A study on the development and wear characteristics of rheocast Al–5Cu–2Pb alloy and Al–5Cu/Pb–18Sn wire composites

Abstract

With renewed search for a low cost material for bearing application in place of conventional and expensive Al–Sn alloy, this paper describes development of an aluminium alloy Al–5wt.%Cu–2wt.%Pb alloy and Al–5wt.%Cu/Pb–18wt.% Sn wire composite by different types of casting routes. Wear characteristics and microstructural analysis of both alloy and composites have been determined. It is found that rheocast Al–5Cu–2Pb has a morphology of Pb rich phase in the form of partly continuous nature along the grain boundaries of spherical α-Al particles resulting in good wear resistance. Bulk wear in the rheocast Al–5Cu–2Pb alloy increases with increasing sliding distance from 38.5 to 92.4 m with severe to mild wear transition occurring at a sliding distance of 46.2 m for a given applied load of 18.1 kg. Also the wear increases with increasing applied load from 18.1 to 24.4 kg for a constant sliding velocity and it increases continuously with increasing sliding velocity at a constant applied load. These results are explained in terms of smearing layer of lead due to frictional heat generated both at high applied loads and at high sliding velocities. Bulk wear and roughness of the rheocast Al–5Cu–2Pb alloy have been correlated through an equation of the type W=a R b , where a and b are constants independent of both applied load and sliding velocity. In the case of Al–5Cu/Pb–18Sn wire composite, containing 0.51–1.95 Pb content, bulk wear ∼0.7×10 −6 kg at a sliding velocity of 25.67×10 −2 m s −1 and applied load of 19.4 kg f −1 was found and it is ∼5 times better than that of rheocast Al–10Pb alloy. This study suggests that for Al–5Cu matrix produced by fast cooling rates are better suited for bearing applications. Reduction in the lead content is also more suitable from the environmental point of view.