Novel multilayer Mg-Al intermetallic coating for corrosion protection of magnesium alloy by molten salts treatment

A novel multilayer Mg-Al intermetallic coating on the magnesium alloy was obtained by AlCl3-NaCl molten salt bath treatment. The molten salt was treated at 400 °C, which is lower than the treatment temperature of solid diffusion Al powder. The thick Al12Mg17, Al0.58Mg0.42 and Al3Mg2 multilayer Mg-Al intermetallic coating forms on the magnesium alloy. The corrosion resistance of AZ91D alloy with and without coating by multilayer of Mg-Al intermetallic compound was evaluated by electrochemical impedance spectroscopy measurements in 3.5% (mass fraction) NaCl solution. The polarization resistance value of the multilayer coating on the magnesium alloy by molten salt bath treatment is greater than that of the uncoated one, which is attributed to the homogenously distributed intermetallic phases.