Effect of cooling rate on eutectic Si in Al-7.0Si-0.3Mg alloys modified by La additions

摘要

The microstructures of eutectic Si in Al-7.0Si-0.3Mg alloys (in wt.%) without and with 0.4 wt% La at different cooling rates (0.2-130 K/s) were investigated by multi-scale microscopy, including optical microscopy (OM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and high-resolution scanning transmission electron microscopy (HRSTEM). The results show that an enhanced modification effect was obtained with increasing cooling rate, and 0.4 wt% La addition modified the eutectic Si to fibrous morphology at the cooling rate of 130 K/s. Moreover, a high-number density of twins and La atoms were found within eutectic Si at high cooling rate (130 K/s). This investigation highlights the high cooling rate promotes the enrichment of La atoms within eutectic Si, which induces the formation of multiple twins and thus modifies the eutectic Si to a fibrous morphology. (C) 2020 Elsevier B.V. All rights reserved.