Preparation And Corrosion Resistance Of Two-Dimensional Thin Films On Magnesium Alloys

Magnesium alloys are widely used in industrial production due to their high specific strength,low density,good manufacturability and recyclability,abundant resources and easy availability.However,the corrosion resistance of magnesium alloy is poor due to its active chemical properties,low standard electrode potential and poor protection ability of natural oxide film,which limits its wide application in industry.The corrosion resistance of magnesium alloy can be effectively improved by surface treatment to prepare a protective film to prevent the magnesium alloy surface from contacting with corrosive medium.Therefore,in this paper,two-dimensional films were prepared on the surface of magnesium alloy by electrophoretic deposition using the special physical and chemical properties of 2D-TiO₂and monolayer MoS₂,and their corrosion resistance was studied.The main contents and conclusions are as follows:（1）Firstly,monolayer TiO₂was prepared by stripping method.By electrophoretic deposition method,TiO₂thin film was prepared on the surface of magnesium alloy substrate with a single layer TiO₂dispersion as electrophoretic solution.And the film forming process was optimized.The prepared TiO₂films were characterized by XRD,SEM and other related tests,and their corrosion behavior in 3.5 wt%Na Cl solution was analyzed by electrochemical polarization curve test.The results showed that 2D-TiO₂thin films were successfully prepared on magnesium alloy surface by electrophoretic deposition method.The control of electrophoretic voltage,deposition time,film sintering temperature and sintering time is the key to prepare dense TiO₂thin films.It can be known by SEM observation and electrochemical test analysis of the film microstructure.When the electrophoretic voltage was 20 V and deposition time was 90 s,the films were most complete and compact after heating at 150℃for 60 min.Under these conditions,the corrosion potential of the films prepared is the most positive,which is-1.27 V,0.20V higher than that of the magnesium alloy matrix,and the corrosion current density is the lowest,which is 1.29×10^-6A·cm^-2,which is two orders of magnitude lower than that of the magnesium alloy matrix.It is proved that TiO₂thin films deposited by electrophoresis on magnesium alloy surface can effectively improve its corrosion resistance.（2）2D-MoS₂thin films were successfully prepared on the surface of magnesium alloy by electrophoretic deposition method.The surface morphology of 2D-MoS₂thin films was analyzed by scanning electron microscope and it was found that the thin films with electrophoretic deposition time of 60 s were the most complete and dense,and could cover the whole substrate.With the increase of electrophoretic deposition time,the thickness of the film increases,and the internal stress of the film also increases,which leads to the damage and crack of the film.Compared with magnesium alloy matrix,the corrosion resistance of magnesium alloy coated with 2D-MoS₂film is improved to a certain extent.The corrosion potential of 2D-MoS₂films deposited by electrophoretic deposition for 60 s is-0.99 V,and the corrosion current density is 9.78×10^-6A·cm^-2.Compared with the magnesium alloy matrix,the corrosion potential of magnesium alloy after electrophoretic deposition increased by 0.46 V,and the corrosion current density decreased by 93%.However,compared with 2D-TiO₂film,the corrosion potential of 2D-MoS₂film is positive,but the corrosion current density increases by 86.8%.Therefore,the influence of adding monolayer MoS₂to two-dimensional 2D-TiO₂film on the corrosion resistance of magnesium alloy will be further studied.By electrophoretic deposition,MoS₂was added into TiO₂dispersion as electrophoretic solution.And TiO₂/MoS₂composite films were successfully prepared on the surface of magnesium alloy.When TiO₂:MoS₂is 1:0.7,the composite film is the most complete and compact,and the composite film prepared at this ratio has the best electrochemical performance.The corrosion potential of the films prepared is the most positive,which is-1.00 V,and the corrosion current density is the lowest,which is 3.69×10^-7A·cm^-2.Compared with the sample with TiO₂film,the corrosion potential of magnesium alloy with TiO₂/MoS₂film moved 0.27 V in the positive direction,and the corrosion current density decreased by 71.4%,which was 96.2%lower than that of MoS₂thin film.After modified by silane coupling agent KH570,the surface wettability of magnesium alloy was changed from hydrophilic to hydrophobic,and the maximum surface water contact Angle reached 131.53°.And the corrosion potential was-0.85 V,and the corrosion current density was 6.73×10^-8A·cm^-2.Compared with TiO₂/MoS₂film modified before KH570,the corrosion potential shifted to positive 0.15 V,and the corrosion current density decreased by 81.8%.These results show that TiO₂/MoS₂composite films can further increase the corrosion resistance of magnesium alloys...