Effect of Current Density on the Wear Resistance of Ceramic Coatings Formed on 7075 Aluminum Alloy via Microarc Oxidation

This study investigates the effects of current density on the tribological characteristics of ceramic coatings formed on 7075 aluminum alloy via microarc oxidation (MAO). Results showed that the specimens improved their performance with the increase in current density parameters; moreover, ceramic coatings with 3-0.3 A/dm2 had the highest thickness and microhardness and the strongest bonding force. The MAO ceramic layer was mainly composed of alpha-Al2O3, gamma-Al2O3, and alpha-Al, as shown by the XRD analysis results, and the wear-resistant Al2O3 (alumina) layer was the main factor that enhanced the microhardness of ceramic coatings. The sharp reduction in friction coefficient and wear scar depth (reduced by 34.5%) and the transition from transition wear to mild wear indicated that the MAO ceramic coating prepared using 3-0.3 A/dm2 exhibits excellent wear resistance. The improvement of the wear performance of the ceramic layers is closely related to the increase in the thickness of the dense alumina layer, and the wear mechanism was mainly of mild abrasive wear and the sub-mechanism of it is microploughing.