ROLE OF MAGNESIUM IN CAST-ALUMINUM ALLOY MATRIX COMPOSITES

Wetting between the dispersoid and the matrix alloy is the foremost re quirement during the preparation of metal matrix composites (MMC) espe cially with the casting/liquid metal processing technique. The basic p rinciples involved in improving wetting fall under three categories: ( i) increasing the surface energies of the solids, (ii) decreasing the surface tension of the liquid matrix alloy, and (iii) decreasing the s olid/liquid interfacial energy at the dispersoid matrix interface. The presence of magnesium, a powerful surfactant as well as a reactive el ement, in the aluminium alloy matrix seems to fulfil all the above thr ee requirements. The role played by magnesium during the synthesis of aluminium alloy matrix composites with dispersoids such as zircon (ZrS iO4), zirconia (ZrO2), titania (TiO2), silica (SiO2), graphite, alumin ium oxide (Al2O3) and silicon carbide (SiC), has been analysed. The im portant role played by the magnesium during the composite synthesis is the scavenging of the oxygen from the dispersoid surface, thus thinni ng the gas layer and improving wetting and reaction-aided wetting with the surface of the dispersoid. The combinations of magnesium and alum inium seem to have some synergistic effect on wetting.