Effect of Micro-arc Oxidation Time on Microstructure and Properties of Micro-arc Oxidation Ceramic Layer Formed on High Strength Magnesium Alloy

Micro-arc oxidation treatment of high strength magnesium alloy with different parameters in silicate system was carried out. The digital coating thickness gauge, SEM, EDS and XRD were used to measure the micro-arc ceramic layer thickness, observe the interface condition layer structure, morphology and characterize the element composition and phase composition. Meanwhile, Tafel polarization curves were used to study the electrochemical corrosion behavior of micro-arc ceramic layer in 3.5% NaCl medium. The results show that the thickness of ceramic layer increases gradually with the prolongation of micro-arc oxidation time. The pore numbers in the ceramic layer is large and the size is small when the oxidation time is short. With the thickness of ceramic layer increasing, the porosity decreases and the size of volcanic crater-shaped pores increase correspondingly, besides micro-cracks or gridded cracks with different degrees appear between the pores. The ceramic layer formed with 5 min micro-arc oxidation is mainly composed of MgO and MgSiO₃. Besides MgO and MgSiO₃ phases, Mg₂SiO₄ phase appear in the ceramic layer when the oxidation time is extended to 10 min and 15 min. The corrosion resistance of high-strength magnesium alloy matrix is significantly improved after the micro-arc oxidation treatment in 3.5%wt NaCl solution, and the self-corrosion current density with 15 min micro-arc oxidation treatment decreases by 2 orders than matrix.