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Are zinc passivation and chromate coating the same thing ?

October 21, 2011

Hello,

Is zinc plating followed by passivation the same thing as zinc plating followed by a chromate conversion coating?

Also, I have a customer that has a general plating specification that requires a top coat applied over the chromate. I have been told by several platers that they do not provide such top coats, and by other platers that the top coat is incorporated into the (Trivalent) chromate coating. I understand that many platers come up with proprietary coatings. Is it possible to have a supplemental top coat incorporated into the chromating process ? How do I certify that the required top coat has been applied in this case ?

Thank you for any help on this.

Ralph Jones
Quality Manager - Arlington Heights, Illinois

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Hi Passivation & Chromate film are the same.
Top coat is applied as per specification or if you require added Salt spray life or "life".
Please not that there is no certification required on top coat from you. Generally your client will specify this to you. alternatively the plater use a top coat to be more assured about the life. But there is one problem.sometimes the color of the passivation takes a "coated" look!!

T.K. Mohan
plating process supplier - Mumbai, India
November 28, 2011

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The expression "top coat" is too broad. At least one of the leading zinc and chromate suppliers has an organic top coat to go over hex or tri chromate. It increases salt spray protection. We cannot name the product here.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

November 28, 2011