Solidification behavior, microstructure and silicon twinning of Al-10Si alloys with ytterbium addition

The solidification behavior, microstructure and silicon twinning of Al-10Si alloys with Yb addition were investigated by thermal analysis, optical microscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results indicate that the nucleation temperature, minimum temperature, and growth temperature of Al-10Si alloys decrease with increasing Yb content. The cooling curves of the Yb-modified alloys exhibit marked recalescence. The recalescence of the modified alloy peaks at 2.3 degrees C when the Yb content is 0.7 wt%. The 3D morphologies of eutectic Si in Yb-modified alloys change from a coarse plate-like structure to a honeycomb structure with many fine fibrous structures. The Al-Si-Yb intermetallic compound is observed in the 1.0 wt% Yb-modified alloy. Meanwhile, XRD analysis and TEM results indicate that the average twin spacing in the Yb-modified alloys is 18-46.2 nm. The average twin spacing of eutectic Si decreases with increasing Yb content. When the Yb content in the modified alloy is increased to 0.7 wt%, the average twin spacing value of eutectic Si reaches to 18 nm, which promotes the formation of twins and refinement of eutectic Si. (C) 2018 Published by Elsevier B.V.