Water-based ZrO2 pretreatment for AA2024 aluminum alloy

Design, development and scale-up of environmentally friendly coatings are very important in order to replace chromate-based coatings for aluminum alloys. 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 pretreatments were developed by means of sol-gel technology. An inorganic salt was employed as Zr precursor in an aqueous solution. The deposition was initially carried out on AA2024 by means of dip and spray technology at laboratory scale. Corrosion inhibitors were introduced to improve corrosion behavior of the films. At a later stage, coating deposition was carried out with a robot-controlled air-pressure gun in spraying cabins in order to evaluate industrial production of the pretreatments. Film morphology and composition were investigated by means of SEM-EDXS and GDOES. The electrochemical behavior of the ZrO2 pretreatments was investigated by means of potentiodynamic polarization. The water-based ZrO2 pretreatment investigated in this work is thin and well adherent on the substrate. Barrier properties are similar to those of chromate conversion coating. Results on samples produced with robot-controlled air-pressure gun indicate that ZrO2 pretreatments are suitable for industrial application. Copyright (C) 2009 John Wiley & Sons, Ltd.