Abstract
Steel structures significantly degrades owing to corrosion especially in coastal and industrial areas where significant amounts of aggressive ions are present. Therefore, anodic metals such as Al and Zn are used to protect steel. In the present study, we provide insights for the corrosion mechanism and kinetics of Al-Zn pseudo alloy coating deposited on mild steel plate via an arc thermal spraying process in 3.5 wt.% NaCl solution in terms of its improved corrosion resistance properties at prolonged exposure durations. Electrochemical studies including open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) on the deposited coating at longer exposure durations revealed enhanced corrosion resistance properties while the morphology of corrosion products through field emission-scanning electron microscopy (FE-SEM) indicated their compactness and adherence. Furthermore, atomic force microscopy (AFM) confirmed reduced roughness when compared with that of unexposed coating. Additionally, X-ray diffraction (XRD) and Raman spectroscopy results confirmed the formation of protective, adherent, and sparingly soluble Simonkolleite (Zn5(OH)8Cl2.H2O) after 55 d of exposure in 3.5 wt.% NaCl solution. A schematic is proposed that explains the corrosion process of Al–Zn pseudo alloy coating in 3.5 wt.% NaCl solution from the deposition of coating and initiation of corrosion to longer exposure durations.
Highlights
Corrosion of steel structures in an aggressive environment is a worldwide problem and is unavoidable
The pull off experiment of coating was performed for four samples and their average value was 3.91 ± 0.09 MPa
The following conclusion are drawn from the present study: 1. The deposited as follows: Vf (Al)-Zn pseudo alloy coating through arc thermal spray process exhibited defects/cracks and inflight particles as observed by field emission-scanning electron microscopy (FE-SEM) due to the limitation of instruments used to deposit the coating
Summary
Corrosion of steel structures in an aggressive environment is a worldwide problem and is unavoidable. Li (2001) reported that the addition of Al in Zn increases the corrosion resistance properties of galvanized coating after two years of exposure in a seawater environment due to its optimum combination that is resistive to uniform www.nature.com/scientificreports/. The hot dip galvanized coating of Al-Zn system provides significant corrosion resistance, the process is neither environmental friendly nor conventional in terms of depositing the Al-Zn coating on corroded or big infrastructure on-site in addition to several negative impacts on humans[18,19,20]. The process exhibits advantage over other coating methods since it is cost effective, highly efficient, and suitable to coat engineering parts with sacrificial metals, such as Zn, Al, and their alloys, to enhance the corrosion resistance properties of steel at longer durations of exposure in aggressive environments[24,25,26]. The process exhibits a high deposition rate of the metallic coating on a substrate, and is attractive in terms of industrial applications[27]
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