Effects of Rolling-Cryogenic Process on Microstructure and Mechanical Properties of AZ31 Magnesium Alloy Sheets

In order to improve the microstructure of AZ31 magnesium alloy sheets and enhance their comprehensive mechanical properties, the effects of cryogenic treatment on the microstructure and mechanical properties after hot-rolled AZ31 magnesium alloy were investigated in this paper by combining different rolling reduction with cryogenic treatment. The results show that fine dynamic recrystallization grains appear at the original grain boundaries, and the grain becomes fine and uniform after rolling and deformation. After cryogenic treatment of the hot-rolled sheets, the grains are further significantly refined, the size tends to be homogeneous, the second phase is precipitated along the grain boundaries, and a small amount of twins are produced. In addition, after 20-min cryogenic treatment, the plasticity of the rolled sheets with 30% reduction was greatly improved, and the elongation at break was up to 14.2%, which was 55% higher than that of the original sheet; its hardness and tensile strength were increased from 64.4 HV and 230 MPa of the original sheet to 76.6 HV and 286 MPa, respectively, which shows that the cryogenic treatment of the hot-rolled sheets could effectively improve mechanical properties. This study provides some theoretical guidance and technical support for the processing and manufacturing of high-performance AZ31 magnesium alloy sheets, which has important academic significance and engineering value.