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Copper Strike on Iron Before Electrogalvanizing

We have been having some internal debate about whether a 0.5-1 micron copper strike before electrogalvanizing steel would have any effect on the corrosion performance in ASTM B117 Salt Spray. On the one hand it is a very small amount, but on the other it is a more noble metal stuck between two less noble metals. I was hoping to obtain some feedback on whether this has ever been done before and if there is any data suggesting the result. My gut reaction is that doubling the potential difference between your zinc coating and a now copper coated steel substrate would increase your corrosion rate and eliminate any scratch resistance due to the newly introduced copper-steel galvanic cell. We haven't gotten around to testing this yet but any advice would be greatly appreciated.

Hunter Martin
Research - Seattle, Washington, USA
December 16, 2010

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Hi, Hunter.

I was involved with the reconstruction of Philadelphia City Hall / William Penn Tower some years ago. A hundred plus years ago it was originally cast iron, with a very heavy copper plating (almost the thickness of a penny in some spots), and a zinc plated topcoat. Much of the original cast iron had to be scrapped due to corrosion and there was no belief that the copper plating had helped at all. To the contrary, the spec was changed so that in the reconstruction the copper plating was avoided.

Regards,

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