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  for Metal Finishing since 1989
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Chromate conversion coating on aluminum

2002

Hi there,

I'm working with coatings for replacement of chromate conversion coatings on metals. I need some information on chromate coating.

Like: how to do chromate treatment on Al2024. Usually what kind of chromate treatment is used for Al2024 (aluminum alloy)? if any one can give me some info on this, it will be highly appreciated!

Thanks in advance!

Yanrong Zhu
UC - Cincinnati, Ohio

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First of two simultaneous responses --

My experience from running this forum for 13 years is that many readers consider the phrase "working with" to comprise a 'guarded question'. You probably won't get forthright answers until you pose the question in a way that the readers consider forthright, Mr. Zhu. Please tell us who you are and what you are doing, and you'll be better off. You might also talk to the vendors of the proprietary chromate conversion coatings you are trying to replace, as they will have the answers; but they may not be eager to help you put them out of business :-)

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

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Second of two simultaneous responses --

Did you try the convensional method used for 1000 and 6000 series alloys as follows?

Degrease - rinse - caustic etch - rinse - desmut in nitric acid solution - rinse - chromate - rinse - DI water rinse - dry at max. 70 °C.

Timur Ulucak
aluminum extrusions & finishing - Istanbul, Turkey
2002

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2002

Hi Yanrong,

Applying a chromate conversion coating to Al is a multi-step process. A basic pretreatment scheme is as follows:

1. Alkaline clean
2. Water rinse
3. Deoxidize
4. Water rinse
5. Chromate
6. Water rinse
7. Dry-off

The actual number of stages and the parameters in each stage will be dependent on the specific application.

George Gorecki
- Naperville, Illinois

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Hi there,

Thanks for the answers! I am working on a project about using conducting polymers as a corrosion protection coating for aerospace alloys like Al 2xxx. Our coatings showed promising properties. Our next step is to compare our coating performance with those commonly used commercial coatings such as chromate conversion coatings and epoxy primer coatings. I haven't found any sources to purchase some samples or to have people make some samples for me to compare with. That's why I'm asking the first question. It seems I can't make chromate coatings myself. If anybody knows where I can buy some, please let me know.

Yanrong Zhu
UC - Cincinnati, Ohio
2002

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Chemetall Oakite, EPI / Electrochemical Products Inc. [a finishing.com supporting advertiser], Heatbath, Macdermid, U.S. Specialty Color, and many others. Good luck with the project!

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