Letter 24128

MIL-C-5541, 1A Conversion Coatings  

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My question involves conversions coatings per Mil-C-5541 [link is to spec at TechStreet]. 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 [link is to spec at TechStreet], 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

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.  finishing.com Brick, New Jersey

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, Inc. supplies this product)

Don Baudrand Don Baudrand, Consultant   Poulsbo, Washington