Study On Preparation And Properties Of AZ91D Magnesium Alloy Micro-arc Oxidation Color Films

In this paper,AZ91D magnesium alloy surface was treated by using micro-arc oxidation technology.Single factor experiment method was used to study the component of electrolyte influence on the quality and properties of films,then determine the composition and concentration.Basis on this study,preparation color films by adding colorants.The coating surface morphology and structure was studied by means of SEM,XRD and EDS,the corrosion resistance was tested by using electrochemical workstation and the wear resistance was tested by using friction and wear tester.Then to explore the impact of each component to the micro-arc oxidation films.Results of this study are as follows:(1)Using single factor experiment to study each composition and their concentration of electrolyte to influences of film thickness and surface topography.With the increased concentration of sodium silicate(sodium aluminate/sodium hydroxide),film thickness increased first and then decrease,pore radius increase,and the number decrease.With the increased concentration of potassium fluoride,film thickness increase continuous,pore radius decreases and the number increase first and then decreases.The optimal concentration ratio for the electrolyte was determined:Na2SiO3 8g/L,NaAlO2 4g/L,NaOH 4g/L,KF 4g/L.(2)The microstructure of ceramic film mainly consists of MgO,MgSiO3,MgAl2O4 and Al2O3.Compared with the substrate,the ceramic film’s self corrosion potential increased about 0.76V and the corrosion current density fall by about 19 times.In 3.5%sodium chloride solution,friction coefficient and its fluctuations of ceramic film bigger than substrate,erosion rate is 0.12 times of substrate and hardness is 5 times.(3)Increased with the concentration of NH4VO3,ceramic film color deepened,from light green to dark brown eventually,the surface microporous radius decreased.Compared with the substrate,its self corrosion potential increased about 0.27V and the corrosion current density fall by about 136 times that the ceramic film was prepared when the NH4VO3’s concentration is 2,4g/L.The microstructure of ceramic film mainly consists of MgO,MgSiO3,MgAl2O4,Al2O3 and VO2.Vanadium oxides makes film showing colors.(4)The yellow-green ceramic film was prepared when the K2Cr2O7’s concentration is 0.6 g/L,its consists of MgO,MgSiO3,MgCrO4,CrO2 and Al2O3.Compared with substrate,the color film’s self corrosion potential increased and the corrosion current density decrease,but compared with ceramic film that prepared by using optimization scheme is converse.