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topic 59332

Zamak 5 parts do not pass humidity tests



July 10, 2013

Q. Hello, I have a problem. Zamak 5 parts do not pass humidity tests. The coating is clear chromate coating. I'd like to replace it with Cu-Ni-Cr. Could you advise?

zamak 5 part

Zbigniew Piotrow
- Auburn Hills, Michigan, USA


July 11, 2013

A. Hi Zbiegniew. Yes, properly copper-nickel-chrome plated Zamak will pass any humidity test. However, it will be much more expensive.

Thank you for the excellent graphic, but I'm not quite sure what I'm looking at. The black item is perhaps powder coated? The baseplate with the phillips or torx screws is apparently a chromated zamak item, but are the castellated nut and stud zamak or are they zinc plated steel? An unaware mechanic would snap a zamak stud in a heartbeat.

Because of galvanic corrosion concerns it is necessary to understand what material all of the items are made of because they are all electrically connected. I think I would lean towards zinc alloy plating everything except the powder coated component. Good luck.

Regards,

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

simultaneous
July 12, 2013

A. That idea might work but only if it is done properly. Done improperly, the part might look good after plating but will fail the testing miserably. Bright acid copper, duplex nickel and tight control of the Cr deposit should be maintained. If you have a small pit or two caused by careless plating or incorrect process the coating will probably fail quickly.

I see you have threaded parts there. No matter what coating you try you might want to go thick. For example, if you try to hone the existing process you could perhaps go much thicker. If you go with Cu-Ni-Cr, a thick duplex Ni would be good.

blake kneedler
Blake Kneedler
Feather Hollow Eng. - Stockton, California


July 12, 2013

Before you switch to Cu-Ni-Cr, try plating some pure zinc over that junk alloy to cover up the metals on the surface that do not "take" the chromate, THEN, apply a good zinc chromate over the pure zinc.

robert probert



Robert H Probert
Robert H Probert Technical Services
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