具有细晶/混晶交替分布组织特征的AZ31镁合金轧板拉伸变形行为仿真

Simulation of tensile deformation behavior of AZ31 magnesium alloy sheet with alternating fine-grain/mixed-grain distribution

通过中等应变速率轧制获取细晶区和混晶区交替分布的AZ31镁合金轧制板材,构建不同组织特征的黏塑性自洽(VPSC)模型,预测板材在室温拉伸下的变形机制、织构演变和力学响应,研究细晶区与混晶区对塑性变形的贡献。结果表明:经410℃、平均应变速率1.9 s^(-1)、4.8 s^(-1)和7.8 s^(-1)制备的轧制板材中细晶区与混晶区呈现板织构特征,细晶区织构组分相较于混晶区更接近ND方向;随着轧制平均应变速率的增加,板材的细晶区与混晶区的织构组分差异逐渐减小。在室温拉伸塑性变形初期阶段,轧制板材的主要变形机制是基面滑移,次要变形机制是棱柱面滑移和锥面滑移,而拉伸孪生几乎不开启。压缩孪生启动时,部分晶粒向TD方向偏转56°,形成TD方向的织构组分。棱柱面滑移活性的降低,有利于增强锥面滑移的分离效应,促使ND方向织构极密度降低和双峰织构形成。轧制板材在拉伸过程中,由于细晶区的织构组分相较于混晶区更接近ND方向,使得在拉伸过程中细晶区相较于混晶区的基面滑移开启较少,非基面滑移开启较多,促使拉伸变形的过程中细晶区起强化作用,混晶区起弱化作用。织构组分差异逐渐减小,使得细晶区与混晶区的变形机制活性趋于一致,促使其在拉伸过程中对抗拉强度贡献也逐渐趋于一致。

AZ31 magnesium alloy rolled sheets with alternating distribution of fine and mixed crystal regions were obtained by medium strain rate rolling.The visco-plastic self-consistent(VPSC)models for different microtructure were built.The deformation mechanism,texture evolution and mechanical response of AZ31 magnesium alloy rolled sheets at room temperature were predicted.The contribution of fine and mixed crystal regions on plastic deformation was studied.The results indicate that the fine-grained zone and the mixed-grained zone show the rolling texture characteristics of the rolled plates prepared at 410℃and the average strain rates of 1.9 s^(-1),4.8 s^(-1) and 7.8 s^(-1),while the texture components in the fine grain zone are closer to the ND direction than that in the mixed grain zone.With average strain rate increasing,the difference of the texture components in the fine grain zone and the mixed grain zone gradually decreases.In the early stage of plastic deformation,the main deformation mechanism is basal slip,while the secondary deformation mechanism is prismatic slip and pyramidal slip,and the extension twinning is hardly initiated.The contraction twinning is initiated,causing that some of the grains deflects 56°in the TD direction.This induces the formation a texture component in the TD direction.The activity of prismatic slip decreases,leading that the separation effect of pyramidal slip is enhanced.This finally contributes to the decrease of texture pole density and the formation of bimodal texture in the ND direction.During the tensile deformation process of the rolled plate,the texture components in the fine-crystal regions are closer to the ND direction than those in the mixed-crystal regions,resulting in the fact that the initiation of basal slip decreases and the activation of non-basal slip increases in the fine-grained zone in contrast to the mixed-grained zone.This makes the fine-grained zone strengthen and the mixed-grained zone weaken.The difference of texture components gradually decreases,leading to the deformation mechanism activity of the fine-grained zone and the mixed-grained zone tends to be the same.Finally,the contribution of the fine-grained zone and mixed-grained zone to tensile deformation is gradually similar.