The effects of surface pretreatment on the cyclic-fatigue characteristics of bonded aluminium-alloy joints

The present work has used an accelerated test method, based upon cyclic-fatigue testing using a fracture-mechanics approach, to study the durability of organosilane-pretreated joints which were adhesively-bonded using a hot-cured epoxy-film adhesive. The silane primer investigated was γγ-glycidoxypropyltrimethoxysilane (GPS). The cyclic-fatigue tests were mainly conducted in (a) a ‘dry’ environment of 25±2 °C with a relative humidity of 55±5% and (b) a ‘wet’ environment where the joints were fully immersed in distilled water at 28±2 °C. However, tests were also undertaken by varying the relative humidity of the environment. The loci of failure of the joints were identified using various surface specific techniques. The use of the GPS-pretreatment has been shown to be effective in increasing the joint durability, compared with a simple grit-blast and degrease (GBD) treatment and, indeed, gives comparable results to using a chromic-acid etch (CAE) pretreatment.