Effect of Y addition on the microstructure and tensile properties of the Mg-12Gd-0.5Zr alloy

The present study examines the influence of Y addition on the microstructural evolution and tensile performance of Mg-12Gd-0.5Zr alloy. The findings reveal that secondary-phases, including fishbone-shaped Mg₅Gd and Mg₅(Gd, Y), are present in both Y-free alloys and those containing 1 wt.% Y, whereas the Mg₂₄(Gd, Y)₅ phase emerges in alloys with higher Y concentrations. Y addition stimulates secondary-phase precipitation and modifies phase constituents due to the enhanced solute concentration and the strong interaction between Gd and Y. Moreover, the presence of Y facilitates grain refinement through constitutional undercooling induced by Y segregation. The alloy containing 1 wt.% Y achieves the most favourable balance of strength and ductility, with an ultimate tensile strength (UTS), yield strength (YS), and elongation of 248.8, 169 MPa, and 3.75%, respectively. However, further increasing Y content to 3 and 5 wt.% precipitates a sharp decline in both strength and ductility, reaching 197.2 MPa, 134 MPa, and 1.72% for the 5 wt.% Y alloy, primarily due to the formation of the brittle Mg₂₄(Gd, Y)₅ phase.