Shelf life of chromic acid anodize coating

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We have an application that calls for unsealed chromic acid anodize as the surface preparation for 6061T6 aluminum. Normally a corrosion inhibiting primer would be applied immediately after the anodize, but for this application the customer has requested that no primer be used. My question is; what is the shelf life of unsealed chromic acid anodize, when it is used as a surface preparation for a structural adhesive bond? I have checked the sources available to me, and have been unable to find a quotable reference. Thank you in advance for whatever assistance you can offer.

Ken W -

Dear Sirs,

Besides anodize bath conc. , bath temp. and plating current density, is there any other process parameter control on phosphoric acid anodize bath? What is the Al content control for the anodize process ?

Thank you for the reply.

T F Chao
- Singapore

Surface Finishing and Treatment of Aluminum and its Alloys, Wernick, Pinner & Sheasby

November 8, 2008

Hi, Ken. Sorry, I'm not familiar with a shelf life limit for chromic acid anodize. Hopefully you'll get some additional input from other readers.

Hi, T.F. You can go by ASTM D3933 [link is to spec at TechStreet]. Additionally there is a Boeing spec for phosphoric acid anodizing, BAC5555. I don't happen to have a copy, but it may contain the parameter information you are looking for.

Regards,

Ted Mooney, P.E.
finishing.com
Brick, New Jersey