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Alodine coating faded after heating

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One of our specification for Alodine is not to blister or peel off after subjected to heat at 250 deg Celsius at around 20 mins.
Does this really happen to Alodine? And why?

What happened was that the plating faded from gold into almost silvery white.
May I know the theory behind this effect?

Ronald
microwave devices - Manila, Metro Manila, Philippines

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It's not clear if you are speaking about aluminum parts or plated parts, and what they are plated with, if so.

Ted Mooney, P.E.
finishing.com
Brick, New Jersey

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Any chromate on zinc, cadmium, or aluminum will be completely destroyed at temperatures over 140 F, however, if you put it on thin and paint over, then you may cure the paint at higher temperatures. Left bare, 140 F is the top limit.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

Editor's note:
   Mr. Probert is the
   author of

Aluminum How-To / Aluminio El Como

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