Epoxy Silane - a Preferred Surface Treatment for Bonded Aluminium Repairs

The effectiveness of eight commercially available organo-functional silane coupling agents as adhesion promoters for the bonding of aluminium with aerospace epoxy structural film adhesives has been investigated and compared with the chromic acid (FPL) etch and two basic non-chemical surface pretreatments. Using shear strength at both ambient and elevated temperatures, and durability as judged using the wedge test, the epoxy silane, gamma-glycidoxypropyltrimethoxy silane was found to be the most effective, its performance almost matching that of the chromic acid etch. Further experiments showed that the epoxy silane pretreatment could provide durable bonds between a variety of aluminium alloys and an epoxy-based structural film adhesive over a diverse range of application conditions. Such versatility gives this relatively simple and non-toxic surface preparation technique significant potential for use in bonded aircraft repairs, particularly under non-ideal conditions.