Layer corrosion

Layer corrosion is a specific corrosion mechanism that occurs in metallic materials consisting of several layers or alloys. This process occurs when two or more metallic layers have different electrochemical potentials and are simultaneously in contact with an electrolytic medium, such as water or moisture in the air.

The differences in the electrochemical potentials between the layers lead to the formation of a kind of "galvanic cell" at the interfaces between them. In this cell, the less noble layer acts as an anode and corrodes, while the more noble layer acts as a cathode and is protected from corrosion. This process can lead to a rapid and localized decomposition of the less noble layer, while the more noble layer remains intact.

A common example of layer corrosion occurs in aluminium alloys that are coated with a protective coating such as paint or anodizing. If the coating is damaged and the underlying aluminum is exposed, a galvanic cell is formed at the interfaces between the damaged and intact coating. This attacks the exposed aluminum while the coating remains intact.

Coating corrosion can have serious consequences as it leads to rapid degradation of the less noble coating, which can result in structural weaknesses and loss of function. To avoid layer corrosion, it is important to use high quality and consistent coatings that provide good adhesion and coverage to prevent the ingress of moisture and corrosive substances. Coatings should also be regularly inspected and maintained to detect and repair damage early before coating corrosion can occur.