STUDIES ON THE MICROSTRUCTURE, MECHANICAL AND HIGH TEMPERATURE WEAR BEHAVIOUR OF A356 ALLOY WITH MINOR ADDITIONS OF COPPER AND MAGNESIUM

摘要

In the present study, the effect of individual additions of copper (Cu) and Magnesium (Mg) on the high temperature wear behaviour of A356 alloy have been investigated using a high temperature pin-on-disc wear testing machine. Effect of alloy composition and normal pressures on A356 alloy at 300°C have been studied. The indigenously prepared Al-15%Cu and commercial Al-20%Mg master alloys, cast alloys and worn surfaces were characterized by XRD and SEM/EDX microanalysis. Results indicate that, the minor additions of Cu in the range of 0.1-0.5% and Mg (0.3-0.7%) additions improves the mechanical properties. The results also suggest that, the weight loss of A356 alloy increases with increase in normal pressures in all the cases studied and decreases with maximum addition levels of 0.5%Cu and 0.7%Mg at the tested temperature. This is due to the partial refinement of α-Al dendrites and solid solution strengthening and precipitation hardening. Also, the addition of Mg (0.3-0.7%) results in improvements in strength and hardness at the expense of ductility. This improvement is probably due to the conversion of unmodified acicular silicon (Si) to lamellar and fibrous structure.