Computer-aided cooling curve thermal analysis of near eutectic Al–Si–Cu–Fe alloy

Abstract

The effects of bismuth (Bi), antimony (Sb) and strontium (Sr) additions on the characteristic parameters of the evolution of aluminium dendrites in a near eutectic Al–11.3Si–2Cu–0.4Fe alloy during solidification at different cooling rates (0.6–2 °C) were investigated by computer-aided cooling curve thermal analysis (CA-CCTA). Nucleation temperature ($T_{\text{N}}^{{\alpha {\text{ - Al}}}}$) is defined with a new approach based on second derivative cooling curve. The results showed that $T_{\text{N}}^{{\alpha {\text{ - Al}}}}$ increased with increasing cooling rate but both the growth temperature ($T_{\text{G}}^{{\alpha {\text{ - Al}}}}$) and the coherency temperature (T _DCP) decreased. Increase in the temperature difference for dendrite coherency ($T_{\text{N}}^{{\alpha {\text{ - Al}}}} - T_{\text{DCP}}$) with increasing cooling rate indicate a wider range of temperature before the dendrite can impinge on each other and higher fraction solid ($f_{\text{S}}^{\text{DCP}}$). Additions of Bi, Sb and Sr to the base alloy produced only a minor effect on $T_{\text{N}}^{{\alpha {\text{ - Al}}}}$. Additions of Bi and Sb resulted in an increase in fraction solid and an increase of 30 % in the value of $T_{\text{N}}^{{\alpha {\text{ - Al}}}} \, - \,T_{\text{G}}^{{\alpha {\text{ - Al}}}}$ to almost 13 °C.