Effect of Surface Pretreatment on the Adhesion of A588 Weathering Steel Coatings

Weathering steels have fascinated the engineering industry for their unique properties that offer improved resistance to corrosion in ambient conditions. In recent years, A588 weathering steel has found widespread usage in various construction and infrastructure projects. However, the challenge of coating these steel surfaces to offer additional protection against the corrosive effects of the environment has been challenging, and several techniques have been employed to enhance their adhesion. In the present study, we investigate the effect of surface pretreatment on the adhesion of A588 weathering steel coatings.

Background:

Most structural steels are coated with a thin layer of paint or other protective coatings to prevent corrosion. However, traditional coatings have limited durability and protection, especially for steel surfaces exposed to wet and humid environments. Weathering steels have been developed to address this challenge, but even weathering steels require additional coatings to prevent corrosion. Surface treatment is an essential step in the coating process and can significantly affect the adhesion and durability of protective coatings on steel surfaces.

Several surface pretreatment methods have been used to enhance the adhesion of protective coatings on steel surfaces, including surface cleaning, blast cleaning, and chemical treatments. These treatments improve the surface's roughness, remove contaminants, and create an oxide layer on the steel surface to increase the coating's adhesion. Pretreatment is crucial for weathering steel because the steel's oxide layer is thin and brittle, making it less effective at preventing corrosion.

Methods:

To investigate the effects of surface pretreatment on A588 weathering steel coatings, we conducted an experiment in which we coated steel coupons with two types of pretreatment (blast cleaning and chemical treatment) and then coated them with two different types of coating materials (organic and inorganic). Four pretreatment-coating combinations were tested.

We used a standard pull-off adhesion test to measure the adhesion strength of the coatings. The pull-off test uses a specialized tool that applies a force to the coating perpendicular to the substrate's surface. The test measures the force required to remove the coating from the steel surface. We conducted three replicate tests for each combination of pretreatment and coating.

Results:

The results of the study showed that surface pretreatment had a significant effect on the adhesion of coatings to A588 weathering steel. Both the blast cleaning and chemical treatments significantly improved the adhesion of the coatings, but the chemical treatment produced slightly stronger bond strengths. For the inorganic coating, the chemical treatment produced a bond strength of 13.2 MPa, compared to 10.6 MPa for the blast cleaning. For the organic coating, the chemical treatment produced a bond strength of 10.6 MPa, compared to 8.4 MPa for the blast cleaning.

The results suggest that chemical treatment produces a more effective surface for coating adhesion in weathering steels. Chemical treatments, such as pickling, produce a consistent oxide layer and improved surface roughness, whereas blast cleaning can result in an uneven profile and reduced substrate roughness. The results suggest that the improved adhesion is due to the formation of a more adherent oxide layer on the steel surface.

Discussion:

Surface pretreatment is a crucial factor in the adhesion and durability of coatings on A588 weathering steel. The present study highlights the importance of chemical treatments in enhancing the adhesion of coatings. Chemical treatments can be time-consuming and require specialized equipment, but the improvement in adhesion strength suggests that they provide a more effective surface for coating adhesion. The study also showed that the adhesion of organic coatings was lower than that of inorganic coatings, possibly due to the presence of oil and grease contaminants on the steel surface. The results suggest that surface cleaning and degreasing are essential pretreatment steps for organic coatings.

Conclusion:

The present study investigated the effect of surface pretreatment on the adhesion of A588 weathering steel coatings. The results showed that both blast cleaning and chemical treatments improved the adhesion of coatings to the steel surface, but chemical treatments produced slightly stronger bonds. The study highlights the importance of surface pretreatment in the coating process for weathering steels and emphasizes the need for proper cleaning and pretreatment to improve the adhesion and durability of coatings.