Influence of Ni and Bi microalloying on microstructure and mechanical properties of as-cast low RE LPSO-containing Mg-Zn-Y-Mn alloy

In this work, the high performance as-cast low RE (rare earths) Mg96.5Zn1Y1.5Mn1 alloys with LPSO (long-periodic stacking ordered) phase were fabricated by Ni and Bi microalloying, and the influences of Ni and Bi additions on microstructural evolution and mechanical properties in as-cast Mg96.5Zn1Y1.5Mn1 alloy were investigated. Results show that the Ni and Bi co-alloying can greatly refine the microstructure and facilitate the precipitation of 18R-LPSO phase. Meanwhile, in the Mg96.5Zn1Y1.5Mn1Ni0.5Bi0.1 alloy, the nucleation and growth ability of 18R-LPSO phase were higher than those of W phase, and the growth pattern of 18R-LPSO and W phase was optimized from coupled to divorced growth. Besides, the Mg96.5Zn1Y1.5Mn1Ni0.5Bi0.1 alloy exhibited superior mechanical properties with yield strength (YS), ultimate tensile strength (UTS) and elongation (EL) of 167 +/- 1 MPa, 239 +/- 1.6 MPa and 12.0 +/- 45%. Grain refinement, continuous 18R-LPSO phase with optimized growth pattern and the LPSO fibers precipitated in W phase were responsible for the outstanding mechanical properties.