COST 507 - Repositório Aberto da Universidade do Porto

Thermochemical Properties and Phase Diagram of
Cu-Mg-Si and Cu-Mg-Y Alloys
A2
Herbert Ipser a , V. Ganesan 3 , and Ferdinand Sommer b
Institut für Anorganische Chemie der Universität Wien, Austria
Max-Planck-Institut für Metallforschung, Stuttgart, F.R.G.
Abstract
This research forms part of the COST 507 program on the two leading systems
Al-Mg-Si-Cu and Al-Zn-Cu-Mg (with the additional/substitutional elements Zr, Cr,
Rare Earths). It includes magnesium vapor pressure measurements in the binary Mg-Y
system as well as in the two ternary systems Cu-Mg-Y and Cu-Mg-Si in Vienna.
Additionally, enthalpies of formation for liquid ternary alloys were determined by a
calorimetrie method in Stuttgart. All thermodynamic data were combined to provide a
full thermodynamic description for liquid ternary Cu-Mg-Y and Cu-Mg-Si alloys.
1 Introduction
Light alloys based on aluminum, magnesium, and titanium are of still increasing
importance for a wide range of technological applications. A knowledge of the thermodynamic
properties and of the phase relationships in the corresponding
multicomponent systems is essential in designing such light alloys for particular
industrial purposes. Many of these materials are based on aluminum containing several
other alloying elements like Cu, Mg, Si, Mn, rare earth elements, etc. For example, it
was found that some of the ternary suicides formed in the Cu-Mg-Si system, such as
Cu 3 Mg 2 Si or Cu 16 Mg 6 Si 7 , may serve as precipitation hardeners in such alloys [73Roc].
On the other hand, small additions of rare earth metals increase the corrosion resistance
of rapidly solidified magnesium alloys by improving microstructural and chemical
homogeneity together with an enhanced solid solubility limit [90Heh]. In order to
understand the solidification behavior of the metastable phases and their
transformation characteristics, a thorough knowledge of the thermodynamic properties
together with the corresponding phase diagram is necessary. Although yttrium is
strictly speaking not a rare earth metal by itself, its properties are very similar to those
of the heavier rare earth elements, and therefor its influence on magnesium alloys
should be very much alike.
Since virtually nothing is known about the thermochemistry of the corresponding
ternary systems it was decided to extend the series of investigations of ternary
magnesium alloys (see for example [94Feu, 94Gna, 95Feu]) with a study of the
thermodynamic properties of ternary liquid Cu-Mg-Si and Cu-Mg-Y alloys.
Furthermore, no Gibbs energy data are available for binary liquid Mg-Y alloys. In
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