ABSTRACT
A method of preparing cast aluminium alloy - graphite particulate composite using uncoated graphite with the addition of 1wt% magnesium to aid wettability was studied. The method consists of introducing and dispersing uncoated but pre-treated graphite particles in aluminium alloy melt and casting the resulting composite melts in suitable moulds. The graphite was pre-heated to 400oC in air for 2 hours just prior to dispersion in the melts. Al-5%Cu and 1%Mg by weight with various additions of graphite particles with 1,3,5,7 and 9wt% were produced using the stir casting method. The resulting materials were solutionized at 520oC for 2 hours and quenched in warm water at 50oC followed by ageing at 100oC, 200oC and 300oC at various ageing times ranging from 60-360 minutes. The properties such as density, apparent porosity, impact strength, hardness, yield and tensile strengths were evaluated. Except for the density and porosity, all other properties were evaluated in both the as-cast and heat treated conditions. The results obtained showed a general decrease in the mechanical properties and a wide scatter indicating some increase and decrease at various compositions of the graphite particles and at various age hardenened temperatures. The wide scatter of results was generally attributed to the behaviour of graphite which is weak and soft acting essentially as porosity in the alloy matrix. The investigation also showed that the composite produced responded to precipitation hardening treatment.