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Mil-C-5541 "gumminess" problem

We had a lot of 6061 AL parts plated per Mil-C-5541.
When the parts were returned the surfaces appeared to be gummy and almost rusty in color. Rubbing the part with your finger removes the rusty color and exposes a clear film.
Any thoughts on what is going here?

Steve Dalessio
- Claremont, New Hampshire, USA
March 1, 2011

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Not processed properly. A quality contrrol problem.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

First of two simultaneous responses -- March 3, 2011

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Hi Steve,

It is a little difficult to tell, but something has gone wrong with the processing so the first thing you need to do is contact the supplier and find out if something has gone wrong with their process.

When the chromate film rubs off like that it is usually an indication of poor pre-treatment prior to the conversion coating, especially as it is not leaving any film at all. You can sometimes get some of the film to rub off if the parts have been over-treated (immersed for too long), but there is usually a residual coating left that you would see.

Another possibility is an imbalance in the pH of the conversion coating tank. Again the supplier can check this out.

I think the important part here is that you need to return the parts as unacceptable and contact your supplier to get them re-processed and for them to analyse what went wrong

Brian Terry
Aerospace - Yeovil, Somerset, UK
Second of two simultaneous responses -- March 4, 2011