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Chromating 6061 T6511

2005

For creating better corrosion resistance (against ASTM ASTM G85 [affil link] -94 A3 (SWAAT)) on 6061 T6511, I am considering conversion chromating. Since it concerns an automotive application, hexavalent chromium is out of the question. Compromising surface finish quality is also not allowed (since the product has sealing surfaces for O-rings).

- Is there a conversion chromating process that meets above requirements?
- Would anodizing meet the above requirements better?
- For volumes >1 million pieces. a year for products 30x20x20 mm what would be cheaper: anodizing or chromating?
- What is the difference between transparent and yellow chromating?

Thanks in advance for all replies.

Jaap Hoftijzer
Automotive Supplier - The Netherlands

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2005

Anodizing will provide superior corrosion (and scratch) resistance and will cost more. I'll get some argument on this one...but, if there is no color, there is no chromate film, so "clear" chromate is a myth. No color = no chromate.

Jeffrey Holmes, CEF
Spartanburg, South Carolina

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2005

Although it is a myth, do you know the difference between so-called clear chromate conversion coating and yellow chromate conversion coating?

Jaap Hoftijzer
Automotive Supplier - The Netherlands