Tribological Performance of 6061 Aluminum Alloy/Graphite Materials under Oil-Lubricated and Dry Sliding Conditions

Abstract

A thrust-on-washer adapter was used to stimulate flat-on-flat-type contacts under lubricated and dry sliding conditions. The upper specimens were made of a cast aluminum alloy, A356.0 Al, and the lower specimens were prepared by powder metallurgy. Fine graphite particles were mixed with 6061 aluminum alloy powders, by means of cold pressing and sintering to create a self-lubricating composite material by means of cold pressing and sintering. The tribological performance of the composite materials was evaluated under both dry and oil-lubricated conditions. The optimum graphite content was determined by frictional performance, Stribeck curves, the product of nominal pressure and sliding speed (PV), graphite content, and wear mechanisms. The results showed that, regardless of contact pressure, the seizure, which often occurs in aluminum, can be avoided by adding graphite. Seizure can be delayed in low-speed dry sliding contacts with high graphite content. However, either too much or no graphite in aluminum alloys increases the risk of surface seizure at higher sliding speeds. Phosphorus-based additives in engine oil fail to form a boundary film on the surface of aluminum-aluminum sliding pairs; the reduced wear is purely a result of oil lubrication.