Grain refinement mechanism of AZ31 magnesium alloy processed by expansion-continuous shear deformation

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, {1012} 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 <a> slip. Grains refinement and uniform microstructure are improved due to the basal and prismatic <a> 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. © 2021, China Science Publishing & Media Ltd. All right reserved.