The role of transfer and back transfer of metals in the wear of binary AlSi alloys

Abstract

Binary melts of AlSi alloys were cast into bars 6.25 mm in diameter which were slid against hard steel bushes on a pin-bush machine. Surfaces, subsurfaces and wear debris were examined with a scanning electron microscope. Simulated studies were also carried out using model asperities in wax. The topographies from sliding were compared with those on cutting tools after machining aluminium. The surfaces of wax models were studied for comparison with machined and slid surfaces. Wear rates were measured. Techniques such as X-ray diffraction analysis were used to identify the nature of the surface and subsurface. Heavy loads produce a topography which has the appearance of roof tiles and these indicate near-seizure conditions. The bulk of the wear debris is produced by craze cracking. It is evident that transfer and back transfer of material occur across the sliding interface throughout a wear run. A critical number of layers build up on both members of the friction couple. Wear particles are produced once this number is exceeded. The wear rates of the AlSi alloys are not linear with load and a near-eutectic alloy is the ideal material from the point of view of wear and load-carrying capacity.