Deformation behavior and microstructure evolution of AZ31 Mg alloy during gradient thermal compression

To achieve a broad range of gradient strain from the rim to the center of a single specimen, the size of the high-throughput double-cone (DC) specimen was optimized using finite-element-model (FEM) simulation. As the deformation increased, the flow stress of the DC specimen quickly reached the maximum value, then gradually declined, and finally tended to be stable. The gradient microstructures corresponding to the gradient strains from the rim to the center of the DC specimen compressed at a certain temperature and strain rate were obtained by only one compression testing. As the equivalent strain increased, the degree of dynamic recrystallization (DRX) gradually rose from the rim to the center of the compressed DC specimen. However, when the equivalent strain and strain rate remained constant, the degree of DRX increased steadily with rising deformation temperature in the compressed DC specimens. Furthermore, during compression of the DC specimens at temperatures of 250 °C and 300 °C, the primary DRX mechanism was continuous dynamic recrystallization (CDRX). At temperatures of 350 °C and 400 °C, the DRX mechanism shifted, as both CDRX and discontinuous dynamic recrystallization (DDRX) were observed. This suggested that the DRX mechanism underwent a change as the deformation temperature increased.