Understanding the relationship between silane application conditions, bond durability and locus of failure

The extent to which an organosilane surface treatment regime can promote durability enhancement of an adhesively bonded aluminium alloy system has been determined. Results have revealed the range of application and film-conditioning parameters which contribute to joint durability in a simple Boeing wedge joint. Organosilane solution parameters relating to solvent type, solution concentration, pH and hydrolysis time have all been shown to influence resultant durability. Interestingly, parameters such as film drying temperature and in-process time delay (time interval between application of the organosilane to the alloy surface and subsequent bonding) have little influence on joint performance. The factors responsible for the durability variations observed have been considered using various surface analytical techniques. Superficially, failure surfaces indicative of interfacial failure between substrate and adhesive have been observed. More detailed characterisation using both XPS and SIMS has indicated failure processes associated with a ‘diffusion zone’ comprising aluminium oxide and the organosilane.