Physical–Mechanical and Corrosion Resistance Characterization of a Water-Based Epoxy Primer Applied to Galvanized Steel

This study presents a comprehensive characterization of a commercial water-based epoxy primer applied to galvanized steel sheets, which are commonly used in building and construction applications. The investigation focused on evaluating the primer’s adhesion, mechanical strength, chemical resistance, and corrosion protection under various environmental and thermal conditions. Particular attention was given to the effect of substrate sanding prior to application, which was found to influence the coating thickness and surface adaptation. The results demonstrated that the primer provides effective barrier properties and good adhesion to the metal surface, with average pull-off strengths remaining consistent across aged and unaged samples. Electrochemical impedance spectroscopy (EIS) confirmed high polarization resistance values, indicating strong corrosion protection, while SEM-EDS analysis revealed the presence of zinc phosphate and titanium dioxide fillers contributing to both passive and active inhibition mechanisms. However, the primer exhibited sensitivity to ultraviolet (UV) radiation, as evidenced by FT-IR spectra showing increased absorbance in the hydroxyl and carbonyl regions after prolonged exposure. A preliminary estimation of the photodegradation rate, based on FT-IR data at the carbonyl peak (1739 cm−1), yielded a value of approximately 2 × 10−6 absorbance units per hour between 3000 h and 5000 h of UV exposure. This value suggests a gradual degradation process, although further quantitative validation is required. Additional limitations were observed, including variability in coating thickness due to manual application and localized blistering at cut edges under salt spray conditions. These findings contribute to a deeper understanding of the primer’s behavior and suggest improvements for its practical use, such as the application of a protective topcoat and optimization of the coating process.