A study on the interaction between a Sr modifier and an Al-5Ti-1B grain refiner in an Al-7Si-0.35Mg casting alloy

Abstract

A Sr modifier and an Al-Ti-B grain refiner were simultaneously added to an Al-7Si-0.35Mg cast alloy and the interaction between Sr and Al-5Ti-1B was investigated. The combined additions of 100 ppm Sr and 500 ppm Ti produced both eutectic Si modification and α-Al grain refinement while increasing the nucleation frequency of Al-Si eutectic grains compared to an alloy with the addition of Sr alone. TEM analysis revealed that Al2Si2Sr phases existed with either TiB2 or AlP and TiB2 coupling particles. This suggests that pre-existing TiB2 particles in the melt form prolific AlP, the most potent nuclei for Si, and thereby promote the nucleation of the eutectic Al-Si grains during solidification despite the deactivation of AlP consumed for the preceding formation of Al2Si2Sr.