A new method for synthesizing Mg-Al hydrotalcite conversion coating on AZ91D Mg alloy was developed by the application of electric field （EF）. By using EF technique, the formation time of the coating can be significantly reduced. The SEM results indicate that a continuous and compact Mg-Al hydrotalcite coating is formed on the surface of Mg alloy after short time EF treatment. However, a long time treatment would make the coating partially exfoliate. The corrosion current density （Jcor ） of the coated sample （EF1＋1 h） is approximately two orders of magnitude lower than that of Mg alloy substrate. The test of electrochemical impedance spectroscopy （EIS） and immersion corrosion also suggest that the coating can effectively protect Mg alloy against corrosion.
