Improved corrosion resistance of magnesium alloy with a surface aluminum coating electrodeposited in ionic liquid

A metallic aluminum (Al) layer was successfully electrodeposited onto a magnesium (Mg) alloy in a Lewis acidic aluminum chloride-1-ethyl-3- methylimidazolium chloride (AlCl3 -EMIC) ionic liquid under a galvanostatic condition at room temperature. Effects of deposition current density on material characteristics of the deposited layers were explored by means of a scanning electron microscope and an X-ray diffractometer. In addition, the improvement in corrosion resistance of the Mg alloy due to the Al coating was evaluated by electrochemical measurements and a salt spray test. The electrochemical impedance spectroscopic data indicated that a bare Mg alloy had a polarization resistance of only 470 cm2 in 3.5 wt % NaCl solution, whereas the Al-coated Mg sample showed its resistance as high as 8700 cm2 in the same environment. Moreover, it was also found that the Al layer deposited at a lower current density was more compact and uniform when compared to that deposited at a higher current density; consequently, this coating revealed a superior protection capability for the Mg substrate against corrosion.