Microstructure and mechanical properties of as casted Al-Si-Sc-Ce alloys prepared by molten salt electrolysis with varied cooling rate

Al-7Si-0.8Sc-0.6Ce alloys were prepared with combined addition of low-cost Ce and high-priced Sc through molten salt electrolysis with controlled cooling process. The phases of as-casted alloys consisted of alpha-Al, eutectic silicon, ternary AlSi2Sc2 and CeAl2Si2. Rapid cooling transformed the huge hollow ternary AlSi2Sc2 blocks (300-500 mu m) into fine Al3Sc particles (dozens of mu m), and simultaneously refined the AlSi2Sc2 with reducing its interlayer thickness from 15.26 mu m down to 1.94 mu m (the cooling rate from 0.05 K s-1 up to 30 K s-1). The eutectic Si became fine fibrous-like clusters and the thickness of CeAl2Si2 phase reduced by 62.6 % when the cooling rate reached 30 K s-1. Micro-hardness measurement and first principles-based calculation were applied for evaluating the individual mechanical performance of each phase in the alloy. The calculated Young's modulus (E) suggests that Al3Sc (E = 168 GPa), AlSi2Sc2 (E = 178 GPa) and CeAl2Si2 (E = 39.2 GPa) can toughen Al-matrix (E = 30.6 GPa). The rapid cooling (30 K s-1) strongly enhances all phase components but diminish the huge hollow AlSi2Sc2 blocks (ultrahigh micro-Vickers hardness similar to 780 HV), making a homogenous Al-RE alloy with improved mechanical property (68 similar to 84 HV balanced among phase components). The refining mechanisms on the improved mechanical performance are also discussed.(c) 2023 Elsevier B.V. All rights reserved.