Aluminum and copper -- Galvanic corrosion

In summary: I'm just trying to understand why it's not a good idea to use aluminium in these situations.I just wanted to understand the corrosion process better.
  • #1
Curiousphy
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If a copper water pipe is connected to a piece of aluminum through a copper wire, where will the galvanic corrosion take place? On the wire to aluminum joint eating away at the aluminum, or will the whole water pipe suffer? (does copper corrode aluminum, or vice versa, or each other?) thanks
 
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  • #2
Curiousphy said:
If a copper water pipe is connected to a piece of aluminum through a copper wire, where will the galvanic corrosion take place? On the wire to aluminum joint eating away at the aluminum, or will the whole water pipe suffer? (does copper corrode aluminum, or vice versa, or each other?) thanks
Well I am not a materials expert by any means, but my years of experience tell me that
1. Copper to aluminum connections should be avoided;
2. It is the copper that corrodes the aluminum, and in the process, both the clamp and wires corrode at the connection;
3. When copper to aluminum wire connections are unavoidable, use as large a mass as possible of an aluminum bolted clamp; and
4. Install the aluminum above the copper, to prevent the copper ‘salts’ from ‘dripping’ onto the aluminum.
 
  • #3
If I treat the aluminum piece and the copper wire as consumable and easily replaceable, is the copper pipe itself totally safe from corrosion through this connection? actually, would this give the copper pipe some protection and effectively make the aluminum piece a sacrificial anode?

What if the copper wire was connected to a metal that was less reactive than copper, would it corrode the wire at the connection or corrode the pipe as well? would the copper wire provide a corrosion buffer for the pipe?
 
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  • #4
Curiousphy said:
If I treat the aluminum piece and the copper wire as consumable and easily replaceable, is the copper pipe itself totally safe from corrosion through this connection? actually, would this give the copper pipe some protection and effectively make the aluminum piece a sacrificial anode?

What if the copper wire was connected to a metal that was less reactive than copper, would it corrode the wire at the connection or corrode the pipe as well? would the copper wire provide a corrosion buffer for the pipe?
Why do you not keep everything copper? Once you introduce aluminium it will create problems however you do it.
 
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  • #5
Bulk aluminium is only stable due to the superficial oxide layer. If this is breached, the metal can corrode rapidly.

Similarly, I've known a copper hot-water tank fail because, the plumber discovered, it was resting directly on a flush floorboard nail...

Examples of rapid aluminium corrosion:
IIRC, Mercury thermometers etc are not allowed on aircraft lest break or spill attacks the structure.

'Waterglass' for sealing eggs is seriously alkaline. It ruined an aluminium pan used in error, tainted that batch of eggs. Although the 'waterglass' was labelled correctly, our complaints department sent the victim a very nice set of steel pans as 'goodwill'.

Our lab had a few aluminium weighing scoops as their 'tare' was significantly less than s/steel. I happened to find one that had sprouted a 'feather' of oxide, like a 'crystal garden', but in air. It continued growing as I watched, several mm/min. Ooh, pretty ! Sadly, I never learned what had set it off, and my few experiments failed to reproduce the effect. But we did replace those few Al scoops...
 
  • #6
Curiousphy said:
If I treat the aluminum piece and the copper wire as consumable and easily replaceable, is the copper pipe itself totally safe from corrosion through this connection? actually, would this give the copper pipe some protection and effectively make the aluminum piece a sacrificial anode?

What if the copper wire was connected to a metal that was less reactive than copper, would it corrode the wire at the connection or corrode the pipe as well? would the copper wire provide a corrosion buffer for the pipe?
The aluminum becomes the anode, but in the failed corroded copper-aluminum cable connections I have seen, the corrosive failure has been limited to the immediate area at the connection. The rest of the aluminum wire and copper wire beyond the joint has undergone just the normal weathering process in forming the copper (green) and aluminum (darkened gray) oxides.
Best to use copper to copper connections, although copper to steel or copper to bronze connections are fine.
 
  • #7
PhanthomJay said:
The aluminum becomes the anode, but in the failed corroded copper-aluminum cable connections I have seen, the corrosive failure has been limited to the immediate area at the connection.

Thank you, that's good to know. I know you can connect two dissimilar metals via non-contact connectors, but it's also good to know that you can use wires as corrosion buffer.
 
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  • #8
tech99 said:
Why do you not keep everything copper? Once you introduce aluminium it will create problems however you do it.

I just wanted to understand the corrosion process better. I already knew what would happen if everything was copper :)
 
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  • #9
@Nik_2213 Interesting story :) reminds me of youtube
 
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  • #10
PhanthomJay said:
although copper to steel or copper to bronze connections are fine.
Copper pipe connected to Galvanized pipe results in removal of the Zinc galvanize and continued corrosion of the steel pipe. Connecting them with a wire does not help; if anything it would make things worse. The Copper and Zinc, or Steel, act as a battery with the water being the electrolyte. When the are in electrical contact the battery is short circuited and starts dissolving the electrode. Same as what happens when a Carbon-Zinc flashlight battery is used, the Zinc case dissolves and it starts leaking

I lived with that for a while where the water heater was connected to the cold water pipe with Copper flex tubing (it should have been Brass or maybe Bronze rather than Copper). The result was we could not drink the tap water and the flow rate was reduced. The Iron content was so high that we got stomach aches from it! Just like if you take Iron supplement pills on an empty stomach. Ouch! (Tasted bad too.)
 
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  • #11
Tom.G said:
Copper pipe connected to Galvanized pipe results in removal of the Zinc galvanize and continued corrosion of the steel pipe. Connecting them with a wire does not help; if anything it would make things worse. The Copper and Zinc, or Steel, act as a battery with the water being the electrolyte. When the are in electrical contact the battery is short circuited and starts dissolving the electrode. Same as what happens when a Carbon-Zinc flashlight battery is used, the Zinc case dissolves and it starts leaking

I lived with that for a while where the water heater was connected to the cold water pipe with Copper flex tubing (it should have been Brass or maybe Bronze rather than Copper). The result was we could not drink the tap water and the flow rate was reduced. The Iron content was so high that we got stomach aches from it! Just like if you take Iron supplement pills on an empty stomach. Ouch! (Tasted bad too.)
That is interesting. The connections I am familiar with involve stranded copper about one-half inch diameter (1.5 cm) cable in contact with a galvanized steel clamp. The clamp is much more massive than the wire, and I am unaware of any problems. I've seen several such connections about 100 years old. The clamps are heavily corroded from decades of exposure to weather, and not from the copper wire within. I still specify bronze or steel clamps when in contact with aluminum (can't afford copper clamps!).
 
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  • #12
PhanthomJay said:
That is interesting. The connections I am familiar with involve stranded copper about one-half inch diameter (1.5 cm) cable in contact with a galvanized steel clamp. The clamp is much more massive than the wire, and I am unaware of any problems. I've seen several such connections about 100 years old. The clamps are heavily corroded from decades of exposure to weather, and not from the copper wire within. I still specify bronze or steel clamps when in contact with aluminum (can't afford copper clamps!).
Different situation. I was referring to connections that were all bare metal immersed in an electrolyte such as water. I agree, exposure to weather is not usually a problem.

The OP was a bit unclear about his exact situation, so I responded to one possibile condition... and as a point of information to others.

Cheers,
Tom
 
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  • #13
Dumb question: if a copper wire bolted to aluminum wire causes corrosion, why doesn't the 90copper/10aluminum version of bronze do the same thing and corrode?

I just started looking into casting bronze (ive done some aluminum before) and it sounded like copper/aluminum is stonger/better than copper/tin. No one mentioned corrosion.
 
  • #14
Good question. I didn’t say that correctly. When connecting copper to copper , use a copper or steel or bronze clamp. When connecting aluminum to aluminum, use an aluminum or steel clamp. Now when connecting copper to aluminum, this is bad and should be avoided, but if unavoidable, use a steel or aluminum clamp where if aluminum clamp, it must be of large mass with respect to the size of the copper, and the copper should be on the bottom side so that it’s salts do not ‘drip’ onto the aluminum. This is all with air as the surrounding medium.
 
  • #15
I'd inadvertently created this Al to Cu corrosion engine, Cu ground strap connected to Al heatsink, after few weeks the ground connection would go higher resistance and subsequently melty melty.

Tinning the copper with solder before assy prevented the effect, or at least slowed it to the point it was no longer noticeable, it was a prototype, that joint was changed for for production intent lol.
 
  • #16
A number of years ago, I worked for a pulp mill. After the wood chips were cooked and pulped, the pulp, at 3% consistency, had to be separated from impurities.

This was accomplished by pumping the stock (under pressure) through cyclonic centi-cleaners attached to a stainless steel header with nylon hoses. The hoses connected to the header with standard garden hose fittings. Since SS fittings were expensive, brass connectors were often subbed in.

The punchline, after all this preamble: The process engineers decided the pulp had to be acidulated, so sulfuric acid was added upstream of the cleaners. It took about 2 days before the brass corroded enough to fail and they all blew out, spraying pulp all over. It was 3 feet deep on the floor and the mill had to shut down for 3 days for repairs.

All because nobody knew that two dissimilar metals in an acid bath would corrode.
 
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  • #17
Curiousphy said:
@Nik_2213 Interesting story :) reminds me of youtube
Yes, serendipitously, I came across that video just this week...


Difference, my experience lacked liquid mercury. Was it a mercury salt which deliquesced ? Or a copper salt, which had reduced to copper at a so-slightly damp scratch ? Having used 'activated zinc' in Uni organic syntheses, 'tis an enduring puzzle...
 

1. What is galvanic corrosion?

Galvanic corrosion is an electrochemical process in which one metal corrodes when it comes into contact with another metal in an electrolyte solution. It occurs when two metals with different electrochemical potentials are connected and exposed to an electrolyte, such as water or saltwater.

2. How does galvanic corrosion occur between aluminum and copper?

Galvanic corrosion between aluminum and copper occurs when they are in direct contact with each other and are exposed to an electrolyte solution. The difference in their electrochemical potentials causes the aluminum to act as the anode, corroding and sacrificing itself to protect the more noble copper, which acts as the cathode.

3. What are the effects of galvanic corrosion on aluminum and copper?

The effects of galvanic corrosion on aluminum and copper can range from discoloration and pitting to severe degradation and failure of the metal. The corrosion can also weaken the structural integrity of the metals, making them more susceptible to mechanical damage.

4. How can galvanic corrosion between aluminum and copper be prevented?

Galvanic corrosion between aluminum and copper can be prevented by using insulation or coatings to separate the two metals, using a more noble metal as a sacrificial anode, or using corrosion inhibitors. It is also important to avoid exposing the metals to electrolytes, such as water or saltwater, which can accelerate the corrosion process.

5. What are some common applications of aluminum and copper where galvanic corrosion may occur?

Galvanic corrosion between aluminum and copper is a common concern in industries such as marine, construction, and electronics. It can occur in structures with aluminum and copper components, such as boats, bridges, and electrical wiring. It is also important to consider galvanic corrosion when selecting materials for plumbing and HVAC systems, as aluminum and copper pipes may come into contact with each other and be exposed to water or other electrolytes.

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