镁合金的孪生与退孪生变形机制及弹粘塑性自洽模型研究

Magnesium alloy has a wide application in automobile, electronic communication and aerospace industry, due to its excellent physical and mechanical properties, such as light weight and high specific strength. Twinning and detwinning are the significant plastic deformation mechanisms for Magnesium alloy at room temperature, which could improve plastic deformability through changing crystal orientation and forming crystal boundary. This project will study twinning and detwinning mechanisms of Mg alloy and elastic visco-plastic self-consistent (EVPSC) model systematically by combining reverse loading experiments and microstructure tests of pre-deformed Mg alloy and polycrystal plastic theory. The main contents are: the change laws of macro mechanical behavior and microscopic structure (texture, twin volume fraction) of Mg alloy during reverse loading; the relations between the change of twin volume fraction during detwinning and the amount of pre-deformation, amount of deformation during reverse loading. The EVPSC model with describing the detwinning behavior quantitatively will be established and a new numerical calculation program will also be developed. The mechanical behavior of Mg alloy under low-cycle fatigue will be numerically studied by new developed EVPSC model to study the role of twinning and detwinning in plastic deformation of Mg alloy. The research achievements will provide scientific basis for developing Mg alloy with high plasticity and strength.

镁合金具有质轻、比强度高等优越的物理力学特性，已成为汽车、电子通信、航空航天等领域的重要材料。孪生和退孪生是镁合金室温下的重要塑性变形机制，通过改变晶粒取向、发挥晶界作用等影响镁合金的塑形变形能力。本项研究以预变形镁合金反向加载实验及微观组织结构测试为基础，借助于多晶塑形理论等，对镁合金的孪生与退孪生变形机制及弹粘塑性自洽模型进行系统研究。主要内容：预变形镁合金反向加载过程中退孪生行为引起的宏观力学响应及微观组织（织构、孪晶体积分数等）变化规律，退孪生过程中孪晶体积分数变化量与预变形量、试样反向加载中宏观变形量的关系；反向加载中退孪生变形规律的定量描述，含孪生、退孪生变形的弹粘塑性自洽模型建立及其数值计算程序开发；镁合金低周疲劳行为的数值模拟研究，低周疲劳条件下孪生与退孪生变形的交替发生对镁合金塑性变形的影响规律。研究成果可为研发高性能镁合金材料及其应用提供科学依据。

镁合金具有优越的物理力学特性，但其较差的塑性变形能力阻碍了更广泛的应用。孪生和退孪生是镁合金室温下的重要塑性变形机制，通过改变晶粒取向、发挥晶界作用等影响镁合金的塑性变形能力。以镁合金AZ31为研究对象，借助于AG-X试验机、MTS材料试验系统、扫描电镜、EBSD等实验手段，应用多晶塑性理论等，从宏观和微观尺度上，对多种加载条件下（单调加载、反向加载、循环加载）镁合金的孪生和退孪生变形行为进行了系统的研究。主要工作和研究成果如下：.①开展了镁合金沿不同方向的单轴拉伸和压缩试验，并建立了镁合金大应变单调加载的数值计算模型，预测了镁合金沿不同方向单调加载的应力应变曲线、微观织构演化和孪晶体积分数演化规律。计算得到了各孪生变体按SF值排序后的孪晶体积分数，分析了不同加载方式下各孪生变体的开启规律。.②利用疲劳试验机，开展了镁合金沿RD方向的大应变压缩-卸载-拉伸试验，得到了不同预压缩量下的应力应变曲线；并通过EBSD，测试了变形过程中织构演化和孪晶体积分数。结果表明：镁合金反向加载中出现了明显的孪晶-退孪晶现象；且随着预压缩量的增加，反向拉伸阶段的屈服极限增大；通过分析孪晶体积分数变化规律，得到了退孪生过程中孪晶体积分数变化量与预变形量间的关系。.③依据预变形量对退孪生行为的影响规律，构建了退孪生变形过程中孪晶体积分数变化量控制方程；基于多晶塑性理论，建立了可定量描述退孪生行为的弹粘塑性自洽模型，并开发了其数值计算程序；将改进的模型应用于镁合金反向加载的数值计算，模型与试验结果有很好的印证性。.④基于弹粘塑性自洽模型，建立了镁合金循环加载的数值计算模型，预测了镁合金循环加载时不同圈数的应力应变曲线、各滑移系/孪生系的开启率和孪晶体积分数演化规律，分析了孪生和退孪生行为在镁合金循环加载变形中的作用。.研究成果在一定程度上丰富了镁合金塑性变形机制的理论，也为研发高性能镁合金材料提供重要依据。