The varied mechanisms of yttrium (Y) modifying a hypoeutectic Al-Si alloy under conditions of different cooling rates

The varied mechanisms of yttrium (Y) modifying a hypoeutectic Al-Si alloy under conditions of different cooling rates were investigated using solidification curves, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD), transmission electron microscopy (TEM) equipped with energy dispersion X-ray detector (EDX) and high resolution transmission electron microscope (HRTEM). The results show that Y could modify the eutectic silicon of a hypoeutectic Al-Si alloy (A357), but the modification mechanism was different at variable cooling rates. At a low cooling rate, Y modified the eutectic silicon by introducing additional nucleation cores during the nucleation process. At a high cooling rate, Y modified the eutectic silicon by promoting the twin formation during its growth process. (C) 2019 Elsevier B.V. All rights reserved.