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Process of Zinc-Nickel Plating

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Q. I have an issue with the Zn-Ni coating on the padbolts I am buying in. The spec calls for 8-14 micron of 12%-16% Ni, and I am getting 1 micron in some regions.

The padbolts are plated assembled and the low coating areas are behind the bolt on the plate. The bolt is about 8mm (5/16") in diameter and has about 2.5mm (3/32") of play above the plate.

I was wanting to know 2 things:
-What degree of reduction in thickness of coating could be expected? Is this a reasonable loss of coating thickness?
-To those coaters who have coated padbolts, were they generally assembled or assembled after coating?

For context, the reason they are coated assembled is to ensure the sizeable pinch would be protected.

Andrew Speer
- Ballarat, Australia
October 13, 2023

⇩ Closely related postings, oldest first ⇩

Shortcuts to specific Q&A's about Zn-Ni Plating:

E-coating on Zn-Ni is blistering
Adhesion problem on stainless
Interpretation of spec

Parts are failing salt spray
Base Metal Erosion
Best temp. for alkaline plating

Pitting problem
Parts & Hull Cell Panel Are Dull
Is 25µ okay or too thick?
Organic sealant prevents insertion

Honda specs
Black spots from cutting oil
Black patches in alkaline Zn-Ni

Q. Sir,
We want to know about the process of Zinc-Nickel Plating. Can you please give us the process. Waiting for your reply at the earliest.
plating shop - Hyderabad, AP, India

A. Zinc/nickel alloy plating formula:
zinc chloride 130 gm
nickel chloride 130 gm
potassium chloride 230 gm
pH 5-6,temp.24-30 °C
separate zinc and nickel anodes.

Good luck!
Goran Budija
- Cerovski vrh Croatia

"Electrodeposition of alloys: principles & Practice"
by Abner Brenner

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A. Hi, Ramarao. Zinc-nickel plating deposits are made of zinc with a few percent of nickel in it (maybe about 6%). The idea is that this plating still offers sacrificial protection to steel like zinc plating does, but due perhaps to incapsulating itself in more stable corrosion products it does not corrode as quickly as zinc, and thereby provides substantially more corrosion resistance than an equivalent thickness of zinc electroplating. It is available as either an acid or an alkaline proprietary process offered by several suppliers in your area.
Although Goran is kind enough to offer a formulation, and although the process is discussed in Brenner,.
... the robust electrodeposition of alloys like this requires specialized chemistry, and plating shops generally do not attempt to formulate such processes themselves. It is one thing to plate one small item in a laboratory from a generic formula, but quite another to do zinc-nickel plating in a production environment. Good luck.
Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

A. Mr Rama Rao Yellamanchi


Zinc Nickel Plating is used for automotive components which are exposed to higher temperatures as found in engine components where other alloys such as Zinc Iron fail easily or Zinc Cobalt does not withstand the tempering caused by engine temperatures.

Zinc Nickel stands Salt Spray 500 hours to white rust and more up to 1000 Hours to red rust with the right passivate.

Processes to plate Zinc Nickel are available within India. Alkaline processes are preferred over acid systems due to the superior distribution and even alloy content all over the component. Cosmetic brightness is possible .

You will need a lined tank, a filter 4-5 times/hr bath capacity, rectifier 6 volts, cathode movement, and a good pretreatment line as if you were doing Nickel. The Passivates are not the common ones used for regular zinc. All colors are possible.

Lastly Zinc Nickel costs 5 to 7 times that of regular zinc, micron for micron over a unit area.
Asif Nurie [deceased] [deceased]
- New Delhi, India
With deep sadness we acknowledge the passing of Asif on Jan 24, 2016

A. Agree with the three previous responses. Use the low pH version of Zn-Ni only if you need shorter dwell times in the plating bath or more ductility.

Randy Lalande
- Hitchcock, Texas

E-coat is blistering on zinc-nickel plated parts

"Electrocoating: a Guidebook for Finishers"
by Electrocoat Association

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Q. Hi, I have a part that has zinc-nickel plating on it. We have an 11 stage immersion pretreat/e-coat system. I ran these parts thru our system in plant water and RO water (rinses only) I did not run them thru our alkaline cleaners because of removing the plating. So I just rinsed the parts and coated them with an epoxy e-coat. When the parts came out of our cure oven set at 375 °F for 45 min. to an hour they had small like popping (BBs) all over the part. I am wondering if the plating was breaking down because of the oven temp. or if there was some contamination on the plated part that caused this. I also had different part that had a cadmium plating on it, ran it the same way thru our system and had the same look to it. Any ideas what may have caused this? Need help. Thanks

Ken Cundy
- Mayville, Wisconsin, USA
July 25, 2012

A. Hi Ken.

Two things to do immediately are: 1. Put some plated parts in that oven or another oven for 45 minutes at 375 °F to see if the temperature alone causes the plating to blister.
2. Pop a few of those BB-sized blisters to see what is on the underside of the blister, and on the part underneath the blister to determine what is separating from what. First guess is the plating is separating from the substrate. Some things to consider are that the plating ought to be able to withstand this temperature, and that a bake is often used as a QA test to try to make parts blister early on, rather than blister later. I suspect that the parts are not clean enough.
Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Dear sir, please give me the formula of zinc nickel bath and others parameters. Thanks and regards.
Muhammad Amir
- Karachi, Pakistan
January 31, 2013

A. Hi Muhammad. We searched the site for you and appended your inquiry to a thread which we think answers it, but please post again if you have remaining questions.
Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Dear sir, please give me the chemical composition of zinc nickel bath and others parameters. I use acid zinc additive of above plating. Thanks and regards.

Muhammad Amir [returning]
- Karachi Pakistan

A. Hi Muhammad. Goran and Asif already answered this question, so I'm not understanding the re-posting. Could you please try your best to frame your question in terms of the answers already offered so we understand in what way the answers were inadequate for you? Thanks!

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

Zinc-nickel plating on 17-4 parts takes too long and blisters

Q. I have a Zinc Nickel line that does mainly Aluminum Bronze and 17-4 parts (aerospace). The Aluminum Bronze parts have no issues with adhesion and plating thickness. The 17-4 parts take twice as long to plate and then at post bake they start to flake or blister. Ideas?

Craig Hutchins
- Fort Worth, Texas, USA
February 5, 2013

A. Hi Craig,

Have you always had a problem with adhesion on 17-4PH steels, or is this something that has developed over time?

My initial thought was that the activation of the steel is insufficient to give good adhesion, but it is difficult to tell with the limited information that you have provided.

If this is a problem that has built up over time I wonder if you have had a build up of copper in the tank from the Aluminum Bronze and that this is depositing on the surface of the steel, causing problems.

Brian Terry
Aerospace - Yeovil, Somerset, UK

A. Hi
Craig Hutchins

To avoid problems of blisters you need a nickel strike before Zn/Ni plating for SS material ( 17-4, 15,5), it is recommended for 52100 material (high carbon) also.

Good luck!

Eduardo Lorona
- Tecate, BC, Mexico

Interpreting thickness and salt spray specifications for zinc-nickel plating

Q. For zinc nickel plating what should be the correct criteria to determine the correct plating thickness? The spec. is 8 microns minimum. The process is rack plating.

My current supplier is taking 3 readings from the part and reporting an average of 12.8 microns; but from these 3 readings one of the readings is below the 8 microns due to the geometry of the part and variation of the thickness. Some areas are as low as 5 microns but the highest areas are 14 microns. Is this a correct criteria to determine the part meets the minimum thickness required of 8 microns or any point inspected should be above the minimum required?

The position of my supplier is that if the part is plated to achieve the minimum of 8 microns in the lower value areas the areas where more plating is deposited might go too high to 16 / 18 microns and create a chip / flaking issue.

Also the SST requirement is 480 hours salt spray for no rust. The parts are showing slight red rust at 480 hours. Should this be considered as a failure or pass?

Thanks for your help!
Ebe Salinas
- San Antonio, Texas USA
March 21, 2013

A. Thanks for an interesting one, Abe :-)

First, if your spec is 8 microns minimum, that's what it says and that's what it means, and parts with 5 micron thickness are not meeting it (usually though, a spec will call for the minimum thickness to apply only to surfaces that can be touched by a 3/4" diameter ball). Of course, that doesn't mean that your plater is necessarily wrong about the parts chipping or flaking if they go to 8 microns minimum :-)

If you are the end customer, you get to decide how thick is thick enough, and how many salt spray hours is enough. If you are happy with the parts and are having no problems in the field, I see nothing wrong with reducing the spec to 5 microns minimum and salt spray hours to 432 hours rather than 480 hours in lieu of developing a whole new process. But if you are a subcontractor yourself, parts that measure 5 microns do not meet an 8 micron spec, and parts that show red rust in 480 hours do not pass a 480 hour test. Good luck.
Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. I have a current assembly with one material type 304 stainless steel and the other is 1008-1010 low carbon steel plated with zinc nickel chromate plus topcoat 8 µm. The assembly needs to pass 336 hours of salt spray, but can only achieve 50% of the required hours. I have attempted to have the 304 stainless steel nickel struck and then plated with zinc nickel chromate, but this did not improve the salt spray performance. I can change plating on the low carbon steel material, but the costs need to be similar to the current plating. Any suggestions on options for either component as far as plating that could offer 336 hours of salt spray performance?
M Gerken
Product Designer - Toledo, Ohio, USA
May 16, 2013

A. Dear Mr. Gerken,

First of all, you should put ONLY THE ZINC-NICKEL PART in salt spray and see the results to compare. If the results are good (more than, I say, 336 without white rust is fair), you have problems only with the assembly:

If the red rust appears in the contact surface or around it, we can think of galvanic corrosion (although you considered that when you zinc-nickel plated the SS304 part) or stress corrosion (if the parts are clamped or bent when assembled).

If it is the first one, you can try using a non-conductive lacquer or topcoat (if the one you are using is conductive) over the zinc-nickel part. This can prevent galvanic effects.

If it is accelerated corrosion by stress the problem, you can try some other chromate conversion coating, there are many vendors, and some top products can withstand up to 600 hours to white rust in salt spray (ASTM B117) for only-zinc-nickel-parts. Assemblies are a world apart.

AND... If you must, or want, to reduce costs and maintain corrosion resistance, you should try some organometallic coating on the low-carbon steel part. These products are conductive, compatible with stainless, corrosion resistance up to 1000 hours in salt spray, and the costs are, I think, lower than alkaline zinc nickel + topcoat. See for yourself!

Regards and good luck!
Daniel Montañés
- Cañuelas, Buenos Aires, Argentina

Q. Our supplier plated Zn-Ni with the average thickness of about 14.1 micron with 13.6% nickel. As per our customer requirement, the part should withstand 720 hours to red rust. But, we checked, the part got white rust at 240 hours and red rust at 552 hours. What is the reason to get rust before 720 hours.

Manikandan Arumugam
- Bangalore, Karnataka, India
May 22, 2013

A. Hi Manikandan. 552 hours is not horrible, and not cause for embarrassment, so communication is key.

Try to find out from your customer where this spec came from. If other plating shops are achieving it on these parts for your customer, you probably need to as well. But sometimes specs just come from a designer reading sales pap and not realizing that the highest salt spray hours come only on ideal parts. Or using the salt spray hours s/he previously obtained on a totally different part. So it may simply be that 720 hours isn't reasonable on this particular part.
Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

Q. Hi Ted,
Thanks for your valuable answer. The same part from other plating shop is achieving 720 hours of SST as per our customer spec. If you give related answer for my query in, I feel happy. Thanks a lot.

Manikandan Arumugam [returning]
- Bangalore, Karnataka, India

A. Hi again. 552 hours is not an embarrassing number, so it's hard to tell precisely why one shop got this while another has managed 720. But it seems that it can only be four possible things: they weren't tested in the same cabinet, or their chromate is better (which I tend to doubt), or their plating is either thicker than the minimum or more evenly distributed, or the composition of their alloy is slightly more corrosion resistant (less zinc).

Of these things, after assuring consistent testing, the easiest fix would seem to be to slightly increase the thickness of the plating if the customer does not object. Good luck.

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

A. Hello Manikandan,

I think that 14 microns of zinc-nickel (13% Ni is a really good alloy) should not show red rust in 500 hours of salt spray. Therefore, I think you should look for spots where the zinc-nickel is not 14 microns thick, and tell your supplier to achieve a minimum of 5 microns (or what it says in the spec you have) everywhere in the part to reach 720 hours of salt spray.

It is important to know (for me, at least) if it is a barrel-plated or rack-plated part. Barrel-plated parts have a more leveled thickness than rack parts, as the last ones don't move in the process.

As Ted mentions, the part is not achieving the corrosion resistance as spec, but it is not "horrible"! Your supplier must improve in leveling thickness (in my opinion, 14 microns even without conversion coating must last more than 400 hours) and maybe add some sealer over the conversion coating to get the white rust above 300 hours.

Hope you can solve this issue! Regards,

Daniel Montañés
- Cañuelas, Buenos Aires, Argentina

thumbs up signGood point, Daniel. A good sealer over the chromate may be the difference.
Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

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