Improving the Adhesion of Organic Coatings to Galvanized Steel Through Mechanical Pretreatment of the Steel Substrate

This study focuses on ways to improve the adhesion of organic coatings in a duplex anticorrosion protection system for S235JRG2 steel. To this end, the steel was mechanically pretreated by blasting with synthetic corundum (F40). Subsequently, the effect of this treatment on the indirect increase in the adhesion of the organic coating applied to the inorganic coating was analyzed. The inorganic coatings comprised electrogalvanized zinc and hot-dip galvanized zinc, while the organic system consisted of a water-borne coating. The reference specimens comprised cold-rolled steel surfaces (without mechanical pretreatment) and chemically pretreated zinc layers (prepared by Cr3+-based passivation). The mechanical surface pretreatments were characterised by surface roughness parameters (ISO 21920-2). The quality of the deposited inorganic coatings was evaluated using metallographic cross-sections. The adhesion of the organic coatings was assessed by a pull-off adhesion test (ISO 4624). The quantitative evaluation (pull-off strength) was carried out using a universal testing machine, while the qualitative analysis, namely the extent of adhesive and cohesive failure, was performed by digital image analysis in ImageJ. Degradation testing was conducted in a neutral salt spray environment (ISO 9227). The results indicate that the most pronounced increase in adhesion can currently be achieved by means of a conversion interlayer. In terms of indirect adhesion enhancement, a statistically significant increase relative to the rolled reference specimen was demonstrated for the electrogalvanized zinc layer. The degradation test results likewise suggest a positive effect on the operational reliability of the components. These findings open up new scope for further research into more environmentally friendly mechanical surface pretreatment methods.