Microstructure and mechanical properties of LPSO phase dominant Mg85.8Y7.1Zn7.1 and Mg85.8Y7.1Ni7.1 alloys

Mg85.8Y7.1Zn7.1 (Mg12Y1Zn1) and Mg85.8Y7.1Ni7.1 (Mg12Y1Ni1) alloys composed primarily of long-period stacking ordered (LPSO) phase were prepared by conventional casting and were further processed by hot extrusion or equal-channel angular pressing (ECAP) to investigate the effect of substitution of Zn with Ni on microstructure and mechanical properties. While a mixture of 18R and 14H structures of the LPSO phase was observed in the cast Mg85.5Y7.1Zn7.1 alloy after homogenisation treatment, the LPSO phase in the Mg85.8Y7.1Ni7.1 alloy was found to consist of 18R only. Beside the LPSO phase, both alloys contained small amounts of alpha-Mg and intermetallic phases, viz. MgZn2Y (W-phase) in the Mg85.8Y7.1Zn7.1 alloy and MgNi2 and MgNi4Y in the Mg85.5Y7.1Ni7.1 alloy. Mechanical testing of the extruded or ECAP processed alloys showed that the substitution of Zn with Ni significantly improved the strength of the Mg85.8Y7.1Zn7.1 alloy, but at the expense of ductility. The mechanical properties of the alloys are discussed in light of the microstructural observations.