Interaction Effect Between Electrolyte And Electrical Parameters On Microstructure And Properties Of MAO Coatings On Magnesium Alloys

Based on the bipolar pulse power mode to AZ91 D magnesium alloy as the research object,using orthogonal experiment design,this paper studied K2 Zr F6 and EDTA-Na,voltage and the interaction among them effect for the properties and structure of micro-arc oxidation ceramic coatings formed on the magnesium alloy surface in phosphate electrolyte system.The thickness,the corrosion resistance and electrochemical corrosion resistance of the coatings are characterized by means of TT260 thickness gauge,drop test and electrochemical experiment.The surface and cross-section morphology of the coatings are observed by SEM.The results show that for the coatings thickness,the voltage is the greatest impact and very significant,the interaction between the K2ZrF6 and the voltage on the second and significant;K2ZrF6 and EDTA-Na and interaction between K2ZrF6 and EDTA-Na and interaction with EDTA-Na and voltage are not significant.For the drop test corrosion resistance,voltage has the greatest impact and is two orders of magnitude higher than the effect of the interaction between K2ZrF6 and EDTA-Na and various factors,which factors in addition to the voltage are in the same magnitude,and the voltage,K2ZrF6 and EDTA-Na and the interaction effect on the corrosion resistance of the drop test are not significant.For the electrochemical corrosion resistance,The effects of K2ZrF6,EDTA-Na and the interaction among them is very significant,voltage has significant effect;EDTA-Na and the interaction of,K2ZrF6 and voltage is not significant,the greatest impact factors were K2ZrF6,EDTA-Na on the second,then the interaction between the K2ZrF6 and EDTA-Na.With the change of K2ZrF6 concentration,coatings thickness and drop test corrosion resistance changes little,but in the high concentration of K2ZrF6 causes the molten material is filled in the discharge pores and reduces holes defects,the chloride ion is not easy to transfer in the coatings,and the electrochemical corrosion resistance increase.EDTA-Na inhibits the intense reaction in the process of micro arc oxidation,and the higher concentration,the more obvious inhibition effect,the more conducive to reduce the micro cracks and other defects,thereby increasing the corrosion resistance of the coatings.With the increase of voltage,while the pore OD of coatings increased slightly,the number of micro-cracks increased slightly,but significantly increases the thickness of the coatings,the drop test corrosion resistance improved,but also makes the coatings electrochemical corrosion resistance increased.The interaction between the K2ZrF6 and the voltage increases the thickness of the coatings,but it may also increase the micro pore OD and the micro cracks of the coatings,which makes the coatings performance not significant.In addition,the interaction of K2ZrF6 and EDTA-Na inhibits large arc discharge generated at the same time,but also fills pores in the ceramic discharge to a certain extent,significantly reduces the surface porosity and coatings defects,improve the electrochemical corrosion resistance of the coatings,which has significant effects on electric chemical corrosion resistance.