| XIN Yanchen,WANG Youbin,CHEN Zhiwen,FENG Jiqiang,GAO Feng,TANG Hongqun.Effect of Impurity Ga on the Microstructure and Corrosion Resistance of Zirconium Titanium Conversion Coating on Pure Al[J],53(4):46-57 |
| Effect of Impurity Ga on the Microstructure and Corrosion Resistance of Zirconium Titanium Conversion Coating on Pure Al |
| Received:December 24, 2022 Revised:May 18, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.04.004 |
| KeyWord:impurity Ga zirconium titanium conversion coating localized corrosion scanning electrochemical microscope (SECM) localized electrochemistry |
| Author | Institution |
| XIN Yanchen |
School of Resources, Environment and Materials,State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, Guangxi University, Nanning , China |
| WANG Youbin |
School of Resources, Environment and Materials,State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, Guangxi University, Nanning , China |
| CHEN Zhiwen |
School of Resources, Environment and Materials,State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, Guangxi University, Nanning , China |
| FENG Jiqiang |
School of Resources, Environment and Materials,State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, Guangxi University, Nanning , China |
| GAO Feng |
School of Resources, Environment and Materials,State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, Guangxi University, Nanning , China |
| TANG Hongqun |
School of Resources, Environment and Materials,State Key Laboratory of Featured Metal Materials and Life-cycle Safety for Composite Structures, Guangxi University, Nanning , China |
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| Abstract: |
| Al alloys are widely used in many applications such as aerospace, rail transit, automobile, and power electronics industry due to the advantage of low density, high strength, and good formability. However, Al alloys are easily corroded in the solution containing Cl− ions, which causes local corrosion, such as pitting corrosion and intergranular corrosion, resulting in the decrease of service life. To improve the corrosion resistance of Al alloys, zirconium titanium (Zr/Ti) conversion coating is usually prepared to protect the Al substrate. Ga is the one of the main impurity elements in Al alloy, and can enhance the electrochemical activity of Al alloy in the corrosive medium, which makes it challenging to generate natural dense oxide film on the surface of Al alloys and significantly reduces the corrosion resistance of the Al alloy. During the preparation process of Zr/Ti conversion coating, Ga dissolved from the Al substrate can be enriched on the surface, which is a hidden danger to the protective performance of the Zr/Ti conversion coating. At present, there is little research on the adverse effect of Ga on the Zr/Ti conversion coating, which needs further exploration. The work aims to explore the effect of impurity Ga on the growth and protective properties of the Zr/Ti conversion coating. The evolution of local corrosion of Zi/Ti conversion coating on pure Al containing gallium in 3.5wt.% NaCl solution was characterized by scanning electrochemical microscope (SECM). The effect of impurity Ga on composition of coating was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and scanning electron microscopy (EDS). The growth of the Zr/Ti conversion coating on Pure Al was studied by open circuit potential (OCP), and the electrochemical impedance spectroscopy (EIS) and polarization curve (Tafel) were used to investigate the variation of corrosion resistance of conversion coating on pure Al with Ga content. The Zi/Ti conversion coating was mainly composed of Na3AlF6 and organic metal complexes, in addition to oxides such as TiO2, ZrO2, and Al2O3. The impurity Ga could inhibit the growth of the Zr/Ti coating, and reduce the integrity of the Zr/Ti coating. The corrosion resistance of the Zr/Ti conversion coating significantly decreased with the increase of Ga content from 0% to 0.5%, the electrochemical impedance of the Zr/Ti conversion coating decreased from 4.75×104 kΩ to 2.49×103 kΩ, the corrosion current density of coating increased from 0.45 μA to 13.4 μA, and the corrosion potential decreased from −0.485 V to −0.890 V. During the evolution of SECM micro-zone corrosion of the Zr/Ti conversion coatings, the self-healing behavior of the coatings could reduce the corrosion tendency. However, Ga enriched on the resurface could inhibit the formation of self-repairing film, leading to severe corrosion of the Al substrate. Therefore, the impurity Ga in Al can directly affect the integrity of the Zr/Ti coating, and reduce the protection of the Al substrate, leading to the occurrence of localized corrosion and dissolution of the Al substrate. |
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