Effect of Phosphate Source on Post-treatment of Cerium-based Conversion Coatings on Al 2024-T3

Abstract

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.

Department(s)

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

International Standard Serial Number (ISSN)

0013-4651

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2009 The Electrochemical Society (ECS), All rights reserved.

Publication Date

01 Jan 2009

Link to Full Text

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