Determination of the Enthalpy of Mixing of Liquid Aluminum-Copper-Magnesium Alloys

Abstract

The integral enthalpy of mixing of liquid Al-Cu-Mg ternary alloys at 986 K was measured using a high temperature mixing calorimeter. Results for four sections with constant concentration ratios of two components are given. Within the range of experimental accuracy, the measured enthalpies of mixing of a single series and of the points of intersection are self-consistent. An association model is used to calculate the thermodynamic mixing functions of ternary liquid alloys based on model parameters which are determined from thermodynamic results of the base binary systems. The calculated enthalpy of mixing shows systematically less negative values than the measured values. The existence of ternary phases and the possibility to obtain metastable quasicrystals by rapid solidification show that these deviations are caused by additional ternary interactions in the liquid state. These ternary interactions are correlated with a value of 1.8 of the mean number of conduction electrons per atom.