Research Of Self-repairing Coating On Magnesium Alloy Based On Mg-Al Layered Double Hydroxide

Magnesium alloys have great potential for applications in chemical,transportation,aerospace and other fields due to their excellent properties,such as light weight,high specific strength,and good heat dissipation,but they also exhibit poor corrosion resistance owing to high chemical activity.Constructing a reasonable and excellent coating on the Mg alloy surface can greatly improve the corrosion resistance.In this paper,the special structure and ion exchange performance of layered double hydroxide?LDH?are mainly employed to improve the corrosion resistance of Mg alloys.The specific research content includes the following three parts:?1?The effect of feeding sequences of chemical reagents on the performance of MgAl-LDH coating grown in situ on Mg alloy was studied.X-ray diffraction pattern?XRD?,Fourier transform infrared spectroscopy?FT-IR?results,scanning electron microscope?SEM?,and electrochemical test show that the surface morphology and corrosion resistance of the MgAl-LDH coating are related to the feeding sequences.The corrosion resistance of the coating using the first?MgAl-LDH/FS1?and third?MgAl-LDH/FS3?feeding sequences are relatively better.MgAl-LDH/FS1 and MgAl-LDH/FS1 were modified by soaking in 8-quinolinol?8HQ?solution.The 8HQ corrosion inhibitor layer was effectively formed on the MgAl-LDH primer coating,resulting in a layer with hydrophobic surface,and increases its physical barrier effect.Compared with the blank MgAl-LDH coating,the composite coating had significantly enhanced corrosion resistance due to the good corrosion inhibition of 8HQ^-.?2?According to the corrosion inhibition mechanism of heteroatom corrosion inhibitor,a new corrosion inhibitor was designed and synthesized,namely N-alkyl-N,N-dimethyl-N-?3-thienylmethylene?ammonium bromide?NTA?,to modify the MgAl-LDH film.SEM,XPS and electron probe microanalysis?EPMA?characterization prove that NTA was successfully adsorbed on the MgAl-LDH primer coating,which significantly improves the compactness of the coating and corrosion inhibition,leading to a much higher level of corrosion protection for the composite coating.Electrochemical tests showed that,compared to conventional commercial corrosion inhibitors such as sodium alginate?SA?,NTA modified MgAl-LDH?NTA@MgAl-LDH?coating had a higher charge transfer resistance?1837 M?·cm²?and lower corrosion current density(0.04001 nA·cm^-2).The calculated results of EDS spectrum and density functional theory prove that the good self-healing ability is mainly because the formation of NTA protective film on the Mg surface can prevent Mg alloy from corrosion.?3?Using the pH response characteristics of LDH,mesoporous silica nanoparticles?MSN?was synthesized and modified with corrosion inhibitor2-mercaptobenzothiazole?MBT?to form pH-stimulated nanomaterial?MSN-MBT@LDH?.After addition of MSN-MBT@LDH into sol-gel solution and coating on Mg ally surface to prepare an acid-responsive smart coating.SEM and TEM results confirmed the spherical structure of MSN and the nanosheet structure of LDH.EDS,XRD and nitrogen adsorption/desorption test results proves that MBT was adsorbed on the surface and mesopores of MSN,and LDH nanosheets successful cover on the MSN surface.The UV test results of MBT controlled release proves that the release rate of MBT is different under different acidic conditions when pH=2,5 and 7for MSN-MBT@LDH.The lower the pH,the faster the release rate.Electrochemical test results show that the charge transfer resistance of the self-assembled nanophase particle?SNAP?coating with MSN-MBT@LDH nanoparticles is as high as 149.7M?·cm²,and the corrosion current density is as low as 0.737 nA·cm^-2,showing excellent corrosion resistance.The research above provides some valuable insights into the corrosion protection mechanism of MgAl-LDH materials,the development and application of corrosion inhibitors,and the design of highly corrosion-resistant smart coatings on Mg alloys and other light alloys.