(華南理工大學 機械工程學院，金屬材料成形及裝備教育部工程研究中心，廣州 510640)
摘 要: 通過金相組織觀察、顯微硬度測試、掃描電鏡分析和應變速率為5×10−5 /s的室溫拉伸力學性能實驗，分別探討多向鍛造中ME20M鎂合金的顯微組織演化機制和力學性能變化規(guī)律。結果表明：顯微組織演化分為3個不同階段，分別對應3種不同機制：第一階段在真應變量ε≤0.60時，為機械式擊碎細化機制，晶粒尺寸由45 μm細化到12 μm；第二階段在真應變量0.60＜ε≤0.80時，為形變誘導動態(tài)再結晶細化機制，晶粒進一步細化至2.1 μm；第三階段在真應變量ε≥1.50時，為熱激活晶粒長大機制，部分晶粒長大至65 μm。經多向鍛造加工，鎂合金室溫力學性能顯著提高，其伸長率、抗拉強度和顯微硬度的最大值分別為26.25%、225.52 MPa、HV 55.1，比初始狀態(tài)分別提高了245%、6.7%和15.5%。拉伸斷口SEM觀察發(fā)現，第6道次前斷口韌窩尺寸明顯減小且其數量隨應變量的增加而增多，使材料延性改善；第6道次后韌窩尺寸變大，其塑性降低。
關鍵字: 鎂合金；多向鍛造；顯微組織演化；力學性能；顯微硬度
（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
