Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Influence of an anodized layer on the adhesion and surface protective performance of organic coatings on AA2024 aerospace Al alloy V. Jothi a , Akeem Yusuf Adesina b , A. Madhan Kumar b, *, Nasser Al-Aqeeli c , J.S. Nirmal Ram a, ** a Center for Research and Development, PRIST University, Thanjavur, Tamil Nadu, India b Center of Research Excellence in CORROSION, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia c Department of Mechanical Engineering, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia ARTICLE INFO Keywords: Epoxy coatings Corrosion Adhesion Anodization ABSTRACT In the present work, the effect of the anodized surface on the adhesion and corrosion protection behavior of epoxy coatings was evaluated on AA2024 alloy. Surface characterization involving the use of scanning electron microscopy (SEM), optical profilometry, and X-ray diffraction (XRD) analysis was conducted to evaluate the anodized layer of Al alloy samples and how it influences the coating. The surface wettability was also assessed using water contact measurements. Electrochemical corrosion analysis of the coated samples in a 3.5% NaCl solution was performed using continuous monitoring of the open circuit potential, followed by electrochemical impedance spectroscopy tests for up to 30 days. Scratch resistance analysis was performed to quantitatively appraise the adhesion strength of the epoxy coatings on the anodized AA2024 samples. The scratch resistance analysis results indicated the adhesion strength was improved when the AA2024 samples underwent anodization treatment. It was concluded that the anodized layer improves the adhesion between the organic coatings and base substrate, which consequently enhanced the surface protection performance against corrosion in 3.5% NaCl solution. 1. Introduction Aluminum (Al) and its alloys are extensively employed in many fields due to their salient features, such as low density, high strength, and high conductivity, with reasonable corrosion resistance. Due to its low weight to strength ratio, Al alloys, including AA2024, AA6060, AA8090, AA7050, and AA7022, have been extensively employed in automobiles and aeronautical and space industries. The AA2024-T3 alloy has been widely employed in the aeronautical industry to man- ufacture different structural components owing to its low cost, ready availability and good mechanical properties and corrosion resistance [1,2]. Though it has numerous merits, it can undergo corrosion that may lead to damage of the structural integrity when used in aggressive environments. To overcome this shortcoming, several surface treat- ments and coating strategies, including chemical oxidation, anodic oxidation, and sol-gel and organic coatings, have been employed to enrich the overall performance of practiced alloys [3,4]. Among the available strategies, the protection of aerospace Al alloys using organic coatings has been recognized as an economically viable and suitable method over the last few decades [5,6]. Epoxy coatings are well-known protective coatings because they are quick drying, tough and easy to apply to metallic materials. An epoxy coating acts as a primer to prevent corrosion and ensure the adhesion of the topcoat on aerospace and military components. Although epoxy primers have been utilized for many years, adhesion to metallic mate- rials is being improved to extend the life span of epoxy coatings. Adhesion strength is strongly affected by chemical interactions between the coating and substrate and can be improved by adopting suitable surface pretreatments. Researchers have dedicated their valuable time to predicting the precise relationship between the pretreated surface of metallic structures and organic coatings in terms of surface features, such as hydrophobicity, surface free energy, and adhesive forces, to ensure protection against corrosion and fouling [7,8]. Surface pretreatments play a significant role in enhancing the ad- hesion between epoxy coatings and base substrates. Among the avail- able surface treatments for Al alloys, the anodization technique is a simple method that is commercially practiced on a large scale in the Al industry [9–11]. In general, Al alloy is immersed in an appropriate https://doi.org/10.1016/j.porgcoat.2019.105396 Received 20 March 2019; Received in revised form 9 October 2019; Accepted 13 October 2019 ⁎ Corresponding authors at: Center of Research Excellence in CORROSION, Research Institute, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia. ⁎⁎ Corresponding authors at: Center for Research and Development, PRIST University, Thanjavur, Tamil Nadu, India. E-mail addresses: madhankumar@kfupm.edu.sa (A.M. Kumar), nirmal.nram80@gmail.com (J.S.N. Ram). Progress in Organic Coatings xxx (xxxx) xxxx 0300-9440/ © 2019 Elsevier B.V. All rights reserved. Please cite this article as: V. Jothi, et al., Progress in Organic Coatings, https://doi.org/10.1016/j.porgcoat.2019.105396