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

Mg 85.8 Y 7.1 Zn 7.1 (Mg 12 Y 1 Zn 1 ) and Mg 85.8 Y 7.1 Ni 7.1 (Mg 12 Y 1 Ni 1 ) 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 Mg 85.8 Y 7.1 Zn 7.1 alloy after homogenisation treatment, the LPSO phase in the Mg 85.8 Y 7.1 Ni 7.1 alloy was found to consist of 18R only. Beside the LPSO phase, both alloys contained small amounts of α-Mg and intermetallic phases, viz. MgZn 2 Y (W-phase) in the Mg 85.8 Y 7.1 Zn 7.1 alloy and MgNi 2 and MgNi 4 Y in the Mg 85.8 Y 7.1 Ni 7.1 alloy. Mechanical testing of the extruded or ECAP processed alloys showed that the substitution of Zn with Ni significantly improved the strength of the Mg 85.8 Y 7.1 Zn 7.1 alloy, but at the expense of ductility. The mechanical properties of the alloys are discussed in light of the microstructural observations.