Durability of adhesively bonded surfaces finished galvanised steels in corrosive environments (DURADH): final report

The aim of this project was to understand the adhesion and de-adhesion mechanisms of adhesively bonded galvanised (Z) and zinc magnesium (ZM) alloy coated steel. In order to investigate the degradation processes occurring at the metal/adhesive interface of the bond-joint a comprehensive and multidisciplinary approach involving ex-situ and in-situ measurements has been carried out. Water uptake analysis of the adhesive was performed by means of EIS and lap shear test. The adhesive delamination studies on adhesive joints as well as the corrosion behaviour of the DURADH coatings were carried out by means of EIS and in-situ backside Raman spectroscopy. The effect of the surface cleaning on the de-adhesion properties has been investigated as well. Adhesion promoters were applied on DURADH coatings and their effect on the interface stability of the adhesive joint was checked. Our results indicated that the interfacial water diffusion through the adhesive is causing the change in the failure mode from cohesive to adhesive. Once water reaches the adhesive/oxide interface, weakening of the bonds between the adhesive and the substrate occurs. Since water diffusion through the adhesive cannot be diminished, different strategies to enhance the strength of the adhesive/oxide interface have been proposed. Surface treatments, application of adhesion promoters and preparation of the coatings under different wiping conditions were found to be promising strategies for the fabrication of adhesive joints with enhanced properties. The improved interfaces with metal ion rich surfaces allow the coordinative bond formation with chelate forming molecules of polymers.