The post-deformation softening and hardening mechanisms of a Mg-2Y-1Zn alloy during double-stage hot compression

Multi-pass hot processing methods are commonly used in magnesium (Mg) alloys to overcome the poor workability due to limited slip systems, which generally involve complicated post-deformation softening and hardening behaviors. In this work, to reveal post-deformation softening and hardening mechanisms of a Mg-2Y-1 Zn alloy, double-stage hot compression tests and microstructural observations were conducted. The results showed that the softening fraction of Mg-2Y-1 Zn alloy showed a non-linear dependence on deformation conditions and could be general coupled by Z parameter. Due to the formation and cross-overlapping of twins and kinks, only static recovery (SRV) occurred during holding process at 300 °C/0.001 s^-1 which led to the least static softening: 5.52 % after 10 s of holding. For samples at 400 °C/0.001s^-1, the enhanced post-deformation softening, which is 11.93 % after 10 s of holding, was attributed to static recrystallization (SRX) followed continuous dynamic recrystallization (CDRX) happened during first deformation stage as well as SRV influenced by the LPSO phases. Under deformation condition of 400 °C/0.1 s^-1, the coupled meta-dynamic recrystallization (MDRX) and SRX resulted in serious stress relaxation, which is 42.83 % after 10 s of holding, and caused hardening phenomenon at reloading stage. The 18R-LPSO and 14H-LPSO phases synchronously worked on deformation behaviors and limited the growth of recrystallized grains. Further, a simplified static softening kinetics model was established based on Johnson-Mehl-Avrami-Kolmogorov equation and employed to rationalize experimental data.