Black oxidation film was obtained on Aluminium Alloy by two-step oxidation.The anticorrosion properties of the film were evaluated by neutral salt spray tests and electrochemical polarization curve.The morphology of the film was studied by scanning electron microscope.The composition of oxidation film was determined by EDS.This experiment result indicated that the oxidation film coatings had large lumps with lots of crackles by SEM experiments and that the oxidation film consisted of oxygen,aluminum,manganese,cobalt and chromium and that the treated Al without sealing had a lower corrosion resistance in 3.5% NaCl solution,but the samples sealed by K2Cr2O7 has a good corrosion resistance in 3.5% NaCl solution.