Deformation Physics of Nanoscale Features in Magnesium Alloys

镁合金可以实现高强度密度比，因此在过去的几十年里，镁合金在取代传统金属以减轻车辆和飞机重量方面一直引起人们的兴趣。镁的晶体结构固有的各向异性导致其变形性差，这是阻碍镁材料广泛应用的主要因素。具体来说，各种变形模式的激活阈值，如基底滑移、非基底滑移和孪生，有很大的不同（即100数量级）。当前镁合金在提高强度的同时提高变形能力，关键在于调节不同变形模式的相对活度，主要是通过引入具有选择性强化作用的纳米尺度特征。与稀土元素相结合，镁在提高强度和延展性方面表现出良好的前景，然而，由于其复杂性，包括不清楚的纳米尺度特征，它们与不同变形模式的相互作用以及随之而来的强化效果，所涉及的机制知之甚少。

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.