挤压态AZ31镁合金的拉压不对称性及微观组织

在考虑滑移和孪生两大塑性变形机制的基础上，通过修正的粘塑性自洽（VPSC）模型，模拟挤压态AZ31镁合金轴向拉-压过程中的力学行为及微观组织。结合EBSD实验与模拟，分析了不同变形机制对初始挤压态丝织构镁合金产生拉压不对称的机理以及塑性变形过程中的微观组织。结果表明，轴向拉伸变形初期以基面滑移系为主，由于基面滑移的施密特因子较低，导致屈服应力较高；随着应变的增加，棱柱面滑移成为主导变形机制，应变硬化率降低，应力-应变曲线较平稳；轴向压缩变形初期，临界剪切应力较低的拉伸孪晶大量开启导致屈服应力较低；随着拉伸孪晶相对活性的快速降低，应变硬化率迅速提高；轴向压缩后期，随着应力的持续升高，压缩孪晶开始启动，塑性变形积累的应力得到释放，导致应变硬化率降低。另外，从典型晶粒的颜色和孪晶迹线方面解释了沿ED方向压缩时孪晶体积分数较小的原因。

Tension-Compression Asymmetry and Microstructure of Extruded AZ31 Magnesium Alloy

The mechanical behavior and texture evolution of extruded AZ31 magnesium alloy during the axial tension-compression process at room temperature were simulated by a modified viscoplastic self-consistent model considering slip and twin plastic deformation mechanisms. On the basis of EBSD experiment and simulation, the mechanism of tension-compression asymmetry caused by different deformation mechanisms and the texture evolution in the process of plastic deformation were analyzed. Results show that basal slip is the main deformation mode in the early stage of axial tension deformation, but the orientation factor of basal slip is low and has a hard orientation, resulting in higher yield stress. With the increase in strain, prismatic slip becomes the main deformation mechanism, and the strain hardening rate is low, so the stress-strain curve is smooth. In the early stage of axial compression, tension twinning has a high activity due to its low critical shear stress, leading to lower yield stress. As the relative activity decreases rapidly with the tension twinning, the hardening rate increases at the same time. In the later stage, with the activation of compression twinning, its relative activity increases rapidly; the accumulated stress during plastic deformation can be released, and the hardening rate decreases. In addition, the less twin volume fraction in the ED direction was explained by the color and the twin trace of typical grain.