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-----Ni strike & Ag cyanide plating don't cover low current density area
Quickstart:
Electroplating involves placing two electrodes into a conductive solution. One of the electrodes is the item you are plating, and is connected to the negative pole (cathode) of a power supply. The other electrode is usually a rod (or some other shape) made of the metal you want to plate with, and is connected to the positive pole (anode).
The power supply pumps electrons from the anode to the cathode; removing electrons from the metal of the anode converts the metal to positively charged ions which dissolve into the solution and are attracted to the negatively charged cathode. The ions migrate through the solution to the cathode. When they reach it the ions and electrons recombine to form metal on the parts.
Some areas on the parts will be further from the anode than other areas and, because the solution has resistance, those parts will receive a lower current density (LCD), which will result in less metal or no metal being deposited in those areas in accord with Faraday's Law. This thread addresses what can be done when no metal is getting deposited on a LCD area.
We don't want to leave any interested readers behind; if any jargon or concepts are presented which you don't understand, please chime in.
Q. I am plating an aluminum part (Al6101) that is U shaped and also has four peaks (with valleys) on the inside of the U shape. Cleaning and adhesion have not been an issue. Standard clean, etch, deox, zincate (single using CN Bondal). My sulfamate Ni strike and Ag strike are having troubling covering the valleys under the peaks inside the U shape.
I have already setup the Ni as follows; lowered Ni to 8 oz/gal, raised Cl to 8 oz/gal, keep pH 3.8-4.4, raised temp to 135 °F, strike for 2/3 mins @ 15/10 asf.
My Ag strike is 0.5 oz/gal Ag, 16 oz/gal KCN. Strike for 1 min at 5 asf.
Everything covers inside the U shape except a barely visible line that runs just under the peaks. All other parts without extreme LCD are plating fine. Any suggestions?
Plating Manager - Houston, Texas
October 16, 2025
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A. Hi Lance.
It might be that you have gone as far as you can with the nickel strike. I would expect better covering power from a complexed cyanide-based solution than from a simple salt like the nickel strike. Have you tried simply skipping the nickel and doing the cyanide silver strike directly on the zincate?
If you can't cyanide silver strike, or cyanide copper strike first, you may need a more complex answer like using an alkaline electroless nickel as the first step, or implementing auxiliary anodes.
If a pic is available (attach in e-mail to [email protected]), it might help.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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Q. I did try straight to Ag strike with live entry. The Al started gassing in 5-10 seconds of going in. I tried hitting them with 20 ASF in the strike and 5 ASF. The bondal Zn looks to be a good layer, but I think the Ag cyanide pH is just too high for the Al.
We do have a Cu cyanide strike further down the line. I didn't try it. I don't know why it would act differently than the Ag cyanide.
The customer spec says to use zincate, Ni layer and then the Ag.
If I had another tank space I would try a EN strike. Maybe I replace the Ni sulfamate. The EN strike would be a little slower but even in the lcd!
- Houston, Texas
A. Lance,
Did you try wood nickel strike?
Nickel chloride 20-30 oz/gal, Hydrochloric acid concentration 10 percent by vol, Ni metal 7-10 oz/gal
i think better throw at LCD.
Popatbhai B. Patel
electroplating consultant - Roseville, Michigan
While I agree Woods strike has better throw, I have tried to woods strike Al years ago. It never worked, pH is just too low. For the same reason I don't just add HCL to my sulfamate strike. To get a low enough pH to reduce cathode efficiency, it would be too low and attack the zincate/Al faster than it would plate it.
- Houston, TX
Q. I have a pulse rectifier available. That should be able to help me. I will try some pulse on/off frequencies, but does anyone have pulse timing for good Ni throw already? A good starting point? My pulse rectifier is high frequency, 0-1000 hz pulsing.
Should I make a second thread asking for pulse timing help?
- Houston, Texas
October 19, 2025
A. Hi again.
I'd suggest not starting a new thread because they get no immediate google coverage, but you might review thread 141/78, "High frequency pulse plating" and thread 356/35, "High Current Density Leveler For Sulfamate Nickel?" and add follow-ups to those threads, or continue the discussion here.
There is a report on those pages that, at least for one reader, frequencies above 500 Hz did not achieve anything due to capacitance effects turning 500 Hz into steady state. There is also mention there of using bipolar anodes, which sounds reasonably practical in your case, and much easier than wired auxiliary anodes.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Need quick confidential answers? $25
Need project assistance? $100/hr.
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