Effect of forced-air cooling on the microstructure and age-hardening response of extruded Mg-Gd-Y-Zn-Zr alloy full with LPSO lamella

Abstract The homogenized Mg-8.2Gd-3.8Y-1.0Zn-0.4 Zr (wt.%) alloy full of plate-shaped long period stacking ordered (LPSO) phases was hot extruded in the atmosphere and cooled by the forced-air, then the effect of forced-air cooling on the microstructure and age-hardening response of the alloy was investigated in this work. The results show that in comparison with the extruded sample cooling in the atmosphere, the forced-air cooling restricts dynamic recrystallization (DRX) and brings about finer dynamic recrystallized (DRXed) grain size, stronger basal texture and higher dislocation density. Furthermore, the forced-air cooling promotes the dynamic precipitation in the DRXed regions and facilitates formation of plate-shaped LPSO phases and γ′ phases with smaller interspacing in the unrecrystallized (unDRXed) regions, then slightly restricts the precipitation of β′ phases during aging. After peak-ageing treatment, the extruded sample with forced-air cooling shows superior tensile properties with a tensile yield strength of 439 MPa, an ultimate tensile strength of 493 MPa, and elongation to failure of 18.6%.