Meaning
Microscopic electrochemical circuits formed when distinct metallurgical phases or composition gradients reside in close proximity on a single metal surface drive localized corrosion reactions. A micro-galvanic cell operates when the potential difference between secondary precipitates and the surrounding metal matrix initiates electron flow in the presence of an electrolyte. This phenomenon causes rapid pitting on apparently uniform metal surfaces.
Phase Heterogeneity
Second-phase particles and intermetallic compounds act as local anodes or cathodes relative to the primary matrix alloy. For alloys containing a micro-galvanic cell, the localized dissolution of the more active phase occurs during exposure to thin liquid films. This behavior is common in multi-element alloys that have undergone improper heat treatment.
Corrosion Path
Rapid penetration into the metal thickness proceeds from these localized reaction points. Because the micro-galvanic cell concentrates anodic dissolution on a tiny area, the rate of localized material loss can be high.
Mitigation Strategy
Composition control and heat treatment optimization can minimize the distribution of aggressive secondary phases. When using alloys susceptible to a micro-galvanic cell, applying homogeneous solution treatments or surface passivation coats prevents the establishment of active electrochemical couples. This protection increases the durability of components in marine and industrial environments.
