Study of ZnAl Hydroxides-Based Thin Films to Enhance the Filiform Corrosion Resistance of Acrylic-Coated AA5005

In recent years, the imperative to adopt a sustainable approach to aluminum coating pre-treatments due to environmental concerns has engaged researchers in corrosion studies. This work investigates Zn-Al hydroxides-based conversion coatings developed on AA5005 to enhance filiform corrosion (FFC) resistance. The conversion coatings were applied as a pre-treatment (200 nm–800 nm thick, depending on synthesis conditions) prior to coating with acrylic paint. The synthesis of the Zn-Al hydroxides conversion coating involves a rapid hydrothermal method at near-neutral pH. Electrochemical tests performed on the ZnAl hydroxides conversion coatings onto AA5005 revealed a substantial improvement in localized corrosion resistance. FFC tests in a climatic chamber exhibit a significant decrease (about 50%) in rust creep filament propagation compared to bare AA5005 after 1000 h. Those results were obtained employing Zn and Al salts at neutral pH for ten minutes at 95 °C. The findings obtained suggest that the synthesis process is of potential interest within the context of chemical surface conversion treatments for aluminum. In fact, eco-friendly metallic salts contribute to a more economical and environmentally friendly waste disposal process, making this treatment a potential solution for industrial applications, considering its simplicity, time efficiency, and use of non-toxic products.