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"Alkaline Zinc Nickel Plating of Hardened Steels"

Current question and answers:

February 9, 2021

Q. I am having trouble Zn/Ni barrel plating high tensile bolts and washers. Parts gas excessively and appear to be plated in Ni only. Problem only happens on 10.9 and 12.9. Not sure if it is a striking problem or a pretreatment problem. Any opinions would be appreciated.

Dan Waters
- Victoria Australia
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February 2021

A. Hi Dan. Is your zinc-nickel plating process alkaline or acid? To my knowledge, cyanide and alkaline zinc will not deposit on high tensile steel due to the hydrogen overvoltage issue, and it's sounding like it's the case with the zinc component of alkaline zinc-nickel plating.

Options would seem to be to switch to acid zinc-nickel plating, start with a strike in zinc, or maybe even carry on, letting the nickel deposit first and act as a strike. But as you'll read below, adhesion of that initial nickel layer may be inadequate.

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Aloha -- an idea worth spreading
finishing.com - Pine Beach, New Jersey
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Previous closely related Q&A's starting in:

1998

Q. I am having difficulty get good adhesion of my rack plated alkaline zinc nickel to a 1566 steel thru hardened 55-62 HRC. My pretreatment consists of alkaline soak, alkaline electrocleaner ( reverse only) muriatic acid activation (6N) with adequate rinsing between each step. The parts are not blistering but when they are tapped together, the plating is chipped off easily. I have also tried a Wood's nickel strike with no success.

JEFF LOGZ
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1998

A. I don't have knowledge of this particular problem, but alkaline zinc-nickel is presumably similar in operation to alkaline zinc, notoriously difficult to plate onto hardened steel due to the hydrogen overvoltage situation. I suspect that you are going to need an alkaline de-ruster, and even then, you may need to put the Wood's nickel or perhaps a flash of cad or acid zinc on first. But you might seek advice from those who offer alkaline zinc-nickel, like Canning-Gumm, rather than relying on my guess.

Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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1998

A. As Ted indicated, hydrogen evolution is a vital factor affecting the adhesion of Zn-Ni plating on the substrate, in addition to cleaning processes. Does the chip-off occur on the parts from high CCD region or the projecting portion on the parts? It is very important to control temperature, concentrations, Ni to Zn ratio, additive, power and plating time. If temperature is too low (<70 °F), caustic concentration is under the specified range, organic additive concentrations are too high, CCD is too high, plating time is too long (over 0.7mil), Ni/Zn ratio is over the specified range, it is common to have chip-off problem. Ted provide you with a method, i.e. zinc-flash. I believe this process should help you a lot in solving this problem if your customer has no restriction on it.

Ling

Ling Hao
- Grand Rapids, Michigan
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