Ability of aluminium alloys to wet alumina fibres by addition of bismuth

Abstract

Metal matrix composites containing Saffil fibres and a common piston alloy were manufactured by the squeeze casting method. An analysis of the interface between the components was then carried out using analytical field emission gun scanning transmission electron microscopy (FEGSTEM). The as cast material was analysed to ascertain the interfacial reactions that occur during infiltration. Experiments were carried out to determine how the wetting between the alloy and the reinforcement could be improved by the modification of the alloy. The modifications were designed to slow or stop the formation of surface oxides. It was found that the addition of bismuth to the alloy disrupted the surface oxide film allowing liquid aluminium to encounter the reinforcement, therefore, allowing wetting to occur between the alloy and the reinforcement. Tensile test experiments showed that the ultimate tensile strength (UTS) of the composite material was improved by 15% compared with the unreinforced alloy at room temperature, therefore, showing that load transfer across the fibre/metal interface was occurring. Tensile tests carried out at 300°C showed that the addition of bismuth was not detrimental to the high temperature properties of the composite material, with the UTS being 5% higher than that of a comparable composite material at the same temperature.