Objective To study the preparation process of the chromate-free conversion treatment on aluminum alloys. Methods The chemical conversion coating was prepared with K2ZrF6 and K2TiF6 as the main salt, KMnO4 as the oxidant and NaF as the accelerant. The surface morphology, structure and composition were analyzed by SEM, EDS, FT-IR, and XPS. The corrosion resistance of conversion coating was studied by copper sulfate dropping, salt water immersion and polarization curve. Results The prepared yellow conversion coating mainly consisted of AlF3·3H2O, AlOx / Al, Al2O3, MnO2, and TiO2. The corrosion potential of the Al alloy sample was positively shifted about 591 mV and the corrosion current density was dropped from 1. 10 μA/ cm2 to 0. 48 μA/ cm2 after conversion treatment. After sealing treatment, the corrosion current density further decreased to 0. 04 μA/ cm2 and the corrosion resistance was significantly improved. Conclusion The conversion coating, which was prepared with K2ZrF6 and K2TiF6 as the main salt, had good corrosion resistance.