Increased Wetting of Saffil™ Reinforcement Preforms by the Addition of Bismuth to Aluminum Alloys

Metal-matrix-composites containing Saffil™ fiber pre-forms and a common piston alloy, were manufactured by squeeze-casting. Analysis was carried out using an analytical FEGSTEM (Field-Emission-Gun Scanning Transmission Electron Microscope), a microscope that allows high spatial resolution chemical analysis. This analysis showed that the alloy did not wet the ceramic because of the formation of a solid oxide film on the molten metal surface.

Experimental alloys, which produced weak surface oxides, were developed and these increased the wetting of the fibers by the molten metal. Room temperature tensile tests showed that these new alloys produced composites that were significantly stronger than those produced with conventional alloys. Tests at 300°C showed that high temperature properties were retained. The new alloys also allowed metal infiltration to occur at a lower pressure. Preliminary studies achieved 100% infiltration with pressures as low as 0.4MPa. With conventional alloys a pressure of over 70MPa is required to achieve 100% infiltration.