Effect of P-N type extreme pressure and antiwear additive on the friction and wear behaviour of aluminum-steel sliding pair

The friction and wear properties of Al2024 alloy against AISI 52100 steel were evaluated on an Optimal SRV friction and wear tester. The friction and wear tests were carried out under the lubrication of liquid paraffin alone and liquid paraffin containing various extreme pressure and antiwear additives including tricresyl phosphate (TCP), dibutyl phosphite (DBP), dodecylamine (DA) and phosphated amine salt (PAS). The boundary film formed on the rubbing surface of the alloy was analyzed with scanning electron microscopy and X-ray photoelectron spectroscopy. The results show that P-containing additives such as TCP and DBP in liquid paraffin significantly increase the antiwear ability and reduce the friction coefficient. PAS in liquid paraffin shows the best antiwear and friction-reducing properties. The improvement in the antiwear and friction-reducing behavior of the Al-steel pair is attributed to the formation of the boundary film composed of aluminum phosphate and/or aluminum phosphite on the lubricated surfaces.