Numerical simulation of micro-galvanic corrosion in Al alloys: Effect of geometric factors

A finite element model for simulating the propagation of intermetallic particle driven micro-galvanic corrosion in an Al-matrix model system is presented. The model revealed dynamic changes related to localized corrosion, including the moving dissolution boundary, the deposition of reaction products (Al(OH)₃), and their blocking effect. Modelling was focused on the effects of key geometric parameters, including the radius of cathodic particle (range 0.5 to 4 μm) and the width of an assumed anodic ring surrounding the particle (range 0.1 to 2 μm). Simulations revealed the dynamic flow of molecular and ionic species, along with influence of geometrical constraints. For ring widths below 0.5 μm, deposition of Al(OH)₃ inside the dissolving volume was inhibited due to limited transport of OH− and O₂ into a constrained volume − resulting in local acidification. An increase in cathodic particle radius at given ring width resulted in a greater dissolution by providing a larger cathodic area for O₂ reduction, quantifying the effect of cathode/anode ratio. The model was also developed to include two cathodic particles to explore any interaction. The present study reveals a physicochemical model that contributes toward a framework for multi-process localized corrosion systems, which can be further adapted to commercial alloy systems.