Effects Of Electrical Parameters On Microstructure And Corrosion Resistance Of Micro-arc Oxidation Coating On Az91d Magnesium Alloys Under Different Power Supply

Micro-arc oxidation (MAO) is one of the most prospective methods of surface treatment technique. The process produces thick, hard and well-adhered ceramic-like coatings to be obtained with high corrosion resistance, thermal stability and dielectric properties. Those reactions are influenced by electrolyte solution, electricity parameter processing temperature, etc, among which the electricity parameter is one of the primary factors.Magnesium alloy micro-arc oxidation coatings are made under the different conditions of oxidation time under three kinds of spark shape and electricity parameters of two kinds of power supply by employing the self-designed new-fashioned MAO series equipments. According to the compare and analysis of the experiment results, the influences of oxidation time under three kinds of spark shape and electricity parameters such as voltage, frequency, and duty ratio on coatings'structure and corrosion resistance have been studied in this article. Simultaneity, the surface pore size and surface porosity of MAO coatings were measured. The difference of input energy of two kinds of power supply can receive by calculating.The results have revealed that the thickness, surface porosity and corrosion resistance of coatings increased accordingly with the oxidation time under three kinds of spark shape. Both thickness and corrosion resistance of coating increased with the increase of constant voltage extending under two kinds of power supply. Both thickness and corrosion resistance of coating first increased and then decreased with the increase of frequency and duty ratio under small arc. The coatings presented the best corrosion resistance when the frequency is 800Hz and duty ratio is 15%, because their surface porosity were about Ml power mode,6.42% and 6.83%, M2 power mode,7.71% and 7.11%, respectively. Under the same oxidation time, the coatings presented the thickest thickness and the best corrosion resistance when the arc is bigger, big arc followed by, and small arc the worst. Under the same thickness, the best corrosion resistance of coatings is bigger arc. In all conditions, the percentage of micropore size ranging less than 3μm reached more than 62%.Among electricity parameters, the voltage demonstrated an important role regarding the microstructure and corrosion resistance of coatings, while the frequency and the duty ratio is less.Two power modes of the two loading modes:very different coating corrosion resistance, constant voltage 375V corrosion resistance than a good small arc over 50s.In addition. Oxidation process the total energy input is calculated as:E=(?). Among these parameters, n is the total oxidation time into n segment,ti is the oxidation time of paragraph i, D is the duty ratio, Ui is the oxidation voltage of ti period of time, Ii is the oxidation current value of ti period of time. In both the power mode, input the total energy, along with the voltage, duty ratio and the oxidation time increases. The MAO coatings'thickness not only have relations with the termination voltage, but also have relations with the loading mode and have exhibited close relationship with the input energy. In order to get the same thickness, Ml is more energy-efficient models.