Effects of Sr and pressure on microstructure, mechanical and wear properties of near eutectic Al-Si piston alloys

Near eutectic Al-Si alloys exhibit smaller coefficients of thermal expansion than those of hypoeutectic and hypereutectic alloys and are thus used preferentially to fabricate automotive pistons. The mechanical properties of near eutectic Al-Si alloys depend on the alloying elements used and the micro structural changes induced by the rate of cooling and the heat treatment to which they are subjected. In this study, Sr is added as a modifier in an Al-Si-Cu-Ni-Mg alloy and subjected the alloy to a pressure and a heat treatment in order to carry out a systematic inquiry to discover and examine the effects of Sr on and wear characteristics of the alloy. The addition of Sr, the application of a pressure, and the heat treatment produced a finer microstructure and resulted better properties. The fracture and wear mechanisms of alloy specimens subjected to tensile and wear tests were investigated using scanning electron microscopy.