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Thermodynamic Modeling and Experimental Investigation of the Magnesium-Aluminum-Strontium-Calcium System

20082840
Journal: Proceedings of the Third International Conference on Light Metals Technology Sept 24-26 2007 Quebec, Canada P53-57
Author: M. Aljarrah, M. Medraj, J. Li, E. Essadiq

The phase equilibria and thermodynamic properties of the Mg-Al-Sr-Ca system were analyzed in this work and a thermodynamic description of the system was obtained using a computerized optimization procedure. The available thermodynamic and phase diagram data were critically assessed for all the binary and ternary sub-systems. Optimized thermodynamic properties of the binary systems were then used to construct a database and calculate the ternary phase diagrams. The phase equilibria in the Mg-Al-Sr and Mg-Al-Ca systems were investigated experimentally by differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM) and quantitative electron probe micro-analysis (EPMA). A new ternary solid solution, MgxAl4xSr, was observed in the Mg-Al-Sr system, which is due to the substitution of Al by Mg atoms in the Al4Sr compound. Maximum solubilities of 21.3 at.% Al in Mg17Sr2 and 11.4 at.% Al in Mg were observed. It was also noticed that Mg38Sr9 dissolved 12.5 at.% Al, In the Mg-Al-Ca ternary system, one of the invariant transformation, predicted by thermodynamic modeling, was verified experimentally and found to occur at 512┬░C with composition close to 10.8 at.% Ca, 79.5 at.% Mg ad 9.7 at.% Al. Large solid solubility of Al in Mg2Ca was observed. The Mg-Ca-Sr and Al-Ca-Sr phase diagrams were also calculated from the established database for the Mg-Al-Ca-Sr system.



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