COST 507 - Repositório Aberto da Universidade do Porto

Thermodynamic Evaluations of the
Al­Li­Cu­Mg­Zr Systems
Marko Hämäläinen,* Helena Braga,**
N. Bochvar, T. Dobatkina, E. Lyssova, L.L. Rokhlin***
*Helsinki University of Technology, Espoo, Finland
**University of Porto, O'Porto, Portugal
***Baikov Institute of Metallurgy, Moscow, Russia
Abstract
The investigation of the Al­Li­Cu­Mg­Zr system is accomplished in this report. The
evaluations of the Cu­Mg­Zr and Cu­Li­Mg systems and the experimental study of the
Al­Li­Cu­Mg system were carried out during the COST 507 second round.
The evaluation of the Cu­Li­Mg system was based on the DSC experiments at the
large range of composition. The parameters of the excess Gibbs energy obtained
agreed quite well with the temperatures of the phase transformations but the fit was
not so good using the experimental enthalpies. The decomposition temperature of the
τ phase was fixed at 702.7 Κ and was not defined earlier in the literature.
The optimisation of the Cu­Mg­Zr system was based on the experimental data from
the literature and on one set of the DTA experiments measured. The calculated phase
diagram was in good agreement with the data used. The existence of the new τ phase
as well as the parameters of formation of the excess Gibbs energy contributed well the
system studied.
The phase relations near to Al­rich corner containing up to 7 wt.% Li, 7 wt.% Mg and
10 wt.% Cu were investigated using microscopy analysis, quality local X­ray spectral
analysis and X­ray phase analysis in the experimental study of the Al­Li­Cu­Mg
system done by Baikov Institute of Metallurgy.
1 The Cu-Li-Mg system
1.1 Introduction
The Cu­Li­Mg system is not well defined in the literature. Melnik [76Mel] carried out
annealing experiments in the Cu­Li­Mg system at 370 °C and detected a new phase
called X phase with the composition of 32 at.% copper, 8 at.% lithium and 60 at.%
magnesium. The stoichiometry of the X phase was estimated as Cu32LigMg6o·
Kripyakevich [71Kri] ascribed the X phase as the τ phase and defined its theoretical
stoichiometry as (Lio.osMgo.92)i2LiCu5. The phase region close to the pure lithium
corner is not well known.
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