Electrochemical Impedance Spectroscopy Study On Film Formation And Film Growth Process Of Aluminum Alloy By Micro-arc Oxidation

After decades of development,micro-arc oxidation technology has made great progress.In order to meet the needs of different fields,films with different corrosion resistance,wear resistance and decorative properties have been prepared on different alloy surfaces.However,there are still unsolved theoretical problems in micro-arc oxidation technology at present.The mechanism of solute elements in the application of alloy micro-arc oxidation technology to the growth of micro-arc oxidation film is unknown,and it is difficult to monitor the growth process of micro-arc oxidation film,which brings difficulties to the theoretical study of micro-arc oxidation.In this paper,1060 aluminum alloy was treated by micro-arc oxidation in four different electrolytes of Na2SiO3,NaAlO2,(NaPo3)6 and Na3Po4,and the effects of different electrolytes on the film formation and film growth of aluminum alloy were studied.The effect of pH value of electrolyte on passivation and film gro.wth rate,and the relationship between solution conductivity and film growth were investigated.The voltage-time curve is obtained by the pre-experiment,and the time of the spark discharge is controlled by the boundary line.The development process of the micro-arc oxidation is two stages:the initial stage of micro-arc oxidation and the growth phase of the micro-arc oxidation film.In accordance with the drawing by means of electrochemical impedance spectroscopy(EIS),the electrochemical parameters were obtained,the electrochemical process of micro-arc oxidation was analyzed,and the change of impedance of alloy film was grasped by means of electrochemical impedance spectroscopy(EIS).Studies have shown that:(1)The film formation speed of 1060 aluminum alloy oxide film was accelerated by four electrolytes.In the micro-arc oxidation film growth stage(NaPO3)6 electrolyte,the inner film layer R2 has the largest impedance,and the film structure is the most dense.(1)The electrochemical impedance spectroscopy of 1060 aluminum alloy film can be divided into the equivalent circuit corresponding to the initial stage of micro-arc oxidation and the growth stage of micro-arc oxidation film.It can be seen that with the increase of pH value of electrolyte,the films formed by aluminum alloy in(NaPO3)6 electrolyte have complete capacitance arc resistance and the greater pH value is,the greater the pH value is to inhibit the growth of oxide film and micro-arc oxidation film.When the pH value of Na3PO4 electrolyte is less than 12,the R2 value of inner film increases,which indicates that the full breakdown of the film leads to the decrease of Ri impedance of outer film,which is beneficial to the increase of R2 impedance of inner film.(2)From the electrochemical impedance diagrams of different conductivity electrolytes,it can be seen that the change of conductivity has little effect on the capacitance arc shape of the electrochemical impedance spectrum of the oxide film and the micro-arc oxide film.According to the two stages of micro-arc oxidation film formation and growth process:the initial stage of micro-arc oxidation and the growth stage of micro-arc oxide film,it can be seen that in the growth stage of micro-arc oxidation film,the R2 value of inner film increases with the increase of conductivity,which indicates that the inner film structure is gradually compact and the charge transfer impedance in outer film hole is increasing.