(1. 湖南科技大学 材料科学与工程学院，湘潭 411201；
2. 湖南科技大学 湖南省新能源汽车产学研海智创新中心，湘潭 411201；
3. 湖南工程学院 湖南省汽车动力与传动系统重点实验室，湘潭 411104)
摘 要: 本文提出了膨胀-连续剪切变形的新方法，利用光学显微镜和电子背散射衍射技术(EBSD)研究了膨胀-连续剪切变形AZ31镁合金的晶粒细化机理。结果表明：AZ31镁合金经变形后晶粒尺寸由150 μm细化至约2.5 μm。在膨胀变形过程中， 拉伸孪晶是主要的变形机制，其孪晶界为动态再结晶提供大量的形核位置，促进了动态再结晶的发生；在开口位置处，镁合金经历了大的挤压比和剪切变形，柱面 滑移被激活，在基面和柱面 滑移共同作用下进一步均匀细化晶粒组织。在整个变形过程中，小角度晶界逐渐转变为大角度晶界，大角度晶界含量由挤压通道处的27.6%增加到板材成形通道处的72.2%，动态再结晶发生程度更加充分。AZ31镁合金的晶粒细化主要是孪晶诱发的动态再结晶和连续动态再结晶共同作用所致。
关键字: AZ31镁合金；膨胀-连续剪切变形；动态再结晶；晶粒细化
（1. School of Materials Science and Engineering, Hunan University of Science and Technology, Xiangtan 411201, China;
2. Hunan Provincial Overseas-wisdom Innovation Center of New Energy Vehicle in Industrial-Academic-Research Cooperation, Hunan University of Science and Technology, Xiangtan 411201, China;
3. Hunan Provincial Key Laboratory of Vehicle Power and Transmission System, Hunan Institute of Engineering, Xiangtan 411104, China）
Abstract:This study proposes a new method of expansion-continuous shear deformation, and the grain refinement mechanism of AZ31 alloy was investigated with an optical microscopy and electron backscatter diffraction. Results show that AZ31 alloy can refine the grains from 150 μm to about 2.5 μm. During the expansion deformation, tensile twinning is the main deformation mechanism, which can offer numerous nucleation sites to trigger dynamic recrystallization. At the opening position, the Mg alloys have undergone large extrusion-ratio and shearing deformation, which can activation of prismatic slip. Grains refinement and uniform microstructure are improved due to the basal and prismatic slip. During the whole process, low-angle grain boundaries are gradually transformed into high-angle grain boundaries. Dynamic recrystallization becomes more sufficient due to the content of high-angle grain boundaries increasing from 27.6% at the position of the extrusion channel to 72.2% at the position of the channel of sheet forming. Therefore, the grain refinement mechanisms of Mg alloys are dynamic recrystallization stimulated by twinning and continuous dynamic recrystallization.
Key words: AZ31 magnesium alloy; expansion-continuous shear deformation; dynamic recrystallization; grain refinement
