Metal finishing Q&As since 1989

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Plating on Sintered Metal Parts

I have a Sintered-Iron part that is powder-coated for its final final finish. The problem we have is that this part has a female thread where the coating is cut off of on the first one or two threads during its normal use in the field. With the substrate being iron, we obviously run into a rusting issue on these small exposed areas.

I'm thinking about putting some type of plated finish on prior to powder coating in an effort to provide corrosion resistance to areas where the coating is removed.

The appearance of the plating is not important - as we will be powder-coating for color and finish. I simply want to put down a reliable "backup" finish as a primer for the powdercoat.

I had thought that something like Zinc-Alloy plating would be a good place to start, but I'm interested in hearing if there might be any suggestions for a lower-cost treatment for this application. I expect that this would be a rack-plated part based on it's configuration.

Thank you,

Philip Sterrett
Metal Component Manufacturer - Rocky River, Ohio
2006

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2006

Philip

It is correct to plate a Zinc Iron Alloy layer using a good alkaline system followed by a Thick Film Trivalent Passivate, which is a great base for Powder coat or for regular paint.

The zinc iron can be a high alloy (0.8 percent iron balance zinc) which Black passivates well but does not take yellows of Blues and is cosmetically poor.
However under powder coat it won't show eventually.

The next alternative is to Plate a LOW zinc iron alloy where Iron is 0.2 percent, rest zinc. This accepts Yellow and blue Trivalent chromate as well as the Thick film Greens as well. All three accept Powder coat and paint.

The High Iron lasts twice to three times as long as the Low alloy all other things being equal.

Hope this helps.

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

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I agree, zinc nickel would be my first choice because of increased hardness and better corrosion protection. Zinc cobalt is a close second. If you need to plate further down into the threaded hole, electroless nickel would be the plating of choice.

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])
2006