CASTING OF GRAPHITIC AL-SI BASE COMPOSITES

Metal matrix composites can be produced by conventional casting techni ques. The reinforcing materials, such as short fibres or particulates of ceramic or graphite, can be added directly into the melt of any met al during its stirring. The resultant mixture is then cast into a perm anent mould. This technique was used to produce Al-Si alloys containin g different percentages of graphite particles ranging from 0 up to 20 wt%. To solve the problem of making the molten Al-Si alloys wet the gr aphite, a special chemical activation was carried out. The description of this technique and its solidification behaviour are demonstrated. The addition of graphite particles has a modifying effect on the struc ture of the Al-Si eutectic and, in the case of Al-Si hyper eutectic al loy, it refines the primary silicon particles and, at the same lime, m odifies the eutectic matrix. These composites showed a drastic decreas e in coefficient of friction. The wear rate of composites decreased wi th graphite content up to 10 wt% compared with unreinforced ones, whil e it increased at higher graphite contents.