Microstructure and Properties of Microarc Oxidation Ceramic Coatings on Aluminum Alloy

The paper discusses structure and property aspects of oxide films formed on 7075 aluminum alloys by microarc oxidation in alkali-silicate electrolytic solution. Microstructure, surface morphology and phase composition of the ceramic coatings were investigated by SEM and XRD. Distribution of hardness along the coating thickness was determined by microhardness analyses. The friction and wear behavior of the oxide films against steel counterparts was evaluated with a friction and wear tester. The results showed that the microarc oxidation coatings composed mainly of α-Al2O3 and γ-Al2O3 phase are dense and uniform, which indicates that the wear resistance of Al alloy could be improved obviously by microarc oxidation. The films possess a beneficial combination of 25~45 μm thickness, HV0.11500 microhardness and provide a low wear rate but a relatively high friction coefficient against GCr15 steel under dry friction condition.