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Zinc plating of copper coated steel

Q. We have a situation where we are trying to zinc plate copper coated bundy tubing (used for auto hydraulic lines) with bright alkaline zinc. We are finding that when the parts are tested by baking at approx. 200 °C that the zinc is blistering and when examined there is a black smut on the part which when rubbed shows steel, not copper, and the back of the blister is also black.

It would appear that all the copper is migrating into the zinc causing it to be stressed, brittle and poorly adherent. It would also seem to be occurring even on heating to 100 oC. Results on plain steel tubing are perfect with excellent ductility and adhesion. Can anyone explain this or suggest any preparatory cycle to minimise this problem.

Geoffrey Whitelaw
- Port Melbourne, Australia
2003

A. Your assumption is totally right. Zinc and copper interdiffuse into each other. Remedy is to plate an intermediate layer of nickel in between.

Guillermo Marrufo
Monterrey, NL, Mexico
2003

Q. Why then does the problem not occur with copper plating zinc based diecastings?

Geoffrey Whitelaw
- Port Melbourne, Australia
2003

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