Characteristics and corrosion resistance of hard-anodised 6061-T6 aluminium alloy

ABSTRACT Hard anodic coatings were formed on 6061-T6 aluminium alloy samples using direct current. Surface morphology and cross-section of coatings, as well as their hardness and corrosion behaviour, were studied. It was found that decreasing the applied current density from 55 to 35 mA cm−2 resulted in more uniform coatings with fewer surface defects, lower porosity, and higher hardness values. The optimum electrolyte concentration and hard-anodising time, where less defective coatings were achieved, were found to be 180 g L−1 and 50 min, respectively. The hardness of the optimum film was around 500 HV, and its corrosion current density was 3.2 × 10−9A cm−2. All other samples that were produced at different current densities (30-55 mA cm−2), times (40-100 min), and electrolyte concentrations (25-220 g L−1) had lower hardness and corrosion resistance than the optimum coating. The polarisation resistance of the optimum coating was about 1100 times higher than the bare substrate.