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

近年来，人们发现含有长周期有序堆积相（LPSO）的镁合金具有优异的性能，这引起了人们对这些材料的强烈研究兴趣。然而，迄今为止的大多数研究都是关注这些材料在纳米尺度上的结构，或在单一性能（例如强度）中产生最大值，而没有考虑实际合金所需的工艺限制或性能要求平衡。本博士将解决将含氧化镁合金的LPSO开发为工业应用的实用材料所需的科学问题。第一步（第一年）将了解当前含LPSO的商用合金如何通过考虑挤压和热处理过程中形成的微观结构和纹理来实现良好的强度、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的作用。通过开发EBSD技术来区分LPSO和矩阵中的纹理演化。在挤压过程中，初级LPSO相的机械破碎及其随后的再分布也将被研究。必要时，实验工作将辅以有限元建模（包括晶体塑性），以预测LPSO和基体相的尺寸、分数和分布如何影响合金的整体性能（和性能各向异性）。接下来的步骤（第2年和第3年）将使用从第1年获得的理解来开发具有优化性能平衡的LPSO合金的实际应用。将考虑诸如最佳分数和选择LPSO相（通过利用不同的LPSO形成元素），晶粒细化，二次LPSO的沉淀以及织构控制等因素。建模将用于设计能够调整到特定性能目标的微观结构（例如，最大强度，最小各向异性等）。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。

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.