The sliding wear resistance and frictional characteristics of surface modified aluminium alloys under extreme pressure

There is an increasing engineering need to broaden the application range of aluminium alloys, particularly in motor vehicles, through appropriate surface engineering. In this way, greater durability to wear and improved energy efficiency should be possible. A series of reciprocation sliding wear experiments have been carried out under lubricated conditions. Micro-arc oxidised (MAO) Al-6 wt.%Mg alloy and LM25 (Al-7 wt.%Si-0.5 wt.%Mg), untreated and laser alloyed with SiC and Al₂O₃, were compared. All the surface treatments provided wear protection of the aluminium based substrates and allowed friction coefficients ∼ 0.15 to be maintained over many cycles of testing. The MAO process provided the greatest wear resistance of the surface treatments investigated. Even when the maximum sub-surface shear stress was sufficient to cause plastic deformation of the aluminium alloy, no collapse of the layer took place. The laser treated materials provided wear protection when mean contact pressures were < 1700 MPa. At higher pressures the outermost SiC and Al₂O₃ enriched layers were removed. This collapse was statistical in nature and was accompanied by a rise in friction coefficient.