There have been numerous attempts to achieve superplasticity in light alloy materials for improving the formability and manufacture efficiency of them. However, the superplasticity of light alloy is difficult to realize for the uniform fine equiaxed grains, which are generally required by superplasticity, tend to rapidly grow during high temperature deformation. That means the superplasticity of light alloys not only requires an equiaxed fine-grained structure, but also needs to ensure the high-temperature structural stability. Thus, adding a second phase or alloying elements become one of the current research hotspots on superplasticity of light alloy materials. Currently, the main strategies for improving stability of the fine-grained structure of superplastic light alloy materials can be summarized as: introduction of second-phase particles pinning grain boundaries, phase structure of dual-phase alloys to inhibit growth between each other and reinforcement of composite materials inhibiting grain growth as well as utilizing solute segregation of single-phase alloys. This paper summarizes the research status of superplastic microstructure stability of light alloys including second-phase-containing alloys, duplex alloys, metal matrix composites and single-phase alloys. Finally, the paper proposes the development trend of superplastic light alloy materials from the perspective of industrial applications and cost-reduction requirements. Increasing the variety of alloying element, decreasing the content of alloying element, simplifying the process of manufacture and achieving low temperature superplasticity and high strain-rate superplasticity will be the development trend of superplastic light alloy materials.

金属材料超塑性一般要求具有均匀细小的等轴晶粒,并且在高温超塑变形过程中能够保持晶粒尺寸稳定性,避免晶粒快速长大。轻合金的超塑性不仅要具备等轴细晶组织,还需要通过引入第二相或合金元素等来保证材料的高温组织稳定性,这也是当前金属材料超塑性的研究热点之一。目前提高超塑性材料细晶组织稳定性的策略主要包括：析出第二相粒子钉扎晶界,双相合金的相结构之间抑制彼此生长,复合材料的增强体抑制晶粒长大以及单相合金的溶质原子偏聚等。本文概述了含析出第二相合金、双相合金、金属基复合材料和单相合金等轻合金超塑性组织稳定性的研究现状,并从工业应用需求及降低生产成本的角度,提出了超塑性材料的发展趋势。

Wrought magnesium alloys have a wide range of applications by controlling the microstructure and optimizing the deformation process to improve the mechanical properties. Low-alloyed magnesium alloys have great advantages in formability, corrosion resistance, and light weight. Moreover, low alloying and high performance have become important trends in the development of wrought magnesium alloys. This study reviews the research progress of low-alloyed, high-strength, high-plasticity, and superplastic wrought magnesium alloys regarding alloy composition design, strengthening and toughening mechanisms, and processing technology. From the perspective of improving production efficiency and expanding application scope, the development trend of low-alloyed wrought magnesium alloys is proposed.

变形镁合金通过调控微观组织、优化变形工艺，提高材料的力学性能，从而具有广泛的应用前景。低合金化镁合金在成形性、耐腐蚀性及轻量化等方面具有较大优势。低合金、高性能成为变形镁合金发展的重要趋势之一。本文重点概述了低合金化高强、高塑、超塑性变形镁合金在合金成分设计、强韧化机制及加工技术等方面的研究进展，并从提高生产效率、扩大应用范围的角度，展望了低合金化变形镁合金的发展趋势。

Grain refinement stands out as the primary strengthening mechanism in magnesium alloys. Zr emerges as the most effective grain refiner for magnesium alloys in the absence of Al, Si, etc. Typically, Zr is introduced in the form of an Mg-Zr master alloy. The crucial factor for achieving effective grain refinement in magnesium alloys incorporating Zr lies in regulating the morphology of Zr elements in the Mg-Zr master alloy, distinguishing between particle Zr and solute Zr. This study presents the theoretical groundwork for grain refinement. Drawing upon the growth restriction theory and heterogeneous nucleation theory, the refinement mechanism of soluble Zr and particle Zr on magnesium alloys is discussed. The discussion also identifies the engineering application bottleneck associated with Zr-refined magnesium alloys. A comprehensive review of advancements in Zr-refined magnesium alloy research is conducted, encompassing particle Zr and solute Zr. This review highlights the synergistic design strategy proposed for Zr-refined magnesium alloys. Ultimately, the anticipated development trends for Zr-refined magnesium alloys is prospected.

This paper briefly reviews the progress on high-temperature oxidation mechanisms of pure Mg and Mg alloys, the thermodynamics and kinetics of high-temperature oxidation of Mg alloys, and the antioxidation mechanism of Mg alloys. The potential of applying advanced characterization techniques in studying the high-temperature oxidation of Mg alloys is envisaged. Finally, the development trends of the oxidation-resistant Mg alloy are also summarized. The main viewpoints are as follows: The protection of magnesium alloys at high temperatures is provided by the formation of a continuous, dense oxide scale that is a specific thickness and prevents the outward diffusion of magnesium vapor and the inward diffusion of oxygen; the oxidation resistance of Mg alloys is usually closely related to the thermal stability of the second phases; when the trace alloy elements are not enough to form the corresponding surface oxide scale, the oxidation resistance can be improved by creating a substitutional solid solution and using the reactive element effect; the size of the oxide grain size decreases and then enhances the oxidation resistance once the surface active elements is enriched on the surface of the alloys; the selective oxidation and synergistic effect of alloying elements are critical to the oxidation resistance of Mg alloys; the addition of nano or microparticles into the Mg alloys improve the high-temperature oxidation resistance of the Mg alloy by reducing the size of specific oxidation sensitive regions. In the future, the research on the high-temperature oxidation of Mg alloys can be based on the following aspects: Investigating the processes and nature of the oxidation resistance of Mg alloys using cutting-edge characterization techniques; constructing the underlying connections between the alloying elements and the oxide scale grain size and mechanical properties; designing and optimizing multi-alloying element composition systems.

基于Pandat相图设计了一种新型的Mg-0.2Ce-0.2Ca (质量分数，%)三元合金，经常规挤压变形后的屈服强度约364 MPa、总合金化含量约0.4%，实现了高强度、低合金化。对挤压过程中不同阶段的组织进行表征，发现Mg-0.2Ce-0.2Ca合金中的孪晶存在于挤压的整个阶段，表现出了高的孪晶迁移阻力，并且在挤压变形的中后期，部分动态再结晶晶粒沿着孪晶变体交割区域形核，导致孪晶界面比例显著降低。Mg-0.2Ce-0.2Ca合金在挤压变形的早期阶段即存储了大量<c + a>位错，这些位错的运动阻力大，因此位错主导的回复再结晶机制直至挤压变形的后期才大量启动，并直接促进了该阶段镁合金中高比例超细晶粒的形成。分析认为，Mg-Ce-Ca合金挤压过程中微观组织演变的主要原因是Ca元素的添加提升了Mg基体孪晶运动阻力，且Ce、Ca元素的共添加诱导了多系滑移。

针对Mg-0.3Al-0.2Ca-0.5Mn合金在热挤压过程中容易形成对称性差的强基面织构从而导致力学性能各向异性的问题，本工作通过稀土元素Ce合金化的方法优化其基面织构进而改善材料的力学性能。利用中子衍射技术，结合SEM和EBSD等微观测试手段，研究稀土元素Ce对Mg-0.3Al-0.2Ca-0.5Mn挤压态镁合金板材的微观组织、体织构和力学各向异性的影响。结果表明，随着Ce含量的增加，挤压态镁合金板材中的第二相颗粒逐渐从Al₈Mn₅转变为Al₈Mn₄Ce和Al₁₁Ce₃，且第二相颗粒数量明显增多。0.05%Ce (质量分数)的添加并未明显改变合金板材的基面织构，而添加0.5%Ce后合金板材沿着挤压方向(ED)的双峰基面织构向双峰非基面织构转变，同时沿横向(TD)分布的丝织构组分明显减少，从而使得沿着ED和TD的拉伸屈服强度比值接近于1，合金板材各向异性显著降低。

Magnesium (Mg) alloys have received a significant interest in the past 20 years, owing to a nonlinearly increasing demand for lightweight structural materials. Magnesium extrusions alloys to date have had lower industrial uptake than their counterpart aluminium extrusion alloys, predominantly due to lower extrudability and formability, tension-compression yield asymmetry and no clear advantage in the specific strength. Any improvement in extrusion alloy properties requires a better understanding of the effects of alloy composition and processing conditions; and how these dictate the final alloy microstructure. This review sheds insightful information on the processing-microstructure-property relationships of extruded magnesium alloys. Historical and recent progress in magnesium extrusion alloys is critically reviewed, including the advances in extrudability, mechanical properties and microstructural characterisation. The challenges associated with the 'gap' in properties between the magnesium and aluminium extrusion alloys are identified, and prospects discussed regarding the development of high performance magnesium extrusion alloys.

In response to the urgent demand for lightweight, magnesium (Mg) alloys have garnered considerable attention owing to their low density. Nonetheless, the intrinsic poor room-temperature formability of Mg alloys remains a major obstacle in shaping precise complex components, necessitating the development of superplastic Mg alloys. Excellent superplasticity is usually acquired in high-alloyed Mg alloys with enhanced microstructural thermal stability facilitated by abundant optimized second-phase particles. While for cost-effective low-alloyed Mg alloys lacking particles, regulating solute segregation has emerged as a promising approach to achieve superplasticity recently. Moreover, the potential of bimodal-grained Mg alloys for superplastic deformation has been revealed, expanding the options for designing superplastic materials beyond the conventional approach of fine-grained microstructures. This study reviews significant developments in superplastic Mg alloys from the view of alloying strategies, grain structure control and deformation mechanisms, with potential implications for future research and industrial applications of superplastic Mg alloys.

Although magnesium alloys, as the lightest structural alloys, offer significant potential for automotive applications, their applications remain limited due to their poor formability at room temperature. Since the strategies used for improving formability usually result in a degradation of strength, there are no high strength magnesium alloys showing good formability. Here we report an alloy design concept that can simultaneously provide high strength and good formability. Such designed alloy when subjected to an appropriate processing technique shows a combination of strength and formability that surpasses those of the existing magnesium alloys reported so far. The alloy design concept used in the present study is based on the utilization of alloying elements that can induce precipitation, as well as maximize the segregation of other texture-controlling alloying elements. Such developed alloy is expected to broaden the application of Mg alloy sheets, which are now starting to gain acceptance by automotive industries.

Clouds of impurity atoms near line defects are believed to affect the plastic deformation of alloys. Three-dimensional atom probe techniques were used to image these so-called Cottrell atmospheres directly. Ordered iron-aluminum alloys (40 atomic percent aluminum) doped with boron (400 atomic parts per million) were investigated on an atomic scale along the <001> direction. A boron enrichment was observed in the vicinity of an <001> edge dislocation. The enriched region appeared as a three-dimensional pipe 5 nanometers in diameter, tangent to the dislocation line. The dislocation was found to be boron-enriched by a factor of 50 (2 atomic percent) relative to the bulk. The local boron enrichment is accompanied by a strong aluminum depletion of 20 atomic percent.

With the increasing requirement of vehicle weight reduction and energy conservation from automobile industry, the investigation and development of high strength steel sheet has been stressed extensively. Bake hardening steel, as a new kind of automotive steel, exhibits low strength and good formability&nbsp; before drawing, after which increases obviously in the yield strength during baking process, and is then widely used in the outer plate of modern cars. Mn and P are often added to sheet steel to increase the strength, and their distributions have significant effect on drawability, bake hardening property and surface quality of bake hardening steels. In this paper, the distributions of Mn and P and their effect on tensile behavior in bake hardening steels were studied. For investigation, two kinds of bake hardening steels (BH&ndash;Mn and BH&ndash;P steels) were heated to 800&nbsp; ℃, held for 2 min and cooled by water quenching. Three dimensional atom probe (3DAP) technique, internal friction experiments and tensile tests were carried out to analysis the effect of Mn and P distribution patterns on the interstitial atom distribution and Cottrell atmosphere in the matrix, so as to obtain the influence of solute istributions on tensile behavior. The results indicate that P segregates mainly in bake hardening steel, and part of P segregates together with C, which strongly pin the dislocations and is the main reason that induces the yield point elongation during tensile process. In BH&ndash;Mn steel, Mn hardly segregates in the matrix and C segregates very little, so the strength of BH&ndash;Mn steel is lower than that of BH&ndash;P steel, whereas the plasticity is better than BH&ndash;P steel. The segregation of P together with C and its pinning of dislocations will influence Snoek&ndash;Ke&ndash;Koster internal friction, and mkes the disappearance of Snoek&ndash;Ke&ndash;Koster peak.

The formability and mechanical properties of many engineering alloys are intimately related to the formation and growth of twins. Understanding the structure and chemistry of twin boundaries at the atomic scale is crucial if we are to properly tailor twins to achieve a new range of desired properties. We report an unusual phenomenon in magnesium alloys that until now was thought unlikely: the equilibrium segregation of solute atoms into patterns within fully coherent terraces of deformation twin boundaries. This ordered segregation provides a pinning effect for twin boundaries, leading to a concomitant but unusual situation in which annealing strengthens rather than weakens these alloys. The findings point to a platform for engineering nano-twinned structures through solute atoms. This may lead to new alloy compositions and thermomechanical processes.

Interface segregation of solute atoms has a profound effect on properties of engineering alloys. The occurrence of solute segregation in coherent twin boundaries (CTBs) in Mg alloys is commonly considered to be induced by atomic size effect where solute atoms larger than Mg take extension sites and those smaller ones take compression sites in CTBs. Here we report an unusual solute segregation phenomenon in a group of Mg alloys-solute atoms larger than Mg unexpectedly segregate to compression sites of {10[Formula: see text]1} fully coherent twin boundary and do not segregate to the extension or compression site of {10[Formula: see text]2} fully coherent twin boundary. We propose that such segregation is dominated by chemical bonding (coordination and solute electronic configuration) rather than elastic strain minimization. We further demonstrate that the chemical bonding factor can also predict the solute segregation phenomena reported previously. Our findings advance the atomic-level understanding of the role of electronic structure in solute segregation in fully coherent twin boundaries, and more broadly grain boundaries, in Mg alloys. They are likely to provide insights into interface boundaries in other metals and alloys of different structures.

Microalloyed, age-hardenable Mg alloys can exhibit an excellent balance between strength and ductility. One such alloy, AXM10304 (Mg-1.31A1-0.33Ca-0.46Mn in wt. %), possesses high extrudability with mechanical properties comparable to 6xxx-series Al alloys at considerably lower density. The mechanical properties are due to the presence of a high number density of disc-shaped GP zones parallel to the basal planes. The present work focuses on providing a mechanistic understanding of the effect of these GP zones, on both basal and prismatic slip. Using crystal plasticity simulations in conjunction with analytical strength modeling, the anisotropy in shear resistance of disc-shaped GP zones is quantitatively evaluated for the first time. It is shown that the passage of dislocations parallel to the zone (basal slip) experience a lower resistance compared to the case when the shearing occurs perpendicular to the zone (prismatic slip). This is not simply a geometrical effect; in fact, the geometry of basal discs favors the strengthening of basal slip when dislocations are not required to bow around the obstacles. Rather, it is hypothesized that the GP zone coherency strain fields contribute less resistance to basal slip as compared to prismatic slip. Furthermore, the possibility of a chemical effect is only present for the prismatic. Despite the fact that the harder mode (prismatic slip) is strengthened more than the soft, it is shown that the net strengthening effects still cause a decrease in the overall anisotropy of the individual grains, which may help to explain why the ductility is good, despite the high strength. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd.