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金属学报  2016, Vol. 52 Issue (3): 264-270    DOI: 10.11900/0412.1961.2015.00324
  论文 本期目录 | 过刊浏览 |
挤压态ZK60镁合金室温拉-压不对称性研究*
林金保(),任伟杰,王心怡
太原科技大学应用科学学院, 太原 030024
RESEARCH ON THE TENSION-COMPRESSION ASYM-METRY OF AS-EXTRUDED ZK60 MAGNESIUM ALLOYS AT ROOM TEMPERATURE
Jinbao LIN(),Weijie REN,Xinyi WANG
School of Applied Science, Taiyuan University of Science and Technology, Taiyuan 030024, China
引用本文:

林金保,任伟杰,王心怡. 挤压态ZK60镁合金室温拉-压不对称性研究*[J]. 金属学报, 2016, 52(3): 264-270.
Jinbao LIN, Weijie REN, Xinyi WANG. RESEARCH ON THE TENSION-COMPRESSION ASYM-METRY OF AS-EXTRUDED ZK60 MAGNESIUM ALLOYS AT ROOM TEMPERATURE[J]. Acta Metall Sin, 2016, 52(3): 264-270.

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摘要: 

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的轴向拉-压不对称性.

关键词 ZK60镁合金黏塑性自洽模型拉-压不对称性孪生    
Abstract

Most wrought magnesium alloys exhibit a significant tension-compression asymmetry in yield and work hardening behaviors. To some extent, the widespread implementation of wrought magnesium alloys is hindered due to this disadvantage in some special conditions. In this work, in order to quantitatively analyze the effects of the deformation mechanisms on the tension-compression asymmetry of wrought magnesium alloys, the plastic deformation behavior of the as-extruded ZK60 magnesium alloy under uniaxial tension and compression at room temperature is investigated by the crystal plasticity simulation and experimental methods. The crystal plasticity constitutive model including slip and twinning mechanism is established by modifying the viscoplastic self-consistent (VPSC) 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 with fiber texture is analyzed based on 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 in higher yield stress. With the rotation of grains, the critical shear stress of basal slip reduces, stress continues increasing and prismatic slip becomes the main deformation mechanism, moreover, pyramidal <c+a> slip also has a 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), leading to a lower yield stress. The tensile twinning gradually saturated after the strain reaches 6.0%. And then, the relative activity decreases rapidly and the hardening rate increases at the same time. Since a large number of twin boundaries hindered the movement of dislocations, slip is no longer the major mechanism. In the later stage, the compression twinning startes activation and its relative activity rises rapidly, the accumulated stress during plastic deformation could be released and then the hardening rate decreases. It can be seen that, the variation in the relative activity of each deformation mode during compression deformation is much more complex than that during 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.

Key wordsZK60 magnesium alloy    viscoplastic self-consistent model    tension-compression asymmetry    twinning
收稿日期: 2015-06-23     
基金资助:* 国家自然科学基金项目51204117, 山西省高等学校优秀青年学术带头人支持计划项目和山西省研究生科技创新项目2015SY67资助
图1  挤压态ZK60镁合金(0002)基面极图和拉伸,压缩试件示意图
Deformation mode Crystallographic type τ0 / MPa τ1 / MPa θ0 / MPa θ1 / MPa
Basal <a> 5 20 450 0
Prismatic <a> 185 80 300 0
Pyramidal <a> 310 150 800 0
Pyramidal <c+a> 205 300 4200 0
Tensile twin 85 0 0 330
Compressive twin 272 0 0 90
表1  298K下用于黏塑性自洽(VPSC)模拟的ZK60镁合金材料硬化参数
图2  ZK60室温轴向拉伸和压缩真应力-真应变曲线
Loading mode σs / MPa σb / MPa
Axial tension 287 369
Axial compression 125 459
表2  ZK60合金室温轴向拉伸/压缩屈服强度和极限强度
图3  挤压态ZK60镁合金初始极图及轴向拉,压过程中不同应变下(0002)和模拟极图的演变
图4  ZK60镁合金在拉伸和压缩变形过程中各种变形机制的相对活动量
图5  ZK60 镁合金拉伸和压缩断裂面附近纵切面显微组织
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