Simulation of pH-controlled dissolution of aluminium based on a modified Scanning Electrochemical Microscope experiment to mimic localized trenching on aluminium alloys

Some constituent intermetallic (IMPs) particles at the surface of aluminium alloys are considered as preferential sites for the initiation of structural corrosion resulting in localized trenching around the particles and the surrounding Al matrix. In this work, a modified scanning electrochemical microscope (SECM) experiment was used to induce such phenomena via a local alcalinisation on 200 nm thick aluminium coatings promoting their local dissolution in an aerated 0.1 M NaCl electrolyte. The local alcalinisation was induced by the oxygen reduction reaction on the tip of a SECM which mimics the surface of an isolated IMP. From a phenomenological point of view, reproducible cylindrical damage develops in front of the platinum ultramicroelectrode (UME). Using a 2D finite element modelling to simulate the SECM experiments, the role of the local alcalinisation was validated and the calculated Al dissolution rate was found in agreement with the experimental evaluation.

► The localised damage of an Al sample by the generation of OH− ions on the tip of a scanning electrochemical microscope approached close from the surface was accurately produced. ► This experiment allows to mimic the reactivity of the surface of an isolated intermetallic particle involved in localized trenching on an aluminium alloy. ► This modified SECM experiment is a valuable tool for validating data entries and boundary conditions used for simulating this corrosion phenomena. ► Using a FEM model, the role of the local chemical change on the dissolution of aluminium in a neutral solution was demonstrated. ► It was found that a pH dependent law must be assumed to simulate the growth of the observed cylindrical damages.