Study On Coloring Mechanism And Corrosion Resistance Of Magnesium Alloy Micro-arc Oxide Film

Magnesium alloy micro-arc oxidation coloring technology can not only solve the problem of protection of magnesium alloys in "3C product"(computer,communications and consumer electronics)applications,but also meet the needs of consumers for appearance and color.At present,the research on micro-arc oxidation coloring technology focuses on the adjustment of electrical parameters and electrolyte process,and there is little research on the coloring mechanism.In this paper,the single factor variable method is used to change the type of coloring salt,electrolyte concentration and current density,to analyze its influence on the color of micro-arc oxidation coloring film,the corrosion resistance of coloring film under different conditions is studied by polarization curve and salt spray test.By means of cyclic voltammetry,the influence mechanism of the types of colored salts and different concentrations of electrolyte on the adsorption characteristics of the magnesium alloy electrode interface and the difficulty of the oxidation-reduction reaction are studied.From an electrochemical point of view,the difference in the coloring of the film under different conditions is analyzed,so as to obtain a better colored film.The following conclusions were drawn:(1)Under different concentrations of colored salt,the blackness and corrosion resistance of the NH4VO3 colored film are higher than those of the NaVO3 colored film.NH4*is introduced into the electrolyte,and the NH3 generated by the decomposition of the electrolyte temperature during the micro-arc oxidation process can be used as a reducing agent to promote the generation of high-valent vanadium oxides to low-valent vanadium oxides,and improve the blackness of the colored film.When the NH4VO3 concentration is 15 g/L,the blackness of coloring film is the highest and the corrosion resistance is the best.(2)When the concentration of sodium phosphate is 15 g/L,the Lab value is 27.27,and the blackness and corrosion resistance of the film are the best.The change of FDTA-2Na concentration has little effect on the blackness of the film,but the color uniformity of the film are improved within a certain concentration range.When the concentration of EDTA-2Na is 9g/L,the corrosion resistance of the film is the best.(3)When the current density is 2.4 A/dm2,the blackness of the film is the highest,and the corrosion resistance of the film is the best when the current density is 3.5 A/dm2.(4)Cyclic voltammetry curves show that the addition of NH4+ increases the adsorption charge at the electrode interface and promotes the redox reaction.When the NH4VO3 concentration is 15 g/L,the sodium phosphate concentration is 15 g/L,the EDTA-2Na concentration is 9 g/L,it is the most favorable condition for electrode electrochemical reaction.