Microstructure and Mechanical Properties of Hot-Rolled AZ31 Mg Alloy Subjected to Cryogenic Treatment After Air Cooling

In this study, the effect of cryogenic treatment after air cooling on the microstructure and mechanical properties of hot-rolled AZ31 Mg alloys was studied using electron backscatter diffraction and transmission electron microscope. After hot rolling, the samples were carried out air cooling, cryogenic treatment after air cooling for 0 s, 10 s, and 15 s, and denoted by AC, CTAC-0, CTAC-10, CTAC-15, respectively. The results show that after cryogenic treatment, twins and the Al 8 Mn 5 phase are introduced in the ​CTAC-0 and CTAC-15 samples, which can significantly hinder the movement of dislocations, while twins also can effectively coordinate deformation. In comparison to the AC sample, the average grain size of the CTAC-0 sample was refined from ~4.2 μm to ~3.2 μm, and the texture strength increased from 13.08 mrd to 19.56 mrd. The average KAM value is lower in AC sample than in CTAC-0 and CTAC-15 samples (0.76 vs. 1.24 and 1.14). The dislocation density of the coarse-grained region in the CTAC-15 sample is low, and the prismatic and pyramid