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topic 55804

Does Chromate on Aluminum Parts degrade ?


September 24, 2010

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


First of two simultaneous responses -- September 27, 2010

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 probert



Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
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Second of two simultaneous responses -- September 28, 2010

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



July 3, 2020

Ed. note:
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abstract questions
Please!!

What is the life of Clear Alodine coating on Al?

Rajasekar
shop employee - Chennai, India


July 2020

A. Hi Rajasekar. 168 hours in a salt spray chamber, longer in a more benign environment. Brian suggests probably as much as the life of the part in an indoor environment. Please see our note about abstract questions, and try to participate more fully. Thanks.

Luck & Regards,

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Ted Mooney, P.E. RET
finishing.com - Pine Beach, New Jersey
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