Destruction Mechanism of Sustained Arc on Magnesium Alloy Coated by MAO

Abstract:

In order to avoid the film were destructed by continuous arc discharge during micro-arc oxidation. This paper used a high-speed camera to capture the discharge phenomenon, combined with the current and voltage wave form of the load to explore the essence of continuous arc discharge. And investigated the destructed area of surface and cross-section morphology and the phase composition relative to the change of normal coating layer. Finally, different duty ratio and frequencies were used to explore the influence of the electrical parameters on the continuous arc discharge phenomenon. The results showed that the surface of the sample exhibits a reciprocating process of arc burning, arc quenching and cooling during micro-arc oxidation. The localized destructed area was characterized by a continuous arc discharge phenomenon. The composition, surface morphology, cross-section morphology and element distribution of the local continuous arc discharge region were very different from that of the normal micro-arc oxidation film layer. And the uniformity, compactness and integrity of the film layer was destroyed, which led to the destruction of the overall uniformity of the film layer, and even caused serious damage to the external size of the sample. The capacitance characteristic of the load caused the arc duration time to be too long while the cooling time of the molten metal oxide was insufficient, the local thermal transmission was insufficient and the heat was concentrated, which was the root cause of the continuous arc destructed. This destruction cannot be repaired after it occurs, so it is possible to avoid the occurrence of continuous arc destruction under different treatment voltages by reasonable matching of frequency and the duty ratio.

Key words:magnesium alloy; micro-arc oxidation; continuous arc destruction; destruction mechanism; electrical parameters