Development and Industrial Scale-Up of ZrO2 Coatings used as Pre-Treatments before Painting Aluminium Alloys

Development of Cr-free coatings is an important issue for replacement of chromate conversion coatings in aerospace and automotive industry. This aspect was targeted in the framework of MULTIPROTECT IP project funded by the European Community. Our research approach in the project considered the development of thin ZrO2 coatings (100-200 nm) by means of sol-gel technology for AA2024 aluminium alloy. ZrO2 films were deposited employing solutions of Zr precursors. Two preparation routes were followed: the first employed a metal-organic precursor in an alcoholic solution; the second one used a water-based solution of a Zr salt. Coating application was carried out by dipping and spraying technology at a laboratory scale. In addition, substrates pre-treated with ZrO2 films were painted with an organic primer and top coat in order to evaluate paint adhesion and electrochemical behaviour of painted systems. At a later stage of the project, coating deposition was carried out with a robot-controlled air pressure gun in spraying cabins in order to evaluate industrial production of the ZrO2 films.