Investigation on microstructure and mechanical properties of hot-rolled AZ31 Mg alloy with various cryogenic treatments

Abstract

AZ31 Mg alloy sheet, prepared by a novel process combining hot rolling and various cryogenic treatments, has been investigated on its microstructure and mechanical properties. The results show that twins and the Al8Mn5 phase were introduced in the sample with rapid cooling and rapid heating and slow heating and slow cooling, which can significantly impede the movement of dislocations, while twins also can effectively coordinate deformation. Compared to the conventional hot rolling sample, the average grain size and texture strength of the cryogenic treatment samples were refined and increased by ∼24% and∼50%, respectively. The dislocation density of the coarse-grained region in the sample with slow heating and slow cooling is low, and the prismatic <a> and pyramid <c+a> slips were activated, which can improve the ductility of the alloy. In comparison to conventional hot rolling, the ultimate tensile strength and elongation of AZ31 Mg alloy after rapid cooling and rapid heating were increased by ∼15% and ∼37%, respectively, while the elongation after slow heating and slow cooling increased by ∼71%. The improvement of the mechanical properties of Mg alloy with cryogenic treatment is attributed to the synergistic effect of the refined grain, twins, residual dislocations, precipitates, texture and non-basal slip.