Chemical conversion coatings for structural adhesive bonding of plain carbon steels

A range of chemical conversion coatings has been considered as an alternative to degreasing, grit-blasting or silane application for the pretreatment of plain carbon steels prior to adhesive bonding. Initial single lap shear (SLS) joint strengths were used to select the best-performing pretreatments. Those selected were then considered in terms of their durability performance with unstressed SLS joints immersed in water at 60°C and measuring residual joint strengths as a function of immersion time. The changes introduced to the surface were studied using a range of analytical techniques. The best-performing process was a two-stage treatment, Bonderite 901–Pyrene 8-90, which provided a micro-rough surface texture and a highly complex but relatively stable surface oxide. These highly desirable surface characteristics were thought responsible for the observed adhesion performance.