Evaluation of the effect of Bi, Sb, Sr and cooling condition on eutectic phases in an Al-Si-Cu alloy (ADC12) by in situ thermal analysis

Al-Si and Al-Cu eutectic phases strongly affect the properties of Al-Si-Cu cast alloys. The characteristic parameters of these two eutectic phases with addition of bismuth, antimony and strontium under different cooling rates (0.6-2 °C/s) were investigated in ADC12 alloy using in situ thermal analysis. Results show that additives affect the Al-Si phase more than the Al-Cu (Al2Cu) phase. Addition elements showed two different scenarios in response to cooling rate in terms of recalescence of the Al-Si eutectic phase. Both Bi and Sb caused an increase in recalescence with increased cooling rate but Sr addition reduced the recalescence. Additions of Sb and Sr increased the nucleation temperature of Al2Cu, but addition of Bi produced an opposite effect. There seems to be relationship between the solidification temperature range and fraction solid of Al-Si and Al2Cu eutectic phases. As the cooling rate increases the fraction solid of Al-Si decreased and that of Al2Cu increased.