Effect of Cooling Rate and Fe/Mn Weight Ratio on Volume Fractions of α-AlFeSi and β-AlFeSi Phases in Al–7.3Si–3.5Cu Alloy

Abstract

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 ThermoCalc®. We observed that β-AlFeSi disappeared when both high (>3.5°C/s) and low cooling rates (<0.1°C/s) were used. The elimination of β-AlFeSi at low cooling rates may be attributable to a decrease in the magnitude of microsegregation associated with low cooling rates. The disappearance of β-AlFeSi at high cooling rates may be related to growth difficulties when this phase precipitates during solidification of eutectic Al−Si: β-AlFeSi precipitation approaches the solidification onset of eutectic Al−Si when the cooling rate is increased. Moreover, the cooling rate at which the β-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 β-AlFeSi (Tβ) and eutectic Al−Si (Teut). The cooling rate at which the β-AlFeSi phase disappears may be even higher as the difference betweenTβ andTeut increases.