Joint Durability Studies with Abraded, Etched, Coated and Anodized Aluminum Adherends

The effect of surface pretreatment on the aluminum oxide surface is critical and intimately related to the bond permanence of aluminum adhesively bonded joints. It is difficult, however, to distinguish the benefit of different surface treatments in the absence of some weathering test condition since the joints will fail cohesively for many different surface-treating conditions when tested without such exposure. Aluminum alloy 6061-T6 was pretreated by various procedures including sanding, grit blasting, hot acid etching, heat-cured epoxy paint priming, Alodining, and sulfuric acid anodizing. Both room-temperature-curing two-part and one-part heat-curing epoxy adhesives were used to fabricate the test specimens. The weathering evaluation procedures included both accelerated laboratory-type and natural atmospheric exposures. The list of weathering conditions included: immersion in room-temperature water, exposure to continuously condensing humidity at 52°C (125 F), and hot water soak/freeze/thaw cycling; as well as, exposure in an industrial-type atmosphere and a seacoast atmosphere.