Have you ever been puzzled by the inexplicable appearance of white powder or green patina on a
copper-aluminum joint? Why does a seemingly solid joint get hot or even burn out? Behind these
headaches, there often hides a seemingly “quiet” but very destructive phenomenon - copper and
aluminum electrolytic corrosion. It is not only a hidden source of equipment failure, but also a threat to
electrical safety and service life of the silent killer. In this article, we will analyze this process and share
practical strategies to deal with it.
Why can't copper and aluminum “hold hands”? Electrochemical
principle is the key
In a humid environment or contact with conductive media, when copper and aluminum two metals are
closely linked, an invisible primary battery system quietly formed. At the heart of all this lies the potential
difference between their electrodes.
* Aluminum (Al): standard electrode potential of about -1.66V (active, easy to lose electrons, is the anode)
* Copper (Cu): standard electrode potential is about +0.34V (inert, easy to gain electrons, is the cathode)
The potential difference of up to 2V between the two is like an invisible “pusher”, which strongly drives the
electrochemical reaction:
1. Anodic reaction (aluminum side): Aluminum atoms lose electrons and become ions (Al → Al³⁺ + 3e-). These
aluminum ions combine with oxygen and water in the medium to form white aluminum hydroxide [Al(OH)₃] or
aluminum oxide (Al₂O₃), the common white powdery corrosion product. The aluminum matrix is continuously
thinned by consumption.
2. Cathode reaction (copper side): Oxygen and water in the medium gain electrons on the copper surface (e.g.,
O₂ + 2H₂O + 4e- → 4OH-). Although the copper itself is not significantly corroded, under alkaline conditions, the
original oxide film on the surface may become unstable or produce green copper salts, giving the appearance of
“corrosion”. This reaction continuously consumes the electrons coming from the anode and maintains the reaction cycle.
Corrosion products accumulate on the contact surface, which not only destroys the conductive pathway leading to
increased resistance and heating, but also accelerates the corrosion process by absorbing water and expanding its
properties, forming a vicious cycle. Eventually, the connection point may overheat, fuse, or suffer a severe reduction
in mechanical strength, resulting in an open-circuit failure or even a fire.
Prone areas: which connection points to focus on prevention?
Copper-aluminum electrolytic corrosion often occurs in some key areas that are easily overlooked:
1. bolt / rivet joints: such as copper and aluminum rows with aluminum or steel bolt crimping, copper
and aluminum direct contact and the bolt itself may exacerbate the potential difference.
2. wire joints: such as copper core wire and aluminum core wire twisted together without the use of transfer
measures. 3. terminal connections: copper equipment and aluminum core wire twisted together.
3. terminal connection: copper equipment terminals directly into the aluminum conductor.
4. pipe connection: copper valves, fittings and aluminum tubes or aluminum alloy structure connected.
Defense strategy: build corrosion prevention line
Thoroughly block the electrochemical channels between copper and aluminum is the fundamental way,
the following practice has proved to be effective methods worth learning:
1. Physical isolation - blocking the current path:
* Special adapters / transition joints: the use of specially designed copper and aluminum composite transition
plate or copper and aluminum transition terminals. The key is the use of a reliable physical isolation layer between
the contact surfaces (such as tin plating, tin potential between copper and aluminum) or special welding processes
(such as friction welding, explosion welding) to form a solid metallurgical bonding interface, completely avoiding
the electrolyte bridging.
* Special gaskets/coatings: Special non-conductive, elastic and environmentally resistant composite gaskets (such
as aramid gaskets containing corrosion-resistant grease) are inserted between the contact surfaces, or long-lasting
conductive anticorrosive coatings (such as tin-plated, hot-dipped zinc or Dacromet coatings) are applied to the
aluminum surface beforehand to provide effective isolation.
2. Environmental Control - Eliminate reaction catalysts:
* Sealing isolation: The joints are wrapped with high quality waterproof tape or specialized insulating sealing boxes to
completely isolate them from moisture and contaminants. It has been found in practice that even in high humidity
coastal areas, reliable sealing can significantly delay the occurrence of corrosion.
* Corrosion Inhibitor Application: Fill joints with a specialized electrical grease compound. A good composite grease
offers triple protection: insulation from airborne moisture, active inhibition of electrode reactions by migrating corrosion
inhibitor molecules, and improved heat dissipation. Ensure that the grease fills the gap and is stable over time. Avoid
non-electrical products. 3.
3. Sacrificial anode trade-offs: In the design of large grounding or cathodic protection systems, the activity of
aluminum is sometimes used as a “sacrificial anode” to protect steel facilities. However, this is a systematic design
and is not applicable to ordinary electrical connections, where direct connection will only accelerate aluminum loss.
Avoid common misconceptions:
* It is not “corrosion on contact”: the reaction is very slow in extremely dry, clean environments or under oil-immersed
conditions. In reality, however, the risk is extremely high, especially outdoors or in wet locations.
* Ordinary oils and greases ≠ specialized anti-corrosion greases: Butter etc. tends to dry out and lose or attract dust,
which does not provide long-term protection and may even accelerate corrosion.
* ● Loose bolts are important: vibration-induced microscopic friction can damage the protective layer, the use of elastic
washers or anti-loosening rubber is indispensable.
Conclusion
Copper and aluminum electrolytic corrosion is like an invisible “time bomb” in the equipment connection area.
Understanding its nature, recognizing high-risk scenarios and adopting the correct isolation and protection measures is
the guarantee to eliminate the hidden danger from the root and to ensure the long-lasting reliability of the electrical
connection. Every well-regulated connection is a wise investment in system safety and operational efficiency. We
recommend that you pay attention to this during the design and maintenance phases, and for a more in-depth
discussion of the application details you can follow up on our Electrical Connection Protection topic.
Do you have unprocessed copper and aluminum connections in your system? The longest way to protect your
equipment is to investigate and protect it immediately.