An Investigation of the Corrosion Mechanisms of Cu-7Ni-3Al-1Fe-1Mn Alloy in Chloride-Containing Environment
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JMEPEG https://doi.org/10.1007/s11665-019-04021-2
An Investigation of the Corrosion Mechanisms of Cu-7Ni3Al-1Fe-1Mn Alloy in Chloride-Containing Environment Ran Yang
, Jiuba Wen, Yanjun Zhou, Kexing Song, and Yucong Zheng
(Submitted October 23, 2018; in revised form February 1, 2019) The corrosion mechanisms of Cu-7Ni-3Al-1Fe-1Mn (wt.%) alloy in a 3.5% NaCl solution are investigated through a multi-analytical approach. The formation, growth and stable corrosion stage of the stable corrosion layer are reflected by the change of electrochemical response with time. EDS and GI-XRD results show the presence of Cu2(OH)3Cl and Cu2O that are the main corrosion products, with the former predominantly present at topmost corrosion layer, and Cu2O is mainly located in the inner part, followed by aluminum oxide closer to the alloy substrate. Keywords
alloy, copper, EIS, interfaces, passive films, SEM
1. Introduction Corrosion is a naturally occurring phenomenon with detrimental impact on most industrial applications, especially marine industries (Ref 1). Copper alloys are widely used in a range of industrial applications due to their excellent heat transfer capacity and excellent resistance to marine environmental corrosion, especially in places where seawater reliability is high. Copper-nickel alloy is often preferred in marine applications including heat exchangers and condensers, such as in power generation and desalination, respectively (Ref 2-5). However, turbulent flow may lead to corrosion–erosion problems; therefore, there are also limitations on the flow velocity in copper-nickel alloy pipe to avoid erosion corrosion (Ref 6, 7). Other alloys such as copper-nickel-aluminum materials are preferred if the flow velocities are too high for copper, which are heat-treated to strengthen the metal matrix by forming precipitates in the structure (Ref 8-10). For example, Cu-7Ni3Al-1Fe-1Mn alloy has shown good mechanical properties as well as excellent corrosion resistance (Ref 11). The corrosion of Cu alloy has been extensively studied (Ref 3, 4, 12). In chloride-containing conditions, Cu undergoes a series of electrochemical reactions to form cuprous oxide and basic copper chloride as follows: Cu þ 2Cl ! CuCl 2 þe
þ 2CuCl 2 þ H2 O ! Cu2 O þ 4Cl þ 2H
ðEq 2Þ
1 Cu2 O þ O2 þ Cl þ 2H2 O ! Cu2 ðOHÞ3 Cl þ OH 2
ðEq 3Þ
It is well known that the corrosion mechanism of coppernickel-aluminum alloy is a rather complicated and gradual process. According to Chang et al., a suitable amount of aluminum can be added to the copper alloy to form a passivation layer containing Cu2O, Al2O3 and Cu2(OH)3Cl. Compared with copper metal, the passivation layer can significantly reduce chloride-induced corrosion (Ref 13, 14). However, no in-depth study has been performed to reveal the changes in the corrosion layer involving the formation and steady growth of copper-nickel-aluminum alloy in sodium chloride solution (Ref 15, 16). Thus, a study of the influence of immersion time of copper-nickel-aluminum alloy on the corrosion mechanisms is necessa
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