Assessment of the Effect of Alkalization in Localized Corrosion of Aluminum Alloys Using Finite Element Modeling

Local alkalization originating from O₂ reduction at cathodic intermetallic particles (IMP) in Al alloys has been formerly shown to have an influence on the propagation of corrosion at the IMP/anodic matrix interface.

A methodology combining finite element modeling, engineered bimetallic Al/Cu systems and EQCM (Electrochemical Quartz Crystal Microbalance) measurements has been implemented to quantitatively describe the effect of pH on localized corrosion propagation.

The bimetallic Al/Cu systems have been used to get experimental currents originating from the galvanic coupling between a Cu particle and its surrounding Al matrix. The current evolution with time exhibited two stationary states : an initiation/passive regime and a propagation/active regime.

The boundary conditions for which the model can provide current distributions that actually fit the experimental current values were determined for both regimes.

The validated model was then used to describe pH evolution.

EQCM measurements were made to provide experimental data concerning the effect of pH on the dissolution of pure Al. Time dependent analysis of the pH evolution shows that alkalization has less importance than expected in the onset of corrosion propagation.