Solidification structures and mechanical properties of Zn–27Al alloy cast in metal moulds

Rectangular and round cross-section test bars of Zn–Al alloy containing (wt-%) 27·67%Al; 2·30%Cu; 0·13%Mg; 0·04%Fe; <0·0025%Pb, Cd, and Sn; balance Zn were cast in metal moulds. The variables studied were: bar cross-section 3–25 mm thickness and 14·5–28 mm dia., pouring temperature 550–700°C, feeder location at bar shoulders or over full gauge length, and cast iron mould preheating temperature 100 or 200°C. The results show that the above variables can lead to variations of 0·14–1·72% bar porosity, 18–0·5% elongation, 428–305 MN m⁻² tensile strength, and 108–128 Brinell hardness. Metallographic examination leads to the conclusion that these properties are influenced by the volume, distribution, and morphology of shrinkage porosity and of eutectic constituent. The observed variations in the microstructure and their effects on the mechanical properties are related to the cooling and feeding conditions of the bars.

MST/549