Remanufacture of Zirconium-Based Conversion Coatings on the Surface of Magnesium Alloy
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JMEPEG DOI: 10.1007/s11665-017-2614-x
Remanufacture of Zirconium-Based Conversion Coatings on the Surface of Magnesium Alloy Zhe Liu, Guo Jin, Jiahui Song, Xiufang Cui, and Zhaobing Cai (Submitted October 6, 2015; in revised form March 1, 2017) Brush plating provides an effective method for creating a coating on substrates of various shapes. A corroded zirconium-based conversion coating was removed from the surface of a magnesium alloy and then replaced with new coatings prepared via brush plating. The structure and composition of the remanufactured coating were determined via x-ray photoelectron spectroscopy, x-ray diffraction, and Fourier transform infrared spectroscopy. The results revealed that the coatings consist of oxide, fluoride, and tannin-related organics. The composition of the coatings varied with the voltage. Furthermore, as revealed via potentiodynamic polarization spectroscopy, these coatings yielded a significant increase in the corrosion resistance of the magnesium alloy. The friction coefficient remained constant for almost 300s during wear resistance measurements performed under a 1-N load and dry sliding conditions, indicating that the remanufactured coatings provide effective inhibition to corrosion. Keywords
corrosion failure, remanufacture, wear resistance, zirconium-based conversion
1. Introduction Magnesium alloys exhibit poor corrosion resistance which, to date, has stymied their production and use (Ref 1-4). To extend the service life of these alloys, coatings that act as barriers to substrate corrosion must be developed. The chemical conversion treatment, which removes and replaces the native oxide with a fabricated layer, is applicable to large complex parts. Although the resulting coatings provide corrosion resistance, drawbacks, including weak long-term corrosion inhibition in an aggressive Cl-ion environment, persist. Recent health and environmental concerns have prompted extensive research on chromate-free conversion coatings (with excellent properties) as a replacement for toxic chromate-based chemical conversion coatings. In addition, the excellent corrosion resistance properties of zirconium-based conversion coatings have motivated several studies on these types of coatings (Ref 4-7). Chemical conversion coatings exhibit excellent anticorrosion performance. However, further application of these coatings has been hindered by their characteristic mud-crack structure. The origin of the net crack has been extensively considered in recent years, and the typical structure has been attributed to significant hydrogen evolution and dehydration (Ref 8, 9). The influence of hydrogen bubble evolution on the coating formation process has also been considered (Ref 10). When tiny hydrogen bubbles become adsorbed onto the Zhe Liu, Guo Jin, Jiahui Song, Xiufang Cui, and Zhaobing Cai, Institute of Surface/Interface Science and Technology, Key Laboratory of Superlight Material and Surface Technology of Ministry of Education, College of Material Science and Chemical Engineering, Harbin Engineering U
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