Numerical Simulation of Aluminum Pitting Corrosion: Influence of Electrolyte Conductivity and Nitrate/Sulfate Ions

This study presents a numerical investigation of aluminum pitting corrosion in a 1 M NaCl solution using a two-dimensional model based on secondary current distribution with deforming geometry implemented in COMSOL Multiphysics. The model evaluates the influence of electrolyte conductivity and the effects of nitrate (NO₃⁻) and sulfate (SO₄²⁻) ions added at concentrations of 0.01, 0.02, and 0.03 M on pit growth and morphology.

The simulations show that increasing electrolyte conductivity enhances ionic migration, resulting in higher anodic current density and increased dissolution, particularly near the pit mouth. This behavior is attributed to the ohmic drop inside the pit, which reduces the anodic current density at the pit bottom and promotes preferential dissolution at the pit entrance, leading to lateral pit expansion.

The addition of nitrate (NO₃⁻) and sulfate (SO₄²⁻) ions further increases the corrosion current density (i_corr), demonstrating that higher ionic strength accelerates pit propagation. Sulfate (SO₄²⁻) ions exhibit a stronger effect on corrosion activity than nitrate (NO₃⁻) ions. Moreover, sulfate (SO₄²⁻) ions predominantly promote lateral pit growth, whereas nitrate (NO₃⁻) ions favor pit deepening. Overall, the results demonstrate that aluminum pitting corrosion kinetics and morphology are strongly controlled by ohmic drop, electrolyte conductivity, ionic strength, and the nature and mobility of the ionic species present in solution.