Studies On The Preparation And Anti-corrosion Property Of The Double Self-healing MgAlY-LDHs Film On Magnesium Alloys

Magnesium and its alloys have excellent properties such as high specific strength and environmental friendliness,which are considered to have broad development prospects.However,the high chemical activity of magnesium makes it vulnerable to corrosion and limits its industrial application.Given the defects of magnesium alloy,it is a direct and effective means to build a protective coating on the surface to improve its corrosion resistance.Although many coating technologies（such as anodic oxidation,Plasma electrolytic oxidation,etc.）have been able to basically meet the corrosion resistance requirements of magnesium alloys,the hole defects on the surface of these coatings will be preferentially eroded and aggravate the corrosion.Moreover,the surface damage caused by mechanical or physical reasons such as collision and scratch will even lead to more serious local corrosion.If this kind of passive protective coating can be sealed and the multiple response and self-healing mechanism can be constructed,the corrosion inhibitor ions can be released spontaneously under the change of corrosion environment（such as temperature,pH,etc.）,which can achieve a certain self-healing protection effect in the damaged area.Based on this,layered double hydroxyl metal oxides（LDHs）were constructed on the phosphate oxide film of magnesium alloy by the in-situ growth method to seal the oxide film.The corrosion resistance of MgAlLDHs nano-container was studied by introducing yttrium into the main layer of LDHs through isomorphous replacement.In this paper,three kinds of magnesium alloys MgAlY,MgZnY and AZ31 were melted and their compositions were confirmed.Three kinds of oxide films were obtained by phosphoric acid anodization,and the possibility of in-situ growth of MgAlY-LDHs on magnesium alloy oxide film was explored by changing the concentration of Y ion in the growth solution of LDHs precursor.By comparing the morphology,structure and corrosion behavior of each sample,the different growth rules of MgAl-LDHs and MgAlY-LDHs nanosheets,and the release and release behavior of rare-earth ions in corrosion environment were studied,and the self-healing ability of ternary LDHs was preliminarily explored.Secondly,the morphology and structure of the samples were characterized by changing the reaction condition（Y ion concentration）,to explore the hydration and dissolution behavior of the oxide film in the reaction solution,and the isomorphous replacement and growth mechanism of ternary LDHs nanosheets.This provides the preliminary theoretical analysis for the establishment of the double self-healing mechanism on the oxide film of magnesium alloy.Finally,by loading guest organic corrosion inhibitor anions in the ternary LDHs structure,we expand the interlayer spacing to capture more erosion Cl ions by the ion exchange of OH^-and NO₃^-in the laminar channel of LDHs.Among them,the coordination between salicylate and rare earth（Y）ions were also studied.The characterization and property test of micro-arc oxidation film,binary LDHs film,ternary LDHs film,and salicylic acid loaded ternary LDHs film showed that salicylic acid could enter the ternary LDHs interlayer and form the more stable structure,which plays the ideal corrosion inhibitive effect in the corrosion solution.Moreover,the synergistic effect of rare-earth ions and organic corrosion inhibitors was further explored through scratch and immersion experiments.X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FT-IR）,back-scattering electron microscopy（BSE）,scanning electron microscopy（SEM）,energy dispersive spectrometer（EDS）,X-ray photoelectron spectroscopy（XPS）,glow discharge spectrometer（GDOES）were used to observe and characterize the microstructure and chemical composition of the samples.The growth process and interface bonding mechanism of LDHs nanosheets were observed by scanning electron microscopy（SEM）.The repairing process of the film scratch was observed and analyzed by OM and LM tests.The electrochemical behavior of the samples was evaluated by the Tafel polarization curve,EIS and immersion tests.The results confirm that Y can enter the main layer of LDHs through the isomorphous replacement,and salicylate can enter the interlayer of LDHs structure through the ion exchange reaction,which can significantly improve the corrosion resistance of the film.Moreover,the coordination effect between them can improve the stability of LDHs nanostructures,and have the synergistic self-healing effect on the scratch area of alloys.