| The main advantages of aluminum metal and its alloy are low density,high specific strength and good formability,so it is widely used in aerospace,electric transportation,automobile,electronics and other fields,and can be used as the preferred material of engine piston.However,the corrosion resistance and wear resistance of aluminum and its alloy are poor,which is prone to corrosion and wear in the reciprocating friction movement of the engine piston.It is an effective method to improve the corrosion resistance and wear resistance of aluminum alloy by surface treatment.The difficulty lies in that the effect of friction reduction and corrosion resistance cannot be achieved simultaneously.This thesis focuses on the preparation of hydrotalcite film layer on the surface of anodized aluminum by in situ growth method and the modification of the film layer to reduce the friction coefficient of the aluminum alloy while improving its corrosion resistance.The porous anodic oxide film was prepared on aluminum surface by anodic oxidation method.At the same time,magnesium aluminum hydrotalcite(MgAl-LDH)with layered bimetallic structure was fabricated by in-situ growth method on the basis of anodic oxide film.The effects of pH,reaction temperature and reaction time on the corrosion resistance and friction reduction of in-situ hydrotalcite film were studied by electrochemical and tribological tests.The microstructure and elemental composition of the film were analyzed by scanning electron microscopy(SEM)and X-ray energy dispersive spectroscopy(EDS).The results show that the structure of the hydrotalcite film is nanosheet with vertical cross-linking.When the pH of the reaction solution is 9,the reaction temperature is 90℃and the reaction time is18 h,the corrosion current density of hydrotalcite film in 3.5 wt.%NaCl solution decreases by 3 orders of magnitude compared with that of aluminum alloy substrate,and the friction coefficient decreases from 0.7 to 0.1.It shows that MgAl-LDH has both corrosion-resistant and friction-reducing effects.The MgAl-LDH membrane was treated by synergistic modification of organic corrosion inhibitor thiourea and stearic acid,and the modified membrane was immersed in 3.5 wt.%NaCl solution for 30 days.The long-term corrosion resistance of the modified film was studied by X-ray photoelectron spectroscopy(XPS),SEM and electrochemical testing.The results show that under the conditions of pH=5 thiourea solution,temperature 45℃,time 5min,stearic acid concentration 0.1 mol/L,temperature 45℃,time 2 min,the self-corrosion current of the modified film decreases by 1 order of magnitude compared with the unmodified material,and the friction coefficient remains unchanged.After soaking for 30 days,corrosion products appeared on the surface of aluminum alloy and anodic alumina.The self-corrosion current density of anodic alumina film increases by 1 order of magnitude,while the self-corrosion current density of anodic alumina film grown with hydrotalcite and modified hydrotalcite film is almost unchanged.It indicates that the MgAl-LDH film modified by thiourea and stearic acid has long-term corrosion resistance.Zinc dibenzyldithiocarbamate(ZBEC)will be selected as corrosion inhibitor to modify the prepared MgAl-LDH film.By means of electrochemical impedance spectroscopy(EIS),infrared spectroscopy(FT-IR),XPS and other methods,the relationship between ZBEC concentration,modification temperature,modification time and the properties of the film was studied.The results show that when the concentration of ZBEC modified solution is 0.03mol/L,the temperature is 45℃and the time is 15 min,the low frequency modulus of EIS of modified MgAl-LDH film increases from 794×10~3Ω·cm~2 to 1995×10~3Ω·cm~2,indicating that ZBEC modification improves the corrosion resistance of MgAl-LDH film. |
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