Investigation of the (sub)surface of commercially pure rolled aluminium alloys by means of total reflectance, r.f. GDOES, SEM/EDX and FIB/TEM analysis

Rolling is known to alter surface properties of aluminium alloys and to introduce disturbed subsurface layers. These layers are characterised by a refined grain structure, rolled‐in oxide particles, a fine distribution of intermetallic particles and various voids and cracks. In previous studies, mostly higher alloyed materials have been investigated. Here, the subsurface of a commercially pure rolled aluminium alloy (99.5% Al) is characterised. Hot and cold rolled sheets, with and without additional annealing are investigated. Measuring total reflectance (TR) of progressively etched samples is used as an optical depth profiling method to derive the thickness of disturbed layers. The in‐depth behaviour of alloying, trace and impurity elements in the subsurface regions is studied with quantitative radio frequency glow discharge optical emission spectrometry (r.f. GDOES). The bottom of glow discharge optical emission spectrometry (GDOES) craters at various depths is investigated with SEM/EDX. Focused ion beam (FIB) thinning is employed to prepare site‐specific cross‐sectional TEM specimens. Analytical TEM is used to investigate the thickness, microstructure and composition of the disturbed subsurface. It can be concluded that rolled commercially pure aluminium exhibits disturbed subsurface layers, consisting of a mixture of Al 2 O 3 and metallic aluminium particles, with cracks and voids. These layers are introduced during hot rolling, and reduced in thickness and redistributed over the surface during subsequent cold rolling. Copyright © 2006 John Wiley & Sons, Ltd.