Discharge characteristics of confined cathode micro-arc oxidation

Confined cathode micro-arc oxidation (CCMAO) has been investigated in Na₂SiO₃-KOH solution with industrial pure aluminum as substrate materials. The effects of the electrode distance (ED) on working current, potential distribution, arcing voltage and so on have been focused on. The energy efficiency as a function of ED has also been evaluated. The results show the working current decreases with increasing ED for the same exposure area of confined cathode and anode. However, the working current increases with increasing ED with only the cathode confined. It is attributed to different electrical field on the anode surface. With increasing ED, the electrical field beneath the confined cathode decreases while that far from the cathode increases. This leads to a different total working current. The arcing voltage increases with increasing ED while the effective voltage on anode surface nearly keeps constant. The thickness of the ceramic coating produced at a small ED is much higher than that at a larger ED. The energy consumption per unit volume of oxides by CCMAO indicates that smaller ED leads to higher energy efficiency.