Revealing the Influence of Zn Content on the Microstructure and Mechanical Properties of Bimodal Mg-Zn-Gd-Sm Alloy

The development of low-cost and high-performance Mg alloys is an important way to achieve further application of magnesium alloys. In this work, the as-extruded Mg_98.3-xZn_xGd₁Sm_0.7 alloy with excellent mechanical properties is successfully prepared by regulating the bimodal-grained structure. The effect of the Zn content on the microstructure evolution and mechanical properties of the as-extruded Mg_98.3-xZn_xGd₁Sm_0.7 alloy is systematically investigated. The results show that the addition of Zn increases the dynamic recrystallization (DRX) fraction and weakens the basal texture of the as-extruded alloy. The Mg_98.05Zn_0.25Gd₁Sm_0.7 alloy exhibits a typical bimodal-grained structure. A large amount of geometrically necessary dislocations (GNDs) are generated at the interface between the soft zone and the hard zone of the bimodal-grained structure during the plastic deformation process, resulting in back stress strengthening, thereby improving the strength of the alloy. And it achieves exceptional mechanical properties with an ultimate tensile strength (UTS) of 330 MPa, a yield strength (YS) of 248 MPa, and an elongation (EL) of 18.5% at room temperature. This paper provides a new idea for introducing a heterogeneous structure and improving the strength of low-cost Mg alloys.