Verification method for Class I Chromate on Aluminum 

Letter 10024

(2001)

I work for a medical manufacturer in Denver, CO. We continually question if an aluminum part that calls out for a Mil-C-5541 [link is to spec at TechStreet] Class 1A finish is chromated or not. We will get parts in that have been yellow dyed, then all of sudden we will get parts that look bare.

Is there any quick test that we could do to verify chromate exists on the part? When we take the part and rub it on a sheet of paper it leaves a line like lead would, leading us to believe that there is no chromate. Is this a valid test? Is there some other quick and easy test that we could do?

A quick response to this question would be appreciated as we are holding product until I can verify.

Jay B
- Lakewood, Colorado

The best thing to do for the future is to specify an iridescent yellow chrome with a color standard, so that light finishes can be rejected.

Tom Pullizzi Platronica.com Falls Township, PA

 

Hi, folks. While Tom's advice to Jay was good at the time, and it could still be considered good with some provisos, things have changed. The world has moved away from hexavalent chromating, and the only chromates that are both hex-free and meet Mil-DTL-5541 [link is to spec at TechStreet] are the so called TCP (tri-chrome passivation) finishes.

TCP is thin and almost clear, and it is generally believed that dyeing them greatly reduces their corrosion resistance. So what you need is a test for the TCP finish. Letter 39839 claims that such tests exist and, further, that a well trained eye can see the TCP finish. Good luck.

Regards,

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