Plating aluminum with copper

A. Hi Aon. I am personally unfamiliar with plating pyrophosphate copper onto zincate. Obviously there are lots of things I'm not familiar with :-)

But the adatom reactions that proceed at the atomic level during plating are not always known and fully understood; it might be that copper pyrophosphate on zincate just will never work as well as Watts nickel. But if you search the site with "copper pyrophosphate zincate" you will find replies from people who are very familiar with this process :-) Luck & Regards,


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

A. Hi again. The pretreatment before plating on aluminum is the same as the pretreatment before anodizing or chromate conversion coating:
vibratory or tumble finishing, non-etch caustic cleaning, etch in caustic soda, desmut ... and then single or double zincate, then cyanide copper.

Luck & Regards,


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

A. Dr. Dovigi:

The surface of aluminum items almost instantly oxidizes, so that the surface is not active and not amenable to plating. A solution is to zincate the item first, replacing the aluminum surface with a zinc surface, which is plateable. Even then, copper is far more noble than zinc and will immersion deposit pulpy and non-adherently from a copper sulphate [affil links to item on Ebay & on Amazon] solution. You would need to cyanide copper plate or copper pyrophosphate plate before you do the acid copper. There is a lot to the process, and you'll need to read a few chapters on this from the plating texts before starting.

Even then I question whether you are approaching things the best way. My belief is that infrared reflectors are usually bright dipped, anodized, and gold dyed, rather than copper plated. It's simpler, less expensive, and more reliable.

A. Sir,

As an anodizer I agree with Ted ... hardly any of the platers I know plate on Aluminum. We process many reflectors here with bright dip and clear and colored anodize.

A. Hi again. Please research whether I am right that bright dipping, anodizing and gold dyeing will deliver the infrared reflectivity you desire. It doesn't make sense to keep struggling to invent a process for adhering gold foil or gold plating onto the aluminum unless the well developed and much cheaper, simpler, and more robust method I described fails to offer something you need. Good luck.

Regards,

A. Plating on aluminum usually requires a zincating step. Your supplier, or the brush plating suppliers listed at www.finishing.com/chemicals, can provide the zincate. The actual process is to clean the aluminum, etch it with caustic, desmut with an acid appropriate for the particular alloy, zincate, strip the zincate in nitric acid, re-zincate, cyanide copper plate, acid copper plate, nickel plate (often 2 or more layers), then gold or chrome.

I don't know of any articles that tell you how to design brush plating systems, but
- The Electroplating Engineering Handbook, edited by Larry Durney is all about designing tank plating systems, and
- Rubinstein's Electrochemical Metallizing is an encyclopedia of info about brush plating.

Best of luck.

A. All of the major brush plating vendors have methods for plating on aluminum.

At least one vendor has a procedure for plating on aluminum (simple shapes) without the zincate and claims good adhesion. You have to be quick and good to do it however.

A. Dear Mr. Ostrovsky,

Thank you for your letter.

It sounds to me that you want to make the circuit paths of a wiring board using aluminum, and you just want to plate "tabs" at the soldering points using some kind of copper plating. Using a robust activation system using a metal cleaner, then a zincate as you describe as the aluminum bonder, followed by an aluminum tolerant electroless nickel, then a electroplated copper, then electroplated tin should provide a solderable surface for your connections.

Regards,

A. Dear Stefan,

It's the other way around. In my experience the Rochelle baths don't work well once you use zincate covered parts in them . A Standard bath works better, has better LCD coverage when using zincate or zinc diecast parts.

A. Hi Stefan,

The best copper solution to use for plating on zincate is follow copper solutions:

Alternative No. 1. Copper cyanide 41 g/l Sodium cyanide 56 g/l Rochelle salt 60 g/l sodium carbonate / washing soda [affil link] 30 g /l pH-range 10-10,5 Free Cyanide 8,0-10,0 g/l Temperature 45-60 °C. Current 2-3 A/dm2

Alternative No. 2. Copper cyanide 26 g/l Sodium cyanide 32 g/l Rochelle salt 30 g/l Sodium carbonate 30g /l Free cyanide 1,5-3,0 g/l Temperature 45-60 °C. Current 2-3 A/dm2.

You should also use pre-contact when you plate on zincate in electrolytic solution. The zincate dissolves in copper solution. Zincate is only one protection for eliminate at the aluminum shall oxidize and thereby create bad adhesion between copper and aluminum. It is only a very thin zincate films on the aluminum substrate under copper deposit.

Regards,

A. I can tell you general plating method of copper on aluminium:

1. etching(NaOH)
2. desmut(HNO3)
3. zincate
4. strip(HNO3)
5. zincate
6. copper cyanide strike
7. copper cyanide(high concentration)
8. acid copper
9. nickel
10. chrome

Why use Pt anode? Copper ion source are solution and anode.

Thank you!

A. Electroplating is more of an industrial science than a hobbyist art, Michal, and it's not clear what facilities, training, and experience you have. But plating copper onto aluminum would require zincating, followed by cyanide copper plating, followed by bright acid copper plating. Our "must-have booklist" will cover each of these subjects in depth.

But I think you should be able to more simply "paint" your bike with a system of primer, copper-based paint, and patinating solution instead. Good luck with it.

A. Hi Venkata. Aluminum bus bar is commonly copper plated because the copper has better surface conductivity (because aluminum quickly oxidizes in air to form an insulative aluminum oxide coating on its surface). But the copper plating is usually not thick enough to significantly alter the DC capacity of the bus bar. For example, if an aluminum bus bar has 50-60% of the conductivity of a copper bus bar of equivalent size, then it will still have 50-60% of the conductivity of a copper bus bar after plating it with copper.

But we have to be careful with general terms like "conductivity" because there is thermal conductivity vs. electrical conductivity, surface conductivity vs. solid conductivity, the fact that high frequency currents are carried by the skin rather than the core of a conductor, etc.

Regards,

A. Hi Jonathan. We appended your letter to a thread where Khozem Vahaanwala and Anders Sundman have offered their opinions on optimum formulation. We'll see whether a third opinion is forthcoming. Good luck.

Regards,

Hi John. You haven't yet introduced yourself (high school student, post-doctorate research, experienced plating shop owner, hobbyist with no plating experience) or what you are actually trying to build (must the anodizing stay in place or may it be stripped, one piece or thousands, etc.) ... which leaves me in the position of having to start with the very basics, at the risk of talking down to someone who may know 10X as much about it as I do -- so I apologize if that's the case but ... you do know that anodized aluminum is non-conductive, non-metallic, and that it's generally considered a non-platable material? Get back to us with your situation please.

Regards,

Hi Mohammad. After zincating the aluminum you can try pyrophosphate copper or proprietary solutions from companies like EPI (Electrochemical Products Inc.) [a finishing.com supporting advertiser]. Good luck.

Regards,

A. To avoid oxidation on my metals I do the cleaning and plating all in an argon gas bath, I'm sure there are lots of explanations on this if you google it.

A. Hi Amish. We appended your inquiry to a thread which already answers it. But get back to us if anything is unclear to you.

Regards,

A. Hi Kamran. I am trying to understand what you have said, but I am a bit confused.
First, you have used the word "anodizing", but I think you meant "electroplating", not the separate & different process of aluminum anodizing? Second, DC voltage is required for electroplating, not AC. Third, 18V is way too much; more like 3V would be right. Fourth, the aluminum must be prepared by cleaning, etching, desmutting, and zincating before plating. Fifth, you cannot use a copper sulphate [affil links to item on Ebay & on Amazon] plating bath on aluminum (actually on zincate).

My apologies if you really did mean "anodizing" and if you are meaningfully using 18V AC (we are having a little bit of language difficulties). In any case, we added your question to a topic about plating copper onto aluminum. Good luck.

Regards,

A. Hi Kamran. Desmutting is a step which is often used in between etching and anodizing (dependent upon the particular aluminum alloy you are treating) to remove alloying materials from the surface because the etch dissolves aluminum but leaves any silicon, copper, and other alloying materials behind on the surface. Apparently you are trying to electroplate copper onto an A.C. anodized surface. Zincating doesn't seem to have anything to do with your experiment, so there's no sense confusing it.

I've never heard of attempting to electroplate onto a sulphuric acid anodized surface, so the ball is in your court. Where did you get the idea for this process, what papers did you read about it (when experimental plating methods remain only experimental methods, it's usually because they didn't work well). Why are you trying to electroplate copper onto aluminum in this odd way instead of using production proven methods? What is the end use of this copper plated aluminum?

Regards,

Hi Kamran
Anodising produces an oxide layer on aluminium. Aluminium oxide is non conductive to electricity. I am very surprised that you get any copper deposited. It is presumably down to the fact that you plate copper immediately after anodising and before the pores in the oxide layer are sealed. Whatever the reason, the adhesion must be very poor.
Can you explain the reason for anodising?
If you are simply aiming to plate copper on aluminium, the zincate process is standard practice and has been for many years.

A. Dear all,

This is very interesting reading, I had by chance to ponder upon plating copper onto aluminium as well, recently. I would go the way of using any of the new alkaline baths with organic binders/complexers, that is completely cyanide-free.

I will not go into detail as there are many competing designs (I mean compositions and usage parameters), some more exotic than others, starting with baths very similar to classical acid or alkaline baths, ending with baths of ionic liquids.

As someone above said: removing all traces of aluminium oxide is the most non-trivial task imaginable, someone above went as far as aerating baths with Argon gas to get rid of all traces of oxygen imaginable!! That is expensive.

Also expensive is what was mentioned above and involved two or three nitric acid baths (yuck!). But then, that process works.

To learn to plate a mixed substrate such as aluminium alloys (unetched) and get SOME adhesion, it would be necessary to learn some or all of the chemistry that is used in semiconductor industry to plate copper onto silicon and similar materials. It requires non-trivial understanding of the competing additives and a lot of reading (not that much, really after reading 100 useful pages out of 1200 found you will have a pretty good understanding of the processes involved), after which you will get the idea how to get to designing your own process (because the bath, substrate, impurities, current density and a myriad of additives interact differently on various alloys).

The keyword here is Damascene process. It can plate and level a 10-nanometer wide pinhole, up to 0.15 mm blind holes (!!) But the additives there are competitive; a mismatch and you're done without understanding what to do.

Alternatively, a similar process of electroless copper deposition can be used, but that also, is very expensive and not to mention instability, heating and limited lifetime of a bath. If you end up activating the surface with SnCl2 and palladium ions, it gets even more expensive.

I do not think that half of the companies offering copper plating on windows use plating in the right sense of the word, you can get copper color onto material in various other, much simpler means. Many special synthetic varnishes would latch onto anodized aluminium, and these could have copper flakes/powder/platelets, etc, together with another additives to keep the copper shiny. (not telling, bwahaha) (...and there are faithful plastic copper imitations as well...)

But honestly, I would try to avoid dangerous stuff, like nitric acid, etc, and as my interest is in simpler shapes (cylinders), I would use mechanical copper blasting to prepare the aluminium surface, or even incorporate copper into it. If you had the money, HVAF would be able to blast as much copper onto aluminium as you'd like. Just clean, shine and protect it afterwards.


And, to add: ANYONE TRYING PLATING ALUMINIUM MUST UNDERSTAND THAT ALUMINIUM WILL QUICKLY FALL APART WITHOUT THE OXIDE LAYER.

Thus, trying to plate aluminium is like trying to paint a burning house. BUT, If the house isn't on fire, it is covered with teflon and your paint won't stick.

I hope the analogy is reasonable.


P.S. When I think about this: anodizing before copper plating does sound like an invitation to a damascene process, as anodizing would create a honeycomb structure into which the copper could be deposited into the deep holes. But then you are in the area of semiconductor specialists, and your level of understanding chemistry of quaternium nitrogen compounds and organosulphur compounds and aromatic rings... would need to catch up, if you want to provide a reliable process.
The dosing of the additives starts at ppm (parts per million) levels, and best if calculated at molar concentrations relative to other key constituents of the plating bath. I have seen pictures (taken by electron microscope), where 0.35ppm of an additive would do one thing and 1.0 ppm would do something else. And if you added 1 ppm of some other additive, it completely counteracted the first additive.


Did I mention that current density vastly changed what was going on in the bath as well? That too needs to be controlled, unlike at anodizing, which doesn't care.

Again: the current density per square decimeter needs to be well controlled, the adequate anode area must be provided, the bath agitation must be provided.

A. Even more: using process similar to classical photography:

1) soak copper salt or complex into the fresh anodized pores -- it must be compatible with the anodizing bath

2) drip off, soak in developer bath (reducer to change copper salt into copper and a soluble salt or complex)

(( alternatively 2a) change copper salt into insoluble precipitate like CuO by a redox reaction, 2b) convert CuO to Cu))

3) leach or wash soluble products sufficiently away

4) neutralize, passivate, seal, varnish, etc. in a usual manner.

I tried a variant of this in a sample of the alkaline complexed bath. First adding alcoholic solution of methylene blue [affil link] seemed to precipitate nanometric black CuO, after some time the dispersed crystals grew, the optical density of solution decreased. Then, dripping in a type of mouthwash, the floating microcrystals seem to grow even more into a metallic glitter instead, which on paper show as red color copper with a very pleasing metallic shine and glitter. The crystals can only move over surface of the paper, while the (blue) liquid soaks into the paper.

A. 3 more notes:
>90% of the published new (=innovative) research on copper and nickel plating, and various compositions of alloys plated (Such as Ni-P-Cu, Ni-P-Sn, etc.) is from 2016, 2017 and newer.

Copper imitation over eloxed aluminium would be best done utilizing the fresh unsealed pores in the oxide, filling them with copper particles. As the pores are small, special size particles have to be used. Solvent: ultra-low viscosity such as dimethylketone (=UN1090, =acetone) or methanol [affil link] or such should be used. Copper passivator must be present in the bath. For me, it is easier to manage a highly flammable solvent in one bath than working with a set of 13 dangerous baths. Pressure spraying/mixing might be tried to increase impregnation, or electrophoretic deposition.

I have tried one complexed bath and oh my, you do need to think before mixing ingredients, order is important. Second, the complexed bath is of exactly methylene blue color, very, very deep. You won't see the sun through 1 inch of liquid.

Jane D. Stanton
- Vienna, (The Coffee City), Austria

A. Hi Qwee. This is a very interesting question, not just with regard to double zincating (which is addressed many times on this site, notably as topic 4074), and as a desmutter for copper-bearing alloys, but because nitric acid & nitrates have many other uses in metal finishing as well. I hope to hear some good suggestions for your problem!

The reason for the bans is probably because it can be used in explosive-making and meth-cooking and other bad stuff. More expensive & more environmentally harmful substitutes will be found for us as nitric acid grows harder to get. But the irony is the age-old one of the human condition of course: as we find & develop those substitutes, and nitric acid gets still harder to find, the explosives-makers and meth-cookers will find their more environmentally harmful substitutes as well :-)

Luck & Regards,

A. Hi Paul. I have never heard of a plating solution comprised of copper, peroxide, and vinegar [affil links to item on Ebay & on Amazon] ... but I'm not going to say it won't work, especially when you are saying that you've done it. If it works on zincated aluminum, yea!

From dealing with thousands of hobbyist plating situations here over the years, I think that, second only to considering the safety of what you are doing, the single most important piece of advice I can offer is to practice and learn on scrap. If your peroxide-vinegar solution appears to work, go ahead and apply it to a piece of scrap and then try to plate heavy copper onto it. Don't ruin your hard-to-replace car parts. Only after you are successfully plating onto scrap should you expose precious parts to these experimental solutions.

As a matter of semantics and common usage, the word 'electroforming' is wrong: you are 'electroplating'. It's called electroforming if the plated layer is an object of its own rather than being a plated layer on an object. If you were making hollow gold earrings by plating onto wax then melting the wax away, or bellows by plating onto aluminum and dissolving the aluminum away, or plating onto a leaf or flower, that would be electroforming.

Luck & Regards,