The surface pretreatment of aluminium-lithium alloys for structural bonding

Transmission electron microscopy examination of ultramicrotomed sections taken through a bonded joint allows both the effect of standard chemical pretreatments and an initial adhesive/adherend interfacial analysis to be made for structural joints prepared using BA 8090C-T3 aluminium-lithium alloy substrates. These observations, when compared with earlier work using Alclad 2024-T3 adherends, show that broadly similar films are formed on the aluminium-lithium surface; a rougher topography has, though, been noted on some specimens. In general, these films appear to be wetted and, in some cases, penetrated by the adhesive used in the same manner as the Alclad controls. Initial measurement of bond strengths shows that the pretreated aluminium-lithium is amenable to adhesive bonding. However, although examination of sections through the environmentally exposed joints shows no apparent interphasial damage, pickled aluminium-lithium substrates perform better than those anodized in phosphoric acid; this is contrary to expectations based on prior work using the more conventional aluminium alloys.