Magnesium Technology 2012

This paper summarizes the development of new cast and wrought magnesium alloys using computational thermodynamics and experimental methods. The work illustrates the role of calculated phase diagrams, solidification paths and phases in predicting and interpreting the final microstructure of Mg-Al-Ca and Mg-Al-Sn cast alloy systems and Mg-Al-Mn and Mg-Zn-Ce wrought alloy systems.

Development of new Mg-alloys needs greater efforts in systematic evaluation of corrosion protection methods under service environments. A deeper understanding of microscale and nanoscale metallurgy is needed to slow down corrosion. Results from our multiscale modeling effort will be presented to demonstrate the power of first-principle theories in predicting the composition-dependent kinetics of corrosion reactions. Our recent results show that the corrosion prevention properties of Mg-alloys can be significantly enhanced by doping rare-earth elements such as Cerium that protects the oxide layer from rapid hydrolysis. Furthermore, we are developing kinetic Monte Carlo and finite-element analysis (FEA) based models to extend the predictions from the atomic length scales to nano- and microscale models that will include grains and alloy microstructure. The potential for incorporating mechanical and corrosion performance in continuum length scale combined with the insights from first-principles based surface chemical models can have powerful impact on the development of Mg-alloys.

Friction stir welding and ultrasonic welding techniques were applied to join automotive magnesium alloys to steel sheet. The effect of tooling and process parameters on the post-weld microstructure, texture and mechanical properties was investigated. Static and dynamic loading were utilized to investigate the joint strength of both cast and wrought magnesium alloys including their susceptibility and degradation under corrosive media. The conditions required to produce joint strengths in excess of 75% of the base metal strength were determined, and the effects of surface coatings, tooling and weld parameters on weld properties are presented.

Magnesium sheet materials AZ31, AM50, ZM21, ZK10, and ZK30 were tested to failure at 450C at a strain rate of 0.001/s. Each of these materials exhibit significant changes in grain structure during deformation, especially in the necked regions of the failed samples. Grain size in the neck is shown to vary with thickness strain and strain rate. Some materials exhibit significant coarsening along the necked region while others show very little change. The results of this work can be used to help validate models for dynamic recrystallization in magnesium.

In recent years the process of shear rolling has seen considerable study, particularly for heavily textured materials such as magnesium. The goal of this work has been to produce sheet with greater formability for industries such as automotive and aerospace. To date, almost all work on asymmetric rolling has been carried out on small strips that are not large enough to produce parts. The current work will discuss scaling-up of the shear rolling process to generate wider sheet. A mill at the Magnesium Elektron North America plant was modified to allow shear rolling at a ratio of 1:1.35 on sheets up to 36” wide. AZ31B and ZEK100 sheets of size 36”x72” were shear rolled and demonstration automotive parts have been formed by Superform USA.

Carbothermal production has been recognized as conceptually the simplest and cleanest route to magnesium metal, but has suffered from technical challenges of development and scale-up. Work by CSIRO has now successfully demonstrated the technology using supersonic quenching of magnesium vapor (the MagSonic™ Process). Key barriers to process development have been overcome: the experimental program has achieved sustained operation, no nozzle blockage, minimal reversion, and safe handling of pyrophoric powders. The laboratory equipment has been operated at industrially relevant magnesium vapor concentrations (>25% Mg) for multiple runs with no blockage. Novel computational fluid dynamics (CFD) modeling of the shock quenching and metal vapor condensation has informed nozzle design and is supported by experimental data. Reversion below 10% has been demonstrated, and magnesium successfully purified (>99.9%) from the collected powder. Safe operating procedures have been developed and demonstrated, minimizing the risk of powder explosion. The MagSonic™ Process is now ready to progress to significantly larger scale and continuous operation.

A broad technology comparison of carbothermal magnesium production with present technologies has not been previously presented. In this paper a comparative analysis of CSIRO’s MagSonic™ process is made with the electrolytic and Pidgeon processes. The comparison covers energy intensity (GJ/tonne Mg), labor intensity (person-hours/tonne Mg), capital intensity (USD/tonne annual Mg installed capacity), and Global Warming Potential (GWP, tonnes CO₂-equivalent/tonne Mg). Carbothermal technology is advantageous on all measures except capital intensity (where it is roughly twice the capital cost of a similarly-sized Pidgeon plant). Carbothermal and electrolytic production can have comparatively low environmental impacts, with typical emissions one-sixth those of the Pidgeon process. Despite recent progress, the Pidgeon process depends upon abundant energy and labor combined with few environmental constraints. Pressure is expected to increase on environmental constraints and labor and energy costs over the coming decade. Carbothermal reduction technology appears to be competitive for future production.

Metal Oxygen Separation Technologies, Inc. (MOxST) is actively developing Solid Oxide Membrane (SOM) electrolysis technology for production of magnesium directly from its oxide. The vital component of this technology is the oxygen ion-conducting solid zirconia electrolyte separating the molten flux (a mixture of salts and oxide) and the inert anode. The zirconia not only protects the anode from the flux but also prevents anode gas back-reaction, increasing the efficiency. This makes it possible to produce low-cost high-purity magnesium and high-purity oxygen as a byproduct with no direct greenhouse gas emissions. In this paper we discuss the design modifications made to address the scaling-up challenges, particularly for producing magnesium in liquid form. The key accomplishment to date is the successful development of a prototype capable of producing few kilograms of magnesium per day. We will also describe the prerequisite properties of an inert anode and suitable materials for the same.

Molten salt electrolysis of MgCl₂ is commonly used for the production of magnesium metal. However, the electrolysis feed must be completely dry with minimum oxygen content. Therefore, complete dehydration of the MgCl₂ brine or the hydrated prill is a required process, which is very challenging because of the ease of thermal degradation due to hydrolysis of magnesium chloride.Fluidized bed dryers are often used, under hot air and HCl environments. The key features of three different types of fluid bed technologies, which can be applied to MgCl₂ dehydration plants, are described in this paper. In addition, a discussion of chemistry, unit operations and advantages associated with each option, is presented.The background information is provided based on open literature sources, including papers and patents. Most calculations are performed using commercially available metallurgical software, for the thermodynamic calculations and mass/heat balances.

Studies of storing solar energy into chemical energy of magnesium (Mg) through reduction from magnesium oxide (MgO) by solar-pumped laser were conducted. We succeeded in solar-pumped laser-induced Mg production. Laser system consists of a 4 m2 Fresnel lens mounting on a sun tracker platform which focus solar radiation into laser head therefore over 100W (CW) output laser can be irradiated. A single laser beam is focused on a mixture of magnesium oxide and reducing agent silicon. High power density of focused laser leads to high temperature and the reduction reaction resulting in Mg production. The resultant vapor is collected on a copper plate and analyzed in terms of magnesium deposition efficiency. As a result, deposition efficiency of 2.3 mg/kJ was achieved.

An experimental electrolytic magnesium production cell was designed to remove chlorine gas from the electrolyte rapidly and demonstrate the beneficial effects of reduced chlorine dissolution into the molten salt electrolyte. The back reaction that is the main cause of current losses in electrolytic magnesium production was reduced as a result of effective separation of electrode products and decreased contact time of chlorine gas with the electrolyte. Moreover, smaller inter electrode distances employed and lower chlorine gas present on the anode surface made it possible to work at low cell voltages. Electrolytic cell was tested at different current densities. Energy consumption of 7.0 kWh kg-1 Mg that is slightly above the theoretical minimum, 6.2 kWh kg-1 Mg, at 0.68 Acm-2 anodic current density was achieved for a MgCl₂/NaCl/KCl electrolyte.

Aluminum-magnesium alloys were prepared from magnesium oxide by molten salt electrolysis method. 10w%RECl₃-63.5w%KCl-23.5w%MgCl₂-3w%MgO was taken as electrolyte. The results showed that RE could be attained in aluminum-magnesium alloy, and it was proved that the RE was reduced directly by aluminum. Magnesium in the alloy was produced by electrolysis on cathode. The content of RE in the alloy was about 0.8wt %-1.2wt%, and the content of Mg in the alloy was lwt%∼6wt% with electrolytic times. The highest current efficiency was 81.3% with 0.8A/cm2 current density. The process of electrolysis was controlled together by electrochemical polarization and concentration polarization.

In order to effectively utilize the ascharite mineral, in Liaoning province of China, the paper studied to extract magnesium from ascharite mineral with aluminum powder as reductant by vacuum thermal reduction process. And boron of the raw material was saved in residue that could be used as raw materials to produce non-alkali glass fiber. Environment cannot be polluted during this process, as well as the process can create great economic value. Calcined material and residue were taken XRD analysis. Based on thermodynamic analysis, the Gibbs free energy and critical temperature of reduction ascharite with aluminum were calculated. As a result, the critical temperature is 1302 °C at ordinary pressure, and addition, the critical temperature will reduce farther when the air pressure is reduce in the retort, The recovery rate was effected remarkably by the mass of reductant and the making briquettes pressure.

Cyclic voltammetry (CV) was used to investigate chlorine and electrolyte intercalation into three different graphite anodes from NaCl-KCl-MgCl₂ melts at 700°C. The three anodes were composed of needle-coke (NC), petroleum-coke (FPC) and common petroleum-coke (CPC), respectively. Chlorine intercalation amount was characterized by the reduction current (reduction electricity quantity) on the reverse scan during the cyclic voltammograms. And the electrolyte intercalation was presented by the increase in oxidation charge between the forward scan and the reverse scan during the CV measurements. The results show that among the three graphite anodes, NC shows the lowest reduction current and nearly no increase in the charges, while about 5–10 times increase in the charge for the PFC and CPC. The above results implied that NC has a better resistance to electrolyte and chlorine intercalation, which were confirmed by the electrolysis experiments results. As a simple and useful method, CV can be used to test graphite anode corrosion resistance to electrolyte and chlorine in chloride system.

The conditions of technique to prepare magnesium oxide by calcination from basic magnesium carbonate were optimized using a central composite design (CCD) of response surface methodology (RSM). Two quadratic equation models for decomposition rate and activity of magnesium oxide were built and effects of main factors and their corresponding relationships were obtained. The statistical analysis of the results showed that in the range studied the decomposition rate and activity of magnesium oxide were significantly affected by the calcination temperature and calcination time. The optimized calcination conditions were as follows: the calcination temperature 666.99°C and the calcination time 2.12 h, respectively. Under these conditions the decomposition rate of basic magnesium carbonate was 92.1971%, and the activity of magnesium oxide was 155.503 mg I₂/g MgO. The validity of the model was confirmed experimentally and the results were satisfactory. In addition, the sample was characterized by X-ray Diffraction (XRD).

In this work, a mean-field self-consistent approach based on a generalization of the Tanaka-Mori method is introduced to predict the mechanical response of polycrystalline Mg. The key idea is to homogenize the response of grains containing twin domains such that a direct coupling between the twin and parent domain is introduced. The work is particularly suited to study Mg as it allows for a direct coupling of the mechanical response of twin and parent domains. Such coupling accounts, for the first time, for relative size and shape effects on the development of internal strains in twin domains.

Three-point bending was performed on an AZ31 magnesium sheet with a grain size ∼8.0 µm at room temperature. In-situ electron backscatter diffraction and metallography examinations revealed an anomalous twinning pattern during bending. In the compression zone, the {101̄2} <101̄1̄> twins appear in an extremely localized fashion, consisting of alternating twin bands. Each band comprises a high density of twins. In between the twin bands, twins are absent. As the bending angle increases, the twin bands grow into the tension zone although the stress disfavors the extension twinning.

Fine grained magnesium alloys show high fracture toughness, associated with void formation. Detailed microstructural evolution during a fracture toughness test of a fine grained Mg-Zn alloy has been studied here by transmission electron microscopy (TEM). Focused ion beam (FIB) technique was used for obtaining samples near crack. Initially, subgrain structures form ahead of the crack tip, after which {101̄1} type twins of width of about 400nm form. They further twin by {101̄2} twinning. Subsequent twinning occurs at a finer scale near the crack, forming configurations of {101̄1}–{101̄2} double twins and low angle boundaries. The scale of the twin domains became progressively finer to less than 50nm. In absence of enough dislocations to pile up causing fracture, deformation continues to occur by the twinning.

Tensile experiments were performed on a rolled AZ31 alloy in an SEM at 323K (50°C), 423K (150°C), and 523K (250°C) in order to analyze the deformation mechanisms in-situ. Electron backscatter diffraction (EBSD) was performed both before and after deformation. The mechanical anisotropy was considerably reduced with temperature. Extension twinning was observed at 323K (50°C), but disappeared at 423K (150°C), indicating that the CRSS of non-basal systems becomes smaller than that of twinning at T<423K (150°C). From 423K (150°C) to 523K (250°C), a transition occurred in the dominant deformation mode from basal + prismatic <a> to mainly prismatic <a> slip. This is consistent with a decrease of the CRSS of non-basal slip systems with increasing temperature. In-situ tensile-creep experiments, performed at approximately the yield stress at 423K (150°C), indicated less slip and more grain boundary cracking occurs under creep deformation as compared to the higher-stress tensile experiments.

Notably the most dominant twinning mode in hexagonal close-packed metals, {101̄2} <101̄1̄> twinning presents abnormal properties such as reversible twinning and non-Schmid effect. The twin boundaries may significantly deviate from the {101̄2} twinning plane. HCP metals also present a strong propensity to develop texture during processing. Through electron backscatter diffraction and high resolution transmission electron microscopy observations, we show that these properties can be well understood from the perspective of the atomic shuffling that dominates in the twinning.

We numerically study the large strain free-end torsion of extruded magnesium alloy bars based on the recently developed Elastic Visco-Plastic Self-Consistent (EVPSC) model, in which both slip and twinning contribute to plastic deformation. It is shown that the predicted second-order length change is very sensitive to the initial texture and texture evolution. Numerical results suggest that the free-end torsion test can provide an effective means for assessing the adequacy of polycrystal plasticity models for magnesium alloys.

Nano-indentation measurements have been performed on {10–12}<10–11> twin and adjacent matrix regions of deformed magnesium single crystals and the hardness values were analyzed by the Oliver-Pharr method. Although the hardness difference between the twin regions and the adjacent matrix was insignificantly small, the hardness values showed orientation dependence regardless of the twins’ size and variants. This observation can be interrupted by texture- softening resulting from the lattice reorientation in the twin regions. In contrast, the experimental evidence for the Basinski hardening mechanism in {10–12}<10–11> twins, which is an increase in strength/hardness as a result of dislocation contributions within twin area, was not obtained from this experiment. This presentation provides framework for the discussion of the hardening/softening effect of {10–12}<10–11> twinning on the plastic flow in single crystalline magnesium and quantitative values for hardening parameters used in the crystal plasticity modeling.

A constrained chip formation technique, large strain extrusion machining (LSEM), was used to produce bulk magnesium alloy (AZ31B) strips with fine grain size (2–6 μm) and non-basal textures. These characteristics are known to enhance the final formability. The deformation temperature during extrusion-machining was varied by preheating the workpiece to a range of temperatures (50°C to 375°C). Microstructural refinement and texture evolution were studied as function of deformation temperature. It was possible to refine the grain size down to ∼2 μm by restricting the dynamic grain growth at low to moderate deformation temperatures (below 320°C). LSEM was shown to be capable of resulting in non-basal textures at low deformation temperatures (below 220°C) as well as at elevated deformation temperatures (above 420°C). The influence of active deformation mechanisms and dynamic recrystallization on the texture development is also addressed.

Published neutron diffraction data on internal strains in a textured polycrystal of AZ31 alloy and tensile data for a random polycrystal of Mg are discussed from two complementary points of view, a purely phenomenological and a formal crystallographic one. It is suggested that the transition to full plasticity involves two different fractions of the grains population, at different strains. The role of texture and twinning are discussed. Critical experiments to test some of the hypotheses on how the elasto-plastic transition develops are proposed.

Magnesium alloys produced by the existing twin roll casting (TRC) technique have coarse and non-uniform microstructures and severe centre-line segregation. Consequenty, TRC strip is cast typically no thinner than 5–9 mm, relying on costly subsequent downstream processing to produce thin strip with an improved microstructure. In the research described herein melt conditioning by intensive melt shearing was used prior to TRC to promote heterogeneous nucleation and provide a refined and uniform microstructure without severe macrosegregation. Additionally, a TRC machine with small diameter rolls was used to cast AZ31 strip of less than 2 mm in thickness suitable for direct component manufacturing such as stamping, without the necessity of hot rolling. The effects of process parameters, such as casting speed and melt superheat, on as-cast microstructure were studied. Experimental results show that the melt conditioning process provided considerable reduction in as-cast grain size and elimination of centre-line segregation. The texture and mechanical properties of melt conditioned strips were much improved over conventional TRC strips, offering the potential for higher quality final components.

A 2-D coupled thermal-fluid-stress model was developed and used to simulate the twin roll casting (TRC) of an AZ31 magnesium alloy using the commercial software package, ALSIM. The model was used to predict the fluid flow, temperature distribution and mechanical behavior of AZ31 magnesium alloy in the roll bite. An important parameter in controlling the TRC process is the set-back distance; the distance between the nozzle entry to the kissing point of the rolls. There are two approaches to increase the set-back: 1) increasing the entry thickness and 2) decreasing the final strip thickness. In this study the effect of set-back distance and casting speed on the thermo-mechanical behavior of the strip during TRC has been studied. The thermo-mechanical behavior of the strip has a significant effect on the final quality as defect formation depends on such behavior.

Rare earths have been added to magnesium alloys in order to improve the creep resistance, corrosion resistance and strength. Solid-to-solid diffusion couples were assembled between Mg (99.9%) and Y (99.9%) to investigate the formation and growth of intermetallic phases and interdiffusion in the Mg-Y system. The diffusion anneals were performed at 450, 500 and 550°C for 360, 240 and 120 hours, respectively. The intermetallic layers that developed were the δ-Mg₂Y and ε-Mg₂₄Y₅ phases, however the MgY phase did not form. A substantial penetration of Y in Mg was observed, however along with Kirkendall porosity that indicates faster diffusion of Mg than Y in Mg solid solution. The activation energies for parabolic growth in ε-Mg₂4Y₅ and δ-Mg₂Y were calculated to be 84 kJ/mol and 77 kJ/mol, respectively.

Over the past decades, the necessity to decrease the weight of automobile parts has created a considerable interest in magnesium alloys. The need to develop magnesium die casting alloys for car components motivates R&D in high temperature magnesium alloy development. In order to improve magnesium alloys with low cost, high strength and with notable elevated temperature properties, the effect of Ce addition (0.5/1.0 wt.-%) on microstructure and mechanical properties of AM50 was studied. Results show that addition of Ce to AM50 resulted in grain refinement and the formation of the secondary phase Al₁₁Ce₃. Mechanical properties of investigated alloys at both room and elevated temperature were remarkably increased. AM50 containing l%wt. Ce showed relatively better refinement and mechanical properties compared to AM50 with 0.5%wt. Ce.

A new melt conditioned direct chill (MC-DC) casting process has been developed for producing high quality magnesium alloy billets and slabs. In the MC-DC casting process, intensive melt shearing provided by a high shear device is applied directly to the alloy melt in the sump during DC casting. The high shear device provides intensive melt shearing to disperse potential nucleating particles, creates a macroscopic melt flow to distribute uniformly the dispersed particles, and maintains a uniform temperature and chemical composition throughout the melt in the sump. Experimental results have demonstrated that the MC-DC casting process can produce magnesium alloy billets with significantly refined microstructure and reduced cast defects. In this paper, we introduce the new MC-DC casting process, report the grain refining effect of intensive melt shearing during the MC-DC casting process and discuss the grain refining mechanism.

This paper investigates the effect of cooling rate on the grain size and microstructure of Mg AZ31B alloy cast at a superheat of 8°C using the Magnetic Suspension Melting (MSM) process, which is capable of melting and casting at superheats less than 5°C. In this study, the Mg alloy was unidirectionally solidified in a bottom-chill mold with stainless steel and copper chill blocks. The solidification parameters, namely growth velocity (V) and temperature gradient (G), were determined from numerical simulation of the cooling curves, which was found to be in good agreement with measurements. For the investigated solidification rates, metallographic examination showed globular solidification morphology, and the grain size was inversely proportional to the square root of the cooling rate. Microprobe analysis of the cast ingots also showed that Al segregation occurs primarily at the grain boundaries, and the solidification rate affects the size and distribution of both the secondary α phase and the intermetallic Mg₁₇Al₁₂ phase.

High-pressure die cast (HPDC) magnesium alloy AM60 is recognized for its versatility in the manufacturing of weight sensitive components of relatively thin cross section. To further expand practical applications of the alloy, squeeze casting has been proposed to allow for thicker castings. In this study, AM60 alloy specimens of 10mm thickness were squeeze cast using a hydraulic press with an applied pressure of 60 MPa. Fracture energies, following a Charpy Impact Testing protocol, of the squeeze cast specimens were characterized in comparison with the HPDC counterparts using both experimental and numerical techniques. The experimental results show the squeeze cast alloy absorbing approximately 46.2% more energy during impact than its HPDC counterpart. Scanning electron microscopy fractography reveals the favourable quasi-cleavage fracture mode of the squeeze cast alloy AM60, relative to the decohesive rupture fracture mode present in the die cast alloy.

Magnesium matrix (AM60) composites reinforced with 9 vol% Al₂O₃ fibres were fabricated using Al₂O₃fibre preform preparation and squeeze casting techniques. Boundary lubricated sliding wear tests were performed on the composites and the matrix alloy at low loads (1.0–5.0 N) to evaluate their wear characteristics. The Mg matrix alloy underwent scuffing and oxidative type wear leading to high rate of material removal. Under the same conditions, the composites’ wear resistance was at least 102 times higher. At 1.0 N load, Al₂O₃fibres protected the matrix from damage for up to 1.0 ×106 sliding cycles. For longer cycles Al₂O₃ fibres underwent fracture and exhibited decohesion at the fibre/matrix interface. At higher loads and sliding cycles, the matrix suffered wear damage leading to an increase in wear rate. The counterface, AISI 52100, worn against the base alloy AM60 revealed slight damage in the form of surface scratches and presence of MgO. The counterface experienced higher amount of material removal when it was worn against AM60-9% (Al₂O₃)_f composite.

The knowledge of as cast microstructure of Mg alloys is of prime importance to design the downstream thermo mechanical processes like rolling and annealing which then follows with commercial applications of Mg alloys in various industrial sectors [1]. Specifically, the emerging technologies like Twin roll casting that require minimal thermo mechanical processing; it is the solidified microstructure at the casting stage which determines the mechanical properties of the final product. Hence, the as cast microstructural information of Mg alloys becomes imperative but there has been little or no work on the same. In this regard, the present study focuses on the influence of the solidification parameters like thermal gradient (G), solidification velocity (V), cooling rate and solute content on the microstructural features of Mg-Al alloys. Directional solidification experiments and gravity experiments have been performed to explore the relationship between secondary dendrite arm spacing (SDAS) of Mg-Al alloys and the solidification parameters. The transition between cellular-columnar growth modes for Mg-Al alloys has also been investigated in context to the solidification parameters.

We have investigated the age hardening behavior of Mg-1.2at.%Sn (T5) based alloys, which are solution treatable at lower temperature as compared to the previously studied Mg-2.2Sn (T10) based alloys. To enhance the age hardening response with the reduced Sn content, Zn and Al were alloyed with the Mg-1.2at.%Sn alloy. Particularly, Mg-1.7Zn-1.2Sn-2.0Al alloy (TZA543) showed the peak hardness of 79 VHN at 200°C. The peak aged Mg-1.2Sn-1.7Zn-2.0Al alloy consisted of cuboida β₂′ precipitates with the size of less than 50 nm, rod shaped precipitates, and lathplate shaped Mg₂Sn phase.

In this paper, magnesium composites are synthesised through the addition of nano-alumina and copper micron size particulates in AZ31 magnesium alloy using the technique of disintegrated melt deposition. The simultaneous addition of Cu and nano-alumina particulates led to an overall improvement in both microstructural characteristics and mechanical response of AZ31. The 0.2% yield strength increased from 180 to 300 MPa (67%), while the ductility increased by almost 24%. The overall tensile properties assessed in terms of work of fracture improved by 66%. An attempt is made to correlate the tensile response of composites with their microstructural characteristics. The results suggest that these alloy composites have significant potential in diverse and wider engineering applications when compared to AZ31 alloy.

The effect of pre-ageing deformation on the precipitate diameter and length distribution in Mg-Zn(-Y) alloys was examined. Extrusion and pre-ageing deformation were used to introduce dislocations while precluding twin formation. Dislocations provided nucleation sites for rod-like ²′₁ precipitates, resulting in a refinement of the precipitate size distribution. In the binary alloy 5% strain reduced the average precipitate length from approximately 450nm to 60nm, and average diameter from 14 to 9 nm. Substantial reductions in precipitate size were also observed in the Mg-Zn(-Y) alloy. The average interparticle spacing of the rod-like precipitates was measured by Delaunay triangulation. The precipitate distribution was found to be significantly inhomogeneous, with measured interparticle spacings approximately 32% greater than predicted. For 5% pre-ageing deformation the yield strength of the binary alloy approached 95% of the ultimate tensile strength.

Mg_98.4Zn_xY_l.5La_0.1 (X=0.25 to 2.0 at.%) alloys were prepared by high-frequency induction melting in an Ar atmosphere. The microstructure 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. Specifically, for extruded Mg_98.15Zn_0.25Y_1.5La_0.1 alloy, the presence of this RE compound after heat treatment was responsible for the observed improvement in tensile and creep properties, which were similar to those of the Mg₉₆Zn₂Y₂ alloy. Excellent tensile yield strength was obtained in the extruded Mg_98.15Zn_0.25Y_1.5La_0.1 alloys, with a yield strength of 275 MPa at 523K.

In the present study, new AZ51/1.5Al₂O₃-1Ca magnesium nanocomposite was successfully synthesized by simultaneously adding 2 wt. % aluminum, 1 wt.% Ca and 1.5 vol.% nano-sized Al₂O₃ (50 nm) into AZ31 matrix using an innovative disintegrated melt deposition technique. AZ51/1.5Al₂O₃ nanocomposite was developed following the same processing route except adding Ca. All nanocomposite samples were then subsequently hot extruded at 400 °C and characterized. Microstructural characterization studies revealed uniaxial grain size, reasonably uniform distribution of intermetallics and minimal porosity. Results also showed that the Ca addition into AZ51/Al₂O₃ nanocomposite helped to reduce the average grain size. Physical properties characterization revealed that addition of Ca reduced the coefficient of thermal expansion when compared to Ca free nanocomposite. The presence of Ca also assisted in improving overall mechanical properties including microhardness, 0.2% yield strength and ultimate tensile strength while the ductility was compromised.

Mg-Zn binary alloys with concentrations between 0 and 2.8wt% Zn have been prepared and processed via hot rolling and annealing to produce specimens with a strong basal texture and a range of grain sizes. These have been deformed in tension, a condition in which the deformation is dominated by prismatic slip. This data has been used to assess the Hall-Petch parameter as a function of Zn concentration for deformation dominated by prismatic slip. Pure magnesium showed non-linear Hall-Petch behaviour at large grain sizes, and this is compared to the values for prismatic slip measured on single crystals. The differences between critical resolved shear stress measurements made through single crystal, polycrystal and mathematical modelling techniques are also discussed.

Effects of Ca element on microstructure and mechanical properties of ZA62 alloys were investigated by using zeiss microscope, scanning electron microscope equipped with an energy dispersive spectrometer, X-ray diffractometer, and electronic universal testing machine. The results show that Ca can significantly refine microstructure and cause the precipitation of Mg2Ca and Al2Ca phases on grain boundary of ZA62 alloys. The addition of Ca can improve the tensile properties of alloys at room temperature. When the content of Ca is 2%, good properties are obtained, the tensile strength and yield strength of Mg-6Zn-2Al-2Ca alloy reaches 240.79MPa and 82.78MPa respectively.

Ignition resistance and tensile properties of Mg-3Al-1Zn and Mg-6Al-1Zn (wt.%) alloys with combined addition of calcium and yttrium were investigated in the present study. The results of this study clearly show that the combined addition of calcium and yttrium can lead to significant increase in both ignition temperature and tensile properties, comparing to 2 wt.% Ca-added magnesium alloys with lamella-shaped eutectic phases. This is because the reduction of calcium content and the addition of a small amount of yttrium bring about a reduced amount of coarse Ca-containing phases and the formation of duplex protective oxide layers that effectively prevent oxygen penetration into the melt.

Phase constitution and microstructure of the Mg-5Sn-xSi-2Sr (x=0, 1, 2) alloys were analyzed by X-ray diffractometer, optical microscope and scanning electron microscope with an energy dispersive spectrometer. The tensile properties of the alloys were tested by electronic universal testing machine, and the fracture surfaces of the alloys were observed with scanning electron microscope. The results show that the microstructure of the Mg-5Sn-2Sr alloy consists of α-Mg, MgSnSr and Mg2Sn phases. The addition of Si element can promote the formation of Mg2Si phase on the grain boundary, and the content of Mg2Si phase increases with increasing the Si element. Mg2Si is a strengthening phase, which can effectively prevent grain boundary sliding and dislocation motion, and thus, the mechanical properties of the alloys were obviously enhanced. The mechanical properties of Mg-5Sn-2Si-2Sr alloy are better than other alloys, the tensile strength, yield strength, elongation and hardness are 147MPa, 110MPa, 5.0% and 47HB respectively.

By utilizing the unique electrochemistry of Mg, a thin organic film can rapidly be deposited on the surface of a Mg alloy by dipping the Mg alloy in a cathodic E-coating bath solution without applying a current or potential. The self-deposited coating is selectively formed on Mg alloy surfaces. Although the “electroless” E-coating pre-film is relatively thin, it can offer sufficient corrosion protection for Mg alloys in a chloride-containing environment. The stability of the film can be significantly improved after curing. The corrosion resistance of the substrate Mg alloy has an important effect on the corrosion protection performance of the coating. The coating is more protective on a corrosion resistant Mg alloy than on a non-corrosion resistant Mg substrate. The coating protection performance is also influenced by the substrate surface condition or pre-treatment process. Wet cleaning + heat-treatment may be a cost-effective surface preparation/treatment for the "electroless" E-coating in industrial applications.

The influence of galvanic current on cerium-based conversion coatings (CeCCs) for magnesium (AZ91, AZ31), aluminum (6016), and electro-galvanized steel (EGS) couples has been studied using zero resistance ammeter (ZRA) measurements in prohesion solution. The galvanic current measured between magnesium-aluminum, magnesium-galvanized steel, and aluminum-galvanized steel couples correlated with significant changes in coating morphology and deposition rate. The ZRA galvanic currents (mA) were 0.02 for 6016-EGS, 0.38 for AZ91-EGS, 0.72 for AZ91-6016, 1.08 for AZ31-EGS, and 1.08 for AZ31-6016 couples. The corrosion performance of the coated couples was evaluated by ASTM Bl 17 neutral salt spray testing. Cerium conversion coated couples performed better in salt spray testing compared to uncoated couples. The correlation of galvanic current, cerium deposition, and corrosion performance will be discussed.

Magnesium is the lightest structural metal with high specific strength and good mechanical properties. However, poor corrosion resistance limits its widespread use in many applications. Magnesium is usually treated with Chromate conversion coatings. However, due to changing environmental regulations and pollution prevention requirements, a significant push exists to find new, alternative for poisonous Cr6+. Therefore, we aim to improve corrosion resistance of anodic coatings on AZ31 alloys using low cost non-chromate electrolyte. Anodizing was carried out in alkaline solutions with tin additives. The effect of tin additives on the coating film was characterized by SEM and XRD. The corrosion resistance was evaluated using anodic and cathodic polarizations and electrochemical impedance spectroscopy (EIS). Corrosion resistance property was improved with tin additives and the best anti-corrosion property was obtained with addition of 0.03 M Na2SnO₃.3H2O to anodizing solution.

Cerium-based conversion coatings (CeCCs) were deposited onto AZ31B magnesium alloy substrates using a spontaneous reaction of CeCl₃, H₂O₂ and gelatin in a water-based solution. The coating thickness was adjusted by controlling the immersion time in the deposition solution. Prior to deposition, the AZ31B substrates were treated using an acid pickling in nitric acid and then an alkaline cleaning in sodium metasilicate pentahydrate. After deposition, the coated samples were immersed in a phosphate bath that converted cerium oxide/hydroxide into cerium phosphate. Electrochemical impedance spectroscopy, potentiodynamic polarization and neutral salt spray testing studies indicated that ~100 nm thick CeCC had better corrosion performance than ~400 nm coatings. Characterization of the CeCCs by transmission electron microscopy (TEM) revealed a three layer structure with different compositions.

Due to the good specific strength and the moderate corrosion rate Mg-RE alloys have found growing interest for medical applications as implant material. In this study extruded MglOGd has been investigated, once by potentiodynamic method and again under cyclic load. Corrosion exposure is known to reduce the fatigue strength strongly. The data are compared to MglOGd as-cast condition and show an increase in fatigue properties and similar corrosion behavior. The form of corrosion and the influence of the temperature during voltammetric tests are discussed. A temperature increase from room to body temperature accelerates the corrosion processes. Due to stress peaks under load pitting corrosion is not preferred. The influence of the microstructure on the corrosion form is discussed. Casted MglOGd reveals large dendrites, which change into a globular microstructure during extrusion resulting in improved mechanical properties, mostly the elongation to fracture up to 20 %.

During the production of magnesium and its alloys, the melt is in contact with steel at various stages of the process. Steel can be eroded and corroded through chemical reactions with molten magnesium and the protective gases such as SF6 or SO2. The dissolution rate and corrosion mechanism of steels in molten magnesium were investigated by the rotating cylinder method. The corrosion behavior of four steel grades, i.e. high carbon and low carbon steel, stainless steel 316 and 400 were examined for AZ31 melt under N₂-l% SF₆ gas atmosphere. The corrosion rates were found to be different depending on steel grades. It is found that the corrosion mechanism of steels in magnesium melts involves a two-stage process consisting of oxidation of Fe and its reduction by magnesium melt.

Mixed-metal joining, especially between magnesium and steel, is one of the critical technologies in achieving light-weighting vehicle body construction. However, galvanic corrosion between mixed metal joints is inevitable but not well quantified. In this study, 1.6 mm thick Mg AZ31B-H24 was joined to 0.8 mm thick hot-dipped galvanized (HDG) mild steel by ultrasonic spot welding in lap-shear configuration. No specific corrosion protection was applied in order to study worst-case conditions for corrosion behavior. The approach used an automotive cyclic corrosion test — Ford Arizona Proving Ground Equivalent Corrosion Cycle (APGE), which includes cycles of dipping in a salt bath, air drying, then holding in constant humidity environment. Lap-shear strength of the joints decreased linearly with the exposure cycles. All the joints were either taken out of test cycle for mechanical test or they separated within the humidity chamber before 25th cycle. X-ray diffraction analysis confirmed the formation of Mg(OH)2 deposit in the crevice between the AZ31 and steel sheets and on the surface of the AZ31. The deposit grew thicker with cycles with exerting enough force to deform the AZ31 and HDG steel and causing a gradual opening of joints. The corrosion of the AZ31 was localized and nonuniform. The most severe corrosion occurred not at the intersection of AZ31 and the steel but rather 15–20 mm away from the spot welds.

The influence of the ß-Mgi7Ali2 phase and, to a lesser degree, the solute content in the a-Mg matrix on the corrosion resistance of Mg alloys was investigated by cyclic potentiodynamic polarization and potentiostatic polarization tests using AZ31B, AM30 and AM60B in contact with a mildly aggressive near-neutral saline solution. Results showed that all three Mg alloys corrode in a partially protective state under open circuit conditions in the test solution. It was also determined that the surface film formed on each exhibits a similar apparent breakdown potential. This indicates that microstructure parameters such as the presence of the ß-phase and the solute content of the a-Mg matrix do not strongly influence the factors controlling the breakdown of the surface films formed. It was further determined that the moderately improved protectiveness of the surface film, rather than the distribution of the ß-MgnAli2 phase, is responsible for the improved (short-term) corrosion resistance exhibited by AM60B at potentials below the breakdown potential.

The corrosion resistance of Mg-Al alloys deteriorates significantly with increasing copper content. Consequently, the tolerance limit of copper is commonly fixed at less than 300 ppm in Mg-Al alloys to ensure they have sufficient corrosion resistance. However, it is desirable to use higher copper tolerance limit in actual operations. To realize this, it is very important to prevent the deterioration in the corrosion resistance with increasing copper content. In this study, Mg-Al alloys with different aluminum, zinc, and copper contents were casted by high-pressure die casting and the corrosion resistances of the castings were investigated. The corrosion resistance of Mg-9% Al alloys decreased significantly with increasing copper content. However, adding zinc to copper-rich alloys prevented the reduction in the corrosion resistance due to copper. The corrosion rate of Mg-Al alloys containing 0.5% copper and 3% zinc was minimized at an aluminum content of 9%. The corrosion resistance of Mg-Al alloys containing copper and zinc was highest at a zinc content of over 3% and an aluminum content of about 9%.

The influence of rolling temperature and the effect of strain rate on the microstructure of AZ31B Mg alloy were determined in order to improve its formability. A plate of AZ31 alloy was found to be sensitive to strain rate at high temperature and anisotropy was adversely impacted in cold rolling sheets. Thus, AZ31B has better workability within the temperature range of 200 to 250 °C, due to the grain refinement, caused by recovery and dynamic recrystallization. The effect of rolling temperature was studied on recrystallized sheets (2 mm in thickness) which were deformed by rolling at different temperatures (25, 100, 200 and 250 °C) and the effect of strain rates was evaluated on two different rolling speed (10 and 20 rpm). The microstructural characterization was achieved using several complementary techniques of microstructural analysis, such as optical microscopy, scanning electron microscopy, X-ray analysis by energy dispersive, X-ray diffraction and microhardness.

The formability of four Mg AZ31B sheets produced by either direct chill or twin roll continuous casting, and having different initial grain sizes, was investigated at 400 °C and 5x10−3 s−1 using the pneumatic stretching test. Blanks were pneumatically bulged through four elliptical die inserts, with aspect ratios ranging between 1.0 and 0.4, producing ellipsoidal domes with different biaxial strain combinations. Testing was carried out in two ways: with the major strains being aligned either along or across the rolling direction of the material. Strain combinations were measured in the deformed specimens, and the forming limit curves were constructed for each of the four sheets in two orientations. The results show great impact of sheet orientation on material formability limits. Additionally, the results reveal significant differences between the four sheets; those differences were correlated back to disparities in grain structure and material inhomogeneities.

An experimental investigation of texture evolution during high temperature compression of Mg-3Sn-2Ca (TX32) alloy containing 0.4%A1 using electron back scatter diffraction (EBSD) technique is reported. Isothermal uniaxial compression tests were performed in the temperature and strain rate ranges 300–500 °C and 0.0003-10 s-1 to examine the influence of processing conditions on the dynamic recrystallization (DRX) behavior and texture evolution. The onset of DRX during compression at low temperatures (300 and 350 °C) and low strain rates (0.0003 and 0.001 s-1 ) gave rise to a fine, partially recrystallized and necklaced grain microstructure, with the basal poles located at 15–30° from the compressive direction although they were split. Specimens deformed at temperatures higher than 450 °C resulted in a fully recrystallized microstructure and an almost random crystallographic texture. It is clear from Schmid factor analysis that the contribution of pyramidal slip system is significant for deformation at temperatures above 450 °C.

Wrought magnesium alloys, such as AZ31 sheet, are of considerable interest for light-weighting of vehicle structural components. The poor room-temperature ductility of AZ31 sheet has been a hindrance to forming the complex part shapes necessary for practical applications. However, the outstanding formability of AZ31 sheet at elevated temperature provides an opportunity to overcome that problem. Complex demonstration components have already been produced at 450°C using gas-pressure forming. Accurate simulations of such hot, gas-pressure forming will be required for the design and optimization exercises necessary if this technology is to be implemented commercially. We report on experiments and simulations used to construct the accurate material constitutive models necessary for finite-element-method simulations. In particular, the effects of strain and stress state on plastic deformation of AZ31 sheet at 450°C are considered in material constitutive model development. Material models are validated against data from simple forming experiments.

Interrupted uniaxial compression tests were performed on an extruded Mg-Al-Mn magnesium alloy (AM30) at 450°C and various strain rates of 0.001 s−1, 0.1 s−1, 0.5 s−1 and 0.8 s−1. Texture and microstructure evolution were examined using electron back scattered diffraction (EBSD) and X-ray diffraction (XRD) techniques. Twinning was found to be ubiquitous at high temperature but provided that a highly enough strain rate was applied. The results show that the deformation microstructure evolves with strong dependence on the strain rate as twinning triggers and non-basal slips become harder. Schmid’s factor and slip traces analyses elucidated the driving forces controlling dynamic recrystallization mechanisms and emphasized on the role played by extension twinning and non-basal slips.

In this work, the effects of strain rate and initial texture on the flow behaviour and microstructure evolution on AZ31 Mg alloy were studied by compression tests. Cast plates were, homogenized and hot rolled and then compression tests were performed on samples with longitudinal axes either parallel to the rolling direction (RD) or the normal direction (ND). Compression tests were performed to various strains and samples were quenched to investigate the effect of dynamic recrystallization on the texture and microstructural evolution. Results show that for the samples machined in both rolling and normal direction, the rate of texture evolution is increased by increasing strain rate. The deformation mechanism was changed by increasing the strain rate for ND samples and at strain rate of 1 s-1 from slip dominated flow to twin dominated flow. By using EBSD, the deformation mechanism and twinning types were investigated and double and tension twins were detected.

Based on thermodynamic calculations, two micro-alloyed Mg-Al-Ca alloys, Mg-0.3Al-0.2Ca and Mg-0.1Al-0.5Ca, were selected in terms of the equilibrium precipitation temperatures of Al₂Ca and Mg₂Ca, respectively. The basic idea is to form precipitates during hot compression to examine their effect on hot deformation. Both alloys, cast by copper mould, were solution treated at 500°C for 8 hours to dissolve eutectic precipitates which formed in the as-cast microstructure, and then isothermally heat treated at 350°C for different times. SEM analysis of the heat treated alloys generally agreed with thermodynamic calculations. Hot compression tests were also conducted on solution treated alloys at 350°C with a strain rate of 0.01s-1 and different strains (10%, 30%, 60%, and 90%). The precipitation behaviour and microstructural evolution which was characterized by optical microscopy and SEM with BSE and EDS detectors during isothermal heat treatment and hot compression were compared.

Growing use and development of lightweight Mg alloys has been the catalyst for more fundamental research in Mg based material systems to be completed. Zinc is one of the most common alloying elements in Mg alloys. Phase layer growth and interdiffusion in the binary Mg-Zn system was investigated utilizing solid-to-solid diffusion couples. Anneals were carried out at 295°, 315° and 325°C for 384, 168 and 120 hours, respectively. The diffusion microstructures that developed were examined by optical and scanning electron microscopy (SEM). Concentration profiles were determined using X-ray energy dispersive spectroscopy (XEDS) and electron microprobe analysis (EPMA). The phases observed were the Mg solid solution, Mg₂Zn₁₁, MgZn₂ and Mg₂Zn₃ in all three couples as well as the high temperature, Mg₅₁Zn₂₀ phase in the 325°C couple. The MgZn₂ phase was observed to grow the thickest layer, followed by the Mg₂Zn₃ and the Mg₂Zn₁₁ phases. Parabolic growth constants were determined for each phase. Activation energies for the growth of the intermetallic phases were calculated as 105 kJ/mol for the Mg₂Zn₃ phase and 207 kJ/mol for the MgZn₂ phase.

The evaluation of plastic deformation processing of materials has been based mainly on uniaxial tensile tests. However, for the analysis of multiaxial stress conditions in sheet-metal plastic forming, more complex tests, such as the controlled biaxial test with cruciform specimens, are required. In this report, we examine the relationship between the biaxial deformation behavior and microstructure of AZ31 magnesium alloy for initial strain rates of 3.0 x 10-3 s−1 and 2.8 x 10−4 s−1 at 573 K and 623 K using cruciform specimens. The results show that the flow stress increases with decreasing sheet thickness, and the occurrence of tensile twins is confirmed during biaxial tensile deformation at an elongation of 30 % in a cross-section of a specimen under 623 K for a strain rate of 2.8 x 10−4 s−1. This deformation behavior and evolution of the micro structure is unique in biaxial tensile tests, and is not recognized in uniaxial tensile tests with the same elongation. Since this controls the width direction of the specimen during deformation, we can only guess that the plate thickness direction can be deformed freely and without restraint. In other words, for biaxial tensile test conditions, the transition point of the microstructure under the influence of the constraint of grain boundary sliding is at 623 K for a strain rate of 2.8 x 10−4 s−1.

Magnesium alloys have found increasing application in the transportation industry due to their low weight and high strength. However, wider application is hindered by limited ductility. Microstructural features, such as porosity, brittle eutectics, and grain size, can significantly influence the macroscopic response of a component. These features can vary widely throughout a component. Our approach to studying the microstructures influence on bulk properties begins with measuring microstructural features in different regions of a component. These measurements are used to create statistically equivalent, 3D synthetic samples of the microstructure. The synthetic microstructures are meshed using finite elements and used to simulate the response and investigate the influence of specific features. We will demonstrate how the digital microstructure samples are generated, how variations in microstructural features influence the bulk properties, and how this methodology can be used to predict component performance and optimize processing.

X-ray diffraction and hardness measurements are used to study recrystallization in fine-grained AZ61L sheet produced by warm-rolling of Thixomolded® material. The as-rolled sheet is partially dynamically-recrystallized, with a strong basal texture and a sub-micron grain size. Significant increases in ductility with moderate reductions in tensile strength were produced by annealing at temperatures greater than 250 °C. A weakening in basal texture was observed in samples annealed at over 250°C. Static recrystallization was determined to be responsible for the reduction in texture and associated increase in elongation.

The mechanical properties, such as strength and fracture toughness, were investigated using caliber rolled Mg-6wt.%Al-1wt.%Zn (AZ61) alloy, which is the material consists of a constrained plane other than the rolling direction plane and is compressed non-simultaneously from two directions. The initial micro structural observations showed that the caliber rolled AZ61 alloy had a high fraction of low-angle grain boundaries and an average grain size of 2.2µm. In addition, particles with an average size of 100 nm existed in the matrix. This alloy showed a yield strength of 423 MPa and a fracture toughness of 34.1 MPam½. A combination of grain refinement, formation of low-angle grain boundaries and dispersion of fine particles is one of the effective micro structural controls to produce the magnesium alloys with fracture toughness similar to the conventional high strength aluminum alloys.

Direct extrusions of commercial casting AZ31 alloy were carried out at elevated temperatures with different extrusion velocities. Microstructure and texture distribution of extruded rods were investigated with optical microscopy (OM) and electron backscattered diffraction (EBSD). Tensile tests were conducted at room temperature using samples from both casting billets and extruded rods. The experimental yield strength can not be solely described by average grain size. In this paper, the grain size and orientation in the extruded samples were characterized by EBSD, and Hall-Petch equation was applied to each individual grain with the input from EBSD results (individual grain size and orientation). The yield strength of tensile sample (polycrystalline aggregate) and individual grain was related by Taylor assumption. The predicted yield strength showed the same trend as experiment results.

The most common commercially available rolled magnesium sheet alloy is AZ31B (typ. 3% Al, 1% Zn, 0.4% Mn, balance Mg). One of the often-cited shortcomings of this sheet is its limited formability at room temperature, which is attributed in part to a strong crystallographic texture in which the basal planes of the hexagonal unit cell are parallel to the plane of the sheet. Attempts have been made to avoid this rolling-induced texture by changing either (a) the alloy composition or (b) the rolling process. Specifically, sheet has been made using the conventional rolling practice, but changing the alloy to ZEK100 (typ. 1% Zn, 0.2 % Nd, 0.2% Zr, balance Mg), or by keeping the AZ31B composition but rolling at a much higher temperature. In this report, both types of sheet are evaluated and compared with conventionally rolled AZ31B sheet. Both show reduced texture and attractive tensile properties, and therefore both are expected to show greater room-temperature formability than conventionally rolled AZ31B.

ZK60(Mg-Zn-Zr) alloys possessed precipitate hardening behavior during aging, and the frequency and size of rod and disc shaped precipitates changed with aging. Strain hardening and texturing of ZK60 alloys were investigated during uniaxial warm compression. Uniaxial warm compression tests were carried out at various deformation rates and temperatures. Heat treatments of solid solution (T4) and aging (T6) affected flow stress behaviors. Aging heat treatment samples (T6) had higher yield stresses and lower strain hardening rates than solution heat-treated samples (T4). Both hardening by deformation and softening by dynamic recrystallization (DRX) at elevated temperatures were observed. Most of precipitates formed during aging contained Zn and Zr elements. Linear strain hardening behavior was examined using a visco-plastic self consistent (VPSC) model.

The strain-rate effects of cast magnesium alloys were investigated with uniaxial compression and compressive impact testing. The compressive material response of specimens cut from sand cast AZ91, AE44, and AM60, and high-pressure die-cast AM60 was determined for strain-rates ranging from quasi-static levels to typical rates experienced during crash situations. Several different constitutive material models (Johnson-Cook, Cowper-Symonds, etc.) were used in an attempt to characterize the experimental results. These material models are typically available in commercial finite-element packages and can be used to model the resulting material response of die-cast automotive components produced with these alloys to more complex loading conditions. The resulting deformed microstructures and fracture surfaces of each alloy at different strain-rates were also analyzed.

Mg and its alloys have drawn great interest in the materials community due to their high specific strength and potential applications in industry. In this work, we present some experimental results on two Mg-alloys, AMX602 and AZXE7 111. We have evaluated the dependence of the mechanical properties of these alloys on the extrusion temperatures under both quasi-static (strain rate ~1*10-3 s-1) and dynamic (strain rate ~4*10-3 s-1) uniaxial compressive loadings. We have observed that the quasi-static yield strength of AMX602 exhibits a slight dependence on the extrusion temperature, whereas the ultimate strength and the deformation-to-failure do not show such dependence. On the other hand, the dependence of the mechanical properties of AZXE7111 is much more complicated. We have also found that the deformation-to-failure of both alloys increases at increased strain rate. For comparison, we have tested two conventional Mg-alloys, WE43 and AZ91C under very similar conditions. We have found that AMX602 and AZXE7111 show significantly improved mechanical properties compared to WE43 and AZ91C under either quasi-static or dynamic loading. Such knowledge is particularly important for applications involving impact loading.

Friction Stir Processing (FSP) to partial sheet thickness can be utilized to engineer unique microstructures in metallic alloys. These composite microstructures consist of three distinct layers associated with stirred, transition and core micro structural regions. The stirred region is of particular interest where severe plastic deformation imparted by the rotating and translating FSP tool under frictional heat leads to grain refinement down to ~ 1 urn grain size. In this work, partial depth penetration into thixomolded AZ91 Mg plate from the top and bottom surfaces by friction stir processing is explored. Furthermore, low temperature aging treatments are applied to the processed material. The present results with AZ91 Mg show that FSP processed material exhibits higher strength (> 300 MPa), and improvement in ductility (> 7 % tensile elongation). It is found that in addition to Hall-Petch strengthening produced by ~ 1 um grain size in the stirred region, the enhanced strength levels and ductility are strongly influenced by dispersoids of the intermetallic precipitates found in this alloy.

In this paper the fatigue behavior in friction stir spot welded coupons of magnesium AZ31 alloy manufactured under different welding conditions are investigated. Two sets of lap-shear coupons were welded based on varying the plunge depth and tool geometry. Metallographic analysis of the untested lap-welds revealed differences in microstructural and geometrical features. Results from the load controlled cyclic tests showed that one set of welds exhibited better fatigue performance compared to the other set. Optical fractography of the failed fatigue coupons revealed that fatigue cracks initiated at the weld interface in both sets of coupons. However, the fracture mode showed variability between the two sets of coupons. As such, the main conclusion of this study is that the effective top sheet thickness, which is largely determined by the shoulder plunge depth, plays a significant role in the fatigue behavior of the friction stir spot welds in magnesium alloys.

To facilitate the use of magnesium and its alloys within automotive structures, it is necessary to characterize their possible mechanical property degradation in typical application environments. This work examines the effect of exposure to NaCl-based corrosive environments on the mechanical properties of friction stir welded (FSW) AZ31B magnesium alloy sheet. A complete microstructural, electrochemical, residual stress and mechanical property characterization of the as-received FSW panels was performed. Samples were subsequently exposed to 0.01 M and 0.1 M NaCl solutions at the corrosion potential for 24 h and any changes in mechanical properties, as a function of exposure, to the corrosive environment monitored. Friction stir welded panels exhibited large decreases in ductility compared to the base AZ31B material. Exposure to 0.1 M NaCl for 24 hours resulted in a degradation in mechanical properties for the base material, as well as the friction stir welded panel, whereas no significant changes were found for samples exposed to 0.01 M NaCl for 24 hours.

When Mg or Mg-alloys are reinforced with T1₂AlC — using a simple pressureless melt infiltration method — the result is nanocrystalline, nc, Mg-matrix composites, with outstanding mechanical properties. As an added bonus, the nc Mg-matrix is extraordinarily thermally stable. When AZ61 is used to infiltrate the T1₂AlC preforms, ultimate tensile stresses of 800 MPa are achieved. The reasons that lead to the formation of the nc-Mg are as of yet not understood. In this study, the different composites' microstructures are investigated by X-ray diffraction, scanning and transmission electron microscopy. A correlation was found between the presence of oxygen and the nc Mg grains. Nanometer sized Mg grains were also found in between some of the T1₂AlC layers.

Deformation behavior and formability limits of thixo-molded Mg AZ61L alloy and regular Mg AZ61 alloy sheets (with similar chemical compositions except for Mn content) were experimentally investigated at elevated temperature. Tensile (uniaxial), hydraulic bulge (biaxial) tests as well as closed-die hydroforming tests were conducted to understand the material behavior at temperatures ranging from 25 °C to 300 °C and strain rates at 0.0013, 0.013 and 0.13 s−1. It was found that flow stress and the maximum plastic strain increased with increasing temperature and decreasing strain rate. Closed-die warm hydroforming tests were also performed to determine the process window for the sheet alloy. Die cavity filling ratios and thinning of the sheet blanks were measured with non-contact optical photogrammetry. Results indicated that lower strain rates and higher temperatures increase formability, particularly above temperatures of 200 °C.

In this present study, the effects of high-temperature shot peening (HSP) on the surface characteristics and fatigue properties of forged AZ31 magnesium alloys were investigated. The HSP process was performed with a low-carbon steel ball under a shot pressure of 0.2 MPa and time of 6 s at a temperature of 523 K. Gradable microstructures were formed in the near-surface region, about 150 µm from the surface edge. These were composed of an ultra-fine-grained region, a residual working strain region, and a twin region. The HSP-processed material showed increased fatigue strength compared with the non-HSP-processed material. From the measurement of the crack-propagation rate, it was found that the improvement in fatigue properties led to a delay in the crack-propagation rate in the ultra-fine-grained region and the residual working strain region.

It has been previously shown that separate additions of 2% rare earth elements (RE) and 0.6% Zr to the AZ91 base alloy improve creep properties. However, in this investigation using impression creep method, it is shown that simultaneous addition of these elements not only cannot improve creep properties but also leads to its deterioration. According to the creep deformation mechanism of the base alloy and microstructural evidences, it is believed that this drop in creep resistance mainly stems from depletion of grain interiors and the areas adjacent to grain boundaries from aluminum solute atoms. Reduction of aluminum content as solute atoms is due to the great affinity of RE and Zr atoms for aluminum. This leads to the weakening of Al solute atoms role as obstacles against dislocation movement, even though the volume fraction of the thermally stable particles tends to be high.

Mg-Zn-Y alloys are well known to possess greatly enhanced strength during plastic deformation because of the presence of kink bands in the LPSO phase and refinement of the grains of the alpha Mg phase. On the other hand, Mg-rare earth (RE) and Mg-Zn-RE alloys with a long period stacking order (LPSO) phase show a high tensile yield strength when subjected to an extrusion process but it is not known whether the LPSO and alpha Mg phases develop during plastic deformation. We examined the effect of the finely dispersed LPSO phase and the alpha Mg phase on the development of high strength in sheets of Mg₉₆Zn₂Y₂ subjected to a few passes of rolling. The mechanical properties and thermal stability of the alloy were also investigated. The tensile yield strength of rolled sheets of Mg₉₆Zn₂Y₂ was 360 MPa and its elongation was 5% when the material was subjected to thermomechanically controlled processing at 673 K with a four-pass rolling schedule. However, the tensile yield strength decreased and the elongation increased at annealing temperature of 623 K or above, because of the presence of grain growth in the alpha Mg phase and the restoration of kink bands in the LPSO phase.

High strain rate deformation of WE43 magnesium alloy was carried out by high velocity impacts, and the characteristics and mechanisms of microstructural damage were examined. Six samples were subjected to a variety of high velocity impact loadings that resulted in both partial and full damage. Optical, scanning and transmission electron microscopy analyses were performed in order to identify regions of shear localization. These regions were used to map, both quantitatively and qualitatively, the effects of deformation on the microstructure. Shear localization was observed in every sample, and its depth was measured. Evidence of shear localization was observed to a greater extent in samples with partial damage while fracturing was observed more frequently in samples with full damage.

Mg-(9-x)Sn-xAl-lZn (x=1, 2, 3 and 4 wt.%) alloys were subjected to indirect extrusion, and the microstructure and mechanical properties of these as-extruded Mg-Sn-Al-Zn (TAZ) alloys were investigated. The TAZ alloys contain only fine Mg₂Sn second-phase particles in the a -Mg matrix, and the amount of precipitates increase with increasing Sn contents. In addition, the TAZ 811 alloy shows finer grain structure than the TAZ 541 alloy due to a larger amount of Mg₂Sn particles, which act as nucleation sites for recrystallization and/or prevention of grain growth by the pinning effect. The textures of the alloys show a typical basal pole orientation and an unusual <11-20> component in which one axis of the HCP unit cell is parallel to the extrusion axis. Tensile yield strength increases with Sn content, while ultimate tensile strength is almost identical due to the increased strain hardenability with Al content. The tension-compression yield asymmetry decreases with reducing Sn content, which is mainly due to the decrease in the amount of particles promoting twin nucleation.

Magnesium alloy sheet metal is potentially attractive for use in automotive structural applications due to its high strength-to-weight ratio. However, application has been hindered by the low room-temperature formability of typical sheet alloys. One approach to effectively increase formability is to change the forming process from one which involves a single stamping hit to one which utilizes two hits plus an intemediate anneal (i.e., “preform anneal process” ). The purpose of the intermediate anneal is to restore some of the softness and ductility which were reduced by deformation during the first hit.In this report, the preform annealing behavior of three rolled magnesium alloy sheets was studied using uniaxial tensile tests. The sheets studied were: conventionally rolled (CR) AZ31B, CR ZEK100, and specially rolled (SPR) AZ31B. The preform annealing process was found to increase the total elongation of all three sheets compared to the elongation in the annealed O-temper. The CR ZEK100 with a thickness of 1.5 mm showed more attractive tensile properties than the 1.6 mm CR AZ31B. Although the SPR AZ31B has a thickness of only 0.7 mm, it still has elongation comparable to the 1.6 mm CR AZ31B

This research examined in-situ creep behavior of three extruded high performance magnesium alloys (AE42, AJ32 and ZE10). Neutron diffraction was used to measure compressive creep behavior at 175°C in the extrusion direction. The AE42 and AJ32 alloys exhibited higher creep strains than the ZE10 alloy. The highest strain was recorded for AE42 (2.4%), while ZE10 exhibited greatest creep resistance (0.2% strain). Microstructure analysis has shown that the distribution and composition of secondary phases was critical for creep resistance. The aluminum containing alloys had acicular and globular intermetallics, whereas the ZE10 alloy contained fine and irregular intermetallics dispersed along grain boundaries, effectively contributing to pinning of grains under high temperature loads. Significant grain re-crystallization was also observed in the aluminum containing alloys, but was absent in ZE10.

The GREEN METALLURGY Project, a LIFE+ project co-financed by the EU Commission, has just concluded its first year. The Project seeks to set manufacturing processes at a pre-industrial scale for nanostructured-based high-performance Mg-Zn(Y) magnesium alloys. The Project’s goal is the reduction of specific energy consumed and the overall carbon-footprint produced in the cradle-to-exit gate phases. Preliminary results addressed potentialities of the upstream manufacturing process pathway. Two Mg-Zn(Y) system alloys with rapid solidifying powders have been produced and directly extruded for 100% densification. Examination of the mechanical properties showed that such materials exhibit strength and elongation comparable to several high performing aluminum alloys; 390 MPa and 440 MPa for the average UTS for two different system alloys, and 10% and 15% elongations for two system alloys. These results, together with the low-environmental impact targeted, make these novel Mg alloys competitive as lightweight high-performance materials for automotive components.

Mg-1% Mn (Ml) and Mg-1% Mn-1.6% Sr alloys have been subjected to hot extrusion and the effect of extrusion conditions on the microstructure and texture has been investigated. Addition of Sr to Ml alloy refines the extruded microstructure. Two different ram speeds of 4 mm/s and 8 mm/s and two different temperatures of 300°C and 350°C have been used in the study. The extent of recrystallization increases with increasing ram speed. The texture of extruded Ml weakens with Sr addition. The mechanism of texture weakening is suggested to be PSN with formation of new grains having orientations different than that of parent grains.

The microstructure of the Mg—6%Gd-3.7%Nd-0.3%Zn-0.18%Y-0.15%Zr (%wt) alloy has been investigated after solution treatment at 540°C for 24hr followed by isothermal aging at 175°C up to 32 days by using of Vickers hardness, optical microscopy, scanning electron microscopy equipped with EDS, X-ray diffraction and transmission electron microscopy. It was observed that the homogenized alloy contained primary α-Mg solid solution, eutectic structures, cuboid shaped phases and Zr-rich clusters. The eutectic structures were the products of a ‘quasibinary eutectic reaction’ L→α-Mg+β-Mg₅RE. The eutectic phase was characterized to be of Mg₅Gd prototype with the composition Mg₅(Gd_xNd_1-x, x≈0.2). The cuboid shaped phases, with the composition Gd₄(Nd_xY_1-x, x≈0.5), grew during aging and reached ~3μm average size. Precipitation of β" and β' phases during aging was observed. The maximum microhardness was achieved after 16 days of aging.

The hot and cold rolled microstructures of a Mg-2.9Y alloy were examined by means of metallography, X-ray texture measurement and EBSD technique. It is found that Y in solid solution suppresses dynamic recrystallization even at 450 °C. After rolling, a heterogeneous microstructure containing twins and bands is obtained. The bands were found to originate form double and compression twins, and are locations of high-stored energy. The bulk texture of the rolled material consists of the typical basal component, and also a component from the ND towards the TD. The latter component results from the presence of parent grains with c-axis along the TD. The strain is accommodated in such parent grains by extension twinning and possibly prismatic slip.

Magnesium alloys have inspired a significant amount of attention from researchers all over the world for cardiovascular and orthopedic applications due to their light weight, mechanical integrity and degradation behavior. In this investigation, cast manufactured binary, ternary and quaternary magnesium alloys were studied for their degradation behavior by potentiodynamic polarization tests in phosphate buffer saline solution (PBS) and PBS containing amino acids (cysteine, C and tryptophan, W) at 37 °C. Electrochemical impedance spectroscopy (EIS) tests were performed to determine the charge transfer resistance and immersion tests were performed to assess corrosion rate and hydrogen evolution from the alloys. Furthermore, the surface morphology and surface chemistry of the alloys were observed by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

One of the current main challenges in green-power storage and smart grids is the lack of effective solutions for accommodating the unbalance between renewable energy sources, that offer intermittent electricity supply, and a variable electricity demand. Energy management systems have to be foreseen for the near future, while they still represent a major challenge. Integrating intermittent renewable energy sources, by safe and cost-effective energy storage systems based on solid state hydrogen is today achievable thanks to recently some technology breakthroughs. Optimized solid storage method made of magnesium-based hydrides guarantees a very rapid absorption and desorption kinetics. Coupled with electrolyzer technology, high-capacity storage of green-hydrogen is therefore practicable. Besides these aspects, magnesium has been emerging as environmentally friend energy storage method to sustain integration, monitoring and control of large quantity of GWh from high capacity renewable generation in the EU.

In order to reduce the oxidizing and volatilizing caused by Mg element in the traditional methods for synthesizing Mg₂Si compounds, solid state phase reaction at low temperature was introduced by microwave field. XRD was used to characterize the powders. At the same time, the influences of parameters during the synthesis processing were discussed. The results suggest that the heating profile is also dependent on the initial green density and higher green density provides lower heating rate while power setting are fixed and the oxidation of Mg can be rest rained by changing microwave heating programs. It was found that high purity Mg₂Si intermetallic compound can be obtained with excessive content of 8at% Mg from the stoichiometric Mg₂Si, 853K and 30min.

Magnesium-carbon powders and Magnesium-lithium powders were used as the anode materials for lithium ion batteries to investigate the structure and electrochemical behavior in room temperature. The composition of Mg-C powders contained 1:1 and 9:1. The powders and the thermal evaporated films of Mg-10Li were compared with Mg-C systems. In addition, Mg-10Li thermal evaporated film was used as the experimental materials to process the annealing treatment. The results show that Mg-C powders system had the interface effect of a Cu foil to reduce the electrochemical reaction. With increasing the carbon powder content, the charge-discharge characteristics of Mg-C powders was raised. Notably, the Mg-10Li specimen had better cycling properties than that of Mg-50C (1:1). After annealing at 200 °C for 1hr, Mg-10Li alloy film not only increased the capacity, but also improved the charge-discharge cyclability.

The solid oxide membrane (SOM) process has been used to produce magnesium by direct electrolysis of its oxide. In this process MgO is dissolved in a molten CaF₂-MgF₂ flux and an yttria-stabilized zirconia (YSZ) SOM membrane separates the cathode and the flux from the anode. YSZ membrane stability limits the operating life of the SOM electrolyzer. The YSZ membrane is known to degrade due to diffusion of yttrium into the flux. Yttrium diffusion can however be decreased by adding YF₃ to the flux. This study investigates the long-term stability of the YSZ membrane. Yttrium composition profiles in the YSZ membrane were determined using WDS as a function of immersion time and YF₃ content in the flux. An analytic solution to the diffusion equation was used to model the diffusion process. This study allows the determination of the optimum YF₃ content needed in the flux to minimize yttrium diffusion and increase membrane stability.

The overall utilization of magnesium and other metals should be systematically considered during the exploration of deficient garnierite .In this paper the thermodynamic analysis of the carbothermic reduction process for extracting metal magnesium from garnierite in vacuum was carried out to investigate its feasibility. The calculation results indicate that it is feasible technically that the carbothermic reduction process for extracting metal magnesium from garnierite in vacuum. Under the temperature of 1500 °С and vacuum degree is less than 300Pa, metal magnesium was obtained. The Nickel content in residue is more than twice as garnierite ore.

In this study, the mechanism of the carbothermic reduction process to extract magnesium from magnesia and the reversion reaction in vacuum were investigated. The carbon monoxide (CO) content of the gas, phases of the condensing product, surface morphology of the reduction slag and phase of the distillation product were measured by means of gas chromatography (GC), XRD, and SEM. The experimental results indicated that Mg was generated by magnesia and carbon at 1623K and 30~100Pa in the carbothermic reduction process.The main gas in carbothermic reduction process is carbon monoxide, no carbon dioxide occurred at any reaction time, the reduction reaction is MgO(_S)+C(_S)=Mg(_g)+CO(_g) The gas-phase reversion will commence as soon as the saturated gas mixture is cooled. The reversion reactions are favored below 1373K.The distillation product by vacuum distillation process produced high purity metal magnesium product, it can be deduced in reversion reaction which occured at low temperature and 30~100Pa during carbothermic reduction. The reversion reaction was calculated, which gave the peak value у less than 9%.

Macro test samples of magnesium alloy AM60B were melted and quenched at maximum instantaneous cooling rates ranging from -5°C/s to -500°C/s and the resultant cooling curves were analyzed. Characteristic reactions on these curves corresponding to formation of individual phases were identified with the aid of literature data as well as metallographic and micro-chemical analysis. The results indicate that these phases, their size and location in the micro structure, their chemistry and their relative proportions all change in response to the increase in the cooling rate. These rapid cooling rates are typical of real industrial solidification processes such as die casting. These findings can be used to improve future computer models of casting solidification processes for magnesium and for other alloys.

Friction stir welding (FSW possesses more advantages than other traditional welding processes because it is a solid-state joint process [1]. In addition, friction stir processing is adopted as a new surface modification approach. It is acceptable that the dynamic recrystallization phenomenon during FSW/FSP results in the generation of fine and equiaxed grains in the stir zone [2–3].

Pure magnesium (Mg) is recycled from 19g of partially oxidized 50.5 wt.%Mg-Aluminum (Al) alloy. During the refining process, potentiodynamic scans (PDS) were performed to determine the electrorefining potential for magnesium. The PDS show that the electrorefining potential increases over time as the Mg content inside the Mg-Al scrap decreases. Up to 100% percent of magnesium is refined from the Mg-Al scrap by a novel refining process of dissolving magnesium and its oxide into a flux followed by vapor phase removal of dissolved magnesium and subsequently condensing the magnesium vapors in a separate condenser. The solid oxide membrane (SOM) electrolysis process is employed in the refining system to enable additional recycling of magnesium from magnesium oxide (MgO) in the partially oxidized Mg-Al scrap. The combination of the refining and SOM processes yields 7.4g of pure magnesium; could not collect and weigh all of the magnesium recovered.

Mg-5Sn-5Zn-xCa(x=0.5, 1, 2) alloys were melted by the vacuum melting furnace. The microstructures and phase compositions were analyzed by the scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical properties were tested by the electronic universal test machine. The fracture surface were observed by scanning electron microscope (SEM). The results indicate that the microstructures of Mg-5Zn-5Sn-xCa alloys are composed of CaMgSn phases, layer MgZn₂ phases and Mg2Sn phases. Matrix precipitates onset Mg₂Ca phase, when the content of Ca is 2 wt%. With the increasing of the Ca content, the needle CaMgSn phases become rods gradually, the layer MgZn₂ phases and plate Mg₂Sn phases become continuous, ultimate tensile strength decrease. The ultimate tensile strength obtained by Mg-5Zn-5Sn-0.5Ca alloy is 184MPa.

As-cast AZ80 Mg alloy contains α-Mg, partially divorce eutectic of α and γ (Mg₁₇Al₁₂), fully divorce eutectic of α and γ, and lamellar eutectic of α and γ phases. During homogenization, second phase (γ-Mg₁₇Al₁₂) gets dissolved can change the mechanical properties. Therefore, the aim of the present work is to bring out the kinetics of dissolution of γ phase and evaluate its effect on mechanical properties. Microstructure evolution during homogenization was investigated as a function of time for 0.5 to 100 h and at the temperatures of 400° and 439°C. In as-cast state, this material was found to contain 70% α-Mg and 30% eutectic phase. With increasing homogenization time, dissolution of lamellar eutectic occurs first which is followed by dissolution of fully divorce eutectic and partially divorce eutectic. The dissolution kinetics of γ phase was analyzed based on the decrease in its volume fraction as a function of time. The time exponent for dissolution was found to be 0.38 and the activation energy for the dissolution of γ phase was found to be 84.1 kJ/mol. This dissolution of γ phase leads to decrease in hardness and tensile strength with increase in homogenization time.

Magnesium alloys are very popular in the automobile industry due to its high strength to weight ratio. However, the use of commercial magnesium alloys as sheet is limited by room temperature ductility. One way to improve the ductility may be to form precipitates during hot rolling. These may delay dynamic recrystallization, possibly leading to grain refinement, which is known to improve ductility. Equilibrium diagrams obtained from thermodynamic modeling software FactSage were used to design Mg-3Al-2Sn alloy, which should form Mg₂Sn precipitates during hot rolling temperatures around 300 °C. To investigate this prediction, the alloy was cast in a copper mould and precipitates formation characteristics were studied by using optical microscope (OM), scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectroscopy (EDS).

The effect of ageing temperature and time on precipitates in AZ80 magnesium alloy were studied by optical microscopy to investigate the influence on mechanical properties. The results show the precipitation is distributed as bands along the extrusion direction, with no twinning. After ageing, the precipitation becomes dispersed uniformly. When ageing at 423 K, discontinuous precipitated phase increases the yield and tensile strength but reduces the ductility of the material. For ageing at 573 K, with increasing the ageing time, static ductility first increases and then decreases. This means that recrystallization induced by continuous precipitation is beneficial to both the strength and ductility. However, the effect of age hardening under 573 K is not better than 423 K. And {for insert mathtype twinning was also activated in compression much more than in tensile samples, which is consistent with the behviour of AZ31.

Squeeze cast light alloys has been approved for advanced engineering design of light integrity automotive applications. An understanding of the effect of section thicknesses on mechanical properties of squeeze cast magnesium alloys is essential for proper design of different applications. The present work studied the microstructure and tensile properties of magnesium alloy AM60 with different section thickness of 6, 10 and 20mm squeeze cast under an applied pressure of 30MPa. The results of tensile testing indicate that the yield strength (YS), ultimate tensile strength (UTS) and elongation (E_f) increase with a decreasing in section thicknesses of squeeze cast AM60. The microstructure analysis shows that the improvement in the tensile properties of squeeze cast AM60 is mainly attributed to the low level of gas porosity and the high content of eutectic phases and fine grain structure which resulted from high solidification rates taking place in the thin section.