Microstructure and Mechanical Behaviour of Mg-4Zn-2Sr Alloy with Varying Zirconium Addition

Grain refinement studies were attempted on the Mg-4Zn-2Sr alloy by varying the Zr content (0.5, 1.0, 1.5, 2.0 wt%). Metallurgical and mechanical characterisations were done on the casted samples, and the findings were analysed. In the Mg-4Zn-2Sr alloy, alpha-Mg and a new ternary compound Mg11Zn2Zr were formed in the triple point junctions of the grain boundary. With the addition of Zr, drastic grain refinement was observed from 110 to 25 mu m. The optimum grain refinement was obtained with 1.5%Zr addition; beyond that, it decreased. Tiny alpha-Zr agglomerates between the alpha-Mg and ternary phases as a cluster pattern when Zr addition increased. The maximum hardness of 72 Hv was recorded for Mg-4Zn-2Sr-2Zr alloy due to the hard particle strengthening and grain refinement. Due to the high grain refinement, the maximum tensile properties were observed for the Mg-4Zn-2Sr-1.5Zr alloy.