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  for Metal Finishing since 1989
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Dichromate substitute

We supply components to the truck industry. Many of the parts have a dichromate finish. Some of our customers have been asking us to investigate an alternate finish that is better for the environment. Do you have any suggestions of a finish that will not sacrifice corrosion resistance and is not a significant cost increase?

Gary Schafer
Project Engineer with 1st tier truck supplier - Grandville, Michigan
2004

The environmental concern is with the hexavalent chromium that is part of the chromate conversion coating. There are bath formulations based on trivalent chromium instead of hexavalent chromium which are being used to comply with the new requirements. If the current parts only require minimal to moderate corrosion protection (clear or yellow/gold chromate), then changing to the new trivalent chromates can be done without any significant loss in corrosion protection. Cost is a concern because of increases in chemical costs, increased process time, and lower availability. Application of a topcoat or sealant can increase the corrosion protection, but generally does not reach the same performance as olive drab chromate. For this you will need to look at zinc-alloy plating (zinc-iron is cheaper than zinc-nickel) with a trivalent chromate. Again, this can have a topcoat or sealer for additional protection. Other coatings to consider for small bulk parts include cathodic epoxy electrocoat and so-called "fastener" coatings applied by the dip-spin process.

Toby Padfield
Automotive module supplier - Michigan
2004

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Apparently you are using a zinc dichcomate finish or perhaps a dichromate conversion coating on aluminum. Most proprietary chemical suppliers have developed trivalent alternatives to hexavalent chromates and dichromates. Have you not contacted your current supplier to see if they have such an alternative? That seems like the obvious place to start.

Daryl Spindler, CEF
decorative nickel-chrome plating - Greenbrier, Tennessee
2004

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Is the dichromate coating a chemical conversion coating or a Sodium Dichromate seal on anodizing? If it is anodizing then there are alternative sealing processes that can be used to achieve corrosion resistance that (while not quite as high as sodium dichromate) is quite high - the most common of which is Nickel Acetate. What type of parts are they? We specialize in bulk anodizing of fasteners and would be happy to discuss alternatives with you if we can be of assistance, feel free to contact me through the link below.

Jim Gorsich
Compton, California, USA
2004