TiO₂ Sol Treatment of Double Rare-earth Conversion Film on AZ31 Mg Alloy

New film was formed on the surface of double rare-earth conversion film,treated by TiO2 sol.The double rare-earth conversion films treated by TiO2 sol were tested by SEM,potentiodynamic polarization and electrochemical impedance spectroscopy(EIS).The SEM showed that some new substance appeared in the cracks at the surface of the double rare-earth conversion films.The inside film wae unexposed and the cracks decreased,then the films became more uniform.The corrosion potential of the specimen was improved from -1.167 V to -0.777 V.the corrosion current density was reduced by two orders of magnitude.The radius of capacitance loops of EIS was enlarged,and the polarization resistance was improved from 1.62 kΩ to 1.81 kΩ.The corrosion resistance of the specimen increased obviously.