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Does Chromate on Aluminum Parts degrade ?

Does Chromate degrade on aluminum parts and if so at what temperature and how long would it take to degrade ?
Thanks
Paul

Paul Reese
employee - Gouldsboro, Pennsylvania
September 24, 2010

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The Mil Spec says do not go over 140 °F. The heat dehydrates the gel coating. I say, time and temp, both, have to be considered, and I do not like to go over 120 ever, or even 110 for 30 minutes. However, it is OK to cure regular paint, but the chromate coating must be very thin. If powder paint, keep the chromate coating down to just barely iridescent.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

First of two simultaneous responses -- September 27, 2010

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Paul,

I am assuming that you are talking about chromate conversion coatings for aluminum with this answer.

Convention says that chromate conversion coatings should not be exposed to temperatures above 60 °C as you will start to dehydrate the gel coating that the chromate forms with the aluminum. In personal experience I have found that even 60 is a little too high and do not like to see the film exposed to temperatures above 50 °C.

Environmental degradation is much harder to judge as it very much depends on the conditions that the parts will be exposed to. For indoor environments with low humidity I would expect a life expectancy equal to the life of the part. In external, marine environments, with aggressive salty atmospheres such as you would find on the back of a frigate then the life expectancy could well be down to months, dependent on how well the parts are managed.

Brian Terry
Aerospace - Yeovil, Somerset, UK
Second of two simultaneous responses -- September 28, 2010

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