Thermochemistry of ternary liquid Cu-Mg-Si alloys
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I.
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 when 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. It was found that some of the ternary silicides formed in the Cu-Mg-Si system, such as Cu3Mg2Si or Cu16Mg6Si7, may serve as precipitation hardeners in such alloys;[1] however, virtually nothing is known about the thermochemistry of the corresponding ternary system. Thus, it was decided to extend the series of investigations of ternary magnesium alloys (refer to References 2 through 6) with a study of the thermodynamic properties of ternary liquid Cu-Mg-Si alloys. The phase diagrams of the binary boundary systems are rather well known,[7,8,9] and a considerable amount of information can also be found on the thermodynamics of the Cu-Mg,[5,7,10,11] Cu-Si,[8,12,13] and Mg-Si systems.[9,14] As far as the ternary Cu-Mg-Si phase diagram is concerned, several investigations were performed in different concentration ranges,[15,16,17] and the existence of a number of ternary phases was reported by different authors.[16,18–20] The most prominent feature appears to be a melting point maximum of about 950 7C around 33 at. pct Mg and 13 at. pct Si.[16,17] It was the aim of the present study to determine thermodynamic properties in the ternary system along an isopleth with a constant concentration ratio of xCu/xSi 5 7/3. This particular section was selected because of a minimum melting temperature of 802 7C at the eutectic point in the binary Cu-Si system (at 30 at. pct Si),[8] in order to warrant a maximum stability range of the liquid phase for the exV. GANESAN, formerly Research Assistant with the Institut fur Anorganische Chemie, Universitat Wien, is Head, Sodium Loops and Facilities Section, Materials Chemistry Division, Chemical Group, Indira Gandhi Centre for Atomic Research, Kalpakkam, Tamilnadu 603 102, India. HARALD FEUFEL, Postdoctoral Fellow, and FERDINAND SOMMER, Research Associate, are with the Max-Planck-Institut fur Metallforschung, D-70174 Stuttgart, Germany. HERBERT IPSER, Professor, is with the Institut for Anorganische Chemie, Universitat Wien, A-1090 Wien, Austria. Manuscript submitted July 24, 1997. METALLURGICAL AND MATERIALS TRANSACTIONS B
perimental measurements which, however, was reduced considerably by the appearance of the aforementioned melting point maximum. Enthalpies of mixing were obtained by a calorimetric method and were combined with partial molar properties of magnesium measured by an isopiestic vapor pressure method. Together with thermodynamic data for the three limiting binary systems, this was hoped to provide a reliable description of the thermodynamics of ternary liquid alloys which would be the basis f
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