Fabrication And Anticorrosion Property Evaluation Of Intercalated Layer Structure Film On AZ91D Magnesium Alloy

Magnesium alloys have the advantages of low density,high strength/weight ratio,good electromagnetic shielding and high radiation tolerance,which have the potential to be widely used in automobile,electronic,aviation and spaceflight fields and so on.However,the engineering applications of magnesium alloys are limited,due to their poor corrosion resistance.At present,a protective film or coating is one of the most effective approaches to improve its corrosion resistance.Traditional chromate conversion coating provides excellent corrosion protection,but hexavalent chromium seriously threatens the ecological environment and human health due to its carcinogenic properties.Thus,it is necessary to develop an effective and environment friendly anti-corrosion film.In recent years,intercalated layer structure material as a novel functional material has rapidly developed due to its diversification and controllable structure.Among them,the layered double hydroxides(LDHs)is a kind of typical intercalated structure material with great potential in the field of environment friendly corrosion protection.Thus,the intercalated layer structure films on AZ91D magnesium alloy were fabricated via a hydrothermal crystallization method in this work.By means of surface chemical modification,anion-exchange and graphene oxide doping,the anticorrosion performance of the films is supposed to be improved.The microstructure and phase composition of those films were investigated by scanning electron microscopy(SEM),energy spectrums(EDS),X-ray diffraction(XRD),transmission electron microscopy(TEM),fourier trandform infrared(FT-IR)spectroscopy and Raman spectroscopy.The corrosion resistance of those films was estimated by electrochemical tests,and the relationship between the anti-corrosion performance and layer films structure was also discussed.The main results in this work are as follows:(1)By controlling the pH value and temperature of the reaction solution,the Zn-Al LDHs films with different microstructure were prepared on magnesium alloy via a hydrothermal crystallization method.After the low surface energy modification,the Zn-Al LDHs films on magnesium alloy showed superhydrophobic wettability with contact angles larger than165.5°.According to Cassie-Baxter model analysis,approximately 1.7%serves as the contact area between the water droplet and the solid surface.Exposuring to the atmospheric environment for more than 100 days,the water contact angles remained above 150°.Thus,the superhydrophobic Zn-Al LDHs films exhibited good long-term stability.Electrochemical results revealed that the corrosion current densities icorr of the superhydrophobic Zn-Al LDHs films were reduced two orders of magnitude compared with the magnesium alloy substrate.The superhydrophobic Zn-Al LDHs films effectively improved the corrosion resistance of magnesium alloys.(2)Using the Zn-Al(NO3)LDHs films as a precursor,the Zn-Al(Cl)LDHs films were obtained via the anion-exchange reaction.Electrochemical measurements revealed that the Zn-Al(Cl)LDHs films effectively improve the corrosion resistance of magnesium alloy,which could be attributed to the blocking effect of chloride anions in Zn-Al(Cl)LDHs films on the diffusion of aggressive chloride ions.(3)Choosing the vanadate anion which possesses inhibitor effect as the object anion,and using the Zn-Al(NO3)LDHs films as precursor,the Zn-Al LDHs films intercalated with vanadate anions were prepared on the magnesium alloy through the anion-exchange reaction.Electrochemical measurements showed that corrosion current densities icorr of the Zn-Al(VOx)LDHs films were reduced more than 2 orders of magnitude compared with the magnesium alloy substrate.Moreover,the artificial scratched Zn-Al(VOx)LDHs films showed self-healing behavior due to the change of vanadate anion’s aggregation state.(4)With the doping of graphene oxide(GO)power,a RGO/Zn-Al LDHs composite film was in-situ synthesized on magnesium alloy.The GO nanosheet was reduced into the reduced graphene oxide(RGO)during the reaction procedure,and it was demonstrated that the RGO nanosheet was dispersed in the film randomly.Because of the labyrinth effect,combined with both the excellent impeameability and good conductively of RGO,the RGO/Zn-Al LDHs composite film showed good anticorrosion performance to magnesium alloy.Electrochemical results revealed that the icorr values of the RGO/LDHs hybrids films were reduced two orders of magnitude compared with the magnesium alloy substrate.