Effects of reverse voltage and oxidation time on oxide film formation

which is prepared by micro-arc oxidation in silicate systems on the AZ91D magnesium

have been investigated

and the phase constituent and cross-section as well as surface morphology of the oxidized film were observed by XRD （X-ray diffraction）

OM （optical microscope） and SEM （scanning electron microscope）. The results show that with increasing in reverse voltage

oxide film thickness and size of surface pore are gradually increased while the number of pores and micro-crack is decreased. With reverse voltage of 120 V

the ceramic coating with 157 μm in thickness can be obtained with the lowest pores and cracks. With extending oxidation time

the thickness of oxide film is increased and growth rate of coating is firstly increased then decreased. The oxide film showing desirable compaction is composed of MgO phase and Mg2SiO4 phase in the absence of Mg phase.