Effect of Cooling Rate and Fe/Mn Weight Ratio on Volume Fractions of a-AlFeSi and P-AlFeSi Phases in Al-7.3Si-3.5Cq Alloy

摘要

The crystallization behavior of iron intermetallic compounds in Al-7.3Si-3.5Cu alloy was investigated using thermal analysis, metallography, and a thermodynamic simulation performed with the Scheil module of Ther-moCalc~R. We observed that P-AlFeSi disappeared when both high (>3.5 deg C/s) and low cooling rates (<0.1 deg C/s) were used. The elimination of p-AlFeSi at low cooling rates may be attributable to a decrease in the magnitude of microsegregation associated with low cooling rates. The disappearance of P-AlFeSi at high cooling rates may be related to growth difficulties when this phase precipitates during solidification of eutectic Al-Si: P-AlFeSi precipitation approaches the solidification onset of eutectic Al-Si when the cooling rate is increased. Moreover, the cooling rate at which the P-AlFeSi phase is suppressed should depend on the chemical composition of the alloy. According to thermodynamic simulations, the alloy composition determines the precipitation onset temperature of both p-AlFeSi (T_(beta)) and eutectic Al-Si (T_(eut)). The cooling rate at which the P-AlFeSi phase disappears may be even higher as the difference between T_(beta) and T_(eut) increases.