Process of Zinc-Nickel Plating

A. Hi, Amit. The supplier you are purchasing your zinc-nickel plating process from will have a "technical data sheet" instructing you how to operate it. It's a fairly complex process because you don't just need the right thickness and brightness, you need to maintain the correct percentage of nickel in the deposit or it will not offer the proper corrosion resistance. Good luck.

Regards,

A. Hi John. For standard zinc plating there is no doubt that 25 microns is better than 8 to 14. Standards like ASTM B633 call for 5 microns for mild exposure, 8 for moderate, 13 for severe, and 25 for very severe. To my knowledge 25-30 microns of zinc-nickel is not deleterious, but you might check with your supplier because there might possibly be difficulty with chromating, roughness, or something else they caution you about for their process at that thickness.

Regards,

A. Hi Manju,
Please enlighten us with:

- Barrel or rack plating?
- Acid Zinc-Nickel: which nickel percentage (low or high)? Do you test in hull cell? What are your parameters (potassium chloride, metallic zinc, voltage, time, temperature)? Do you test for iron?

I think that we can help you if you can give us more information.

Best regards!

Daniel

A. to Mr.Srinivasan:
Dear Sir:
As I got, in the production line you are having some kind of heat treatment i forging. May you should have a look to the Hydrogen Brittleness effect on your parts. to remove hydrogen from your surface, you can have a solution with HCl and a corrosion inhibitor such as Hexamine and a wetting agent like Texapon (or N70 as a gel or viscose liquid). All the materials should be there in the solution.

Regards.

A. Hi Gagandeep. Sorry, but there are whole aisles in technical libraries about how to do plating. Please start with a paragraph or two summarizing your situation, and hopefully we can begin a back & forth and make progress. For example, if you are an experienced zinc plater now venturing into zinc nickel, we can probably explain the differences. Thanks.

Luck & Regards,

A. Hi Kamaldeep.
Because the problem is visible before passivation, passivation is obviously not what is causing it. It sounds like your rinsing after plating is not adequate.
Luck & Regards,


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

A. Hello Jaime!

Finigard 200A has an (approximate) friction coefficient of 0,22. This is a little high for this application. Talk to you vendor to use another sealer with a friction coefficient more like 0,12-0,10. I think that with this values you will have a better (and stable) performance in this application.

Best of luck!

A. Hi Ravinder. If you are a Honda supplier, ask for this spec. They should give it to you because they are the only source of up-to-date Honda specs. I don't recall the "B" in Zn-Ni Honda specs, so it may be a new type of topcoat or a typing error.

Best of luck!

A. Hello Mr. Ramdasi,
Some waterborne cutting fluids can be rather caustic. They may contain detergents, and also substances to prevent mould growing. To begin your troubleshooting, you should determine the pH of the fluid in question. That information will give you a clue as to what the reaction could be.

  That was a concise and practical answer, Rachel. Should have thought of it myself … maybe I will next time :-)

Regards,

There's a first time for everything. Even brevity ;)

A. Hi Mangesh. For some fast ideas, please read this thread which we appended your inquiry to.

To take it further, please give us some data: pictures of the defects, substrate material, barrel vs. rack plating, alkaline vs. acid plating, chromate and sealer details. Is this a problem that just came up or have you been suffering from it for years? One reject per hundred parts or 99?

I'm not sure if we have a language difficulty or if you are actually looking for a salvage method rather than corrective action, so please clarify that point. Thanks.

Regards,

A. for black spots or pits on your alkaline Zn-Ni plated components, your Zn-Ni bath might be low in caustic -- this for me is the most common cause of blackness in the final product. So ensure you do a thorough bath analysis and check your level of Zn and caustic in your zinc nickel bath, then you can add a calculated amount of caustic or zincate concentrate. Also, ensure your pre-treatment process is effective,

I do hope this is helpful
Thanks,
Zik

  Thanks Zik.

Regards,

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

  Thanks ZIK sir.
After checking all parameters, definitely will come back with you.

Mangesh Taware [returning]
- Pune, Maharashtra, India

A. Kindly Check your Pre-treatment -- maybe acid pickle concentration is not in desired range.

A. Hi Mohan. Although there is a lot of discussion about black spots and patches on this thread, it is not clear to me why the 'machining supplier' cleans these plated parts. Are they assembled into something and then the whole assembly cleaned?

It is not a sure thing, but certainly possible, that the ultrasonic cleaning is harming the parts. Zinc nickel plating is invariably chromate conversion coated; the chromate is necessary, and it is certainly possible that an undefined cleaning solution in the ultrasonic cleaner is stripping the chromate. For example, thread 9406 says that you can remove the chromate conversion coating by immersion into alkaline cleaner or by boiling for 15 minutes.

Regards,

A. Hi Mohan. Although there is only 10% rejection, you said they get white rust in 60 hours whereas a good chromate conversion coating should deter white rust for 96 hours minimum, and a 192-hour or 256-hour requirement is often expected.

Other readers are welcome to offer their takes, but my first guess remains that the ultrasonic cleaning is harming the chromate conversion coating ... and it should be very easy to test by simply putting some plated parts and some ultrasonic cleaned parts in a salt spray cabinet together and tracking what happens. Good luck.

Regards,

A. Hi Mr Mohan,

I don't think your plating guy is doing a very good job with the plating.

Please also check the water quality of the process line.

A.
Hi Serhat!

Did you dilute all the bath or only zinc content? Did you use the same water you use in the process or distilled water? Is it alkaline or acid zinc-nickel?

Zinc content of 7 g/l for an alkaline bath isn't a problem, you get more plating time but not triple. You should see if anything is off parameters in this "dilution". High nickel content (in relation with zinc) decreases your throwing power, too, so as a complex bath as it is, you need to watch all the parameters at once and not one to one.

Help me with the other data and we can solve this mystery!

Regards,

A. Hi, Jonathan you are using wrong process so that your plated component has became blackish. you should follow the given process Zn Ni plating-drag out-water rinse - wr - hot water rinse - 0.2% sulfuric dip (not necessary)- water rinse dm water -passivation - two times water rinse - top coat/sealer. You will get very good colour as well very good salt spray life also more than 1000 hours. Awadhesh Avasthi - New Delhi, India A. Hi. Just to share my experience in Zn Ni alloy plating (alkaline). If you increase Zn concentration, it will reduce plating time, but you cannot increase too much, 9.5g/L, it will ruined your appearance. If you increase Ni concentration (still within the range), it will increase plating time. But too much Ni will take longer time to complete plating (my exp. up until 3 hours plating time. But, you need to be careful, make sure there is a balance between ZN an Ni content. I will control Zn between 7.5- 8.3 g/L and Ni 1.3-1.7 g/L Please bear in mind, current density will effect your throwing power and appearance. Thank you, Izzuddin Jaafar Asahi Aero Malaysia Sdn Bhd - Selangor, Malaysia

Hi Raja. I give up :-)
Google finds me no pages with that spec number or alloy. Please tell us whose spec it is or exactly what the substrate is. Thanks.

Regards,

A. Hi. If parts last 1000 hours (42 days) in an accelerated corrosion test, but the same parts don't survive 14 days when packed in boxes and shipped to your customer, it sounds like there are three possibilities:
1. The salt spray test results are extremely suspect, or
2. The parts were not dry when packed, or
3. Your cardboard boxes are high in sulfides or other materials that are causing rapid corrosion, or something about the transit conditions is extreme (tremendous vibration causing fretting of the coating, bold corrosive conditions in transit).

Take a few sample pieces and make sure they are absolutely dry, and seal them in polythene bags before throwing them in the carton with the other parts and see what your customer tells you about them. And leave one of those cardboard boxes on your own loading deck for the 14 days. This should not be hard to solve.

Luck & Regards,

A. Hi Stanislav. I'd vapor degrease a few if that is available to you, or otherwise let a few sit in the soak clean tank for an hour before continuing the processing and see what happens. I'd also scrub a few with pumice. It doesn't look to me like a problem that would develop in the plating tank, but earlier in the cycle.
Luck & Regards,

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

A. Hi Stanislav,
I don't have much experience with rack plating, but I do have some with hardened bolts and Zn-Ni plating. Do you use alkaline Zn-Ni? If you do, I suggest you make a flash plate in an acid plating (zinc or zinc-nickel if you can), bake for hydrogen embrittlement, and Zn-Ni plate after activating in caustic soda [affil links] the previous plate. This is how we do if our customer allows us. If not, you only can put the parts in the plating tank and make an extended cycle, of 3 or 4 times the standard plating time, to make all the parts plate.

Hardened bolts make it difficult for alkaline baths. Additives to make hydrogen overpotential rise don't work and almost all the electrons go to hydrogen making on the surface of the parts you plate. So, thickness is very low and not even.

If you are making this with an acid plating process (doesn't seem the case because of the low brightness of the passivated parts), you REALLY should improve the previous cleaning as Ted mentioned.

Best wishes,
Daniel
Daniel Montañés
Process Engineering Manager - Cañuelas, Buenos

A. Hi. That doesn't look to me like a high current density area unless the parts are racked horizontally with that end facing the anodes.

How are the parts hung on the racks? Is the end with the line marks at the top when they are racked?
Luck & Regards,

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

? Hi again. Maybe another reader will have a possible cause -- I don't see one. Any chance that those ends look suspicious before plating?
Luck & Regards,

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

? Wow! I've never seen such dramatic rack marks. I have no clue and am hoping to learn something from our readers.

Luck & Regards,


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

A. Hi Lamberto
1. Nice photos
2. It looks that many parts on the rack may require significant current. Sharp stainless steel tips of the rack are not good electrical contacts. Is there any chance that those tip-contacts just overheating (and it affects the plating conditions around them)?
Just my guess...
Good luck

A. Hi Lamberto
1. Nice photos
2. It looks that many parts on the rack may require significant current. Sharp stainless steel tips of the rack are not good electrical contacts. Is there any chance that those tip-contacts just overheating (and it affects the plating conditions around them)?
Just my guess...
Good luck

Hmm,
Alloy plating is always tricky, with one or both metals requiring complexing in order to allow deposition of both, and requiring that pretty rigid parameters be enforced. Somewhat counterintuitively, the contact points are the lowest current density spot on the part; still, the black deposits at the contact point when current is too low are quite surprising -- so thanks for sharing!
Luck & Regards,


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