Effect of La/Zn on Microstructural Evolution and Mechanical Properties of Extruded Mg-9Gd-3Y Alloy

This study investigated the impact of La and Zn additions on the microstructure and mechanical properties (at room and high temperatures) of extruded Mg-9Gd-3Y (GW93) alloy. The incorporation of La and Zn induced the precipitation of granular second phases and LPSO phases, increasing the second-phase area fraction in the Mg-9Gd-3Y-0.6La-1Zn (3GW93) alloy to 14.6%. Within the 3GW93 alloy, the Mg12La phase exhibited the following crystallographic orientation relationship with the α-Mg matrix: (020)Mg12La//(011¯0)α-Mg and [101¯]Mg12La//[2¯110]α-Mg. The 3GW93 alloy containing both La and Zn demonstrated the highest strength under both room- and high-temperature conditions. At room temperature, its yield strength (YS) and ultimate tensile strength (UTS) were 284 MPa and 354 MPa, respectively. This represents an increase of 83 MPa in YS and 70 MPa in UTS compared to the GW93 alloy (YS: 201 MPa, UTS: 284 MPa). Similarly, at 300 °C, the 3GW93 alloy (YS: 249 MPa, UTS: 285 MPa) exceeded the GW93 alloy (YS: 182 MPa, UTS: 244 MPa) by 67 MPa in YS and 41 MPa in UTS. The enhanced mechanical properties of the 3GW93 alloy are attributed to synergistic grain refinement and dispersion strengthening effects originating from the LPSO, Mg5RE, and Mg12La phases.