Solidification characteristics of Al–Si–Mg–Fe/Al2O3 metal matrix composites

Abstract

The aim of this paper was to explain the influence of Al2O3 particles on the solidification characteristics of the matrix within metal matrix composite (MMC). This matrix consisted of AlSi7Mg alloy and elemental Mg (5 mass%). MMCs were prepared by the stir cast method with additions of alumina up to 10 mass%. The solidifications of the said prepared MMCs were monitored using thermal analysis. Their microstructural constituents were analysed using scanning electron microscopy, optic microscopy and X-ray diffraction analysis. Thermal analysis showed increased liquidus temperatures and decreased eutectic temperatures in those samples with higher additions of alumina particles. The alumina reacted with Mg within the melt during stirring, thus producing MgO·2Al2O3 spinel which lowered the amount of Mg in the melt causing different liquidus and eutectic temperatures according to the Al–Mg–Si phase diagram. The microstructure of the matrix alloy differed with the additions of different amounts of alumina in terms of increased amount of αAl phase and decreased the Mg2Si phase. The dendrite arm spacing was reduced, and the sizes of the eutectic phases decreased by higher additions of alumina.