Zn-Al layered double hydroxide as an inhibitive conversion coating developed on AA2024-T3 by one-step hydrothermal crystallization: Crystal structure evolution and corrosion protection performance

Abstract

In the present work, a ZnAl layered double hydroxide (LDH) conversion coating was synthesized on 2024-T3 aluminum alloy by a one-step hydrothermal method. For this purpose, the effect of synthesis parameters, including the amount of Zn2+ cations and hexamethylenetetramine molecules, on the structural changes were evaluated by using the scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS) analysis and X-ray diffraction (XRD) spectroscopy. Also, benzimidazole (BI), as corrosion inhibitor of the AA2024-T3, was intercalated into the LDH film structure by an anion-exchange process. The intercalation of BI molecules into the LHD structure was studied using the SEM-EDS and XRD analysis. Furthermore, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PD), and electrochemical current noise measurements were employed in 3.5 wt% NaCl solution to assess the protection performance of the LDH coating. The PD test results showed that the LDH conversion coating's polarization resistance increases from 24.05 to 131.1 kΩ/cm2 after the intercalation of the BI molecules into the structure of the ZnAl LDH layer. The induction of active protection performance for the LDH film modified with BI molecules was demonstrated through the EIS test results.