Electrochemical characterization of anti-corrosion coatings formed on 6061 aluminum alloy by plasma electrolytic oxidation in the corrosion inhibitor-enriched aqueous solutions

Abstract

• PEO in the borate bath brought more anti-corrosion effect than in the silicate bath. • The PEO oxide coatings were modified with the use of corrosion inhibitors (CIs). • The single-step method was the addition of 0.1 g L −1 of a CI to the Si or B bath. • The sequential method was the dipping of the coating in a CI solution and DC PEO. • Mullite, α - and γ -Al 2 O 3 were detected in the PEO oxide coatings. • Acrylic acid was the most effective CI in both single-step and sequential methods. The 6061 aluminum alloy was surface-treated by plasma electrolytic oxidation (PEO) in silicate- and borate-based electrolyte systems. The authors attempted to incorporate selected corrosion inhibitors (8-hydroxyquinoline, 2-mercaptobenzothiazole, poly(acrylic acid) with molecular weights of 1800 and 450,000 g mol −1 , and acrylic acid) into the oxide coating to provide long-lasting protection of the substrate. These inhibitors were either added directly to the electrolyte for the treatment or loaded into the coatings through a sequential PEO procedure. Electrochemical corrosion tests showed that acrylic acid-modified coatings provided the best protection. In general, of the two methods, the sequential PEO gave more reproducible anti-corrosion effects.