Letter 42088

Does any one know anything about the Cr3+ Yellow chromate?  

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We just received some parts from our supplier. it is claimed as zinc plating with yellow chromate. However, it doesn't look yellow at all. it more looks like clear chromate. our supplier told us that this is Cr3+ yellow chromate instead of traditional yellow chromate. does anyone know anything about this kind of finishing?

Ken zhang
A-1 - Miami, FL

Many of us know a reasonable amount about it, Ken, but you might want to ask a specific question if you have a specific concern. In general, shops are moving away from hexavalent chromating because of its toxicity, and are substituting trivalent chromates. These are inherently clear because the yellow color was the color of chromium in the hexavalent state. There are several different proprietary processes for trivalent chromating, and your plater should be explaining exactly what he has done and why. Some of these processes are not adequate substitutions depending on what your product is because some involve non-conductive topcoats, or aren't compatible with subsequent painting, or don't offer the corrosion resistance of hexavalent chromium. I''m not implying that this is the case, only saying that a substitution like this has to be thought out between the buyer and the plater.

Ted Mooney, P.E.  finishing.com Brick, New Jersey

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