Zinc-Nickel Plating Intro, What & Why

A. Hi Anna,

Although it's possible that the plating does not have enough adhesion, it seems more likely that it's too stressed and brittle. Is it possible to reduce the amount of brighteners or other organic addition agents which harden the plating?

Luck & Regards,


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

A. Hi Esmail.

Let's see what other readers have to say, but in my opinion it will not be brighter nor more ductile. It's big advantage is additional corrosion resistance but the increased cost may be a difficult sell in the mild environment of paper clips and stationary products.

Luck & Regards,


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

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!

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A. Hi, Ramarao. Zinc-nickel plating deposits are made of zinc with a few percent of nickel in it (often 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.

A. Mr Rama Rao Yellamanchi

Namaskaramandi.

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.
Regards,

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.

A. Hi Ken.

Three things to try 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.
3. I suspect that the parts are not clean enough. Scrub some samples with a tampico scrub brush ⇦ this on eBay or Amazon [affil links] and a solution of pumice ⇦ this on eBay or Amazon [affil links] with a little detergent before running them through your 11-stage system and let us know if they still blister.

Some things to consider are that the plating ought to be able to withstand this temperature, and parts are often baked at this temperature as a QA test to try to make them blister immediately, rather than later.
Regards,

A. Hi Muhammad. We searched the site and appended your inquiry to a thread which we think answers it, but please post again if you have remaining questions.
Regards,

Regards,

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.

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!

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. But you should try to find a recognized international standard and require compliance with it; it will reduce such questions and contract disputes.

Good luck.
Regards,

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 B-117 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!

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.
Regards,

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.

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,

Good point, Daniel. A good sealer over the chromate may be the difference.
Regards,

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

A. Hi Roopak,
Your electroclean tank should be equipped with a grease skimmer/grease trap arrangement. This consists of a separate overflow compartment with a pump which returns the solution to a perforated pipe which skims the floating graphite into the trap.

Luck & Regards,

A. Hi Srin,
I have never seen erosion like that before. A few guesses:

I think that you are having an interaction of some of your chemicals on the pre plate steps. There are some strange combinations of chemicals that can become extremely aggressive. Think of aqua regia for example. Makeup chemicals are not terribly aggressive but together they can dissolve gold.
A touch of fluoride can make a world of difference in an anodic bath.

When you say alloyed steel, what alloy?

That said, I cannot think of any steel that you can activate with NaOH.

A. Hi Srinivasan. I think the part hit the anodes in one of the electrified tanks.

Regards,

A. Hi, Srinivasan. I appreciate the rack sketch, but I'm not there and can't explain what may have happened. But I persist that this doesn't look like chemical attack to me -- it definitely looks like an electrical burn from a short circuit, with this area of the part touching an anodic or grounded item. Good luck.

A. Dear Srinivasan,

Zinc Nickel plating is one type of zinc alloy plating which is having high temperature & corrosion resistance among zinc alloy plating.

Zinc nickel ratio composition in zinc nickel alloy chemical (bath Solution) is Zn:Ni = 10:01 and normally bath parameters range is Zn (8 to 12 grams/litre) Ni (0.8 to 1.2 grams/liter which is controlled by AAS ⇦ this on eBay or Amazon [affil links] method or XRF method.)

zinc nickel plating ratio deposition in zinc nickel alloy plating is Zn (85 to 90 %) Ni (10 to 15%) which is high resistance.

While nickel percentage is more than 18% in deposition and zinc percentage is less than 82% in deposition, during environmental tests ( salt spray test) direct appear red rust. Salt spray corrosion resistance is less when nickel % is more than 18 in deposition.

? Hello Norazma,
Are you plating with an acid or alkaline Zn - Ni solution?

A. Hello Norazma,
Most alkaline Zn - Ni baths run at about 25 °C (77 °F). The best bet is to consult the Tech Data Sheet for the bath from your Zn - Ni supplier. If you don't have one, ask your bath supplier. Proprietary plating solutions dictate temperature ranges. As far as the second part of your question, higher temps would normally speed up the deposition process. Are you having trouble maintaining the bath temp? Keep in mind higher bath temps will have an effect on the final finish cosmetics. Good solution movement, cathode bar agitation, and maintaining tight bath temp ranges is the key to consistent plating.

A. Hi Rao. That product is a powdered chromate formulation from Atotech for bronze iridescent chromating on zinc-nickel plating. Other suppliers such as Macdermid and Enthone presumably can offer equivalent products if access to Atotech products is not possible in your region. Good luck.

Regards,

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A. Hi Oscar. I think it should be possible to determine whether the nickel strike layer is peeling from the stainless steel substrate, or the zinc-nickel plating is peeling from the nickel strike layer. The corrective action would differ based on where the problem originates.

If the nickel strike is not sticking, I suppose it's possible that the parts aren't really clean. Try to get a look at Dini's "Electrodeposition", which has a chapter on "Adhesion" with lots of good data on nickel striking of stainless steel .

If the nickel strike is sticking, but the zinc-nickel plating doesn't stick to it (which seems to be what you are reporting) there may be too long a delay between the strike and the plating. The strike is a nickel-rich surface which rapidly passivates. Possibly the cadmium plating is better at dealing with this marginal passivation of the nickel strike. You may learn something from plating "stress tabs" in a Hull Cell. Good luck.

Regards,

? Good day Daniel.

I have been following this thread as I will soon be implementing the process.
I do not have any experience as yet with the process, but I am doing research.
My question to you is, "Both parts are pickled in hydrochloric around 10% (1/3 diluted 32%)".
I would believe this is a 33% HCl solution.
What are the process parameters for pre-dip?

Regards,

A. The localized attack to the ends of the parts could suggest something in the material. Is this limited to one coil/material of manufacture? I know it is the same material.

If you rule that out, I could be an End grain pitting/inter-granular attack. Is your acid inhibited? Are the pits visible prior to plating? Post acid activation? Inspect the barrels after every operation to help with trouble shooting.

A. Hi Lokesh. You can read the above for some ideas, but for substantive help you'd need to share significant data rather than just an abstract question, e.g., Is this a new installation not yet plating satisfactorily, or an existing installation that went bad? Acid or alkaline? Barrel plating or rack? Any Hull Cell panel info to share? What kind of parts, what kind of steel? Frequency and timing of the pitting, i.e., 100% of the parts all the time vs. 1% of the parts on the night shift. Gas pits (bright, hemispherical) or acid attack pits? Have you looked at parts after the acid dip and before plating? Photos to mooney@finishing.com for posting here if possible please. Thanks!
Luck & Regards,


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