Preparation And Properties Of Magnesium Alloy Surface Corrosion Resistant Composite Film

Mg alloys are widely used in aerospace field,but their extensive application is strongly limited due to the poor corrosion resistance.Therefore,the ameliorate on the corrosion resistance of Mg alloy has become a pressing matter of the moment.In this paper,the silane/corrosion inhibitor nanocomposite coating was prepared by screening corrosion inhibitors.In addition,the surface morphology and elements desperation of composite coating was analyzed by Scanning Electron Microscope（SEM）equipped with Energy Disperse Spectroscopy（EDS）,and the microstructure of the film was characterized by Fourier Transform Infrared Spectrometer and X-ray photoelectron spectroscopy（XPS）.Finally,the mechanical performance and corrosion resistance of the film was analyzed by Nano indentation technology and electrochemical tests.The conclusions are as follows:The best corrosion inhibitor formulation obtained by weight loss method was anode type organic-inorganic composite corrosion inhibitor which was composed by sodium phosphate,sodium carbonate,sodium stearate and cerium nitrate.The corrosion inhibition rate of magnesium alloy can reach to 97.91%after the addition of selected corrosion inhibitor in 3.5 wt.%Na Cl solution.The silane/corrosion inhibitor nanocomposite film layer was prepared on the surface of Mg alloy by using a combination of silanization treatment and corrosion inhibitor surface treatment to alternate film formation on the surface of Mg alloy.Meanwhile,some Si O₂ nanoparticles were added to the composite coating.It was shown that the composition of substrate and composite coating was chemical bond（Si-O-Mg）and the higher corrosion resistance of composite coating was obtained due to the construct of hydrophobic barrier layers.Finally,the mechanical performance and corrosion resistance of the film was analyzed by Nano indentation technology and electrochemical tests.The results showed that the composite coating had a strong inhibition on the cathodic and anodic processes.In addition,the EIS results showed that there was a significant increase in linear resistance.The low-frequency impedance modulus shows a trend of decreasing,then increasing and finally decreasing,with a maximum of 90.0 kΩ·cm².Meanwhile,the Nyquist plot showed that there was no inductive resistance occurrence,which indicated that the composite coating had a high pitting resistance.Scratching experiments showed that the impedance of the composite coating displayed a huge decrease after scratching.However,the self-healing phenomenon of the composite film was observed,and its low-frequency impedance modulus started to increase after 2 h which increased from 2.50 kΩ·cm² to 12.0 kΩ·cm².However,the low-frequency impedance modulus showed a decreasing trend after 8 h.The results of nanoindentation experiments showed that the nanohardness and nanoelastic modulus of magnesium alloy were 1.15 GPa and 48.7 GPa,respectively,and the nanohardness and nanoelastic modulus values of the composite coating reached to 65.22%（0.75 GPa）and 19.51%（9.5 GPa）of the base material,respectively.The combined nanomechanical properties of the composite coating were 0.034,which was significantly better than that of the base material（0.024）.