The Prevention of Galvanic Corrosion in Bimetallic Assemblies

It is difficult to avoid the use of bimetallic assemblies in the manufacture of most products. When these combinations of dissimilar metals are exposed to an electrolyte, corrosion of one of the metals can be accelerated; this is referred to as galvanic corrosion. The tendency for it to occur depends on the thermodynamic instability of the metals involved, and the rate at which it occurs depends on the resistance of the system to the corrosion processes. The critical parameters affecting galvanic corrosion are the potential difference between metals, the polarization behavior of the metals in a particular environment, the characteristics of the electrolyte, and the ratio of the cathode to anode areas.

Galvanic corrosion can be minimized through good design. Metal combinations that lead to excessive corrosion should be avoided. In some cases a metallic coating can be applied to reduce the potential difference between metals or to provide sacrificial protection. If susceptible metal combinations must be used, it is necessary to disrupt the metallic contact by the use of insulators, sealers, coatings, or other nonconductive materials. Equal consideration should be given to fabrication techniques, methods of joining bimetallic assemblies, and means for minimizing exposure to corrosive environments.