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Trivalent bright chrome plating offers no corrosion resistance

I have recently come upon an interesting issue. A company that I work with has their zinc die cast parts coated with hexavalent bright chrome. They have tried trivalent as well, but it did not provide adequate corrosion resistance. The difference was quite dramatic: the hexavalent chrome coated parts last years in an outdoor environment, whereas the trivalent chrome coated parts last less than a day. Is this normal? If so, why is there such a great difference?

Jim Treglio - scwineryreview.com
PVD Consultant & Wine Lover - San Diego,
California
December 19, 2010

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Hi, Jim.

The usual complaint against trivalent chrome plating is that the coating is darker and not quite as aesthetic. It is possible that the corrosion resistance is somewhat less, but in the absence of other facts my guess is that the two parts came from different shops that are doing a lot of things different, not just the chrome plating.

Without any chrome plating at all, the underlying nickel plating on high quality nickel-chrome plated parts should last a very long time. Finishing.com recently had some zinc diecast parts nickel plated for an IZA study and the parts did very well in a 6-month accelerated corrosion test.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
December 20, 2010

I will guess that there is a major difference in the thickness of the chrome. Trivalent used to be limited in the thickness that could be applied.

James Watts
- Navarre, Florida
December 23, 2010