The Effect of Oxidation Time on the Organization and Corrosion Performance of 6061 Aluminum Alloy Micro-Arc Oxidation Coatings

This study investigates the influence of micro-arc oxidation (MAO) duration on the formation and characteristics of ceramic coatings on 6061 aluminum alloys. MAO treatments were conducted in a silicate-based electrolyte for varying durations. The effects of oxidation time on film thickness, surface roughness, morphology, and phase composition were meticulously assessed using a film thickness gauge, surface roughness meter, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. The corrosion behavior of the coatings was evaluated in a 3.5% NaCl solution using an electrochemical workstation. The experimental results demonstrate that both the film thickness and surface roughness exhibit a positive correlation with oxidation time. Notably, the film growth rate initially increased before plateauing, suggesting an optimal oxidation duration. The coatings primarily comprise γ-Al2O3, α-Al2O3, and Al phases, with the proportions of γ-Al2O3 and α-Al2O3 increasing progressively with extended oxidation times. Comparative electrochemical tests revealed that the treated specimens exhibited significantly higher corrosion potential and reduced corrosion current densities compared to the untreated aluminum alloy substrate. Specifically, a coating produced with a 20 min oxidation time demonstrated an exceptional corrosion current density (Jcorr) of 1.545 × 10−6 A·cm−2 and a corrosion resistance (Rp) of 2.716 × 104 Ω·cm2, signifying the best corrosion resistance achieved in this study. These results underscore the pivotal role of oxidation time in tailoring the properties of micro-arc-oxidized layers on 6061 aluminum alloys, offering valuable insights for enhancing corrosion protection in practical applications.