Galvanic Reactions - Aluminum/SS

Yes. If there is contact between the two and any moisture is present from rain, dew, or even just humid air, there will be a galvanic reaction. We typically use a dielectric material when using SS fasteners in aluminum masts arches and superstructures on boats truck or campers.

It is not clear if you mean a metal carrying bonding agent or a non conductive adhesive intended to join metals together.

On boats in salt water (worst case scnario) we often use 3M adhesive 5200 for a super bond. However surface preparation ( cleaning) of both stainless steel and aluminum is still required.

Yes. Galvanic series is metals, not just carbon steels.

http://www.corrosionsource.com/technicallibrary/corrdoctors/Modules/Aircraft/galvseri-table.htm

Depends on the adhesive's formulation.

Eventually it could. adherence problems are more likely attributed to initial cleaning /surface prep. But if there is water...

milo

Some adhesives like silicone caulking/sealants have acidic properties. Under the right conditions this acid will also make trouble. - especially with aluminum.

Aluminum is ampothetic and thus very reactive to a lot of different things. I trust no electrical current is involved. I have seen truck/van bodies disintegrate at the floor seams from this.

The clearance lights and interior light current return to chassis ground via the aluminum body shell. Contact with things like SS floor plates, door sills and fasteners become miniature galvanic cells and literally rot the aluminum.

Once again, a rather open-ended question as there is not sufficient info given.

The link already given (to the galvanic series/seawater) is a good beginning reference. Remember though that a series will change, depending on the environment (electrolyte). That's why all Galvanic Series Tables must list the electrolyte that is applicable to it. Your SS exhibits corrosion resistance due to a passive layer on its surface, which is bound, chemically, more tenaciously than any paint/coating ever could. Aluminum, tho normally very anodic, will ALSO develop a film on its surface (oxide) that tends to act like a passivation layer, lending it more corrosion resistance than one would be led to believe it possessed.

You state that these are to be bound by an adhesive. Who is specifying the surface preparation standard prior to application of the adhesive, and what will it entail? And, after the process is completed, what will the environmental exposure of the end-product be? You might, or might NOT have anything to worry about. If you need the best advice available on bonding metals, visit www.lord.com. Mr. Lord began the empire by helping to hold our military might together (rubber-to-metal motor mounts) many decades ago, and they're still on the cutting-edge.

Also, visit the National Association of Corrosion Engineers International (www.nace.org) and sign-up for the [nace] Corrosion Network (free) List-Server. Participation from pros around the world ... ask the real experts!

Best of luck in your endeavor.

Was certain you'd be offerring great advice.

Not disappointed.

milo

Well I don't believe my question is all that open ended. But I guess I failed to supply the adhesive and the environment. The adhesive is in fact Lord 410 slow set metal bonding adhesive. And the environment is 80' up in the air, suspended inside a combination hockey rink/ basketball court venue. It will be a controlled but changing environment. It is the central 4-sided scoreboard display we see at the games.

The specific application is this: My colleague has a design for the bottom surface of this display. The bottom surface consists of a 20' diameter disk that needs to show a stainless steel surface. His idea is to build an aluminum support structure for this disk, which would include a 20' diameter aluminum disk. He then plans to laminate a disk made of a sheet of 20 GA stainless steel onto this aluminum disk. He plans to use the Lord adhesive for this.

My fears are that there are several factors that may cause the steel disk to release itself from the aluminum. i.e.

• galvanic issues affecting the bonding agent,
• thermal expansion differences between the two materials that would either warp the disk, or effect the bond
• humidity changes between hockey and basketball seasons
• even if VHB tape is used, similar dangers may exist.

The steel disk weighs 475 lbs with a surface area of 315 sq. ft.

I fear that what would result is a 475 lb razor edged disk fluttering toward a crowd of tens of thousands of people. I have alternate solutions to this design, but must first dissuade people from what I consider a very dangerous design.

Does it have to be stainless? Can it just look like stainless. Companies like Nevamar and Wilsonart make high pressure phenolic laminates (like Formica) with metal surfaces (aluminum) that come in a variety of finishes. One that looked like brushed stainless could then be applied to the aluminum disk with standard laminate fabricating techiniques bonded with spray contact cements like Sta-Put. Going this route you eliminate the problem altogether.

Yes it does have to be stainless, as per the arena's specs. Nothing but the best for our millionaire sports heroes! I have dealt with the laminate products from Nevamar, Wilsonart, Chemetal, etc. They don't find that acceptable. Actually, I was really pushing for a foam-core steel laminated material that has amazing stiffness to span great distances with minimal support and weight. Seemed ideal for this application. Again, that was nixxed. Too far out of the box. So we're back to plain old SS.

In the end I believe I've driven the design away from gluing the steel disk to the aluminum disk, and I will go with a full steel construction that can be securely welded to stiffening members. There's nothing like a good weld and a single material throughout, to reduce variables. (i.e. K.I.S.S.)

Thanx all, for your valuable insight and suggestions.

You can now be sure I won't allow that scoreboard to come crashing down upon your heads when you go to your next game.