Letter 17722

Simple test for presence of clear chromate  

(2002)

We are trying to confirm the presence of a clear chromate conversion on an aluminum extrusion. Is there a simple chemical (or other) test that can confirm that the chromate is there? Specifically, the coating is per Mil-C-5541 [link is to spec at TechStreet]E Class 3, and the base metal is 6063-T5 aluminum. Is it possible to determine that it meets the class 3 thickness? We are trying to avoid the costs of outside material testing.

Thanks,

Mark Mozgowiec
- Cambridge, Massachusetts

My shop does chromating both clear and yellow.

Our testing indicates that we can not meet the mil-spec with a clear coating.

At our shop we offer the customer the choice:
- they can have clear chromate, not certed to a spec or they can have yellow chromate with a cert

I know of no test you can do, BUT, I do know to get a truly clear coating you need to put on very light coating.

I would be interested in hearing if you find a test & if so, if your parts meet the mil-spec. I have posted this question here many times re: meeting mil spec with clear chromate & some finishers respond that they do clear chromate & it does meet the spec - but no one referenced a specific QPL approved chemical to do this.

David A. Kraft Anacote Corporation Long Island City, NY

Gentlemen,

I am an engineering student at a company that offers in house chromating. Recently we've switched to a trivalent chromium to meet a new European directive that limits the use of hex chrome (among other heavy metals).

The problem I was facing with this new tri chromate is that the finish is practically invisible if no zinc plating is done previously. I was asked to find a simple test for the presence of chrome. Upon searching i found your site.

Our base alloy is 99% zinc so this might not work for aluminium. The process is as follows.

Lead Acetate Tri Hydrate [Pb(C₂O₃H₂)₂*3H₂O]

Mix 50 g in about 1 litre of water. Filter for white precipitate or use acetic acid to dissolve. The solution should have a pH of 5.5 - 6.8

Place a drop of this solution on the part and wait 5 seconds. With a cotton swab, gently blot.

A dark deposit or black stain equates NO COATING.

The Spec for this test is:

ASTM B201-80 [link is to spec at TechStreet]

I suggest reading that first and also obtaining a proper MSDS for Lead Acetate.

This test is for Zinc and Cadmium surfaces... Perhaps it is worth an experiment.

Cheers,

JG

Jeff Gilchrist
- Peterborough, Ontario, Canada

There is a newly developed trivalent chromium conversion coating two drop test kit on the market yo detect the presence of Trivalent Chromium on aluminum substrates, Trivalent Tester LLC.

James Savoy
- Columbia, Maryland