Achieving good comprehensive mechanical properties Mg–7Y–2Zn–1Mn alloy via regulating heat treatment prior to hot extrusion

The influence of heat treatment prior to hot extrusion on microstructure evolution and mechanical properties are elaborated for Mg–7Y–2Zn–1Mn (wt. %) alloy containing long-period stacking ordered (LPSO) phase. Solution and aging treatment are shown to increase obviously tensile strength of the alloy, while keeping relatively high ductility. Good comprehensive mechanical properties with the ultimate tensile strength of 396 MPa, yield strength of 314 MPa, and elongation of 9.7 % are achieved by the aging treatment. It is closely correlated with the formation bimodal structure and the enhanced precipitation of γ′ and lamellar 14H-LPSO phase. While the granular 18R-LPSO phase and the kink deformation of lamellar 14H-LPSO phase are found to promote the dynamic recrystallization process during hot extrusion, the formation of large amount of γ′ and lamellar 14H-LPSO phase tends to uniform the stress and hinder the dynamic recrystallization process. Balance of the two factors contributes to the formation of bimodal structure and the improved mechanical properties. The present advances enhance the understanding required for the optimal design of thermo-mechanical process of LPSO-containing Mg alloys.