ABSTRACT
Abstract-The goal of the present study was to understand the relative importance of chemical bonding and interfacial stability when thin silane layers were used as pre-treatments for adhesive bonding of aluminium with epoxy adhesives. The main focus was on hydrolysed y-APS and BTSE, used either alone or in combination. Samples were subjected to wedge tests, acetic acid salt spray tests (ASSTs) and surface characterisation. BTSE used alone was found to be the most efficient, its performance approaches that of a standard pre-treatment developed by the Boeing Company for use on airplanes. BTSE might reinforce the adhesive bond by interacting with silanes in the adhesive. Samples were bonded using silane-containing and silane-free adhesives to test this hypothesis. The results suggested that BTSE improves the durability of adhesive bonds by decreasing the hydrolysis and/or corrosion rate at the adhesive-metal interface, while /-APS increases the original adhesive bond strength by interacting chemically with the adhesive. Bis-silanes with and without amino groups were tested in an attempt to combine chemical bonding and corrosion protection. The samples with the highest amine concentration initially gave the strongest adhesive bond, while the best durability was obtained for samples providing good protection against interfacial hydrolysis and corrosion. It seems that it is not necessary for a silane to react with the adhesive in order to obtain a durable adhesive bond, and judging from the current results, two non-functional bis-silanes, BTSE and bis(trimethoxysilyl)hexane, actually show the greatest promise with respect to replacing current, chromium-containing pre-treatments.
