The growing importance of Al-Sn based alloys as materials for engineering applications necessitates the development of uniform microstructures with improved performance. Guided by the recently thermodynamically assessed Al-Sn-Cu system, two model immiscible alloys, Al-45Sn-10Cu and Al-20Sn-10Cu, were selected to investigate the effects of intensive melt shearing provided by the novel melt conditioning by advanced shear technology (MCAST) unit on the uniform dispersion of the soft Sn phase in a hard Al matrix. Our experimental results have confirmed that intensive melt shearing is an effective way to achieve fine and uniform dispersion of the soft phase without macro-demixing, and that such dispersed microstructure can be further refined in alloys with precipitation of the primary Al phase prior to the demixing reaction. In addition, it was found that melt shearing at 200 rpm and 60 seconds will be adequate to produce fine and uniform dispersion of the Sn phase, and that higher shearing speed and prolonged shearing time can only achieve minor further refinement.

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Experimental work using differential scanning calorimetry, differential thermal analysis, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray analysis was conducted on key samples with more than 33 at.% Mg in the Mg-Al-Sn system. In addition to the thermal analysis and study of the solidification microstructure, an equilibration at 400°C was performed. The results were used together with all available phase equilibria and thermodynamic data from earlier experimentation to create a consistent thermodynamic description of the MgAl-Sn alloy system. No ternary stable phase was discovered, and no ternary solubilities of the binary intermetallic phases were found. With the addition of a single Gibbs energy parameter describing the interaction between Al and the associate Mg 2 Sn in the liquid phase, the thermodynamic model of the system could be made to describe all pertinent experimental data throughout the ternary system. The phase precipitation sequence during slow solidification of all present samples is reflected by the thermodynamic calculations as well. Intricate details of the liquid miscibility gap, occurring in ternary alloys only, are also highlighted.