Which factor helps explain why galvanic corrosion is often pronounced at sharp edges or corners?

• A. The proximity of dissimilar metals and high local current density at edges
• B. The presence of a continuous electrolyte
• C. The absence of a metallic path
• D. The lack of electrolyte

Answer: (A)

The key idea is that galvanic corrosion is driven by a galvanic couple and by high local current density where geometry concentrates the current. When two dissimilar metals are in contact in an electrolyte, electrons flow from the more active metal (anode) to the more noble metal (cathode). The rate of corrosion depends on how much current is forced through the tiny path at a given spot. Sharp edges or corners concentrate this current because the remaining metal path around the edge is effectively smaller and has irregular geometry, which reduces impedance locally and drives a higher current density there. In addition, edges often have thinner protective coatings, microcracks, and moisture accumulation that trap electrolyte, further lowering resistance and enhancing dissolution at that spot. So the combination of close metal proximity and a geometry that concentrates current makes corrosion particularly severe at sharp edges.

The other options don’t explain this localization as well: a continuous electrolyte is required for galvanic action but would affect surfaces more uniformly rather than focusing at edges; the absence of a metallic path would stop the current flow; and lacking electrolyte would prevent galvanic corrosion entirely.