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Zinc cobalt plating


Q. Need some information on Zinc Cobalt plating.

John Davies


A. I don't know if you were looking for the following information, but I needed to write it down anyway.

Zinc-Cobalt plating, quality issues for (may be used for other plating processes)

Specify alloy content and thickness at a specific site on the part, on your print, specify the usual things like brightness, smoothness, adhesion, general good plating etc, on some document you reference on the print.

The alloy content is not going to be easy to hold. The platers will scream bloody murder when you specify alloy content for a specific area, and most people will be convinced by their specious arguments to leave this out, but alloy plating will get a bad name if we don't do this. They will say 'we know what we are doing', 'we're the experts', you can't do this or that, you can't hold that alloy content, etc. This part of the business is quite fun.

Some of the parts I have seen for zinc alloy plate are fuel system components, shaped tubing etc. You will want to audit the specific racking procedure for each part to see if they are compliant with good plating practice, otherwise, the reject and failure rate on the parts will be high enough to drive you batty, and zinc alloy plating will again get the bad name.

Alloy plating will require more than the usual training OR more than the usual documentation for a plating line. Adding the alloying element is tricky, since it is present in such low concentrations in the bath. The alloy content in the bath can easily go to zero, which only means you are now paying premium prices for a zinc plate.

From what I have seen of it, zinc alloy plating is a nice finish, but requires special care in equipment, maintenance, training, instrumentation, documentation, and auditing. Just because you ran a Cadmium cyanide line doesn't mean you can run Zn-Co.

tom pullizzi portrait
Tom Pullizzi
Falls Township, Pennsylvania


A. Hello, John. This kind of inquiry for general information, may be best answered by vendors forwarding you brochures about the process, so you might want to leave an address.

Basically, zinc cobalt is an alloy plating system designed to give some advantages not obtainable with plain zinc. Usually chief ones are a more favorable electrochemical potential, a corrosion product which does a better job of sealing the underlying metal from the environment, and corrosion products which don't gum up the works. People who are replacing cadmium look to zinc cobalt (among a range of other alloys such as zinc nickel and tin zinc) as a possible replacement coating.

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


A. There have been a few articles in the trade magazines and several at the last Sur Fin (1996) which you can get copies of (for a fee) from AESF. Virtually every plating supplier carries it and would dearly love to bury you with information and your closest plater that uses their product if you are not a plater. It is a nice product but make sure that it is not nickel or iron zinc that best suits your purpose . None of them truly replace cadmium, but that has become a four letter word in our politically correct world.

James Watts
- Navarre, Florida


A. Alloy plating is not as bad as it seems to be. I will not recommend you a propriety product as it will sound commercial but make sure you use an alkaline solution, not an acidic version. It is true that you need to monitor cobalt content in solution and in deposit but it can be done with the aid of a spectrophotometer. Sara

sara michaeli
sara michaeli signature 
Sara Michaeli
chemical process supplier
Tel-Aviv, Israel


A. I recently heard a talk by Mr. Ed Budman, there are lots of choices in zinc alloy plating, with new ones popping up every month. Maybe an acidic version has some advantages in some applications.

Tom Pullizzi
Falls Township, Pennsylvania

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