Avaliação da camada de conversão nanocerâmica em substratos metálicos galvanizados e não-galvanizados combinados com tinta poliéster

Abstract

Corrosion causes losses in all sectors of the world economy that make use of metallic materials, making necessary the use of preventive techniques. The use of pretreatments is one of the most applied techniques in the prevention of corrosion, an example of these is the phosphating. It is a well established industrial process for surface treatment and stands out for the increased adhesion of organic coatings. However, the large production of environmental contaminants has generated the need for cleaner technologies. Pretreatment with zirconium oxide has been increasingly prominent in the market, especially in automotive and home appliances, as an economically and environmentally friendly alternative. Hence, the objective of this work was to evaluate the phosphate free surface pretreatment (commercially available as TecTalis®) with a concentration of 1 to 5% hexafluorzirconium acid and 0.2 to 1 mg /m3 of Cu as an alternative to phosphatization, in galvanized and non-galvanized carbon steel followed by powder coating with polyester resin based inks. The samples investigated in this work were provided by USIMINAS (Usinas Siderúrgicas de Minas Gerais S.A).The specimens were evaluated through exposure to accelerated test chambers: Salt spray (ASTM B117) and Saturated Humidity Chamber (ASTM D2247).The degradation process was monitored by means of electrochemical impedance technique (EIS). In addition, immersion tests were performed in 0.1 M NaCl, atmospheric exposure, open circuit potential, adhesion and scanning electron microscopy coupled with dispersive energy spectroscopy. The zirconium oxide treated galvanized sample showed better performance in the salt spray test, maintaining the constant resistance value up to 39 days, suggesting that zirconium oxide contributed more effectively to the protection of the substrate surface. In saturated humidity, immersion and adhesion tests, the aggressiveness of the media was not sufficient to classify the samples for the corrosion resistance of the coating.