The Effect of Phosphate Source on the Post-treatment of Cerium Based Conversion Coatings on Al 2024-T3 and Its Correlation to Corrosion Performance


The surface morphology, electrochemical characteristics, and salt spray corrosion performance was studied for cerium-based conversion coatings (CeCCs) that were post-treated in heated aqueous solutions of orthophosphate, pyrophosphate, and polyphosphate compounds. Phosphate post-treatment reduced cracking in the coatings, which resulted in better corrosion protection compared to coatings that were highly cracked or contained other defects. In addition, post-treatment in orthophosphate solutions converted the as-deposited hydrated cerium oxide to hydrated CePO4, which further improved corrosion protection. Electrochemical analyses showed that CeCCs that contained hydrated CePO4 after post-treatment had the highest resistance (~100 kΩ-cm2), most noble pitting potentials (~ -270 mV), and best corrosion protection of the post-treatments that were tested. While pyrophosphate and polyphosphate post-treatments reduced cracks in the film, they did not promote formation of CePO4⋅H2O. The results suggest that the corrosion protection of CeCCs on Al 2024-T3 is dependent on both the surface morphology and phase of the coating.


Materials Science and Engineering

Keywords and Phrases

Corrosion; Passivation; Anodic Films

Document Type

Article - Conference proceedings

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