Summary for zamak 5 humidity tests Discussion
Zamak 5 parts do not pass humidity tests with a clear chromate coating, and the questioner asked whether switching to Cu-Ni-Cr would help. Ted Mooney notes the issue as a finishing problem on a difficult alloy, but the only direct technical advice in the thread comes from Robert H. Probert, who suggests trying a different approach before abandoning the system: plate pure zinc over the Zamak 5 to mask the surface metals that do not "take" chromate well, then apply a good zinc chromate over that zinc layer. The thread does not report a final tested result or confirm that Cu-Ni-Cr is the best replacement, so the discussion is more of a troubleshooting suggestion than a definitive solution.
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?
Zbigniew Piotrow
– Auburn Hills, Michigan, USA
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, P.E.
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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 | 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.
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.
July 12, 2013 |
