Exfoliation corrosion commonly results in delamination along which feature?

• A. Threadlike filaments under coating
• B. Pitting at grain boundaries
• C. Delamination along grain boundaries
• D. Uniform corrosion on surface

Answer: (C)

Exfoliation corrosion causes layers to peel apart because corrosion products form between layers of the metal along the grain boundaries, lifting and separating them parallel to the surface. The grain boundaries are planes of weakness with different electrochemical behavior than the grain interiors, so intergranular attack strengthens along those boundaries and drives the sheet-like delamination. That’s why the delamination occurs along grain boundaries. Filiform under coatings would show threadlike growths, pits would be localized, and uniform corrosion would eliminate the surface evenly—none of these describe the layered separation along grain boundaries like exfoliation does.