EFFECTS OF SULPHUR ADDITION ON MICROSTRUCTURAL MODIFICATION AND MECHANICAL PROPERTIES OF SAND CAST Al-12wt% Si ALLOY

Abstract

The effects of sulphur addition on the microstructure and mechanical properties of sand cast Al-12wt%Si alloy have been investigated in this study. For this purpose, different amounts of sulphur were added to Al-12wt%Si alloy in an induction furnace to produce sand castings for micro-structural and mechanical properties analyses. Tensile and hardness tests were carried out to determine the mechanical properties while optical microscopy was used to investigate the microstructure of the cast samples. The results showed that the addition of sulphur to Al-12wt%Si alloy modified the Al-Si eutectic morphology from needle-like (flake-like) eutectic silicon structure to fine-globule eutectic silicon structure. The optimum modification level of sulphur was found to be 0.02-0.05% of the weight of the alloy. Increase in concentration of sulphur above the optimum level of modification decreased the degree of fineness of the eutectic silicon structure with significant decrease in mechanical properties of the alloy and this is suggested to be a result of the formation of brittle sulphur compound at the grain boundaries of the alloy when the optimum concentration was exceeded.