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The effects of feeding sequence of reactants on the properties of a MgAl layered double hydroxide (LDH) coating on Mg alloy are reported herein for the first time. Based on the X-ray diffraction (XRD) patterns and Fourier transform infrared (FTIR) spectra, MgAl-LDH coatings were successfully obtained with different feeding sequences. However, characterizations of scanning electron microscopy (SEM) and electrochemical methods show that the surface morphologies and corrosion resistance of the MgAl-LDH coatings are dependent upon the feeding sequence. Furthermore, the MgAl-LDH coatings were modified in an 8-quinolinol (8HQ) solution by a facile soaking measurement. Energy dispersive X-ray spectroscopy (EDS) maps and X-ray photoelectron spectroscopy (XPS) spectra demonstrate the effective adsorption of 8HQ layer on the MgAl-LDH primer. The high-resolution N 1s XPS spectra manifest the existence of chemisorption owing to formation of a complex chelate, (bis (8-hydroxyquinolinato) magnesium, Mg(HQ)2), between 8HQ anions and dissolved Mg2+. The modified MgAl-LDH coatings, which are named as 8HQ@MgAl-LDH coatings in the body text, show significant enhancement in corrosion resistance and remains excellent corrosion protection even exposure to a NaCl aqueous solution for one month. The mechanism of corrosion inhibition for the 8HQ@MgAl-LDH coatings is proposed finally, which mainly includes the increase in water contact angles, Cl− and CO32− anion-exchangeability, and redeposition of Mg(HQ)2 precipitation. These findings of this study provide some valuable insights into the corrosion protection mechanism of the MgAl-LDH coatings and the designment of a highly corrosion resistant coating on Mg alloy and other lightweight alloys.
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•MgAl layered double hydroxide (MgAl-LDH) coatings grew in situ on AZ31 Mg alloy.•Properties of the MgAl-LDH coatings are feeding sequence dependence.•Corrosion inhibition of MgAl-LDH coating is enhanced after 8-quinolinol treatment.•Chemisorption of 8-quinolinol on the MgAl-LDH coating surface was identified.•A mechanism of corrosion protection for the MgAl-LDH coatings has been proposed.