CHARACTERIZATION AND CORROSION RESISTANCE OF GALVANIZED STEEL/PASSIVATION COMPOSITE/POLYURETHANE PAINT SYSTEMS

A.R. DI SARLI; C.I. ELSNER; C.R. TOMACHUK

BRITSH JOURNAL OF APPLIED SCIENCE & TECHNOLOGY

SCIENCEDOMAIN International

Año: 2014 vol. 4 p. 853 - 878

2231-0843

The corrosion performance of electrogalvanised steel sheets pre-treated with a Cr3+ orCr+6-based conversion layer and then covered with polyurethane-waterborne topcoatpaint has been studied. The pre-treated metallic panels were coated with one of the threetested polyurethane (PU) topcoat paints, in which the dispersion type was the formulationvariable. The pigment was TiO2 (rutile) with a PVC value of 10. Before and after theimmersion in 0.05 M NaCl (pH 5.70) or 0.1 M Na2SO4 (pH 6.36) solutions, replicates ofthe different samples were subjected to standardized tests (porosity, gloss and color,hardness, flexibility). During the immersion, blistering and rusting degrees were evaluatedthrough periodical visual inspections, while the coated steel performance was monitoredby Electrochemical Impedance Spectroscopy (EIS) measurements. Initial (dry) and final(wet) paint adhesion was also determined. EIS data were interpreted and discussed interms of the time dependence of the electrical (paint coating) and electrochemical (steelsubstrate) parameters associated with interfacial processes describing the metal/paintsystem deterioration. According to the electrochemical properties, visual inspection and standardized tests results, it was concluded that the studied polyurethane-basedpolymeric films applied on pretreated electrogalvanised steel provided a very effectiveprotection against corrosion as a result of their excellent barrier properties.