Influence of the interaction between Si and Sc on the microstructure and tensile properties of as casted Al-Si-Sc alloys

Scandium (Sc) and silicon (Si) are effective for modifying Al based alloys, while their combined effect may be limited by some Si-Sc interaction, which was rarely reported. In this work, Al alloys with varying Si and Sc additions were prepared for microstructure characterization and tensile testing. The results show that Sc refines the alpha-Al grain via a heterogeneous nucleation induced by in-situ formed primary Al3Sc. A network AlSi2Sc2 phase was formed via a eutectic reaction and a bulk AlSi2Sc2 was generated from a peritectic reaction. Both AlSi2Sc2 competitively consumed the Sc solute in the same alloy, weakening the refining effectiveness of Al3Sc. The Sc also refined the eutectic Si to more ordered fiber/plate-like structure, and a proper ratio of Si to Sc could avoid the AlSi2Sc2 formation. When increasing Sc from 0.3 to 1.0 wt% in Al alloys containing 6 wt% Si, the ultimate tensile strength (UTS) and yield strength (YS) increased, but the EL decreased due to the presence of AlSi2Sc2 phase. The UTS and YS can increase along with a 41% raise in EL by a strategy combining higher Sc (> 0.6 wt%) and a lower Si (< 4 wt%) with Al3Sc in a dominant role in soli-dification reactions without AlSi2Sc2 formation. The mechanisms of microstructure modification with Si-Sc interaction are also discussed.(c) 2022 Elsevier B.V. All rights reserved.