Metal finishing Q&As since 1989

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Is copper galvanically safe to use with a ZINC PLATE - Chromate

2006

What is the Galvanic response between Copper and ZINC PLATE - Colorless - (Clear) - Chromate - ASTM B633/85?

I can find lots of information about how pretty it is but the real question is, will corrosion occur when it is electrically connected to copper?

Will the copper corrode or is the galvanic response lower than that of Zinc and Copper by itself?

The Galvanic response between Copper and Zinc is .85 and electrical safety requirements are that the Galvanic response be less than .6 So what is the Galvanic response factor for Zinc/Clear Chromate?

Mark Derickson

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Mark, see MIL-DTL-14072 [on DLA]D FINISHES FOR GROUND BASED ELECTRONIC EQUIPMENT, available from ASSIST.
Paragraph 3.13.1.a. "Passivated Coatings. For a compatible couple selection, passivated coatings specified herein shall be ignored and only the plating or basis metal considered. For example, all chromate or phosphate coatings of zinc...shall be ignored..."

So, only consider the metals involved. Chromate may not be reliable protection between dissimilar metals, and may even act as electrolyte. Perhaps use tin plating rather than zinc.

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.
2006

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2006

Ok, now I may have mispoke about the material content.

The base material is Mild Steel. It is coated with Zinc and then passivated with the Clear Chromate.

If I can ignore the Chromate coating, Can I then Ignore the Zinc coating also?

Mild steel to copper has a galvanic response of 0.45 which is an acceptable level per the testing standard.

Mark Derickson