挤压态AZ31合金小应变变形时的孪生行为

Twinning Behavior in Extruded AZ31 Alloy Under Low Strain Deformation

摘要:

在室温下对挤压态AZ31合金沿棒材径向进行拉伸变形（RDT试样）和沿挤压方向进行压缩变形（EDC试样），2种变形应变速率均为10^-4 s^-1。采用金相显微镜（OM）和背散射电子衍射（EBSD）研究了变形过程中合金的孪生行为。结果表明：拉伸孪晶影响了合金的屈服点，EDC试样的屈服点为139 MPa，高于RDT试样的屈服点88 MPa。2种变形应力状态下，随应变增加，合金的应变硬化速率都是先快速下降，但EDC试样的硬化速率随后明显上升，并一直持续到断裂，而RDT试样则几乎保持稳定的硬化速率。EDC试样硬化速率的升高与合金中产生大量的拉伸孪晶以及孪晶织构诱导的滑移行为有关。基于EBSD测试结果，给出了一种计算晶粒内孪晶体积分数的方法，得出RDT试样在应变为0.04时，（0002）晶粒中拉伸孪晶体积分数约为45%。

Abstract:

Tension parallel to the radial direction (RDT) and compression along the extrusion direction (EDC) of an extruded AZ31 Mg alloy bar were conducted under a strain rate of 10^-4 s^-1 at room temperature. Twinning behavior was characterized by optical microscopy (OM) and electron backscatter diffraction (EBSD). The results demonstrate that extension twins have an effect on the yield point; the yield point of the alloy under EDC is 139 MPa which is higher than 88 MPa of the alloy under RDT. With increasing strain, strain hardening rates under these two stress states show a trend of fast decline at first, and then the hardening rates under EDC start to increase obviously till fracture while that under RDT keeps almost a constant. The increase in the hardening rate under EDC is related to the formation of extension twins and the twinning texture-induced slip activity. A method to measure the twin volume fraction in grains based on EBSD results was proposed. Under RDT, the volume fraction of extension twin in (0002) grains is about 45% at the strain of 0.04.