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Electroplating - zinc alloys compared to pure zinc

I would like to know what the difference in corrosion protection is for bolts/fasteners electroplated with pure zinc, versus bolts/fasteners electroplated with zinc-cobalt, zinc-nickel or zinc-iron alloys. What will be the difference in price if you have parts electroplated with a zinc alloy versus parts plated with pure zinc ?

Pascal Verbiest- Ohio
- Belgium
2002

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2002

Zinc nickel, properly applied will be the best for fasteners. 1000+ salt spray hours expected. Zinc salt spray expectation is 350 hours. Zinc iron is the least expensive, Zinc cobalt is also good provided there is enough cobalt. All three are more expensive that zinc alone. But what price failure?

Don Baudrand
Consultant - Poulsbo, Washington
(Don is co-author of "Plating on Plastics" [on Amazon or AbeBooks affil links]
           and "Plating ABS Plastics" [on Amazon or eBay or AbeBooks affil links])

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Hello Pascal,

Look for papers on Cadmium replacement. As cadmium has been used in this application for quiet a few years and is now in disfavor for environmental reasons, there has been a fair bit of research on alternatives for fastener plating. "Evaluation of Environmentally Acceptable ALternatives for Cadmium Plating" by OCRC (ocean city research something), is an excellent document. Brooman has articles in Metal Finishing and Plating and Surface Finishing. Budman has also had fair bit to say in Metal Finishing. There are many others, but as far as I've read the issue is too complex for a simple answer. It does appear that zinc alloys often provide the galvanic protection of pure zinc. I've been researching a tin zinc chromium alloy for years and have looked into other alloys as part of my thesis, if you wish I'll send you what I've taken from what I've read.

Ian Brooke
university - Glasgow, Scotland
2002