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Galvanic Compatibility of Aluminum and Copper




(2001)

Q. We would like to know the galvanic effect when we have a bolted joint Aluminum-copper, maybe there is a table experience or calculated values data.

Thanks for your help.

Gonzalo Ramirez
- Mexico city, Mexico


(2001)

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.

larry hanke
Larry Hanke
materials testing laboratory
Minneapolis, Minnesota




(2001)

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

Chris Snyder
plater - Charlotte, North Carolina


(2001)

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.

W. Carl Erickson
- Rome, New York


(2001)

Q. I am also thinking about placing copper and aluminum in contact, this time in an antenna installation. Every comment above I can relate to and understand until W. Carl Erickson's about silver.

The only galvanic tables I can find relate to corrosion in seawater, but they still rank metals from most anodic to most cathodic. For example: www.eaa1000.av.org/technicl/corrosion/galvanic.htm

On that page, the author lists some design rules, including the need to have a low C/A Ratio (corollary IV). Therefore, tin/aluminum is better than copper/aluminum. But silver is at the far end of the cathodic spectrum, and by this logic making silver/aluminum very undesirable. Other sources say silver/gold/graphite are very noble. What does this mean for corrosion of the poor little anodes?

Also, electrical conduction is optional for me. Would conformal coating of the copper board, or anodization of the aluminum part, be better?

Mark Nelson
- Melbourne, Florida


(2004)

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.

Kam Dianatkhah
- Dallas, Texas


June 22, 2010

Q. Hi! I am interested in the subject as I intend to connect copper pipe to aluminium part (threaded connection, nipple on aluminium with crox nut for copper pipe, or similar). Water flowing through the system is clean water (potable). Is there an issue with this joint? Is it going to help if I insert a section of PVC pipe in between?

All the heat transfer coils around the world are built with aluminium fins mechanically fixed onto a copper pipe, and they all work very happy for many years on the roofs and various environments, without corrosion. How come they do not rust?

Chris Moana
- Auckland, New Zealand


November 19, 2012

Q. I've been thinking of building a solar collector using the instruction found at www.n3fjp.com/solar but am concerned the copper tubing with aluminum snap on absorbers will be setting up the system for premature failure? Or is that not likely as there will be no fluids passing between these dissimilar metals?
Hope to hear back from someone with knowledge about this.

Thanks,

Kenneth Forrester
- Richmond, Virginia, USA


March 1, 2013

Q. In the presence of galvanic corrosion, can other dissimilar metals be drawn to the area of galvanic corrosion? Example: when aluminum and copper create a galvanic corrosion nodule, can soluble iron be drawn to that nodule?

Robert Aguirre
- Naperville, Illinois USA


March 7, 2013

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



May 14, 2013

Q. A contractor has attached short pieces of 25 mm copper to the aluminium corner posts by flattening one end and fixing with ZINC bolts. The posts were mistakenly cut short by one of his operatives. The copper will then extend into the sill/floor and will be filled with concrete.
Should I worry? The aluminium/copper joint itself will be covered with clip on PVC, and exposed to IRISH damp air only.

Patrick Mullin
- Omagh Tyrone Ireland


June 16, 2013

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

khozema
Khozem Vahaanwala
Saify Ind supporting advertiser
Bangalore, Karnataka, India

saify logo


June 2013

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

Regards,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Compatibility of copper wall caps on aluminum vent piping

May 12, 2014

Q. My homeowners association is very strict and requires copper for flashing and other exposures. I obviously have aluminium vent piping for my dryer and range vent hood. If I put copper wall caps on these pipes am I asking for trouble or does it matter?

Bryan Ellis
- Chesapeake Virginia


May 2014

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



June 16, 2014

Q. I have a related question on this topic. We are investigating the use of copper in an appliance application. I have a thick copper plate (99.9% pure) and put an aluminum pan on it. When I heated the plate (gas flame below), we got a flaky black oxidation on the copper surface where the two metals touched. It also took longer for the water to boil (vs. a typical cast-iron plate). However, the copper should have higher thermal conductivity. So how could it have been slower to boil? We're thinking we had a galvanic response between the two and the black oxidation acted like an insulator and slowed the heat transfer. Does this sound plausible? Is there a coating or plating we could use on the copper to prevent this oxidation layer from forming? Many pots and pans are aluminum, or anodized aluminum, so just using SS pots is not a good enough solution.

Hans Wenzel
- Fullerton, California USA


August 2014

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



7897
August 12, 2014

Q. I'm interested in this subject because I'll be connecting two AA batteries through an Aluminum foil (aluminum conductive 3M tape) jumper -- do you think galvanic corrosion can be raised in this connection? It will be only 3 volts.

I'll appreciate your help

Carlos Villanueva
- Chihuahua, Mexico


August 2014

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


August 15, 2014

Q. I'm building a spot welder and I'm thinking about using aluminum bars to hold copper electrodes. Obviously, this has the potential for a galvanic reaction, but it will stay in my garage and will not get wet. Will a slow galvanic reaction be a problem? Will it affect the conductivity of the copper-aluminum junction? I'll be running close to 1000 amps through this, so good conductivity is critical.

Lee Ratliff
- McKinney, Texas, USA


"No-Ox-Id" Compound

August 2014

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



December 10, 2014

Q. It seems contrary to galvanic corrosion, but if I put a Cu pan in the dishwasher with SS flatware, everything comes out fine, but if I include an Al pan, the Cu comes out black. Can you explain this?

David Denley
- Houston, Texas, USA


December 2014

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,

Ted Mooney, finishing.com
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Magnesium Anode Rod


Solar Ionizer


April 28, 2015

Q. Hello. I would like to put a solar copper "ionizer" in a cedar wood fired hot tub. I wish not to add chemicals such as bromine, chlorine, etc., to the water, which will be changed about once a week. The "stove" is an aluminum box immersed in the fresh water. The metals would not be in direct contact. Should I worry about damaging my stove? Would placing a sacrificial zinc bolt protect the aluminum? Thanks!

Bruce Baird
- Watertown, New York, usa


April 2015

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,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 13, 2015

Q. I don't know anything about all the technical stuff people are posting, but I am hoping to find out if it will be a problem to install my new gutter guards made of "mill finish aluminum" our our copper gutters. They also have a stainless steel mesh but don't think that would come in contact. The company said I could apply a coating on the aluminum but that sounds like a lot of extra work.
thank you!!

Lulu Cucuel
- Santa Cruz, California USA


December 2015

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 at all. Galvanic corrosion requires a conductive liquid and rainwater is quite non-conductive.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



December 2, 2015

Q. Hello,

I'm researching the effects of galvanic corrosion due to copper chips and dust imbedded in aluminum coils from high pressures in machining. I am trying to find cost effective ways to remove copper dust from the machine (steel) before introducing aluminum.

If that isn't a plausible solution, would it be better to plate the aluminum with a sacrificial metal to prevent pinholes in the coil? Would this significantly impact the heat transfer of the coil? If not what metal would you suggest to plate it with?

Thanks!

Nick

Nick Scott
- Grenada, Mississippi, USA


December 2015

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,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Galvanized framing nails and copper siding

September 8, 2016

Q. Hello, my entire house is copper cladded with 4x2 sheets interlocking. We are building an addition and instead of removing copper, contractor nailed framing directly into copper sheets with hot dipped galvanized nails. Do I need to worry about corrosion and my addition falling apart? It's such a mass of copper around the framing nails, I was unsure how I felt about it. I see that hot dipped galv. is basically steel with a zinc coating. Let me know if picture of house would help

Brittany Kelly
- Rock Hill, South Carolina


September 2016

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,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


September 28, 2016

Q. I have a client that wishes to purchase a copper rain chain that will be draining water out of an aluminum gutter. I typically dissuade my clients from doing so due to electrolysis. However the website where the rain chains are advertised says it is not a problem as long as you do not put them in direct contact with each other which seems like it would be difficult since the attachment piece needs to be placed inside the gutter. They advised to spray clear lacquer or piece of plastic underneath attachment piece. I wish to get a second opinion concerning this matter.

Nadia Crowther
- KYLE, Texas US


October 17, 2016

A. It's true that dissimilar metal corrosion can be stopped by insulating one metal from the other, but you need to be sure of the disconnection. If you were sure that an insulator between the metals is good, then this would work.
So the chain cannot be electrically connected to the rain gutter. Perhaps a plastic link between?

Geoff Crowley
Geoff Crowley
galvanizing & powder coating shop
Glasgow, Scotland



October 19, 2016

I am looking to make a thermoelectric (Peltier) system where the peltier chip is cooling a block of copper. Then an aluminum rod that is hard anodized will be threaded into this block using thermo paste.
I am doing this two piece design because copper is not food safe but has a very high thermo conductivity. I want maximum thermo transfer and effectiveness of the Peltier chip. ie, get that aluminum rod as cold as possible. The aluminum piece will be submerged in beer to chill the beer. That is why the aluminum is hard anodized, to help with the food safe-ness. This is long term storage (1-2 months max at a time)
The copper will never touch the beer, only most of the aluminum will.

My questions are:
1. Even with the hard anodize, and the thermo paste between them (Though not perfectly distributed), and the copper not being in contact with the beer. Is there a plating or anything I can add to the copper to slow or even stop that galvanic corrosion on the aluminum? Since cost is a factor, what is the second thing I can do?

Example, I am assuming the best answer is to plate the copper with maybe Silver or something. Is the second best option to plate in Nickel? Something that is presumably less expensive?

2. If there were a way to make copper food save via plating of some sort or what have you, and I could make the whole thing out of copper (Likely expensive btw), what plating or treatment might that be?

Thank you
Kelly

Mr. Kelly Johnson
- Burnsville, Minnesota


October 2016

A. Hi Kelly. We'll see if anyone else has a second opinion but I don't foresee any galvanic corrosion at all because hard anodizing is an excellent electric insulator.

However, you might want an o-ring to make sure your thermal paste doesn't get into the beer. And you might want to tin plate the copper because lack of galvanic corrosion does not guarantee lack of corrosion.

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey



Aluminum saildrive is pitting; is copper bottom paint the problem?

November 15, 2016

I use copper based antifoul paint on the hull of my sailboat. At the end of season I see pitting on the boats aluminum lower saildrive unit and the aluminum prop. I use magnesium anodes, and they show significant galvanic reaction. What do I need to do to reduce the pitting on the aluminum saildrive and prop?
P.S. the boat is used in a fresh water lake.
Rick

RA Swinton
- Orillia ON Canada


November 2016

Hi RA. One necessary step is to make sure there is no metallic connection, if that's possible to arrange, from the copper-based paint to the aluminum because that would definitely cause galvanic corrosion.

Antifoul paint is often deliberately ablative; but whether that actually means in practice that the aluminum is going to find itself surrounded by copper ions that cause it to pit, I don't personally know. Can you consider painting the aluminum saildrive and prop (not with copper based paint!), or is that a problem?

BTW, I didn't think ablative paint was required in fresh water in most cases, although low copper content paint is used :-)

Regards,

pic of Ted Mooney
Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


November 16, 2016

Q. The aluminum prop and saildrive leg are annually cleaned up and painted with OMC zinc based primer and marine enamel.
The pitting problem persists. The copper antifoul paint is not applied to the aluminum parts.

7897-2a  7897-2b

Here is a photo of the saildrive leg showing the pitting. The prop has similar pitting.

RA Swinton
- Orillia ON Canada

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