Factors influencing the durability of epoxy adhesion to silane pretreated aluminium

Factors that may influence the durability of bonds formed between epoxy adhesive and γγ-glycidoxypropyltrimethoxy silane (γγ-GPS) pretreated aluminium were investigated. A precision milling apparatus or grit-blasting was used to alter the surface roughness of aluminium adherends prior to adhesive bonding. Addition of γγ-GPS to the roughened aluminium surface improved bond durability, but the overall performance was also influenced by the initial surface roughness of the aluminium. The milled ultra-flat aluminium surface exhibited the worst bond durability and the grit-blast and milled surface with a 60° surface profile exhibited the best bond durability. Comparison of the γγ-GPS with a range of phosphonate hydration inhibitors also provided information about the influence of interfacial chemical interactions on bond durability. The coupling mechanism between the phosphonate organic ligand and the adhesive influenced bond durability performance. Surface analysis of failed wedge samples, together with characterisation of the structure of the γγ-GPS and phosphonate films deposited on aluminium, suggested that the γγ-GPS film structure could also affect bond durability performance.