Exploiting Magnesium Alloys Containing Long-Period Stacking Order (LPSO) Phases

最近发现的含有长周期有序(LPSO)相的镁合金可以获得优异的性能，这在过去的十年里引起了人们对这些材料的浓厚兴趣。然而，到目前为止，大多数研究都是关于这些材料在纳米尺度上的结构，或者是在单一性能(如强度)上产生最大值，而没有考虑到实际合金所需的工艺限制或性能要求平衡。第一步(第1年)将通过考虑挤压和热处理过程中形成的微观组织和织构，了解当前包含商业合金的LPSO如何实现良好的强度、延展性和各向同性的良好组合。将研究初级LPSO阶段与次级(沉淀)LPSO阶段的作用。LPSO和基质中的纹理演化将通过开发EBSD技术来区分这些贡献。还将研究挤压过程中初级LPSO相的机械破碎及其随后的重新分布。在必要时，实验工作将由有限元模拟(包括晶体塑性)来补充，以预测LPSO和基质相的尺寸、分数和分布如何影响整体合金性能(和性能各向异性)。下一步(第2年和第3年)将利用从第一年获得的理解来开发用于实际应用的LPSO合金，并优化性能平衡。将考虑LPSO的最佳组成和相的选择(通过利用不同的LPSO形成元素)、晶粒细化、二次LPSO的析出和织构控制等因素。建模将用于设计能够根据特定性能目标(例如，最大强度、最小各向异性等)进行调整的微结构。合金优化策略将通过使用显微镜和机械测试来生产和评估材料来测试。

The recent discovery of the excellent properties that can be obtained using magnesium alloys that contain long period stacking ordered (LPSO) phases has led to intense research interest in these materials over the last decade. However, most of the studies to date have been concerned with the structure of these materials on the nano-scale, or on producing the maximum value in a single property (e.g. strength) without consideration of the process limitations or property requirement balance needed in a practical alloy.The present PhD will address the scientific issues required to exploit LPSO containing magnesium alloys as practical materials for industrial application. The first step (year 1) will be to understand how the current LPSO containing commercial alloys achieve their favourable combination of good strength, ductility, and isotropy through a consideration of the microstructure and texture developed during extrusion and heat treatment. The role of primary LPSO phase vs. secondary (precipitated) LPSO will be studied. Texture evolution in the LPSO and matrix will be distinguished by developing an EBSD technique to separate these contributions. The mechanical break up of the primary LPSO phase and its subsequent redistribution during extrusion will also be investigated. Where necessary, the experimental work will be complemented by finite element modelling (including crystal plasticity) to predict how the size, fraction, and distribution of the LPSO and matrix phases influence the overall alloy properties (and property anisotropy).The next steps (years 2 and 3) will be to use the understanding gained from year 1 to develop LPSO alloys for practical use with an optimized property balance. Factors such as optimum fraction and selection of LPSO phase (by utilization of different LPSO forming elements), grain refinement, precipitation of secondary LPSO, and texture control will be considered. Modelling will be used to design microstructures capable of being tuned to particular property goals (e.g. maximum strength, minimum anisotropy etc.) The alloy optimization strategies will be tested be producing and evaluating material using both microscopy and mechanical testing.