Composite anticorrosion coatings for AZ91D magnesium alloy with molybdate conversion coating and silicon sol-gel coatings

In order to get a further improvement of corrosion protection for AZ91D magnesium alloy, three layers of silicon sol-gel coatings were successfully deposited on the molybdate conversion coating pre-applied to AZ91D alloy. The surface morphology and the corrosion protection performance of the composite coatings were investigated in detail using scanning electron microscope, electrochemical impedance spectroscopy as well as potentiodynamic polarization tests. The results demonstrated that the composite coatings could greatly improve the corrosion protection performance of the AZ91D magnesium alloy.