Microstructure and mechanical properties of Mg-Gd-Zn-Zr alloy after hot extrusion

Abstract

The microstructural evolution and mechanical properties of the Mg-6Gd-1Zn-0.5Zr (wt.%) alloy during heat treatment and composite extrusion were studied in this work. The (Mg, Zn)₃Gd phase and a small amount of 14H long-period stacking ordered (LPSO) phase formed in the cast alloy, and more lamellar 14H-LPSO phases formed in the alloy during homogenization treatment. The bimodal grain structure composed of coarse deformed microstructure and fine dynamic recrystallization (DRX) grains formed in the alloy after extrusion. The γ′ phase and β´ phase precipitated after the extrusion process and after the solution and aging treatment, respectively. The kinking of the lamellar 14H-LPSO phase occurred during the extrusion process. DRX grains formed in the alloy during extrusion process through continuous dynamic recrystallization (CDRX), particle stimulated nucleation (PSN), and kinking-assisted DRX. The yield strength, tensile strength and elongation of the extruded alloy were 227 MPa, 320 MPa, and 20.68%, respectively. The strength and elongation of the extruded alloy are enhanced by the strengthening effect from the bimodal structure, kinking of the LPSO phase, and LPSO phase. The tensile properties of the alloy decreased after the solution and aging treatment. The bimodal structure and kinking of the LPSO phase disappeared after the solution and aging treatment.