Metal finishing Q&As since 1989

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What does Alodine do to the part?

2002

I have a request from our customer to coat a 6061-t6 aluminum component with Alodine. There is no specific type of Alodine requested yet. This part has some tight clearances between sliding components. ".0003in min" There will be non reactive thermal grease present in the assembly. "like bergquest xtic 3000".

My questions are: What type of Alodine would be best? Does the Alodine react with high molecular weight oils? Does the process erode the aluminum? How much? Does the coating build up? How much? Does the coating get hard? Does it stay sticky? Does the coating dry up and fracture when exposed to heat? How much heat? What else am I missing? Where is this going to go wrong?

Thanks,

Craig Hornung
- Harrisburg, Pennsylvania, USA

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Alodine is a trade name. The process you are speaking of is chromate conversion coating, also sometimes referred to as MIL-C-5541 or chem-film.

The coating can dry up, especially if heated within 24 hours of application. But it is very, very thin and I don't think you'll be able to even detect the thickness, let alone have to worry about clearances when you have a few ten thousandths of an inch.

Not always an optimist, but I don't think anything is going to go wrong.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

Also, if the grease is applied before the Alodine, there must be no problem (oil is generally hydrophobic and unreactive). If it is present before the chemical treatment then Alodine won't work.

Dado Macapagal
- Toronto, Ont
2002