Avaliação da resistência à corrosão de aços revestidos ou não com zinco fosfatizados e pintados

Abstract

Corrosion problems have led the automotive industry to improve its corrosion performance with the introduction of different pretreatments and painting techniques. The use of galvanized steels has expanded a great deal in diverse sectors such as automotive, construction and home appliances industries. The aim of this work is to evaluate the corrosion resistance of galvanized, phosphated and painted steels. This evaluation was carried out by Electrochemical Impedance Spectroscopy (EIS) technique, in order to elucidate the corrosion mechanisms and to represent the corrosion process using electric circuits. Four types of painted samples were evaluated: carbon steel (C), electro galvanized steel (EG), hot-dip galvanized and phosphated steel (HDG GI), heat galvanized and phosphated steel with heat treatment (HDG GA). The choice of corrosive solution was NaCl 0.05 mol/L. For EIS tests, the frequency range was 0.0001 to 10000 Hz, with the amplitude of 0.01 V. For open circuit potential stabilization curves, the total exposure time was 7200 seconds. It was observed that HDG GI sample showed the best results both in thermodynamic aspect (stabilization potential) as well as in the electrochemical corrosion. Different control mechanisms for the painted steels corrosion processes were detected. For carbon steel (C), a diffusion controlled process was observed while for EG, HDG GI and HDG GA samples, a charge transfer process was identified. Scan Electronic Microscopy analyses were performed before and after electrochemical tests, in order to examine sample surface aspects.