Correlation between intragranular precipitation, DRX, and mechanical properties in multi-directional forging Mg-Zn-Gd-Y alloys

This work investigates the effect of multi-directional forging (MDF) temperature on the dynamic precipitation, dynamic recrystallization (DRX), work hardening and softening behavior of Mg-5Zn-1Gd-1Y (ZGW511) alloy. The addition of rare earth (RE) elements restricts Zn diffusion due to their drag effect and low diffusivity, promoting in-situ intragranular precipitation. The W phase (Mg₃Zn₃RE₂) with lower Gibbs free energy preferentially undergoes dynamic precipitation. And the pinning effect of the intragranular precipitated W phase on the dislocation inhibits the nucleation of DRX. Increasing forging temperature promotes Ostwald ripening, enlarging W phase particles and enhancing their pinning effect, leading to a gradual decrease in DRX volume fraction. Concurrently, the reduced dislocation density and increased grain size weaken work-hardening and softening. While the intragranular W phase hinders the dislocation motion and triggers local dislocation accumulation, its periodic distribution forms sub-micron dislocation channels that facilitate the transfer of dislocation slip, resulting in the increasing $∆{\sigma }_p/{\sigma }_0$ with the increasing number of stress relaxation cycles.