A comparative study and optimization of corrosion resistance of ZnAl layered double hydroxides films intercalated with different anions on AZ31 Mg alloys

Layered double hydroxides (LDHs) have great potential as protective coatings on magnesium alloys due to their nanolamellar structure and exchangeability of interlayer anions. ZnAl layered double hydroxides films intercalated with nitrate anions (ZnAl-NO3--LDHs) was synthesized on the AZ31 magnesium alloy by hydrothermal method. In order to obtain better corrosion resistance, ZnAl-X-LDHs (X = Cl-, VO43-, PO43-, or MoO42-) were prepared by using ZnAl-NO3--LDHs as a precursor, and Cl, VO43-, PO43-, and MoO42- anions intercalated into the LDHs interlayers to replace NO3- through anion-exchange reaction. X-ray diffraction (XRD), scanning electronic microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy were used to investigate structure, morphology and composition of the ZnAI-LDHs. The corrosion resistance of ZnAl-LDHs intercalated with different anions was compared by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results show that the corrosion resistance of ZnAl-LDHs films is ranged in order as follows: ZnAl-VO43--LDHs > ZnAl-MoO42--LDHs > ZnAl-PO(4)(3-)LDHs > ZnAl-Cl-LDHs > ZnAl-NO3- LDHs. ZnAl-VO43--LDHs has the largest basal spacing distances don) value and strongest ability to release anions and absorb chloride ions, so ZnAl-VO43--LDHs films has the optimal corrosion resistance and can provide enhanced anticorrosion protection for magnesium alloys substrate.