含LPSO结构Mg-Gd-Y-Zn-Zr合金循环塑性变形及疲劳裂纹萌生机制研究

新型含低能共格界面LPSO结构的Mg-Gd-Y-Zn-Zr合金，呈现优异的强韧性能和疲劳性能，具有重要的轻量化应用前景；但由于显著的疲劳寿命应变幅值敏感性和疲劳寿命台阶，以及其循环塑性变形和疲劳损伤机制不清楚，限制其在航空航天和武器装备上的应用。本项目将设计和制备含不同LPSO结构形貌和体积分数的Mg-Gd-Y-Zn-Zr镁合金，基于原位微观二维物理网格变形，揭示LPSO结构对应力集中和裂纹萌生的影响机制；研究挤压镁合金的循环塑性变形和疲劳裂纹萌生行为，阐明非基面滑移和扭折对含LPSO结构镁合金塑性变形影响机制；表征二维、三维裂纹形貌及裂纹附近晶粒特征等，定量化地揭示驻留滑移带、晶界、块状内部、片层晶内和相界等裂纹萌生竞争机制，深入阐明LPSO结构对疲劳裂纹萌生、疲劳寿命台阶形成和改善疲劳寿命等影响机制，为调控变形镁合金强韧性能和疲劳性能以及开发高强韧耐疲劳镁合金零件等提供理论基础。

Mg-Gd-Y-Zn-Zr alloy with the LPSO structures of the low-energy coherent interface presents important lightweight potential for achieving higher strength-elongation and fatigue life simultaneously. However, significant strain amplitude sensitivity and fatigue life step existing, and the mechanism of cyclic plastic deformation and fatigue crack initiation is not clear, which greatly limits the designation and application of high-strength magnesium alloy. In this work, the extruded Mg-Gd-Y-Zn-Zr magnesium alloys with different morphologies and volume fractions of LPSO structures will be designed and manufactured. First, the effects of LPSO structures on stress concentration and crack initiation will be examined based on in-situ deformation of microscopic two-dimensional physical grid. Secondly, the fatigue lives of extruded GWZ alloy will be obtained after cyclic plastic deformation and fatigue crack initiation behavior examined. As well, the mechanism of non-basal slip and kinking on the cyclic deformation can be quantitatively clarified. Finally, after characterizing 2D and 3D crack morphology and grain features near the cracks, the mechanism of crack initiation competition among persistent slip bands, grain boundaries, interior of block structure, interior of the grain with lamellar structure, phase boundaries, etc., is going to be quantitatively revealed. Moreover, the effects of LPSO structures on the mechanism of fatigue crack initiation, fatigue life step formation and fatigue life enhancement will be illustrated. This work will lay the foundation for regulating the strength-toughness and fatigue property of the magnesium alloy and developing high performance components.