EFFECT OF COOLING RATE ON MECHANICAL PROPERTIES OF EUTECTIC AND HYPOEUTECTIC Al-Si ALLOYS

Abstract

In this research the effect of cooling rate and mold type on mechanical properties of the eutectic and hypoeutectic (Al-Si) alloys has been studied. The alloys used in this research work were (Al- 12.6%Si alloy) and (Al- 7%Si alloy).The two alloys have been melted and poured in two types of molds with different cooling rates. One of them was a sand mold and the other was metal mold. Mechanical tests (hardness, tensile test and impact test) were carried out on the specimens. Also the metallographic examination was performed. It has been found that the values of hardness for the alloys(Al-12.6%Si and Al-7%Si) which poured in metal mold is greater than the values of hardness for the same alloy when it poured in a heated metal mold at different temperatures or in sand mold. The strength and impact resistance for the alloys (Al- 12.6%Si and Al-7%Si) are greater when these were poured in a metal molds than that when it poured in a sand mold. Furthermore, the higher cooling rates enhance the strength, hardness and impact resistance for the two alloys, while the low cooling rates reduces these mechanical properties. The percentage of elongation and the amounts of formed porosity decreased when the cooling rates increased

Keywords

• cooling rate, eutectic, hypoeutectic alloys, mechanical properties, molds