Effect of contaminant on the durability of epoxy adhesive bonds with Alclad 2024 aluminium alloy adherends

Surface preparation of aluminium alloy adherends is designed to minimize the influence of organic contaminant on the durability of epoxy adhesive bonds. The organic contaminant molecules have the potential to inhibit the bonding of the adhesive with the surface oxide on the adherend. X-ray photoelectron spectroscopy (XPS) shows that a freshly exposed aluminium surface quickly adsorbs over ten atomic layers of organic contaminant. Models to fit XPS data measured at various specimen take-off angles indicate that this contaminant is not adsorbed uniformly. Experiments show that for mechanically prepared adherends treated with an organosilane coupling agent, the bond durability depends strongly on the contaminant concentration and the time of administration during the preparation sequence. The observed variations in bond durability can be explained in terms of inhomogeneities in the strength of adhesion between the adhesive and the metal oxide.