Corrosion protection of AA2024-T3 aluminium alloy by sealed anodic layers using two alditols as corrosion inhibitors

摘要

The former conventional pre-treatment of AA2024-T3 aluminium alloy involves formulationscontaining chromium (VI) but restrictions were imposed for the use of hexavalent chromium in EU,due to the negative impact of these compounds in environment and human health. In recent yearsthere has been renewed interest in the search developing new corrosion protection alternatives thatcould be efficient and more environmentally and human-friendly, to replace the chromium (VI)based treatments.The objective of this study is to evaluate the anticorrosion character imparted by two alditols(xylitol and sorbitol), and compare their performance with tartaric acid containing bath, which isused (e.g. AIRBUS) in the sulphuric anodising the aluminium alloy used in aeronautical andaerospace industry, the AA2024-T3 alloy.The corrosion resistance of the treated samples was monitored by potentiodynamic polarizationassays and Electrochemical Impedance Spectroscopy analysis. Cyclic voltammetry was used tocharacterize the electrochemical behaviour of the two alditols.Morphology of the anodic films was assessed by high resolution microscopy, being the wettabilityof the modified surfaces evaluated by contact angle goniometry. Characterization of obtainedanodic films formed was done by Fourier Transform Infrared Spectroscopy (FTIR).The conversion coatings formed on the aluminium alloy revealed that the use of thesecarbohydrates provide an improved corrosion protection, making this pre-treatment a promisingalternative for chromium (VI) based chemical conversion coatings.