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Water diffusion in a sandwich-structured composite film on a Mg-Gd-Y alloy was experimentally investigated using electrochemical impedance spectroscopy (EIS). The composite film contained an inner integration layer and an outer fluorocarbon (FC) layer. The integration layer was prepared by depositing an environment-friendly self-assembled nanoparticle film on the surface of a plasma electrolytic oxidation film. The resulting structure is therefore referred to as PSF. The measured value of the diffusion coefficient of the PSF film by the EIS method was compared to the value predicted using a mathematical model. The noncontinuity of the water concentration at the interface of the integration and FC layers resulted in a significant difference between the diffusion coefficients obtained by the experimental EIS method and mathematical model. A coefficient "ke" was introduced to the Fick's first law of diffusion, and a PSF model validation was used to confirm the concentration jump on the FC-integration boundary of the PSF film. When ke [?] 1, the calculated diffusion coefficient (DMeff) of the PSF film by the mathematical model was found similar to that obtained by the EIS experimental method.

The effect of exported energy density on the plasma electrolysis oxidation (PEO) process was studied under transient self-feedback control (TSFC) mode. Properties of the Al2O3 PEO films were characterized by scanning electron microscopy (SEM), Vickers hardness test and electrochemical impedance spectroscopy (EIS). Experimental results indicated that a hard and compact PEO film was obtained at a correct energy density due to the uniform action of the high-frequency square voltage waveform (HFSVW). On the contrary, the high energy density greatly weakened the uniform action of the HFSVW which resulted in large pores and microcracks in the PEO films.

Different microstructures of the Al2O3 plasma electrolytic oxidation (PEO) films were obtained by controlling the frequency of applied high-frequency square voltage waveform (HFSVW) under different transient self-feedback control (TSFC). The morphology and compactness of the PEO films were characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Experimental results indicated that uniform, compact, small-grained TSFC PEO films can be produced by applying high-frequency HFSVWs.

A composite film was prepared by depositing layers of plasma electrolysis oxidation (PEO) film and self-assembled nanoparticle (SANP) film on a Mg-Gd-Y alloy. The electrochemical impedance spectroscopy (EIS) results showed that the structure of the PEO + thin SANP layers greatly increased the corrosion protection of the composite film. In addition, two water diffusion coefficients (D) of the composite film were obtained using EIS and Kalnin's model. The D values indicated the composite film had a good barrier property against water.

An interlayer film between a magnesium alloy substrate (MAS) and electromagnetic wave absorption coatings (EWACs) has been produced by micro-arc oxidation (MAO) method. A new voltage mode has been developed for use in the MAO technique. The corrosion resistance of MAS has been investigated in 3.5 wt% NaCl solution. The results show that the MAO interlayer not only delays interaction of chloride electrolyte with MAS but also changes corrosion behavior of the metal substrate. The film restricts propagation of filiform corrosion at the coating/substrate interface and simultaneously eliminates galvanic couples by separating absorbents in the EWAC from the MAS.

Water diffusion in a sandwich-structured composite film on a Mg-Gd-Y alloy was experimentally investigated using electrochemical impedance spectroscopy (EIS). The composite film contained an inner integration layer and an outer fluorocarbon (FC) layer. The integration layer was prepared by depositing an environment-friendly self-assembled nanoparticle film on the surface of a plasma electrolytic oxidation film. The resulting structure is therefore referred to as PSF. The measured value of the diffusion coefficient of the PSF film by the EIS method was compared to the value predicted using a mathematical model. The noncontinuity of the water concentration at the interface of the integration and FC layers resulted in a significant difference between the diffusion coefficients obtained by the experimental EIS method and mathematical model. A coefficient “ke” was introduced to the Fick's first law of diffusion, and a PSF model validation was used to confirm the concentration jump on the FC-integration boundary of the PSF film. When ke≪ 1, the calculated diffusion coefficient (DMeff) of the PSF film by the mathematical model was found similar to that obtained by the EIS experimental method.

The effect of exported energy density on the plasma electrolysis oxidation (PEO) process was studied under transient self-feedback control (TSFC) mode. Properties of the Al2O3PEO films were characterized by scanning electron microscopy (SEM), Vickers hardness test and electrochemical impedance spectroscopy (EIS). Experimental results indicated that a hard and compact PEO film was obtained at a correct energy density due to the uniform action of the high-frequency square voltage waveform (HFSVW). On the contrary, the high energy density greatly weakened the uniform action of the HFSVW which resulted in large pores and microcracks in the PEO films.

A composite film was prepared by depositing layers of plasma electrolysis oxidation (PEO) film and self-assembled nanoparticle (SANP) film on a Mg-Gd-Y alloy. The electrochemical impedance spectroscopy (EIS) results showed that the structure of the PEO + thin SANP layers greatly increased the corrosion protection of the composite film. In addition, two water diffusion coefficients (D) of the composite film were obtained using EIS and Kalnin's model. The Dvalues indicated the composite film had a good barrier property against water.

Different microstructures of the Al2O3plasma electrolytic oxidation (PEO) films were obtained by controlling the frequency of applied high-frequency square voltage waveform (HFSVW) under different transient self-feedback control (TSFC). The morphology and compactness of the PEO films were characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). Experimental results indicated that uniform, compact, small-grained TSFC PEO films can be produced by applying high-frequency HFSVWs.

Transient self-feedback control (TSFC) was employed to prepare plasma electrolytic oxidation (PEO) coatings on 2024 Al alloy. Compared with Al2O3PEO coating by the custom pulse voltage (CPV) process, the PEO coating using the TSFC mode generated a thinner outer layer and more compact inner layer. In order to study the microstructure effect on the practical corrosion properties, three Al2O3PEO coatings using the CPV and TSFC processes were studied during long term immersion in a corrosive environment by electrochemical impedance spectroscopy (EIS) and neutral salt spray test (NSST). Two groups of electrical equivalent circuits were employed based on different microstructures. During the initial immersion period a double-layer element (CPEdlRt) appeared due to the CPV PEO coating having a porous outer layer and thinner inner layer. Thereafter, continuous corrosion reactions happened at the metal/PEO interface, which resulted in the appearance of diffusion elements. However, for specimens prepared by TSFC, corrosion reactions only happened in the later stages of the immersion. The compact and thick inner layer mainly contributed to excellent barrier properties, stable microstructure after 380 h immersion in 3.5(wt%) NaCl solution and excellent performance in the salt spray test.

An interlayer film between a magnesium alloy substrate (MAS) and electromagnetic wave absorption coatings (EWACs) has been produced by micro-arc oxidation (MAO) method. A new voltage mode has been developed for use in the MAO technique. The corrosion resistance of MAS has been investigated in 3.5 wt% NaCl solution. The results show that the MAO interlayer not only delays interaction of chloride electrolyte with MAS but also changes corrosion behavior of the metal substrate. The film restricts propagation of filiform corrosion at the coating/substrate interface and simultaneously eliminates galvanic couples by separating absorbents in the EWAC from the MAS.