SummaryThe composition of chromium free conversion layers on aluminium, based on zirconium has been determined using complementary surface analytical techniques: SEM, AES, XPS, SIMS. The zirconium based chromium free conversion layer consists of a two layered structure, with total thickness less than 10 nm, in which the bottom layer contains only Al and O, while the top layer contains also a fluorinated zirconium compound and probably a polymer that is concentrated towards the outer surface. In a second part the influence of the conversion time on the thickness of the film was studied using AES, SE and EIS. It is concluded that the zirconium based conversion layers are formed within ten seconds and a successive increase in conversion time results only in a very slight thickening of the layer.
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