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Über dieses Buch

The Magnesium Technology Symposium, the event on which this collection is based, is one of the largest yearly gatherings of magnesium specialists in the world. Papers represent all aspects of the field, ranging from primary production to applications to recycling. Moreover, papers explore everything from basic research findings to industrialization. Magnesium Technology 2017 covers a broad spectrum of current topics, including alloys and their properties; cast products and processing; wrought products and processing; forming, joining, and machining; corrosion and surface finishing; ecology; and structural applications. In addition, there is coverage of new and emerging applications.

Inhaltsverzeichnis

Frontmatter

Magnesium Technology 2017: Keynote Session I

Frontmatter

Multi-scale Investigation on Yield “Symmetry” and Reduced Strength Differential in an Mg–Y Alloy

Mg and its alloys are promising candidates for light-weighted structural applications, e.g., aircraft, automobile, electronic, etc. However, the inherent hexagonal close packed crystal structure makes the deformation of Mg anisotropic, namely deformation only occur by dislocation slip in the close-packed (0001) plane (i.e., basal plane), or by deformation twinning in $$ \{ 10\bar{1}2\} $$ planes. Consequently, polycrystalline Mg alloys undergone thermos-mechanical processing usually contain strong texture, i.e., preferred crystallographic orientation in grains. The texture in turn leads to anisotropic deformation in wrought Mg alloys. For example, in extruded Mg alloys, the compressive yield strength is usually much lower than the tensile yield strength (so-called yield asymmetry and strength differential). It is the anisotropy that hinders the broader application of Mg alloys. Recent modeling study on Mg predicts that certain alloying elements, particularly rare-earth elements (e.g., Y, Ce, Nd, Gd, etc.), could alter the active deformation modes, and promote more homogeneous deformation and overall mechanical properties in Mg. Therefore, this work aims to investigate experimentally the effects of alloying element Y in reducing the intrinsic and extrinsic anisotropy, modifying texture, and enhancing the overall strength and ductility for Mg. Fine-grained Mg 2.5 at.% Y alloy (FG Mg–2.5Y) was prepared by powder metallurgy method, including gas atomization for producing Mg–2.5Y powder, degassing and hot isostatic pressing (HIP), and hot extrusion. Both the as-HIPed and the as-extruded materials were characterized by electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM), and/or atom probe tomography (APT). Tension and compression tests were carried out along the extrusion direction (ED) for FG Mg–2.5Y. Unlike common Mg alloys exhibiting yield asymmetry, the FG Mg–2.5Y exhibits virtual yield “symmetry” and significantly reduced strength differential. Namely the deformation is more isotropic. In addition to post-mortem TEM characterization for deformed FG Mg–2.5Y, in situ TEM was also performed at the National Center for Electron Microscopy (NCEM), in an effort to understand the fundamental deformation mechanisms in FG Mg–Y that lead to reduced anisotropy. In situ TEM for single-crystal Mg–Y nano-pillars reveals that deformation twinning is replaced by dislocation slip in non-basal planes (i.e., prismatic planes), which diametrically differs from any other Mg alloys.

Dalong Zhang, Lin Jiang, Xin Wang, M. Arul Kumar, Irene J. Beyerlein, Julie M. Schoenung, Mo Li, Subhash Mahajan, Enrique J. Lavernia

Targeting High Impact R&D for Automotive Magnesium Alloys

Reducing vehicle weight improves the fuel efficiency, driving dynamics, and performance of vehicles ranging from traditional internal combustion engine (ICE) powered to battery electric vehicles (BEVs), fuel cell vehicles (FCVs), and the full range of hybrids [1]. However, along with tremendous opportunities, introduction of novel lightweight materials and architectures presents numerous engineering and commercial challenges. For the case of magnesium (Mg) the weight reduction potential, which exceeds 50% for some components, is offset by manufacturing, mechanical property, corrosion, and material cost hurdles, among others. While the vision of an all-Mg vehicle is laudable in its ambition, a more practical reality features Mg playing an important role in a multi-material vehicle architecture. In order to pursue the most promising and relevant Mg research and development, we need to assess several important questions: for which parts (or kinds of parts) is Mg best suited? What are the predominant engineering challenges preventing use of Mg for these parts? Where do we, as a materials science and engineering community, start in pursuing solutions to these challenges?

William J. Joost

Magnesium Development as a Lightweight Material—In Competition with Other Structural Materials

Magnesium is emerging as a lightweight material for mass reduction and structural efficiency in the automotive, aerospace and consumer industries, but is currently only a niche material competing with other structural materials such as advanced high-strength steels, aluminum and carbon-fiber-reinforced polymers. This talk will discuss what the magnesium community can learn from our competition, what critical technologies needed for magnesium to become a main stream material for automotive lightweighting. This talk will also present successful examples of multi-material lightweighting in the automotive industry, and highlight the role of magnesium in providing lightweight solutions when competing with other structural materials. Opportunities and challenges for automotive applications of magnesium will be discussed.

Alan A. Luo

The Continued Quest for Low-Temperature Formability in Mg Alloys: Historical Developments and Future Opportunities

It is well-known that opportunities for the application of wrought magnesium alloys have been limited by the limited low-temperature formability. The roots of this problem lie in the limited number of active slip mechanisms and strong basal textures, which result in strong deformation anisotropy, and thus brittle behavior. Historically, there have been many studies on approaches that aim at activation of non-basal deformation mechanisms and weakened or randomized texture to lend magnesium allows more formability. On the processing side, these approaches include rolling variants such as cross-rolling, twin-cast rolling, and differential speed rolling. On the alloying side, it has been shown that the addition of rare-earth elements (REs) activates non-basal slip modes and simultaneously weakens texture, therefore improving the plasticity, however the cost and availability or REs has encouraged the search for similar, yet cheaper alternatives. In this regard, Ca has emerged as a strong candidate replacement element, with Mg–Ca alloys showing many similar behaviors to Mg-RE alloys. Another less-common approach to enhanced formability is grain refinement. It is commonly believed that fine grained Mg-alloys will not behave in a uniform plastic manner due to the suppression of the twinning mechanisms that are critical to c-axis deformation. New studies, however, indicate that reduction of grain sizes to the sub-micrometer, and even nanoscale, can alter plasticity mechanisms and promote more uniform material flow. Other novel approaches to enhancing formability, including nanoparticle dispersions and tension-twin promotion will be presented. The scientific opportunities and challenges for each mechanism will be deliberated, and future research and development opportunities will be considered.

Suveen N. Mathaudhu

Magnesium Technology 2017: Alloy Development

Frontmatter

Using the Crystal Plasticity Approach to Parse the Effects of Alloying and Aging on the Mechanical Behavior of Wrought Mg Alloys

Predicting the collective effects of solid solution alloying, precipitation, and grain size on the mechanical properties of a given alloy is one of the “holy grails” of mechanical metallurgy. For alloys with a cubic crystal structure, this is challenging enough to have been solved only in specific cases, and even there, predicting the anisotropies induced by crystallographic texture is very difficult. In the case of hexagonal close packed Mg alloys, this challenge is even greater and arguably more important. Research over the past decade has also highlighted the significant impact precipitatePrecipitate shape and orientation can have on the strength of Mg alloys. This review lecture will show, with examples from conventional and rare earthRare earth containing Mg alloys, that the crystal plasticity approach has enabled the level of our predictive capability to rapidly approach the level, which exists in other more mature alloys systems.

Sean R. Agnew, Jishnu J. Bhattacharyya, Fulin Wang, Patrick J. McQuade

Development of High-Strength High-Speed-Extrudable Mg–Al–Ca–Mn Alloy

We investigated the effect of Al content on tensile property and microstructure of Mg–(0.6, 1.1, 1.6)Al–Ca–Mn (wt.%) alloys extruded at an extraordinary high die-exit speed of 60 m/min. All the extruded alloys showed fine grain structure with strong alignment of (0001) planes parallel to the extrusion direction. Especially, the sample containing 1.6 wt.% of Al had stronger alignment of (0001) planes than that of the other alloys. The alloy with 1.6 wt.%Al exhibited the highest ultimate tensile strength of 311 MPa and the proof stress of 284 MPa. However, the addition of 1.6 wt.% Al formed coarse Al–Mn particles and resulted in the low elongation of 16% compared to the other samples. Although the addition of 1.1 wt.% of Al also resulted in the formation of Al–Mn particles, the particle size was smaller, and their number density was lower than those in the sample containing 1.6 wt.% of Al. Therefore, high ultimate tensile strength of 297 MPa, proof stress of 263 MPa, and large elongation of 24% were simultaneously achieved in the sample containing 1.1 wt.% of Al.

T. Nakata, C. Xu, T. T. Sasaki, Y. Matsumoto, K. Shimizu, K. Hono, S. Kamado

Development of Ultra-High Strength and Ductile Mg–Gd–Y–Zn–Zr Alloys by Extrusion with Forced Air Cooling

Magnesium alloys containing heavy rare earth metals (HRE) have been attracting wide attention due to their remarkable age-hardening response. ExtrusionExtrusion of Mg-HRE alloys generally requires high ram force, leading to heat generation during the extrusion. In this study, by simply utilizing forced air cooling, high strength Mg–8.2Gd–3.8Y–1Zn–0.4Zr (wt%) alloy with good ductility was successfully developed via tailoring the microstructureMicrostructure. The dynamic recrystallizationDynamic recrystallization (DRX) ratio, grain size and texture can be controlled by cooling during the extrusion process, that is, the forced air cooling reduces the extrusion temperature and brings about rapid cooling of the extrudate after extrusion. Consequently, the alloy extruded with forced air cooling exhibits high tensile yield strength of 378 MPa, ultimate tensile strength of 436 MPa and high elongation to failure of 12.5% due to a bimodal microstructure consisting of finer DRXed grains with relatively random orientations and coarse unrecrystallized grains with a strong basal fiber texture.

C. Xu, T. Nakata, M. Y. Zheng, S. Kamado

Effect of Extrusion Ratio on Microstructure and Resulting Mechanical Properties of Mg Alloys with LPSO Phase

The WZ21 (Mg + 1.8 wt% Y + 0.7 wt% Zn) magnesium alloy having an addition of 0.5 wt% of CaO was extruded with different extrusion ratios (4:1, 10:1, 18:1) at 350 °C. In all alloys, a long-period stacking-ordered (LPSO) phase composed of Zn and Y is formed. The microstructure was analyzed by electron backscatter diffraction (EBSD) mapping. The WZ21 alloy after extrusion with the extrusion ratio of 4:1 contains large grains. The fraction of recrystallized grains increases with increasing extrusion ratio. All samples have basal planes oriented parallel to the extrusion direction (ED) and this texture weaken with increasing extrusion ratio. Mechanical properties of the samples were investigated during compression along ED at room temperature and at a constant strain rate of 10−3 s−1. Concurrently, with the deformation tests, the acoustic emission (AE)Acoustic Emission (AE) response of the specimens was recorded. The maximum of the AE count rate in all cases corresponds to the macroscopic yield point.

Klaudia Horváth, Daria Drozdenko, Gerardo Garcés, Kristián Máthis, Patrik Dobroň

Mechanically Alloyed Magnesium Based Nanostructured Alloy Powders for Biomedical Applications

Mechanical alloyingMechanical alloying (MA) is one of the most commonly used methods in preparing metallic materials. We are especially interested in its ability to produce nanostructured materials. MA has rarely been used in producing nanostructured magnesium base alloys due to the process complexity and flammable nature of the alloy. In this work, high energy ball milling of elemental powders, Mg, Zn and Zr, was investigated for the MA of ZK50 alloy. Crystallite size, lattice strain, as a function of total milling energy (required for complete alloying) were characterized using X-ray diffraction. Scanning electron microscopy was employed to determine the influence of milling time on powder morphology. Consolidation of the milled powders into thin sheets was conducted via hot pipe rolling at 0.4 Tm. Results showed that complete alloying was achieved at 45 milling hours which was associated with particle size reduction to 600 nm and crystallite size of 8.8 nm.

P. Morcos, K. I. ElKhodary, H. G. Salem

Combined Effects of Grain Size Refinement and Dynamic Precipitation on Mechanical Properties of a New Magnesium Alloy

Two well-known methods for enhancing the strength and controlling the anisotropy in magnesiumMagnesium alloys are precipitation hardening and grain size refinement. In this study, both methods are combined in an attempt to achieve optimal strengthening and anisotropy control: this was done via severe plastic deformation using Equal Channel Angular Processing (ECAP)Equal channel angular processing (ECAP) of a precipitation hardenable magnesium alloy, Mg–6Zn–0.6Zr–0.4Ag–0.2Ca (wt%), within the temperature range of 125–200 °C. ECAP specimens were processed along different routes, where mechanically several of the ECAP samples show ultra-high strength levels approaching 400 MPa. The roles of grain size, texture, and precipitate morphology on mechanical properties are systematically investigated. It is shown here that the resulting microstructures generally show a refined grain size around 500 nm with a complex distribution of Mg-Zn enriched precipitates, which via ECAP either dynamically precipitate or are redistributed from the starting condition.

M. W. Vaughan, J. M. Seitz, R. Eifler, H. J. Maier, I. Karaman

Zn Segregation at Precipitate/Matrix Interface in Mg–Sn–Zn Alloys

Magnesium-tin based alloys have received considerable attention in the past 15 years for developing high strength alloys. Mg–Sn binary alloys are precipitation hardenable, but their age-hardening response is moderate. Additions of Zn can significantly improve the age-hardening response of binary Mg–Sn alloys by refining the distribution of Mg2Sn precipitates. To understand the role of Zn in the precipitation process, Mg2Sn precipitates with different morphologies and orientations in under-, peak- and over-aged samples of a Mg–9.8Sn–1.2Zn (wt%) alloy are characterized by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and STEM X-ray mapping. It is found that Zn atoms always segregate to the precipitate-matrix interface, irrespective of the interfacial structures and orientation relationships of the Mg2Sn precipitates. This finding provides an insightful clue to the understanding of the enhanced nucleation and thermal stability of Mg2Sn precipitates in the Mg–Sn–Zn alloys.

Chaoqiang Liu, Houwen Chen, Jian-Feng Nie

Machinability Investigation in Micro-milling of Mg Based MMCs with Nano-Sized Particles

Magnesium based metal matrix composites (MMCs) have been employed in various areas such as automobile and aerospace due to their weight saving potential, high specific mechanical properties and excellent damping capacity. Recently, improved strength and ductility have been observed due to the incorporation of nano-sized reinforcements into magnesium. This paper presents the experimental results on the machinability of Mg based metal matrix composites (MMCs) with nano-sized particles (Mg/BN MMCs and Mg/ZnO MMCs) produced by liquid-state processing during micro-milling process. The effect of reinforcement materials and weight fraction, as well as the varying cutting parameters such as feed per tooth, spindle speed and depth of cut on the cutting force, surface morphology and chip formation were studied. The results show that the cutting force for machining pure Mg is larger than that for other MMCs specimen except of Mg/2.5 wt% ZnO and MMCs reinforced containing ZnO particles exhibit higher cutting force than that containing BN particles. Moreover, compared to the pure Mg, chips with different morphology can be found in machining MMCs.

Xiangyu Teng, Dehong Huo, Wai Leong Eugene Wong, S. Sankaranarayanan, Manoj Gupta

Magnesium Technology 2017: Solidification and Processing I

Frontmatter

Microsegregation in High Pressure Die Cast Mg Alloys

Expanding Integrated Computational Materials Engineering (ICME) capabilities for High Pressure Die Cast (HPDC) and Super Vacuum Die Cast (SVDC) magnesium alloys will result in significant reductions in the time and cost required to develop components and optimize the casting and heat treatment processes. In this work, a description of segregation in SVDC Mg–Al binary and Mg–Al–Mn ternary alloys is obtained by combining quantitative Electron Probe MicroAnalysis (EPMA) mapping in conjunction with an EPMA forward simulation model. This approach was used to demonstrate that solute trapping near the casting surface can be described though use of a solidification front velocity dependent partition coefficient within the Scheil solidification model framework.

Tracy D. Berman, Mei Li, John E. Allison

Numerical Simulations of TRC Equipped with a Core

TRC (Twin-Roll Casting) has been used for production of sheets of aluminum alloys and stainless steels. Recently, the technology began to be applied to production of magnesium alloy sheets. In the present investigation, HTRC (Horizontal Twin-Roll Casting) was analyzed for AA3003 and Mg-AZ31 by the rigid-thermo-viscoplastic finite-element method to investigate differences between these materials in various aspects of fabrication. The result of the present investigation was expected to help set properly process parameters of HTRC for magnesium alloy sheets. In addition, a core was introduced in the nozzle at the roll gap to investigate its efficiency in those aspects. As a result, the core was found to lower roll-separating force as well as roll torque by reducing not only vortex development but also volume of the melt in the melt pool. It also reduced temperature discrepancy through thickness of a sheet at the roll exit.

Jong-Jin Park

Growth of Al8Mn5 Intermetallic in AZ91

Al8Mn5 is crucial for impurity control and corrosion resistance of AZ91. We study the growth morphology of primary and eutectic Al8Mn5 after the equiaxed solidification of AZ91 cooled at ~1 K/s. Primary Al8Mn5 grew as ~10 μm equiaxed faceted crystals with multiple growth facets. The eutectic Al8Mn5 grew with a complex faceted morphology ranging from rod to sheet and folded plate-like, often with growth steps on the largest facets. The results are compared with the AZ91 solidification path predicted by PanDat with the PanMg8 database.

G. Zeng, J. W. Xian, C. M. Gourlay

Influence of CaO Grain Refiner Addition on the Microstructure and Mechanical Properties of As-Cast Mg Alloys

The current work provides a comparison between the effect of Ca solute and CaO powder addition on the grain refinement and mechanical properties of Mg alloys. Two groups of samples were produced in order to compare. One through Ca solute addition to the melt whilst the other through the addition of CaO powder. Grain size measurements showed that values were very close for the two samples groups. Vickers harness results showed better results for Ca solute containing alloys. Based on tensile testing experimental results, the empirical relations between elastic modulus, Ultimate tensile strength, yield strength and elongation versus alloys concentrations were established. It has been found that grain refinement is not the main strengthening mechanism in both systems but the effect of grain refinement strengthening component is higher in Mg–CaO system than that in Mg–Ca system.

Yahia Ali, Dong Qiu, Ming-Xing Zhang

Grain Refinement of Mg and Its Alloy by Inoculation of In Situ MgO Particles

Significant grain refinement of commercial purity Mg and AZ91D Mg alloy was achieved by intensive melt shearing imposed to the melts prior to solidificationSolidification without addition of grain refiner. Heterogeneous nucleationHeterogeneous nucleation mechanism was investigated using analytical electron microscopy. It was demonstrated that the grain refinement was resulted from the promoted heterogeneous nucleation by inoculation of in situ MgO particles, which had been effectively dispersed by melt shearing. It was shown that MgO formed in pure Mg and AZ91D alloy melts were {1 0 0} and {1 1 1} faceted, respectively. For pure Mg sample, high resolution TEM revealed two orientation relationships OR I: (1 0 0) [0 −1 1] MgO // (0 −1 1 2) [0 1 −1 1] Mg, and OR II (1 0 0) [0 −1 1] MgO // (1 −1 0 2) [−2 4 −2 3] Mg. For the alloy sample, however, α-Mg grain was found to nucleate on the faceted {1 1 1} planes of MgO particles according to the OR III: (1 1 1) [0 −1 1] MgO // (0 0 0 1) [1 1 −2 0] Mg. The large number of MgO particles dispersed by intensive melt shearing acted as the substrates to promote heterogeneous nucleation process, leading to the significant grain refinement.

Yun Wang, Guosheng Peng, Zhongyun Fan

Numerical Study of Magnesium Production by Pidgeon Process and Pre-prepared Pellets Silicothermic Process: Comparison of Heat Transfer

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. After calcinations, porous pellets were obtained due to the decomposition of dolomite in the pellets. Heat transfer of the porous pellets is different from that of pellets used in Pidgeon process. In the present paper, a comparative study on heat transfer of the novel process and Pidgeon process was carried out by numerical method. The results indicated that heat transfer in Pidgeon pellets is slightly better than that in the porous pellets. For the novel process, the center temperature in a retort of 300 mm-diameter reaches 1473 K after heating the retort at 1523 K for 2.3 h (without considering reaction heat), which needs 4.8 h for the Pidgeon process.

Daxue Fu, Ting-an Zhang, Zhi-he Dou, Lukui Guan, Ming Wen

On the Age Hardening Response of Aluminum Containing Magnesium Sheets with Zinc or Manganese (AZ- and AM Series Alloys)

A higher content of Al in Mg alloys leads to the formation of the precipitation hardening intermetallic compound Mg17Al12. However, the rollability and the resulting ductility and formability of sheets of such alloys are reduced with increasing Al content. In this study, Mg alloys of the AZ- and AM- series were used to investigate the impact of the Al content on the rollability, the resulting sheet properties and the ability to precipitation strengthen the sheets subsequent to the rolling process. Alloys with 6 and 8 wt% content of Al were used. The higher content of aluminum leads to a decrease of rollability at a given rolling schedule as well as a decrease of the ductility of the sheets after rolling and annealing. Alloys of the AM series perform more advantageously compared to AZ series alloys. However, Mn limits the ability to precipitation strengthening. The ability to balance both properties is discussed.

Jan Bohlen, Ander Telleria Iparragirre, Gurutze Arruebarrena, Dietmar Letzig

Performance Evaluation of High-Pressure Die-Cast Magnesium Alloys

Over 90% of the magnesium (Mg) alloys in commercial applications are produced by high-pressure die-casting. This paper presents our efforts in evaluating castability and properties of commercial and near-commercial magnesium alloys to demonstrate how the currently available alloys can be applied to different situations across a range of property space. For high temperature applications, i.e. 175 °C and above, Mg–RE and Mg–Al–Ca based alloys have creepCreep properties at least comparable to aluminium (Al) alloy A380 although these alloys have some challenges with casting or cost. For moderate temperatures, Mg–Al–RE based alloys, especially AE44, are most attractive due to an excellent combination of creep resistance, strength and castability. For automotive structural applications where a good combination of strength and ductility is required, Mg–Al alloys provide the baseline, but Mg–Al–RE based alloys can provide outstanding performance, especially with recent discoveries about its response to age hardening treatments. Therefore, high-pressure die-cast Mg alloys hold great promise for continued growth in automotive applications.

Mark Easton, Suming Zhu, Mark Gibson, Trevor Abbott, Hua Qian Ang, Xiaobo Chen, Nick Birbilis, Gary Savage

Simulation Study on Direct Desulfurization of Molten Iron by Magnesium Vapor

A new technique of bottom blown method was proposed for desulfurization of molten iron, which uses inert gas to carry magnesium vaporMagnesium vapor and combines with mechanical stirring. A water model was established based on the similarity principle. Experimental phenomena were recorded by a high-speed camera combining with image processing method. The influence factors on bubbles disintegration and dispersionBubbles disintegration and dispersion of molten pool were researched. By the stimulus response technique measuring changes of conductivity in the molten pool, influence factors of mixing time were studied. Results show that: the new technique is conducive to the bubble disintegration and dispersion of the molten pool, which shortens the uniform mixing time and prolongs the residence time of bubbles in the molten pool. The desulfurization efficiencyDesulfurization efficiency can be enhanced and the removal time of sulfur is shortened. It can also reduce the temperature drop during desulphurization and be beneficial to improve the efficiency utilization of magnesium in iron industry.

Yan Liu, Yongkun Yang, Dongxing Wang, Xiaolong Li, Ting-an Zhang

Magnesium Technology 2017: Mechanical Behavior: Twinning, Plasticity, Texture, and Fatigue I

Frontmatter

Twinning Super Dislocations to Help Understand Strength

The present article provides a short look at the strength of magnesium when twinning dominates the yielding behavior. The twin is approximated by a super dislocation to draw some tentative conclusions regarding the stresses required to: (1) thicken a twin to the aspect ratio observed experimentally, (2) propagate a twin over a grain, (3) thicken a twin within a stress concentration and (4) bow the propagating twinning front between particles. In all cases, relaxation of the twin stress field is important.

Matthew R. Barnett

Transmutation of Basal Dislocations by Twinning in Magnesium

Basal dislocations in hexagonal close-packed materials remarkably can enhance the mobility of $$ \{ 10{\bar{\text{1}}\text{2}}\} $$ twin boundaries which absorb them. This behavior has been extensively studied and leads to complex faceting, disclination content, and mobile disconnections. However, we recently uncovered that under loading which suppresses $$ \{ 10{\bar{\text{1}}\text{2}}\} $$ twin mobility, certain basal dislocations can punch through the boundary, generating $$ \left\langle {c + a} \right\rangle $$ dislocations inside the twin. The transmutation requires two mixed basal dislocations to move into the boundary and produces a mixed $$ \left\langle {c + a} \right\rangle $$ dislocation on the prismatic plane of the twin along with a mobile twinning disconnection. This reaction is nearly identical to one predicted decades ago by Price. The reaction is both stress and temperature sensitive and depends heavily on complex faceting reactions at the boundary. By studying the dependence of transmutation versus absorption upon stress and faceting, we have uncovered general new insights showing how interfaces react with dislocations.

Christopher Barrett, Fulin Wang, Sean Agnew, Haitham El Kadiri

Ductility Enhancement in Mg Alloys by Anisotropy Engineering

A mean-field theory suggests that certain forms of plastic anisotropy hinder ductile damage accumulation. Here, a proof-of-concept is presented in the case of Mg–Al–Zn alloys. Textures produced by severe plastic deformation are compared with the as-received rolling texture in terms of their anisotropy-ductility correlations at ambient temperature. The 3D plastic anisotropy is characterized in each material using compression specimens. The ductility is characterized using tensile bars. A micromechanical model is introduced to rationalize the trends in terms of the anisotropy effect on ductility (AED) index. Here, this index is tuned via texture manipulations at fixed chemical composition and grain size. The main finding suggests that plastic anisotropy can be engineered to aid ductility.

S. Basu, E. Dogan, B. Kondori, I. Karaman, A. A. Benzerga

Modeling the Effect of Alloying Elements in Magnesium on Deformation Twin Characteristics

HCP magnesium metals are widely used in different industries due to their low density and high specific strength. Their applicability is restricted due to poor formability and high anisotropy in deformation behavior. The formability of magnesium can be improved by alloying additions and this modification can affect macroscopic plastic anisotropy. Alloying additions can also significantly control the twinning process. In this work we use a crystal plasticity based Fast Fourier Transform model to characterize deformation twinning in different alloy types. In the model, the influence of alloying additions is represented through their effect on the critical resolved shear stress (CRSS) values for all slip and twinning modes. From this study, we build an understanding of the influence of alloying elements on twin growth and twin transmission behavior. A new plastic anisotropy measure is proposed to quantify the effects of alloying elements on some important twinning characteristics in magnesium alloys.

M. Arul Kumar, I. J. Beyerlein, R. A. Lebensohn, C. N. Tomé

Simulating Discrete Twin Evolution in Magnesium Using a Novel Crystal Plasticity Finite Element Model

An advanced, image-based crystal plasticity FE model is developed for predicting discrete twin formation and associated heterogeneous deformation in the single and polycrystalline microstructure of Magnesium. Twin formation is sensitive to the underlying microstructure and is responsible for the premature failure of Mg. The physics of nucleation, propagation, and growth of deformation-twins are considered in the CPFE formulation. The twin nucleation model is based on dissociation of sessile dislocations into stable twin loops, while propagation is assumed by layer-by-layer atoms shearing on twin planes and shuffling to reduce the energy barrier. A non-local FE-based computational framework is developed to implement the twin nucleation and propagation laws, which governs the explicit formation of each individual twin. The simulation matches satisfactorily with the experiments in the stress-strain-response and predicts heterogeneous twin formation with strain localization.

Jiahao Cheng, Somnath Ghosh

The Effect of Twin Boundary on the Evolution of Defect Substructure

Pure Mg single crystalsSingle crystal were deformed at room temperature along two orientations in sequence, in order to activate a specific dislocation slip mode followed by $$ \left\{ {10\bar{1}2} \right\} $$ twinning. The defects in both the matrix and twin crystals were analyzed with a transmission electron microscope (TEM)Transmission electron microscope (TEM). This study reveals the collective evolution of the defect substructure when a dislocated crystal is “invaded” by a moving twin boundaryTwin boundary. When primarily $$ \left[ c \right] $$-containing defects in the matrix were incorporated by a moving twin boundary, including $$ \langle c + a\rangle $$, pure $$ \left[ c \right] $$ dislocations and $$ I_{1} $$ stacking faults, the twin contains homogeneously distributed $$ I_{1} $$ stacking faults, which in some instances appear to be connected on twin boundary to the faults in the matrix.

F. Wang, C. D. Barrett, K. Hazeli, K. D. Molodov, T. Al-Samman, A. Oppedal, D. A. Molodov, A. Kontsos, K. T. Ramesh, H. El Kadiri, S. R. Agnew

Magnesium Technology 2017: Solidification and Processing II

Frontmatter

Optimization of a TRC-Tip for Producing of Mg-Sheet Material

Twin roll casting (TRC) is an effective and therefor cost saving method for the production of Mg sheet material. This is essential for widening the areas of application of magnesium especially in the automotive sector. Part of the ongoing project SubSEEMag which is focused on the substitution of rare-earth elements in Magnesium wrought alloys is the improvement of the TRC process. One problematic aspect producing magnesium strip material in the TRC process is based on the temperature profile of the melt inside the tip. This could result in freezing of the melt inside the tip and its destruction. For resolving this problem various coated and non-coated ceramic materials were investigated regarding their thermal isolation capability and their durability in contact to molten Magnesium. For improving the flow behavior a new geometry of the tip was developed based on numerical simulations.

D. Letzig, R. Hoppe, J. Isakovic, G. Kurz

Effects of Mn and Zn Solutes on Grain Refinement of Commercial Pure Magnesium

The effects of Mn (peritectic system) and Zn (eutectic system) on the grain refinement of commercial pure Mg were investigated. Interdependence model and solute paradigm theory were applied to evaluate the grain nucleation and growth for these two alloy systems. Both Mn and Zn can refine the grain of pure Mg. Compared to Mg–Zn, the nucleant particles in Mg–Mn alloys are more potent, but the relatively activated number of nucleation sites is much fewer. Zn with relatively high value of growth restriction factor increases the initial rate of development of the constitutional supercooling (CS) zone at the earliest stage of grain growth, which plays a key role in determining the final grain size. Moreover, heavy segregation of Zn during solidification provides a driving-force to activate further nucleation in the CS zone, which may trigger some unknown native nucleation particles to sever as nuclei.

Jian Gu, Yuanding Huang, Mingxing Zhang, Karl Ulrich Kainer, Norbert Hort

Experimental Investigation of Continuous Magnesium Production by Carbothermal Reduction

Magnesium production by carbothermal reduction (CTR) has the potential to significantly reduce operational and capital costs relative to reduction by ferrosilicon or electrolysis of magnesium chloride. As magnesium is gaseous at CTR temperatures the challenge remains in the effective separation of magnesium vapor and CO by-product, which can recombine unproductively. Our initial investigations focused on CTR kinetics and magnesium yield in batch reactions at isothermal and isobaric conditions. Further experimentation simulated continuous production; magnesium metal was boiled in a thermogravimetric system and mixed with CO in a tubular condenser. Monitoring of the CO signal by nondispersive infrared absorption (NDIR) allowed for determination of the extent of reversion, and analysis of deposits revealed the purity of the product Mg. The effect of pressure and temperature were investigated in both systems. Based on these results a continuous moving bed condenser was fabricated to determine the feasibility of vapor product capture from CTR.

B. Chubukov, S. Rowe, A. Palumbo, I. Hischier, A. Weimer

Precipitation Behavior of Mg–Al–Sn–Zn–(Na) Alloy

The precipitation behavior of Mg–Al–Sn–Zn alloys was investigated in this study. By artificial aging treatment, maximum hardness values of ATZ821 and ATZ651 alloys were higher than ones of AZ61 and AZ81 alloys without any change in the peak aging time. Based on TEM analyses, it was confirmed that Mg2Sn precipitates formed on edge-tip sides of pre-formed Mg17Al12 precipitates on the basal plane of α-Mg matrix. It indicates that Mg17Al12 precipitates play a heterogeneous nucleation sites for Mg2Sn precipitates. In addition, Mg17Al12 and Mg2Sn precipitates could be dramatically refined and homogeneously dispersed by a dilute addition of sodium which caused an increase in maximum hardness value and significant decrease in peak aging time. Unlike previous reports, Mg17Al12 precipitates which could serve nucleation sites for Mg2Sn were refined by a dilute addition of sodium, as a result of which Mg2Sn precipitates were also refined.

Su Mi Jo, Yohan Go, Bong Sun You, Young Min Kim

Study on the Direct Oxidation Thermal Decomposition of Magnesium Chloride by Product in the Sponge Titanium Production Process to Prepare Magnesium Oxide

Molten MgCl2 generally sold as a kind of waste at low price after cooling, which caused the waste of resource and energy. In order to solve the problem, a new method named “situ pyrolysis of molten magnesium chloride” was proposed. The molten MgCl2 produced by vacuum distillation in magnesium thermal reduction process was treated by the direct oxidation thermal decomposition method to produce super fine MgO with high purity. The magnesium produced by thermal reduction of MgO could be returned to the boiling chlorination of high titanium slag. The new cycle of magnesium and chloride in titanium sponge production was achieved. Based on the thermodynamic analysis of the reaction between O2 and MgCl2, the single factor experiments had been done. The optimal reaction condition was determined and the impact of each factor in the pyrolysis process was studied.

Liping Niu, Ting-an Zhang, Guozhi Lv, Baojing Zhang

Thermal Decomposition Kinetics of Dolomite in Pre-prepared Pellets for Magnesium Production

A novel silicothermic process was put forward in order to some the problems in Pidgeon process, including a loss of 5% fine powder produced during the calcination of dolomite and the easy deliquescence for calcined dolomite. For this method, pre-prepared pellets, which consist of dolomite, ferrosilicon, fluorite, and binder are prefabricated before calcination, and then the calcined pellets are used directly for magnesium production. The difference of decomposition behavior and thermal decomposition kinetics between pre-prepared pellets and pure dolomitePre-prepared pellets and pure dolomite were studied by thermogravimetry (TG) and differential thermal analysis (DTA) under non-isothermalNon-isothermal TG and DTA conditions at different heating rates (4, 8, 16, and 30 K/min). The thermal decomposition data were analyzed using non-isothermal models and some isoconversional methodsIsoconversional methods. The decomposition temperature of dolomite in pre-prepared pellets was lower than that in pure dolomite due to the higher thermal conductivity of ferrosilicon. The values of the activity energy for the two stages decomposition of dolomite are 270 and 280 kJ mol−1 respectively in pre-prepared pellets, which were lower than pure dolomite.

Lukui Guan, Ting-an Zhang, Zhi-he Dou, Daxue Fu

Thermal Stability of Cryomilled Mg Alloy Powder

In this paper, the thermal stabilityThermal stability of cryomilled nanocrystalline (NC)Nanocrystalline (NC) AZ31 powder was evaluated by annealing at elevated temperature ranging from 350 to 450 °C. The results show the NC AZ31 powder exhibited excellent thermal stability during short anneals at 350–450 °C, and the mechanisms were investigated in detail. There were two separate growth stages with a transition point at around 400 °C. More specifically, between 350 and 400 °C, NCNanocrystalline (NC) Mg grains were stable at approximately 32 nm, even after 1 h annealing. At 450 °C, the nano grains grew to 37 nm in the first 5 min and grew quickly to approximately 60 nm after 15 min. However, the grain growth was limited when the annealing time was increased to 60 min. The average grain size remained stable less than approximately 60 nm even after long anneals at temperatures as high as 450 °C (0.78 T/TM), indicating an outstanding degree of grain size stability. This excellent thermal stability can be mainly attributed to solute drag and Zener pinning.

Dikai Guan, W. Mark Rainforth, Joanne Sharp, Junheng Gao

Thermomechanical Processing of Thixomolded Alloys

A wide variety of Mg alloysAlloys have been processed by ThixomoldingThixomolding® followed by thermomechanical processingThermomechanical processing (TMP)—to increase tensile, creep and fatigue strength, ductility and formability. These alloys encompass variations in Al, Zn, Ca, Mn, Sr, Y, Zr and Rare Earths (RE) in the Mg base. Due to the fine microstructure and low porosity rendered by Thixomolding, TMP has been feasible using high strain warm rolling and warm pressing. Thus, grain size is further reduced and texture can be moderated. Data is presented on the above alloys along with more extensive information on the commercial alloys AM60 and AZ61; but also the newly developed AZ70L-TH and AXJ810-TH alloys. In discussing the above processing, properties are related to microstructures.

Raymond Decker, Stephen LeBeau, Tracy Berman, Tori Miller, J. Wayne Jones, Tresa Pollock, Nir Moskovich, Boris Bronfin

Magnesium Technology 2017: Mechanical Behavior: Twinning, Plasticity, Texture, and Fatigue II

Frontmatter

Dynamic Behavior of an AZ31 Alloy Under Varying Strain Rates and Stress Triaxialities

Determination of microstructural and mechanical response to real-world loading conditions is imperative for the development of accurate models to predict the failure behavior of structural materials. The dynamic behavior of magnesium alloys is of particular interest to structural industries as lightweight materials must be able to withstand high impact loading. This study examines the influence of dynamic strain rate on the deformation behavior of a polycrystalline, hot-rolled AZ31 Mg alloy under varying stress triaxialities. The high strain rateHigh strain rate testing results indicate that an increase in triaxiality leads to a transition in the deformation mechanisms. Subsequent characterization of microstructure and fracture surfaces were correlated to the mechanical response observed. Finally, these findings provide critical insights into the role of stress-state on dynamic behavior of an AZ31 alloy.

C. Kale, M. Rajagopalan, S. Turnage, B. Hornbuckle, K. Darling, S. N. Mathaudhu, K. N. Solanki

Enhancing the Tensile Response of Magnesium Through Simultaneous Addition of Aluminium and Alumina Nanoparticulates

Lightweight metals, alloys and composites are extremely attractive for weight critical applications in automotive; aerospace; electronics and transportation sectors. The addition of hybrid reinforcementsHybrid Reinforcement may help to improve both strength and ductility of composites. In the present study, an attempt was made to simultaneously reinforce magnesium with aluminium and varying volume % of alumina nanoparticulates using liquid based casting technique followed by hot extrusion. Microstructural characterization studies revealed minimal porosity, good distribution of intermetallic second phase and good retention and distribution of alumina nanoparticulates. Overall, the tensile properties of the Mg–Al/Al2O3 nanocompositeMagnesium nanocomposite exhibited enhanced 0.2% yield strength (~40%), ultimate tensile strength (~50%) and ductility (~52%) when compared to magnesium reinforced with similar volume % of Al2O3.

Wai Leong Eugene Wong, Manoj Gupta

Effect of Solutes Additions on the Microstructure and Mechanical Properties of Cast Mg–Al Based Alloys

Aluminium is an essential alloying element in most commercially used Mg alloys and particularly AZ series. That is due to its outstanding ability to increasing castability, formability and mechanical properties of Mg. However, seeking higher mechanical properties alloys has always been a hot topic in this research area. Grain refinement, solid solution strengthening and precipitation hardening are all mechanisms to increasing the as-cast mechanical properties of the alloys. In the current work, the effects of 6 different solutes addition, namely titanium, silicon, manganese, copper, calcium and tin, on the microstructure and mechanical properties of Mg–Al based alloys have been studied. In terms of microstructure, results showed that even though higher Q-values can be obtained through increasing the solutes addition, grain refinement is not always associated with the Q-values. In addition, intermetallic compounds played a major role in enhancing the hardness of the alloys.

Yahia Ali, Ming-Xing Zhang

Enhanced Mechanical Properties of Extruded Mg–9mass%Al–1mass%Zn–2mass%Ca Alloy

In order to investigate the relationships between microstructure and mechanical properties of extruded Mg–9mass%Al–1mass%Zn–2mass%Ca (AZX912) alloy, the AZX912 alloy ingots with and without solution treatment (ST) were extruded at a low temperature of 523 K, and some extrusions were subsequently annealed at 473–573 K. The as-extruded bar exhibited dynamically recrystallized fine grains, and the amount of fine Mg17Al12 precipitates in grains. Grain coarsening occurred with an increased grain size from ~2 to ~8 μm after annealing. Solution treatment seems to affect grain coarsening during extrusion. All extruded bars exhibited basal texture, and the extruded bar annealed at 573 K exhibited slightly lower texture intensity than the others. The extruded bar exhibited high mechanical strength of 377 MPa and medium elongation of 6.6%, when solution treatment before extrusion and final annealing were not applied. The high mechanical strength was likely attributed to the small grain size, large work hardening and a great amount of fine Mg17Al12 precipitates in the extrusions.

Xinsheng Huang, Yasumasa Chino, Hironori Ueda, Masashi Inoue, Futoshi Kido, Toshiharu Matsumoto

Influence of Strain Path Change on the Microstructure and Mechanical Properties of Duplex Mg–Li Alloy

The microstructures, texture evolution, and mechanical properties of unidirectionally-rolled and cross-rolled Mg–9Li–6Er alloy were investigated in this paper. The results show that the Mg–9Li–6Er alloy mainly consists of α phase and β phase along with Er5Mg24 eutectic. The strain path was changed between rolling passes during the cross-rolling process, which led to a weaker texture development compared to the conventional unidirectional-rolling method. At the same time, cross-rolling process makes the alloys have a much significant deformation strengthening effect than that of the unidirectionally-rolling process, which can be mainly attributed to the change in strain path, making the α phase distributes disorderly in the β phase and interacts with each other into a network. On the other hand, due to the disordered distribution of matrix phases, uniform plastic deformation is blocked, and thus the ductility is greatly lowered.

Yun Zou, Yang Li, Hao Guo, Songsong Xu, Yu Zhao, Milin Zhang, Zhongwu Zhang

Mechanical Properties and Deformation Mechanism of Mg–Y Alloy with Various Grain Sizes

In the present study, a Mg–Y dilute alloy was provided for a severe plastic deformation by high pressure torsion (HPT) and subsequent annealing. After the HPT by 5 rotations, nanocrystalline (NC) structures with an average grain size of 240 nm having deformed characteristics were obtained. Subsequent annealing at various temperatures for 2–60 min resulted in fully recrystallized structures with different average grain sizes ranging from 0.66 to 8.13 μm. Good balance of tensile strength and ductility could be realized in the fine grained specimens. For the specimen having a mean grain size of 2.13 μm, the yield strength and total tensile elongation were 180 MPa and 37%, respectively, which were much higher than those of pure Mg with a similar grain size. The significant contribution of Y on the microstructure and mechanical properties is discussed.

Ichiro Kawarada, Ruixiao Zheng, Akinobu Shibata, Hidetoshi Somekawa, Shigenobu Ogata, Nobuhiro Tsuji

Microstructure and Mechanical Properties of High Pressure Die Cast Mg–Al–Sn–Si Alloys

The effect of a small addition of silicon (Si) was studied to increase the mechanical properties of Mg–Al–Sn alloys. Test specimens were produced by a vacuum die casting process which makes it possible to perform various heat treatments on the alloy which was not possible with conventional high pressure die casting (HPDC). The addition of Si leads to the formation of a binary Mg2Si phase which contributes to an increase in strength in the as-cast condition. Artificial aging treatments were performed to further increase the strength of the alloys by precipitation of fine Mg2Sn, Mg2Si, and Mg17Al12 phases. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques were used to observe these fine precipitates at different stages of the heat treatment and mechanical testing was performed to compare strength and ductility to previous magnesium alloys.

Andrew D. Klarner, Weihua Sun, Jiashi Miao, Alan A. Luo

Microstructure and Mechanical Properties of an Extruded Mg-1.58Zn-0.52Gd Alloy

Mg-1.58Zn-0.52Gd (wt%) alloy was indirectly extruded at different temperatures and the resulting microstructureMicrostructure, texture and mechanical propertiesMechanical properties were investigated. The alloy extruded at 350 °C exhibited a typical bimodal microstructure, consisting of fine dynamically recrystallized (DRXed) grains of ~3.1 μm and coarse unDRXed grains elongated along the ED with many fine spherical Mg3Zn3Gd2 phase, and a strong $$ \left[ {10\bar{1}0} \right] $$ fiber texture, thereby resulting in high yield strength of 283 MPa and low elongation of 10.0%. With increasing extrusionExtrusion temperature, the yield strength gradually decreased mainly due to increased DRXed grain size from the Hall-Petch relation, and the elongation increased due to the weakened extrusion texture and increased DRX fraction, suppressing crack initiation at twins in coarse unDRXed grains. As a result, the alloy extruded at 400 °C showed yield strength of 161 MPa and elongation of 24.7%.

M. G. Jiang, J. C. Chen, H. Yan, C. Xu, T. Nakata, S. Kamado

Modelling Magnesium Alloys for Improved Isotropic and Symmetric Yield Behaviour

Age-hardenable wrought magnesium alloys suffer from high mechanical anisotropy and asymmetry which can be reduced by the correct choice of precipitate shape and habit plane. In this paper, the effect of combining precipitates of different types has been predicted using modified Orowan strengthening theory and visco-plastic self-consistent modelling, with the goal of designing more isotropic magnesium alloys. It was predicted that the correct combination of $$ \left\langle {11\bar{2}0} \right\rangle $$ basal laths and c-axis rods would be expected to reduce yield anisotropy and asymmetry, whilst also providing high strength, consistent with published data on a Mg-Sn-Zn-Al-Na alloy. The model was further expanded to relate precipitate volume fractions to alloying content so that weight-optimised alloys with desirable isotropy, symmetry and strength could be designed.

A. E. Davis, J. D. Robson

Magnesium Technology 2017: Solidification and Processing III and Magnesium-Rare Earth Alloys I

Frontmatter

Scaled-Up Fabrication of Thin-Walled ZK60 Tubing Using Shear Assisted Processing and Extrusion (ShAPE)

Shear Assisted Processing and Extrusion (ShAPE) has been scaled-up and applied to direct extrusion of thin-walled magnesium tubing. Using ShAPE, billets of ZK60A-T5 were directly extruded into round tubes having an outer diameter of 50.8 mm and wall thickness of 1.52 mm (extrusion ratio of 17.7). Due to material flow effects resulting from the simultaneous linear and rotational shear intrinsic to ShAPE, the ram force and k-factor during extrusion were just 40 kN (9000 lbf) and 3.33 MPa (0.483 ksi) respectively. This represents a >10 times reduction in k-factor, and therefore ram force, compared to conventional extrusion. The severe shearing conditions inherent to ShAPE resulted in microstructural refinement with an average grain size of 3.8 μm measured at the midpoint of the tube wall. Tensile testing per ATSM E-8 on specimens oriented parallel to the extrusion direction gave an ultimate tensile strength of 254.4 MPa and elongation of 20.1%. Specimens tested perpendicular to the extrusion direction had an ultimate tensile strength of 297.2 MPa and elongation of 25.0%.

Scott Whalen, Vineet Joshi, Nicole Overman, Dustin Caldwell, Curt Lavender, Tim Skszek

Biocompatible Magnesium Alloy ZNdK100—Adaptation of Extrusion Parameters to Tailor the Mechanical Properties to Different Implant Applications

Neodymium containing magnesium alloys like MgNd2 and ZNdK100 offer high corrosion resistance and biocompatibility due to low amounts of alloying elements, and are thus attractive for biomedical applications. Compared with common bioresorbable magnesium alloys, which frequently contain mischmetal, the use of neodymium as a single rare earth element provides for good reproducibility of the degradation behavior while improving the ductility, leading to high fracture strains of 25–30%. Thus, stents made from these alloys allowed dilatation without failure. The MgNd2 alloy’s strength, however, turned out to be low. Recent investigations proved that the strength of a ZNdK100 alloy can be significantly increased by an adaptation of the extrusion parameters, such as billet temperature and extrusion ratio, which govern recrystallization of the microstructure. In the current study, it is demonstrated how the mechanical properties can be adjusted by the extrusion process, allowing the future use of the same alloy for both bone implants and soft tissue implants.

Rainer Eifler, Florian Schäfke, Hans Jürgen Maier, Christian Klose

Characterization of Semi-Closed Die-Forged ZK60 Mg Alloy Extrusion

The present research aims at characterization of ZK60 Mg-alloy processed through semi-closed die-forging at the temperature of 450 °C with the ram speed of 0.4 mm/s by investigating the compression behavior along the extrusion directions (ED) and radial directions (RD). Microstructural analysis shows a bimodal grain structure in the extruded sample, while the forged samples exhibited grains elongated along the perpendicular direction of forging with no evidence of dynamic recrystallization. It is also seen that the samples in as-extruded condition obtained the ultimate compression strength (UCS) of 449 and 335 MPa along the ED and RD, respectively. After forging the attained UCS were decreased by ~14 and ~11% for the ED and RD, respectively, while a significant improvement in fracture strain between ~48 and ~76% is observed in the forged samples. It is concluded that the forging of magnesium is a beneficial technique for manufacturing of load-bearing components.

S. M. H. Karparvarfard, S. K. Shaha, A. Hadadzadeh, S. B. Behravesh, H. Jahed, M. A. Wells, B. Williams

Optimization of Nitrogen Bubbling Conditions for Mg Extruded Alloy with Balanced Mechanical Properties

Mg alloys have gained a great attention as light-weight structural materials recently but it could not replace the conventional materials which are being used in automobile and other industries because of high cost of manufacturing processes. Mg alloy must be fabricated under protection gas atmosphere due to high oxidation reaction during melting. This reaction makes a sludge and dross when the melt is not well maintained. The sludge and dross generated during melting is barely removed before cast into the mold. According to our pre-test, the extruded Mg–3Al–1Zn–0.5Mn–1Ca alloy which were treated with N2 gas bubblingNitrogen gas bubbling process during the melting had higher mechanical properties than alloy which was cast without N2 gas bubbling. However, in our previous work we did not get the optimum conditions for N2 bubbling process. In this study, mechanical properties of extruded Mg–3Al–1Zn–0.5Mn–1Ca alloy, which were fabricated with different melting temperatures and amounts of N2 gas flow was investigated to optimize the variables in N2 bubbling process for melt. The specimen treated and untreated N2 gas bubbling process were extruded by indirect extrusionExtrusion with billets of diameter of 40 mm after casting. The extrusion temperature and extrusion reduction ratio were 270 °C and 20:1, respectively. In addition, effect of N2 bubbling on microstructure and mechanical properties was also studied.

Wonseok Yang, Youngkyun Kim, Taeyang Kwak, Shae K. Kim, Hyunkyu Lim, Do Hyang Kim

Effects of Gadolinium and Neodymium Addition on Young’s Modulus of Magnesium-Based Binary Alloys

In order to investigate the influence of solute atoms and particles on Young’s modulus of magnesium, series of binary Mg–Gd and Mg–Nd alloys were prepared using hot extrusion. With increasing Gd content from 0 to 2.654 at.% Young’s modulus of Mg–Gd alloys increases linearly from 44.0 to 45.3 GPa. Regarding Mg–Nd alloys, Young’s modulus firstly decreases to 42.5 GPa until 0.184 at.% Nd, and then increases to 43.4 GPa at Mg–0.628 at.% Nd. The different influences of solutes Gd and Nd on Young’s modulus of Mg are attributed to their different solid solution behaviors in magnesium, which can lead to the alterations of crystal cell parameters and/or different amount of second phases. For Mg–Gd alloys the lattice parameters increase and the axial ratio (c/a) decreases with Gd content increasing. In contrast, for Mg–Nd alloys they almost keep unchanged due to small solubility of Nd in Mg when Nd content increases.

Yuling Xu, Jie Li, Zhengye Zhong, Karl Kainer, Norbert Hort

Aging Behavior of Mg Alloys Containing Nd and Y

Magnesium rare earth (Mg–RE) alloys form unique precipitate structures during aging that make these materials desirable for applications where a high strength to weight ratio is important. Commercial alloys such as WE43 are quite complex, making it difficult to fully understand the factors controlling precipitation, which are needed in the design of new and improved alloys. Here, we present our initial observations of the different precipitate phases that form in Mg–Nd, Mg–Y, and Mg–Y–Nd alloys using scanning transmission electron microscopy and atom probe tomography and relate the microstructure to measured changes in alloy hardness via post-mortem observations of deformed alloys.

Ellen L. S. Solomon, Timothy Chan, Andrew Chen, Benjamin Uttal-Veroff, Emmanuelle A. Marquis

Variation of Rare Earth Elements in the Magnesium Alloy ME21 for the Sheet Production

Sheet properties of magnesium like ductility, strength and corrosion resistance are improved by alloying with rare earth elements. This paper reports on the variation of the rare earth elements in the aluminum-free magnesium alloy ME21 (2 wt% Mn and 1 wt% RE) in order to investigate the sensitivity to the amount and kind of the rare earth elements regarding strength and ductility. The paper will show the results of casting and rolling experiments of some alloy variations of ME21 which contain different amounts of Cerium based misch metal and Neodymium. The influence of these different alloying elements on the microstructure of the billets before and after heat treatment is shown. Furthermore, rolling trials with different schedules were conducted and the mechanical properties of the sheets are presented and discussed with respect to arising textures and the average grain sizes. The results of this casting and rolling trials are used to discuss how to tailor the mechanical properties of the magnesium alloy ME21.

G. Kurz, T. Petersen, J. Bohlen, D. Letzig

Phase Stability and Formation in Mg–Gd–Zn Alloys—Key Data for ICME of Mg Alloys

Thermodynamic databases of multicomponent alloy systems are the indispensable basis to apply and develop ICME of Mg alloys. Among the multicomponent Mg alloysMagnesium alloys with rare earths (RE) and Zn the Mg–Gd–Zn system is found to be a prime example of complex phase formation, both under stable and metastable conditions. This alloy system was studied by a combination of dedicated experiments and thermodynamic modeling. Two metastable phases, I and H2, have been identified in as-cast Mg-rich Mg–Gd–Zn alloys by TEM characterization. Quantitative thermodynamic descriptions of the metastable Mg–Gd–Zn phases and metastable phase diagrams are developed, embedded in a complete Calphad modeling of all stable phases. Dedicated thermodynamic calculations using constrained Scheil solidification simulation reveal conditions for I and H2 phase formation and transformation.

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

Magnesium Technology 2017: Corrosion

Frontmatter

An Electrochemical Investigation of Mg–Ni Hydrogen Storage Alloys by Mechanical Alloying

The characteristics and mechanisms of enhanced electrochemical properties for Mg–Ni alloy produced by mechanical alloyingMechanical alloying MA were investigated by electrochemical measurements. Electrochemical hydrogen storageHydrogen storage properties were characterized by cyclic charge–discharge experiment, electrochemical impedance spectroscopyElectrochemical impedance spectroscopy (EIS) and potentiodynamic polarization methods. The phase composition and microstructure of Mg–Ni alloy were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD showed that the alloys exhibit dominatingly amorphous structures. And also, 20 h milling was enough to obtain amorphous/nano-crystalline alloy structure. The best initial discharge capacity (489 mA h g−1) and acceptable capacity retaining rate (48%) were obtained for the 20 h milled Mg50Ni50 alloy.

Gökçe Hapçı Ağaoğlu, Gökhan Orhan

Corrosion and Creep Resistance of Thixomolded® Magnesium Alloys

Process optimization is one pathway to maximizing strength of a given alloy. Thixomolding® is a semi-solid casting process that combines pores reduction with a typical bimodal grain size distribution that can lead to enhanced strength. AZ91D and AZX911 were processed via Thixomolding® using two different processing conditions to change fraction solid of primary particles at the point of injection into the mould. The tensile properties, creep resistance and corrosion behaviour of the alloys were investigated. The creep resistance was measured in the range of 135–150 °C for stresses of 50–85 MPa. The corrosion behaviour was measured via hydrogen evolution for the two alloys and was smaller than that for die-cast AZ91. The AZX911 alloy showed improved creep resistance compared to the AZ91D. The differences in the property profile of the chosen alloys are correlated with their chemical compositions as well as with different microstructures obtained through the different processing conditions.

R. Buzolin, H. Dieringa, C. Blawert, H. Frank, C. L. Mendis, A. Lohmüller, K. U. Kainer, N. Hort

Corrosion Properties of Mg–6Al–0.3Mn–aSn–bZn Alloys

The effect of addition of Sn and/or Zn on corrosion properties of Mg–6Al–0.3Mn alloy was investigated systematically by immersion and salt spray tests. In case of immersion test, average corrosion rate increased by addition of 1 wt% Sn but it decreased by addition of 1 wt% Zn. When the half of the amount of Sn addition was replaced by Zn, the average corrosion rate decreased in comparison with the average corrosion rate of Mg–6Al–0.3Mn–1Sn alloy. In case of salt spray test, the change of average corrosion rate according to composition of the alloy was similar to the result of immersion test. It seemed that the change of corrosion properties according to composition of the alloy was strongly related to the microstructural changes including the sort, fraction and morphology of second phase.

Chang Dong Yim, Sang Kyu Woo, Nam Ryong Kim, Ha Sik Kim, Bong Sun You

Corrosion of Magnesium–Aluminum (Mg–Al) Alloys—An Interplay Between Al Content and CO2

In course of their practical applications, magnesium-aluminum (Mg–Al) alloysMagnesium-aluminum alloys are frequently exposed to the ambient atmospheric, and thus, are susceptible to environmental degradation. In this study, we exposed several Mg–Al alloys (including AM20, AZ31, AM50, and AZ91) with different Al content to atmospheric environment to examine the effect of most important environmental factor, i.e., carbon dioxide (CO2)Carbon dioxide and its relation to the alloys’ Al content. The surface films formed on alloys at two temperatures (−4 and 22 °C) were examined using auger electron spectroscopy (AES). The results show that CO2 inhibits long-term atmospheric corrosion behavior of the alloys and that the thickness of the carbon-rich layer in the surface film increases with increasing Al content. We suggest that; (a) the inhibitive effect of CO2 on the atmospheric corrosion behavior of Mg–Al systems, and (b) the positive influence of Al content on the corrosion performance of Mg–Al alloys are partly linked to the occurrence of compounds that exhibit characteristics close to that of the layered double hydroxides (LDHs).

M. Esmaily, J. E. Svensson, L. G. Johansson

Excimer Laser Processing of Al Containing Mg Alloys for Improved Corrosion Resistance

The implementation of Mg-based alloy components in Cl− containing environments is limited by the poor intrinsic corrosion resistance of the wrought alloys. Galvanic coupling of cathode secondary phase particles to the anodic Mg matrix combined with a low electrochemical potential result in an accelerated H2 evolution reaction, the controlling reaction of Mg corrosion. This behavior is closely followed by anodically induced cathodic behavior. To mitigate the accelerated corrosion rates, localized dissolution of secondary phases was performed by laser processing on three Al containing Mg alloys: AZ31B-H24, AM60B, and AZ91D. Mixed dissolution of the secondary phases was observed by electron and chemical microscopy. An order of magnitude increase in the electrochemical impedance estimated corrosion resistance was observed for the laser processed specimens immersed in a 0.6 M NaCl solution (18–60 h). The substantial increase in corrosion resistance stems from the reduced density of electrochemically noble secondary phase particles and localized enrichment of Al.

M. A. Melia, M. L. Serron, D. C. Florian, J. P. Weiler, J. R. Scully, J. M. Fitz-Gerald

Effect of Al and Sn on Discharge Behavior of Mg Alloy as Anode for Mg-Air Battery

In this study, we researched the effect of Al and Sn on discharge behavior of Mg alloy as anode for Mg-air battery. The as-cast and rolled AT alloys mainly consisted of α-Mg matrix and Al–Mn phases, Mg2Sn phase. With increase of Al and Sn contents, the discharge property of AT alloy was improved. In case of AT63 alloy, it can be seen that many fine cracks formed on discharge products promote electrochemical reaction from NaCl electrolyte to Mg anode surfaces, and finely dispersed pits formed by micro-galvanic corrosion between α-Mg matrix and Mg–Sn phases promote continuously reaction during discharge test.

Sang Hyun Kim, Jun Ho Park, Hee San Kim, Jae Joong Kim, Oh Duck Kwon

Utilization of a Partially Non-aqueous Electrolyte for the Spatial Mapping of Mg Corrosion Using a Model Mg–Al Electrode

In-situ techniques to spatially map micro-galvanic corrosion are particularly important for alloys with heterogeneous microstructures. In particular, scanning electrochemical microscopy (SECM)Scanning electrochemical microscopy (SECM) has been utilized to map microstructural features on Mg which may control the corrosion rateCorrosion rate. However, rapid corrosion rates of Mg in fully aqueous environments interfere with mapping capabilities. A mixed aqueous and non-aqueous electrolyte, containing methanol and H2O, is proposed which is capable of mapping the active corrosion on Mg with time. However, thorough understanding the effect of methanol additions on the corrosion rate was required. Therefore, the intrinsic corrosion rates of Mg in varying amounts of methanol (0–100 wt%) were investigated using electrochemical impedance spectroscopy (EIS) by exploring the corrosion rate on an Al wire embedded in Mg as a galvanic couple. The nature of the non-aqueous electrolyte on the EIS response is discussed. The evolution of this intrinsic corrosion behavior at the galvanic couple was investigated using a combination of optical microscopy, SECM and mixed potential theory.

L. G. Bland, R. F. Schaller, J. R. Scully

Voltammetric Studies of Extruded Pure Magnesium in Different Electrolytes and Its Corrosion Morphology

This study concerns the voltammetric behavior in different electrolytes of pure Mg processed by direct extrusion. The recrystallized microstructure is fine grained and homogeneously distributed. Mg is known to suffer pitting corrosion when exposed to chloride solutions. To cause a high anodic dissolution, corrosion has been evaluated with potentiodynamic polarization in Ringer, HBSS and DMEM up to 500 mV. The anodic current density within the active corrosion region and the current density and potential for passivation were used to compare the corrosion behavior. Corrosion in DMEM showed a tendency to passivation, Mg in HBSS only pseudo-passivated. Corrosion in Ringer showed the highest current density without passivation up to 500 mV. Corrosion morphology is discussed by using the pitting factor and size of corroded area. These values are correlated to the current density-potential curves. With decreased corroded area due to passivation the pitting factor increases. Corrosion behavior is compared to immersion tests.

Petra Maier, Leon Gentzsch, Norbert Hort

Magnesium Technology 2017: Magnesium-Rare Earth Alloys II

Frontmatter

Microstructure and Mechanical Properties of Mg–Zn–Gd Alloys After Rolling or Extrusion Processes

A series of Mg–Zn–Gd alloys were developed for large strain hot rollingRolling, cold rolling and high-speed extrusionExtrusion. The hot rolled Mg–2.0Zn–0.3Gd (wt%) alloys can be successfully rolled at 300 °C for a single pass reduction of 80% without any edge cracks, and the rolled sheet exhibited high yield strength of ~210 MPa and moderate elongation of ~22% due to fine grains and weak basal texture with broad angle distribution. The hot rolled Mg–2.0Zn–0.8Gd sheet showed excellent cold rollability due to the activation of {$$ 10\bar{1}2 $$} extension twins and dislocation slips. Cold rolling could further modify the texture and enhance the strength. Besides, Mg–1.58Zn–0.52Gd alloy can be successfully extruded at high die-exit speed of 60 m/min without any surface defects in a wide temperature range due to the absence of thermally unstable eutectic phase and high solidus temperature. The high-speed extruded alloy showed high ductility of ~30%, which was twice than AZ31 alloy, because of the formation of rare earth texture.

R. S. Chen, M. G. Jiang, J. Luo, H. Yan, C. Xu, S. Kamado

A Comparative Study on the Microstructure, Mechanical Properties, and Hot Deformation of Magnesium Alloys Containing Zinc, Calcium and Yttrium

Some magnesium alloys are considered as biocompatible materials because they are biodegradable or bioabsorbable in body fluids without causing health hazards. Zinc (Zn) and calcium (Ca) are essential micronutrients in the body and their bio-absorption is beneficial when an orthopedic implant made of magnesium alloy corrodes in a controlled manner. Yttrium (Y) in small quantity can be added to improve the mechanical properties. Cast alloys are hot worked to obtain wrought microstructures so as to develop components of superior and consistent properties. In this study, the microstructure, mechanical properties, and hot deformationHot deformation behavior of four cast magnesium alloys containing zinc, calcium and yttrium in different combinations are compared. It is found that calcium is an excellent grain refiner whereas yttrium enormously increases the grain size. While all these elements provide strengthening, calcium is found to be the most effective one in combination with zinc and yttrium or zinc alone. The hot working behaviors of these alloys over broad ranges of temperature and strain rate are compared using processing maps. Mg–1Zn–1Y alloy exhibits higher level of workability compared to the other alloys and over entire strain rate range of 0.0003–10 s−1 and 460–540 °C, although the initial grain size of the cast alloy is extremely large.

K. P. Rao, K. Suresh, H. Dieringa, N. Hort

Addition of Holmium and Erbium and Hot-Rolling Effects on the Microstructure and Mechanical Properties of Mg–Li Based Alloys

Magnesium–Lithium Rare Earth based alloys being ultra-light and strong offer suitability for wide industrial applications. This is because they form stable strengthening phases and activate extra deformation modes under optimized conditions. Effects of introducing Holmium (Ho) and Erbium (Er) elements in Mg–8Li–3Al alloy followed subsequently by aging and hot-rolling deformation were studied. The alloys microstructure morphology was examined using scanning electron microscope (SEM) and energy dispersive spectroscopy (XEDS). Phase analysis depicted the presence of both α-and β-phases alongside intermetallic compounds. Mechanical tensile test results showed increased Yield Strength (YS) and Ultimate Tensile Strength (UTS) on introduction of rare earth elements with optimized thermo-mechanical treatment. The as-cast Mg–8Li–3Al alloy exhibited an elongation of 9.5%. Thermo-mechanically treated Mg–8Li–3Al–3Er and Mg–8Li–3Al–3Ho alloys exhibited an increased optimal elongation of 19.1 and 21.4% respectively. Synergistic effects of adding Holmium and Erbium elements, with aging and hot-rolling deformation enhanced the alloys mechanical properties through work hardening and solution strengthening mechanisms.

C. O. Muga, Y. Zhao, H. Guo, S. Xu, Y. Zou, Z. W. Zhang

Bonding Environments in a Creep–Resistant Mg–RE–Zn Alloy

Density functional theory (DFT)Density functional theory (DFT) based first principle calculations was used to examine the effect of transitional element Zn addition on the bondingBonding environment of Mg–Gd solid solutions. Our calculations reveal that Zn strongly interacts with Gd, while simultaneously disperses the p-orbital valence electron density of Zn along the [0001]Mg and $$ \left\langle { 1 1 {\bar{\text{2}}}0} \right\rangle_{\text{Mg}} $$ directions of hcp-Mg lattice. These results suggest that Zn addition stiffens the Mg–Mg bonds between the {0002}Mg-basal planes, and along $$ \left\langle { 1 1 {\bar{\text{2}}}0} \right\rangle_{\text{Mg}} $$. The enhanced bonding between the Mg basal planes may potentially drives basal precipitation in Mg–Gd–Zn alloys seen in experiments. On the other hand, bond stiffening along $$ \left\langle { 1 1 {\bar{\text{2}}}0} \right\rangle_{\text{Mg}} $$ noticeably increased the vacancy migration barrier for basal plane diffusionDiffusion in Mg. This increase has bearing on the high temperature creep properties, because vacancy diffusion is a dominant creep deformation mechanism at operation temperatures of 150–300 °C for Mg-alloy parts. Thus, our calculations predict that Zn addition to Mg–Gd alloy will strongly influence its microstructure and creep response.

Deep Choudhuri, S. G. Srinivasan, Mark A. Gibson, Rajarshi Banerjee

Microstructural and Numerical Investigation on the Shear Response of a Rare-Earth Magnesium Alloy Sheet

ShearShear tests were performed on an anisotropic rare-earth magnesiumMagnesium alloy rolled sheet (ZEK100-O) to study the constitutive plastic behaviour of the material under quasi-static conditions at room temperature. The shear response was characterized in three orientations by setting the shear loading direction at 45°, 90°, and 135° with respect to the rolling direction. Each orientation displayed unique trends in terms of yielding and the work hardening rates. Electron Backscattered Diffraction (EBSD) analysis was used to analyze the microstructure of the deformed samples and to determine the twinningTwinning modes and twin fraction in each specimen. The results suggest that these parameters have a significant impact on the constitutive behavior of the material. Furthermore, the viscoplastic self-consistent twinning-detwinning (VPSC-TDT) model was used to understand the activity of the various deformation mechanisms and validate the experimental observations.

Michael J. Nemcko, Armin Abedini, Clifford Butcher, Peidong Wu, Michael J. Worswick

Solute Effect on Strength and Formability of Mg: A First-Principle Study

In wrought magnesium alloys, room temperature plasticity is largely controlled by limited slip systems such as basal slip and tension/compression twins. The insufficient number of active slip systems limits strength and ductility preventing broader structural applicability of Mg-alloys. Hence, we employ first-principle calculations to investigate the effects of Y and Al alloying elements on shearability and dislocation motion on various slip systems through ideal shear resistance and generalized stacking fault energy calculations. YttriumYttrium is seen to lower the ideal shear resistanceIdeal shear resistance and dislocation motion energetics on all the slip systems. On the other hand, aluminumAluminum increases the ideal shear resistance but decreases the energy barrier for dislocation motion on various slip systems. The profound effects of solute addition result from the charge transfer between the solute atom and surrounding magnesium atoms.

P. Garg, M. A. Bhatia, S. N. Mathaudhu, K. N. Solanki

Understanding on the Role of Rare Earth Elements in Activation of Slip in Magnesium: An Atomistic Approach

The effect of Li addition on the slip behavior of Mg has been investigated using a molecular dynamicsMolecular dynamics simulation. Based on a previous study on Mg–Y alloys concluding that a reduction of the anisotropy in critical resolved shear stress (CRSS)Critical resolved shear stress (CRSS) among difference slip systems activates the $$ \left\langle {\text{c}} + {\text{a}} \right\rangle $$ slip, the effect of Li, an element known to improve the room temperature ductility of Mg is chosen as an alloying element to examine the robustness of the above-mentioned conclusion. It is found that Li increases the CRSS of the basal slip more than that of the non-basal slip, reducing the difference in the CRSS among different slip systems. The reduced anisotropy in CRSS is believed to activate the non-basal $$ \left\langle {\text{c}} + {\text{a}} \right\rangle $$slip<c+a> slip and eventually improve ductility in Mg–Li alloys. This understanding can be further extended into an alloy design of more cost-effective Mg alloysMg alloy with improved room temperature formability.

Hyo-Sun Jang, Ki-Hyun Kim, Nack Joon Kim, Byeong-Joo Lee

Stabilisation of Disordered bcc Phases in Magnesium-Rare Earth Alloys

In magnesium-based alloyMagnesium alloy systems, a stable disordered bccBcc magnesium phase is known to exist only in the Mg–Li-based system. However, it is known that Mg is an intense stabiliser of high temperature betaBeta magnesium-rare earth phases (also disordered bcc) that often have a high solubility of Mg which can be sustained via quenching. This work focuses on stabilising Mg-rich beta-rare earth phases through targeted alloying additions of specific rare earth elements to generate more stable beta and alpha + beta Mg-based alloys. The mechanical properties present a large variation across small changes to the composition allowing for targeting desired properties for specific light-weight applications.

Patrick L. J. Conway, Adam L. Shaw, Lori Bassman, Michael Ferry, Kevin J. Laws

The Effect of Ca Addition on Microstructure and Mechanical Properties of Gravity Cast Mg–Zn–Y Alloy

Mg–Zn–Y alloy with I-phaseI-phase (Mg3Zn6Y) is particularly attractive because of the coherent interface between the I-phase (Mg3Zn6Y) and matrix phase, which sustains a strong bond and has low interfacial energy improve plastic deformation in the process like rolling and extrusion. Therefore, these Mg–Zn–Y alloysMg–Zn–Y alloys with I-phase (Mg3Zn6Y) have been focused a lot recently for wrought Magnesium alloys. However, these alloys can be used as the cast alloys because the I-phase (Mg3Zn6Y) exhibits better thermal stability than many other phases, which could enhance creep resistanceCreep resistance at elevated temperature.In this study, the effect of Ca addition on microstructure and mechanical properties of I-phase (Mg3Zn6Y) containing Mg–Zn–Y alloys were investigated to develop creep resistant Mg alloys.

Young-Gil Jung, Youngkyun Kim, Shae K. Kim, Hyun Kyu Lim, Do Hyang Kim

Magnesium Technology 2017: Mechanical Behavior: Twinning, Plasticity, Texture, and Fatigue III

Frontmatter

Microstructure and Texture Evolution During Hot Deformation of Cast-Homogenized ZK60 Magnesium Alloy

Forgeability of as-cast ZK60 magnesium alloy was investigated by isothermal uniaxial hot compression of cylindrical samples using the Gleeble® 3500 thermal-mechanical simulation testing system. Computational thermodynamics predictions (by FactSage™) along with differential scanning calorimetry (DSC) experiments showed incipient melting of low melting temperature precipitates in the as-cast material at around 340 °C. Therefore, the as-cast material was subjected to homogenization heat treatment at 400 °C for 4 h. Hot compression test were then conducted at 400 and 450 °C using a variety of strain rates (0.001–1.0 s−1). The microstructure of the samples deformed at low strain rates consisted of dynamically recrystallized (DRXed) grains. By increasing the strain rate, the volume fraction of the DRXed regions reduced. The material also exhibited sensitivity to deformation temperature in terms of DRX volume fraction. Texture of the deformed samples was also characterized using the XRD method to investigate the effect of hot deformation conditions on the texture evolution.

Amir Hadadzadeh, Sugrib Kumar Shaha, Mary A. Wells, Hamid Jahed, Bruce W. Williams

Development of Texture During Tensile Test at Room Temperature

The preferential orientation of $$ \left\langle {10\bar{1}0} \right\rangle $$ axis along tensile direction in magnesium (Mg) sheet alloys is still controversial. By using a quasi-in situ electron backscatter diffraction (EBSD) method, the present study provides an interpretation about the origin of the $$ \left\langle {10\bar{1}0} \right\rangle $$ texture. It is found that a strong $$ \left\langle {10\bar{1}0} \right\rangle $$ texture is developed after tensile stretching in the Mg alloys with different compositions. The occurrence of the $$ \left\langle {10\bar{1}0} \right\rangle $$ texture is predominantly caused by the preferential formation and growth of twins, whose $$ \left\langle {10\bar{1}0} \right\rangle $$ axes are nearly parallel to the tensile direction. In contrast, the dislocation slip only leads to a small-scale change of grain orientations, and therefore is unlikely to result in the occurrence of $$ \left\langle {10\bar{1}0} \right\rangle $$ texture.

Zhuoran Zeng, Mingzhe Bian, Shiwei Xu, Chris H. J. Davies, Nick Birbilis, Jian-Feng Nie

Effect of Ca on the Microstructure, Texture and Mechanical Properties in Mg–Zn–Mn Based Alloy

We investigated the role of Ca and hot-rolling condition in the microstructure evolution and mechanical properties in the ZM40 alloy sheets. While the strong basal texture was developed in the as-rolled ZM40 alloy regardless of rolling conditions, the specimen reheating between rolling passes resulted in the weakening of the basal texture in the as-rolled ZMX400 alloy. The solution treatment after the hot-rolling led to the grain coarsening to ~20 μm while keeping the strong basal texture in the ZM40 alloy. The solution treated ZMX400 alloy showed bimodal grain structures consisting of larger grains than those observed in the ZM40 alloy, and the basal texture was further weakened. This resulted in a significant improvement of room temperature formability to the index Erichsen value of 6 mm. In spite of the coarser grain structure and weakened basal texture, the solution treated ZMX400 alloys showed comparable strengths with the ZM40 alloy. This is because higher number density of fine α-Mn phase particles are distributed in the ZMX400 alloy than the ZM40 alloy.

Byeong-Chan Suh, Taisuke Sasaki, Taiki Nakata, Shigeharu Kamado, Kazuhiro Hono

Evaluation of In Vitro Fatigue Properties of Biodegradable Mg–0.3at.%Ca Alloy

Recently, biodegradable bone fixation devices have been demanded when considering the patient’s quality of life (QOL). During the fracture healing, the devices must support the repeated load due to daily performance. At the same time, surface of the magnesium devices was affected by body fluid. Thus in this research, in vitro fatigue properties of biodegradable Mg–0.3at.%Ca alloy was evaluated by using simulated body fluid. Though there was fatigue limit when the test was conducted under the ambient condition, it cannot be confirmed during the test in the simulated body fluid. Inspection of fracture surface revealed that crack propagated along the grain boundary after both the fatigue tests.

Naoko Ikeo, Akihito Taguma, Taichi Uemura, Toshiji Mukai

Mechanical Properties and Fatigue Strength of Extruded Cobalt-Containing Magnetic Magnesium Alloys

Magnetic magnesium alloys have inherent magnetic properties due to the alloying element cobalt. Thus, the entire structural component made from such an alloy can be utilized for mechanical load measurements using the harmonic analysis of eddy current signals. Because the solubility of cobalt in the magnesium matrix is negligible, the magnetic properties mainly originate from cobalt-rich precipitates. Both the mechanical properties and the magnetic properties are influenced significantly by other alloying elements, such as zinc, as well as the material’s microstructure. Two issues of the ternary magnetic magnesium alloy Mg-Co4-Zn2 are described in this study. The magnetic properties were characterized by using the magnetoelastic effect and the harmonic analysis of eddy current signals. In addition, the mechanical properties of specimens made from the extruded profiles were determined using tensile and rotating bending tests. A substantial dependence on the processing conditions was observed both for the mechanical and magnetic properties.

Christian Demminger, Christian Klose

Neutron Diffraction and Acoustic Emission Measurement During Loading and Unloading of Magnesium Aluminium Binary Alloys

The neutron diffractionNeutron diffraction and acoustic emissionAcoustic emission were measured during compression loading-unloading tests in randomly textured cast magnesium and magnesium 2 and 9 wt% aluminium binary alloys. The anelastic behavior and the change of twinned volume related to the detwinningDetwinning phenomena can be observed during the unloading. The decrease of twinned volume fraction during unloading is most pronounced for Mg 9 wt%Al.

Jan Čapek, Kristián Máthis

Texture Weakening and Grain Refinement by High Speed Rolling and Annealing of an AZ31 Magnesium Alloy

High-speed rollingHigh speed rolling of 1000 m/min has been used to produce Mg AZ31 alloy sheets at an initial temperature of 100 °C with increasing reductions to generate different as-rolled microstructures. After a reduction of 30%, a heavily twinned and shear-banded microstructure was seen, while after a reduction of 49%, a partially dynamically recrystallized (DRXed) and twinned microstructure was observed. The as-rolled specimens were then annealed at temperatures from 200 to 500 °C. Texture weakeningTexture weakening and grain refinement were achieved at both reductions during annealing by static recrystallizationStatic recrystallization (SRX). However, the 49% reduction specimen showed a much higher kinetics of SRX and a higher rate of texture weakening, comparing to the 30% reduction specimen. The weakest texture achieved in the former was slightly lower than that in the latter, which indicates that texture weakening is more effective in the specimen with heavily twinned and shear-banded microstructure than that with partially DRXed and twinned microstructure. Nevertheless, the average size of the SRXed grains at the full recrystallization condition of the specimen after the reduction of 49% was only half of that after 30%.

Jing Su, Stephen Yue

The Relative Contributions of Deformation Modes to AZ31 Rolling Textures in Different Temperature Regimes

Key differences in the textures of cold-, warm-, and hot-rolled Mg alloy AZ31AZ31 sheets and plates are identified. It is shown that incorporation of compression twinning within Visco-Plastic Self-Consistent (VPSC) Viscoplastic self-consistent (VPSC) polycrystal plasticity simulations reproduces key features of the cold-rolling textureRolling texture that have not previously been predicted. Discussion of recent observations of recrystallization and grain growth provide explanations for the hot-rolled texture. Finally, it is demonstrated that starting with the correct initial texture is essential to produce observed features in all the rolling textures, including warm-rolling.

Matthew A. Steiner, Jishnu J. Bhattacharyya, Sean R. Agnew

Effects of Texture and Triaxiality on the Plasticity of Magnesium Alloys

Understanding the role of triaxiality is key in the damage evolution of engineering alloys. In low symmetry materials, e.g. magnesium, the role of triaxiality in damage evolution is complicated by the presence of protean deformation mechanisms, which exhibit high crystallographic plastic anisotropy. We present the results of detailed finite element study of smooth and notched round bar polycrystalline specimens of magnesium, subjected to quasi-static tensile loading. Initial simulated textures mimicking and deviating from typical rolled Mg sheet textures are adopted. Using three-dimensional HCP single crystal plasticity, the effect of these textural variations is highlighted. The role of out-of-plane textural variation is compared to the in-plane variation, and the analysis indicates that out-of-plane deviations in $$ [10\bar{1}0] $$ result in subtle changes to the macroscopic deformation anisotropy and the underlying microscopic deformation slip and twin activity. The role of these textures in the activation of twinning mechanisms is discussed. These results, in conjunction with our recent works, help develop a systematic understanding of the texture-triaxiality-anisotropy interaction in magnesium alloys.

Balaji Selvarajou, Shailendra P. Joshi, A. Amine Benzerga

Magnesium Technology 2017: Poster Session

Frontmatter

Processing and Properties of As-Cast Magnesium AM60-Based Composite Containing Alumina Nano Particles and Micron Fibres

Magnesium alloy AM60 based metal matrix composites (MMCs) reinforced with micron alumina (Al2O3) fibres and/or nano-size particles were successfully fabricated by preform-squeeze casting techniques under an applied pressure of 90 MPa. Tensile testing was performed and microstructures were analyzed on as-cast unreinforced AM60 Alloy, fibre reinforced AM60 metal matrix composite, and hybrid AM60 composite containing alumina fibresAlumina fibre and nano-particles. The microstructure analysis revealed the homogeneity of reinforcements in the matrix alloy. With the addition of fibres, the tensile properties of the fibre-reinforced composites were improved with the considerable reduction of ductility compared with AM60 alloy. The introduction of additional nano-particles into the metal matrix not only significantly improved the tensile properties of the composites, but also simultaneously restored the ductility reduction caused by the reinforcement of fibres.

Junxiang Zhou, Xuezhi Zhang, Li Fang, Henry Hu

In-Situ Methods for Unraveling Structure-Property Relationships in Light Metals: Imaging and Acoustic Emission

Frontmatter

Overview of In Situ X-Ray Studies of Light Alloy Solidification in Microgravity

Gravity has significant effects on alloy solidification, primarily due to thermosolutal convection and solid phase buoyancy. Since 2004, the European Space Agency has been supporting investigation of these effects by promoting in situ X-ray monitoring of the solidification of aluminium alloys on microgravity platforms, on earth, and in periodically varying g conditions. The first microgravity experiment—investigating foaming of liquid metalsMetal foaming—was performed on board a sounding rocket, in 2008. In 2012 the first ever X-ray-monitored solidification of a fully dense metallic alloy in space was achieved: the focus was columnar solidification of an Al–Cu alloy. This was followed in 2015 by a similar experiment, investigating equiaxed solidification. Ground reference experiments were completed in all cases. In addition, experiments have been performed on board parabolic flights—where the effects of varying gravity have been studied. We review here the technical and scientific progress to date, and outline future perspectives.

D. J. Browne, F. García-Moreno, H. Nguyen-Thi, G. Zimmermann, F. Kargl, R. H. Mathiesen, A. Griesche, O. Minster

Morphological Transition of α-Mg Dendrites During Near-Isothermal Solidification of a Mg–Nd–Gd–Zn–Zr Casting Alloy

Microstructure evolutionMicrostructure evolution in the Mg–Nd–Gd–Zn–Zr commercial casting alloy Elektron21 and in a Zn-free alloy variant, solidified under near-isothermal conditions at six constant cooling rates, has been studied via in situ X-ray radiographyX-ray radiography. In the Zn-free alloy, equiaxed α-Mg primary dendrites are always observed to develop with a steady growth rate. Conversely, in the Elektron21 alloy, primary dendrites undergo a morphological transition after nucleation and an initial transient growth for cooling rates $$ \dot{T} $$ ≤ 0.075 K/s. Such transition leads to a change in the growth morphology from volume spanning 3D to anisotropic sheet-like growth occurring mainly along $$ \left\langle {11\bar{2}0} \right\rangle $$ directions, with 4–5 times increase in the growth velocity. Experiments and simulations highlight the pivotal role of Zn, indicating that the morphological transition occurs due to the formation of ordered rare earth-zinc arrangements in the $$ \{ 10\bar{1}1\} $$ pyramidal and $$ \{ 0001\} $$ basal planes of the α-Mg lattice within a layer extending a few micrometres from the solid-liquid interface into α-Mg.

Daniele Casari, Wajira U. Mirihanage, Ken V. Falch, Inga G. Ringdalen, Jesper Friis, Rainer Schmid-Fetzer, Dongdong Zhao, Yanjun Li, Wim H. Sillekens, Ragnvald H. Mathiesen

Real-Time Observation of AZ91 Solidification by Synchrotron Radiography

The equiaxed solidification of AZ91 has been studied by time-resolved synchrotron radiography of 150 µm thick samples. Primary Al8Mn5 and α-Mg dendrite growth has been observed and analysed during solidification at a cooling rate of 5 K/min. Morphological, compositional and kinetic information of AZ91 solidification has been extracted from quantitative image analysis on synchrotron radiographs combined with thermodynamic calculations. α-Mg dendrites appeared to grow largely independently of the surrounding Al8Mn5 particles. Solute partitioning mainly occurred during the dendrite coarsening stage and Zn/Al solute build-up was studied in a region that remains a liquid channel until a late stage of AZ91 solidification.

G. Zeng, K. Nogita, S. Belyakov, J. W. Xian, S. D. McDonald, K. V. Yang, H. Yasuda, C. M. Gourlay

3D Microstructural Evolution on Solidifying Mg–5Nd–5Zn Alloy Observed via In Situ Synchrotron Tomography

In situ synchrotron tomographyIn situ synchrotron tomography is a unique technique to study 3D microstructure evolutionMicrostructure evolution during solidificationSolidification due to the high brilliance of the beam and the short acquisition time of the detector systems. In this work, in situ synchrotron tomographic observations were performed during the solidification of Mg–5Nd–5Zn (wt%) alloy with a cooling rate of 5 °C/min. The experiment was performed at the TOMCAT beamline of the Swiss Light Source (Paul Scherrer Institute (PSI), Villigen, Switzerland). The sample was melted using a laser-based heating system and then cooled until completely solidified. 3D tomograms were acquired during solidification. The microstructural analysis starts after the coherency point until the end of solidification. A differential thermal analysis (DTA) experiment was performed to estimate the liquidus and solidus temperature of the alloy. These values were used to correct the measured temperature from the in situ solidification experiment. Different microstructural parameters such as the volume fractions of the phases, i.e. α-Mg dendrites, interdendritics and pores, as well as the interconnectivity and skeletonization results are discussed.

Tungky Subroto, Chamini L. Mendis, Francesco D’Elia, Gábor Szakács, Julie L. Fife, Norbert Hort, Karl Ulrich Kainer, Domonkos Tolnai

An Acoustic Emission Study of Deformation Behavior of Wrought Mg Alloys

The influence of the pre-compression level on subsequent tensile deformation behavior has been investigated for two extruded Mg alloys with a different grain size distribution. The Mg–Zn–R are earth alloy has homogeneous microstructure, while the Mg–Al–Zn alloy exhibits bimodal microstructure. Deformation tests were performed at room temperature and at a constant strain rate of 10−3 s−1. Three pre-compression stress levels were chosen to receive microstructure containing a low number of twins, partially and fully twinned grains, respectively. The concurrent acoustic emission (AE)Acoustic emission (AE) measurement provides real time information about collective dislocation motion and twin nucleation. Active deformation mechanisms during tensile loading are discussed in term of the AE response.

Patrik Dobroň, Daria Drozdenko, Sangbong Yi, Jan Bohlen

Effect of Thermo-mechanical Treatment of Extruded Z1 Mg Alloy on Resulting Mechanical Properties

The formability and mechanical properties of Mg alloys are strongly influenced by a formation and growth of twins. The contribution of twinningTwinning to plastic deformation can be modified by initial texture, introducing solute segregationSegregation and precipitationPrecipitations at the twin boundaries. The interaction of solute atoms and precipitates with grain and twin boundaries during thermo-mechanical treatment and their effect on mechanical properties will be discussed in term of acoustic emission (AE). An AE signal, recorded during deformation tests, can provide information about active deformation mechanisms during plastic deformation with respect to the microstructure and texture as well as to solute segregation and precipitates along dislocations, grain and twin boundaries. The microstructure development of the extruded Z1 Mg alloy prior and after pre-treatment as well as after subsequent loading will be investigated by scanning electron microscopy (SEM) including electron backscattered diffraction (EBSD)Electron backscattered diffraction (EBSD) technique.

Daria Drozdenko, Jan Bohlen, Sangbong Yi, Patrik Dobroň

In Situ Investigation of Deformation Mechanisms in Mg–Zn–Y Magnesium Alloy with LPSO Phase by Diffraction Methods and Acoustic Emission

The influence of the LPSO (long-period stacking ordered) phase orientation and the microstructure of the magnesium matrix on the deformation mechanisms of Mg–Zn–Y magnesium alloy has been investigated by diffraction methods and acoustic emission (AE) measurements. The adaptive sequential k-means analysis (ASK) method, offering identification of the dominant deformation process (basal, non-basal slip, twinning, kinking) in a given time period, has been used for AE data evaluation. The results indicate that the kinking mechanism, twinning and activation of non-basal slip exhibit a significant dependence on the initial texture and the orientation of the LPSO phase with respect to the loading axis.

Kristián Máthis, Gerardo Garcés, Klaudia Horváth, Daria Drozdenko, Patrik Dobroň

In-Situ Methods for Unraveling Structure-Property Relationships in Light Metals: Diffraction and Other Novel Methods

Frontmatter

Structural Evolution of Metals at High Temperature: Complementary Investigations with Neutron and Synchrotron Quantum Beams

In situ neutron and synchrotron X-ray diffraction deliver unique and complementary insight into the microstructural evolution of metalsMetals at high temperatureHigh temperature. Neutrons illuminate a larger bulk volume and reveal quantitative phase abundance, bulk texture, lattice parameter changes and other ensemble averaged quantities. In contrast, fine-bundled high-energy X-rays deliver reflections from a number of individual grains. For each constituting phase, their statistics and behavior in time reveal information about grain growth or refinement, subgrain formation, static and dynamic recovery and recrystallization, slip systems, twinning, etc. The complementarity between neutron and synchrotron radiation is demonstrated to study atomic order under ambient and extreme conditions. Examples are given on various metallic systems including magnesium, zirconiumZirconium alloys and titanium aluminidesTitanium aluminides.

Klaus-Dieter Liss

Advanced Aluminum Alloy Development and In Situ Fitness-for-Service Testing for Automotive Lightweighting

Lightweighting has led to an increased use of aluminum alloys in many automotive systems, including the powertrain, body-in-white, and suspension. Fitness-for-service certification of new alloys for these applications frequently requires development of new testing methods that would subject the test components to realistic conditions of temperature and load, while studying the long-term materials’ response. As the typical lifetime of a vehicle exceeds 3000 h, the new testing methods must provide clear indication on the material’s suitability for a target application over a more realistic timeframe. An in situ study of the creep behavior using neutron diffraction quickly reveals the response of individual crystallographic planes to the applied load under the in-service operating conditions, yielding the critical information on the expected lifetime of the targeted component. This knowledge helps to identify alloy chemistry and processing conditions that result in manufacturing components capable of sustaining the thermal mechanical loads over the expected life cycle of a vehicle. Two advanced aluminum alloys, based on Al–Si and Al–Cu systems, have been the focus of this research.

Dimitry Sediako, David Weiss, Ahmed Nabawy

In Situ X-Ray Synchrotron Profile Analysis During High Pressure Torsion of Ti

X-Ray Line Profile Analysis is a powerful method to characterize the microstructure of deformed materials, especially when high energy and brilliant Synchrotron radiation enables investigations with high time and spatial resolution. Parameters like dislocation density, dislocation arrangement as well as scattering domain size and it’s distribution are parameters of a physical model of peak broadening, which can be applied to high quality diffraction measurements. A small high-pressure-torsion-machine was designed in order to perform in situ diffraction experiments during the deformation process at hydrostatic pressures up to 8 GPa in order to follow the strain as well as pressure induced microstructural characteristics of any material deformed. This was possible with the ideal design and equipment at the High-Energy-Materials-Science-beamline at PETRA III in Hamburg. Recent and First results of experiments on HPT-deformed Ti show that at 6 GPa the high pressure $$ \omega $$-phase is initiated only with additional shear deformation.

Erhard Schafler, Michael B. Kerber, Florian Spieckermann, Torben Fischer, Roman Schuster, Cornelia von Baeckmann

The Effect of Grain Refinement on Hot Tearing in AZ91D Magnesium Alloy

The AZ91D magnesium alloy is a popular casting alloy used for diverse automotive applications, despite its high susceptibility to hot tearing during casting solidification. In the metalcasting industry, hot tearing is manipulated via cooling rate, alloy composition or mold design optimization. In this work, the effect of grain refinement on hot tearing was quantitatively studied and the relationship between the alloy’s cooling rate and in situ force evolution during casting solidification was related to the severity of hot tears. The results suggest that the load evolution rate and microstructure were critical determinants of the hot tear severity for both unrefined and grain-refined alloys. The grain refiners were seen to significantly reduce the overall force and force-rate evolution, which contributed to the elimination of hot tearing in the AZ91D alloy under standard casting conditions.

T. Davis, L. Bichler, F. D’Elia, N. Hort

Formability of Magnesium Alloy AZ31B from Room Temperature to 125 °C Under Biaxial Tension

Magnesium AZ31B sheets of 2 mm thickness were stretch formed using a 101.6 mm diameter punch at room temperature and subsequent increments from 25 to 125 °C. Surface strains were measured using a digital image correlation method in order to ensure that biaxial stretching was achieved. The punch height versus load curve was found to be the same for temperatures of 25 and for 50 °C, while at 75 °C the load for a given punch height was less. This difference seems to indicate a change in deformation mechanism between 50 and 75 °C. Electron Backscatter Diffraction (EBSD) was used to quantify features of the microstructure in the as-received and the strained specimens. Rather than a sudden transition from twinning to slip at low temperatures, it appears that twinning gradually decreases and slip activity increases as temperatures rise across the range from 25 to 125 °C. This confirms recent predictions found in the literature. The twin activity predominantly involves the formation of compression twins which rapidly transform further to create secondary twins for easier strain accommodation.

Isaac Chelladurai, Andrew Orme, Mike P. Miles, David T. Fullwood, John E. Carsley, Raj K. Mishra, Irene J. Beyerlein, Marko Knezevic

In Situ Real-Time Monitoring of Aging Processes in an Aluminum Alloy by High-Precision Dilatometry

A detailed understanding of the atomistic processes governing the age hardening response of light metal alloys is of vital importance for the optimization of their properties. While a static characterization of metastable precipitates is possible, e.g., by advanced microscopic techniques, the kinetic aspects of the underlying formation of phases are by far more difficult to assess. In this work we present isothermal, high-stability laser dilatometric measurements, during the natural and artificial aging of a commercial aluminum alloy (Al-Mg-Si), with a rate resolution below 1 nm/h. The results of this case study show that the presented dilatometric technique allows for direct monitoring of the precipitation process with an unprecedented accuracy on the volume as well as on the time scale.

Martin Luckabauer, Elisabeth Hengge, Gregor Klinser, Wolfgang Sprengel, Roland Würschum

Effect of the Zn Content on the Compression Behaviour of Mg5Nd(Zn): An In Situ Synchrotron Radiation Diffraction Study

The properties of commercially viable Mg alloysMg alloys are not sufficient for many of the envisaged applications. The combination of Zn and rare earth metals is one of the most effective ways to enhance the mechanical properties of Mg alloys. In situIn situsynchrotronSynchrotron diffraction radiation diffraction is a unique method to investigate the dynamic microstructural processes occurring during deformationDeformation. Azimuthal angle–time plots give information on grain structure changes that can be correlated with grain rotation, twinning, recovery and recrystallization. As-cast Mg5Nd, Mg5Nd3Zn, Mg5Nd5Zn and Mg5Nd7Zn alloys were investigated during compression at room temperature, at 200 °C and at 350 °C with a strain rate of 10−3 s−1 until 10% deformation. The results and post mortem metallography were compared. At high temperatures grain rotation and sub-grain formation are active to obtain the final texture, while at room temperature twinning is the dominant deformation mechanism.

Domonkos Tolnai, Tim Kärcher, Ricardo Buzolin, Tungky Subroto, Francesco D’Elia, Serge Gavras, Andreas Stark, Norbert Schell, Norbert Hort, Karl U. Kainer

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