Corrosion behaviour of sol–gel treated and painted AA2024 aluminium alloy

Design, development and scale-up of environmentally friendly coatings are very important in order to replace chromate based coatings for aluminium alloys. Barrier properties, paint adhesion and possibly self-healing ability are relevant aspects for replacement of chromate-based pre-treatments. Sol–gel materials are candidates for use in protective coating applications, as it is possible to form highly adherent and chemically inert oxide films on metal substrates.ZrO2 based pre-treatments were developed by means of sol–gel-technology. ZrO2 films were deposited on AA2024 by means of dip-coating technique in sol obtained from metal-organic precursor in an organic solvent. In addition, an inorganic salt was employed as Zr precursor in an aqueous solution. Cerium nitrate was introduced in multilayer films in order to improve the corrosion behaviour. In addition, AA2024 substrates pre-treated with ZrO2 films were painted with an organic primer and top coat in order to evaluate the electrochemical behaviour of painted systems.The morphology, thickness and composition of ZrO2 films deposited on AA2024 were investigated by means of SEM-EDXS and GDOES (glow discharge optical emission spectroscopy). The electrochemical behaviour of ZrO2 pre-treatments was studied by means of potentiodynamic polarization measurements. AA2024 samples pre-treated and painted with an organic coating were subjected to paint adhesion tests and electrochemical characterization by means of electrochemical impedance spectroscopy.