Microstructure and high mechanical properties of Mg–9RY–4Zn (RY: Y-rich misch metal) alloy with long period stacking ordered phase

The microstructure and mechanical properties of Mg–9RY–4Zn (wt.%) alloy were investigated. In the as-extruded condition, the typical microstructure is plenty of fine DRX grains and 14H long period stacking ordered (LPSO) structure with two forms: the secondary phase with bending long strip morphology distributed along the extruded direction and the fine lamellar phase in the interior of DRX gains. The latter form of LPSO structure suggests that the effect of external force is one of the mechanisms of forming LPSO structure. The as-extruded Mg–9RY–4Zn alloy exhibits high strength and ductility whether at room or elevated temperatures. The yield strength, ultimate tensile strength and elongation are 265 MPa, 353 MPa and 9.7% at room temperature, 204 MPa, 247 MPa and 29.2% at 300 °C, respectively. The fine DRX gains containing LPSO lamellae and the bending LPSO strips along the direction of extrusion with good characteristics such as high microhardness, plasticity and thermal stability as well as good combination with the Mg matrix are mainly responsible for the excellent mechanical properties of this alloy.