Partial Substitution of Gd with Y on the Lattice Parameter, Microstructure, and Mechanical Properties of the As-Cast Mg-4Gd-2Zn Alloy

In this research, a rare earth element yttrium in ternary Mg alloys is selected to substitute gadolinium to enable lightweight and enhanced mechanical properties. The results indicate that when the alloy does not contain Y, alpha-Mg, and W-phase are major phases. The volume fraction of the W-phase decreases gradually by substituting Gd with Y, while the long-period stacking order (LPSO) phase increases gradually. Meanwhile, Rietveld refinement results show that the lattice parameters and cell volume of alpha-Mg increase, and the axial ratio (c/a) of alpha-Mg decreases. Preliminary tensile tests in air show that the alloy containing 2 wt% Y has the best strength, with yield strength of 103.4 MPa and ultimate tensile strength of 197.8 MPa, while the alloy containing 4 wt% Y has the highest ductility with an elongation of 11.2%. The synergistic strengthening of the W-phase and 18R-LPSO phase, the high fraction of the 18R-LPSO phase, and its kink bands formed during deformation make the alloy contain 2 wt% Y has a higher elongation. However, if the alloy only contains the W-phase, its properties will be reduced.