Effect of Y addition and cooling rate on refinement of eutectic Si in Al–5 wt-%Si alloys

Abstract

A series of Al–5 wt-%Si alloys with or without 200 ppm Y addition have been produced using conventional casting and melt spinning respectively. The effects of Y addition and cooling rates on the refinement of eutectic Si have been investigated using thermal analysis, differential scanning calorimetry and multiscale microstructure characterisation techniques. In the case of conventional casting, the addition of up to 200 ppm Y was found to cause no modification effect. The eutectic Si presented a plate-like structure rather than a fibrous morphology. No significant Si twinning was observed. In the case of melt spinning, a higher cooling rate caused a much finer eutectic Si and Si twinning. The addition of 200 ppm Y promoted heavier multiply Si twinning. After a continuous cooling from 873 to 673 K, an Al2SiY phase was observed beside or within the Si particle. The refinement mechanism was also discussed.