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 eutecticand hypoeutectic (Al-Si) alloys has been studied. The alloys used in this research work were (Al- 12.6%Sialloy) and (Al- 7%Si alloy).The two alloys have been melted and poured in two types of molds withdifferent 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 metallographicexamination was performed.It has been found that the values of hardness for the alloys(Al-12.6%Si and Al-7%Si) which poured inmetal mold is greater than the values of hardness for the same alloy when it poured in a heated metalmold 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 asand mold.Furthermore, the higher cooling rates enhance the strength, hardness and impact resistance for thetwo alloys, while the low cooling rates reduces these mechanical properties.The percentage of elongation and the amounts of formed porosity decreased when the cooling ratesincreased