Effects of Cu content in Al-Cu alloys on microstructure, adhesive strength, and corrosion resistance of thick micro-arc oxidation coatings

In this work, effects of Cu content from 1 to 4.5 wt.% on morphologies, phase composition, and residual stress of micro-arc oxidation (MAO) coatings on Al-Cu alloys at the oxidation of 40 min were investigated. Furthermore, the adhesive strength (AS) and corrosion resistance of the MAO coatings were evaluated. The MAO coatings were characterized by SEM, XRD, and laser scanning confocal microscope. The MAO coating on the Al-1Cu alloy showed the low porosity (6.0%), high AS (20 N), and excellent corrosion resistance. The corrosion behavior of the MAO coating on the Al-3Cu alloy was poor due to the high porosity. The results indicated that the thermal conductivity of the substrate affected the micropores and residual stress of the MAO coatings. The AS of the MAO coating on the Al-3Cu alloy was 15% lower than that on the Al-1Cu alloy. The residual compressive stress, high hardness, and low porosity contributed to the excellent adhesion. In addition, the simultaneous occurrence of residual tensile stress and compressive stress in the coatings on the Al-1Cu and Al-4.5Cu alloys were attributed to the inhomogeneous distribution of micropores. • Thermal conductivity did not affect coating thickness and phase composition. • Residual compressive stress resulted in a 15% reduction in adhesive strength. • Coatings on Al-1Cu alloy possessed excellent adhesion and corrosion resistance. • Inhomogeneous distribution of micropores affected the nature of residual stress.