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 still need to be further studied.In this paper,Al alloys with varying Si and Sc additions were prepared for microstructure characterization and tensile testing.The results showed that Sc refines the α-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%Si,the ultimate tensile strength(UTS)and yield strength(YS)increased,but the EL decreased due to the presence of AlSi2Sc2 phase.When the Sc content was 1%and the Si content reduced from 6%to 3%,the tensile strength,yield strength and elongation increase by 2%,12%and 21%,with Al3Sc in a dominant role in solidification reactions without AlSi2Sc2 formation.The mechanisms of microstructure modification with Si-Sc interaction were also discussed.
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