A novel approach to determine cathodic passivation characteristics and semiconducting properties of pure aluminium 99.5 wt% and aluminium alloy 7075-T6 with an electrochemical pen electrode

Localised electrochemical impedance spectroscopy and Mott-Schottky analysis were carried out to investigate the electrochemical behaviour of pure aluminium 99.5 wt% and aluminium alloy 7075-T6. Functionally graded surface films were generated using a Hull cell set-up, with the nature of the resulting surface assessed as a function of cathodic current density. Defect donor densities, oxide thicknesses, and impedance moduli were determined, resulting in sub-mm to mm-sized response characteristics. Mott-Schottky analysis provided access to n-type characteristics in the cathodic polarisation regime and p-type behaviour towards the anodic polarisation direction. Electron microscopy analysis of the contact area revealed the occurrence of localised corrosion.