Relationship between La and Ce additions on microstructure and corrosion resistance of hot-dip galvanized steel
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ORIGINAL PAPER
Relationship between La and Ce additions on microstructure and corrosion resistance of hot‑dip galvanized steel Hong‑qiang Fan1,2 · Wen‑can Xu2 · Liang Wei2 · Zhi‑hong Zhang1 · Yu‑bao Liu1 · Qian Li2 Received: 17 August 2019 / Revised: 26 November 2019 / Accepted: 2 December 2019 / Published online: 1 September 2020 © China Iron and Steel Research Institute Group 2020
Abstract Scanning electron microscopy, X-ray diffraction, a neutral salt spray test, and electrochemical methods were applied to observe the microstructure and test the corrosion resistance of hot-dip galvanized steel before and after the addition of La and Ce. La/Ce mixture existed in the form of (La, Ce)Zn13 on the coated surface, decreased the coating thickness and accelerated the zinc dendritic growth. The corrosion current density of Zn–0.1La–0.1Ce coating was 63% less than that of pure Zn coating. This phenomenon can be explained that La/Ce mixture inhibited the transformation of Zn5(OH)8Cl2·H2O into Zn5(CO3)2(OH)6 or ZnO, reduced the time for appearance of red rust, and thus enhanced the stability of corrosion products and delayed the oxidation and corrosion processes of galvanized coating. La/Ce mixture improved the corrosion resistance compared to a single La or a single Ce addition. A competitive relationship between La and Ce was observed in the corrosion resistance improvement of hot-dip galvanized steel. Keywords Hot-dip galvanized steel · Rare earth · Coating · Corrosion resistance · Scanning vibrating electrode technique
1 Introduction The low cost, the formability, and the high strength of hotdip galvanized steel account for its wide use in automotive and construction industries and in electrical home appliances [1–5]. The protection of the galvanized coating on the steel is mainly reflected in two aspects: barrier protection and galvanic protection [1, 6–9]. However, traditional hot-dip galvanized coating faces some problems, such as poor structure uniformity, large coating thickness, and moderate corrosion resistance [10–13]. Hong-qiang Fan and Wen-can Xu have contributed equally to this work. * Qian Li [email protected] 1
State Key Laboratory of Baiyunobo Rare Earth Resource Researches and Comprehensive Utilization, Baotou Research Institute of Rare Earths, Baotou 014030, Inner Mongolia, China
State Key Laboratory of Advanced Special Steel and School of Materials Science and Engineering and Shanghai Key Laboratory of Advanced Ferrometallurgy and Materials Genome Institute, Shanghai University, Shanghai 200444, China
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The addition of rare earth (RE) elements to a zinc molten bath improved the microstructural homogeneity of a galvanized coating, decreased the coating thickness, and enhanced the appearance and corrosion resistance of hot-dip galvanized steel [14–18]. Amadeh et al. [14] pointed out that the addition of RE elements to a zinc molten bath decreased the inclusion within the coating layer. Gui and Luan [19] reported that the addition of Ce to the galvanized coating rest
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