Ordering and disordering of in situ grown MgAl-layered double hydroxide and its effect on the structural and corrosion resistance properties

A MgAl-layered double hydroxide (MgAl-LDH) protective film was developed on AA6082 substrates via the in situ hydrothermal growth method to obtain a distinct cauliflower-like LDH structure, and coated substrates were further heat-treated in air at temperatures from 100 to 250°C to further improve the corrosion resistance of MgAl-LDH by taking advantage of the LDH memory effect; also, the effect of calcination on MgAl-LDH structural stability and the corresponding corrosion resistance properties were investigated. The structural characterization of uncalcined and calcined LDH films were examined using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, thermogravimetric analysis, differential scanning calorimetry, and Fourier transform infrared spectroscopy. The corresponding corrosion protection efficiency of the developed coating was studied through potentiodynamic polarization experiments and by electrochemical impedance spectroscopy. Compared with uncalcined MgAl-LDH, the calcined film showed a relatively lower corrosion current density and a higher impedance value, especially after heat treatment at 250°C. The findings demonstrate that calcination strongly affects the oriented growth of the LDH and causes an increase in the surface area and contraction of the basal spacing, which in turn caused a compact structure that substantially influenced the LDH corrosion resistance properties.