Analysis of differential scanning calorimetric measurements performed on a binary aluminium alloy

A mathematical procedure is proposed to calculate fraction solid in the solidification interval of a binary alloy using cooling curves obtained with a power compensated Differential Scanning Calorimeter (DSC). The procedure takes advantage of using a validated thermodynamic model to enhance the accuracy of fraction solid evaluations, since the enthalpy of the phases vary according to their solute mass concentrations and temperature. Solute mass concentrations are deduced from the Brody-Flemings relationship to take into account the effect of solute diffusion kinetics occurring during the solidification. The procedure is applied to the fraction solid determination of aluminum-4.5% copper alloy submitted to different cooling rates. It was found that the fraction liquid remaining just before eutectic solidification was 2.45, 2.92 and 3.66 w% for a cooling rate respectively equal to 5, 10 and 60 K/min. The back diffusion parameter defined in the Brody-Flemings relationship was found to diminish as the cooling rate increases, as this is expected from basic kinetics consideration.