置换原子钉扎镁合金变形孪晶的微观机制及强韧化效应

Magnesium is the lightest metal materials for engineering application. However, magnesium has poor plastic deformation ability, which leads to that the application magnesium has been restricted greatly.In this project, the twin lamellar thickness will be refined for substitutional atom to pin twin boundary in order to improve strength and toughness of magnesium alloy. To reasonably choose the alloy elements pining twin boundary, the mechanism of substitutional atom pining twin boundary will be analyzed and the diffusion thermodynamic equation of substitutional atom to twin boundary will be established. On this basis, the interaction of pining twin boundary and dislocation, second phase, other twin boundaries will be systematically studied by using of EBSD and TEM. The effect of pining twin boundary on texture evolution and twin system in magnesium alloy will be analyzed. The deformation mechanism of magnesium alloy containing pining twin boundary will be revealed. Meanwhile, lamellar thickness and fraction of twin in magnesium alloy will be altered by using of these methods such as predeformation, increase of deformation rate, decrease of stacking fault energy, and multi-direction forging and then the relationship between lamellar thickness and fraction of twin and mechanical property of magnesium alloy will be analyzed.

镁是最轻的金属结构材料，但强度低塑性差，限制了镁合金的开发应用。在发现置换原子钉扎孪晶界阻碍孪晶生长的基础上，本项申请提出利用置换原子钉扎镁合金孪晶界的方法来细化孪晶片层厚度，提高镁合金的强韧性。系统分析置换原子钉扎镁合金孪晶界的微观机制，建立置换原子向孪晶界扩散的热力学方程，为合理选择置换原子奠定理论基础。在此基础上，采用电子背散射衍射、透射电镜等技术，重点研究被钉扎孪晶界与位错、第二相以及其它孪晶界等晶体缺陷之间的交互作用，明确后续变形中被钉扎孪晶界对镁合金变形孪晶开动和织构演变的影响规律，揭示含钉扎孪晶界镁合金的变形机理。同时，结合预变形、增加变形速率、调节合金元素减小材料的层错能以及多向锻造等方法，调控镁合金的孪晶片层厚度和孪晶体积分数，明确被钉扎孪晶界其孪晶片层厚度和体积分数与镁合金力学性能之间的关系。

本项目在发现置换原子钉扎孪晶界阻碍孪晶生长的基础上，利用置换原子钉扎镁合金孪晶界的方法实现了细化孪晶片层厚度，提高了镁合金的强韧性。系统分析了置换原子钉扎镁合金孪晶界的微观机制，为合理选择置换原子奠定了理论基础；重点研究了被钉扎孪晶界与位错、第二相以及其它孪晶界等晶体缺陷之间的交互作用，明确后续变形中被钉扎孪晶界对镁合金变形孪晶开动和织构演变的影响规律，揭示了含钉扎孪晶界镁合金的变形机理；同时，结合预变形、增加变形速率、调节合金元素减小材料的层错能以及多向锻造等方法，调控镁合金的孪晶片层厚度和孪晶体积分数，明确了被钉扎孪晶界其孪晶片层厚度和体积分数与镁合金力学性能之间的关系；分析了间隙和置换原子对锯齿温度范围、锯齿类型、临界应变、平均应力跌幅等锯齿特征的影响规律；揭示了镁合金退孪晶现象与钉扎孪晶界镁合金的塑性变形机制。研究成果不仅为开发新型高强韧性镁合金提供理论依据，还丰富了镁合金孪生变形的研究，完善了孪晶强韧化金属材料的理论体系。