Effects Of Electrical Parameters On Micro-arc Oxidation Coatings On AM60B Under Different Power Supply Modes

Micro-arc oxidation(MAO)technology is a new process for forming ceramic membranes on the surface of light metals by high-voltage discharge in electrolyte.The in-situ formation has high hardness,good corrosion resistance,excellent insulation and matrix metallurgy.It has strong bonding force and is one of the important means for surface modification of valve metals such as magnesium and aluminum and their alloys.It is very promising.In this paper,the regression orthogonal test method is used to utilize the pulse power supply with various output modes and volt-ampere characteristic curves.The common die-cast magnesium alloy AM60B is used as the base material and processed under the silicate electrolyte system.The thickness,macroscopic and microscopic surface morphology,cross-sectional morphology,and corrosion resistance of the film were examined and analyzed.The effects of power mode,frequency and duty ratio on the micro-arc oxide film were investigated.In particular,under constant voltage,a significant mathematical model of electrical parameters for different response values is established.The RSM is used to analyze the variation law and trend of frequency,duty ratio and interaction on response values.In the power mode(M2 and M1),the film layer performance is similar under the three conditions of pulse equivalent loading and same loading.The introduction of arcing and arc extinction,reflects the effects of the combination of frequency and duty ratio on the performance of the film from the microdomain.In M2 mode,the order of influence on film thickness,drip corrosion resistance and corrosion current density,corrosion current density,frequency and duty ratio and their interaction are:A>B>AB,all of which are very significant.The comprehensive optimal process electrical parameter combination and corresponding response indicators are(1800Hz,33.19%,25.47?m,209.56s,1.1E-0010A/cm~2).In M1 mode,based on equivalent loading,the order of influence on film thickness,spot corrosion resistance,frequency and duty ratio and their interaction are:A>AB>B,for corrosion current density,A>B>AB,all three are very significant.The combination of the best process electrical parameters and the corresponding response indicators are(3600Hz,71.63%,24?m,218.36s,1.12E-0010A/cm~2).There are more combinations of parameters that are not feasible under this scheme.In M1 mode,based on the same loading,the feasibility of the whole experimental scheme is good,and the film formation is improved.the order of influence on film thickness,drip corrosion resistance,corrosion current density,frequency and duty ratio and their interaction are:A>B>AB,all three are very significant.The overall film thickness increases with increasing frequency and duty ratio,and monotonously increases in one direction on the response surface.The combination of the best process electrical parameters and the corresponding response indicators are(1800Hz,45%,23.19?m,168.59s,1.01E-0010A/cm~2).The scheme is the most feasible,and the area of the superior area is significantly larger than the other two experimental schemes.The RSM is used to obtain the optimal frequency and duty ratio combination interval.The film thickness and the drop corrosion resistance are both the“hot red”“convex top”area of the response surface;and the corrosion current density is the response surface.Irregular“hot red”“pit”area;areas with poor feasibility and film formation are located in the“cold blue”area.Clearly demonstrate and predict the optimal process for micro-arc oxidation and provide directional guidance for optimal combination of frequency and duty cycle.Under different power modes,the equivalent loading comparison shows that the overall film thickness,spot corrosion resistance and corrosion current density are small;the micro-arc oxidation late M3 mode is larger than M1 mode,and the M2 mode is more feasible.and controllable,the apparent quality of the film is good,the experimental infeasible interval M2brought by the combination of low frequency and large duty ratio is small,the film porosity M2 is lower than the M1 mode;the overall M2 mode of the film layer is higher than the M1mode;M2 forced arc extinguishing effect is beneficial to micro-arc oxidation to improve the feasibility and film formation,and inhibit the sintering of the film layer caused by large arc.In the same power mode,the comparison of the two loading modes shows that the difference is large.The thickness of the film under the M1 equivalent loading mode is much larger than that of the M1 in the same loading mode,but the feasibility and film forming property of the M1 in the same mode.Both are better than the equivalent loading mode,and the porosity of the film layer is large.The pore size is smaller and the distribution is uniform in the same loading mode.The long arc extinguishing effect in the M1 mode is beneficial to the feasibility and film formation of the micro-arc oxidation and the film is improved in layer performance.The termination current is highly correlated with the loading frequency.The termination current M2 mode is slightly larger than the M1 equivalent loading mode,which is much larger than the M1 same loading mode.The microscopic porosity,surface microcracks and macroscopic flatness of the film layer can reflect the quality characteristics of the surface and the arcing and arc extinguishing time reflected by the micro-arc oxidation.The more effective the arc-extinguishing effect,the better the surface quality.The growth process,feasibility,film formation and single-cycle arcing duration of the magnesium alloy are closely related to the duration of arc-extinguishing and the duration of arc-extinguishing and arc-burning.When the arcing time is too large,more than about 0.8ms,the feasibility and film formation will gradually decrease with the increase of arcing.At this time,increasing the arc extinguishing time can significantly improve the feasibility,and the film forming property can be improved and the reaction is violent.It can be suppressed but not eliminated,but it grows when the arc is extinguished,which affects the power supply efficiency and reduces the thickness of the film.When the arcing time is 0.2ms,the ratio of arc extinguishing to arcing is about 1.4~2,and the comprehensive performance of the film is better.When the ratio of arc extinguishing and arcing is less than 1.2,the reaction is severe due to insufficient cooling.The performance of the film layer is gradually declining,especially the feasibility is obviously insufficient,and ablation at the connecting rod is prone to occur.