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topic 3759

To Alodine, or not to Alodine?


I guess I am hoping for the best with this question. I have researched a lot of articles, and some were helpful, some were not... I am polishing an aluminum bike frame, and would like to know if it would be in my best interest to hit it with a coat of Alodine, followed by a urethane clearcoat, or similar protective coating. Would this be a complete waste of time, or would it help keep my frame in good condition, both physically and aesthetically in the long run?.. Also, does Alodine stay clear, or does it discolor the clear topcoat? Is this method similar to the system used by the companies that manufacture polished aluminum bicycle frames?... Thanks to all who can help!

Martin Cattani 
- Huntington, New York


Alodine is a trade name for a brand of chromating solution used for Mil-C-5541 [link by ed. to spec at TechStreet] conversion coating of aluminum. Iridite is another trade name.

The conversion coating can be done in clear, yellow, or yellow-and-leach (leach back to clear). Normally, the conversion coating is either for stand-alone use or for use as a base coat before painting.

I could be in error on this, and we have more knowledgable readers who will hopefully correct me, but I would not expect conversion coating under a clearcoat to maintain a nice polished shine.

I don't know the manufacturing process for the polished bikes in question, but would expect that they are either anodized or clear-coated without chromate.

Ted Mooney, Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey


I am trying to find the best, most economical and maintenance-free clear top-coat for a polished aluminum bike frame. Am I to understand that Alodine will etch the surface of polished aluminum so that it will not retain a polished look?... And if this is so, is it possible to get a polyurethane or similar automotive finish clear-coat to stick to polished aluminum directly, or should I try a powder coat as my clear? Can I just leave it bare, or would this simply be asking for trouble in the long run as far as maintenance and life of the metals' surface?... I have been told aluminum won't oxidize. Please help, because I polished my knuckles to the bone on this frame, and it really came out well. It would kill me to have it get pitted and ugly prematurely.

Martin Cattani
- Huntington, New York

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