Influence of pH value and Zn/Ce cations ratio on the microstructures and corrosion resistance of LDH coating on AZ31

Abstract

To prepare a compact and anti-corrosion Zn-Ce LDH coating on AZ31 magnesium alloy, the various molar ratios of Zn/Ce cations, and different pH values were employed during preparation of the precursor solution. The composition, morphology, structure, and wettability of the deposited coatings were comprehensively characterized via scanning electronic microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and the static sessile drop method. Besides, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements were conducted to evaluate the corrosion resistance of the coatings comparatively. Also, the self-healing ability of the coating was investigated by monitoring the scratched areas of the samples immersed in 3.5% NaCl solution for a long time up to 21 d. The results reveal that the coated Mg alloy shows the lowest corrosion current density (icorr = 1.29 × 10−8 A/cm2) when the Zn/Ce ratio is 2, and the pH value of the precursor solution is approximately 11.

Keywords

• LDH coating
• Magnesium alloy
• Corrosion protection
• Self-healing
• Cerium
• XPS