Letter 12057

Trivalent Chromium Plating with Different Colors 

I am researching if you can get different colors with the Trivalent Chromium Plating. We have a lot of similar looking parts in our manufacturing process and one of the ways we visually identify these different parts is by plating them with different colors using Hexavalent Chromium. I would appreciate if anyone has any info. on the above question.

Santosh Hombal
BorgWarner Automotive - Dixon, IL, USA

I think you are doing chromate conversion coating on zinc plated parts, not chromium plating. Chromium plating is the bright silvery color you see on the bumpers of pickup trucks.

Chromate coatings will absorb dye, and that is probably the best way to color them. After chromate conversion coating and rinsing, the parts are immersed in a hot water tank with dye in it.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

It is quite common these days in the auto industry to talk about "Hexavalent Chrome Plating" and "Trivalent Chrome Plating" when they really are not referring to chrome plating at all. Changing hexavalent chromate conversion coatings to trivalent chrome substitutes is a big, important issue for the automotive industry. However, technical familiarity with finishing processes is not common in the auto industry. So, many people in the industry will use the above terms when talking about the conversion coatings of zinc or zinc alloy electroplatings. It is not correct, but be aware that it is a commonly used term now.

And no, there really isn't any "true" colored trivalent chrome conversion coating yet. There are some yellows and maybe some blacks out there, but as Ted was saying, I'll bet they are all using dyes to achieve the different color. The R&D folks at the plating chemical companies are hard at work on this issue.

Tim Neveau
- Rochester Hills, MI

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