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MIL-C-5541, 1A Conversion Coatings

My question involves conversions coatings per MIL-C-5541. For a long time this is something we have sent out to be done. As time has gone on, the parts that we make have gotten bigger and more difficult to outsource. Our non-aluminum parts are generally cleaned (washed or blasted), wash primed ( TT-C-490 [from DLA] , Type III), Primed and painted.

This process has worked well. As for the Aluminum parts, I am generally required to used MIL-C-5541, 1A and then prime and paint. After doing some research, it appears that some 1A conversion coatings can be "sprayed" on. My question..... Is there a 1A conversion coating that can be sprayed on my aluminum parts in a simple and similar fashion as the wash primer I am using on my steel parts?

The last requirement would be that is must meet MIL-C-5541 and be present on the government QPL list since my products are for the military. This is something that has bothered me for a while and most of the QPL chemical suppliers don't seem to give me the time of day when it comes to answering my questions.

I would appreciate some insight to find out how realistic my wishes are!

Mark Schutt
- Antigo, Wisconsin
2003

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Mark, what you are thinking of doing is possible but unusual. Pretreatment is just as necessary for spray processing as for immersion processing, so you still need to clean the parts, rinse them, etch them, rinse them, desmut them, and rinse them before spraying. Parts often need varying treatment times, or perhaps a double cycle of etch followed by desmut, and it can be easy to do this in immersion tanks and hard to do on a spraying machine. Finally, the chromate conversion process involves toxic hexavalent chromium, so people (including the vendors) are reluctant to advocate pressurizing it and spraying it.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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2003

What you are asking is done regularly by aluminum coil coaters. If you use a mild phosphoric acid type cleaner, water rinse, and apply the chromate coating by flooding onto the parts or sheet, for enough time to form the yellow coating (40 sec - 3 minutes) there is no need for etching (considered detrimental to corrosion protecting) nor desmutting. Iridite 14-2 meets all the requirements you mentioned. (Macdermid supplies this product)

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])