Dissimilar metal corrosion refers to the electrochemical process that destroys metal, reducing its strength and thickness. This type of metal corrosion is closely linked to phenomena like cracking paint. When two dissimilar metals come into contact within a corrosive setting, one metal undergoes galvanic corrosion while the other one maintains galvanic protection.
Dissimilar metal corrosion may also be known as galvanic corrosion or bimetallic corrosion.
When dissimilar metals come into contact with electrolytes such as condensation, rainwater or other sources such as oil, dirt and airborne particles, it can produce an electrochemical reaction. This event allows electron flow from one metal to another. The byproducts of corrosion such as hydroxides, sulfates and oxides take the position of the original matter, but these byproducts can be carried by an electrolyte.
Metals in the galvanic series that are close to each other have little effect on one another. This is due to the fact that when the separation that occurs between two metals in the series elevates, the effects of corrosion are greater on metals that occupy a higher position in the series.
The surface areas of dissimilar metals in contact are also significant in identifying which metal is more prone to accelerated corrosion. It is not a good idea to have a large cathodic surface that is in contact with a small anodic area.
In order to prevent galvanic corrosion, these measures can be implemented:
- Insulate two metals electrically.
- Keep metals away from ionic compounds such as bases, acids and salts.
- Use protective layers like plastic, varnish and paint.
- Select metals with the same electropotentials.
- Use electroplating and cathodic protection systems.