Kinetics and mechanism of multilayer Mg-Al intermetallic compound coating formation of magnesium alloy by AlCl3-NaCl molten salt bath treatment

Abstract The interaction between the Mg substrate and AlCl 3 – NaCl molten salt at 573–673 K was investigated. The interaction resulted in the formation of a multilayered structure, consisting of δ (Mg), α (Al) solid solution and Al 12 Mg 17 , Al 0.58 Mg 0.42 , Al 3 Mg 2 Mg–Al intermetallic compound layers. The multilayer coating was found to grow by a parabolic law with apparent activation energy of about 46 ± 2 kJ/mol for diffusion process. Then, an approach to study the interdiffusion coefficient of each phase layer, the phase growth and the interface displacement based on the solutions of the diffusion equations is presented. A qualitative model describing the formation of such a multilayered structure in the Mg/molten salt system is exhibited.