Magnesium Technology 2015

Today’s land, sea and air transportation industries — as a business necessity — are focused on technology solutions that will make vehicles more sustainable in terms of energy, the environment, safety and affordability. Reducing vehicle weight is a key enabler for meeting these challenges as well as increasing payload and improving performance. The potential weight reductions from substituting lightweight metals (advanced high-strength steels, aluminum, magnesium and titanium alloys) are well established. For magnesium castings, weight savings of 60% have been reported [1]. The value of weight reduction depends on the transportation sector and ranges from about $5/kg saved for automobiles to over $500/kg saved for aircraft [2]. The challenge is to optimize the material properties and develop robust, high volume, manufacturing technologies and the associated supply chain to fabricate components and subsystems at the appropriate cost for each application.

The commercial aircraft market is forecast to steadily grow over the next two decades. Part of this growth is driven by the desire of airlines to replace older models in their fleet with newer, more fuel efficient designs, to realize lower operating costs and to address the rising cost of aviation fuel. As such the aircraft OEMs are beginning to set more and more demanding mass targets on their new platforms.

In the next decade, fundamental research in metals and metallic nanostructures (MMN) has the potential to continue to transform science into innovative materials, devices, and systems. This talk summarizes the findings of a workshop to identify emerging and potentially transformative research areas in MMN. The metals and metallic nanostructures (MMNs) workshop aimed to identify significant research trends, scientific fundamentals, and recent breakthroughs that can enable new or enhanced MMN performance, either alone or in a more complex materials system, for a wide range of applications. Additionally, the role that MMN research can play in high-priority research and development (R&D) areas such as the U.S. Materials Genome Initiative, the National Nanotechnology Initiative, the Advanced Manufacturing Initiative, and other similar initiatives that exist internationally was assessed. The workshop also addressed critical issues related to materials research instrumentation and the cyberinfrastructure for materials science research and education, as well as science, technology, engineering, and mathematics (STEM) workforce development, with emphasis on the United States but with an appreciation that similar challenges and opportunities for the materials community exist internationally.

The addition of adequate amounts of rare-earth (RE) alloying elements can produce appreciable effects on microstructures, formability and mechanical properties of magnesium alloys. At low concentrations, it can weaken the basal texture in the as-deformed and the recrystallized conditions in wrought alloys and improve the creep resistance of casting alloys at elevated temperatures; at high concentrations, it can bring significant age hardening effects and thus improve the alloy strength. While this knowledge has been known for some years, the precise roles of RE solutes in texture weakening and the early stage of precipitation remain unclear.

Electron backscatter diffraction has transformed microstructural analysis. Its advent enabled the microstructure to be correlated with crystallographic orientation in an unprecedented manner. This correlation has taught us many things about the physical metallurgy of magnesium and its alloys. Some highlights from three decades of research are presented in this talk. Chief among these is the insight the technique has provided into mechanical twinning, which plays a major role in the deformation of magnesium. The technique has also shed important light on deformation mechanisms, heterogeneity of material flow and, of course, the processes of texture development during wrought processing. It also promises more. In coming years, careful analysis of electron backscatter diffraction patterns and maps will in all likelihood continue to highlight the dominating mechanisms and phenomena that must be captured in microstructurally honest models of material response.

Our community has learned a great deal about twinning in Mg alloys over the past decade. Some of these things were known qualitatively in prior decades, but we have now developed a proficiency in characterization and computational modeling which permits a quantitative description of these twinning-induced effects over a wide range of strain rates, temperatures, loading conditions, and in a variety of alloy families. These capabilities could only be dreamed of by prior generations. This lecture will review the effects of the main twinning mode, {10.2} extension twinning (e.g., tension-compression yield asymmetry, yield plateau, anisotropy, rapid strain hardening, detwinning, etc.); characterization, primarily by diffraction-based techniques (electron, X-ray, and neutron); and modeling by crystal plasticity-based methods. Strategies to control these effects through microstructure, texture, and alloy design will be proposed. Finally, outstanding questions which merit further research will be highlighted.

Mg-alloys are highly applicative at the automobile and aerospace industries due to their high specific mechanical properties. Mg-Al-RE alloy design was motivated by the formation of Al-RE intermetallic at the grain boundaries (GB) and Mg₂Sn precipitates inside the α-Mg matrix. The presence of precipitates at the GB can inhibit GB sliding, while the precipitation inside the α-Mg matrix grains inhibits dislocation climb responsible for a bulk creep. Thermodynamic simulations were used for optimal composition and process parameters derivation. Mg-Al-Zn-Sn alloys with additions of Nd and Ce were examined in terms of creep resistance and microstructure development during aging and creep. The evolution of the microstructure was monitored by scanning electron microscopy and X-ray diffraction. Mechanical properties were examined by creep testing and Vickers microhardness measurements. A directional growth of the MgZn₂ precipitates was found in the crept specimens in contrast to the aged counterparts.

Magnesium alloys have recently received much attention for their weight-saving potential in transportation systems. Their implementation is hindered, however, by poor formability. The present work compares the mechanical response to warm isothermal compression of two recently developed magnesium extrusion alloys, AM30 (Mg-3Al-0.4Mn)1 and ZE20 (Mg-2Zn-0.2Ce). It was found that AM30 exhibits higher initial hardening hardening followed by softening, while ZE20 exhibited only slight softening and ended at a higher steady-state stress than AM30.

Because of ever increasing demanded of Magnesium alloys in various industries, high temperature deformation of Mg-Al-Zn alloys (AZ31) at constant stress (i.e. creep) were studied at a wide range of stresses and temperatures to characterize underlying deformation mechanism and dynamic recrystallization (DRX) Various microstructures (e.g. grain growth & DRX) are noted during steady-state creep mechanisms such as grain boundary sliding (GBS), dislocation glide creep (DGC) and dislocation climb creep (DCC). Although a combination of DRX and grain growth is characteristic of low stacking fault energy materials like Mg alloys at elevated temperatures, observation reveals grain growth at low strain-rates (GBS region) along with dynamic recovery (DRV) mechanism. Scanning Electron Microscopic (SEM) characterization of the fracture surface reveals more inter-granular fracture for large grains (i.e. GBS region with DRV process) and more dimple shape fracture for small grains (i.e. DGC & DCC region with DRX).

A significant improvement in creep resistance was achieved by adding Zn to a Mg-Nd-La alloy. Such an improvement is indicated by an order of magnitude reduction in minimum creep rate by and maintaining remarkably low creep-strain for prolonged duration compared to the non-Zn containing alloy. Addition of Zn resulted in the formation of high number density of fine scale γ” precipitates which presumably enhanced the load bearing capacity of Mg-Nd-La-Zn alloy. Observation of dislocation substructures further revealed that both intragranular precipitates as well as the interdendritic phase retarded dislocation motion.

We are exploring the commercial viability for producing Mg from MgO for which thermal energy is supplied to the cell as a substitute for some electric energy. The thermal input source may be concentrated sunlight or natural gas. Laboratory-scale electrochemical studies near 1250 K for two cell concepts show that we reached current densities above 0.5 A-cm−2at an overvoltage of 1.0 V. Current efficiency values exceeded 80%. The discussion of the relationship between these bench-top experimental results and the industrial potential of the process has been initiated.

A novel process of magnesium production has been developed by changing the preparation method of pellets of silicothermic process. For the method, the pellets consist of dolomite, ferrosilicon, fluorite and binder, which need to be roasted before reduction. However, the discharge of carbon dioxide reduces compressive strength of the pellets during the calcinations. Therefore, the present paper reports the effects of calcination atmosphere, temperature and insulation post-processing conditions on compressive strength of pellets. The results indicated that compressive strength was increased with increasing calcination temperature and post-processing temperature. The value of compressive strength obtained in air was larger than that in other atmospheres. The compressive strength value reached 80N in the experimental condition. The pellet was reduced at 1473K for 60min and the reduction ratio reached 86.75%.

Carbothermal production has been recognized as conceptually the cleanest and energy-efficient route to magnesium metal, but has suffered from technical challenges of development and scale-up. Work by National Engineering Laboratory for Vacuum Metallurgy of China has overcome some barriers of carbothermal production. By changing the condition of condensation, the magnesium vapor is condensed into bulk, so that the risk of magnesium powder explosion can be avoided, and it can reduce the oxygen content, enhance the recovered of magnesium. The mechanism of the carbothermic reduction process has be investigated, the reversion reactions are favored below 1373K at 30~100Pa, and reversion below 9% at bulk in condensation. Purification of magnesium by distillation is known technology, but difficulties with continuous operation are also known. In terms of process control, distillation temperature and pressure are controlled, the magnesium vapor is condensed into liquid, and then solidified into a solid, the solid magnesium is purified (>99.9%).

To increase both the recovery rate and purity of magnesium in carbothermic reduction process, magnesium vapor was condensed in a certain concentration of argon to avoid the occurrence of reverse reaction of CO and magnesium vapor. A cylinder by pressing a mixture of graphite and MgO with a molar ratio (2:1) was reacted at 1723K for 2.5h in an vacuum atmosphere of 1(±0.05) KPa. Then the mixture was cooled in different flow rates of argon atmosphere at a constant cooling rate. The condensation products were collected and characterized by XRD and SEM/EDS. The results show that increasing the argon flow rate enhanced diffusion of magnesium vapor and CO, meanwhile, diluted the CO concentration resulting in restraining the adverse reaction. The recovery rate of the condensation product reached a maximum of 95.6% with magnesium (strip-like) purity of 94.8% when the argon flow rate was 3.5 L/min.

Based on the practice of magnesium production via carbothermic reduction in vacuum, the pollutants were calculated for exhaust gas, waste water, waste residue, noise. And a quantitative evaluation of the environmental impact was carried out.

A LCA feasibility study was undertaken to determine the environmental impact of an Eco-magnesium process route by recycled chips to manufacture panel for the automotive sector to be compared with comparative scenarios, a non-recycled carbon fiber reinforced polymer (CFRP) and a baseline steel-made component scenario. The objective of this LCA study was to assess the actual benefits of a lightweight solution considering the whole life cycle, including the dirty-phase (i.e. the “cradle-to-exit gate” stage) that impacts differently for the different materials. For this reason the analysis has regarded the net “cradle-to-grave” scenario. Different automotive floor pans were then compared considering the rate of fuel consumption during vehicle operation — i.e. the fuel-mass correlation factor — and the different material substitution factors allowed by the different materials selected.

In situ synchrotron radiation diffraction experiments were performed during the solidification of Mg15Gd at the P07 (HEMS) Beamline of PETRA III at DESY. The measurements were carried out in the chamber of a modified DIL 805A/D dilatometer with a beam energy of 100 keV. The temperature was controlled by type S thermocouples welded on the steel lid of the graphite crucibles containing the samples. The two dimensional diffraction patterns were recorded with a Perkin Elmer 1621 Flatpanel. The phase evolution observed during cooling at rates of 5, 20 and 100 K/min show formation of GdMg₃ at elevated temperatures, which transforms into GdMg₅ during continued cooling. Phases were identified with the information from the Pearson´s database for crystalline structures. This is different from that predicted with thermodynamic databases. Although the equilibrium phase diagram suggests a simple eutectic solidification, the experiments show a metastable phase formation and its transformation. The formation of GdMg₃ becomes more pronounced at higher cooling rates.

Influences of trace boron on microstructures and tensile properties of Mg-4Al-4La-based alloys prepared by cold-chamber high-pressure die-casting method were thoroughly investigated. The results indicate that adding trace boron to Mg-4Al-4La-based alloy can refine the dendrite arm spacing of primary alpha-Mg phases, which are mainly due to the little inoculating AlB₂ particles. In addition, we found that adding 0.01–0.02 wt.% boron can drastically changes the eutectic morphology, with secondary particle dispersion becoming irregular and eutectic volume fraction being reduced. These phenomena can be attributed to the competitive nucleation between alpha-Mg and AlB₂ particles for Al₁₁La₃ phases, and to the fact that more Al and La atoms saturate into the α-Mg matrix. Considering the tensile properties, although adding 0.01–0.02 wt.% boron decreased the strength of Mg-4Al-4La-based alloy, adding 0.03 wt.% boron significantly improved the tensile properties due to dispersion strengthening and, to a certain extent, solid-solution strengthening.

The effect of Bismuth addition on the microstructure evolution of Mg and AZ31 Mg-alloy is studied at different cooling rates. A wedge-shaped copper mould was used to achieve continuous variation in cooling rates. Mg containing a small amount of bismuth produced a large decrease in the α-Mg grain size and suggested that that the presence of bismuth makes Mg less sensitive to the cooling rates employed. The macrostructure study of the static-mould direct-chill (DC) cast billets of AZ31 also supports the solute effect of bismuth on grain refinement of Mg and its alloys. The efficiency of Bi as a grain refiner solute can be seen with 50% average grain size reduction of AZ31 alloy at 0.2wt% Bi addition.

In-situ neutron diffraction experiments were carried out on solutionized and randomly textured Mg-Zn alloy castings with similar grain sizes but variation in Zn content from 1.7 to 6.6 wt %. The evolution in internal elastic strains and diffraction peak intensities with increasing load were analyzed. The macroscopic stress strain curve shows an increase in yield strength with an increase in zinc content. Neutron diffraction results indicate that the strength of basal slip, tension twinning and <c+a> slip/compression twinning modes increases with increase in zinc content. However, the strength of prismatic slip appears to be unaffected by zinc content at lower concentrations and increases with zinc content only at higher concentrations. These results are discussed in light of prior work on the Mg-Zn system.

As-cast Mg-4Zn-0.5Zr, Mg-4Zn-2Gd-0.5Zr and Mg-4Zn-2Nd-0.5Zr alloys were investigated by in situ synchrotron radiation diffraction during hot compression at 350 °C using the facilities of P07 beamline of Petra III at Deutsches Elektronen Synchrotron (DESY), Hamburg, Germany. The specimens were heated at a rate of 100 K/min and compressed with an initial strain rate of 1.1 x 10–3 s-1 up to 30 % strain. The addition of rare earth elements improved the yield strength from 23 MPa in the Mg-4Zn-0.5Zr alloy up to 40 MPa in the alloy with Nd and Gd. Continuous dynamic recrystallization played an important role in the Mg-4Zn-0.5Zr alloy during deformation and twinning was not dominant. Discontinuous dynamic recrystallization was observed in the in the Mg-4Zn-2Gd-0.5Zr along the grain boundary regions while the grains remained largely without any recrystallization. In the Mg-4Zn-2Gd-0.5Zr and Mg-4Zn-2Nd-0.5Zr alloys the contribution of twinning to deformation was observed at 350 °C. Reasons for these differences will be discussed with respect to microstructures of the alloys.

The tensile deformation behavior of as-cast and cast-then-extruded Mg-1Mn-1Nd(wt%) and Mg-1Mn-0.3Nd(wt%) alloys was studied by performing in-situ tests inside a SEM. A slip/twin trace analysis technique was used to identify the distribution of the deformation systems. Cast-then-extruded Mg-1Mn-1Nd(wt%) exhibited superior elevated-temperature strength retention compared to cast-then-extruded Mg-1Mn-0.3Nd(wt%). Basal slip and extension twinning were observed in the as-cast Mg-1Mn-1Nd(wt%) and Mg-1Mn-0.4Nd(wt%) alloys deformed at 50°C. In cast-then-extruded Mg-1Mn-1Nd(wt%), basal slip, prismatic slip, and pyramidal <c+a> slip were active at all temperatures. In cast-then-extruded Mg-1Mn-0.3Nd(wt%), at lower temperatures, twinning dominated the deformation and no non-basal slip activity was observed. The extent of twinning decreased with increasing temperature and basal slip was the major deformation mode at 150–250°C in both cast-then-extruded materials. The estimated CRSS ratio of extension twinning with respect to basal slip in Mg-1Mn-1Nd(wt%) was close to unity, suggesting that the addition of Nd results in an increase in the CRSS of basal slip.

Constant strain rate compression tests were performed on Mg-2Zn-2Nd samples over the temperature range 25 to 400 °C and strain rate range 0.001 to 0.1/s. The deformation conditions under which dynamic strain aging (DSA) takes place were determined. In this range, a peak is observed in the temperature/flow stress relationship and the strain rate sensitivity (SRS) is negative. At temperatures above the negative rate sensitivity region, abnormally high positive SRS’s were detected. Interrupted compression tests were also carried out to follow the microstructural evolution. Metallographic examination indicated that shear bands form when samples are deformed under negative SRS conditions and are absent when the rate sensitivity is highly positive.

Twinning dislocations (disconnections) are examples of a unique type of defect which migrate an interface as a result of glissile propagation. These defects produce a well-defined plastic deformation due to their motion occurring exclusively in the interface. In most cases, their deformation gradient is more complex than the simple shear of slip and twin systems. Twins and relatable asymmetric tilt boundaries have deformation gradients which are associated by rotation. For example, the <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo> </mrow> </math>$$\{ 10\bar 12\}$$ twin interface and the basalprismatic interface have misorientations which differ by only four degrees and are joined on a faceted boundary by an interfacial disclination line. The deformation due to glissile disconnections on the basal—prismatic boundary may be multiplicatively decomposed into the simple shear deformation of the <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo> </mrow> </math>$$\{ 10\bar 12\}$$ twin and a four degree rotation. A comprehensive understanding of the deformation on faceted and asymmetric boundaries enables more accurate analysis and modeling of twinning.

Discrete arcs of twins were observed in an AZ31 rolled sheet Mg alloy after three point bending at room temperature. The arcs geometrically followed the contour of the bent specimens and were present in the tension zone where the stress state strongly disfavors the extension twinning. Electron backscatter diffraction analysis indicated that the twins in the arcs are <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo><mo>&#x003C;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x003E;</mo> </mrow> </math>$$\{ 10\bar 12\} < 10\bar 1\bar 1 >$$ extension twins, instead of <math display='block'> <mrow> <mo>&#x007B;</mo><mn>101</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x007D;</mo><mo>&#x003C;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mover accent='true'> <mn>2</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x003E;</mo> </mrow> </math>$$\{ 101\bar 1\} < 10\bar 1\bar 2 >$$ contraction twins. Calculations showed that the twinned grains in the arcs have very low values of Schmid factor, even close to zero. The main tensile stress component in the tension zone was nearly perpendicular to the c-axis of the parent grains. Thus <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo><mo>&#x003C;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x003E;</mo> </mrow> </math>$$\{ 10\bar 12\} < 10\bar 1\bar 1 >$$ twinning in the tension zone was activated in a most unlikely scenario. The mechanism for such unusual twinning behavior was analyzed from the perspective of strain components that are generated by the <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo><mo>&#x003C;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x003E;</mo> </mrow> </math>$$\{ 10\bar 12\} < 10\bar 1\bar 1 >$$ twinning. It was demonstrated that the <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo><mo>&#x003C;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mo>&#x003E;</mo> </mrow> </math>$$\{ 10\bar 12\} < 10\bar 1\bar 1 >$$ twins in the arcs in the tension zone of the bent specimen can be treated as “geometrically necessary twins”, similar to geometrically necessary dislocations and boundaries.

Different twinning types can be formed on rolling deformation, even at high rolling temperatures. In this work, mechanical twins were studied on cold (at 25°C) and warm (at 250°C) rolled samples of AZ31B magnesium alloy. The influence of the mechanical twins on microstructure and texture evolution was examined by electron back scatter diffraction (EBSD), comparing the twin morphologies and determining their orientation relationships with matrices around them. The results showed that {101̄2}<121̄0> and {101̄1}<121̄0> twins and double twinning affect grain orientations during rolling processes. In addition, on rolled samples were evidenced that the shear bands were developed from doubly-twinned regions, but most of them quickly lost their morphology when applying high rolling temperature due to dynamic recrystallization.

Transmission electron microscopy (TEM) was performed to study the defect structures in a cold deformed AZ31 magnesium alloy. The materials were compressed at room temperature along the rolling direction to promote the formation of {10–12} extension twins. Dislocation character and configuration in both the twin and adjacent matrix were investigated. It was found that basal <a> dislocations are dominant in the matrix, though some dislocations immediately adjacent to the twin boundary have <c> component. An abundance of dislocations with a <c> component were observed inside the twin, even at relatively low strain level of 2%. Defects on the twin boundary and in the proximity were further investigated, including stacking faults on the basal plane which appear to have resulted from partial dislocations emanating from the twin boundary.

In this work, the mode I fracture response of a rolled Mg AZ31 alloy is investigated by conducting experiments using notched compact tension specimens. It is found that the notched fracture toughness J _c ∼ 42 N/mm which is moderately high. Detailed examination using EBSD and optical metallography indicates that profuse tensile twinning occurs almost over the entire uncracked ligament ahead of the notch root. This leads to considerable hardening as evidenced by slope of the load versus displacement curve and toughness enhancement by plastic dissipation. Strong texture changes are also observed near the extended crack tip. The fracture morphology involves dimpling at the specimen mid-plane and shear lip formation close to the free surfaces. The fracture resistance of the Mg alloy is discussed in the context of the above observations.

In this paper, for the first time it is demonstrated that only by accounting for the combined effects of the tension-compression asymmetry and strong anisotropy of AZ31 Mg it is possible to predict the very unusual buckling of this material, and most importantly capture the energy absorbed prior to buckling. It is shown that by using an elastic/plastic model based on Cazacu et al. [1] criterion that accounts for both anisotropy and strength differential effects, a strong influence of the direction of crushing is predicted. However, if Hill’s [2] criterion is used i.e. strength differential effects are not taken into account, the predictions indicate that the orientation of the tube has no influence on the final geometry of the crushed specimen. Furthermore, the location and cross section of the buckle are not correctly captured by the Hill [2] yield criterion.

Using molecular dynamics (MD) simulations, we show that the maintenance of strong deformation texture during dynamic recrystallization of magnesium deformed at high temperature is controlled by the existence of energy landscape cusps and mobility spikes associated with specific grain boundaries generated by active deformation modes during the polygonization process. As the subgrains rotate to a final recrystallized state, they settle at misorientations with particular tilt axes that give out a best combination between low energy and high mobility of the associated grain boundary. Having identified the grain boundary types induced by extrusion of a commercial Mg alloy, AM30, we reconstructed them by MD simulations (notably of pure Mg) to identify their intrinsic defect structure via interfacial defect theory. These analyses enabled formal understanding of their excess potential energy variation with misorientation angles and their associated mobility. It is hypothesized that the change in the energy landscape and intrinsic defect structure induced by RE element additions, which highly segregate to the GBs, permits the subgrains to settle at more diverse misorientation angles, thus causing a weakening in the final texture.

Understanding the high strain rate behavior of Mg alloys is of interest for applications ranging from armor to automobile crash worthiness. Toward this end, the viscoplastic self-consistent (VPSC) polycrystal plasticity code, including the recently developed twinning-detwinning (TDT) model, is used to describe the homogeneous plastic flow of the rare earth element containing Mg alloy, WE43-T5, plate. The model accounts for the presence of an initial, moderate texture and its evolution as during deformation. It reveals that the moderate texture is responsible for the difference between the plate through-thickness and in-plane behaviors. The model also helps to reconcile why the in-plane response is nearly isotropic, despite the presence of orthotropic (not radially symmetric) texture. Note that a single set of parameters was used to fit the entire set of results, i.e. it is a model, which can describe all of the observed strength, strain, and strain hardening anisotropies and asymmetries.

Accurate description of the mechanical response of AZ31 Mg requires consideration of its strong anisotropy both at the single crystal and polycrystal level and their evolution with plastic deformation. In this paper, we apply the self-consistent mean field model developed by Lebensohn and Tomé [1] and the VPSC code to the description of the behavior of a rolled AZ31 plate. The predictive capabilities of the model are demonstrated. It is shown that with the same set of parameters, which were identified based on a few mechanical tests, it is possible to predict with great accuracy both the mechanical stress-strain response and texture evolution for loading paths that were not used for calibration, such as off-axis loadings, and simple shear loadings.

Understanding and predicting the evolution of recrystallized microstructures is an important part of the Integrated Computational Materials Engineering (ICME) toolset required for magnesium alloys. In this study, the recrystallization behavior of a new magnesium-rare earth alloy, ZE20, was investigated at typical temperatures (i.e. 375 °C, and 425 °C). The characteristics of recrystallization in ZE20 were analyzed via microscopic observations. The recrystallization microstructure was characterized and quantified using a Grain Orientation Spread (GOS) technique based on electron back scatter diffraction (EBSD) scans. The evolution of texture and grain size during recrystallization at 425 °C was examined by EBSD analysis. Static recrystallization kinetics at both temperatures was obtained experimentally and modeled using the JMAK relationship.

The US Army Research Laboratory (ARL) and the Osaka University Joining and Welding Research Institute (JWRI) formed a collaborative partnership with Taber Extrusions, Epson, Pacific Sowa, Kurimoto, and National Material LP to domestically reproduce and scale-up military grade magnesium alloy AMX602 at the Taber Extrusion manufacturing facility in Gulfport, MS. AMX602 material was provided in the form of 38.1-mm (1.5-inch) wide bars, 101.6-mm (4-inch) wide plate, and 152.4-mm (6-in) wide plate. The ARL and the JWRI conducted mechanical analysis and dynamic impact examination to evaluate the lateral dimension scale-up of AMX602. The results were parametrically analyzed and compared to conventionally processed AZ31B-H24 and AA5083–H131. Details of the scalability of the AMX602 alloy are provided.

Weight reduction of automobiles and aircrafts improves fuel economy and reduces greenhouse gas emissions. Use of Mg alloys may allow weight reduction because of their low densities, but adoption is hindered because they exhibit limited ductility at ambient temperatures [1]. In a previous study of fracture toughness in a Mg alloy, crack readily propagated near twin boundaries and resulted in poor durability [2]. It has been shown that pile-up of dislocations at the interface between the matrix and deformation twins caused stress concentration to form cracks [2]. Another study suggested that the ductility of Mg alloys is further limited under dynamic loading due to lowered activity of dislocations [3]. It has also been reported that a Mg-Al-Mn alloy had pronounced mechanical anisotropy at high strain rates of around 1.0 ×103 s-1 [4]. Therefore, the mechanical properties of Mg alloys should be evaluated accurately for applications involving possible dynamic loading.

A constitutive framework based on a rate-dependent crystal plasticity theory is employed to simulate large strain deformation in hexagonal closed-packed metals that deform by slip and twinning. The model allows the twinned zones and the parent matrix to rotate independently. ZEK100 magnesium alloy sheets which significant texture weakening compared to AZ31 sheets are investigated using the model. There is considerable in-plane anisotropy and tension compression asymmetry in the flow behavior of ZEK100. Simulations of uniaxial tension in different directions at various strain rates and the accompanying texture evolution are performed and they are in very good agreement with experimental measurements. The effect of strain rate on the activation of the various slip systems and twinning show that differences in the strain rate dependence of yield stress and Rvalues in ZEK100 have their origin in the activation of different deformation mechanisms.

Improving mechanical properties of magnesium and understanding fracture behavior under impact loading are necessary to apply magnesium alloys to structural components of automobiles. We have investigated the fracture behavior of binary magnesium alloys by three-point bending experiment and conducted a first principle calculation to estimate the effect of solute segregation on fracture energy. In this paper, we have focused on experimental result of impact three-point bending test for Mg-0.3at.%Y alloy and the results of the test were compared with that of AZ31 commercially available alloy [1]. As a result, the crack propagation speed of Mg-0.3at.%Y was found to be slower than that of AZ31 alloys. Moreover, the absorbed energy of Mg-0.3at.%Y was more than twice as high as that of AZ31 alloys. These results suggested that yttrium solute in magnesium improved the fracture toughness of magnesium under impact loading. Then, fracture surface was observed by SEM to consider the effect of microstructure on crack propagation speed.

Recent investigations suggest that it is possible to achieve dramatic modifications to both strength and ductility of magnesium alloys through a combination of alloying, grain refinement, and texture control. The current work explores the possibility of altering the texture in extruded thin-walled magnesium alloy tubes for improved ductility during axial crush in which energy is absorbed through progressive buckling. The texture evolution was predicted using the viscoplastic self-consistent (VPSC) crystal plasticity model, with strain path input from continuum-based finite element simulations of extrusion. A limited diversity of textures can be induced by altering the strain path through the extrusion die design. In some cases, such as for simple bar extrusion, the textures predicted can be connected with simple shape change. In other cases, a subtle influence of strain path involving shear-reverse-shear is predicted. The most promising textures predicted for a variety of strain paths are selected for subsequent experimental study.

We investigated the role of Zr in the microstructure evolution in Mg-Zn-Zr based wrought alloys fabricated by twin-roll casting and hot rolling (TRC-HR) process and extrusion process. In the as-cast condition, the Mg(Zn, Zr) precipitates are observed in the as-cast Mg-6.2Zn-0.5Zr (ZK60) alloys indicating that the Mg(Zn, Zr) precipitates are formed during melting, solidification or cooling process. The ZK60 alloy exhibited finer grain structure compared to the Mg-6.2Zn (Z6) alloy in both as-cast and solution treated conditions since the Mg(Zn, Zr) inhibited the grain growth. The Mg(Zn, Zr) particle also contributed to the fine-grain structure formation during the extrusion and TRC-HR processes. During the wrought processing, the recrystallization starts to occur from the grain boundaries of the homogenized sample, and spread to the grain interior. Since the Mg(Zn, Zr) particle inhibited the grain growth, the fine recrystallized grain structure is formed in the ZK60 wrought alloy.

Earlier, we reported very high yield strengths of 400 MPa accompanied by total elongations of over 12% in Mg-6xZn-xY alloys, where x=1.0, 0.5, 0.35 and 0.2 in at%, dispersed with quasicrystalline phase and processed by extrusion. Here we report on the effect of low amount of alloying elements zinc and yttrium on the texture and anisotropy of the Mg-Zn-Y alloys. With decreasing amount of the alloying elements, the yield strength of the extruded alloys remains close to 400 MPa with total elongation to failure of about 12%, while the anisotropy keeps increasing. Thus very high tensile strengths with moderate ductility are achieved even in very dilute alloys. With lesser amount of alloying elements the degree of dynamic recrystallization is reduced and the intensity of the basal texture is increased, resulting in higher yield anisotropy.

This article presents an extruded Mg-5Gd-3Y-1Zn-Zr alloy produced by conventional ingot metallurgy, exhibiting high-strength and excellent ductility at room and elevated temperatures, with a low density of 1.84g/cm3. The 0.2% yield strength (YS), ultimate tensile strength (UTS)and elongation-to-failure (EL)at room temperature, of samples in T5 condition, can reach 324MPa, 382MPa and 9.3%, respectively. At 250°C, the UTS can be still higher than 317MPa, with EL of 21%. The excellent mechanical properties were attributed to the high density of the static aging prismatic precipitates in the matrix, dynamic β phase precipitated on the dynamic recrystallization grain boundaries, and bimodal grain size distribution with fine recrystallized grains and large deformed grains with intense basal texture and LPSO phase inside the grain.

Commercial Mg alloys, compared to other engineering materials such as steels or aluminum materials have inferior strengths (Y.S. = ~120 MPa), limited ductility and poor formability. Furthermore, due to high costs their use in structural applications for transportation industry is still rather limited. Therefore, there is significant interest in developing microstructure modification routes to produce novel Mg base alloys with an attractive combination of strength and ductility at room temperature as-well as warm temperature formability. In order to promote use of such microstructurally engineered Mg materials, better understanding of the relationship between microstructure, texture etc. with mechanical properties must be developed for a range of different alloys. In this work, microstructure evolution and mechanical response of two thermomechanically processed Mg alloys AZ61L and AZ70-TH were investigated. Initial findings of this work are presented here. The processed materials exhibited a good combination of strength and tensile ductility at room temperature that was further enhanced (Y.S. > 250 MPa, El. % > 10%) by low temperature (180°C) annealing treatment for 1 hr. The ductility and in-plane anisotropy in mechanical property was found to be related to basal texture formation in the sheet plane. In addition to the Hall-Petch strengthening due to near ultrafine grain size, β-particles from as-molded microstructure, complement strengthening by sub-dividing and possibly solutionizing/re-precipitating into nano-sized, well-dispersed, obstacles to dislocation motion and grain growth.

A number of researchers have reported the mechanical properties of Mg alloys processed with high-pressure torsion (HPT), which is a typical method of severe plastic deformation. However, the effect of alloying elements on the mechanical properties of HPT-processed Mg alloys was unclear.In this study, to clarify the influence of the additional elements on the microstructures and mechanical properties of magnesium alloys, Mg-1at%x alloys (x=Al, Zn, Sn, Bi, Y) were produced by HPT processing. The microstructures and mechanical properties were investigated, and the effects of the various alloying elements were compared. The specimens were heat treated to maximize the amount of solute content in the matrix, and then subjected to HPT processing. Significant grain refinement was achieved by HPT prpcessing, with solute segregation at the grain boundaries. The hardness of the alloys was increased by the HPT processing, and this effect cannot be explained by grain refinement alone. Finally, the different strengthening effects of the various alloying elements are discussed.

Wrought magnesium alloy AZ31 was pre-compressed and subsequently subjected to tensile loading. Due to a strong fibre texture of the alloy the level of pre-compression stress significantly influences the following tensile test. The results of acoustic emission (AE) measurement are correlated with the stress-time curves and differences in the AE count rate were used to reveal changes in underlying deformation mechanisms. First, the compression-tension test was recorded by using the AE technique and then the test was repeated to specific points on the deformation curve, where the AE count rate exhibits strong changes in its activity. A pronounced S-shape of the tensile curve and AE peaks were observed. It highlights the role of detwinning and the nucleation of new twins during the tensile test. The subsequent analysis of microstructure using electron back scattered diffraction (EBSD) method opens a detailed insight into microstructural changes.

Mg-0.3Al-0.2Ca-xMn (x=0.1, 0.2, 0.4at.%) alloys were extruded at an extraordinarily high speed of 60 m/min, and the effect of Mn content on the extrudability, age-hardening response, and tensile properties was investigated. An increase in Mn content improves the surface quality of the high-speed extruded alloys. Moreover, the as-extruded Mg-0.3Al-0.2Ca-0.4Mn alloy shows much higher strengths than the as-extruded Mg-0.3Al-0.2Ca-0.1Mn alloy and also exhibits enough elongation of about 25%; the proof stress was improved from 135 MPa to 190 MPa with an increase of Mn content from 0.1% to 0.4%. Whereas the Mg-0.3Al-0.2Ca-0.4Mn alloy shows a minorage-hardening by T5-treatment compared to the Mg-0.3Al-0.2Ca-0.1Mn alloy, the proof stresses of both alloys are increased about 20 MPa. The high proof stress despite of its minor age-hardening is attributed to the strong basal texture observed in the high Mn containing alloy.

As heat dissipation material, magnesium alloys have smaller specific gravity and bigger specific heat capacity than copper alloys and aluminum alloys. The object of this study focused on the Mg-2.5Nd-1.0Zn-0.5Zr (wt.%) alloy. A research on Mg-xNd-yZn-0.4Zr (x=1.25–3.25,y=0–2.0,wt.%) alloys had been carried out systematically, but there was few reports about the research on heat dissipation performance of Mg-Nd based alloys. In this work, the effects of hot extrusion and heat treatment on mechanical properties and thermal performance of Mg-2.5Nd-1.0Zn-0.5Zr (wt.%) alloy were studied. The results show that the heat treatment and extrusion processing can improve the ultimate tensile strength (UTS) from 188.2Mpa to 231.2MPa. While the breaking elongation is also improved from 1.1% to 2.3%. Then, a patented way[1] to evaluate the dissipation performance is used in this work. And results reveal that with proper solution treatment, aging treatment and extrusion processing, the heat dissipation performance of this alloy can also be improved obviously.

The effects of alloying elements and processing parameters on cold-rollability of RE-free magnesium alloys were investigated. Several representative alloys with different microstructural features such as solution or precipitation hardening were selected and extruded to control the initial microstructures by changing extrusion speed and temperature before cold-rolling. The results show that the uniform elongation and the work hardening exponent reflecting inclusive microstructural features of grain size, precipitates and dislocation density is linearly correlated with cold-rollability. It can be concluded that an alloy with weak basal texture can possess improved cold-formability depending on microstructural features effectively affecting work hardening exponent besides basal texture intensity. In particular the fraction of precipitates and deformed grains sensitively affected work hardening exponent and thus the cold-rollability of magnesium alloys. It was confirmed that poor cold-rollability of the precipitation-hardened alloys such as TAZ531 and TAZ711 could be improved by removing precipitates and deformed grains via a homogenization treatment.

The studies was conducted in order to improve the corrosion properties of magnesium alloys by forming on the surface a thin layer of a luminum alloy. As the feedstock material MgAlZn alloy (AZ series) have been used. Cladding process was realized in direct and indirect extrusion process. As feedstock to extrusion process billets with sleeve pipe (cladding material) pressed on them were used. The resulting claded rods have been used for forging process trials, which allowed to determine their susceptibility to further plastic forming. After forging micro-and macrostructure of samples were tested, paying particular attention to the welding zone of both materials (claded alloy and clad layer). In the final stage of work forgings used in trials in salt spray chamber which allowed to verify the corrosion properties of technology being developed.

Mg alloy sheet materials often exhibit plastic anisotropy at room temperature as a result of the limited slip systems available in the HCP lattice combined with a commonly strong basal texture. Less well studied is plastic anisotropy developed at the elevated temperatures associated with warm and hot forming. At these elevated temperatures, particularly above 200°C, the activation of additional slip systems significantly increases ductility. However, plastic anisotropy is also induced at elevated temperatures by a strong crystallographic texture, and it can require an accounting in material constitutive models to achieve accurate forming simulations. The type and degree of anisotropy under these conditions depend on both texture and deformation mechanism. The current understanding of plastic anisotropy in Mg AZ31B and ZEK100 sheet materials at elevated temperatures is reviewed in this article. The recent construction of material forming cases is also reviewed with strategies to account for plastic anisotropy in forming simulations.

ZK60 strip with 4mm thickness was fabricated by Twin Roll Casting technology. The effect of annealing, solid solution and artificial aging heat treatment on microstructures, mechanical properties and damping capacities were discussed in this paper, and the optimized heat treatment parameters was also determined. Fine equiaxed structure was obtained after annealing treatment. The room temperature damping value (Q-1) of annealed ZK60 strip was 0.0085. There was a damping peak at 279.7°C after 350°C annealing treatment; this was caused by the grain boundaries sliding at a higher temperature. The room temperature damping value (Q-1) of ZK60 strip was 0.0071 after solid solution heat treatment. A very broad damping peak appeared from 280°C to 330°C. The T6 treatment parameters were solution at 375°C for 3hrs, then artificial aging at 175°C with different holding time. The best damping capacity and mechanical properties were obtained after artificial aging at 175°C for 1hr.

The influence of texture on deformation behavior has been investigated for conventionally rolled magnesium slab and rolled twin roll cast (TRC) magnesium strip in form of sheets. The Mg-Zn-Rare earth alloy sheets were deformed at room temperature with the tensile axis oriented in the rolling (RD), 45° and the transversal direction (TD). The basal pole intensity aligned with the sheet normal direction is lower for the conventionally rolled sheet by comparison with the rolled TRC strip. Higher yield strength (YS) in the RD than in the TD for conventionally rolled sheet and higher YS for TD than RD in rolled TRC strip was observed. The acoustic emission (AE)analysis correlates the microstructure and the stress-time curves to the active deformation mechanisms. This aspect relates to the activity of the basal slip and tensile twinning, particularly during TD tension, which corresponds with the AE activity.

A study has been made on the effects of texture and alloying elements on stretch formability of Mg alloys. AZ31, AT31, and ZX11 alloys having different textures have been subjected to uniaxial tensile loading and bi-axial stretch forming tests, and their microstructures and textures before and after deformation have been analyzed. It shows that the deformation of AT31 alloy is mainly controlled by the activation of prismatic <a> slip besides the basal slip. On the other hand, there is a significantly high activity of tension twinning in ZX11 alloy regardless of tensile loading directions, resulting in the smallest Lankford values in ZX11 alloy among three alloys, followed by AT31 and AZ31 alloys. Nevertheless, the results of Erichsen cup tests in these alloys show the different behaviors such that AT31 alloy has the best stretch formability, followed by ZX11 and AZ31 alloys. It has been shown that the excellent stretch formability of AT31 alloy comes from an increased activity of prismatic <a> slip and its characteristic texture counterbalanced by broadened distribution of basal poles along the transverse direction and split basal poles along the rolling direction. Although ZX11 alloy shows an increased activity of tension twinning during stretch forming, its orthotropic texture would lead to significant anisotropic deformation at a late stage of stretch forming, resulting in a premature failure.

Integrated thermodynamic software packages are a powerful tool to analyze phase formation in multicomponent Mg alloys, providing key data for focused alloy and process development. The thermodynamic database of the alloy system is the indispensable basis for this direct application, but also needed for any further step towards Integrated Computational Materials Engineering. The database quality, which may vary widely, is crucial for the reliability of such applications. Progress in development and extension of the large thermodynamic database for magnesium alloys is reported, with emphasis on consistency, coherency and quality assurance. One aspect is the coherent description of large solid solution ranges of intermetallic phases in multicomponent Mg alloys with rare earths. Further addition of Zn may produce complex icosahedral, long-period stacking order (LPSO) or other hexagonal phases. All these may form highly efficient secondary phase precipitates in the (Mg) matrix. Examples are given for Mg-Ce-La, Mg-Ce-Y, and Mg-Gd-Nd-Y-Zn-Zr alloys.

The precipitation kinetics and microtructure in Mg-Sn binary and Mg-Al-Sn ternary alloys are simulated using PanPrecipitation coupled with Mg thermodynamic database and a newly established mobility database of the Mg-Al-Sn ternary system. Both Mg₂Sn and Mg₁₇Al₁₂ precipitates are considered in this work. The obtained kinetic parameters for these two precipitates can be used in the simulation of both individual and concurrent precipitations of Mg₁₇Al₁₂ and Mg₂Sn in Mg-Al-Sn alloys. The simulated microstructure evolution, such as the particle size and number density, are in agreement with experimental data.

We elucidate the strengthening mechanisms of Mg-Zn-Y alloys containing long-periodic stacking ordered (LPSO) structures, based on comprehensive electron microscopy investigations. Kinking of the LPSO structures is not only an important way to accommodate plastic deformation effectively, but also simultaneously strengthens the alloy as a result of microstructural refinement. In addition, kink boundaries in the LPSO structures can effectively restrict propagation of microcracks, benefiting both the alloy’s strength and ductility. Using atomic-resolution imaging, we found that the stacking-faults with Zn and Y segregation and the dynamic dislocation-solute interactions in Mg matrix also play important roles in strengthening the alloys, besides the LPSO structures. The stacking-faults can hinder the generation and propagation of <math display='block'> <mrow> <mo>&#x007B;</mo><mn>10</mn><mover accent='true'> <mn>1</mn> <mo>&#x00AF;</mo> </mover> <mn>2</mn><mo>&#x007D;</mo> </mrow> </math>$$\{ 10\bar 12\}$$ deformation twins, reducing the potential nucleation sites for microcracks. Interactions between solute atoms with dislocations promote the dissociation of both “a” and “a + c” dislocations, leading to nanometer-sized structures similar to GP zones that can act as obstacles for dislocation motion in Mg matrix. Both the wide stacking-faults with Zn and Y segregation formed during solidification, and nanometer-sized stacking-faults produced by dislocation dissociation have significant contributions to the mechanical properties at elevated temperatures.

Interest in magnesium alloys as temporary implant materials continues to grow. However, significant processing and performance gaps exist between material needs for medical devices and traditional magnesium processing technology. To help close this gap, a process to enable cold-drawn magnesium alloy wires has been developed. Cold drawing offers processing and property enhancements including strengthening through work-hardening and grain refinement. Tensile strengths exceeding 600 MPa have been achieved in WE43 wires after significant cold reduction. Understanding the mechanical fatigue performance of these wires will be critical when designing an absorbable implant. In this work, WE43 wires were drawn to a diameter of 127 microns with 90% cold work, and then either aged or annealed to effect various grain sizes. Rotary beam fatigue testing was performed on cold-drawn and thermally treated wires in both ambient air and body-temperature saline with a goal to inform the relationship between processing, environment, and fatigue performance.

This paper characterizes microstructure, mechanical properties, and the plastic flow and fracture behaviors of the high strength and high ductility, ultra-fine grain (UFG), magnesium alloys AMX602 (Mg-5.4Al-0.39Mn-l.77Ca) and ZAXE1711 (Mg-7.28Al-1.20La-1.18Ca-0.93Zn). Rapidly solidified processed (RSP) powders produced by Spinning Water Atomization (SWAP) were formed into compacts that were subsequently extruded into flat bars. Specific characteristics of the mechanical properties, and deformation and failure modes and features are revealed in response to loading conditions in tension, compression, shear, and impact. The material behaviors are shown with numerical and stress-strain test data, and power law hardening constitutive plastic flow parameters. Fracture modes and features are shown with optical and SEM microscopy. The ZAXE1711 alloy reveals lower yield strength, a high rate of strain hardening, greater ultimate strength and impact toughness, and more homogeneous less localized plastic flow and fracture.

The effect of Sn:Zn ratio on corrosion behavior of magnesium alloys containing Sn and Zn was evaluated systematically by potentiodynamic polarization and immersion tests. The hydrogen evolution rate during cathodic polarization and the average corrosion rate measured by immersion test increased with increasing Sn content and Sn:Zn ratio. The changes of fraction of second phase with more positive corrosion potential and solute contents in the matrix phase were responsible for the change of corrosion behavior according to Sn content and Sn:Zn ratio. Mg₂Sn particle accelerated the corrosion by formation of micro-galvanic cell, which resulted in faster corrosion rates of Mg-5Sn-xZn alloys than those of Mg-2Sn-xZn alloys. The increase of Zn in the matrix was harmful to the corrosion resistance because Zn accelerated the hydrogen evolution although ZnO was beneficial to the passivity of surface film.

ZEK100 magnesium alloy has attracted considerable interest for automotive body structure applications in light-weight vehicles due to its excellent formability at room temperature. However, the intrinsic tendency of magnesium alloys to corrode under wet conditions has been a concern. Reports on the corrosion resistance and, in particular, the stress corrosion cracking (SCC) susceptibility of ZEK100 under automotive service conditions have been scarce. In this work, the SCC of ZEK100 magnesium alloy was characterized by slow strain rate testing method. The effects of microstructure and corrosion environment on the SCC resistance of the alloy have been investigated. The results represent outcomes from a US-Canada-China collaborative research and development project — Magnesium Front End Research and Development (MFERD) currently underway.

It is well known that ignition temperature increases dramatically through combined addition of Ca and Y to AZ series Mg alloys. Therefore, the industrial application of Mg alloys is expected to be expanded gradually. However, studies on corrosion behavior of these alloys have been carried out rarely even though the evaluation and understanding of corrosion behavior are necessary for wide application. In this study, the changes of microstructure and corrosion behavior of AZ series alloys according to the content of Ca and Y were systemically evaluated by immersion and salt spray tests. The corrosion resistance of AZ series alloys was improved dramatically by combined addition of Ca and Y without degradation of mechanical properties. It implies that the AZ series alloys containing optimized amounts of Ca and Y have the excellent combination of ignition resistance, corrosion resistance and mechanical properties.

Incorporation of magnesium alloys in self-pierce rivet (SPR) joints poses several unique challenges among which are the creation of spurious galvanic cells and aggravated corrosion of adjacent magnesium when coated steel rivets are employed. This work firstly reviews efforts on development of coatings to steel fasteners for the diminution of galvanic corrosion when used with magnesium alloys. Secondly, approaches, based on several electrochemical methods, for the measurement of the galvanic-limiting effect of a number of commercially-available coatings to hardened 10B37 steel self-piercing rivets inserted into alloy couples incorporating several grades of magnesium are reported. Electrochemical impedance spectroscopy (EIS), zero-resistance ammeter (ZRA), corrosion potential and potential-mapping visualization methods (e.g. scanning vibrating electrode technique — SVET) are illustrated for the several rivet coatings considered.

The US Automotive Materials Partnership through the Magnesium-Intensive Front End Development Project (MFERD) is currently investigating a number of joining, coating and corrosion mitigation strategies to incorporate magnesium components into the automotive body-in-white with the ultimate goal of decreasing vehicle curb weight, thus improving fuel economy. Because Mg is anodic to all other structural metals, this is a key hurdle to Mg component implementation in vehicles. This paper will discuss the results of a study to examine the effectiveness of different corrosion mitigation strategies in joined plate assemblies and provide some insight into the systems challenges of incorporation of Mg parts into a vehicle. Details of a statistically-designed experiment developed to explore the interaction of several materials of construction (magnesium, steel and aluminum), pretreatment and topcoatings, joining methods and standardized test protocols including SAE J-2334 and ASTM B-117 are discussed. A number of avenues have emerged from this study as potential strategies for corrosion mitigation.

Micro arc oxidation process is recently developed as a promising surface modification technique applying high voltage and current density onto the light metals. The magnesium alloys exhibit nearly the lowest density among metallic structural materials but its poor characteristics in corrosion resistance, wear resistance, hardness and so on, limit its wide-range of applications. Through micro arc oxidation, thick and wear-resistant ceramic coatings are directly formed on the surface of magnesium alloys. In this study, oxide coatings were formed on AZ91D magnesium alloy in a silicate-based electrolyte by micro arc oxidation (MAO) process. MAO process was applied in an alkaline electrolyte with different pulse time and the contribution of applied pulse time in micro structural and wear resistance was systematically investigated. Structure, composition and tribological characteristics of the coatings were studied by scanning electron microscope (SEM), X-ray diffraction (XRD) and dry sliding reciprocating wear tests.

The application of Mg-Li alloys is restricted in practice due to mainly poor corrosion resistance and wear resistance. Electroless nickel plating is one of the common and effective ways to protect alloys from corrosion. In this study, nano-SiO₂ particles with Ni-P matrix have been successfully co-deposited onto dual phase Mg-8Li base alloy through electroless plating, generating homogeneously Ni-P/nano-SiO₂ composite coating. The morphology, elemental composition and structures of coatings were investigated. Coating performances were evaluated using hardness tests and electrochemical analysis. The results indicate that the Ni-P/nano-SiO₂ composite coating can significantly improve the wear and corrosion resistance.

In this paper, we characterize the local micro structure and mechanical properties of an AM60 magnesium alloy high-pressure die-casting in order to further develop predictive process-structure-property models. The casting process is simulated using the commercial code ProCAST™ in order to extract information regarding mold-filling and local solidification conditions including solidification rate and expected levels of shrinkage porosity. This data is used to predict the presence of knit lines, local porosity and the through-thickness variation of grain size (i.e. determination of skin and core thickness). Micro structural data is then used to predict upper and lower bounds on local mechanical properties including yield strength, tensile strength and ductility. A high degree of correlation between predicted and measured mechanical properties is found.

Magnesium alloys are important materials since they can be used to significantly reduce the weight of automobiles, but their application has been limited thus far. One possible way to extend the usage of magnesium alloys is applying them to peripheral parts of the engine that are large, have complicated shapes, and are exposed to high temperatures under the loaded condition. However, heat-resistant magnesium alloys always have poor castability, since such alloys have a lot of intermetallic compounds with poor ductility.In this study, hot cracking tests of Mg-Al-Ca cast alloys were performed in a high-pressure die-casting machine using a die with an I-shaped cavity to investigate the castability. At the same time, the heat resistance of the cast alloys was evaluated using a bolt load retention test. It was found that adding tin to heat-resistant Mg-Al-Ca improved its hot cracking behavior without reducing its excellent heat resistance.

The effect of microstructure on thermal expansion of AZ91D cast alloy was studied. Samples with equiaxed grains and a controlled secondary dendrite arm spacing (SDAS) were fabricated using gradient solidification. SDAS was chosen to represent the range of micro structural scale found in sand castings down to that of high pressure die casting. Optical microscopy and electron backscatter diffraction (EBSD) were used for micro structural characterization. The relation between thermal expansion and micro structural scale of existing phases precipitated, in particular grain size, SDAS and fraction of Mg₁₇Al₁₂ was analyzed.

In this research, aging behavior and precipitation sequence in an age-hardenable Mg-4Sm-1.3Zn-0.4Zr (wt%) alloy were investigated, using Differential Scanning Calorimeter (DSC) and Transmission Electron Microscopy (TEM) techniques. The precipitation sequence was determined to be Super Saturated Solid Solution (S.S.S.S) → solute atom clusters → γ″ → γ′ → γ, which changes drastically compared to those reported for Zn-free Mg-Sm-Zr alloys. Among them, γ″, with a GP zone structure, lies on {0001}_α basal planes, and is the dominant precipitate responsible for age hardening effect. γ′ has a hexagonal structure, with a=0.556nm, c=0.521nm.

The performance of structural materials is commonly associated with such design parameters as strength and stiffness relative to their density; a recognized means to further enhance the weight-saving potential of low-density materials is thus to improve on their mechanical attributes. The European Community research project ExoMet that started in mid-2012 targets such high-performance aluminum- and magnesium-based materials by exploring novel grain-refining and nanoparticle additions in conjunction with melt treatment by means of external fields (electromagnetic, ultrasonic, mechanical). These external fields are to provide for an effective and efficient dispersion of the additions in the melt and their uniform distribution in the as-cast material. The consortium of 27 companies, universities and research organizations from eleven countries integrates various scientific and technological disciplines as well as application areas — including automotive and (aero)-space.

In the previous study, to modify the morphology of Mg₂Si phase, we added CaO in Mg-Al-Si alloy. However, CaMgSi phase was formed by the addition of CaO in Mg-Al-Si alloy and the morphology of CaMgSi phase is needle type. Therefore, CaMgSi phase would deteriorate the mechanical properties. On the other hand, when adding Sr in CaO added Mg-Al-Si alloy, the modified CaMgSi phase was confirmed.This study is aimed at the evaluation of formed phase by Sr and CaO addition in Mg-Al-Si alloys and the investigation of mechanical properties and modification mechanism on the modified CaMgSi phase by the addition of Sr in CaO added Mg-Al-Si alloy.

Mg-based metal matrix nanocomposites (MMNCs) are expected to provide significant enhancement of properties by introducing thermally stable ceramic nanoparticles into the metal matrix. However, it is extremely difficult to achieve a uniform distribution of nanoparticles in the magnesium matrix for the predicted significant property enhancement. In this study an unprecedented uniform distribution and dispersion of 6 vol.% SiC nanoparticles in Mg6Zn matrix was obtained through a novel scalable processing method that combines semi-solid mechanical mixing and solid-state friction stir processing. The resulting Mg6Zn nanocomposites exhibit tremendous hardness and strength enhancement. The results provide a viable pathway for the development and production of high performance Mg-based nanocomposites for numerous applications.

This study elucidates about the development and characterization of novel magnesium (Mg) materials containing amorphous Copper-Titanium based (Cu₅₀Ti₅₀) alloy particles. It involves the incorporation of Cu₅₀Ti₅₀ amorphous alloy powder (prepared using high-energy ball milling process) in pure Mg matrix using microwave sintering assisted powder metallurgy technique followed by hot extrusion. The microstructure and mechanical properties of the developed Mg/Cu₅₀Ti₅₀ composite were evaluated. Microstructural studies revealed the retention of amorphous structure of reinforcement, its uniform distribution in Mg-matrix without interfacial reaction products. Mechanical properties under indentation loads indicated hardness improvement due to amorphous Cu₅₀Ti₅₀ particle addition. Under compression loads, the developed composites exhibited enhanced strength with negligible change in ductility. The observed mechanical properties are discussed using the process-structure-property relationship.

The mechanical and corrosive properties of two Magnesium wires are studied in the field of microhardness, tension-, compression-and 3-point-bending tests, corrosion and its influence on the mechanical properties. Due to recrystallization during their complex forming processes (casting, extrusion, wire drawing), both wires show a fine grained microstructure resulting in high strength and ductility. However, the ductility is mostly evaluated by 3-point bending and compression; due to the notch effect in the clamp area, the maximum tensile strength and elongation under tension cannot be measured. Both alloys show a tensile-compressive yield asymmetry. Even RE-elements are known to reduce this asymmetry, the Mg-Gd alloy shows 100 MPa higher strength in tension than compression. The asymmetry of the Mg-Ag wire is similar. Overall the wires show very high strength and hardness, Mg6Ag slightly higher compared to Mg4Gd. Strong pitting corrosion is found and reduces strongly the tensile and bending strength.

For applying a magnesium alloy to nails in the guided bone regeneration (GBR) method, sufficient strength and appropriate degradation speed are required to fix a membrane. In the case, the nails are exposed to body fluid after penetrating the alveolar bone. Therefore, in this research, degradation behavior after penetration of magnesium-calcium alloy which is expected to possess high biocompatibility was investigated. As a result, the Mg-Ca alloy nails were degraded inhomogeneously after immersion for 4 weeks in simulated body fluid. The degraded portions corresponded to the distribution of residual strain estimated by finite element analysis. Mg-Ca nails without precipitates possessed comparatively gradual degradation rate. It can be also confirmed that the region with residual strain degraded preferentially when compared the CT images and the residual strain distribution after penetration.

Magnesium alloys suffer from accelerated corrosion in physiological environment and hence their use as a structural material for biodegradable implants is limited. The present study focuses on a diffusion coating treatment that amplifies the beneficial effect of Neodymium on the corrosion resistance of magnesium alloys. The diffusion coating layer was obtained by applying 1 µm Nd coating on EW10X04 magnesium alloy using Electron-gun evaporator and PVD process. The coated alloy was heat treated at 350°C for 3 hours in a protective atmosphere of N2+0.2%SF₆. The micro structure characteristics were evaluated by SEM, XRD, and XPS; the corrosion resistance was examined by potentiodynamic polarization and EIS analysis. The corrosion resistance of the diffusion coated alloy was significantly improved compared to the uncoated material. This was related to: (i) formation of Nd2O3 in the outer scale, (ii) integration of Nd in the MgO oxide layer, and (iii) formation of secondary phase Mg41Nd5 along the grain boundaries of α-Mg.

Mg alloys have unique characteristics such as high specific strength, low density, high corrosion rate, etc., as functional as well as structural materials. Mg-Zn alloys have good biocompatibility because Mg and Zn are abundant nutritional elements in the human’s body. However, Mg alloys with multi-phase cause galvanic corrosion by corrosion potential differences among constituent phases. Therefore, the application of Mg alloys on bio-material parts are limited.In this study, bio-corrosion properties of Mg-Zn-Mn alloys according to the solid solution and distribution of phases by various Mn contents and heat treatment condition were evaluated. The results of tensile and in-vitro corrosion tests indicated that tensile and bio-corrosion properties could be adjusted by controlling the Mn contents and heat treatment. The tensile yield strength (TYS), ultimate tensile strength (UTS) and Elongation of Mg-Zn-Mn alloys increased up to 0.5 wt.% and then slightly decreased with Mn contents. However, TYS, UTS, and Elongation of T4 treated Mg-Zn-Mn alloys increased with increasing Mn contents. When MgZn phase and Mn particle were dissolved in the matrix, bio-corrosion properties were improved in hank’s solution. From the results of immersion test, the Mg-3Zn-0.5Mn alloy has good corrosion properties at 2 steps T4 treatment.

Mg 1 vol.% Ti and Mg 1 vol.% TiB₂ composites containing Ti (30–50 nm) and TiB₂ (~ 60 nm) nanoparticulates were successfully synthesized using disintegrated melt deposition technique followed by hot extrusion. In vitro degradation of synthesized pure magnesium and composites were assessed by immersion testing in Dulbecco’s Modified Eagle’s Medium (DMEM) + 10% Fetal Bovine Serum (FBS) solution for a maximum duration of 28 days. Determination of corrosion rates by weight loss technique reveals that after 28 days of immersion testing, Mg 1 vol.% Ti exhibited the best corrosion resistance followed by pure magnesium and finally by Mg 1 vol.% TiB₂ composite. The room temperature mechanical properties of the synthesized composites were found to surpass those of pure magnesium. On tensile and compressive loading, substantial strengthening of pure magnesium was observed with 1 vol.% Ti addition whereas appreciable increase in tensile and compressive fracture strains of pure magnesium was observed with 1 vol.% TiB₂ addition.

In recent years, some magnesium alloy systems have received attention to serve as potential materials for orthopedic implants due to their biocompatibility and biodegradability. Besides acceptable mechanical strength and corrosion rate, also non-toxicity is an important criterion in the development of these degradable magnesium alloys. Zinc and calcium are essential micro-nutrients in the body, therefore are not expected to be harmful, and positively influence strength by grain refinement and age hardening. To identify biomedical as well as other applications, the as-cast Mg-1Zn-1Ca (ZX11) material was tested for standard corrosion resistance as well as compression and creep strength, also at elevated temperatures. Microstructural investigations complete the determination of relevant characteristics for the use of ZX11. Grain size reduction is observed along the radius of the cylinder and SEM-EDX analysis reveals Mg₂Ca and Mg₆Ca₂Zn₃ phases have formed on the grain boundaries. Dislocation climbing seems to be the rate controlling deformation mechanism for creep. Compression strength increases with temperature gradually increased up to 100 °C, plateaus between 100 and 175 °C and decreases after that. Acceptable corrosion properties have been observed.

Magnesium alloys with acceptable or even controllable corrosion rates, where mechanical properties are not significantly modified or worsened, have been increasingly investigated in the last decade for use as biomaterials. This work shows an approach with a magnesium metal matrix composite (Mg-MMC), composed of ZK60 as base material and hydroxyapatite (HA) particles. The composite was produced by mechanical alloying followed by hot extrusion, as HA in contact with molten magnesium releases toxic gases such as phosphine (PH₃). This work will present the influence of different amounts of HA on corrosion behaviour and mechanical properties of the investigated composites. Compared to the ZK60 alloy, corrosion is expected to be delayed, without localized corrosion. The mechanical properties are not expected to be compromised with such composite during tissue’s healing period.

Magnesium and its alloys are being investigated worldwide for application in biodegradable implants, yet there are no commercially available alloys specifically developed for this application. Magnesium is an essential element in the human body and it would be logical then to explore the development of alloys that contain only elements which are known to be biocompatible because they are already part of the human body.In this work, Ca, Si and Sr were selected to develop magnesium alloys for biomedical application due to their good biocompatibility. A number of ternary Mg-Ca-Si and Mg-Si-Sr alloy compositions were explored. The alloys were cast in steel molds and their phase content was measured and compared with thermodynamic predictions. The effect of the characterized phases on the hardness and compressive strength was evaluated.

The corrosion resistant properties of 1–2 μm thick Al coatings deposited by radio frequency magnetron sputtering on polished Mg surfaces, within Ar and Ar/H₂ environments, have been appraised. The coatings were heat-treated at 300°C for 5 h to induce the formation of bioinert Al₂O₃, and samples were corroded within phosphate buffered saline solution at 37°C to mimic the biological environment. Both the as-deposited and heat-treated coatings were found to delay the onset of corrosion, but showed higher initial corrosion rates, once established, as compared with polished Mg surfaces. Slightly improved performance of the coatings was achieved through the addition of H₂ to the system which acted to inhibit Al-Mg alloying and MgO formation. However, localized accelerated corrosion associated with substrate polishing damage emphasized the need for improved process control and coating uniformity.

Magnesium alloys with their weight saving advantage exhibit unique application potential in the automotive and aerospace industries. Recent years have seen significant progress in the development of rare earth containing Mg alloys, as rare earth addition is considered a promising route to enhance the mechanical characteristics of Mg. In the present study, a new Mg alloy containing 5.16 at. % aluminum and trace (0.05 at. %) erbium was synthesized using the disintegrated melt deposition technique followed by hot extrusion. The microstructural and mechanical properties of the developed Mg-Al-Er alloy were evaluated in comparison to that of pure Mg. Microstructural investigation revealed significant grain refinement and the presence of Mg₁₇Al₁₂ intermetallic phases. Evaluation of mechanical properties under indentation loads showed significant improvement in microhardness by +50%. Under tensile loads, the developed Mg-Al-Er alloy exhibited +86%, +115% and +95% enhancement in yield strength, ultimate strength and ductility respectively. Similarly, an enhancement in yield strength by +115%, ultimate strength by +37% and ductility by +25% were observed under compressive loads. The overall effects of Al and Er addition on the mechanical properties of the Mg are discussed using structure-property relationship.

The inherent magnetic properties of lightweight alloys based on magnesium and cobalt offer a novel way in order to measure mechanical loads throughout the entire structural component using the magnetoelastic effect. Because the solubility of cobalt in the magnesium matrix is negligible, the magnetic properties mainly originate from Co-rich precipitates. Thus, the size and distribution of Co-containing phases within the alloy’s microstructure wields a major influence on the amplitude of the load-sensitive properties which can be measured by employing the harmonic analysis of eddy-current signals. In this study, Mg-Co-based alloys are produced by several casting methods which allow the application of different cooling rates, e.g. gravity die casting and high-pressure die casting. The differences between the manufactured alloys’ micro- and phase structures are compared depending on the applied cooling rate and the superior magnetic and mechanical properties of the high-pressure die cast material are demonstrated.

The thermal conductivities of quaternary Mg-Zn-CaO-La alloys have been investigated by evaluating the effect of La on Mg-4Zn-0.5CaO alloys, with an emphasis to develop a new Mg alloy without compromising thermal conductivity, process-ability and mechanical property. The thermal conductivity of these alloys had been determined by tests for thermal properties, such as specific heat and diffusivity, from room temperature to 200 °C. The microstructures of specimens were observed by OM and SEM, and the phase analysis was performed by XRD, EDS. The fluidity was also investigated by using a spiral fluidity mold for improved process-ability during actual die casting. To evaluate the mechanical properties of tested alloys, tensile tests were carried out at room temperatures.As a result, although the La addition decreased the thermal conductivity of Mg-Zn-CaO alloy, with increasing La contents, thermal conductivities of La added alloys maintained and the yield strength of room temperature increased. In addition, the average spiral flow lengths of Mg-Zn-CaO-xLa alloys were almost same levels with Mg-Zn-CaO alloy.