COST 507 - Repositório Aberto da Universidade do Porto

Thermodynamic Investigations of Cu-Mg-Si, Cu-Mg-Y, AI-Mg-
Zn, Al-Cu-Mg, Al-Mg-Si, Al-Cu-Li and Al-Cu-Zr Alloys
D2
Y.B. Kim, H. Feufel, U. Stolz and F. Sommer
Max-Planck-Institut für Metallforschung
Seestr. 75, D-70174 Stuttgart, Germany
Abstract
The enthalpy of mixing of liquid ternary aluminium and magnesium alloys has been
determined to understand the thermodynamics and the phase equilibria of these light
alloys. The experiments were performed using a high-temperature isoperibolic type of
solution calorimeter.
Results for four sections with constant composition ratios of two components are
obtained for liquid Al-Cu-Mg alloys at 986 K. 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.
The enthalpy of mixing of liquid Al-Mg-Zn ternary liquid alloys was determined in the
temperature range between 883 K and 933 K. An association model is used to
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