The Role of Copper Incorporation in Improving the Electrical Insulation Properties of Microarc Oxidation Coatings on Aluminum Alloys

This study explores the effect of varying copper content on the electrical conductivity of microarc oxidation (MAO) coating films applied to aluminum alloy substrates. The experimental setup involved preparing (Al-X%Cu) alloys and subjecting them to MAO treatment. The MAO coatings were analyzed via scanning electron microscopy (SEM) and X-ray diffraction (XRD) to examine their chemical composition, surface morphologies, and phase structures. Results revealed that increasing Cu content up to 3 wt.% in Al alloys led to the formation of α-Al2O3 and -Al2O3 phases, which serve as electrical insulators, thereby reducing the electrical conductivity and enhancing the dielectric properties of the coating layer. Despite this, electrical conductivity measurements of MAO coatings on (Al-6% Cu) and (Al-9% Cu) alloys yielded values of 4.17 and 5.27 S/m, respectively, because of the presence of CuO phases, which improved electrical conductivity in these alloys. Thus, the findings indicated that higher Cu content increases electrical conductivity of coatings and makes it not fully insulated, despite that the MAO coating films have insulating properties as indicated in previous studies.