Metal finishing Q&As since 1989

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HiTemp impact on Alodine WRT US Army Helos

I am a contractor working for the US Army and attempting to track down the validity/criticality that Alodine breaks down in high temperatures. This is significant if required to switch processes for newly manufactured aircraft and even more so if required to "retrofit" existing aircraft. Can someone speak to the short and long term effects of an Alodined aircraft in this environment? Also, is it of such concern that this process be abandoned?
Don Estes
QTEC Inc.
UH-60M Black Hawk
Systems Engineering

Donald Estes
US Army Systems Engineering - Huntsville, Alabama
2005

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First of three simultaneous responses -- 2005

Any one of the several shops in Huntsville can apply chromate to your panels and then you can bake them at 120 °F, 140 °F, etc. and see where and how long it takes to completely dehydrate and fall off. I remember when NASA had three shops at MSFC that had chromate tanks.

Or you can just take the word of MIL-C-5541 which limits post treatment on bare chromate to 140 °F.

It is common knowledge that heat dehydrates the gel and causes it to fall off.

Look up Max Sharpe who used to manage one of those NASA shops, look in the phone book, he is probably retired and out shooting doves or ducks.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

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Second of three simultaneous responses -- 2005

The military built those helicopters for a number of years to rigid specs. Is there a problem that might have a root cause by the high temp? If there is no problem, then why fix it?
The problem with chem film (Alodine is a trade name of only one brand) and heat is it dehydrates the "gell" film turning it to a powder which will rub off. Once it is painted, the dehydration is significantly retarded so it can stand a much higher temp for a longer period of time.
The exact point of failure to a painted part has not been determined, because there are too many variables.

James Watts
- Navarre, Florida

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Third of three simultaneous responses --

Indeed conventional chromate conversion coatings on aluminum (a.k.a. chem film) and widely called both Iridite and Alodine (chemical suppliers under trade names of Macdermid and Henkel) all START to lose their corrosion resistance when subjected to temperatures over 140 °F. Basically these chromate films owe their protection to a gel-like film that dehydrates upon exposure to these elevated temperatures. This fact has been known for years and despite serving as a heat cured paint-base and in electronic applications that are obviously over 140 °F, these dehydrated chromate films are still providing the necessary degree of protection. This is not to say we should disregard this cautionary measure, however, the Black Hawk fleet is still functioning and other aircraft employing the use of this coating are still air worthy.

Milt Stevenson, Jr.
Syracuse, New York
2005