Effect of Aging Treatment on the Precipitation Behavior and Mechanical Properties of Mg-9Gd-3Y-1.5Zn-0.5Zr Alloy

Aging heat treatments of an extruded Mg-9Gd-3Y-1.5Zn-0.5Zr (wt.%) alloy at 200, 225, and 250 A degrees C for various times were studied. The results show that dynamic recrystallization (DRX) occurred during the extrusion process and the alloy exhibited a significant aging hardening response at temperatures ranging from 200 to 225 A degrees C. The precipitation sequence of the alloy at 225 A degrees C was supersaturated solid solution (SSSS) -> beta aEuro(3) (D0(19), Mg3RE) -> beta' (bco, Mg15RE3), where the beta' phase was the primary precipitated phase. A large amount of discontinuous lamellar-shaped 14H-structure long period stacking ordered (LPSO) phase was also observed in the alpha-Mg matrix before and after aging treatments. Owing to the combined strengthening effect of fine DRXed grains, beta' nanoparticles, and widespread LPSO phases, the ultimate tensile strength and tensile yield strength of the peak-aged extruded alloy reached 409 and 303 MPa, respectively. The elongation in this circumstance was similar to 7.1%, which was slightly lower than that of the alloy before aging treatment.