Effect of Substituting Y with Gd on LPSO Phase Dispersion and Mechanical Properties of Mg-2Ni-2Y Alloy

The aim of this study was to substitute Y with Gd for Mg–2Ni–2Y alloy and investigate the effect on the alloy’s microstructures and mechanical properties. To achieve this purpose, the following three test alloys were investigated: Mg–2Ni–2Y, Mg–2Ni–1Y–1Gd, and Mg–2Ni–2Gd (at%). These alloys mainly consisted of α-Mg, Mg₂Ni, and long-period stacking ordered (LPSO) phases. The Y-to-Gd substitution and the solution treatment minimally altered the phase composition. However, the substitution decreased a volume fraction of the LPSO phase by more than 10%, regardless of the solution treatment. This led to a reduction of mechanical strengths up to 124 MPa. The ability of Gd to form the LPSO phase was weaker than that of Y. However, Gd promoted the dissolution of the LPSO phase in α-Mg matrix during solution treatment. The mechanical properties of the alloy can be explained in terms of the dispersion of the LPSO phase. Increasing the volume fraction of LPSO in the cast alloy resulted in an increase in uniformity of the phase dispersion after subsequent extrusion (0.056 to 0.100 in the degree of dispersion), thereby enhancing the strength of the alloy.