Studies on the effect of phosphorus addition on microstructure mechanical and elevated temperature sliding wear behaviour of some commercially available hypereutectic al si alloys

Abstract

Aluminum alloys are the most versatile of all common foundry alloys. The use of aluminum silicon (Al-Si) alloys are widespread in different fields of application, including the military, automobile, aerospace, marine and general engineering industries because of a number of distinct benefits. Such benefits include low specific gravity, excellent castability, fluidity, high resistance to wear, reduced thermal expansion because of the presence of silicon and adequate physical and mechanical properties at elevated temperatures. It is clear that there is growing interest in hypereutectic Al-Si alloys as a candidate material instead of the conventional hypoeutectic Al-Si alloys. This is because, the engine blocks cast from hypoeutectic Al-Si alloys such as Al-6%Si, Al-7%Si or Al-8.5%Si, must use cast iron cylinder liners due to poor wear and scuffing resistance. The use of iron based liners in aluminum engine blocks adds extra steps to the manufacturing cycle, which increases the cost of production, reduces weight savings and complicates recycling of the blocks. newlineIn hypereutectic Al-Si alloys, the primary silicon can be presented in several different forms like star shape, polyhedral shape and dendritic shape. Large unevenly distributed primary Si particles causes greater tool wear than smaller ones that are more uniformly distributed. Thus, even distribution of the fine primary silicon is an essential feature of cast hypereutectic Al-Si alloys. A fine primary silicon particles and shorter eutectic silicon particles generally achieved by chemical treatment with minor amount of phosphorus (P) to the melt. It has been noticed that there are two modification mechanisms, one is heterogeneous nucleation; refining of primary silicon particles by Al-P compound and the other is phosphorus atoms modify the morphologies of silicon particles. The modification of hypereutectic Al-Si alloys mainly depends on heterogeneous nucleation mechanism stimulated by Al-P particles.