Abstract
This study investigated a conversion coating based on hexafluorozirconic acid solution on cold-rolled (AISI 1006) steel sheets, in situ, at different pH values and immersion times. Electrochemical characterization was carried out by electrochemical impedance spectroscopy (EIS) with hexafluorozirconic acid bath as the electrolyte. Laser scanning confocal microscopy (LSCM) was used to evaluate the morphology of the coating in situ, i.e., during the coating formation. According to the results, the polarization resistance (Rp) of the conversion coating is affected by the immersion time and by the pH of the conversion bath. The electrochemical analyzes point out conversion baths at pH between 3.5 and 4.5 and immersion times from 600 to 900 s as optimal operating conditions, achieving an average polarization resistance of 713 ± 107 Ω cm2.
Highlights
Metallic substrates receive organic coatings to improve their appearance and increase the protection against corrosion
For the purpose of applying painting, the phosphate conversion coating is usually associated with a chromium conversion coating, used as pore sealing, supplementing the protection obtained with the phosphate conversion coating[3]
The best anticorrosive properties we found, yielding a polarization resistance of 713 ± 107 Ω cm[2], were achieved from samples C, D and E, which were treated in conversion baths at pH 3.5, 4.0 and 4.5, respectively, in immersion times between 600 and 900 s
Summary
Metallic substrates receive organic coatings to improve their appearance and increase the protection against corrosion The application of this coating is usually associated to a pretreatment to modify the metal surface in order to improve the organic coating adherence, increasing the protection against corrosion[1]. The chromium conversion coating, in most cases, is obtained by immersing the phosphate-coated material (or the bare material) in an aqueous bath of hexavalent chromium. Both phosphate and chromium conversion processes generate highly pollutant effluents, namely, rinsing water and spent solutions, which need costly treatment and disposal methods for effluents and wastes
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