To improve the corrosion resistance of aluminum and its alloys, an anodic coating formed via acid can be sealed to achieve maximum barrier layer protection. Research was conducted to investigate the effectiveness of sealing sulfuric acid anodic coatings with a commercial trivalent chromium process (TCP) conversion coating. Comparison studies were performed using specimens that were anodized and unsealed and specimens that were anodized and sealed (i) hydrothermally in hot water and (ii) by exposure to a nickel acetate solution. The unsealed and sealed anodized specimens were characterized using electrochemical methods, digital optical microscopy, optical profilometry, scanning electron microscopy, and depth profiling glow discharge optical emission spectroscopy. The anodized specimens sealed with the TCP coatings showed improved corrosion resistance in naturally aerated 0.5 M Na2SO4 + 0.01 M NaCl, as compared to the unsealed anodized specimens and the anodized specimens sealed hydrothermally and with nickel acetate. This was evidenced by suppressed anodic and cathodic polarization curve currents, increased polarization resistance, and reduced damage during continuous neutral salt spray exposure. The improved barrier layer protection results from the TCP covering the outer oxide surface and penetrating the pores by 1-2 μm.

Sealing sulfuric acid anodized aluminium alloy 2024-T3 with a trivalent chromium process conversion coating

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