Adhesion of epoxy cataphoretic coatings on Zn alloys

Abstract

One of the most important factors in corrosion prevention by protective coatings is the loss of coating adhesion under environmental influence. In this work, the adhesion of epoxy cataphoretic coatings was examined on steel and steel modified by Zn-Fe and Zn-Co alloys. The dry and wet adhesions of epoxy primers were measured by the direct pull-off standardized procedure, as well as indirectly by the NMP test. The corrosion stability of the coated samples was investigated by electrochemical impedance spectroscopy. It was shown that under dry testing conditions all the samples exhibited very good adhesion. However, different trends of adhesion loss of different protective systems during exposure to a corrosive agent (3 % NaCl solution) were observed. The lowest adhesion values were obtained for epoxy coating on the steel substrate. The change in adhesion of the epoxy coating on steel modified by Zn-Co alloy during immersion in 3 % NaCl solution for 24 days was the smallest of all the investigated samples. Electrochemical impedance measurements in 3 % NaCl solution confirmed the good protective properties of this protective system, i.e., greater values of pore resistance were obtained.

Jedan od najvažnijih faktora u zaštiti od korozije organskim prevlakama je gubitak adhezije organskih prevlaka pod uticajem korozione sredine. U ovom radu proučavana je adhezija epoksidnih kataforetskih prevlaka na čeliku i čeliku modifikovanom legurama Zn-Fe i Zn-Co. Ispitivane su tzv. suva i mokra adhezija standardnim pull-off postupkom, kao i NMP testom. Koroziona stabilnost svih uzoraka je ispitivana spektroskopijom elektrohemijske impedancije. Svi uzorci su imali dobru početnu adheziju, međutim tokom delovanja korozionog agensa (3 % NaCl) promena adhezije se značajno razlikovala kod različitih zaštitnih sistema. Najmanje vrednosti adhezije su dobijene u slučaju epoksidne prevlake na čeliku. Ukupno smanjenje adhezije tokom 24 dana ispitivanja je najmanje za epoksidnu prevlaku na čeliku modifikovanom Zn-Co legurom. Najveće vrednosti otpornosti u porama epoksidne prevlake tokom celokupnog ispitivanog perioda delovanja korozionog agensa kod prevlake na čeliku modifikovanom Zn-Co legurom takođe ukazuju na veliku stabilnost ovog zaštitnog sistema.