Mechanism of Microarc Oxidation Treated Ti6Al4V Alloy in a Magnetic Field

The growth kinetics mechanism of microarc oxidation (MAO) coatings on Ti6Al4V alloy in a magnetic field with a low current density of 2 A/dm2 was studied using scanning electron microscopy, energy dispersive spectroscopy, atomic force microscope, X-ray diffraction, and potentiodynamic polarization. The results show that the magnetohydrodynamics effect increased the electron current density during the MAO process. Then, a higher breakdown voltage of the anodic oxide film, faster growth of the MAO coatings, stronger and more concentrated microarc are obtained. Consequently, thick uneven coatings with high content of co-deposition oxides were obtained on samples rotating at 500 r/min in the magnetic field, resulting in uneven dense layer and poor corrosion resistance of the coating; the thin uniform coatings with a few co-deposition oxides were obtained on samples rotating at 3500 r/min in the magnetic field and also have poor corrosion resistance; both thickness and uniformity of the coatings are improved only for the sample rotating at 1500 r/min, resulting in good corrosion resistance of the coating. The thickness of the MAO coatings obtained on the low-speed rotating samples in the magnetic field increased parabolically with time, whereas that on high-speed rotating samples tends to increase linearly with time.