Cast aluminium alloy composites containing copper-coated ground mica particles

Abstract

An electroless method of coating copper on ground mica particles using copper sulphate solution is described. The effects of time of sensitization, PdCl₂ concentration and time of stirring the activated particles in electroless solution, on the extent of copper coating on mica particles are reported. Using this method it is possible to deposit up to about 35 wt% copper on mica particles. A process for making cast aluminium alloy-mica particle composite alloys using these coated particles is also described. The process involves stirring the copper-coated mica particles into liquid alloys using an impeller, and casting the melts containing suspended mica particles in suitable permanent moulds. Coating of copper on mica particles makes possible the dispersion of ground mica particles in molten aluminium alloys with high recoveries which is otherwise difficult, even when magnesium is added to the surface of the melts. Copper coating on ground mica particles masks the basal planes, and apparently increases their wettability with aluminium alloy melts. Recoveries of ground mica particles in composite castings made using copper-coated mica particles are as high as 80%, which is three times higher than the corresponding recoveries in the castings made using uncoated particles. The mechanical properties of cast aluminium mica composites made using copper-coated ground mica powders are adequate for a variety of bearing and antifriction applications.