Investigation on Hardness of Gravity Die Cast Secondary Al-10Si Piston Alloy with Trace Addition of Sr, Fe and Mn

Abstract

This paper investigates the effect of minor elements on Brinell hardness properties of Al-10Si alloy. This investigation was carried out with the aim of improving the properties of recycled cast Al-Si alloys so as to enhance their performance. The research therefore came up with the most suitable level of element composition that gives the recycled Al-Si alloys enhanced mechanical properties. The results obtained are deemed beneficial to the local foundries that utilize scrap aluminium alloys to cast their products both for commercial and domestic purposes. Al-Si alloys were produced using gravity die casting process upon which strontium, iron and manganese were added in varying proportions. T6 heat treatment procedures were also carried out on the obtained casting in order to determine the effects of heat treatment on Al-Si alloys. Addition of Sr at weight levels of 0.025%, 0.048% and 0.06% increased the Brinell hardness by 4.64%, 11.42% and 14.57% respectively. The results on addition of Fe at 0.50% and 0.78% weight levels showed improved alloy hardness by 3.48% and 2.15% respectively. Addition of Fe combined with Mn at levels of 0.50% Fe and 0.25% Mn resulted in hardness increase of 8.61% while a combination at 0.78% Fe and 0.39% Mn levels resulted in increasing the material hardness by 6.46%. Upon heat treating the base alloy material, its hardness value improved compared to its non-heat treated value. T6 heat treated alloys with 0.025%, 0.048% and 0.06% Sr levels showed hardness increment by 7.83%, 14.94% and 25.30% respectively. In addition, the heat treated alloys with Fe levels at 0.50% and 0.78% resulted in increased hardness by 5.42% and 4.46% respectively. On the other hand, when the Fe levels were neutralized with Mn at ratio of 2:1, the heat treated alloys bearing 0.50% and 0.78% Fe resulted in hardness increase by 12.05% and 10% respectively.