Abstract:The aluminizing of AZ91D Mg alloy by AlCl₃-NaCl molten salts at a lower temperature of 380 ℃ were investigated, and a diffusion alloyed layer was prepared. The microstructure and composition of the diffusion alloyed layer were studied by optical microscopy, scanning electron microscopy, energy dispersive spectrum and X-ray diffractometry. The nano-hardness of the alloyed layer was studied by nanoindentation. The corrosion resistance of the treated AZ91D Mg alloy was evaluated in 3.5% (mass fraction) NaCl solution by electrochemical impedance spectroscopy and potentiodynamic polarization. The results show that a continuous and dense alloyed layer can be formed on the surface of the AZ91D Mg alloy by aluminizing in molten salts at low temperature. The aluminum-alloyed layer consists mainly of Mg₂Al₃ and Mg₁₇Al₁₂ intermetallic layers. The formation of the Mg-Al alloyed layer is associated with a displacement reaction mechanism and diffusion process that takes place during the molten salt treatment. The alloyed layer substantially improves the hardness as well as the corrosion resistance of the AZ91D Mg alloy, which is attributed to the high volume fraction of intermetallic compounds in the surface alloyed layer.

Key words: AZ91D Mg alloy; molten salt; diffusion; hardness; corrosion resistance