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topic 6173

Cadmium vs Zinc Electroplating


In general, which plating process introduces the most hydrogen into a high-strength steel part: Cadmium electroplating or zinc electroplating? Is there a significant difference? In other words,which process poses the most risk for hydrogen-assisted cracking in the future?

Marc Pepi
US Army Research Lab - APG, MD 21005-5069


Neither standard bath is highly efficient, so both introduce the problem. Baking is the usual relief process, but some people who know more material science than I do say that the cadmium or zinc entraps the hydrogen so it can't get out.

Perhaps your best bet is a low embrittlement cadmium plating process, one which has pores to allow the hydrogen to escape. One I'm familiar with is Boeing's TiCad process; a small amount of titanium dissolves into the bath and, when plated, the coating is porous.

Ted Mooney, Teds signature
Ted Mooney, P.E. RET
Pine Beach, New Jersey


Both of the above replies are correct in many respects. First it should be noted that the preplate cycle can cause hydrogen adsorption both from acid pickling and if cleaning is done with the work anodic(not preferred). Secondly, chloride zinc plating, because it has a much higher efficiency, tends to have less embrittlement from hydrogen; however, frequently the deposit itself is brittle!

Gene Packman
process supplier - Great Neck, New York

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