Deformation Physics of Nanoscale Features in Magnesium Alloys

镁合金可以实现高强度-密度比，因此数十年来在替代传统金属以减轻车辆和飞机的重量方面引起了持续的兴趣。镁的更广泛应用的主要障碍是其差的可变形性，这源于镁晶体结构的固有各向异性。详细地，各种变形模式（诸如基底滑移、非基底滑移和孪生）的激活阈值在很大程度上不同（即，100号命令）。目前的重点是提高镁合金的变形能力，同时提高其强度，关键是调整不同变形模式的相对活性，主要是通过引入具有选择性强化效果的纳米级特征。与稀土元素合金化，镁显示出改善强度和延展性的希望，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。 拟议研究的五年目标是进行系统和全面的研究，以充分了解原子和纳米尺度下镁合金的变形物理学。本文将利用最新的原位热机械测试技术和高分辨率成像技术，结合电子显微镜技术，以二元和三元镁-稀土合金为模型系统，在三个方面进行研究：1）稀土溶质对塑性变形的主要载体--不同位错结构变化的影响; 2）位错与孪晶界和晶界的相互作用，含有稀土元素的偏析; 3）溶质团簇或具有各向异性形貌的细小沉淀物的选择性强化作用。这项研究的预期主要成果将是加深对镁合金纳米尺度特征和随之而来的强化效应的了解。这些结果将为镁合金在原子和纳米尺度上的变形动力学提供全面的理解，并为进一步发展六方合金奠定坚实的基础。该项目将培养3名博士。和3名硕士生，他们将获得经验并在轻质合金的微观结构设计和表征方面产生新知识。这项工作将对涉及轻质合金的关键行业具有重要价值，如通用汽车和麦哲伦航空航天。在镁领域的发现将有助于保持加拿大在这一研究领域以及在航空航天和汽车工业中生产轻质合金方面的领先地位。

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.