Influence of surface pre-treatments on disturbed rolled-in subsurface layers of aluminium alloys

Rolling is known to alter the 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, various voids and cracks. In this study, the effects of some surface pre-treatments, i.e., alkaline etching at various temperatures and chemical cleaning with Nabuclean and CrO3/H3PO4, on these rolled-in layers are investigated by means of surface analytical techniques. The changes in composition and morphology of the (sub)surface are studied with scanning electron microscopy/energy dispersive X-ray analysis and backscattered electron imaging (SEM/EDX+BEI). The presence of incorporated oxide particles is evaluated by measuring the total reflectance. The (re-)distribution of alloying, impurity and trace elements upon these surface treatments is investigated with radiofrequency glow discharge optical emission spectrometry (rf-GDOES).