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Black Zinc Cobalt vs Electroless Nickel plating over Aluminum

I would like to know what is the difference between using Black Zinc Cobalt versus Electroless nickel over aluminum in terms of corrosion resistance. Which one is better for land use or marine applications.

Joey Madison
Distributor of Electrical Industrial components - South Bend IN
May 15, 2009

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Hi, Joey. If you were applying these coatings to steel rather than aluminum, the difference would be very clear: zinc cobalt would be a sacrificial coating that offers cathodic protection (in the event of a scratch or pinhole) whereas electroless nickel is a very stable and corrosion resistant coating, but a barrier layer coating.

In the case of plating onto aluminum, electroless nickel is an outstanding coating as long as it is not breached, in which case it anodically accelerates the corrosion of the aluminum. Zinc-cobalt does not offer cathodic protection to aluminum, but the electrochemical potentials are at least fairly close.

I would say that if the coating is likely to get breached, zinc-cobalt is a better choice; if not, electroless nickel is better.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
May 15, 2009

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Maybe I am missing something but zinc cobalt is plated from a highly alkaline solution. IT will dissolve the zincate layer and attack the aluminum in no time.
I have seen a lot of EN on aluminum but never seen zinc cobalt on aluminum

Sara Michaeli
Tel-Aviv-Yafo, Israel
June 4, 2009