Hot Deformation Behavior and Microstructural Evolution of a High-Strength Mg-Gd-Y-Zr Alloy

Mg-Gd-Y-Zr alloys, with strong age-hardening and thermal stability, are ideal for lightweight load-bearing components, yet forming large complex parts is limited by high sensitivity to hot deformation parameters. This work investigates the hot deformation behavior and microstructure evolution of a Mg-9Gd-4Y-0.5Zr (wt.%) alloy via hot compression at 400 to 510 °C and strain rates of 0.001 to 10 s−1. An Arrhenius constitutive equation with an activation energy Q of 158.63 kJ/mol was established, and a hot processing map was constructed. EBSD characterization revealed the dynamic recrystallization, grain size evolution, and texture transition. The results show that flow stress depends strongly on temperature and strain rate. At strain rates of 0.001~1 s−1, a dynamic balance between work hardening and dynamic softening is achieved, and the post-peak flow stress gradually stabilizes. At a high strain rate of 10 s−1, the flow stress continues to decrease because the competition between softening from dynamic recrystallization and work hardening is disrupted by deformation-induced heating. Low strain rates (≤0.01 s−1) and high temperatures (≥470 °C) promote dynamic recrystallization and significant grain refinement. Two optimal processing windows were determined: 400 to 430 °C at 0.001 to 0.01 s−1, giving fully recrystallized fine equiaxed grains, and 440 to 460 °C at 0.01 to 0.1 s−1 with a power dissipation efficiency η of 0.43 to 0.51, balancing processing efficiency and microstructural uniformity. This work provides systematic theoretical and data support for optimizing hot forming parameters of large Mg-Gd-Y-Zr load-bearing components and offers guidance for applying high-strength magnesium alloys in high-end equipment.