Characterization of the anodic oxide layer deposited on severely deformed and aged AA6063 aluminum alloy

Abstract

The aim of this study was to investigate the effects of severe plastic deformation (SPD) and thermal treatment on the nanostructure and properties of the anodic oxide layer of AA6063. SPD was conducted using up to 6 passes of equal channel angular pressing (ECAP) which was followed by post-deformation aging treatment. Two-step anodization via hybrid pulse voltage was utilized to form highly ordered anodic coatings. Positive pulse and reverse pulse modes were used for the first and second steps of anodization, respectively. Nanostructure, uniformity, porosity, roughness, micro hardness and brightness of the anodic oxide layers were investigated. It was found that with increasing deformation, the size of intermetallic particles decreased which improved the order and uniformity of the Al2O3 layer. This was attributed to increasing micro- and nano-scale orders of anodic structure. The micro-scale order of anodic structure increases due to high density of grain boundaries after SPD. With increasing deformation, two-dimensional ordering in micro and nano-scales was observed. In addition, micro hardness and brightness of coatings were increased and the roughness and porosity were decreased. This may be due to the fact that a more uniform current can establish between anode and cathode during anodization of samples with more significant deformation which leads to uniform and highly ordered anodic layers. In addition, application of aging treatment leads to higher non-uniformity in established current and causes reduced ordering and uniformity of anodic layer in addition to enhanced roughness and porosity and reduction in brightness.