A self-curing konjac glucomannan/CaCO₃ coating for corrosion protection of AA5052 aluminum alloy in NaCl solution

A composite coating containing konjac glucomannan (KGM) and CaCO₃ was fabricated on AA5052 alloy through a self-curing process, and its surface morphology and component were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). The effect of Ca(OH)₂ content on the protective property of the composite coating for aluminum alloy in 3.5 wt% NaCl solution was evaluated by electrochemical impedance spectroscopy measurements. Moreover, the inhibitory performance of the coating on the pitting corrosion of metal was examined by potentiodynamic polarization curves and atomic force microscopy (AFM). The images of scanning electron microscope show the composite coating with a thickness of 50 μm has well-defined branch-shaped structure. The FT-IR spectra confirm the successful fabrication of the polymer coating through the formation of CaCO₃. The results of electrochemical impedance spectroscopy suggest that the resistance of the aluminum alloy sample coated with such protective layer is improved by six orders of magnitude, compared with the bare metal. After 60 d of immersion, the polarization curve data and AFM analysis show the pitting corrosion occurring on AA5052 surface is prevented due to the barrier property of coating.