STUDY OF THE COMPOSITION OF ZIRCONIUM-BASED CHROMIUM FREE CONVERSION LAYERS ON ALUMINUM

The composition of chromium free conversion layers on aluminium, based on zir conium has been determined using complementary surface analyti cal techniques: SEM, AES, XPS, SIMS. The zirconium based chromiu,m fre e conversion layer consists of a two layered structure, with total thi ckness 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 thickne ss of the film was studied using AES, SE and EIS. It is concluded that the zirconium based conversion layers are formed within ten seconds a nd a successive increase in conversion time results only in a very sli ght thickening of the layer.