Effects of Substitution of Gd with Er on the Microstructure and Mechanical Properties of Mg–Gd–Er–Ni Alloys with Long‐Period Stacking Ordered Phases

The microstructure and mechanical properties of Mg 97 Gd 1.5 Er 0.5 Ni 1 , Mg 97 Gd 1 Er 1 Ni 1 , and Mg 97 Gd 0.5 Er 1.5 Ni 1 (at.%) alloys with long‐period stacking ordered (LPSO) phases are investigated. In the as‐cast condition, all alloys consist of an α‐Mg matrix and the 18R LPSO phase, with its volume fraction increasing notably as Er substitutes for Gd. Solution treatment induces a partial transformation of the 18R LPSO phase to the 14H LPSO phase in the Mg 97 Gd 1.5 Er 0.5 Ni 1 alloy, accompanied by the precipitation of nanoscale (Gd,Er)Mg 2 Ni 9 particles. In contrast, the Er‐rich Mg 97 Gd 0.5 Er 1.5 Ni 1 alloy retains the 18R structure, demonstrating the stabilizing role of Er on the 18R LPSO phase. Tensile tests reveal that both the yield strength (YS) and ultimate tensile strength (UTS) of the as‐cast alloys increase with Er content, peaking at 122 ± 4 MPa (YS) and 220 ± 6 MPa (UTS) for the Mg 97 Gd 0.5 Er 1.5 Ni 1 alloy. After solution treatment, the Mg 97 Gd 1 Er 1 Ni 1 and Mg 97 Gd 0.5 Er 1.5 Ni 1 alloys exhibit moderate improvements in both strength and ductility, whereas the Mg 97 Gd 1.5 Er 0.5 Ni 1 alloy shows enhanced strength but reduced ductility due to the precipitation of (Gd,Er)Mg 2 Ni 9 phases.