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.S. Nafisi, J. Hedjazi, S.M.A. Boutorabi and R. Ghomashchihttp://www.tms.org/meetings/annual-04/annmtg04home.htm