预压缩-反向拉伸加载路径下镁合金AZ31轧制板材的孪生-退孪生行为

Twinning and detwinning behavior of rolled Mg alloy AZ31 plate under compression-tension loading

为了定量研究孪生和退孪生行为在镁合金塑性变形中的作用,开展了镁合金AZ31板材沿轧制方向单调拉伸、单调压缩及预压缩-反向拉伸下的宏观力学行为及微观EBSD试验,并基于考虑孪生-退孪生行为的弹黏塑性自洽模型(EVPSC-TDT),模拟预测了镁合金板材的宏微观塑性变形行为。结果表明:随着压缩量的增大,(0002)极图在RD附近的强度值逐渐增大,孪晶体积分数增加;反向拉伸时,RD附近的强度值逐渐减弱,孪晶体积分数降低;当反向拉伸量与预压缩量相同时,孪晶体积分数几乎减小到0,几乎所有晶粒c轴均转动至ND方向;随着预压缩量的增加,位错密度逐渐提升,增强了对滑移和孪生的阻碍作用,导致反向拉伸时的屈服应力随着预压缩量的增加而增大。反向拉伸初始阶段各滑移-孪生系的开启率相似,表明拉伸阶段的屈服应力与压缩后各滑移和孪生系的硬化有关;EVPSC-TDT模型可准确预测镁合金在以孪生-退孪生为主导的变形模式下的宏观力学行为、织构演化规律及孪晶体积分数。

In order to quantitatively study the role of twinning and detwinning on plastic deformation of Mg alloys,the macroscopic mechanical behavior and microscopic EBSD tests of Mg alloy AZ31 plate under monotonic tension-compression and compression-tension loading along rolling direction were carried out.In addition,the macroscopic and microscopic behaviors were predicted by the elastic visco-plastic self-consistent model with twinning and detwinning scheme(EVPSC-TDT).The results show that both the intensity of(0002)pole figure near rolling direction and twin volume fraction gradually increase during compression along rolling direction.During the reverse tension after compression,the intensity of(0002)pole figure near rolling direction gradually weakens and twin volume fraction reduces.When the reverse tension strain is equal to pre-compression strain,twin volume fraction nearly decreases to zero,and c-axis of almost all grains rotate to the ND direction.With the increase in compression strain,dislocation density gradually increases,and the inhibition effect on slips and twinning are strengthened,leading to the increase of yield stress,but the relative activity of each slip/twinning system at the early deformation during reverse tension is similar,indicating that the yield stress of reverse tension is related to hardening of each slip-twinning system after compression.Moreover,the EVPSC-TDT model can forecast well the macroscopic behavior,texture evolution and twin volume fraction of Mg alloys under the loading dominated by twinning and detwinning.