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

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.