Boiling water and silane pre-treatment of aluminium alloys for durable adhesive bonding

Three series of aluminium alloys received a surface pre-treatment including immersion in boiling water followed by soaking in a 1% aqueous solution of 3-glycidoxytrimethoxysilane. When aluminium was pre-treated in this manner, adhesive joints formed with a range of epoxy resins produced notable improvements in bond durability in comparison with simple abrasion pre-treatments. In some cases, the pre-treatment improved joint durability to the level observed for the phosphoric acid anodise process. The development of a platelet structure in the outer film region combined with the hydrolytic stability of adhesive bonds made to the epoxy silane appear to be critical in developing the bond durability observed. Generally, immersion of the aluminium alloys at temperatures above 80°C for periods between 4 and 60 min provide the optimum conditions required to prepare a surface film, which will produce durable bonds with epoxy adhesive.