A Study on the Corrosion Behavior of 7072/3004/7072 Clad Aluminum Alloy in Different Media
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JMEPEG https://doi.org/10.1007/s11665-020-04948-x
A Study on the Corrosion Behavior of 7072/3004/7072 Clad Aluminum Alloy in Different Media I. Tunc, B.D. Karahan, and O. Keles (Submitted January 3, 2020; in revised form June 8, 2020) Cladding is an easy and economical method to design multifunctional aluminum structures with improved corrosion resistance, mechanical strength, and physical appearance. In this study, the electrochemical properties and corrosion behavior of an aluminum-clad product made of 7072/3004/7072 aluminum alloys were investigated by Tafel extrapolation and impedance spectroscopy. 3004 aluminum sheet was used as core, and it was cladded with 7072 aluminum sheets on both sides. The long-term corrosion behavior of clad samples was examined after being immersed in tap water, rainwater, and 3.5 wt.% NaCl solution for 4 weeks. The results show that because of the potential difference between 7072 and 3004 aluminum alloys, 7072 alloy behaves more anodic and corrodes preferentially (with a slower rate) compared to 3004 aluminum alloy. Cladding 3004 with embossed 7072 alloy improves the corrosion resistance of the alloy. Moreover, the electrolyte comparison demonstrates that the carbonate-forming ions (such as Ca) in tap water and HCO32, NO32, and SO422 in rainwater decelerate the corrosion rate. Keywords
3004, 7072, cladding, corrosion behavior, impedance spectroscopy, Tafel extrapolation
1. Introduction Aluminum has become attractive for designers due to its low density and naturally formed protective oxide layer. Pure aluminum has moderate corrosion resistance and insufficient mechanical strength for structural applications. Cladding is used to achieve better mechanical strength with high corrosion resistance and minimum cost. So, a metallurgically bonded composite design is made by attaching corrosion-resistant layers to both sides of a strong core alloy. Clad combinations could be 2219/7072, 3003/7072, 3004/7072, 6061/7072, 7075/ 7008, and 7075/7072. In military applications, 2xxx series core alloys are preferred due to their high mechanical strength, while in commercial applications 3xxx series alloys are favored. In general, 7xxx series alloys are used as electro-active cladding layer (Ref 1). 3xxx series aluminum alloys can be strengthened by deformation. Manganese and magnesium additions provide good workability and medium strength, making these alloys suitable for heat exchangers, can bodies, roof applications, etc. The mechanical properties of 3xxx series alloys depend on their tempers, which can change between 50 and 98 HB (Ref 2). Up to now, two strategies have been proposed to improve the corrosion resistance of an aluminum alloy. The first is to design a new corrosion-resistant alloy. The second is to cover the surface of 3xxx aluminum with another aluminum sheet. By I. Tunc and O. Keles, Department of Metallurgical and Materials Engineering, Istanbul Technical University, 34469 MaslakIstanbul, Turkey; and B.D. Karahan, School of Engineering and Natural Sciences, Istanbul Medipol Unive
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