Failure Mechanisms in the Boundary Layer Zone of Metal/Polymer Systems

A systematic optimization of the long term stability of polymer/metal systems in the boundary zone requires the exact knowledge of the mechanisms producing the so-called adhesional failure particularly under the influence of humidity. Strong and water-stable adhesion, for example, between organic primers and aluminium alloys is obtainable if the metal surface is coated with a porous oxide layer, which can be produced by special etching and anodizing processes. The relatively small molecules of the primers can penetrate practically the whole oxide structure. But despite this, it is easy to demonstrate that very small differences in the parameters of the surface treatment, leading to small differences in the surface morphology, can change the water stability of the boundary zone considerably. The transition zone between the oxides and primers in such systems was investigated by using the wet peel test, transmission-electron microscopy of ultra-thin cross sections from the boundary zone before and after delamination and ESCA on the fracture surfaces.