Corrosion behaviour of two duplex systems in salt spray testing.

P.R. SERÉ; C.I. ELSNER; A.R. DI SARLI

Corrosion Prevention & Control

Scientific Survey

Año: 1998 vol. 45 p. 109 - 117

0010-9371

Experience has shown that the anticorrosive behaviour of galvanized steel is considerably improved when it is covered with an adequate painting scheme, thereby forming a so-called duplex system. Such a scheme gives better protection than that provided by either galvanic or organic coatings alone. The synergistic effect is mainly due to the combination of the double protective effect (galvanic and barrier) afforded by the metallic coating and the paint. With this in mind, the protective capacity of several duplex systems submitted to exposure in the ASTM salt-spray cabinet test was evaluated using electrochemical measurements and standardized physicochemical tests. Low-carbon steel sheets hot-dip coated with Zn or 55%Al-Zn alloy were covered with the following painting schemes: a) synthetic wash primer and synthetic alkyd enamel; b) wash primer and topcoat paint (both epoxy); or c) wash primer and topcoat paint (both polyurethanic). From the experimental results it was concluded that, under the current environmental conditions, the duplex system, including the polyurethanic-based scheme, showed the best protective properties.