Effect Of Micro-arc Oxidation Power Pulse Parameters And Optimization Method On Magnesium Alloy

Micro-arc oxidation is a metal surface in-situ growth of the ceramic layer surface treatment technology. In this paper, the Micro-Arc Oxidation processing on AZ91D magnesium alloy was carried out by using self-developed with variety methods and characteristics pulse power. Large numbers of experiments were taken under the DC, unipolar, bipolar and the discharge circuit pulse output modes. It studied the requirements of power source in magnesium alloy micro-arc oxidation. And the requirements of power pulse parameters are optimized.The MAO film is accumulation of imbalance structure metal oxides undergone suddenly heating and cooling cycle result from numerous discrete arc discharge, in which the gas based oxygen inside conduct channel bearing electric field intensity is ionized, changed from insulator to conductor that cause sharp negative resistance effect, and produce partially high temperature. The micro-arc oxidation process can be divided into three stages:anodic oxidation, micro-arc oxidation and macro arc discharge. The separate arc model is described as 4 courses:creating gas from electrolysis, arc discharging, metals oxidizing, cooling and shrinking of oxides. The film components for MgO, Mg2SiO4, MgAl2O4 and uncertainty phase. Compared with the anodic oxidation reaction process, it has no electronic participation and the reaction process has the characteristics of thermal cycle.The purpose of pulse supply is to break the macro arc discharge by proper cooling time, which cannot be actualized by unipolar pulse mode because of the strongly capacitive load characteristic and the film is burning and failure, and can be reached by bipolar pulse supply because the negative pulse period impose as cooling time. Using a discharge circuit to remove the influence of load capacitive, with which the macro arc problem is resolved effectively, the film forming efficiency is improved, and the pollutions of film and electrolyte due to negative voltage is avoided.The macro arc discharge can be effectively restrained by various parameters rationally on magnesium micro-arc oxidation by using a discharge circuit. In the process of micro-arc oxidation, the proper oxidation and cooling time can effectively avoid macro arc discharge. The adaptation of oxidation and cooling time were effected by way of voltage level, and also cause of conducting channel number of arc discharge and the volume of the gas in it. Through the experiment, it was regard that the out put pulse frequency was 667Hz or 500Hz and the duty cycle was 30%can effectively avoid macro arc discharge and the film forming efficiency is improved.