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Procedure for hard chrome plating onto electroless nickel coating

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Q. Aluminum material per customer requirement has hard chrome plating (only a few µm) after mid-P EN (about 8 µm). However peel off or blistering is found after 2-3 month.
Initially I thought that is somehow related to pre-treatment, so further standardized it, but problem unchanged.
Then I am looking into the EN might be getting a bit passive before entering the Chrome bath, so I cut down the rinse to 2X with 1 min each and quickly go into chrome bath, but problem still exists.
Now I suspect it might due to the EN is Ni-P alloy, which conductivity is not as good as pure Nickel. Maybe the acceptance for chrome process is not that good. So I will try Ni strike in between.
Any other ideas, your inputs are much appreciated.

Raymond Wang
- Singapore
October 15, 2020

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November 16, 2020

Q. This is the follow up of said issue.

Done Ni strike right after EN, by using NiCl2 and HCl, run at 3ASD for 5 min, then quick rinses and put into Chrome bath, serious blistering at edges (same Chrome parameters as previous thread, but blistering condition is more serious than w/o strike). So Ni strike failed.

  

  

Guys, any inputs?

Raymond Wang [returning]
- Singapore

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November 19, 2020

Q. Hi, Jeffrey,

Thanks for the comments.

Meanwhile, we have done some further studies on this issue, below are some findings.
(1) We took out the peel off layer and found it happened in between EN and Alu base material.
(2) wWe suspect maybe something related to the degreasing or the double zincate process, had done the new make up for the whole line; problem still exist (for this part).
(3) We uses flat Alu panel, repeated the exact same process, no problem.
(4) We tested Fe material, EN then Chrome, no problem.

So it seems the shape of this part, caused very high current density at edges during Chrome plating, and seems the high penetrating power of chromic "drag" out the EN layer from Alu material. This is my guess.

Next I will try to do Acid copper process after EN, hopefully the much better conductivity of Copper could help.

Will update afterwards.

Regards
Raymond

Raymond Wang [returning]
- Singapore

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November 20, 2020

Q. Hi, Jeffrey,

Well noted your points.

Below are some info related to your comments.

(1) material of said parts is 6061.
(2) the flat panel used to simulate entire process is the same batch of material as said parts. However there is no blistering found for flat panel.
(3) yes, there is micro-etch and desmutting before the double zincate. 5% of caustic 1 min for etching. For desmutting, 25% of HNO3 + 50% H3PO4 and additives from our supplier; consulted them: there is F in additives.

Regards
Raymond

Raymond Wang [returning]
- Singapore

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⇩ Related postings, oldest first ⇩

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Q. Dear all,

I want to deposit a hard chrome layer over an electroless nickel coating. Could anyone give me the proper activating procedure? Is there a difference if both coatings will be deposited as a plating sequence (from the nickel bath directly to hard chrome bath) or when the EN has already been plated (the previous day, week, month - whatever)?

Thank you in advance

Christos Sigalas
- Athens, Greece
2006

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A. Electroless nickel in not an advisable undercoat for subsequent chrome (nor for most anything else). It can be activated in a highly acidic nickel bath called Wood's activator. Although there might be issues if the surface geometry is complicated with entrant angles, slots or irregular contours. Since the Woods is an electrolytic treatment it will not cover up these areas adequately. Guillermo Marrufo Monterrey, NL, Mexico 2006 2006 A. Dear Mr. Watts, thank you for answering. First of all I am talking about rack plating only. Haven't tried yet the direct (EN bath - rinse - Cr bath) method. I will do it in the future but there are some questions even regarding this "simple" process. 1. Hot or cold rinse? (probably hot) 2. Standard water or deionised? 3. What if some nickel areas need masking or geometry of the part requires auxiliary anodes to be placed for chrome to reach hard to access areas? Or, on the contrary, if thieves need to be put, in order to avoid edge roughness? These actions take time. Will the EN coating dry during this time? As for the difficult one (old EN), what is the proportion in the acid mixture you mention? I have been told (and found in bibliography) that a Nickel Strike is necessary. I have tried alkaline cathodic cleaning, then a mild sulfuric acid dip, and then Woods strike before hard chrome. Sometimes it works, sometimes the chrome appearance is rather odd - rough matte surface like sandblasted in an area and good (like polished) elsewhere, or sometimes it is a total failure (chrome peels off). Any help would be much appreciated since my nerves are cracking, my boss is complaining and customers are impatient. Chris Sigalas [returning] - Athens, Greece

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2007 Dear Sir Please inform me about electroplating iron with chrome; the points I need: 1- procedures 2- quantity for chrome crunet equipment 3- safety issue for this procedure 4- if you have any troubleshooting Regards, Hassan quzmar student - Amman, Jordan Hi Hassan. There is a lot to it. Those subjects fill whole shelves in technical libraries, but for a quick introduction please see our "Introduction to Chrome Plating". After that, we have dozens of threads on the subject, but this one is about chrome plating onto electroless nickel rather than steel :-) Good luck. Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey June 2013

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