Selection of appropriate electrochemical deposition regime for cerium conversion coating on anodized AA2024-T3 aircraft alloy

The reliable and durable corrosion protection of commercially attractive aluminum alloys like AA2024-T3 is the subject of world-wide intensive scientific research. Thus, the quality of the preliminary treatments and the coating primers is of key importance in this field. In this aspect, Anodic Aluminum Oxides (AAO) and Cerium Conversion Coatings (CeCC) appear to be the most perspective approaches for the formation of coating primers. The present systematic study offers results of a comparative elucidation of the properties of CeCC deposited under different regimes on AAO formed on the AA2024-T3 aircraft alloy. The formation of CeCC was performed either spontaneously, or under different electrochemical regimes. The samples were subjected to analyses that included: (i) preliminary color characterization and contact angle measurements, (ii) surface observations by optical metallographic (OMM) and scanning electron (SEM) microscopy, (iii) element distribution by means of Energy dispersive X-ray (EDX) and X-ray Photoelectron (XPS) spectroscopy and (iv) corrosion tests. The latter were performed by applying Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Scanning (PDS) after 24 h of exposure to a 3.5% NaCl model corrosive medium (MCM). For completeness, the experiments were extended to 672 h of exposure for the samples with superior barrier ability. The analysis of results obtained from the employed analytical techniques has revealed that spontaneous and cathodic depositions at low current densities are suitable for formation of uniform CeCC layers. Conversely, the application of higher current densities and alternating current (AC) or anodic deposition regimes had adverse effects. Graphical abstract