Electrically Conductive Aluminum Anodizing

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

(note: this book is two volumes)

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A. An anodized surface is an aluminum oxide surface, Gary; aluminum oxide is often selected because it is non-conductive, so anodizing would not be the most obvious finish for conductivity.

You might be able to apply a black chromate conversion coating, but I don't know if it would be attractive enough or robust enough. Another possibility might be to black chromium plate or black nickel plate the panel. But this would require zincating, followed by copper-nickel-chrome plating.

Or you might chromate conversion coat the inside of the front panel to keep it electrically conductive, then anodize and black dye the outside? This involves masking and might be more costly than you'd like though.

I guess my opening question should have been why do you want it anodized? Good luck.

A. I may be wrong ... but I seem to remember a company, a few years ago--I believe it may have been Metalast--that offered a "conductive" anodizing ... I believe that Ag was added to the bath to make the coating conductive. Once again, I may be wrong on the company, but I know someone out there was advertising conductive anodizing. But this may fall into the same category as Teflon "Impregnated" Anodizing.

A. Metalast does have an Ag bath that "seals" the anodic "pores", color varies from gold to brown depending on oxide thickness and alloy. This process lowers the resistance of the anodize and does NOT make the anodize conductive as the barrier layer is not penetrated.

Thanks Marc. Thanks Bill.

A. There is such a thing as an electrically conductive hard anodize. The maximum thickness is about 1.0 mils.

A. Gary,

I stumbled across this thread while researching a similar need for the same reasons for my work in the semiconductor industry. US Patent 6228241 applies to the multi-step anodize process required to achieve a conductive anodized coating on aluminum. The patent was filed in the late 90's and there are several companies that provide that service.

Regards,

Stephen Coomer, ME/EE
- Tempe, Arizona, USA
October 8, 2010

A. Hi Goncalo. Is this a diecasting, pressure casting, or sand casting? Diecastings and pressure castings (automobile wheels for example) are routinely electrolessly plated or electroplated after zincating. Choices include zinc with black chromate, zinc alloy (such as zinc-iron, zinc-cobalt, or zinc-nickel) with black chromate, black nickel, or black chrome; there are several black precious metal platings, but they probably won't be affordable enough. We probably have many applicable threads on all of these subjects; please search the site.

It's hard to comment on your "appearance not great" because we know nothing about the casting method or quality yet, nor about how much skill and time & effort went into the attempt to plate with electroless nickel and black chrome. If you've spent months on the plating effort and it's not working, it's not working; but if you gave it a single shot and weren't happy with the result, that's pretty much to be expected of every finish :-)

Luck & Regards,

A. I think Metalast has a process that can give you hard coat anodizing with the conductivity you need.

A. Cast aluminum can be a nightmare to plate because of its porosity. Common approaches are a heavy copper plate after zincate followed by nickel or electroless nickel and then the chrome. You need help from a specialist to get this down to a cold hard science as minute variables make a lot of difference.

Another approach would be to use a special formulation of the EN that could bridge the pits better. This may give you blisters later.

Finally, vacuum impregnation before plating has been used by several with good luck.

A better quality of casting might be the cure.

You might have to go to a high quality forging.

Possibly a less porous grade aluminum of aluminum casting metal (alloy).

Anodizing that is impregnated with silver to make it conductive may work. It would require testing to find out. Not many companies have that process. Metalast International is one. If you made your request more specific, people may be able to tell you.

A. NO.

You can mask an area off to ground to and have it chem-filmed for some corrosion protection, but anodize is an electrical insulator and I know of no way to make it conductive.

A. The best way to make it electrically conductive is to leave bare unanodized areas such as threaded holes. Another option would be electroless nickel. Electroless nickel offers the same as-plated hardness as hardcoat with better lubricity and is electrically conductive.

A. Hard anodize is an electrically insulating coating.

You have 2 possible options:

1- You could mask off areas you need conductive, & finish those masked areas with a chromate conversion coating, & hardcoat the balance of the part.

2- METALAST - supposedly offers a way to restore conductivity to anodize / hard anodize coatings, but I know nothing about it.

Earlier entries on this thread might be of interest to you; it discusses methods to make the anodize coating itself conductive.

Good luck,

A. Hi Fred,

Your thinking would work.

Anodizing: You may achieve the required cosmetic finish, but more than that the anodic layer is Bad conductor of electricity.

Regards,

A. Hi Ojie. One company was already mentioned 5X on this page; google them. This forum is free for us because supporting advertisers generously provide it for camaraderie & technical information exchange, and it's already pushing the envelope to mention their competitor 5X. Billing them the cost of maintaining contact details for that competitor might be a bit too much generosity to request :-)

Regards,