A contribution to the mechanistic understanding of the improvement of the delamination resistance of adhesives on steel by grit-blasting

Grit-blasting of structural steel S355 was shown to inhibit the corrosive delamination of epoxy adhesives. Grit-blasted and polished steel surfaces were comparatively analyzed to provide deeper insights into the effects of the different surface states. The chemical, morphological, and electrochemical property changes of the steel surfaces were investigated using X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The comprehensive analysis revealed a modified chemical composition of the surface layer, and an increased surface area after grit-blasting. Peel-tests of the free-standing adhesive films showed significantly higher wet-adhesion forces on the grit-blasted surface, mainly due to mechanical interlocking. Although the grit-blasted surface shows higher corrosion current densities in chloride-containing electrolytes, the cathodic delamination kinetics for epoxy-coated substrates are drastically reduced in comparison to the solely polished surface. Overall, the results show that the corrosive delamination strongly depends on the wet-adhesion of the adhesive film. Grit-blasting in combination with a low-viscosity epoxy adhesive is therefore an excellent on-site surface treatment before adhesive joining. • Grit-blasting inhibits the corrosive delamination of adhesively bonded steel. • The corrosive delamination resistance is determined by the adhesive strength. • Grit-blasting increases the adhesive strength primarily by mechanical interlocking.