镁合金混晶结构调控与高周疲劳行为的关联性研究

本项目将材料-力学-物理等不同学科相结合，研究具有混晶结构特征镁合金材料在弹性循环加载条件下的高周疲劳行为及其微观失效机制，建立疲劳性能与微结构之间的内在关联，着重探讨混晶结构中粗晶粒和细晶粒的晶体学取向、空间分布、尺寸大小、所占体积分数等对合金疲劳强度的作用规律，研究循环加载过程中粗晶粒和细晶粒内微观变形机制（位错滑移和/或孪晶）的启动和演变行为，揭示疲劳裂纹萌生和扩展与晶界（细晶粒/细晶粒、细晶粒/粗晶粒和粗晶粒/粗晶粒界面）和孪晶界面等位置处存在的局部循环塑性变形不协调性、粗/细晶粒内部各自的主控微损伤机制、微缺陷等之间的内在关联，确定诱发疲劳裂纹萌生的竞争性机制和疲劳裂纹扩展的择优路径，获得可显著提升镁合金抗疲劳性能的优化混晶结构，探索相应的大塑性变形加工工艺和后续退火制度，为高性能镁合金在工程领域中的安全应用提供理论和实验基础。

On the basis of the combination of material-mechanics-physics, this project is to research the high cyclic fatigue behavior and micro failure mechanism of Mg alloys with a typical characteristic of bimodal grain structure and establish the relationship between fatigue properties and microstructure under elastically cylic loading conditions. The emphases are to investigate the influence of the crystallographic orientation, spatial distribution, size and volume fraction of coarse and fine grains on the fatigue strength; to research the activation and evolution of micro deformation mechanisms (cyclic slips and/or activated twins) occurred in thecoarse and fine grainsduring the fatigue process; to explore the relationships between the initiation and propagation of fatigue cracks and the localized incompatibility of cyclically plastic deformation at grain boundaries (fine/fine, fine/coarse and coarse/coarse grain interfaces) and twin boundaries, the dominant micro-damage mechanisms occurred in corase and fine grains, and micro defects; to determine competitive mechanisms for causing the fatigue crack initiation and the preferential propagation routes for fatigue cracks; to obtain the optimized bimodal grain structure and explore the associated severe plastic deformation processes and subsequent annealing procedues for remarkably enhancing the fatigue resistance of Mg alloys; to provide theoretical and experimental bases for ensuring the safe applications of high-performance Mg alloys in the engineering fields.