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Galvanic Compatibility of Aluminum and Copper

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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


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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.

hanke Larry Hanke
  materials testing laboratory
Minneapolis, Minnesota


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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


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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


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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


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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

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 join? 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", Mrs. 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,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, 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
  ^- Privately contact this inquirer -^


June 16, 2013

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

khozema Khozema Vahanwala
Saify Ind
 
Bangalore, Karnataka, India


June 2013

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

Regards,

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

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