Micro-arc Oxidation Behavior of Magnesium Alloy at Different Voltages

For making clear the role of voltage in micro-arc oxidation of magnesium alloys, experiments were carried out in the bipolar pulse output mode and under constant current load to investigate the influence of voltage on oxidation time, film thickness and surface morphology. The results indicated that when the negative voltage was zero and duty cycle was 20% and 30% respectively, the oxidation time at 380 V was less than that above 380 V. When the negative voltage was 0 V and 40 V, the oxidation time and film thickness at 340 V were greater than those of above 340 V, but the surface morphology below 340 V was letter than above 340 V. It is clearly seen that there is a critical voltage in micro-arc oxidation process and it would separate the micro-arc oxidation process into two stages, i.e., pre-and post-oxidation. In both phases, the micro-arc oxidation mechanisms are different.