[galvaniccorrosionquestion]

Hi, I was recommended to post in this subsection of the forums.

I am studying mechanical engineering, and have always had an extremely weak understanding of chemistry.

What I am tasked with doing is designing a welding table.

Bellow, I'll post an image of the weld table. The part that is labelled with the number 1 is what I'll call the top plate. It's function is simply to clamp down onto the copper base plate (labelled with the number 2). Due to the requirements of the welding that will occur on the table, as well as the force requirements, this top plate will likely be made out of 7075 Aluminum.

The part that is labelled with the number 2 is the base plate. It will be made out of C110 Copper. Not shown in the picture, two copper tubes are passed through this part for cooling. The coolant used will be normal tap water.

Summary:

There is a 7075 aluminum plate clamping down onto a copper base plate. Passing through this copper base plate will be two copper tubes filled with tap water.

It's my understanding that galvanic corrosion will occur when two dissimilar metals are electrically connected in the presence of an electrolyte. Is this the case as described above? The aluminum and copper are definitely electrically connected, and there IS an electrolyte present, but not directly. The copper and aluminum are in "dry" contact (what I mean is non of the electrolyte will be directly in contact with any of the aluminum top plate, just electrically).

I hope that someone is able to start me in the right direction.

Thank-you

EDIT: Forgot to add the picture. Im in the process of doing so right now.

EDIT2: Added in the picture. Hope it works for you guys.

[Arkcon]

Ah...yes the setup involves dissimilar metals and something like an electrolyte.  But the water doesn't touch both dissimilar metals at the same time, so no, you won't get galvanic corrosion.  Over time, exposed to the normal atmosphere, and under mechanical use that might remove the natural oxide that aluminum forms (and to a lesser extent copper as well,) you may encounter some oxidation and corrosion.  But not much more than would happen in a harsh environment anyway. 

Have you compensated for other things in the environment, for example, any acidic or alkaline fluxes, as an example?

[galvaniccorrosionquestion]

Thank-you for the response, that helped a lot.

As for your question, I am still trying to assemble a list of everything that might cause a problem.

The style of welding we use does not involve any large amount of flux. Instead, the flux is infused with the metal powders used to make the overlay. The powders we use are tungsten carbide and nickel. These powders don't tend to bind to copper and aluminum, which is why I was limited to using these two metals for the top plate and base plate. Also, this powder has not caused any trouble with our previous welding tables which have been made using copper and aluminum. This is just the first time we've ever made a table using BOTH metals.

The only problem I can thing of with this powder is the fact tungsten carbide is so much more abrasive than aluminum and copper. Fortunately, however, we will be able to replace the top plate and bottom plate as needed (even if that means every 6 months or so).

Once again, thank-you for your help.

[Borek]

As Arkcon said, you would need BOTH metals to touch each other and to be in contact with the same electrolyte for the galvanic corrosion to occur (electrolyte has to close the circuit). Situation you have here is not different from the setup in which there is no water cooling at all, just two dry metals touching each other. As long as there is no condensation present (and I suppose when the table is closed and in use it is hot, when it is not in use and cold it is open, so there is no contact) there should be no galvanic corrosion at all.