The Influence Of Load Waveform And Parameters On Magnesium Alloy Micro-arc Oxidation Coatings

Micro-arc oxidation is surface treatment technology in the pulse power that the initial oxide film formed in the stage of the magnesium alloy anode oxidation is breakdown,the gas from the local conductive channel produces instantaneous discharge leading to local high temperatures, metal surface oxidation of metal oxide ceramic, which forms a ceramic coating after cooling. From the current arc oxidation research point of view, many studies focused on ceramic coating of the organization, structure, performance analysis and the impact of process parameters, while the film growth mechanism and micro-power and micro-arc oxidation the process of matching MAO of the study is relatively shortage, However, what kind of power form, what kind of output waveform is most suitable for micro-arc oxidation, the film possessed the best overall performance, meanwhile the most energy-saving and efficient.For these questions, the topics based on previous studies using self-developed MAO power respectively study MAO morphological characteristics in the unipolar pulses, bipolar pulse and pulse discharge circuit. According to the experimental features and arc physics and electrochemical theory, the model of micro-arc discharge is proposed. The influence of MAO load of waveform parameters, including waveform, voltage, duty cycle and frequency on micro-arc oxidation is studied .The results showed that discharge circuit power mode can control large arc; the MAO process exists the critical voltage, the film forming speed below the threshold voltage is less than that of the above critical value, which of the layer morphology smooth and uniformity is better than the voltage above the threshold; with the cooling time extending , the film deposition rate first increases and then decreases, corrosion rate first decreased and then increased, the number of surface melt reduce, larger size, surface roughness increased. The influence of waveform parameters on the maximum film thickness is studied. The results showed that with the oxidation time extending, the maximum thickness with discharge circuit power mode is greater than that of bipolar power supply, the maximum thickness increases and then decreases with the frequency and duty cycle increasing respectively, when the frequency and duty cycle is 300Hz and 15%, the terminate thickness is up to maximum...