镁合金微弧氧化持续电弧对膜层的破坏机制

Destruction Mechanism of Sustained Arc on Magnesium Alloy Coated by MAO

摘要:

为了避免微弧氧化过程中的持续电弧放电对膜层的破坏,本文使用高速摄像机拍摄放电现象,结合负载的电流、电压波形探究持续电弧放电的实质,并研究了被破坏区域的表面、截面形貌及相组成相对于正常膜层的变化,最后搭配不同的占空比和频率,探索出电参数对持续电弧放电现象的影响规律。研究结果表明：在微弧氧化过程中,试样表面呈现出燃弧—熄弧—冷却的往复过程,而局部破坏区域则表现为连续的电弧放电现象。局部持续电弧放电区域的组分结构、表面形貌、截面形貌及元素分布均与正常微弧氧化膜层有很大差异,该膜层的均匀性、致密性和完整性均被破坏,导致膜层整体的均一性被破坏,甚至造成试样的外形尺寸发生严重的破坏。负载的电容特性导致电弧持续时间过长而熔融金属氧化物的冷却时间不足,局部热交换不充分和热量集中,这是造成持续电弧破坏根本原因。该破坏发生后无法修复,因此可以通过对频率和占空比的合理搭配,在不同的处理电压下避免持续电弧破坏现象的发生。

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.