On the Evolution of Cathodic Activity during Corrosion of Magnesium Alloy AZ31B in a Dilute NaCl Solution

Sequential potentiodynamic polarization and scanning vibrating electrode technique measurements were made on Mg alloy AZ31B immersed in dilute 0.05 M NaCl solution to corroborate the suspected role of noble metal (relative to Mg) solute enrichment at the filament/alloy interface in sustaining the cathodic activation exhibited by corrosion filaments. The electrochemical measurements revealed that the extent of cathodic activation (i.e. current density) measured over a corrosion filament was sustained with immersion time. This resulted in a continual increase in the total anodic current measured over the AZ31B surface as new filaments initiated and propagated. The sustained cathodic activation coupled with observations of zinc (Zn) enrichment at the filament/alloy interface during the life of a corrosion filament is argued to be indicative of a solute enrichment mechanism being a significant factor in this process.