Investigation of alloying element Mg in the near surface layer of micro-arc oxidation coating on Al-Mg-Sc alloy

This paper presented a new research perspective about the MAO coating on Al-Mg-Sc alloy, which based on the main alloying element Mg. From this perspective, the paper firstly analyzed the spatial distribution, phase structure and chemical states of the alloying element Mg in the near surface layer of MAO coating by SEM, EDS, XRD and XPS. SEM observations suggested that the surface porosity and Mg content of the MAO coating was reduced with the increase of Na2SiO3 concentration. EDS analysis revealed that Mg was deposited at the bottom of the discharge channel and the Mg content in the MAO coating gradually increased along the thickness direction. XRD analysis manifested the formation of MgAl2O4 and MgO in the near surface layer of MAO coating, which was detected similarly by XPS spectra. ARXPS detection proved that MgO was distributed at the surface and MgAl2O4 was distributed at deeper regions, which was attributed to the fact that further oxidation promoted the transformation of MgO into MgAl2O4 due to instantaneous high temperature and high pressure. Finally, MgAl2O4 gradually became the main magnesium oxide in the near surface layer of MAO coating with the process of MAO reaction.