Corrosion resistance and self-repairing behaviour of Cr(III) contained conversion coating on AA2024-T3

Abstract

A Cr(III) contained conversion coating on AA2024-T3 was prepared in solution containing Cr₂(SO₄)₃ and K₂ZrF₆. Its composition was analysed using X-ray photoelectron spectroscopy, and its corrosion resistance was characterised by electrochemical measurements and neutral salt spray exposure. To investigate its self-repairing effect, the coupling current between a small uncoated sample and a large coated sample was monitored through an artificial scratch cell. The coating mainly consists of zirconium oxide and chromium oxide and hydroxide; no Cr(VI) species is detected. It improves the corrosion resistance by hindering the anodic process as well as the cathodic process. Meanwhile, it possesses self-repairing effect, which is generated from the release of Cr(III) species from the coating, migration and then deposition on the nearby scratch area.

Keywords:

• Aluminium alloy
• Trivalent chromium
• Conversion coating
• Corrosion resistance
• Self-repairing effect

Acknowledgements

The authors wish to acknowledge the financial support of The Project sponsored by SRF for ROCS, SEM.