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How to nickel plate aluminum?
Quickstart (no readers left behind):
It is generally not possible to electroplate directly onto aluminum because it instantaneously oxidizes, whereas for proper adhesion the plating has to grow onto raw metal not an oxidized surface.
What is almost universally done is to "zincate" the aluminum first. This involves immersing the aluminum into a concentrated solution of zinc and caustic soda, which forms an "immersion" or "replacement" coating of zinc on the aluminum; then the zinc surface can be electroplated with any plating which is plateable onto zinc.
As an alternative to electroplating onto the zincate layer it's also possible to do electroless nickel plating on it, and some people find this more reliable.
For reasons that are debatable, adhesion onto aluminum is sometimes improved by "double zincating" -- zincating the aluminum, stripping the zincate in nitric acid, and re-zincating.
Q. I am trying to electroplate a bright nickel coating onto aluminum. I have a zincate layer followed by a copper strike layer. I have tried adding brighteners to our nickel sulfamate bath but the plate is very brittle. I have also tried a Watts nickel bath but the same thing happens. Every bath that I have tried is always brittle. I need shine with great adhesion.
Molnar- Canada
2001
A. Skip the Copper undercoat as this will give you adhesion problems contrary to popular belief. Double Zincate your parts carefully and directly plate in a normal Watts Bath.
Regards
Khozem Vahaanwala
Saify Ind
Bengaluru, Karnataka, India
A. After the double zincate I would advise to use an alkaline electroless nickel and then you can use a Watts nickel. If you skip the alkaline EN then you will need a cyanide copper followed by a Watts nickel.
One more thing, are you sure that the problem is brittle nickel? Maybe it is a poor adhesion coming from inadequate pretreatment. You did not mention a deoxidizer prior to the zincate. I hope a deox is a part of your preplating processes otherwise you will have adhesion problems.
Sara Michaeli
Tel-Aviv-Yafo, Israel
Multiple threads merged: please forgive chronology errors and repetition 🙂
Q. I have just plated bright nickel on 6061 aluminum but the nickel peeled off after heating. My pretreatment can process A356 and ADC12 aluminum casting without peeling. What do I have to change : Etching, desmut or zincate?
Thank you for all answer.
electroplating co. - Bangkok, Thailand
2007
A. It needs a proper alkaline cleaning, a deoxidation/desmut, double zincate, a strike and then plate. I think that the alkaline EN strike is the best one for this step. If not that, I would look at the sulfamate nickel to strike (the Woods nickel strike is tough to use here, because it is a very very strong acid and slow to strike),(it will wipe out your zincate before it can get a good strike)and then immediately into a quick rinse and into the bright nickel tank
James Watts- Navarre, Florida
Q. Thank you for your advice. But I try to plate it with your recommendation, It does not work. I etch the Al with alkaline etching and go to desmut (Tri acid with Ammonium bifluoride) and double cyanide zincate then strike with Watts nickel strike for 10 minute and go to bright nickel and chrome. After heating it to 220 °C degree for 1 Hour ,the strike layer peeled off from the aluminum.
My customer confirmed that their aluminum is 6061 T6 for sure, they show me certificate for ensure these aluminum.
Does anybody have another to accomplish this case.
Thank you so much for your kind.
[returning]
electroplating co. - Bangkok, Thailand
A. Tell me exactly how you do your double zincate step, including concentrations.
James Watts- Navarre, Florida
Q. Thank you James watt that followed my question
I got better adhesion. There was not any peeling or bubbles after 1 hour baking but many bubbles came after 24 hours.Why
My zincate is 60% by volume and first zincate is 1 min and second zincate is 30 seconds.
Strip zincate with 50% nitric acid.
I notice that after desmut the aluminium is not stained or and smut; and there is no peeling of both first zincate and second zincate.
Someone told me that 220 °C may well too much, that 150 °C is more appropriate. What do you think, James, what should I do next for getting better adhesion?
Thank you again
[returning]
electroplating co. - Bangkok, Thailand
Readers may also be interested in these related threads:
• Topic #464/76 "Electroless Nickel (EN) Plating on Aluminum"
• Topic #275/75 "Preparing electroless nickel surface for better adhesion"
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