Preparation and Properties of Silicon-Zirconium Hybrid Coatings by Electrophoretic Deposition on LC4 Aluminum Alloy

Silicon-zirconium hybrid coatings were prepared by cathode electrophoretic deposition (EPD) method on the surface of LC4 aluminum alloy. The influence of deposition conditions on the morphology, structure and corrosion resistance of the hybrid coatings was studied. Silicon sol and zirconium sol with a molar ratio Si/Zr=3 : 1 were prepared separately and then mixed. The silane solutions used here consist of GTMS (3-glycidoxypropyltrimethoxysilane) and absolute ethanol and deionized water mixed solvent, with pH adjusted by acetic acid. The obtained solutions were vigorously stirred at room temperature for 1 h. On the other hand, TPOZ (zirconium n-propoxide) was complexed with ethyl acetoacetate and diluted with absolute ethanol up to a molar ratio ethanol/H2O=3 : 1. The Zr-solution was stirred for 1 h at room temperature. After then Si-solution and Zr-solution were mixed under stirring at room temperature for 30 min. Two-electrode system in which Plumbum and LC4 aluminum alloy as the anode and the cathode respectively was applied for the deposition of silicon-zirconium organic-inorganic hybrid coatings. The electrodeposition was mainly carried out at different cathodic potentials (0, 2, 5, 10, 20 V, respectively), for 10 min. Finally the silane films were dried at room tempreture and then cured at 60 degrees C for 2 h, 90 degrees C for 30 min, 100 degrees C for 15 min at air atmosphere in an oven. Further heat treatment provides the thermal energy for the condensation reaction. The zeta potential of different solution was measured by nano-particle size analyzer. The morphology and roughness of the hybrid coatings were detected by using scanning electron microscopy (SEM) and atomic force microscope (AFM), respectively. The chemical structure of the silicon-zirconium hybrid coatings was investigated by using Fourier transform infrared spectroscopy (FTIR). The corrosion resistance of the hybrid coatings was studied by electrochemical impedance spectroscopy (EIS). Finally, the corrosion resistance mechanism of the coatings was discussed. The results showed that the optimum pH of the hybrid solution was 1.6 and the best cathode voltage was 5 V, under which the hybrid coatings are of best performance with uniform surface, dense structure, less roughness, and excellent corrosion resistance in 3.5% NaCl solution.