Achievement in grain-refining hypoeutectic Al-Si alloys with Nb

It is a practically significant issue to overcome the Si poisoning for the grain refinement of commercial Al-Si casting alloys. By understanding the anti Si-poisoning mechanism of Nb, a solution to greatly reduce the grain size of alpha-Al from over 1000 mu m to <100 mu m is obtained. Specifically, the Si content for the fine-grained hypoeutectic Al-Si-Nb alloys should be made at <= 12 wt% Si. During the melting step, sufficient stirring and/or short holding duration should be applied to prevent the inoculant NbAl3 substrates being neutralized by the in-situ formed NbSi2 shells. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.