Abstract
Chromic acid anodizing is important for the corrosion protection of aerospace aluminium alloys. Previous study has demonstrated that SO42− impurity in the chromic acid affects the film growth on aluminium at a voltage of 100V. The present work further investigates aluminium and extends the study to industrial anodizing conditions (Bengough-Stuart (B-S) process) and to the AA 2024-T3 alloy. It is shown that SO42− concentrations between ~38–300ppm reduce the film growth rate for aluminium anodized at 100V in comparison with an electrolyte than contains ≤1.5ppm SO42−, whereas ~1500–3000ppm SO42 have an opposite effect and lead to an unstable pore diameter. Under the B-S process, the film growth depends on the substrate composition, the SO42− content of the film, the film morphology and, for the alloy, oxygen generation. Corrosion tests of the alloy in 3.5% NaCl solution revealed better protection with films formed in chromic acid containing 38ppm SO42− compared with ≤1.5ppm SO42−, which are within the specified limits for sulphate impurity for chromic acid anodizing. The difference in corrosion protection is proposed to be related to the observed differences in the film morphologies; it is speculated that this may influence the retention of residues of chromate ions in the films.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
