Self-healing vanadate-doped NiAl-layered double hydroxide (LDH) coatings synthesized for active corrosion protection of 2024 aluminum alloy

In the current research, vanadate-doped NiAl-layered double hydroxide (LDH) conversion coatings were synthesized on the anodized 2024-T4 aluminum alloy to provide efficient corrosion resistance and self-healing behavior. The effect of various pH values on the nanostructure and electrochemical behavior of synthesized coatings was investigated. Various techniques such as field emission scanning electron microscopy (FESEM), energy dispersive spectrometry (EDS), confocal Raman micro spectrometry, Fourier transform infrared spectrophotometry (FTIR), X-ray diffraction analysis (XRD), potentiodynamic polarization test and electrochemical impedance spectrometry (EIS) were applied to characterize the nanostructure of LDH coatings and their electrochemical behavior. The results indicated that the synthesized LDH coating at pH=7.5 indicated the highest interlayer spacing of 7.75 Å. The electrochemical behavior study revealed that the formation of LDH coating with the highest interlayer spacing improved the inhibitive performance by about ten times due to its excellent ion exchangeability as confirmed by ion chromatography (IC) analysis. To enhance the inhibition performance of NiAl LDH coating, it was doped with an efficient vanadate inhibitor. It was demonstrated that vanadate doping significantly improves the inhibition performance of NiAl LDH coating by about 20 times compared to bare aluminum alloy. One of the notable findings of the current study was the controlled release of the vanadate inhibitor, which was determined through UV-Vis spectroscopy. This attribute led to the self-healing ability of synthesized coatings, which was confirmed by the open circuit potential (OCP) examination of scratched coatings. The self-healing mechanism was proposed based on the passive complex formation on the corroded surface.