PREPARATION OF CAST ALUMINUM - SILICA PARTICULATE COMPOSITES

α-quartz particles (average size 53 μm) were dispersed in the matrix of aluminium castings by mechanically stirring these particles in the melts, followed by casting of the melts in suitable permanent moulds. For obtaining good composite castings with more than 2 wt % SiO2 dispersions, the silica particles should be preheated to 700° C and added while they are hot (>500° C) together with magnesium pieces (3.5 wt %) to the surface of the melts, kept between 720 to 790° C. Microscopy of castings indicated a reaction zone at the outer periphery of the dispersed SiO2 particles, and the electron microprobe analysis confirmed that the magnesium added to the surface of the melt concentrates around the periphery of the silica particles dispersed in the matrix, apparently imparting some wettability to the particles. The hardness of Al-2.5 wt % SiO2 particulate composite was found to be four times that of pure aluminium, and abrasion resistance was found to be three times that of pure aluminium under the conditions of the present investigation. © 1979 Chapman and Hall Ltd.