An FT-IRRAS-study of anodic oxide films on aluminum alloys and the impact of bath aging

•The oxide formation kinetics strictly depends on the bath aging.•The incorporation of sulfate decreases with ongoing bath aging.•Neither copper nor copper oxides are detectable in the layers. This present work studies the influence of the anodizing bath aging on the oxide formation and the oxide layer structure. The ongoing bath aging was mainly monitored by measurements of the electrolyte conductivity and concentration of Al3+ in the electrolyte. SEM measurement clearly shows the changing of the oxide thickness as well as the porosity with ongoing bath aging. The molecular structure of the oxide film studied by FT-IRRAS shows that SO42− and PO43− are incorporated in the oxide layers. With ongoing bath aging the part of incorporated amount of sulfate decreases, whereas the amount of phosphates increases as confirmed by EDX analysis. No significant incorporation of copper or copper oxides were detected inside the anodic oxide layer.