AZ31镁合金棒材循环扭转变形及其对力学性能的影响

Cyclic torsion of AZ31 magnesium alloy rod and its effect on mechanical property

在室温条件下,对AZ31镁合金挤压棒材进行循环扭转变形,测试了扭转变形过程的力学性能以及变形后的微观组织和织构特征,并对扭转变形对镁合金棒材的力学性能影响进行了分析。结果表明:镁合金棒材在循环扭转过程中得到了严格对称的应力-应变滞回线,并且随着循环周期的增加,由于加工硬化和内部微裂纹扩展的共同影响,应力-应变滞回线上的应力峰值呈现先增加后减小的特征。在最大扭转角分别为60°和90°条件下,应力峰值出现在第四周期。镁合金棒材扭转变形后的晶粒中出现大量的拉伸孪晶带,孪晶启动使晶粒的 C 轴转向棒材轴线方向。镁合金棒材扭转变形后的力学性能测试结果显示,循环扭转变形明显提高了镁合金棒材压缩变形的屈服强度,其值由扭转前的约100MPa最大提高至约200MPa。

The cyclic torsion was carried out on the extruded AZ31 magnesium alloy rods at room temperature by using a computer controlled torsion testing machine. The texture of initial extruded magnesium alloy rods was measured by the XRD technique, which displays a typical basal texture. The mechanical properties during deformation were measured, and the microstructure and texture feature after torsion were analyzed by the EBSD. Meanwhile, the effect of cyclic torsion on mechanical properties of magnesium alloy rods was also investigated. The results show that the symmetrical stress-strain hysteresis curves are obtained during the cyclic torsion of magnesium alloy rods, revealing that sliding is the dominant deformation mode during former torsions, moreover, the stress peak values of the hysteresis curves present an increasing first and then decreasing trend with the increase of cycle period, which is dominated by work hardening and internal micro-crack propagation. The stress peak forms at the 4th cycle under conditions of 60°and 90°maximum torsion angles, respectively. Amounts of extension twinning bands formed within grains after torsion of magnesium alloy rods, c -axis of grains is rotated to the axial direction of bars caused by the activation of twinning. Mechanical properties of twisted magnesium alloy rods tested by computer controlled universal testing machine show that the compression yielding strength of magnesium alloy bars is increased by the cyclic torsion, the value of which is increased from about 100MPa before torsion to about 200MPa after torsion at most.