Galvanic Compatibility of Aluminum and Copper

A. Hi Steve. Pop rivets with copper heads and aluminum cores are sold, so some vendors think it's okay, and your installation location is relatively non-corrosive, so you could certainly take a chance.

On the other hand, there is essentially no galvanic couple that is worse than copper and aluminum, and if it was me, I'd look for copper colored all-aluminum rivets, and if I couldn't find them I might talk myself into black :-) Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

A. Aluminum will be very susceptible to galvanic corrosion in contact with copper, assuming that the two metals are also in contact with a common electrolyte (such as water with some ionic content.) Almost any text or handbook on corrosion will have galvanic series table. The farther two metals or alloys are separated on the table, faster the corrosion of the less noble of the two will be when they are in contact.

A. Just additional note - Tin plate the copper bolts or other copper parts this will help stop or slow the galvanic attack.

A. Also look into getting your copper busbar with a silver coating factory applied. This will improve bolted joints by reducing the resistance, and resists corrosion. Also, since it turns reddish black copper to a nice uniform grey, it blends nicely with the natural aluminum color. "Silver Flash" coatings are very thin, so additional cost runs only pennies more, per foot than plain busbar.

A. Take a look at this link www.corrosionsource.com/handbook/galv_series.htm to see the galvanic series. There appears to be -.50 volt difference between copper & aluminum using a standard hydrogen electrode.

Despite all the responses here. Aluminum/copper corrosion is quite complex. Why? Because aluminum has an oxide on the surface and the oxide stability determines its performance. Galvanic series does not always predict the reaction in absolute terms since we would need to take into effect the area of the 2 metals. Chloride & copper can cause pitting in aluminum. Finally a table of corrosion rates is specific to an area. In Mexico, pollution is highest in the world. SO4, CO2, Cl-, F-2 can easily form acids with moisture and create corrosion. Atmospheric corrosion varies from place to place.

A. Hi Robert. Your understanding of the phenomenon may be deeper than mine, and I may be misunderstanding the question, but I'd say "no".

Let's start by looking at a single metal unconnected to any other metal. It is made of atoms that have positively charged nucleuses (okay, "nuclei", Miss Crabapple) which are surrounded by electrons which balance the charges, and all is well. Then let's say these atoms become exposed to a corrosive media (an electron stealer). The corrosive media steals an electron. Now that atom is no longer an atom, but a positively charged ion in search of an electron; so it dissolves into the media in search of an electron to balance it. So, what actually causes corrosion is the loss of electrons from the metal.

Metals are electrically conductive, i.e., electrons can run through them from one spot to another just as they run through a wire. So if two different metals are mechanically connected in any fashion at all without an electrical insulator between them, electrons can run through them.

Now take a chunk of two different metals connected together and expose them to a corrosive media which is stealing electrons. The way galvanic protection/corrosion occurs is: when the nobler metal (the copper in this case) has an electron stolen from it by the corrosive solution, it has a greater affinity for electrons than the baser metal and immediately steals back an electron from the baser metal (aluminum in this case). The result is that the copper atom remains a balanced atom of metal, and the aluminum atom comes up short and corrodes into solution.

Regards,

A. The zinc plating on the bolts will be the first to go.

A. Hi Patrick. A photo would sure help me -- sorry, I'm lost :-)

Regards,

A. Hi Bryan. Theoretically, the aluminum will galvanically corrode near the area where it's connected to copper when it's wet. But it's not a critical application like on an airplane, and rainwater is not highly conductive. As a practical matter I just wouldn't worry about it.

Regards,

A. Hi Hans. No. it doesn't sound plausible to me. Galvanic corrosion involves two electrical paths: a metallic path which electrons can flow through, and an ionic path (liquid) through which ions can flow. If one path doesn't exist (in this case a liquid path), I don't think you can have galvanic corrosion.

Galvanic corrosion is certainly not the only possible kind of corrosion though.

Regards,

A. Hi Carlos. Galvanic corrosion is not usually as issue in the favorable environment that electronic devices are usually in. I'm not really familiar with that conductive tape, but I believe that the adhesive is conductive, as bare aluminum would not serve properly as a contact surface of this type. What happens when the batteries need to be replaced if one end of them is taped together? (I think the contacts on both ends of the batteries should be nickel or electroless nickel plated rather than aluminum tape).

Regards,

A. Hi Lee. You're probably right that galvanic corrosion per se won't be a problem in a dry environment -- but the surface of aluminum oxidizes to a high resistance film, and non-plated aluminum is rarely a satisfactory conductor for this reason. If the joint is assembled with a "No-Ox-Id" compound it will probably be okay though.

Regards,

A. Hi David. I'm not sure that I understand what you are describing, but galvanic action requires a conductive metal path between the two metals. If the aluminum pan is not touching the copper pan, and neither is touching the flatware, then no galvanic corrosion is taking place. If two of those three metals are touching, but not the third, galvanic action may be occurring between the two, but not the third.

Aluminum pans don't belong in a dishwasher. The usual detergents are highly alkaline and readily attack the aluminum.

Regards,

A. Hi Bruce. There can be no galvanic corrosion if the parts aren't touching, but that doesn't necessarily mean that copper and aluminum can completely resist corrosion. Zinc anodes will not protect aluminum in fresh water -- you would need magnesium anodes.

Although I'm not really familiar with copper "ionizers", it sure sounds like they are designed to put copper ions into the water. That copper would try to plate out onto the aluminum, and it could be an issue (I know that copper dust is very corrosive to aluminum), but hopefully the magnesium anode will protect it. Good luck.

Regards,

A. Hi Lulu. Assuming you don't use salt on the roof, or spray mildew preventer or anything on it, so the only moisture is rain water, I doubt that it will be any problem. Galvanic corrosion requires a conductive liquid and rainwater is rather non-conductive. Further, gutter guards are not a critical application at all.

Regards,

A. Hi. I don't really understand what you mean by "coils" or what heat transfer you're talking about. Keeping the dust away is probably the best solution, but you could copper or nickel plate the coils, or even electroless nickel plate them.

Regards,

A. Hi Brittany. As a homeowner myself, I wouldn't expect it to take much time to remove the siding; and the copper siding has good scrap value. So it does sound a little strange to me to leave the old copper siding in place rather than removing it. But I'm not a builder, and I suppose it's possible that he didn't think it was practical to attach the now loose end of the siding to the house if he cut it instead of just leaving the whole sheets attached.

Galvanic corrosion is an issue in wet environments, so if you told me he cut the sheets and nailed the edges with galvanized nails, I'd probably expect severe staining at the nail heads. But in what will now be dry interior framing, I don't think I'd expect corrosion of the nails.

Regards,