Abstract: The conversion film without chromium was prepared on aluminum alloy LY12 in zirconate solution.The coating thickness,bubbling time in NaOH-glycerol dropping solution and adhesion with coating were tested.The zirconate treatment process was optimized by orthogonal experiments and one factor experiments as follows: K2ZrF6 3 g/L,polyglycol 2 g/L,phosphoric acid 1 g/L,temperature 35 ℃.The thickness of conversion film was 2.8 μm.The bubbling time was 64 s.The adhesion with paint coating was first class.