Effect of substitution of Zn with Ni on microstructure evolution and mechanical properties of LPSO dominant Mg-Y-Zn alloys

The microstructures and mechanical properties of Mg96Y2Zn2 (MYZ), Mg96Y2Zn1Ni1 (MYZN), and Mg96Y2Ni2 (MYN) (at.%) alloys have been systematically examined in this study. The as-cast alloys contain alpha-Mg matrix, long-period stacking order (LPSO) phase and compounds. By substituting Zn with Ni, the volume fractions of the LPSO phase and compounds increase gradually, leading to higher yield strength and poorer ductility of the as-cast alloys. Moreover, the morphology of the LPSO phase transform from block to lamella gradually. After homogenization at 500 degrees C for 12 h, the fraction of the LPSO phase increase and compounds decrease, moreover, the morphologies of the LPSO phase remain unchanged. Tensile tests indicate that the yield strengths of the extruded MYZ, MYZN, and MYN alloys are 325, 340, and 385 MPa, respectively; the increase can be explained by the higher fraction of the LPSO phase and different stress-withstanding capacity of the LPSO phase with different morphologies. In addition, the enhancement of strength is accompanied by slight drop in ductility.