Separate Arc Discharge Mechanism and Requirements of Power Source in AZ91D Magnesium Alloy Micro-arc Oxidation

In order to study the effects of pulse width,a pulse power supply with discharge loop was designed and an experiment on magnesium micro-arc oxidation(MAO) with a steady rate of voltage rise was conducted.The pulse frequency was held constant at 667 Hz and the duty cycle was adjusted between 10%～90%.The results showed that with increase of the pulse width: 1)the arc voltage gradually reduced and the large-arc tendency increased;2)the number of surface pores declined while pore size increased slightly and 3)the efficiency of MAO coating increased at first and then reduced.The best efficiency of coating was obtained when the duty cycle was about 30%,when the lowest corrosion rate of the film was also received.Therefore,for magnesium alloy oxidation with the frequency of 667 Hz,the best efficiency and higher quality of MAO coating can be obtained when pulse width is between 300～600 μs.