Galvanic Corrosion
The accelerated wasting away of the more active metal when two dissimilar metals touch in a damp and conductive environment. Contact between copper and aluminium is the classic example; the aluminium is sacrificed and the connection resistance rises quickly. Without moisture the process practically does not start.
Two dissimilar metals and the moisture between them form a small battery. The metal that is more active in the electrochemical series behaves as the anode and dissolves. The larger the potential difference between the metals and the more moisture and salt there is, the faster the process runs.
- Risky pairs: aluminium-copper, steel-copper, a zinc-plated surface with a stainless bolt.
- Prevention: pairing identical or electrochemically close metals, using a tinned transition terminal in between, insulating the connection from moisture.
- Practice: using tinned lugs on copper lugs bolted to the vehicle chassis and applying a protective grease or coating after tightening is the common solution.
- Symptom: white powder or blistering at the contact area, a connection that does not look loose but has risen in resistance.
This effect speeds up markedly on agricultural and work machine installations operating by the sea, in fertiliser and on salted roads. After the choice of metal, keeping the connection points away from moisture is the most effective measure.
The context in which this term is used: Installation, redundancy and field continuity