Friction Reduction of Aluminum Alloy Micro-arc Oxidation Coating by Filling Graphene Oxide

In this study, three kinds of micro-arc oxidation (MAO) coatings based on the 2A12 aluminum alloy were prepared with molybdenum disulfide (MoS2), tungsten disulfide (WS2), and graphene oxide (GO) in hexametaphosphate composite electrolyte to improve the tribological performance, respectively. Voltage–time responses were recorded. The microstructure, composition, and element distribution were analyzed by x-ray diffractometer (XRD), SEM, and energy-dispersive x-ray spectroscopy (EDS). The ball-on-disk friction tests were performed to investigate the tribological properties. The wear tracks were observed by SEM. XRD and EDS results indicated that during the MAO treatment process, all three types of particles were effectively incorporated into the oxide coating, with GO displaying a more active participation in the film-forming process due to its solubility in water. The addition of solid lubricants increased the hardness of the coatings and reduced surface roughness, with graphene oxide (GO) being the most effective, achieving the lowest friction coefficient at 0.32. Further investigation into coating Al2O3/GO revealed the heat generated during friction process caused the oxidation of iron elements from the counterpart, which then adhered to the wear scar. GO altered the wear mode between the coating and the counterpart, transitioning from abrasive wear to adhesive wear.