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Non-toxic Chromate Conversion Coating

 

My cast aluminum parts have been coated with chromate conversion coatings per MIL-C-5541 Class 3. However, many automotive OEM's will not accept chromate (specifically Hexavalent chromate) effectively within 2 years due to toxicity. Trivalent chromate, if available, is considered short term alternate. Is there a coating that meet MIL-C-5541 class 3 (salt spray and electrical conductivity) but without chromate, and as cost effective as chromate?

Richard Leung
- Lowell, Massachusetts

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Hello Richard! Yeah, we have the same problem for military products that are to be sold in Europe. We are just starting to use a vendor that uses the SanChem process, and that vendor will certify the coating as meeting Mil-C-5541 Class 3. There are some specsmanship games you have to play with your customer since Mil-C-5541 has a Qualified Products List which doesn't include any non-chromate products yet. But we've been satisfied so far with SanChem's salt spray and conductivity results. Good luck! Lee Gearhart metallurgist - E. Aurora, New York   Will anodising work for you ? Khozem Vahaanwala Saify Ind Bengaluru, Karnataka, India

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Hexavalent chromate would not have to be outlawed to restrict its use if there were alternatives that were as simple, reliable, and cost-effective. But there are alternatives available from Sanchem and others.

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

Thanks for all the response. I'll try and test some proprietary non-chromate conversion coatings.

Richard Leung
- Lowell, Massachusetts

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Warning. If you use the no-chromated conversion BE SURE YOU SALT SPRAY TEST BEFORE YOU SHIP PARTS BY BOAT TO EUROPE.

And find out if your customer will allow a wax top coat because that is where they get the salt spray protection. The non-chromate conversion washes right off in salt spray in just very few hours.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

 

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My cast aluminum parts have been in production for 6 months with the non-chromate conversion coating from SanChem. No corrosion issue. Part is inside a Housing. A few lessons learned:

1. No spec. that I'm aware of.
2. Though not important, color appearance is not as uniform nor smooth as chromate.
3. Coating is even softer than chromate so have to handle with care. Color is dark so scratch is very obvious.

Richard Leung
Electronics - Lowell, Massachusetts

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Thanks for taking the time to update us, Richard. These threads often end to the sound of waiting for the other shoe to drop. This time you gave us the update. Thanks.

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