrix, with the orientation relationship [−2110](0001)Mg || [−2110](0001)β″ and [−1100]Mg|| [−1100]β″. The Zn2Zr3 rods serve as additional nucleation sites for precipitation during aging. The heterogeneous nucleation occurs in two ways: precipitates nucleate on the basal planes and on the side planes of the Zn2Zr3 rods. After 8 days of aging, these precipitates were identified as β′. During the 16÷32 days of aging, β” precipitates in the grain interior transform into β′ precipitates with an FCC structure. The β′ precipitates are semi-coherent ith the Mg matrix and have the following orientation relationship: [0001](2-1-10)Mg || [101](11–1)β, and [−1100]Mg||[−112]β′. In the late stage of aging, the β′ precipitates transform into a stable incoherent β (Mg,Zn)12Nd phase. The growth, coarsening and phase transformations were followed by microhardness tests.

G. Atiya, M. Bamberger, A. Katsman

Precipitation Process in Mg-Nd-Zn-Zr-Gd/Y Alloy

Transmission electron microscopy (TEM) and atom probe tomography (APT) were employed to investigate the solute clusters and precipitates formed in different Mg-Nd-Zn-Zr-Gd/Y alloys aged at 200 °C up to 100 h. TEM characterizations confirmed the precipitation in these alloys involved the formation of precipitates such as β″, β′, β1 and β. Most precipitates habited on (0110)α-Mg and a few thin plate (of 1–2 atomic layers in thickness) lying on (0001)α-Mg. APT analyses revealed that the precipitates were enriched with Nd, Zn and Gd. Moreover, Nd partitioned more strongly into the precipitates than Gd and Zn. In contrast, Y was less prone to partition into precipitates than other alloying elements in these alloys.

J. H. Li, G. Sha, P. Schumacher, S. P. Ringer

Mechanical Properties and Microstructures of Twin Roll Cast Mg-2.4Zn-0.1Ag-0.1Ca-0.16Zr Alloy

In our previous study, we reported that the additions of 0.1 at.% Ag and 0.1 at.% Ca to Mg-2.4Zn-0.16Zr (at.%) alloy enhanced the age hardening response, and extruded alloy showed tensile yield strength of 325 MPa with the T6 heat treatment. Considering its excellent age hardenability, we attempted to develop high strength sheets from the alloy by twin-roll casting (TRC). TRC sheet of 2 mm in thickness were hot rolled to −1.2 mm. The TRC Mg-2.4Zn-0.1Ag-0.1Ca-0.16Zr alloy sheet showed tensile yield strength of ~ 320MPa and an elongation to failure of 17% after T6 heat treatment. EBSD study indicated the average grain size is ~ 18±2.5μm and the grains have a weak basal texture. TEM, showed a uniform distribution of ~5 nm diameter MgZn2 phase. The high yield strength was attributed to the dispersion of rod-like precipitates.

C. L. Mendis, J. H. Bae, N. J. Kim, K. Hono

The Solidification Microstructure and Precipitation Investigation of Magnesium-Rich Alloys Containing Zn and Ce

Mg-Zn-Ce system has been identified as the alloy system for high-ductility wrought magnesium alloy development for automotive applications. The solidification micro structure and precipitation of Mg-Zn-Ce alloys were investigated to understand the phase equilibria and strengthening phases in this alloy system. The characterized microstructures of four directionally solidified Mg-Zn-Ce alloys agree well with the calculated solidification paths using computational thermodynamics coupled with the Scheil model. The precipitation of Mg7Zn3 intermetallic phase upon heat treatment was characterized using high-resolution transmission electron microcopy (HRTEM), a potential strengthening mechanism which will be explored in future research.

Chuan Zhang, Alan A. Luo, Y. Austin Chang

Deformation Mechanisms I

Frontmatter

Crystal Plasticity Analysis on Compressive Loading of Magnesium with Suppression of Twinning

The compressive loading behavior of single crystals and bicrystals of magnesium without consideration of deformation twinning has been investigated by crystal plasticity finite element analysis with the aim of fundamental understanding of kink band formation in magnesium alloys with long period stacking ordered structure (LPSO) phase. The basal plane of the single crystal model is set to be parallel to the compressive direction. The result of the compressive loading analysis of single crystals indicates the significant influence of suppression of twinning on the activation of nonbasal slip systems and stress-strain behavior. The compressive analysis of symmetric bicrystal is also performed to clarify the influence of the angle between basal plane and the loading axis. The influence of the introduction of grain boundary and the slight change of crystal orientation is discussed in terms of activated deformation modes.

Tsuyoshi Mayama, Tetsuya Ohashi, Kenji Higashida, Yoshihito Kawamura

Crystal Plasticity Modeling of Pure Magnesium Considering Volume Fraction of Deformation Twinning

In this study, a novel crystal plasticity model for pure magnesium involving the deformation twinning is presented. The deformation twinning is an important deformation mechanism of magnesium and other HCP metals. The deformation twinning has two important issues: first, the large rotation of crystal lattice caused by twinning occurs. Second, in the crystalline scale, the twinned and untwinned regions may simultaneously exist in a grain. Therefore, a crystal plasticity analysis of magnesium should introduce both of them, and the present framework takes these two key features into account. To represent the second issue, the volume fraction of deformation twinning is considered. This paper provides a framework of crystal plasticity model involving the effect of tensile twinning, and a numerical example is conducted to evaluate the evolution of volume fraction of twinned region. It is shown that the present scheme can describe the mixed state of twinned and untwinned regions. The obtained results suggest that the twinned and untwinned regions simultaneously exist even under the large deformation and the volume fraction of twinned region should be considered.

Yuichi Tadano

Nucleation Mechanism for Shuffling Dominated Twinning in Magnesium

We observed nucleation of {10–12} twinning under tensile loading in magnesium rectangular rod system using atomistic molecular dynamic simulation. The rod axis is normal to basal plane of Mg crystal. The tensile deformation in c-axis nucleates {10–12} twinning starting at the corner of square of cross section of the rod. The twin boundary is spherical at the beginning and become a linear boundary in {10–12} planes as time goes by. The twinning and shuffling processes are described. The nucleation mechanism of the shuffling dominated twinning is explained.

Sungho Kim, H. El Kadiri, M. F. Horstemeyer

On the Impact of Second Phase Particles on Twinning in Magnesium Alloys

Deformation twinning is an important deformation mode in magnesium alloys. Despite this, little is known on the extent to which the stress for twinning can be altered by a dispersion of second phase particles. The current paper presents a series of findings on the role of differently shaped particles on the characteristics of the twins that form. It is shown that coherent rod shaped particles in Mg-Zn alloys have little obvious effect locally on the twin boundaries but that the twin number density is increased by their presence. Plate particles in a Mg-Al-Zn alloy cause obvious perturbations to the twin interface. Loops of twinning dislocations left around the particles eventually collapse into the particle interface, a phenomenon that is evidently facilitated by stress concentration on leading twin dislocation and stress relaxation in the adjacent material.

M. R. Barnett, N. Stanford, J. Geng, J. Robson

Influence of Crystallographic Orientation on Twin Nucleation in Single Crystal Magnesium

Experimental plasticity on single crystals has found substantial non-Schmid effects in both twinning and non-basal slip in pure magnesium. The deviation from Schmid’s law has been attributed to the strong sensitivity of both twinning and slip to small lattice heterogeneities [1] and the effect of pre-slip and non-planar dislocation dissociation [2]. However, most molecular dynamics simulations use heterogeneities so the effect of slip on twin nucleation and vice-versa has been shrouded. This has motivated us to investigate the influence of crystal loading orientation on homogeneous slip and twin nucleation using molecular dynamics. These simulations allowed us to appreciate the propensity and nature of twin nucleation when pre-existing defects are absent. Analyses of deformation mechanisms and stress-strain responses shows that homogeneous dislocation nucleation on the basal slip system is correlated with the highest Schmid resolved shear stress, while homogeneous nucleation of tensile twins did not always correlate with the highest Schmid resolved shear stress.

C. D. Barrett, M. A. Tschopp, H. El Kadiri, B. Li

Twinning Multiplicity in an AM30 Magnesium Alloy under Uniaxial Compression

Twinning under compression along two perpendicular directions of an AM30 alloy with a {101̄0} fiber texture was investigated. The primary extension {10 1̄ 2} twinning occurred for both compression normal to the fiber and compression parallel to the fiber. These primary extension twins took forms of fully residual twins parallel to the fiber and the “stopped elastic” twins normal to the fiber. Both the {101̄1}-{101̄2} and {101̄3}-{101̄2} double twinning occurred in the matrix grains at the last stage of compression normal or parallel to the fiber, but as the “combined two shears” mode of the double twinning. Another time-sequence type of {101̄1}-{101̄2} double twin also activated early normal to the fiber. The primary extension twinning and contraction twinning seem to obey the Schmid law according to the texture evolution.

Q. Ma, H. El Kadiri, A. L. Oppedal, J. C. Baird, M. F. Horstemeyer

Inhomogeneous Deformation of AZ31 Magnesium Sheet in Uniaxial Tension

Inhomogeneous plastic deformation during uniaxial tensile test of AZ31 magnesium sheet has been studied using digital image correlation and electron backscatter diffraction techniques. It is shown that large strain gradients exist on the sheet surface parallel and perpendicular to the loading direction and very little deformation occurs in the thickness direction. The lack of thinning leads to abrupt fracture right after the formation of a premature but profound diffuse neck without transitioning to any localized neck. Such inhomogeneous deformation arises from the strong basal texture of the starting sheet and the resultant need for contraction and double twinning to accommodate strain. The strain distribution on the sheet surface evolves nonlinearly with strain, impacting the measured r-value.

Jidong Kang, David S. Wilkinson, Raja K. Mishra

Limitation of current hardening models in predicting anisotropy by twinning in hcp metals: Application to a rod-textured AM30 magnesium alloy

When a strongly textured hexagonal close packed (HCP) metal is loaded under an orientation causing profuse twinning or detwinning, the stress-strain curve is sigmoidal in shape and inflects at some threshold. Authors have largely attributed the dramatic stress increase in the lower-bound vicinity of the inflection point to a combined effect of a Hall-Petch mechanism correlated to grain refinement by twinning, and twinning-induced reorientation requiring activation of hard slip modes. We experimentally and numerically demonstrate that these two mechanisms alone are unable to reproduce the stress-strain behaviors obtained under intermediate loading orientations correlated to in-between profuse twinning and nominal twinning. We argue based on adopting various mechanistic approaches in hardening model correlations from the literature. We used both a physics dislocation based model and a phenomenological Voce hardening model. The HCP material is exemplified by an extruded AM30 magnesium alloy with a <math display='block'> <mrow> <mrow><mo>&#x2329;</mo> <mrow> <mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>0</mn> </mrow> <mo>&#x0232A;</mo></mrow> </mrow> </math>$$\left\langle {10\bar 10} \right\rangle$$-fiber parallel to the extrusion direction.

A. L. Oppedal, H. El Kadiri, C. N. Tomé, J. C. Baird, S. C. Vogel, M. F. Horstemeyer

Deformation Behavior of Mg from Micromechanics to Engineering Applications

We have investigated the influence of the underlying microstucture of Mg on its macroscopic deformation behavior. Using microcompression experiments on Mg single crystals, we have identified the orientation dependent deformation slip and twinning systems. These experiments have aided the development of an energy based crystal plasticity model for the twinning in polycrystals. This model has been applied to representative volume elements to identify the flow surface for a macroscopic model, which is used to predict the forming limit diagram. Validation of the results has been realized through Nakazima tests. Additionally an outlook is given on the prediction of the forming behavior of laser beam welded Mg sheets and its dependence on welding direction.

E. Lilleodden, J. Mosler, M. Homayonifar, M. Nebebe, G. Kim, N. Huber

Effect of Substituted Aluminum in Magnesium Tension Twin

Atomistic simulations are performed in order to study the Aluminum substitution effect on Magnesium twinning mechanism. Multiple twin boundaries are found in pure Mg single crystal under tensile loading condition along <math display='block'> <mrow> <mo stretchy='false'>(</mo><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>012</mn><mo stretchy='false'>)</mo> </mrow> </math>$$(\bar 1012)$$ crystallographic direction. However, no twinning has occurred under compression loading. Al substitution has been done for 2, 5, 7, and 10% doping. For 2 and 5% Al substitution, number of twins increase when the system is monitored under tensile loading. On the other hand, for 7 and 10% Al doping under tensile loading, no twin has been found. We found that dislocation-twin and dislocation-dislocation interaction are majorly responsible for this behavior and it is important that which one is prevalent.

K. N. Solanki, A. Moitra, M. Bhatia

Deformation Mechanisms II: Formability and Forming

Frontmatter

Influence of Solute Cerium on the Deformation Behavior of a Mg-0.5 wt.% Ce Alloy

The effect of solute Ce was investigated on the deformation behavior of a Mg-Ce binary alloy at elevated temperature. Compression and tension tests were performed on samples taken from extruded bars of Mg-0.5 wt.% Ce. Dynamic strain aging (DSA) was observed to occur during both tension and compression testing. Under the latter conditions, the effect of DSA on increasing the flow stress was greater than that of extension twinning. The occurrence of DSA also led to a decrease in the ductility. After heat treatment, the detrimental effect of the DSA taking place during compression was reduced significantly to an extent that depended on the cooling rate employed. However, these heat treatments did not lead to appreciable improvements in the tensile ductility.

L. Jiang, J. J. Jonas, R. Mishra

Texture Weakening Effect of Y in Mg-Zn-Y System

The CALPHAD (Calculation of Phase Diagram) method was successfully used in this study to select the alloys from Mg-Zn-Y system, aimed at determining the mechanism(s) of texture weakening in Y-containing Mg alloys: PSN (particle-stimulated nucleation of recrystallization) and/or solute effects. The selected alloys are Mg-6Zn-1.2Y, Mg-5Zn-2Y, Mg-2.9Y and Mg-2.9Zn (in wt%). After heat treatment, the ternary alloys contain (nearly) the same amount of ternary intermetallics in equilibrium with &#x03B1;-Mg at 350 °C, and the microstructure of the binary alloys is composed of &#x03B1;-Mg solid solution at 350 °C containing the same solute amount as that in the ternary alloys. The hot deformation and post-deformation annealing of these alloys at a constant temperature (i.e., 350 °C) showed that the texture weakening happens during growth of recrystallized grains in deformed and annealed samples where Y element is in &#x03B1;-Mg solid solution.

S. A. Farzadfar, M. Sanjari, I.-H. Jung, E. Essadiqi, S. Yue

In-Situ Scanning Electron Microscopy Comparison of Microstructure and Deformation Between WE43-F and WE43-T5 Magnesium Alloys

In-situ tensile testing in the scanning electron microscope was used to investigate the quasi-static deformation behavior and fracture mechanism of WE43 magnesium alloys. The in-situ tensile experiments were conducted at room temperature at a constant crosshead speed of 0.5 mm / min. One set of samples was a rolled and quenched F temper alloy and the other set was an artificially aged T5 temper alloy. The objective of this research was to determine the effect of tempering on precipitates chemistries, microstructure, and mechanical properties. The sample orientation is known to affect the tensile properties. Hence tensile specimens with different sample orientation were tested. The crystallographic orientations were characterized by electron backscattered diffraction. Strong textures were observed with rolling plane crystals indicating a basal plane orientation.

Tomoko Sano, Jian Yu, Bruce Davis, Richard DeLorme, Kyu Cho

A molecular dynamics study of fracture behavior in magnesium single crystal

The analysis of crack growth in magnesium crystals was performed using molecular dynamics simulation with Embedded Atom Method (EAM) potentials. Four specimens with increasing sizes were used to investigate the influences of material length scale on crack growth of magnesium single crystals. Furthermore, the effects of temperature, loading strain rate, and the size of the initial crack were also verified. The specimens were subjected to uniaxial tension strain up to the total strain level of 0.2 with a constant strain rate of 109s&#x2212;1 except in the studies of strain rate effects and the uniaxial stress strain curve was monitored. The simulation results show that the specimen size, loading strain rate, temperature, and the size of initial crack strongly influence the yield strength at which the twin nucleated and subsequently the crack grew. The initial slope of the uniaxial stress strain curve is independent of the loading strain rate and temperature. Moreover, high temperatures induce increased atomic mobility, and thereby atom reorganization, which, in turn, releases the stress at the crack tip

Tian Tang, Sungho Kim, Mark F Horstemeyer, Paul Wang

Microstructural Relationship in the Damage Evolution Process of an AZ61 Magnesium Alloy

The damage evolution process of magnesium AZ61 alloy under monotonic tensile loading conditions is investigated. Specimens that have been subjected to interrupted tensile loading were examined under optical microscopy to quantify the number density of cracked intermetallic particles as a function of applied strain. Digital image analysis of the optical images was employed to automatically quantify damage by separating cracked from non-cracked particles. Lastly, an internal state variable damage model was shown to adequately capture the experimentally-observed damage of intermetallic particles in the magnesium AZ61 alloy.

M. Lugo, J. B. Jordon, M. F. Horstemeyer, M. A. Tschopp

Formability Enhancement in Hot Extruded Magnesium Alloys

The effects of cerium (Ce), aluminum (Al) and manganese (Mn) additions on the microstructure and mechanical properties of hot extruded magnesium alloys have been investigated. Seven different compositions of Mg alloys — Pure Mg, Mg-0.2Ce, Mg-0.5Ce, AM30, AM50, Mg-3Al-0.2Ce and Mg-5Al-0.2Ce were hot extruded under optimized process conditions. Minor addition of Ce to Mg was found to enhance its ductility from <10% to >30% and 3 – 5% Al addition resulted in ~40% and 50% increase in strength respectively, compared to pure Mg. A combination of 5% Al and 0.2% Ce addition resulted in concurrent improvement in strength and ductility as a result of concurrent grain size refinement, texture randomization and solute strengthening.

Raja K. Mishra, Anil K Gupta, Rajiv Sikand, Anil K. Sachdev, Li Jin

Deformation and Evolution of Microstructure and Texture during High Speed Heavy Rolling of AZ31 Magnesium Alloy Sheet

An AZ31 magnesium alloy sheet was rolled to 71% by one pass operation at 473K at a rolling speed of 500m/min. During rolling, the mill was suddenly stopped and the sheet was withdrawn from the gap of work rolls. The evolution of micro structure and texture of the AZ31 magnesium alloy sheet during rolling deformation was revealed by observing micro structure and texture at the plane perpendicular to the transverse direction from the entry to the exit of the zone of deformation of the withdrawn sheet. Grains with their orientation other than basal texture preferentially deform at the initial stage of rolling deformation. Dynamically recrystallized grains are observed in the deformation zone. The double peak texture developed during recrystallization.

Tetsuo Sakai, Akinori Hashimoto, Go Hamada, Hiroshi Utsunomiya

Formability of Magnesium Sheet ZE10 and AZ31 with Respect to Initial Texture

The commercial application of magnesium alloy sheets is hindered by their low formability and therefore technological and economic constraints. Tailoring the texture has been identified as playing a major role in enhancing the formability of magnesium sheets. In this study, the formability of magnesium sheet ZE10 and AZ31 was investigated. While the texture of AZ31 is of unfavourable basal type, ZE10 shows a significantly different texture with the basal planes being randomly distributed. More basal planes are oriented favourably for basal slip, promising higher formability and thus, lower process temperature. Formability is assessed by means of forming limit diagrams as a representation of material response to various strain paths. Nakajima tests were carried out from room temperature to 250°C. Local strain data is correlated with the microstructural evolution. This study reveals a significant influence of texture on formability with ZE10 sheet showing superior formability compared to AZ31.

Lennart Stutz, Jan Bohlen, Dietmar Letzig, Karl Ulrich Kainer

Hot Workability of Alloy WE43 Examined Using Hot Torsion Testing

While rare earth additions can impart a variety of property improvements in magnesium alloys, they can also limit the processing parameter window inside which the alloys may be successfully wrought in commercial production routes such as extrusion and rolling. In the present work, hot torsion testing is used to explore the temperature and rate sensitivity of the flow stress of the alloy WE43 in order to establish the boundaries of this processing window. Two mechanisms appear to be important from a fundamental perspective: first, dynamic recrystallization appears to be a prerequisite for significant plastic flow; second, serrated flow and negative strain rate sensitivity are observed at lower deformation temperatures (T ≈ 150–250°C). The Sellars-Tegart model and simple power law, both of which have been successfully applied to describe the temperature/strain-rate/flow stress relationship in AZ31 and many other Mg alloys, are explored in the context of WE43.

F. John Polesak, Bruce Davis, Rick DeLorme, Sean R. Agnew

Enhancement of Superplastic Forming Limit of Magnesium Sheets by Counter-Pressurizing

As often reported for various metallic materials, fine-grained wrought magnesium can exhibit extensive superplasticity at elevated temperature, which makes superplastic forming (SPF) of magnesium a promising process for manifacturing complex-shaped, lightweight thin-walled structural components. The superplastic tensile deformation of magnesium is commonly accompanied by substantial cavitation in its failure stage, which is also typical to quasi-single phase aluminum alloys.In this regard, a series of bulge test have been conducted with independent inflating/counter-pressure control. By evaluating the superplastic forming limit along Limit Dome Height (LDH), considerable improvement was reproduced by counter-pressurized conditions. Constitutive modeling and microstructural analysis imply that this is mainly achieved by the retardation of nucleation and growth of cavities under hydrostatic stress.

Wonkyu Bang, Hyun-Seok Lee, Hyung-Lae Kim, Young-Won Chang

Microstructure Evolution during Roller Hemming of AZ31B Magnesium Sheet

The evolution of microstructure and texture during multipass roller hemming (flanging, pre-hemming and flat hemming) of commercial grade AZ31B-O sheet has been studied using electron backscatter diffraction. The pre-hemming operations were performed with and without local heating using a laser source. It was observed that samples pre-hemmed at room temperature could not be flat hemmed even after applying heat; whereas flat hemming was possible in the sample pre-hemmed with laser heating. The major difference between these samples was the formation of contraction/double twins on the outer radii of the bend in the sample pre-hemmed at room temperature. It is believed that such twins contributed directly or indirectly to the fracture of this sample upon the third pass by leading to the formation of shear bands and/or by significantly hardening the material and not allowing for further deformation.

Amanda Levinson, Raja K Mishra, John Carsley, Roger D Doherty, Surya R Kalidindi

The Warm Forming Performance of Mg Sheet Materials

The warm forming performance of five different magnesium sheet materials was evaluated using a heated pan die. Forming maps were generated to determine the optimum temperature and die conditions for successful forming. All five materials exhibited excellent formability above 325°C, with a robust forming window. Below 300°C, significant differences in the materials were observed. Some materials could be formed into a pan at temperatures as low as 175°C while others could not be formed below 300°C. The differences in forming performance were investigated considering material properties, tribology, and micro structure. These trials included both continuously cast and direct chill cast materials, and demonstrated that the continuously cast materials can be successfully warm formed.

P. E. Krajewski, P. A. Friedman, J. Singh

New Applications (Biomedical and Other)

Frontmatter

Current Research Activities of Biomedical Magnesium Alloys in China

The potential biomedical application of magnesium alloys as bioabsorbable / biodegradable implants in the human body has been extensively studied worldwide, and becomes an emerging and promising application direction.The author served as the chairman in two recent conferences relating to biomedical magnesium alloys: (1) the 12th Annual Conference on Biomaterials in December 2009, organized by the Chinese Society of Biomedical Engineering, and (2), a symposium on Biodegradable Metallic Materials in May 2010 at Peking University. Based on the papers presented in these conferences (about 50 in each), the frontier research activities of biomedical magnesium alloys in China for orthopedic and cardiovascular implants will be systematically summarized and comprehensively reviewed in this paper [1]. The research highlights the alloying system design, novel structure, degradation rate control, and surface modification methods; results will be demonstrated via plenty of in vitro and in vivo study data.

Yufeng Zheng

Design Considerations for Developing Biodegradable Magnesium Implants

The integration of biodegradable and bioabsorbable magnesium implants into the human body is a complex undertaking that faces major challenges. The complexity arises from the fact that biomaterials must meet both engineering and physiological requirements to ensure the desired properties. Historically, efforts have been focused on the behavior of commercial magnesium alloys in biological environments and their resultant effect on cell-mediated processes. Developing causal relationships between alloy chemistry and micro structure, and its effect on cellular behavior can be a difficult and time intensive process. A systems design approach driven by thermodynamics has the power to provide significant contributions in developing the next generation of magnesium alloy implants with controlled degradability, biocompatibility, and optimized mechanical properties, at reduced time and cost. This approach couples experimental research with theory and mechanistic modeling for the accelerated development of materials. The aim of this article is to enumerate this strategy, design considerations and hurdles for developing new magnesium alloys for use as biodegradable implant materials [1].

Harpreet S. Brar, Benjamin G. Keselowsky, Malisa Sarntinoranont, Michele V. Manuel

Coating Systems for Magnesium-Based Biomaterials — State of the Art

Magnesium and its alloys have the potential to be used for biodegradable orthopedic implants. However, the corrosion rate in physiological conditions is too high for most applications. For this reason, surface modification to slow the corrosion rate is of great interest. Such modifications must remain biologically compatible as well as protective in corrosive environments. What follows is a brief review of recent research in inorganic coatings and surface modifications to create coatings for magnesium-based biomaterials.

J. Waterman, M. P. Staiger

Corrosion, Surface Modification, and Biocompatibility of Mg and Mg Alloys

This manuscript summarizes recent studies on the corrosion behavior of Mg and Mg alloys in simulated biological environments, as well as interactions between corroding Mg (alloy) surfaces and cells. The influence of different types of simulated body solutions on the corrosion behavior of Mg is discussed. The effects of different types of chemical surface treatments on cell adhesion and spreading is presented. Moreover, possible routes to further optimize the corrosion and the biological performance of Mg alloys by surface modification are discussed.

Sannakaisa Virtanen, Ben Fabry

Magnesium Alloys for Bioabsorbable Stents: A Feasibility Assessment

Today, stent designs consist of permanent metal alloy scaffolds which hold arteries open after percutaneous coronary intervention (PCI) to maintain arterial blood flow. Bioabsorbable stents are being investigated as an alternate for permanent stents, that disintegrate and dissolve in the body. In this article, we profile magnesium (Mg) alloy as a candidate for bioabsorbable stent material, and discuss aspects of its properties and challenges. Experimental data are generated in effort to draw correlations between in vivo vessel absorption and in vitro degradation, and to provide an overview of alloy mechanical properties, stent designs, and electrochemical behaviors. Preclinical porcine coronary model test results exhibit early on-set and rapid corrosion presenting a challenge to researchers to establish material design concepts that balance degradation time, duration for need of scaffolding, and healing.

Charles Z. Deng, Rajesh Radhakrishnan, Steve R. Larsen, Dennis A. Boismer, Jon S. Stinson, Adrienne K. Hotchkiss, Eric M. Petersen, Jan Weber, Torsten Scheuermann

Processing Aspects of Magnesium Alloy Stent Tube

Biomedical applications are an emerging field of interest for magnesium technology, envisioning biodegradable implants that resorb in the human body after having cured a particular medical condition (such as artery clogging or bone fractures). This challenges research in a sense that the materials to be used need to dissolve in vivo in a controlled fashion without leaving harmful remainders and while maintaining sufficient strength and other (mechanical) attributes as long as necessary.To comply to the requirements, magnesium alloys as well as their processing routes into implants need to be tailored. While new alloy compositions are receiving ample attention, the paper at hand addresses the processing issue. The application of choice is the (cardio)-vascular stent. Different steps in manufacturing magnesium AZ-alloy stent tube are considered, including equal channel angular pressing, extrusion and subsequent drawing operations. Results show that the processing route has an important influence on the micro structure of the finished stent tube and hence on its functional performance.

R. J. Werkhoven, W. H. Sillekens, J. B. J. M. van Lieshout

Ballistic Analysis of New Military Grade Magnesium Alloys for Armor Applications

Since 2006, the U.S. Army has been evaluating magnesium (Mg) alloys for ballistic structural applications. While Mg-alloys have been used in military structural applications since WWII, very little research has been done to improve its mediocre ballistic performance. The Army’s need for ultra-lightweight armor systems has led to research and development of high strength, high ductility Mg-alloys. The U.S. Army Research Laboratory contracted through International Technology Center-Pacific Contract Number FA-5209–09-P-0158 with the Joining and Welding Research Instituteof Osaka University to develop the next generation of high strength, high ductility Mg-alloys using a novel Spinning Water Atomization Process for rapid solidification. New alloys AMX602 and ZAXE1711 in extruded bar form were characterized for microstructure, mechanical, and ballistic response. Significant increases in ballistic performance were evident when compared to the baseline alloy AZ31B.

Tyrone L. Jones, Katsuyoshi Kondoh

Mg17AL12 Intermetallic Prepared by Bulk Mechanical Alloying

In a last decade, nano-crystallized or amorphous materials are widely investigated. Such materials provide other directions for solving several issues in the field of materials science. Ball milling processes are general tools for preparing the nano-crystallized or amorphous material. The samples, however, show the fine powder-form and the most of those are very sensitive against circumstance around. The bulk-form samples are desirable. The present work proposes the newly developed bulk mechanical alloying (BMA) technique as an alternative method for the ball milling. Successful solid-state reaction and the formation of nano-scale crystalline of Mg17Al17 phase will be demonstrated.

Kenji Sakuragi, Masashi Sato, Takamitsu Honjo, Toshiro Kuji

Corrosion Behaviour of Mg Alloys in Various Basic Media: Application of Waste Encapsulation of Fuel Decanning from UNGG Nuclear Reactor

The dismantling of UNGG nuclear reactor generates a large volume of fuel decanning. These materials are based on Mg-Zr alloy. The dismantling strategy could be to encapsulate these wastes into an ordinary Portland cement (OPC) or geopolymer (aluminosilicate material) in a form suitable for storage. Studies have been performed on Mg or Mg-Al alloy in basic media but no data are available on Mg-Zr behaviour. The influence of representative pore solution of both OPC and geopolymer with Mg-Zr alloy has been studied on corrosion behaviour. Electrochemical methods have been used to determine the corrosion densities at room temperature. Results show that the corrosion densities of Mg-Zr alloy in OPC solution is one order of magnitude more important than in a geopolymer solution environment and the effect of an inhibiting agent has been undertaken with Mg-Zr alloy. Evaluation of corrosion hydrogen production during the encapsulation of Mg-Zr alloy in both OPC and geopolymer has also been done.

David Lambertin, Fabien Frizon, Adrien Blachere, Florence Bart

Advanced Materials and Processing

Frontmatter

Characterization of Hot Extruded Mg/SiC Nanocomposites Fabricated by Casting

Mg-1%SiC nanocomposites were fabricated using an ultrasonic-cavitation based casting method, resulting in the dispersion of the reinforcing SiC nanoparticles to form Mg-metal matrix nanocomposite (Mg-MMNC) billets. The MMNC billets were then processed using hot extrusion at 350°C. Micrographic observations illustrate a significant grain size reduction and the presence of micro-bands that align the SiC nanoparticles parallel to the direction of extrusion for Mg-MMNCs. Observations from the cross-section at 90° of the extrusion direction show uniform nanoparticles dispersion contrasting previous observations. Results from the extruded Mg-MMNCs tensile testing at different temperatures (25°C, 125°C and 177°C) reveal an increase of the yield strength, ultimate tensile strength, and ductility values as compared to the un-reinforced and extruded Mg-alloy; such increase was also observed from the microhardness testing results where an increase from 19 to 34% was measured.

Sunya Nimityongskul, Noé Alba-Baena, Hongseok Choi, Milton Jones, Tom Wood, Mahi Sahoo, Roderic Lakes, Sindo Kou, Xiaochun Li

Effects of Silicon Carbide Nanoparticles on Mechanical Properties and Microstructure of As-Cast Mg-12wt.% Al-0.2wt.% Mn Nanocomposites

Microstructure and tensile properties of as-cast Mg-12Al-0.2Mn alloys with SiC nanoparticles were studied. SiC nanoparticles were dispersed into Mg-12Al-0.2Mn melts through an ultrasonic based nanoparticle-dispersion method. The content of SiC nanoparticles varied from 0 to 2 wt.%. The microstructural analysis with optical and scanning electron microscopy (SEM) showed that the massive brittle intermetallic phase (β-Mg17Al12) as well as α-Mg grain was significantly refined, enhancing both strengths and ductility of as-cast Mg-12Al-0.2Mn alloys. Transmission electron microscopy (TEM) showed that there were SiC nanoparticles in both a-Mg and β-Mg17Al12 phases of the Mg-12Al-0.2Mn nanocomposites. It was found that there was a partial reaction between Mg/Al and SiC nanoparticles, producing Mg2Si intermetallic phases. X-ray diffraction (XRD) analysis confirmed also that the content of Mg2Si phases increased with increasing SiC content, limiting a further ductility enhancement for Mg-12Al-0.2Mn-SiC nanocomposite.

Hongseok Choi, Hiromi Konishi, Xiaochun Li

Thermally-Stabilized Nanocrystalline Magnesium Alloys

Advanced nanocrystalline alloys have shown remarkable property improvements, particularly, order-of-magnitude strength increases, when compared to their coarse-grained counterparts. However, a major obstruction to the widespread application of such materials is the degradation of properties via rapid grain growth at even ambient temperatures. Conventional methods for circumvention of this problem at low temperatures have largely steered toward kinetically pinning the boundaries with disperoids, or through misorientation of grain boundaries, yet even these methods have limited utility at elevated temperatures needed for routine sintering and forming operations. In this work, we will present a synergistic approach to the development of thermally stable nanostructured Mg-alloys which incorporates elements of predictive modeling of suitable alloy systems, fabrication of nanostructured alloy powders by high energy ball milling and consolidation of the powders at elevated temperatures.

Suveen Mathaudhu, Laszlo Kecskes, Kristopher Darling

TiNi Reinforced Magnesium Composites by Powder Metallurgy

Rod shaped Mg-TiNi composite samples were manufactured by powder metallurgical route in which the samples were heated and deformed simultaneously using rotary hot swaging technique. Firstly, encapsulated argon filled copper tubes which contained compacts of pure magnesium and pre-alloyed TiNi alloy powder mixtures were deformed about 45% in two steps at 450°C. Pre/post annealing heat treatments were applied at 450°C for 20 mins between the stages of coaxial deformation to enhance the sintering degree and to homogenize the heavily deformed composite structures. Next, copper peeled and machined samples were compression tested under quasi-static conditions to investigate the mechanical properties, i.e. yield and peak strength, and ductility. Transmission and Scanning Electron Microscopy studies were carried out to examine the Mg-TiNi interface and fracture surfaces of the compression tested composites, respectively.

Ziya Esen

Nanocrystalline Mg-Matrix Composites with Ultrahigh Damping Properties

Recently, we reported on the processing of 50 vol.% Ti2AlC-nanocrystalline magnesium, nc-Mg, matrix composites using a pressureless melt infiltration method. Herein we report on composites with up to 80 vol.% Mg. These composites are readily machinable, relatively stiff, strong and light, and exhibit ultrahigh damping. Increasing the nc-Mg volume fraction leads to lighter composites with higher damping characteristics at lower stresses (~30% of the mechanical energy is dissipated at 250 MPa). In some cases the Mg nanograms are also extraordinarily thermally stable which renders these composites good candidates for applications at temperatures higher than ambient. Due to the simple inexpensive melt infiltration technique used to fabricate these novel nanocomposites, it is possible to produce samples as large as ones made via normal powder metallurgy methods.

Babak Anasori, Shahram Amini, Volker Presser, Michel W. Barsoum

Effect of Fiber Reinforcement on Corrosion Resistance of Mg AM60 Alloy-based Composites in NaCl Solutions

There is great interest in developing low-cost, magnesium-based MMCs because of their high stiffness-to-weight ratio for aerospace and automotive applications. However, corrosion resistance of metal-matrix composites is often a concern for components to be used in harsh environment. In this study, the corrosion behavior of Al2O3 fibres reinforced magnesium AM60 composite, in aqueous solutions containing various concentrations of NaCl, was studied in comparison to that of matrix AM60 alloy by potentiodynamic polarization measurements. The micro structure of the composite and matrix alloy AM60 before and after corrosion testing was analyzed by optical microscopy, and scanning electron microscopy (SEM). The results show that the presence of Al2O3 fiber deteriorates the corrosion resistance of the matrix magnesium alloy AM60. The effect of Al2O3 fiber reinforcement and NaCl concentrations on the corrosion behavior of the composites are discussed. The corrosion mechanisms of the composite are proposed in light of metallographic observation on the formation of corrosion products.

Qiang Zhang, Henry Hu

The Production of Powder Metallurgy Hot Extruded Mg-Al-Mn-Ca Alloy with High Strength and Limited Anisotropy

Rapidly solidified Mg-Al-Mn-Ca alloy produced by Spinning Water Atomization Process (SWAP) was hot extruded into rectangular bars, from which tensile and compression samples have been cut at 0°, 45° and 90° from the extrusion direction to study their anisotropy. Electron Back Scattered Diffraction (EBSD) has been used to investigate the texture evolution during the hot extrusion process. Both the Schmid factor and the intensity of the basal plane in the pole figure have been evaluated and correlated to the mechanical properties. Results have shown that the extruded rods exhibit high strength and limited anisotropy compared to many previously reported values for magnesium alloys. The reasons for that limited anisotropy were both the fine grained micro structure of the extruded material and the transverse component of the texture evolution.

Ayman Elsayed, Junko Umeda, Katsuyoshi Kondoh

Thermal Effects of Calcium and Yttrium Additions on the Sintering of Magnesium Powder

The low density and good mechanical properties make magnesium and its alloys attractive materials for use in automotive and aerospace applications. Powder metallurgy P/M can be used to alleviate the formability problem through near-net-shape processing, and also allows unique chemical compositions that can lead to new alloys with novel properties. However, the surface layer formed on the Mg powders during processing acts as a barrier to diffusion and sintering is problematic. The layer, characterized using focused ion beam milling and transmission electron microscopy (FIB-TMS), as well as x-ray photoelectron spectroscopy (XPS), contains oxides, hydroxides and carbonates of magnesium, formed by reactions with the atmosphere. To overcome this barrier, small additions were made of calcium and yttrium the oxides of which are thermodynamically more stable than magnesium oxide. The present work reports on the thermal effect of Ca and Y additions to magnesium powder during sintering, utilizing differential scanning calorimetry (DSC).

Paul Burke, Chloe Petit, Sonia Yakoubi, Georges J. Kipouros

Microstructure and Mechanical Properties of Solid State Recycled Mg Alloy Chips

Recycling of Mg alloy chips generated in machining processes such as turning and sawing through a melting process is difficult because the chips are very fine and can burn easily during heating. In this study, two machined Mg alloy chips were solid-state-recycled into a bar by hot pressing and hot extrusion, and the mechanical properties of the recycled chips were examined. The recycled AZ91 and AZX911 alloys showed a fine microstructure with a grain size of less than 10 μm. The compressed yield stresses at room temperature were 208 and 210 MPa for the recycled AZ91 and AZX911, respectively, which are higher than those for non-recycled samples. A backward extrusion test revealed that the recycled AZ91 and AZX911 alloys have good forgeability at temperatures above 573 K and slightly higher hardness than non-recycled samples. Therefore, solid-state-recycled Mg alloys have good formability for forging at elevated temperatures with good mechanical properties and have potential for use as forging material

Kunio Matsuzaki, Youichi Murakoshi, Toru Shimizu

Corrosion and Coatings

Frontmatter

Salt Spray Corrosion of Mechanical Junctions of Magnesium Castings

The corrosion of cast, 3 mm thick, AE44 magnesium-alloy plates fastened to aluminum-alloy threaded counterparts, either constituting the screw or the nut, were tested in neutral salt spray for 48 hours, with or without interposed AA5051 spacers (washers). Steel nuts or screws were used, always insulating from corrosion the steel sides. Couplings between magnesium alloy plates and coated steel counterparts (screw heads) with interposed AA5051 washers were also tested, while insulating the nut side. Every 4 or 8 hours the test was halted and the samples were rinsed and photographed for manual image analysis. Then the plates were unmounted, slightly polished (highlighting the deep corrosion pits), and scanned for automatic image analysis. Different image analysis methods were compared. The least corrosion occurs, in couplings with aluminum alloy counterparts, when AA5051 washers are interposed; whereas the most effective coupling with steel counterparts is the one with nylon coated steel heads.

Sabrina Grassini, Paolo Matteis, Giorgio Scavino, Marco Rossetto, Donato Firrao

Comparing the Corrosion Effects of Two Environments on As-Cast and Extruded Magnesium Alloys

Magnesium is easily corroded in the presence of saltwater, limiting its use in the automotive industry. The magnesium microstructure greatly affects the corrosion rate, due to various additional elements. In the Center for Advanced Vehicular Systems at Mississippi State University, the effects of immersion and cyclical salt spray testing on various as-cast and extruded magnesium alloys is currently being examined. Previous work on an as-cast AE44 magnesium alloy has demonstrated that individual pit characteristics, such as pit depth, pit area, and pit volume, were deeper and larger following exposure to the immersion environment. However, the data elucidating the corrosion effects on individual pit characteristics has only been seen on as-cast magnesium containing rare earth elements, not on extruded magnesium alloys or zinc-containing magnesium alloys, both common magnesium forms. The research presented here will cover the effects of individual pit characteristics formed on various magnesium alloys due to the different environments.

H. J. Martin, C. Walton, J. Danzy, A. Hicks, M. F. Horstemeyer, P. T. Wang

Influence of Lanthanum concentration on the Corrosion Behaviour of Binary Mg-La Alloys

Different contents of Lanthanum have been added to Magnesium and have been investigated on their influence on the microstructure and the corrosion properties. The microstructure was studied by optical microscopy. Corrosion performance was evaluated using potentiodynamic polarization measurements. Immersion tests were carried out using distilled water and 0.1 M sodium chloride solution. The corrosion products were investigated by X-ray induced photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) which lead to detailed information on phase formation. The oxide and hydroxide formation have been correlated to the chemical states and formed intermetallics, i.e by taking into account the XPS peak shift and peak splitting of the the Mg-2p state. Additionally, the results have been verified by means of AES on the Mg-KLL, O-KLL and La-MNN excitation and by XRD. Latter suggests the supplemental formation of a nanocrystalline phase.

Rosario Silva Campos, Daniel Höche, Carsten Blawert, Karl Ulrich Kainer

Cryogenic Burnishing of AZ31B Mg Alloy for Enhanced Corrosion Resistance

Poor corrosion resistance is limiting applications of Mg alloys. However, the corrosion performance of an Mg alloy can be enhanced through modification of its microstructure. It has been reported in the literature that the microstructure, especially grain size of AZ31 Mg alloy, has a significant influence on its corrosion resistance. In this study, AZ31B discs were subjected to a novel mechanical processing method-cryogenic burnishing; the surface of AZ31B work piece was burnished with a custom tool under a liquid nitrogen spraying condition. The processing led to a more than 3 mm thick surface layer with remarkably changed microstructures formed on the disc surface. Significant grain refinement occurred within this surface layer due to dynamic recrystallization induced by severe plastic deformation and effective cooling by liquid nitrogen. Both electrochemical method and hydrogen evolution method indicate that the corrosion resistance of the burnished surface was significantly improved.

Z. Pu, G.-L. Song, S. Yang, O. W. Dillon, D. A. Puleo, I. S. Jawahir

Advanced Conversion Coatings for Magnesium alloys

Magnesium and its alloys have excellent physical and mechanical properties due to their high strength-to-weight ratio and are ideal for various applications in automotive, aerospace and defense sectors. However, Mg alloys are also highly susceptible to corrosion under harsh environments. Owing to this carcinogenicity as well as environmental impact of hexavalent chromium fueled by stringent environmental regulations, an environmentally green alternative to the carcinogenic hexavalent chromium coatings on magnesium is due.In this work, a novel trivalent chromium based conversion coating has been developed to improve the corrosion resistance and paint adhesion properties of Mg alloys. Coating performance characterization has been investigated via hydrogen evolution, weight loss measurement and electrochemical corrosion analysis techniques. Results have shown that the novel environmentally green trivalent chromium based coating on magnesium has indeed performed comparable to hexavalent chromium and thus establishing a viable alternative.

Syam Nibhanupudi, Alp Manavbasi

Development of Zirconium-based Conversion Coatings for the Pretreatment of AZ91D Magnesium Alloy Prior to Electrocoating

This work examines the use of hexafluorozirconic acid based solutions at concentrations from 0.025 M to 0.100 M and pH values of 2.0 to 4.0 for the creation of a zirconia-based conversion coating less than 1 micron thick to protect magnesium alloy AZ91D. Similar coatings have been found to give excellent protection for steel and aluminum alloys, but little research has been conducted on its application to magnesium. Work was performed to gain an understanding of the film formation mechanisms and related kinetics using x-ray photo-electron spectroscopy, scanning electron microscopy, and open circuit potential monitoring techniques. A design of experiments approach was taken to determine the effects of acid concentration, pH, and soak time on the corrosion properties both as-deposited and with an application of electrocoat. It was found that the application of the zirconia-based coating significantly increased corrosion resistance, and allowed for an acceptable e-coat application with excellent adherence.

James Reck, Yar-Ming Wang, Hong-Hsiang Harry Kuo

Use of an AC/DC/AC Electrochemical Technique to Assess the Durability of Protection Systems for Magnesium Alloys

One task under the U.S. Automotive Materials Partnership (USAMP) “Magnesium Front End Research and Development” (MFERD) Project has been the evaluation of methodologies for the assessment of protective capability for a variety of proposed protection schemes for this hypothesized multi-material, articulated structure. Techniques which consider the entire protection system, including both pretreatments and topcoats are of interest. In recent years, an adaptation of the classical electrochemical impedance spectroscopy (EIS) approach using an intermediate cathodic DC polarization step (viz. AC/DC/AC) has been employed to accelerate breakdown of coating protection, specifically at the polymer-pretreatment interface. This work reports outcomes of studies to employ the AC/DC/AC approach for comparison of protective coatings to various magnesium alloys considered for front end structures. In at least one instance, the protective coating system breakdown could be attributed to the poorer intrinsic corrosion resistance of the sheet material (AZ31) relative to die-cast AM60B.

Sen Song, Robert C. McCune, Weidian Shen, Yar-Ming Wang

Effects of Oxidation Time on Micro-arc Oxidized Coatings of Magnesium Alloy AZ91D in Aluminate Solution

Micro-arc oxidation coatings were prepared on magnesium alloy AZ91D at different oxidation times in aluminate solution. The effects of the oxidation time on the microstructure, growth rate and corrosion resistance of the coatings were investigated. The results indicate that the coatings are uniform in thickness and mainly composed of MgAl2O4 and MgO. There were many residual discharging channels on the coatings surface. The coatings improved the corrosion resistance of magnesium alloy AZ91D considerably. With increased oxidation time, the crystalline substances content and thickness of the coatings increased, while the growth rate of the coatings decreased, and the resulting coatings surface had lower porosity and larger pore sizes. In addition, the corrosion resistance of the coatings on magnesium alloy AZ91D surfaces is superior to the magnesium alloy AZ91D substrate in the NaCl solution, and the effect is more remarkable with longer oxidation times.

Weiyi Mu, Zhengxian Li, Jihong Du, Ruixue Luo, Zhengping Xi

Composite Coatings Combining PEO Layer and EPD Layer on Magnesium Alloy

Protective composite coatings were prepared combining plasma electrolytic oxidation (PEO) treatment and cathodic electrophoretic deposition on magnesium alloy AZ91D. The corrosion protection of composite coatings were evaluated using potentiodynamic polarization measurements in 3.5% NaCl solution, copper accelerated acetate salt spray (CASS) test and immersion test in acid solution. The adhesion of composite coatings was evaluated using cross-cut test and pull-off test. It is indicated that the corrosion resistance of magnesium alloy AZ91D with the composite coatings is improved obviously compared to it merely with PEO coating and it is also shown that pitting corrosion of PEO coating on magnesium alloy is decreased with EPD post-treatment. The adhesion of composite coatings could be up to 11.3 N/mm2 in quantitative method due to the interlocking effect of organic layer in pores of PEO layer.

Yongfeng Jiang, Yefeng Bao, Ke Yang

Poster Session

Frontmatter

Growth Kinetics of γ-Al12Mg17 and β-Al3Mg2 Intermetallic Phases in Mg vs. Al Diffusion Couples

Increasing use and development of lightweight Mg-alloys have led to the desire for more fundamental research in and understanding of Mg-based systems. As a strengthening component, Al is one of the most important and common alloying elements for Mg-alloys. In this study, solid-to-solid diffusion couple techniques were employed to examine the interdiffusion between pure Mg and Al. Diffusion anneals were carried out at 300°, 350°, and 400°C for 720, 360, and 240 hours, respectively. Optical and scanning electron microscopies (SEM) were employed to observe the formation of the intermetallics γ-Al12Mg17 and β-Al3Mg2, but not ε-phase. Concentration profiles were determined using X-ray energy dispersive spectroscopy (XEDS). The growth constants and activation energies were determined for each intermetallic phase.

Sarah Brennan, Katrina Bermudez, Nagraj Kulkarni, Yongho Sohn

Development and Characterization of New AZ41 and AZ51 Magnesium Alloys

In the present study, new AZ41 and AZ51 magnesium alloys were successfully synthesized by adding 1 wt. % and 2 wt. % aluminum into AZ31B matrix, respectively, using an innovative disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization studies revealed equiaxed grain morphology, reasonably uniform distribution of intermetallics in the matrix and minimal porosity. Physical properties characterization revealed that addition of Al reduced the coefficient of thermal expansion (CTE) of monolithic AZ31B. The presence of higher percentage of aluminum also assisted in improving overall mechanical properties including microhardness, modulus of elasticity, 0.2% yield strength, ultimate tensile strength, and work of fracture of AZ31. The results suggest that these newly developed AZ magnesium alloys have significant potential in diverse engineering applications when compared to AZ31 alloy.

Md Ershadul Alam, Samson Han, Abdelmagid Salem Hamouda, Quy Bau Nguyen, Manoj Gupta

Engineering a More Efficient Zirconium Grain Refiner for Magnesium

Zirconium is currently used as a grain refiner for high temperature magnesium alloys. However, currently around 1 wt% is used for grain refinement, and much of this is wasted as sludge due to settling, as zirconium has a density almost four times that of magnesium. Since a recent study suggested that only faceted particles were activated as nucleation sites during casting solidification, ECAE processing of a magnesium-15wt% zirconium grain refiner master alloy was attempted to try to increase the number of faceted particles. ECAE processing of the master alloy only resulted in a modest decrease in grain size, even though the percentage of faceted particles doubled as a result of ECAE processing, since only 1.6% of zirconium particles in the as-received master alloy were faceted and deemed to be likely nucleation sites. The results from this work provide insights for the future development of more efficient grain refiners.

S. Viswanathan, P. Saha, D. Foley, K. T. Hartwig

Microstructure and Mechanical Properties of Mg-1.7Y-1.2Zn Sheet Processed by Hot Rolling and Friction Stir Processing

The use of lightweight structural materials is an integral part of mass reduction strategy in transportation applications. Magnesium based sheet products have gained significant interest in the automobile industry. Newer magnesium alloys such as Mg-Y-Zn have potential to develop sheet products with superior mechanical properties owing to improved precipitation hardening response. In the present work, rolled sheet of an Mg-1.7Y-1.2Zn alloy containing small amounts of Al and Ce was investigated. Microstructure and mechanical properties were examined in as-rolled, rolled+aged, friction stir processed (FSP) and FSP+aged conditions. Mechanical properties (YS, UTS and %El) of the sheet showed certain anisotropy in rolling and transverse directions, which was marginally reduced upon ageing. However, FSP led to a significant range of mechanical properties depending on the test direction. Ageing of the FSP sheet showed improvement in mechanical properties and reduced anisotropy in the two directions. The static recrystallization due to ageing caused reduced anisotropy in FSP treated sheet. The overall strength-ductility variation is discussed in terms of relative contributions of grain boundary strengthening, texture and precipitation strengthening.

V. Jain, J. Q. Su, R. S. Mishra, R. Verma, A. Javaid, M. Aljarrah, E. Essadiqi

The microstructure and mechanical properties of cast Mg-5Sn based alloys

The effects of 1 wt.% Ce-rich misch-metal, 3 wt.% Bi, 0.4 wt.% Sb, and 2 wt.% Ca additions on the micro structure, mechanical properties, and creep resistance of a cast Mg-5Sn alloy were studied. Impression creep tests were carried out at 150 and 225 °C under constant stresses of 300 and 175 MPa. The results showed that creep resistance, hardness, and shear strength of the base alloy were significantly enhanced with the addition of ternary alloying elements. This was attributed to the concurrent formation of Mg2Sn particles with the more thermally stable CaMgSn, Mg3Sb2, Mg3Bi2 and MgSnRE phases which strengthen both matrix and grain boundaries during deformation in the investigated system. Among all tested materials, the Mg-5Sn-2Ca alloy indicated the highest mechanical properties and creep resistance due to the refined microstructure as well as the type and volume fraction of the intermetallic phases present in this alloy.

M. Keyvani, R. Mahmudi, G. Nayyeri

Effect of Cooling Rate and Chemical Modification on the Tensile Properties of Mg-5wt% Si Alloy

Hypereutectic Mg-Si alloys are a new class of light materials usable for aerospace and other advanced engineering applications. In this study, the effects of both cooling rate and bismuth modification on the micro structure and tensile properties of hypereutectic Mg-5wt% Si alloy were investigated. It was found that the addition of 0.5% Bi, altered the morphology of primary Mg2Si particles from bulky to polygonal shape and reduced their mean size from more than 70 μm to about 30 (am. Also, the tensile strength and elongation of the modified alloy increased about 10% and 20%, respectively, which should be ascribed to the modification of Mg2Si morphology and more uniform distribution of the primary particles. Moreover, an increase in tensile strength value with increase in cooling rate were observed which is attributed to finer micro structure of alloy in higher cooling rates. It was observed that Bi addition is significantly more effective in refining the morphology of primary Mg2Si particles than applying faster cooling rates.

Farshid Mirshahi, Mahmood Meratian, Mohsen Mohammadi Zahrani, Ehsan Mohammadi Zahrani

On Predicting the Channel Die Compression Behavior of HCP Magnesium AM30 using Crystal Plasticity FEM

Deformation of polycrystalline aggregates of HCP crystals was investigated by employing crystal plasticity and finite element simulations. Results were validated using channel die compression tests. The three dimensional polycrystal, represented by Voronoi techniques, was assigned an initial distribution of crystallographic orientations determined from X-Ray Diffraction. The mechanical properties from the channel die compression tests were used to correlate the material parameters of the crystal plasticity model. Simulations predicted grain-to-grain interactions and the resulting texture evolution under channel die compression. The inhomogeneous deformation among grains was mapped by a stress and a strain distribution and grain orientation spread. The simulation results were compared with experimental observations of an HCP polycrystal subjected to channel die compression.

Q. Ma, E. B. Marin, A. Antonyraj, Y. Hammi, H. El Kadiri, P. T. Wang, M. F. Horstemeyer

Investigation of Microhardness and Microstructure of AZ31 Alloy after High Pressure Torsion

Cast commercial magnesium alloy AZ31 was processed by high pressure torsion (HPT) at room temperature for 1, 3, 5 and 15 rotations (strain ranged from 1 to 7). Micro structure evolution with strain imposed by HPT was observed by light and electron microscopy. HPT was shown to be a very effective method of grain refinement. The initial coarse grain structure was refined by a factor of almost 200 already after one HPT turn (ε ≈ 4). Mechanical properties were investigated by detailed 2-D microhardness measurements. HPT straining was found to introduce a radial inhomogeneity in the material which is manifested by a pronounced drop in the center and the maximum near the specimen periphery. With increasing strain due to HPT this inhomogeneity is continuously smeared out tending to saturate with increasing strain. Integrated 3-D meshes across the total surface of disks revealed the undulating character of microhardness variations. The strain imposed by HPT was shown to saturate with increasing number of HPT turns.

Jitka Vrátná, Miloš Janeček, Josef Stráský, Hyoung Seop Kim, Eun-Yoo Yoon

Plastic Deformation of Magnesium Alloy Subjected to Compression-First Cyclic Loading

In-situ neutron diffraction has been employed to study the deformation mechanisms in a precipitation-hardened and extruded Mg-8.5wt.% Al alloy subjected to compression followed by reverse tension. The starting texture is such that the basal poles of most grains are oriented normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis. Diffraction peak intensities for several grain orientations monitored in-situ during deformation show that deformation twinning plays an important role in the elastic-plastic transition and subsequent plastic deformation behavior. Significant non-linear behavior is observed during unloading after compression and appears to be due to detwinning. This effect is much stronger after compressive loading than after tensile loading.

Soo Yeol Lee, Michael A. Gharghouri, John H. Root

Microstructure Evolution in AZ61L During TTMP and Subsequent Annealing Treatments

Microstructure evolution is studied in Thixomolded® Thermomechanical Processed (TTMP) AZ61L sheet at various stages of processing. Transmission electron microscopy (TEM) is utilized to examine (1) grain refinement and recrystallization and (2) refinement and re-distribution of the β-Mg17Al12 phase in the as-Thixomolded, as-TTMP, and annealed conditions. Electron backscatter diffraction (EBSD) is used to study texture evolution through TTMP and annealing. The influence of microstructure produced by TTMP and annealing on the mechanical properties will be discussed.

T. D. Berman, W. Donlon, R. Decker, J. Huang, T. M. Pollock, J. W. Jones

Modeling the Corrosive Effects of Various Magnesium Alloys Exposed to Two Saltwater Environments

The use of magnesium within the automotive industry is limited by its corrosion rate in the presence of saltwater. By adding various elements, the magnesium micro structure and corrosion rate can be altered. In the Center for Advanced Vehicular Systems at Mississippi State University, a model is being developed to elucidate the total corrosion of magnesium alloys and is comprised of general corrosion and pitting corrosion, respectively, as shown below: where pitting corrosion is based on the pit number density, pit surface area, and a nearest neighbor distance function, respectively, as shown below: The exposure environment resulted in differences in the amount of pit nucleation, in the size of the pits formed, and in the rate of coalescence. Time also affected the surface characteristics, as general corrosion began degrade the number and size of the pits. The research presented here will cover the model development, calibration, and validation.

H. J. Martin, C. Walton, J. Danzy, A. Hicks, M. F. Horstemeyer, P. T. Wang

Corrosion Performance of Mg-Ti Alloys Synthesized by Magnetron Sputtering

Mg is difficult to alloy with Ti through a conventional metallurgical approach due to their insolubility in each other and big difference in melting point. However, Mg, if alloyed with Ti, may become corrosion resistant. This hypothesis is verified in this study.Mg1-xTix alloy thin films (with x=0, 0.2, 0.4, 0.6, 0.8 and 1) were deposited by magnetron sputtering onto a glass substrate. Film compositions were analyzed by electron probe micro-analysis (EPMA). The electrochemical behavior of these alloys was characterized in saturated Mg(OH)2 solutions with and without 0.1M NaCl. The macrostructures of the thin film alloys were compared before and after polarization and immersion measurements. The results showed that the corrosion resistance of the alloy was improved with increasing Ti content. No material loss or corrosion damage was observed for alloys with 80% or more Ti content in both solutions.

Zhenqing Xu, Guang-Ling Song, Daad Haddad

Structure and Mechanical Properties of Magnesium-Titanium Solid Solution Thin Film Alloys Prepared by Magnetron-sputter Deposition

Mg alloys are being considered for wider application in automotive industry. Designing new alloys with improved mechanical properties is important to the development of new Mg alloy parts. Mg-Ti is an interesting alloying system that may have good corrosion resistance due to high passivity of Ti. However it is difficult to form through a conventional metallurgical method due to the mutual insolubility of Mg and Ti and the big difference in their melting point. Nevertheless, if the alloy can be formed, it may have other unexpected physical and chemical performance. Therefore, it is of significance to understand the properties of Mg-Ti alloy produced by non-conventional approach.In this report, Mg(1-x)Tix thin film alloys containing 0, 21, 41, 51, 58, 81 and 100 at.% Ti were deposited by dc magnetron sputtering on Si substrates. The mechanical properties of the thin film alloys were obtained using nanoindentation. Electron probe microanalysis (EPMA) was used to determine the film compositions. X-ray diffraction (XRD) measurements showed that single phase magnesium-titanium solid solutions were obtained across the full range of magnesium and titanium mixtures. The topography and the rms roughness of the different alloys were studied using atomic force microscopy (AFM). The mechanical properties of the Mg(1-x)Tix thin films were determined by analyzing the nanoindentation load-displacement curves based on the Oliver-Pharr method. The nanoindentation results show that both the elastic modulus and hardness of the Mg(1-x)Tix alloy thin films are higher than those of conventional Mg alloys.

Daad Haddad, GuangLing Song, Yang Tse Cheng

Effect of Adding SiO2-Al2O3 Sol into Anodizing Bath on Corrosion Resistance of Oxidation Film on Magnesium Alloy

Due to the widely use in automobile and construction field, AZ91D magnesium alloy need to be protected more effectively for its high chemical activity. In this paper, three kinds of films were formed on magnesium alloy. The first kind of film, named as anodic oxidation film, was prepared by anodic oxidation in the alkaline solution. The processes for preparing the second kind of film, named as multiple film, involved coating sol-gel on the samples and heat-treating before anodic oxidation. The third kind of film was prepared by anodic oxidation in the alkaline oxidation solution containning 5% (vol) SiO2-Al2O3 sol, named as modified oxidation film. The corrosion resistance of the three different films was investigated. The results showed that the modified oxidation film had the highest corrosion resistance due to the largest thickness and most dense surface morphology. Sol was discussed to react during the film forming process, which leaded to the difference between modified oxidation film and anodic oxidation film.

Huicong Liu, Liqun Zhu, Weiping Li

Monotonic and Fatigue Behavior of Mg Alloy Friction Stir Spot Welds: An International Benchmark Test in the “Magnesium Front End Research and Development” Project

This paper presents the experimental results of benchmark coupon testing of monotonic and cyclic conditions on friction stir spot welded coupons of Mg AZ31 alloy. The results presented here are a product of a collaborative multinational research effort involving research teams from Canada, China, and the United States. Fatigue tests were conducted in load control at R=0.1 at two different maximum loads: 1kN and 3kN. Good agreement was found between the participating labs regarding the number of cycles to failure. Differences in the failure modes were observed for the two different loading conditions tested. At the higher load, fatigue failure was caused by interfacial fracture. However, at the lower load, fatigue cracks formed perpendicular to the loading direction, which led to full width separation. For additional comparison, the monotonie and cyclic results of the friction stir spot welds are compared to resistance spot welded coupons of similar nugget size.

H. Badarinarayan, S. B. Behravesh, S. D. Bhole, D. L. Chen, J. Grantham, M. F. Horstemeyer, H. Jahed, J. B. Jordon, S. Lambert, H. A. Patel, X. Su, Y. Yang

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