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

In the present work, a Zn-Al 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 k Omega/cm(2) after the intercalation of the BI molecules into the structure of the Zn-Al LDH layer. The induction of active protection performance for the LDH film modified with BI molecules was demonstrated through the EIS test results.

Automated summary

In this study, a Zn-Al layered double hydroxide (LDH) conversion coating was synthesized on 2024-T3 aluminum alloy using a one-step hydrothermal method, and the corrosion inhibitor BI was successfully intercalated into the LDH film structure. Electrochemical tests confirmed that the polarization resistance of the LDH conversion coating increased after the intercalation of BI molecules, demonstrating improved protection performance.