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Eliminate Hexavalent Chrome on Cast Zinc

We purchase a zinc die cast part that has a hexavalent chrome coating to meet corrosion resistance requirements. As a result of new EU requirements we must immediately eliminate the hexavalent chrome finish. Our supplier has indicated that there is no other coating that will meet standard automotive corrosion (salt spray at temperature) requirements.

David Haney
automotive components - Flint, Michigan, USA
2004

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First of two simultaneous responses --

I am assuming that your zinc die cast parts are chromated, which is where the hexavalent chromium is introduced. Zinc electroplated parts are now using trivalent chromates instead of hexavalent chromates, but the corrosion resistance is not the same. There are several ways to improve this such as using a sealer on top of the chromate (silicates, etc.), or by applying an organic coating (acrylic, epoxy, etc.). Other options include replacing the chromate entirely with some type of organic coating-- paint, Zn- or Al-rich coatings that are bulk applied (fastener coatings), etc.

Toby Padfield
Autmotive suspension modules - Michigan
2004

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Second of two simultaneous responses --

Mr David Haney,

Trivalent Chromates have replaced Hex Chrome to meet ELV needs. Please contact your Plating Chemical Supplier. They will provide you with a wide choice of viable high corrosion resistant systems. There are more than 20 such suppliers in the USA.

Good Luck,

Asif Nurie [deceased]
- New Delhi, India
With deep regret we sadly advise that Asif passed away on Jan 24, 2016
2004