Microstructure and Hardness Evolution in Magnesium Processed by HPT

High pressure torsion provides an opportunity to process materials with low formability such as magnesium at room temperature. The present work shows the microstructure evolution in commercially pure magnesium processed using a pressure of 6.0 GPa up to 10 turns of rotation. The microstructure evolution is evaluated using electron microscopy and the hardness is determined using dynamic hardness testing. The results show that the grain refinement mechanism in this material differs from materials with b.c.c. and f.c.c. structures. The mechanism of grain refinement observed at high temperatures also applies at room temperature. The hardness distribution is heterogeneous along the longitudinal section of the discs and is not affected by the amount of deformation imposed to the material.

高压扭转（High Pressure Torsion）技术可为室温条件下加工镁等低成形性材料提供可行途径。本研究针对经6.0吉帕（Gigapascal, GPa）压力、至多10转扭转加工的工业纯镁，分析其微观组织演化过程。采用电子显微镜（Electron Microscopy）对微观组织演化进行表征，并通过动态硬度测试测定材料硬度。研究结果表明，该材料的晶粒细化机制与体心立方（Body-Centered Cubic, b.c.c.）及面心立方（Face-Centered Cubic, f.c.c.）结构材料存在显著差异。此前在高温工况下观测到的晶粒细化机制，同样适用于室温加工场景。试样圆盘纵截面上的硬度分布呈非均匀特性，且不受材料所受变形量的影响。