Microstructural Evaluation of Double-Dip Galvanized Coatings on Carbon Steel
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Microstructural Evaluation of Double-Dip Galvanized Coatings on Carbon Steel Yraima Rico1 and Edwuin J. Carrasquero2 1
Universidad Nacional Experimental Politécnica "Antonio José de Sucre" UNEXPO, Vicerectorado Barquisimeto, Departamento de Ingeniería Metalúrgica. Venezuela.
2
Grupo de Investigación en Caracterización, Procesamiento y Protección de Materiales, Facultad de Ciencias de la Ingeniería, Universidad Estatal de Milagro. Ecuador.
Abstract: The objective of this research is to evaluate the microstructure of a coating layer composed of Zn / Zn-5 % Al. It was performed by the double-dip method of a steel AISI 1020. The temperature of the immersion bath was 550°C and the coatings were performed using different immersion times. Microstructural characterization was done using optical microscopy, SEM, EDX and XRD. All coatings showed three defined zones. The first zone, corresponding to the steel/coating interface, it presents typical properties of a traditional galvanization process at high temperatures. In zone II, a very heterogeneous microstructure was observed; zone III showed a Zn-Fe matrix with compounds particles of Fe2Al5Znx. The XRD characterization detected the presence of Zn and Fe2Al5Zn0,4. It was concluded than microstructural properties of the coatings were similar for the three immersion times. It is important to remark that the presence of Fe and Al throughout the coating, due to the diffusion of iron from the base metal and aluminum, presents in the second immersion bath.
Introduction: Galvanized coatings on steel are one of the most important processing techniques used to protect steel components from the environmental corrosion. From a technological point of view, the principles of galvanization have remained virtually unchanged for a long time. However, due to new applications in the automotive and construction industry, there is currently a considerable amount of research done in this field, for example, development of new types of zinc coatings, the influence of the chemical composition of the bath on microstructure and properties of galvanized coatings [1,2]. It has been shown in several investigations that Galfan® coatings (Zn-5 wt. % Al) provide better corrosion resistance compared to a conventional galvanized coating, but two basic problems have been noted in the manufacture of Galfan® coatings. The first is the non-compatibility of the Zn-5% Al alloy with the fluxing systems used in conventional industrial galvanizing processes; the second problem concerns the amount of aluminium that enters into the coating, which reduces the Al concentration in the Downloaded from https://www.cambridge.org/core. Faculty of Classics, University of Cambridge, on 04 Dec 2017 at 18:16:48, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/adv.2017.608
Galfan® bath, this brings with it the need for constant monitoring and exhaustive control of Al in the liquid bath [3]. These limitations of the manufacturing process of the coatings
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