Role and Characterization of Surfaces in the Aluminium Industry

Aluminium is used extensively in the transportation, architecture, electronic and packaging industries. Aluminium presents particular characteristics such as low density, high ductility and a highly protective natural oxide film. However, formability, corrosion resistance, weldability, adhesion and surface aspect depend on the chemistry and microstructure of the metal surface. Properties of particular importance include the oxidation state, the degree of hydration and surface modifications induced by transformation and storage. For surface finishing processes it is necessary to determine the nature of chemical species created and their interactions with the substrate. Modern methods of surface characterization are extensively applied to solve these issues. Techniques such as X ray photoelectron spectroscopy (XPS), Auger microscopy, secondary ion mass spectrometry (SIMS) and electron microscopy (TEM and SEM) are used routinely. In addition novel approaches are starting to be used systematically for industrial research (X ray absorption spectroscopies, time of flight static SIMS and atomic force microscopy) after an initial phase of development in university laboratories. The use of these methods combined with studies of adsorption of model compounds leads to a better understanding of interfacial phenomena. For surface analysis to successfully contribute to R&D programmes, the representativity and data quantitation have to be assured. Use of several, complementary, methods enables interpretations to be confirmed. The principal applications of aluminium involving a high degree of surface technology are reviewed together with recent examples of the use of the aforementioned methods, in particular concerning the optimization of aluminium surfaces before subsequent surface finishing.