Abstract: In order to clarify the effect of sample area on the load characteristics and film properties of micro-arc oxidation, four AZ31B magnesium alloy samples with different areas were treated by micro-arc oxidation in unipolar pulse power supply mode. In the treatment, the equivalent resistance and equivalent capacitance of the load are collected by a LCR tester, the voltage and current waveforms of the load are recorded by oscilloscope, and the load voltage waveform is fitted by using software MATLAB, so as to investigate the effect of sample area on the load characteristics in the process of micro-arc oxidation. Our results indicate that with the increase of treatment voltage, the equivalent capacitance of all loads decreases continuously, the equivalent resistance increases continuously, and the discharge time constant of the loads increases continuously as well. The increase of the equivalent resistance indicates that the thickness of the film increases with increase of the treatment voltage. In addition, with the increase of the treated area, the equivalent resistance of the loads decreases, the load capacitance increases, and the discharge time constant of the loads decreases either. This indicates that the growth of the film becomes slower with increase of the treated area, and the larger the treated area is, the closer the load waveform is to the square wave. Therefore, it is more practical for the unipolar pulses. The equivalent resistance of the loads can reflect the thickness of the film.

Key words: magnesium alloy, micro-arc oxidation, treated area, load characteristics, time constant