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How can brass (an alloy) be electroplated?

I am a mechanical engineer who specifies fasteners and small parts for a variety of different kinds of equipment. I have run across numerous references to "brass-plated" components, but I have always been under the impression that electroplating deposits pure metals from the anode, therefore brass, being an alloy of copper and zinc, cannot be electroplated onto a metallic cathode.

Am I all wet here? If brass can be electro-deposited, how do the two separate metals from the anodes (copper and zinc) recombine on the cathode?

Gary McCormick
engineer - Sunnyvale, California
April 13, 2010

Hi, Gary. You are right that it's somewhat difficult electrochemically, but it is nonetheless commonplace. Copper is so much more noble than zinc that it would seem impossible to get any zinc in the deposit, but the copper is strongly complexed with cyanide or other agents in a way that makes it so sparsely available that sufficient zinc will also deposit to make brass platings of whatever the desired copper-zinc ratio.

In fact, it is even possible to plate brass compositions that are impossible to cast.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 14, 2010