Deformation Physics of Nanoscale Features in Magnesium Alloys

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Magnesium alloys can achieve a high strength-density ratio and thus attract continuous interest over decades in replacing conventional metals for the weight reduction in vehicles and aircrafts. The main impediment to the greater use of magnesium is their poor deformability, originating from the inherent anisotropy of the crystal structure of magnesium. In detail, the activation thresholds for various deformation modes, such as basal-slip, non-basal slip, and twinning, are largely different (i.e., of order 100). With current emphasis on improving the deformability of magnesium alloys while increasing their strength, the key is tuning the relative activities of different deformation modes, mainly through introducing nanoscale features with selective strengthening effects. Alloying with rare earth elements, magnesium shows promise in improving both strength and ductility, however, the involved mechanism is poorly understood due to its complexity, including unclear nanoscale features, their interaction with different deformation modes, and consequent strengthening effects. The five-year objective of the proposed research is to perform a systematic and comprehensive research to gain an adequate understanding of the deformation physics within magnesium alloys at atomic and nano scale. Using state-of-the-art in-situ thermo-mechanical testing and high resolution imaging techniques integrated with electron microscopy, research will be undertaken, with model systems of binary and ternary magnesium-rare earth alloys, in three areas: 1) the effect of rare earth solutes on the structure changes of different dislocations, the main carriers of plastic deformation; 2) the interaction between dislocations and twin boundaries and grain boundaries, containing rare earth segregations; and 3) the selective strengthening effects of solute clusters or fine precipitates with anisotropic morphology. The expected major outputs of this research will be an enhanced understanding of nanoscale features and consequent strengthening effects within magnesium alloys. These results will provide a comprehensive understanding of deformation dynamics at atomic and nano scale in magnesium alloys, and can form a solid foundation for further advancing hexagonal alloys in general. The proposed program will train 3 Ph.D. and 3 master's students, who will gain experience and will generate new knowledge in microstructure design and characterization of light-weight alloys. This work will be of great value to the key industries involved in light-weight alloys, such as General Motors and Magellan Aerospace. Discoveries in the areas of magnesium will help maintain Canada's status as a leader in this research area and in the production of light-weight alloys in aerospace and automotive industries.