(华南理工大学 机械工程学院，金属材料成形及装备教育部工程研究中心，广州 510640)
摘 要: 通过金相组织观察、显微硬度测试、扫描电镜分析和应变速率为5×10−5 /s的室温拉伸力学性能实验，分别探讨多向锻造中ME20M镁合金的显微组织演化机制和力学性能变化规律。结果表明：显微组织演化分为3个不同阶段，分别对应3种不同机制：第一阶段在真应变量ε≤0.60时，为机械式击碎细化机制，晶粒尺寸由45 μm细化到12 μm；第二阶段在真应变量0.60＜ε≤0.80时，为形变诱导动态再结晶细化机制，晶粒进一步细化至2.1 μm；第三阶段在真应变量ε≥1.50时，为热激活晶粒长大机制，部分晶粒长大至65 μm。经多向锻造加工，镁合金室温力学性能显著提高，其伸长率、抗拉强度和显微硬度的最大值分别为26.25%、225.52 MPa、HV 55.1，比初始状态分别提高了245%、6.7%和15.5%。拉伸断口SEM观察发现，第6道次前断口韧窝尺寸明显减小且其数量随应变量的增加而增多，使材料延性改善；第6道次后韧窝尺寸变大，其塑性降低。
关键字: 镁合金；多向锻造；显微组织演化；力学性能；显微硬度
（Engineering Research Center of Metallic Materials Processing and Equipment, Ministry of Education, School of Mechanical Engineering, South China University of Technology, Guangzhou 510640, China）
Abstract:Microstructural evolution and mechanical property of ME20M magnesium alloy processed by multidirectional forging (MF) were analyzed through OM, microhardness, SEM and mechanical tensile test at room temperature with the strain rate of 5×10−5 /s. The experimental results show that the microstructural evolution is divided into three stages according to different evolution mechanisms: the mechanical splitting mechanism with the grain size fined from 45 μm to 12 μm; the deformation- induced dynamic recrystallization mechanism with the average grain size of 2.1 μm and thermal activated grain growth mechanism with maximum grain size reached to 65 μm, when the true strains are ε≤0.60, 0.60＜ε≤0.80 and ε≥1.50, respectively. After MF, mechanical property of ME20M magnesium alloy is greatly improved. The maximum value of elongation, tensile strength and microhardness are 26.25%, 225.52 MPa and HV 55.1, which are 245%, 6.7% and 15.5% more than those of as-received Mg alloy, respectively. The density and size of ductile dimples on tensile fractured surface of the MF magnesium alloy increase with increasing strain before the sixth pass, which demonstrates that the ductility is improved, and then the ductile dimples enlarged result in the decreasing of plasticity.
Key words: magnesium alloy; multidirectional forging; microstructural evolution; mechanical property; microhardness
