Eutectic growth mode in strontium, antimony and phosphorus modified hypoeutectic Al-Si foundry alloys

The effect of strontium (Sr), antimony (Sb) and phosphorus (P) on nucleatio n and growth mode of the eutectic in hypoeutectic Al-10 mass%Si alloys has been investigated by electron back-scattering diffraction (EBSD) mapping. S pecimens were prepared from a hypoeutectic Al-10 mass%Si base alloy, adding different levels of strontium, antimony and phosphorus for modification of eutectic silicon. By comparing the orientation of the aluminium in the eut ectic to that of the surrounding primary aluminium dendrites, the solidific ation mode of the eutectic could be determined. The results of these studie s show that the eutectic nucleation mode, and subsequent growth mode, is st rongly dependent on additive elements. The EBSD mapping results indicate th at the eutectic grew from the primary phase in unmodified and phosphorus-co ntaining alloys. When the eutectic was modified by strontium or antimony, e utectic grains nucleated and grew separately from the primary dendrites.