| Microstructural development and corrosion characteristics of prior copper coated hot dip galvanized dual phase steel Harikrishna Kancharla1; Gopi Kishor Mandal2; Kallol Mondal3; Sudhanshu Shekhar Singh1; 1INDIAN INSTITUTE OF TECHNOLOGY (IIT), KANPUR, KANPUR, India; 2CSIR - NATIONAL METALLURGICAL LABORATORY, Jamshedpur, India; 3IIT KANPUR, Kanpur, India; PAPER: 201/Coatings/Regular (Oral) SCHEDULED: 16:45/Tue. 29 Nov. 2022/Andaman 2 ABSTRACT: Galvanised or Zn coated steel provides corrosion protection to underlying steel due to sacrificial effect of Zn, where Zn dissolves and Fe acts a cathodic part in the electrochemical reactions [1]. Galvanised steels are used in wide range of applications such as, constructions (rebar), beams, etc., piping industries, automobile industries, roof covers, etc. [1]. However, for many years, the galvanization of high strength steels brings a great challenge to galvanizers mainly due to selective surface oxidation of minor alloying elements (such as Si, Mn, Al etc.) present on the steel surface during annealing, which drastically reduces the wettability of liquid Zn on the steel surface [1-3]. In the present investigation, the role of copper (Cu) pre-coat has been studied for the development of good quality defect free hot dip galvanized (GI) coating on a dual phase (DP 590) steel substrate. The application of Cu pre-coating, prior to reduction annealing process, greatly influences the microstructural development of the GI coatings and corrosion behavior. The X-ray diffraction (XRD) analysis reveals the presence of hexagonal closed packed (hcp) structure in both the GI samples, with and without Cu pre-coating. Moreover, Cu pre-coated GI steel exhibits the pronounced texture coefficient (TC) of preferred high atomically dense (0002) crystal plane in comparison to without pre-coated GI steel sheet. High quality GI coating, free from any surface defects, is obtained on the Cu pre-coated steel substrate. However, coating quality is inferior on the steel substrate without Cu pre-coat due to the presence of several bare spots on the top surface of the coating. In addition, Cu pre-coated GI steel reveals the formation of a continuous iron aluminide (Fe-Al) intermetallic interfacial layer with uniform distribution of dense and equiaxed Fe-Al crystals at the interface between the substrate and the coating. It is also noted that the corrosion resistance of Cu pre-coated GI steel is superior as compared to the GI steel without pre-coat. It is concluded that the formation of a continuous compact interfacial layer along with highest atomically dense (0002) crystal plane has resulted in high quality defect free coating, facilitating to attain the lowest corrosion rate of Cu pre-coated GI steel. References: 1. S.M.A. Shibli, B.N.Meena, R. Remya, Surface & Coatings Technology 262 (2015) 210–215. 2. Huachu Liu, Fang Li, Wen Shi, Srinivasan Swaminathan, Yanlin He, Michael Rohwerder, Lin Li, Surface & Coatings Technology 206 (2012) 3428–3436. 3. Yun-IL Choi, Won-Jin Beom, Chan-Jin Park, Doojin Paik, Moon-Hi Hong, Metallurgical and Materials Transactions A, 2010, Volume 41A, 3379-3385. |
