Study of the near-surface of hot- and cold-rolled AlMg0.5 aluminium alloy

Rolling is known to alter the surface properties of aluminium alloys and to introduce disturbed near-surface microcrystalline layers. The near-surfaces of mostly higher alloyed materials were investigated by various techniques, often combined with a study of their electrochemical behaviour. Cross-sectional transmission electron microscopy (TEM), after ion milling or ultramicrotomy, indicated the presence of disturbed layers characterized by a refined grain structure, rolled-in oxide particles and a fine distribution of intermetallics. Those rolled-in oxide particles reduce the total reflectance of rolled Al alloys. Furthermore, various depth profiling techniques, such as AES, XPS, SIMS and qualitative glow discharge optical emission spectroscopy (GD-OES) have been used to study the in-depth behaviour of specific elements of rolled Al alloys. Here, the surface and near-surface of AlMg0.5 (a commercially pure rolled Al alloy with addition of 0.5 wt.% Mg) after hot and cold rolling, and with and without additional annealing is studied with complementary analytical techniques. Focused ion beam thinning is introduced as a new method for preparing cross-sectional TEM specimens of Al surfaces. Analytical cross-sectional TEM is used to investigate the microstructure and composition. Measuring the total reflectance of progressively etched samples is used as an optical depth profiling method to derive the thickness of disturbed near-surface layers. Quantitative r.f. GD-OES depth profiling is introduced to study the in-depth behaviour of alloying elements, as well as the incorporation of impurity elements within the disturbed layer. The GD-OES depth profiles, total reflectance and cross-sectional TEM analyses are correlated with SEM/energy-dispersive x-ray observations in GD-OES craters. Copyright © 2005 John Wiley & Sons, Ltd.