Effects Of Electric Parameters On Micro-arc Oxidation Coatings On AM60B Under Different Power Supply Modes Based On Orthgonal Experiments

Micro-arc oxidation?MAO?coatings were prepared on the surface of AM60B magnesium alloy in silicate electrolyte.Range analysis and variance analysis methods was used to study the order and significance of the effects of frequency,duty ratio,and their interactions on coatings thickness,spotting corrosion resistance,and electrochemical corrosion resistance by orthogonal experiment design.Digital eddy current thickness gauge,scanning electron microscope?SEM?and X-ray diffraction?XRD?were used to analyze the thickness,microstructure and phase of the coating.The corrosion resistances of the coatings were characterized by the spot test and the potentiodynamic polarization test.The arc extinction time and arcing time are introduced to discuss the influence rules and the causes.In 0:0 mode,the influencing order of frequency,duty ratio and interaction on coatings thickness,spotting corrosion resistance,and electrochemical corrosion resistance is frequency>duty ratio>interaction.The optimal solution for the electrical parameters of the coating thickness is?1800Hz,30%?and the thickness is20.71?m.the optimal solution of the spotting corrosion resistance is?1800Hz,40%?,and the spotting time of the droplets is 149.1s.The best solution of the electrochemical corrosion resistance is?300Hz,20%?,and the corrosion current density is 4.549×10^-9A·cm^-2.In the 0:0 equivalent mode,the order of frequency,duty ratio and their interaction on coatings thickness and spotting corrosion resistance is frequency>duty ratio>interaction,and the order of influence on electrochemical corros ion resistance is duty ratio>frequency>interaction.The optimal solution of electrical parameters of coating thickness is?3600Hz,90%?,and the film thickness value is 19.79?m.the optimal solution for spotting corrosion resistance is?3600Hz,60%?,and the spotting time is 194.3s.The best solution for electrochemical corrosion resistance is?1200Hz,80%?,and the corrosion current density is 5.78×10^-9A·cm^-2.In 1:1 mode,the order of influence of frequency,duty ratio and their interaction on coating thickness and electrochemical corrosion resistance is frequency>duty ratio>interaction,and the order of influence on spotting corrosion resistance is duty ratio>Frequency>Interaction.The optimal solution for electrical parameters to coating thickness is?600Hz,45%?,and the coating thickness is 17.40?m;the optimal solution for spotitng corrosion resistance is?600Hz,45%?,and the corrosion time is 106.8s.The best corrosive solution of electrochemical resistance is?1800Hz,20%?,and the value of corrosion current density is 4.57×10^-9A·cm^-2.The effects of frequency and duty ratio on coating thickness,surface pores,and coating density under the three power modes are the same.As the frequency increases,the thickness of the coating layer increases,the porosity decreases,and the corrosion resistance of the coating layer becomes better.As the duty ratio increases,the thickness of the coating increases significantly,the surface pore diameter of the coating layer becomes larger,the porosity increases,and the spotting corrosion resistance becomes better,but the electrochemical corrosion resistance becomes worse.The interaction between frequency and duty cycle has a greater impact on the coating thickness and corrosion resistance of the film layer.The interaction increases the thickness of the film layer,and suppresses the generation of macropores and microcracks,making the film layer denser.Frequency and duty ratio will not only affect the film layer alone,but the two together will affect the coating layer.In the silicate electrolyte system whose main components are Na ₂SiO₃,NaOH and KF,the main phase composition of the micro-arc oxide coating layer is MgO and Mg₂SiO₄.Due to the low KF concentration in the electrolyte,XRD did not detect the fluorine in the film layer.Different combinations of compounds,frequencies and duty ratio,and different power modes have no effect on the phase composition of the micro-arc oxide layer.When the arc extinction time and arcing time are the same in a single cycle,the coating layer generated in the 0:0 equivalent mode has better corrosion resistance and fewer micro-defects.and the energy required for film growth is slightly lower than in the 0:0 mode.