How to Silver Plate Aluminum

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

(note: this book is two volumes)

on eBay or

AbeBooks

or Amazon

(affil links)

A. Hi M. Two-part silvering isn't the best way to plate onto aluminum. There are two possible methods: phosphoric acid anodizing followed by plating, or, more conventionally, zincating (or proprietary zincate alternatives like Alstan or Bondal) followed by plating.

Briefly--and you'd need to consult a handbook for more detail--you clean, etch, and desmut the aluminum, zincate it, strip in nitric acid, re-zincate, and alkaline copper plate. Then you may need a barrier layer of nickel, then you silver plate. Obviously, there are alternatives here and there, but it is quite a bit more complex than simply dipping the aluminum into a silvering solution.

A. Aluminum cannot be plated directly; it will require zincating followed by copper or electroless nickel plating. The other materials can be silver plated but all except gold are less noble than silver, so silver may "immersion plate" on them. You may need to employ a silver strike and/or a 'hot lead' for silver plating.

Whether diffusion will be an issue depends upon the application. If the plating is decorative rather than functional, and the temperature the item sees ion service are moderate, a barrier layer of nickel between the copper and silver may not be necessary.

A. At our company we plate various gold and copper alloys with a silver strike then an antique silver plate. The plating is on jewelry, so it is purely decorative. Since I have been here we have never had any problems with diffusion. At least, it has never caused customer returns that I am aware of.

A. The first thing I would do is to vacuum deposit a few microns of pure aluminium over the formed material. This can be done with a simple vacuum deposition device. You can make your own for under $1000 and the rate of the device is near 1/minute. This is very common in the lighting industry.

Ashok,

You have low free cyanide concentration in your silver solution.

Regards,

A. Hi,

First of all, do you want to inhibit PIM in junctions (connections, etc.) or just in the device itself? The silver plating for the reduction of PIM in metallic walls of RF devices is DC standard electroplating. For the case of connectors, etc., the process used can be the same or maybe it is even better to use a softer metal. Anyway, silver always shows very good PIM response.

Regards,

A. The most direct process would seem to me to be to zincate the aluminum after giving it a pretreatment similar to what you use when Alodining, strike it with a copper cyanide, cyanide copper plate it, cyanide silver strike, and cyanide silver plate. This sequence uses cyanide in all five processes, but at least there's no going back and forth between acid and cyanide processes, and I don't think there's anything "iffy" in it. It may be possible to skip the copper plate and/or the silver strike, but that would require some testing to verify.

You may need approvals and mil specs for aerospace applications though.

A. Mahboob,

Ted is right, cyanide plating lines are very easy to maintain, consistent and work relatively well when used in conjunction with a zincate or double zincate prior to your copper strike. But there are also Nickel strike and electroless Nickel baths that can be used successfully, if a good process is put in place. Start with your chemical suppliers. They should be more than happy to provide you with all the technical support you will need to find the process that best suits your needs.
Good Luck,

A. Try to find good plating shop--most of silver plating solutions are cyanide based.If you want you can use do it yourself cyanide free solutions.
Ferrocyanide based plating solution:
40 gm silver chloride
200 gm potassium ferrocyanide ⇦this on eBay or Amazon [affil links]
20 gm potassium carbonate
1 lit water, stainless steel anodes
Dissolve ferrocyanide in boiling water, add carbonate and then add chloride(fresh, you can make it by mixing AgNO3 solution with kitchen salt solution),boil 30-180 minutes, then filter it when cold, then you may use it!
Never try to mix it with strong acids!
Phosphate based solution:
25 gm silver nitrate (or better, pyrophosphate)
100 gm potassium pyrophosphate
25 gm ammonium carbonate
1 lit water
Stainless steel anodes
Aluminium must be zincated!Hope it helps and good luck!

A. Street vending of plating services would likely be illegal in the USA -- I don't know about Australia -- because it would not comply with the requirements for discharge permits. The scientific principles of electroplating, including examples for students, are addressed in our FAQ about How Plating Works.

Are you sure it's silver, not just something shiny? Decorative silver electroplating can only be successfully applied from cyanide-based plating baths. But it is possible to do a thin immersion plating of silver onto copper objects from relatively safe solutions. See our FAQ about Silver Plating at Home. Good luck.

A. Anodizing is a very good electrical insulator which makes it impossible to directly electroplate Type II anodized aluminum, Kevin. Is it possible to electroless nickel plate the aluminum instead of anodizing it? This is probably a more typical and direct route towards eventual silver plating.

Regards,

A. Ted,
The anodizing process vendor out near Reno, NV has a process where they silver treat anodizing to make it conductive. My guess is that it is a bit like the two step anodizing process which electroplates cobalt or another metal into the anodize for color.
If I remember correctly, one of the anodizing greats, possibly Charlie Grubbs, mentioned a similar process a couple of years ago.
Now, if that is enough to make it anti microbial is a good question.

A. Hi Steve. Thanks for bringing this one up. Antimicrobial finishes seem to be the next big thing. We received a press release from Macdermid on the subject this week, and I'm sure they'd be happy to try to answer your question as it relates to their potential solutions. Other major vendors are no doubt also intensely involved with the subject.

I doubt that anodizing and dyeing with a copper-colored dye would do much, and that you would need to plate the aluminum to achieve anti-microbial properties.

Regards,