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挤压态ZK60镁合金室温拉-压不对称性研究
发布人：上海艾荔艾金属材料有限公司www.shailiai.com
更新时间：2015-12-23
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。
挤压态ZK60镁合金室温拉-压不对称性研究RESEARCH ON THE TENSION-COMPRESSION ASYMMETRY OF AS-EXTRUDED ZK60 MAGNESIUM ALLOYS AT ROOM TEMPERATURE
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<c+a>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轴向拉-压不对称。
Most wrought magnesium alloys exhibit a significant tension-compression asymmetry in yield and work hardening behavior. To some extent, the widespread implementation of wrought magnesium alloys is
hindered due to this disadvantage in some special conditions. In order to quantitatively analyze the effects of the deformation mechanisms on the tension-compression asymmetry of wrought Mg alloy, in this paper, the plastic deformation behavior of the as-extruded ZK60 magnesium alloy under uniaxial tension and compression at room temperature was investigated by the crystal plasticity simulation and experimental methods. The crystal plasticity constitutive model which includes slip and twinning mechanism was established by modifying the viscoplastic self-consistent (VPSC) model. With this model, the activation and evolution of basal slip, prismatic slip, pyramidal slip, {1012}1011 tensile twinning and {1011}1012 compression twinning are quantitatively studied during the process of uniaxial tension and compression deformation. Tensile-compression asymmetry of the as-extruded ZK60 alloy which has initial extruded fiber texture is analyzed from the microscopic plastic deformation mechanism. The results show that the tension and compression twinning in the axial tension-compression process are difficult to active, basal slip is the main deformation mode in the early stage of deformation, but the orientation factor of basal slip is low and has a hard orientation resulting higher yield stress. With the rotation of grains, the critical shear stress of basal slip reduced, stress continues increasing and prismatic slip became the main deformation mechanism, pyramidal<c+a> slip also has a very high activity. At this stage, the strain hardening rate is low and the stress-strain curve is smooth. In the early stage of compression, the tensile twinning has a high activity due to its low critical shear stress (CRSS), which leading to a lower yield stress. The tensile twinning gradually saturated after the strain reaching 6.0%. And then, the relative activity decreased rapidly and the hardening rate increased at the same time. Since the large numbers of twin boundaries hinder the movement of dislocation slip, slip is not the major mechanism. In the later stage, the compression twinning start activation and its relative activity rise rapidly, the accumulated stress during plastic deformation can be released and then the hardening rate decreased. It can see that, the variation in the relative activity of each deformation mode during compression deformation is much more complex than tension. The yield asymmetry and different work hardening behavior could be attributed to the combined effects of the strong fiber texture and the polar nature of twinning.
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