Effect of Phosphate Source on Post-treatment of Cerium-based Conversion Coatings on Al 2024-T3
The surface morphology, electrochemical characteristics, and salt spray corrosion performance were studied for cerium-based conversion coatings on Al 2024-T3 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 cerium-based conversion coatings that contained hydrated cerium phosphate after post-treatment had the highest resistance (∼100kΩcm2) , the most noble pitting potentials (∼−270mV) , and the best corrosion protection of the post-treatments that were tested. While pyrophosphate and polyphosphate post-treatments reduced cracks in the coatings, they did not promote the formation of hydrated cerium phosphate. The results suggest that the corrosion protection of cerium-based conversion coatings on Al 2024-T3 is dependent on both the surface morphology and the phase of the coating.
D. K. Heller et al., "Effect of Phosphate Source on Post-treatment of Cerium-based Conversion Coatings on Al 2024-T3," Journal of The Electrochemical Society, The Electrochemical Society (ECS), Jan 2009.
The definitive version is available at http://dx.doi.org/10.1149/1.3224005
Materials Science and Engineering
Keywords and Phrases
Aluminum Alloys; Cerium Compounds; Corrosion Protection; Corrosion Protective Coatings; Corrosion Resistance; Cracks; Electrochemical Analysis; Surface Morphology; Surface Treatment
Article - Journal
© 2009 The Electrochemical Society (ECS), All rights reserved.