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Plating combination

I would like some help in deciding the best combination of material plating for my application. I have a 6061 aluminum with a black anodized finish per MIL-A-6625C, type II, class III and I would like to use a nickel plated brass nut with it. However, I could use a zinc plated brass nut (zinc plating is less expensive).

Which is the best corrosive protective combination?

I would also like to learn more about the different plating processes, and corrosion protection. Where can I find reference material or resources?

Thank You,

John J. Gillis
- Saco, Maine
2002

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The nickel will look nicer both originally and with age. While nickel is significantly more noble than zinc, it probably won't cause the aluminum to corrode around the plated nut unless the exposure is severe. And the nut itself will be fine. The best plating to avoid corrosion of the aluminum is actually cadmium, but that is so much of an environmental no-no that it almost surely should be dismissed.

The best way to learn about these subjects is to consult some specialty books and journals and/or to join a professional society like the American Electroplaters and Surface Finishers society.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2002

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Thank you for your response Ted Mooney. I interpret from your response that Zinc is the better of the two? Nickel plate is acceptable if I'm looking for a aesthetically pleasing part.

Thanks,

John J. Gillis
- Saco, Maine, USA
2002

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2002

Yes the zinc is the better of the two. But I guess I'm saying that while zinc is closer to aluminum than nickel is, if the environmental exposure is adverse, zinc is not close enough anyway. Whereas if the environment is benign, the fact that nickel is further away should not be that much of a problem.

Further, none of the proposed finishes is particularly robust even on its own, so I am assuming the exposure will be benign. But that's only speculation--which is why I need to nag you to post the details of your "real world situation" rather than post abstract questions :-)
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey