Conductive, wear and corrosion resistant coating for aluminumMay 15, 2012
Q. Mr. Mooney,
First of all, thank you for Finishing.com.
Short version: I am looking for a finish for 7075-T7351 which is wear and corrosion resistant but is also conductive. I had originally spec'd 8625, Type III, but we need an easy way to get an electrical bond.
Long version: We are developing an external structural component for a sea-based aircraft. It will be installed/deinstalled daily with all the abuse you would expect to follow from that. For multiple reasons we need to achive an electrical bond directly through the structure vice a grounding strap. The requirement for corrosion would be approx 300 hrs B-117. The interface does not use a bolted joint, so keeping the anodizing and just burnishing areas is not ideal. We will go to that if necessary, but I feel like there should be a finish out there which will meet all the requirements.
I had proposed electroless nickel, but there are people very against it citing bulletins regarding nickel plated connectors and the fact that MIL-C-26074 only calls for 100hrs salt spray. We do have finishes folks here, but I'm looking for a new perspective (it's complicated).
Thanks for your help.
product designer - Houston, Texas
A. One possibility is PVD TiN. It is both conducting and wear resistant. This is not an easy thing to do, to coat aluminum, and often does not provide all of the wear resistance it should because of the soft subsurface. You might need to put down an electroless nickel coating first.
American Faucet & Coatings Corporation
A. It is not complicated at all.
Nickel brush plating will provide a localized, hard, rather thick (0.0005" or more if needed), conductive and corrosion resistant coating just where you need to make contact. It could also be re-applied on site should it wear out. Good luck,
Guillermo Marrufo - Monterrey, Mexico
Monterrey, NL, Mexico
Thanks for your help. I'll have to talk with vendors about my specific substrate compatibility, as you hinted in your message. A lot of times my discussions with people keep coming back to electroless nickel. I'd love to find a spec for it which calls for better than 100 hr under ASTM B-117.
- Houston, Texas
A. You could also use a Metallic Ceramic Coating, that is conductive and while softer than Ni has tremendous corrosion resistance. Currently our CermKarome is over 8400 hour salt spray ASTM 117B and has an excellent bond to aluminum.Leonard Warren
Tech Line Coatings, Inc - Murrieta, California
August 3, 2012
Q. This is a similar situation. The intended product is a small housing (2 inch diameter x 10 inches long) that will be subjected to deep sea (3500 PSI) dives of short duration. The housing is 6061 Aluminum, with a glass window at one end. The prototype has a stainless steel wave spring in a groove that will apply pressure to the window to seal the O-ring. But this assembly will be hard to flush clean when the device is recovered. Therefore some combination of treatment for the aluminum (anodizing?) and the spring (coating) is needed to prevent galvanic corrosion. Luckily, the spring only has to be installed once, so wear is not the big issue.
Any and all ideas are welcomed and appreciated. This is currently a very small order, so the answers must work for a small quantity. The reward is that this will aid environmental research.