Differential scanning calorimetry analysis of solidification and precipitation behavior in Al-Si alloys

Solidification and precipitation behavior for Al-Si alloys were investigated by differential scanning calorimetry (DSC). Solidus values measured by DSC method agreed with calculated solidus values from equilibrium phase diagram. Liquidus values measured by DSC was deviated from calculated values by phase diagram. Comparison of solid fraction calculated from specific heat curves and calculated values from phase diagram were showed partially deviation. Since Al-Si alloys used in this study were contained about 0.1% Fe, solidification behavior was considered to be slightly different from Al-Si binary phase diagram. From the measured heat flux curves for solution treated Al-Si- alloys, exothermic reaction due to precipitation of solute Si and endothermic reaction due to dissolution of Si precipitates were detected. With heating of specimens, solute Si were considered to be precipitated from the supersaturated solid solution first, and then precipitated Si during cooling after solution treatment and during measurement were dissolved. For Al-1.4mass%Si alloy, the amount of precipitated Si during measurement analyzed from DSC curves was estimated to be about 84% of solute Si, corresponding to 1.26vol.% in volume fraction. In this study, it was indicated that solidification and precipitation behavior can be quantitatively analyzed by DSC measurement for systems with known phase diagram.