Copper vs Aluminum galvanic corrosion

I know that copper and aluminum will corrode with an electrical connection as well as an ionic connection (water). Will there be
galvanic corrosion if the only connection is through water / glycol? More specifically I'd like to make some coolant plumbing for an automobile engine conversion out of copper pipe. The engine is almost entirely aluminum.
I was thinking if I attached the copper to the aluminum (engine block) with rubber hose, and insulate the copper pipe from the chassis that there may not be galvanic corrosion. I do know though that the antifreeze solution will act as somewhat of an electrical conductor so this could void my theory.
What do you guys think? Please CC my email address as well.
Thanks,
Ryan
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snipped-for-privacy@hotmail.com (Ryan) wrote in message

Ryan:
You really need to think hard about whether you want to try this. If you are absolutely sure you have perfect corrosion inhibition by your antifreeze, then you might make it work. Otherwise, proceed at your own risk, since your theory is void.
Cursory discussions of galvanic corrosion talk first about potential difference and second about relative areas. Small aluminum anode plus large copper cathode equals big trouble. You don't have that to begin with, but you have a flowing system. Thus you must worry about the possibility of some copper dissolving and plating out at local areas on the surface of the aluminum. If it happens, then the you might wind up with a large effective copper cathode area, with this deposition corrosion resulting in intense pitting. This is briefly mentioned in the Alubook "How to avoid or minimize galvanic corrosion", Topic 11065. See:
http://www.alu-info.dk/Html/alulib/modul/A00109.htm
For a more detailed discussion, go to a good library and look in the ASM (Metals) Handbook, Volume 13 on Corrosion (1987). Read the article on "corrosion of aluminum and aluminum alloys" on pages 583-609. You will find deposition corrosion mentioned on page 589. Just 0.05 ppm copper ion concentration is threshold for initiation of pitting.
There is also a good general discussion of galvanic (bimetallic) corrosion in the Guides to Good Practice in Corrosion Control series in a big 579K file at
http://www.npl.co.uk/npl/cmmt/ncs/docs/bimetallic.pdf
Another NPL guide mentions that if you similarly put aluminium downspouts on a building with a copper roof then you will have big problems.
Pittsburgh Pete
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This is a key point. While one common corrosion process requires both direct electrical and an electrochemical connections, there are other corrsion processes that do not. Any significant levels of copper ions in your fluid will initiate corrosion of the aluminum. This just can NOT be avoided in practice.
Don't mix them.
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Pittsburgh Pete wrote:

Each pit will become an individual "cell" with currents of electrolyte circulating in it, taking away corrosion products and leaving further fresh metal to be corroded - an absolutely perfect system! It just couldn't be any better!
Dave (UK)
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Theoretically possible with the right control of inhibitor solution, in practice don't do it if you have any choice.
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snipped-for-privacy@hotmail.com (Ryan) wrote in message

Some autos with aluminum block, water cooled engines have copper radiators. I know that individually, propylene glycol reacts neither with copper or aluminum. Your concern seems to be where the copper connects to the aluminum or comes in contact with the chassis. Since propylene glycol doesn't seem to react with other metals (i.e. steel) in the water pump, I think it's safe to assume that your only concern would be contact between dissimilar metals and any stray current from other sources. I think the propylene glycol can safely be assumed to add no additional electrical conductivity to the water to be mixed with the propylene glycol. It may be that if you use pure propylene glycol (cost permitting), and it's to your advantage to have a direct connection between the copper pipe and the engine block and the chassis, you may be able to get away with having the connection points of the copper pipe electroplated with silver (very inexpensive) and that should solve your problems. High voltage copper bus bars are routinely electroplated with silver and connected to aluminum or steel anchor points in high voltage switches and I've yet to see a corroded connection on one even in places close to salt water.
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snipped-for-privacy@gis.net (Barry P. Chepren) wrote in message

------------------------------------- Barry: It is NOT safe to assume that the only concern would be contact between dissimilar metals.
There is a good discussion of galvanic (bimetallic) corrosion in the Guides to Good Practice in Corrosion Control series in a big 579K file at
http://www.npl.co.uk/npl/cmmt/ncs/docs/bimetallic.pdf
Look at Section 4.0, which is titled "Bimetallic corrosion without physical contact." This is known under the term "deposition corrosion".
From CORROSION BASICS: An Introduction, edited by L.S. Van Delinder, National Association of Corrosion Engineers, Houston, Texas, 1984, page 99:
"DEPOSITION CORROSION is a form of pitting corrosion that can occur in a liquid environment when a more cathodic metal is plated out of solution onto a metal surface. It generally occurs with the more anodic metals such as magnesium, zinc, and aluminum. Common cathodic "activators" are mercury and copper ions in solution. For example, soft water passing through a copper water pipe will accumulate some copper ions. If water is then admitted to a galvanized or aluminum vessel, particles of metallic copper will plate out, i.e., deposit on the surface and stimulate pitting by local cell action. Deposition corrosion can be avoided by preventing the pick-up of cathodic ions that will enter the equipment, or by scavenging them by passing the contaminated product through a tower packed with more anodic metal turnings on which the ions can deposit."
Pittsburgh Pete
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