ZHI technique was used to form a corrosion resistant layer on LC4 alloy. The composition of the layer was studied by X-ray photoelectron spectroscopy (XPS). It is found that the layer is composed of oxides of metals on the substrate, such as Al2O3, ZnO, MgO2, CuO, and MnO2. The electrochemical impedance spectrums (EIS) of LC4 aluminum alloy specimen were measured in NaCl solutions to study the mechanism of the corrosion resistance of the alloy treated with ZH 1 technique. The results show that in NaCl solutions the capacitance of the Helmholtz layer and space charge layer of the oxide coating formed on the surface of LC4 alloy is less than that of a normal metal electrode while its ohmic resistance is relatively greater. At the same time, the thickness of the Helmholtz layer is 1-3 exponentially greater than that of a normal metal electrode. Compared with a normal metal electrode, all these characteristics make it more difficult for charges to transfer between the solution and the surface of the electrode. That is why the polarized current density of LC4 alloy treated with ZHI technique kept small in 3.5% NaCl solution within a wide range of potential, and why the polarized curves of LC4 alloy treated with ZH1 technique changed a little in 3.5% NaCl solution of different pH values. Moreover, according to the capacitance of the space charge layer (Csc) obtained at different potentials in 3.5% NaCl solution, 1/C2sc-E curve was laid out. It is found that there does not exist a simple linear relation between 1/C2sc and the potential. Therefore, the oxide coating formed on LC4 alloy with ZH1 technique is not a semiconductor at room temperature.
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