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 α-Al, eutectic silicon , ternary AlSi 2 Sc 2 and CeAl 2 Si 2 . Rapid cooling transformed the huge hollow ternary AlSi 2 Sc 2 blocks (300–500 µm) into fine Al 3 Sc particles (dozens of μm), and simultaneously refined the AlSi 2 Sc 2 with reducing its interlayer thickness from 15.26 µm down to 1.94 µm (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 CeAl 2 Si 2 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 Al 3 Sc (E = 168 GPa), AlSi 2 Sc 2 (E = 178 GPa) and CeAl 2 Si 2 (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 AlSi 2 Sc 2 blocks (ultrahigh micro-Vickers hardness ∼ 780 HV), making a homogenous Al-RE alloy with improved mechanical property (68 ∼ 84 HV balanced among phase components). The refining mechanisms on the improved mechanical performance are also discussed.