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基于室温轴向拉伸和压缩实验研究了挤压态ZK60镁合金的拉-压不对称性.通过修正黏塑性自洽模型,建立了耦合滑移和孪生的晶体塑性力学模型,模拟了挤压态ZK60镁合金轴向拉、压力学行为,分析了基面、柱面、锥面滑移及{1012}<1011>拉伸孪生和{1011}<1012>压缩孪生在塑性变形过程中的激活及演变情况.结合实验与模拟,从微观塑性变形机制角度分析了具有初始挤压态丝织构的镁合金产生拉-压不对称性的机理.结果表明:轴向拉伸过程中拉伸孪生和压缩孪生都较难激活,变形初期以基面滑移为主,由于基面滑移取向因子较低,导致屈服应力较高;随着晶粒转动,基面滑移分切应力降低,应力逐步升高,变形机制转为以柱面滑移为主,辅以锥面滑移,应变硬化率较低,应力-应变曲线较平稳.轴向压缩前期,临界剪切应力较低的拉伸孪生大量激活,导致屈服应力较低;应变达到6.0%后拉伸孪生逐渐饱和,相对活动量快速降低,硬化率迅速提高,由于大量孪晶界对位错滑移形成阻碍,滑移机制未出现大量激活;轴向压缩后期,随着应力的持续升高,压缩孪生启动,相对活动量迅速上升,塑性变形积累的应力得以释放,硬化率降低.因此,挤压丝织构状态决定了镁合金在室温轴向拉、压变形过程中的变形机制存在明显区别,从而导致挤压镁合金产生显著的轴向拉-压不对称性.
The tension-compression asymmetry of the as-extruded ZK60 magnesium alloy was studied based on the axial tensile and compressive tests at room temperature. The plastic-plastic coupling model of twin slip and slip was established by modifying the self-consistent visco-plastic model. ZK60 magnesium alloy was investigated. The basal, cylindrical and conical surface slip and the activation of {1012} <1011> and {1011} <1012> compression twin during plastic deformation were analyzed. And its evolution.According to the experiment and simulation, the mechanism of tension-pressure asymmetry of the magnesium alloy with the initial extruded silk structure was analyzed from the perspective of micro-plastic deformation mechanism.The results show that the tensile twinning And compression twin are more difficult to activate, the initial deformation of the base surface slip based, due to the base surface slip orientation factor is relatively low, resulting in higher yield stress; with the grain rotation, the basal plane shear stress reduction, stress Gradually increased, the deformation mechanism turned to cylindrical sliding, supplemented by the cone slip, the strain hardening rate is low, the stress-strain curve is relatively smooth.At the initial stage of axial compression, the critical shear stress Lower tensile twins massively activated, resulting in lower yield stress; after strain reached 6.0% The twins gradually saturate, the relative activity decreases rapidly and the hardening rate increases rapidly. Because a large number of twin boundaries obstruct the dislocation slip, the slip mechanism does not appear to be activated in large quantities. In the late stage of axial compression, as the stress continues to increase, Compression twin starts, the relative activity rapidly increases, the stress accumulated by plastic deformation is released, and the hardening rate is reduced.Therefore, the texture of extruded silk determines the deformation mechanism of magnesium alloy in axial pull and compression deformation at room temperature, there is a clear difference , Resulting in a significant axial tension-pressure asymmetry of the extruded magnesium alloy.