Which term describes corrosion caused by contact between dissimilar metals forming galvanic cells?

• A. Fretting
• B. Galvanic corrosion
• C. Intergranular corrosion
• D. Filiform

Answer: (B)

Galvanic corrosion happens when two different metals touch in a conductive environment, forming a galvanic cell. The metal that is more anodic (higher in the electrochemical series) will preferentially lose material, while the more cathodic metal is protected. The rate depends on the potential difference between the metals, the presence and nature of an electrolyte, and the relative surface areas of the metals; a larger anodic area accelerates the corrosion of that metal, especially if paired with a small cathodic area. In practice, dissimilar-metal joints in damp or seawater environments are common scenarios where this occurs, which is why isolating metals or applying coatings is important. To minimize it, you can insulate the metals from each other, use compatible materials, apply protective coatings, or introduce a sacrificial anode to corrode in place of the structural metal. Other terms describe different processes: fretting is wear from micromotions at the contact point, intergranular corrosion targets grain boundaries in certain alloys, and filiform corrosion runs under coatings as worm-like patterns due to moisture.