Sub-surface Electrochemical Effects on the Spontaneous Deposition of Cerium Conversion Coatings on Aluminum Alloys
The combination of CeCl3 and H2O2 in cerium-based conversion coating (CeCC) solutions causes the dissolution of the aluminum alloy substrate, resulting in formation of voids a few microns below the surface during deposition. Localized, excessive dissolution of aluminum occurs near intermetallic particles over approximately 10% of the substrate surface. Alternate deposition methods were explored whereby either H2O2 or chloride content was reduced to minimize dissolution. an alternative oxidant, NaClO4, added to offset the impact of lower H2O2 content. CeCCs were deposited without sub-surface voids, but the resulting coatings had poor corrosion protection compared to CeCCs deposited with H2O2 alone. Coatings prepared with alternate Ce3+ salts using different ratios of CeCl3 and Ce(NO3)3, along with higher concentrations of H2O2, were thicker and more uniform than coatings with lower H2O2 content. However, CeCCs deposited from solutions containing H2O2 and CeCl3 had the highest overall electrochemical impedance and exhibited the best corrosion protection.
B. L. Treu et al., "Sub-surface Electrochemical Effects on the Spontaneous Deposition of Cerium Conversion Coatings on Aluminum Alloys," ECS Transactions, Wiley-Blackwell, Jan 2009.
The definitive version is available at http://dx.doi.org/10.1149/1.3259802
Materials Science and Engineering
Keywords and Phrases
Corrosion; Passivation; Anodic Films
Article - Conference proceedings
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