Microstructure and mechanical properties of rapidly solidified/powder metallurgy Mg–6Zn and Mg–6Zn–5Ca at room and elevated temperatures

Abstract

Rapid solidification/powder metallurgy (RS/PM) Mg–6Zn and Mg–6Zn–5Ca (wt.%) alloys in form of rods were prepared by hot extrusion with RS powders, produced via atomization of the alloy melt and subsequent splat-quenching between a couple of water-cooled copper rolls. The microstructure and mechanical properties of the alloys at both room and elevated temperatures were investigated. The results showed that with an addition of 5wt.%Ca to the Mg–6Zn alloy, the microstructure of the alloy was refined significantly, in which the grain size ranged from 500nm to 1μm and the number of finely dispersed particles increased substantially. This resulted in an increase in the compressive strength of alloy up to 408MPa at room temperature. Although the strength of both the alloys decreased with an increase in test temperature, the Mg–6Zn–5Ca alloy exhibited a high strength of 202MPa at 200°C, which resulted mainly from the formation of particles of the stable intermetallic phase Ca2Mg6Zn3, which were effective in pinning dislocations and grain boundaries at elevated temperatures. In addition, the formation of deformation twins and their intersections, and the interaction between the twins and the Ca2Mg6Zn3 particles during compressive deformation at 200°C contributed to the strengthening of the alloy. However, the Mg–6Zn alloy exhibited a very low strength of 41MPa at 200°C, which resulted from dynamic recrystallization softening.