A novel self-healing composite coating was fabricated on magnesium alloy by using polycaprolactone (PCL) as resin matrix and iron-based metal-organic framework MIL-53 modified with tannic acid (TA) as function filler. The surface morphology, structure and wettability of composite coating were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) and sessile water droplet static contact angle. The corrosion resistance and healing performance of PCL coatings was determined by electrochemical impedance spectroscopy (EIS) and photothermal tests. Results indicate that MIL-53@TA/PCL coating possesses a flatter surface, a higher corrosion resistance and better photothermal effect than that of blank PCL coating and MIL-53/ PCL coating. Under the near-infrared (NIR) laser irradiation with the wave length of 808 nm, the scratched MIL-53@TA/PCL coating could be healed within 10 min because of the excellent photothermal conversion ability of MIL-53@TA component.

Zinc coordinated 1-hydroxyethylidene-1,1-diphosphonic acid (Zn-HEDP) film was fabricated on steel surface by coordination self-assembly method. The surface morphology and chemical composition of Zn-HEDP film were investigated by scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), and the structural and valence state of Zn-HEDP film was determined by Fourier transform infrared spectroscopy (FTIR), Raman spectra and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of Zn-HEDP film in 3.5wt% NaCl solution was investigated by using potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) techniques. The experimental results show that Zn-HEDP film is in a smooth surface with disturbed nanoparticles. The protection efficiency of Zn-HEDP film to steel in 3.5 wt% NaCl solution is firstly increased and then decreased with the increasing of zinc concentration, pH value and assembly time. The optimum preparation conditions for Zn-HEDP film are the zinc concentration of 10 mmol/L, pH value of 5.0 and assembly time of 30 min, under which the protection efficiency of film is reached to 95.79 %. The coordination between zinc ions and HEDP can effectively increase the binding energy with Q235 steel. Zinc ions can improve the compactness and thickness of Zn-HEDP films as bridging agents, which prevent Q235 steel from corrosive solution.

In this work, an economical and environmentally friendly polyaspartic acid-zinc (PASP-Zn) film was successfully prepared on the surface of Q235 steel by coordination self-assembly, and the preparation conditions of PASP-Zn film were optimized by single factor method. The surface morphology and thickness of PASP-Zn film were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the structure and composition of PASP-Zn film were determined by X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The corrosion resistance of PASP-Zn film on Q235 steel in 3.5wt % NaCl solution was analyzed by electrochemical impedance spectroscopy (EIS) and polarization curves. The results show that PASP film and PASP-Zn film are successfully prepared on the surface of Q235 steel, and the single PASP film is self-assembled monolayers with thin thickness and loose structure. Whereas PASP-Zn film shows a rough morphology, accompanied by appearance of a large amount of nanoparticles, and the thickness of PASP-Zn film is about 98.0 nm. PASP-Zn film exhibits much better corrosion protective performance than PASP film in 3.5 wt % NaCl solution, and the highest protection efficiency can reach 94.48 %. The excellent coordination ability between PASP and zinc ions can effectively improve the compactness and thickness of PASP-Zn film, and prevent the corrosive ions from contacting the Q235 steel surface. By adjusting the preparation conditions, a PASP-Zn film with optimal corrosion resistance was prepared in the film-forming solution containing PASP/Zn ratio of 1:8 and pH value of 5.0 for 30 min.