Bimodal Phenomenon of the Stress–Strain Curve During Hot Compression of LA43M Mg–Li Alloy

In this study, the samples of LA43M Mg–Li alloy were compressed to the true strains of 0.12, 0.16, 0.36 and 0.60 under 300 °C and the strain rate of 0.1 s−1. Under this condition, the stress–strain curves present a special bimodal phenomenon at the early deformation stage, which is caused by twinning and dynamic recrystallization. In the process of hot compression, extension twins generated first. Twinning accommodated strain and the glide of twinning dislocations dissipated local strain energy, resulting in the first local stress drop. Then extension twins coarsened and devoured all the matrix, leading to the change of grain orientation. Subsequently, dislocations accumulated at the grain boundaries and resulted in the increase in stress. With further strain, dynamic recrystallization occurred, discontinuous dynamic recrystallization is the main dynamic recrystallization mechanism. The generation of dynamic recrystallization resulted in the strain softening and leaded to the second local stress drop. Twinning retards the occurrence dynamic recrystallization and has a crucial influence on the microstructure development during the hot compression of LA43M.