Selective Leaching (Dealloying Corrosion)

Dealloying, also called selective leaching, is a rare form of corrosion where one element is targeted and consequently extracted from a metal alloy, leaving behind an altered structure. The most common form of selective leaching is dezincification, where zinc is extracted from brass alloys or other alloys containing significant zinc content. Left behind are structures that have experienced little or no dimensional change, but whose parent material is weakened, porous and brittle. Dealloying is a dangerous form of corrosion because it reduces a strong, ductile metal to one that is weak, brittle and subsequently susceptible to failure. Since there is little change in the metal’s dimensions dealloying may go undetected, and failure can occur suddenly. Moreover, the porous structure is open to the penetration of liquids and gases deep into the metal, which can result in further degradation. Selective leaching often occurs in acidic environments.