Corrosion mechanism and kinetics of Al-Zn coating deposited by arc thermal spraying process in saline solution at prolong exposure periods

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 (Zn 5 (OH) 8 Cl 2 .H 2 O) 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.

Electromagnetic Shielding Performance of Carbon Black Mixed Concrete with Zn–Al Metal Thermal Spray Coating

“…The presence of phases was determined by XRD and results are shown in Figure 4c. The XRD results show that the Zn-Al coating mainly contain Zn and Al (Figure 4c) phases which is a parent metal used for the deposition of the coating [28]. There is no other phase found rather than Zn and Al as revealed by XRD.…”

“…The arc thermal metal spraying method (ATMSM) was used to address the problem of metal plate in construction for existing shielding facilities owing to the cost effectiveness. In the arc thermal metal spraying method, a metal wire rod is coming out from the nozzle of a spray gun that blows compressed air, and is dispersed and cooled on the surface of the specimen to be coated [14,[28][29][30][31][32][33][34][35][36][37]. Subsequently, the specimen after spraying is allowed to quench, solidify, and laminate.…”

“…The SEM result of the Zn-Al coating is shown in Figure 4a. The top surface of coating exhibits splat, pores, and cracks which is an inherent property of the arc thermal spray coating process [28]. However, this coating is compact and adherent with the surface.…”

“…from the effect of EMP. Generally, the Zn-Al coating is being used for corrosion protection of smart cities infrastructure using thermal spray techniques [27,28] but we have used it to reduce the effect of EMP on construction.…”

Effect of Sodium Phosphate and Calcium Nitrate Sealing Treatment on Microstructure and Corrosion Resistance of Wire Arc Sprayed Aluminum Coatings

“…The higher coating thickness reduces the penetration of chloride ions, thus the corrosion resistance properties of the Al coating can be improved [22]. Some of the researchers have used alloying of Zn, Si, Mg, and rare earth metals with Al using thermal spray process onto the steel substrate and found that the corrosion resistance properties of the coating have increased owing to the deposition of corrosion products in the pores/defects of the coating [23][24][25][26][27][28]. There are many sealants such as organic, inorganic, polymer, ceramic, etc.…”