Sound technical content, curated with aloha by
Ted Mooney, P.E. RET
Pine Beach, NJ
The authoritative public forum
for Metal Finishing since 1989
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PLATING ON ALUMINUM Q&A
Q. Dear sir,
This is our process flow for silver plating on aluminium:
Rinses
Activation
Rinses
Caustic (earlier we used nitric acid results were not consistent)
Zincate
Rinse
Zincate
Copper followed by silver
Can you suggest a process in between activation to zincate rather than using caustic or nitric?
Apurv patwardhan- Pune, India
October 11, 2022
A. Hi Apurv. Sorry, I don't understand what you mean by "Activation" ... what sort of chemicals are in that tank?
A more conventional sequence would be:
Rinse
Caustic Etch
Rinses
De-smut (tri-acid or dilute nitric acid depending on alloy)
Rinses
Zincate
Rinse
Cyanide Copper Plating followed by Silver Plating.
I suggest you start with some lab scale testing.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Activation = Combination of nitric sulfuric givtane 70
Patwardhan apurv [returning]- Pune, India
October 14, 2022
A. Thanks, Patwardhan. I still don't know what 'givtane 70' is, but this does generally sound like a de-smut process :-)
Usually there is no step between desmut and zincate although occasionally an aluminum processor will go back for a very short 2nd caustic etch after de-smutting (which it sounds like you are doing), or a 2nd etch followed by a 2nd de-smut. But you are sort of asking us to suggest a 'silver bullet' because you want a suggestion of a chemical step to add to solve a problem but you have not described the problem :-)
We would probably like to hear what kind of parts you are processing, what the alloy is, and what is the principal problem. After that there might be follow-up questions about times, concentrations, temperatures, etc.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Sir the alloy is aluminium 6061. Yes activation is same as desmut process. Should I use temperature for caustic for better etching should it generate roughness at the end?
Apurv patwardhan [returning]- Pune, India
October 16, 2022
Aluminum How-To"Chromating - Anodizing - Hardcoating"
by Robert Probert
Also available in Spanish
You'll love this book. Finishing.com has sold almost a thousand copies without a single return request :-)
A. Hi again. Thank you for telling us the alloy. 6061 should be readily plateable.
Robert Probert suggests 120-140 °F in his book ⇨
If you don't want the finish to be rough, then no, your etch should not generate roughness at the end. Unfortunately, despite you telling us the process sequence and the alloy, your question remains rather abstract because all we can determine here is that the finish is not to your liking in some way or other. But I think we at least now have a clue that one problem is that the finish has too much roughness for you :-)
Is your etch a properly formulated etching solution or just straight caustic? Can you just etch for a much shorter time and tell us why that is not satisfactory? Thanks.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
A. You can plate directly on aluminium by immersion in 25g nickel chloride and 100 ml of HCl acid for 40 sec and then wash with water. This bath gives a layer of nickel on Al by dispersion method, then you can electroplate in any bath.
Ahmed Abo ouf- Egypt
May 6, 2024
⇩ Related postings, oldest first ⇩
Q. I WANT TO KNOW HOW TO PLATE ON ALUMINUM, FOR EXAMPLE IS NECESSARY, ETCH BEFORE ZINCATE? IS IT NECESSARY TO BRIGHTEN THE SURFACE BEFORE ZINCATE?
THANKS,
Cromoplastic - Caracas, Venezuela
2001
A. Etching is usually necessary, Rafael; bright dipping is not necessary and not recommended. Thanks.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Please, I want to know what is the appropriate method for cleaning aluminum before Zincate, I think is is:
1-Wash in gasoline and make friction with abrasive paper number 500.
2-Rinse, and wash with detergent soap, friction with some cotton on all sides
3-Rinse and now is the immersion on first zincate?
If you tell me the best methods for cleaning, I'll appreciate it so much.
Thanks for your attention, Mister Ted Mooney.
Cromoplastic - Caracas, Venezuela
Treatment &
Finishing of
Aluminium and
Its Alloys"
by Wernick, Pinner
& Sheasby
(note: this book is two volumes)
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A. Gasoline is never an appropriate cleaner; it's too flammable! You can clean the items with detergent, pumice
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Amazon [affil links] . Then dip it in water and assure that it is so clean that there is no water break.
Then etch for a few seconds in warm caustic soda.
Then rinse and, if the aluminum is a rather pure alloy, I think you should be able to zincate without a de-smutting/de-oxidizing step between etching and zincating.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Hi,
Thanks Mister Mooney. The etching with caustic soda, was the most important point of method for plating on aluminum forgotten by me. Now I'm etching after the cleaning described by you (with detergent, without gasoline), but the type of etching with caustic soda done by me is an electrolytic anodizing/cleaning in caustic soda with good results. I think is the same with warm caustic soda, because two pieces of cover aluminum motorcycle made yesterday came out well.
Thanks so much for your help Mister Mooney.
Cromoplastic - Caracas, Venezuela
A. Thanks, Rafael. I am sorry that I am still having some trouble completely understanding your questions, but you should not use electricity in the etch process, just warm caustic soda solution.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Q. Hi,
Again about etching aluminum before zincate. Please, how many seconds is the correct time into the caustic soda for etching. The last time I etched 15 seconds in anodic electrolytic etch in caustic soda. This is the same as I use for electrolytic degreaser, and was find, but if I plated different sizes of pieces I think is one maximum time to caustic soda.
Thanks so much,
Cromoplastic - Caracas, Venezuela
2001
Thanks, Mister Mooney.
Yes, everything is okay, for plating on aluminum. First step, clean and degreaser with detergent, soap, desmut and etching electrolytic caustic soda, with sodium cyanide (this is my electrolytic degreaser) 10 to 15 seconds 2 volts, and after zincate, strip with nitric acid, zincate again, and alkaline copper plate 10 minutes at 2 or 4 volts. Next, acid copper 10 to 15 minutes and nickel and chrome or gold or brass. All trials went very well and the brightness is good. Thanks again Mister Mooney.
Your Venezuelan Friend,
Cromoplastic - Caracas, Venezuela
2001
Hi, Rafael. It was my pleasure to help in a small way, but it sounds like you actually achieved success pretty much on your own. Thanks for the nice words.
Your American Friend,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ed. note--
Readers: we have nearly countless threads about plating on aluminum. Please search the site using a fairly tight search term.
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Q. Hi, I have a small old riveted aluminium boat. It has had bad oxidization on it between the seat and the floor of the boat I have taken the seats out by removing the rivets and want to remove the white oxidation before welding the seats back in again and repairing the holes with aluminium special rods that melt 200 degrees before the aluminium melts. I was thinking of using caustic soda but was not sure of the risks. How long to paint the solution on and I gather wash it off with water Ashley Dawsonrepair - Australia October 8, 2008 A. Hi Ashley. You are understanding correctly. Caustic soda does remove aluminum oxide but, given sufficient time, it also dissolves raw aluminum. I would not make it up too strong, probably 20%, and leave it on for about half a minute to one minute before rinsing thoroughly. Caustic soda is a dangerous chemical; make sure you are wearing goggles ⇦this on eBay or Amazon [affil links] & rubber gloves ⇦this on eBay or Amazon [affil links] , and always add caustic to lukewarm water; never add water to caustic. You appear to be a consumer rather than an aluminum processing shop, so we should mention that oven cleaner ⇦this on eBay or Amazon [affil links] is based on caustic soda and is also a dangerous chemical, but some people find spraying with oven cleaner more convenient than making up a caustic soda solution. Luck & Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey |
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