Enhanced nucleation and refinement of eutectic Si by high number-density nano-particles in Al-10Si-0.5Sb alloys

The mechanism of refinement of eutectic Si with Sb additions in an Al-10 wt.% Si alloy is studied. The increased holding time designates a transition of the eutectic nucleation temperature from a decreased value to an increased one, accompanied by a morphological transformation of eutectic Si from lamellar to a shorter, rod-like shape. By ab initio molecular dynamics simulation, the chemical short-range order of 0.002 demonstrates weak affinity in the Al-Sb pair, which does not favor the existence of AlSb clusters in the melts. Sb-Sb segregation and the Sb-Si repulsive force are revealed, which promote the formation of Al-enriched precursors and the accumulation of Si atoms adjacent to precursors, inducing precursor nucleation. Continuous attachment of precursors and individual Si atoms during Si growth results in the high number-density nano-particles and suppresses the formation of twin grains within eutectic Si. (C) 2017 Elsevier Ltd. All rights reserved.