A numerical study of irregular eutectic in Al-Si alloys under a large undercooling

The eutectic structure has significant effects on the mechanical properties of Al-Si alloys. However, predicting the formation and morphology of the eutectic structure is difficult, especially under a large range of undercooling. In this paper, a comprehensive model taking account of the eutectic point migration and a dynamic concentration nucleation criterion was developed based on a cellular automaton method to predict the irregular eutectic structure of Al-Si alloys, and the evolution mechanism of the Al-Si irregular eutectic under a large range of undercooling of 5–20 K was numerically investigated. This model was then applied to predict the hypoeutectic microstructures of two processes with greatly different cooling rates: a traditional casting process (copper mold casting) and an additive manufacturing process (selective laser melting), in which the cooling and solidification characteristics of AlSi10Mg alloys were calculated by a double-solid-liquid interface enthalpy model. The results indicate that the eutectic Al and Si present a synergistic effect to promote the crystallization rate significantly, the solidification rate of eutectic is much higher than that of primary, and the morphology of eutectic Si changes from coarse lamellar structure to refined particles as the increase of the eutectic undercooling.