Influence of nanoporous structure on mechanical strength of aluminium and aluminium alloys adhesive structural joints

The influence of surface treatments on the mechanical strength of adhesivejoints was investigated. The attention was focused on AA2024 alloy becauseit is extensively used in both the automotive and aerospace industries. Adhesivejoints fabricated with pure aluminium were also investigated in order toevidence possible differences in the surface features after identical treatments.Before joining with a commercial epoxy adhesive, metal substrates weresubjected to different kinds of treatment and the surfaces were characterizedby SEM analysis. The formation of a microporous surface in the AA2024alloy, upon etching and anodizing, is discussed on the basis of the role ofthe intermetallic particles and their electrochemical behaviour with respectto the aluminium matrix. Moreover, nanostructured porous oxide layers onboth type of substrate were also formed, as a consequence of the anodizingprocess. Differences in their morphologies were revealed as a function of boththe applied voltage and the presence of alloying elements. On this basis, anexplanation of the different values of fracture energy measured by means ofT-peel tests carried out on the corresponding joints was attempted.