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topic 31663

Silver plating on aluminum


(2002)

Q. Hello all,

The company I work for design and make and finish all in house screening enclosure for Rf purposes we make and design all our enclosure by first using chemical machining techniques then mechanical forming and then chemical finishing.

The job this problem is in regards to is a particularly complex enclosure which has the need for the circuit to only see silver within the enclosure

Well let's get on with it. I am not really conversant with plating processes but I require an answer to a problem that I have. In our company we have an in house finishing shop. But the supervisor of that department can be difficult at the best of times. He is telling me it is impossible to plate aluminium with silver without using a nickel underlay when only a few weeks ago he suggested something about a copper underlay. But we couldn't process that in house so it would have to be subcontracted which was agreeable to me but now he's saying it can't be done full stop.

Also we have another problem with this job. The customer is asking for around 20 microns of 60/40 tin lead to be plated to the bottom edge of the enclosure. This is giving us immense problems as we only want it on the edge and not on the wall at all if you can give me a workable process for doing this I would much appreciate it.

Best regards,

James Reynolds
- Weymouth, Dorset, England


(2002)

A. Silver can be plated directly on aluminium provided you have right type of zincate with you. We in India plate up to 30 microns of silver on aluminium castings used for hi voltage circuit breakers on automatic lines. For plating Tin-Lead in selected are masking taps are used with controlled immersion of the article to be plated.

RAMESH KHARE
- Mumbai, India



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



(2003)

Q. We have RF components that have silver plating on their flanges which in turn match against aluminum alloy waveguide. These waveguides are exposed to salt fog and need to last 10 years. Obviously the silver to Al alloy galvanic match is less than workable. What would be the best approach to removing the dissimilar metals problem here. We are pumping 2.5 kw of RF power thru these waveguides so I cannot have any arcing going on due to corrosion or gaps in the waveguide flange faces due to an uneven coating at the corners. Would electroless nickel on the aluminum flange be the best choice here for the money and fabrication cost incurred due to the selective plating?

Bob Smithy
- Palm Bay, Florida


(2003)

A. Leaving the galvanic phenomena to other responders, I want to address the problem of silver "migration".

Most likely the aluminum received an immersion zinc(ate) coating before the silver was applied. Silver will march right through zinc, aluminum, gold, and almost anything.

Find a precious metal supplier listed on finishing.com and talk to him about using nickel as a diffusion barrier, or if the galvanic thing is turned around, consider Palladium as a diffusion barrier.

Be aware that proprietary silver brighteners usually contain selenium or antimony both of which co-deposit and lower the RF. You should use the carbon disulfide type brightener.

And I do not believe you will ever get 10 years with bare silver on top.

robert probert
Robert H Probert
Robert H Probert Technical Services
supporting advertiser
Garner, North Carolina
Editor's note: Mr. Probert is the author of Aluminum How-To / Aluminio El Como
and co-author of The Sulfamate Nickel How-To Guide


(2003)

A. Aluminum has an electronegativity of 1.5, silver is 1.9 and nickel is 1.8. Nickel offers a slight improvement over silver.

Todd Osmolski
- Charlotte, North Carolina, USA


Historical reprint on silver plating and other early electroplating
from Abe Books

or

(2003)

Q. I experienced a similar problem between aluminium parts (6061T6) and silver-coated C-ring (used for hermetic seal in a non-saline humid environment, expected life: a few decades).

I attempted electroless Nickel of the highest quality (high-phosphor type, thickness 30 microns, no cracks). Absolute failure! After only a limited time in hot wet chamber the Ni turned brown,pits formed, starting a wild reaction with the substrate. I have little explanation,and would welcome some advice.

The next step (in my case) is anodising, as electrical insulation is both possible and desirable. Question: any experience around on highly protective anodising compatible with perfect hermeticity? (insulating with polymers is not an option).

Guillaume FIAULT
- Limeil-brevannes, FRANCE



To minimize your searching efforts and to offer multiple viewpoints, we've combined some threads into the dialog you're viewing. Please forgive any resultant repetition or failures of chronological order.



2004

Q. Sir,

For silver coating on aluminium we give a coat of copper on aluminium. Can't it be possible to coat silver directly on aluminium? And will it be feasible for mass production, because at our company it takes 120 min for plating silver. Can I reduce the cycle time & how?

Parag K [last name deleted for privacy by Editor]
- Nashik, Maharashtra, India


"Surface Treatment & Finishing of Aluminium and Its Alloys"
by Wernick, Pinner & Sheasby

from Abe Books
or
info on Amazon

2004

A. How do you plate copper onto the aluminium? If you don't give us your process, how can we answer your question? I suspect you use a zincate process - if so, the most common "next step" is to use a copper deposit. I have, in the past, used a nickel layer, but that's by-the-by. I have never heard of silver being used, but as long as it is a near-neutral bath, it may work. Give it a try and let us know how you do. The problem with aluminium, as you must be aware, is the tenacious oxide layer on it; I have succeeded in directly plating nickel onto aluminium by using high speed "jet plating", but only on a very small laboratory sample. Alternatively, you can directly plate aluminium with silver by using vacuum technology. When you try these ideas, let us know how you get on.

trevor crichton
Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK



2006 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. Why do we need to plate copper first before silver plating on aluminum?

Bipin Kumar
- Nasik, India


A. Hi Bipin. We appended your inquiry to a thread which discusses the general issues. If you post the details of your own situation we can probably expand upon the subject. Good luck.

Regards,

Ted Mooney, finishing.com Teds signature
Ted Mooney, P.E.
finishing.com
Pine Beach, New Jersey



March 28, 2018

Q. Ag plated Aluminum reacts fast in Salty environment (Salt spray test) whereas Sn+Ni plated Al reacts very slow in same environment. What is the reason?

Bharatsinh Sindha
Student - Vadodara, Gujarat, India


March 2018

A. Hi Bharatsinh. School can be fun, but one of the onerous parts of school, which few remember kindly, is the quizzes. So, asking people to volunteer to take those quizzes may end in disappointment. But we do have an outstanding podcast on Tin-Nickel plating which may help you answer that question if no volunteer steps forward. Good luck.

Regards,

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



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