Abstract
Some foundry techniques for adding nickel-coated graphite particles to molten aluminum alloys were investigated. The first method was that of introducing graphite particles by injecting argon gas stream from the bottom of the moten bath (injecting method). The second method was that of plunging pellets prepared from a mixture of aluminum powder and graphite particles into the melt (pellet method) and the third method was that of pouring graphite particles directly into a deep vortex of the melt created by an impeller mixer in the melt (vortex method). The vortex method was judged to be the most suitable technique of graphite dispersion for the small scale production of graphite-aluminum alloys. Using the vortex method, up to 17wt% graphite can be dispersed into the aluminum alloy. Coarse graphite particles (420−840μm) with continuous nickel coating of about 6μm thickness ware successfully introduced into the melt of Al-Si alloys. Optimum mixing temperature of the melt for addition was about 50°C higher than the liquidus of the alloy. There is a floatation of the graphite particles in sand mold casting, but a uniform distribution of the particles is obtained in the water-cooled chill casting.
