Study The Preparation Technology Of Micro-arc Oxidation Coloring Coating On AZ91D Magnesium Alloys In Sodium Silicate Solution

Micro-arc oxidation coloring technique can be obtained good corrosion resistance and color uniformity and stability of the ceramic layer in non-ferrous metals surface,significantly improves corrosion resistance and can be decorative,breakthroughs many problems of the current surface coloring treatment technology on magnesium alloys,has broad application prospects.This paper studied the AZ91D magnesium alloy formula composition of micro-arc oxidation colored liquid in sodium silicate solution. Fixed on the basis of electrical parameters,studied formula components on the impact of the color film using single factor experimental method. With SEM,EDS,XRD analysis,observed the surface morphology of the ceramic layer,determined the phase composition and element distribution,and discussed the mechanism of each component.The results have shown that good corrosion resistance and uniform brown color ceramic coating can be obtained in sodium silicate solution with the appropriate amount of the ammonium metavanadate. However,when the concentration of the ammonium metavanadate exceeded 8g/l,larger defects appeared on the surface,pore size increased,the corrosion resistance decreased and the surface quality decreased.Added appropriate amount of phenol,the film thickness and corrosion resistance increased,the color darken.However,when the concentration of the phenol exceeded 8g/l, more microcracks and gray pitting appeared on the surface,causing the film properties deterioration,otherwise EDS and XRD detected that the carbon phase existed in the film, which indicated that carbon is also participated in micro-arc oxidation reaction,produced the carbonate which grayed out the film.With the addition of silicate and sodium hydroxide,the conductivity of the solution increased,the breakdown voltage reduced,which promoted the passivation film,film thickness increased rapidly,the surface state of the film improved. However,high content had a negative impact on the film.With the addition of glycerol,the point discharge reduced,the electrolyte stabilitied, improved the film thickness and corrosion resistance,the film performance changed for the better.The XRD analysis on brown film shows that,the film contains+3,+5 price vanadium, which descriptes that VO3- anion is also entered into the discharge channel participating in the thermal chemical physics reaction,generating vanadate and oxide which deposited in the bottom of the discharge channel,resulting in the film presentd some of the yellow color.