Preparation and Corrosion Resistance of Tin Salt Conversion Film on Aluminum Alloy Surface

A chrome-free chemical conversion film with good corrosion resistance was prepared by chemical conversion method using stannous sulfate as main salt.Effects of stannous sulfate concentration,film-forming oxidant concentration,film-forming accelerator concentration,reaction temperature and reaction time on corrosion resistance of the coating were studied.Corrosion resistance of the conversion coating was examined by electrochemical testing.At pH 2～3,the optimal preparation technologic conditions of chrome-free chemical conversion film were SnSO4 0.15 g/L,KMnO4 1.5 g/L and NaF 2 g/L,reaction temperature 30 ℃,reaction time 1.5 min.The tin salt conversion film has simple preparation technology,rapid film-forming speed and good corrosion resistance.