Factors influencing the modification and refinement of hypereutectic Al-Si alloys for production of automotive pistons

The effects of refinement and modification of commercial hypereutectic piston alloy (17-19% Si) have been investigated using the thermal analysis technique. Addition of 0.1 %P results in achieving an optimum refined microstructure. The results show that variations in silicon nucleation and liquidus temperatures and freezing range are the best parameters to indicate Si-refinement. With adding of Sr to the P refined alloy, primary silicon particles become larger with less uniform distribution. Furthermore Sr-addition changes the morphology of blocky primary silicon in to dendrites. The results show that with addition of Sr, nucleation sites for silicon particles decreased.