*Article* **Corrosion Behavior of High-Strength C71500 Copper-Nickel Alloy in Simulated Seawater with High Concentration of Sulfide**

**Xin Gao 1,2,\* ,† and Ming Liu 3,\* ,†**


**Abstract:** The corrosion behavior of high-strength C71500 copper-nickel alloy in high concentrations of sulfide-polluted seawater was studied by potentiodynamic polarization measurements, electrochemical impedance spectroscopy (EIS), immersion testing, and combined with SEM, EDS, XPS, and XRD surface analysis methods. The results showed that the C71500 alloy shows activation polarization during the entire corrosion process, the corrosion rate is much higher (0.15 mm/a) at the initial stage of immersion, and the appearance of diffusion limitation by corrosion product formation was in line with the appearance of a Warburg element in the EIS fitting after 24 h of immersion. As the corrosion process progressed, the formed dark-brown corrosion product film had a certain protective effect preventing the alloy from corrosion, and the corrosion rate gradually decreased. After 168 h of immersion, the corrosion rate stabilized at about 0.09 mm/a. The alloy was uniformly corroded, and the corrosion products were mainly composed of Cu2S, CuS, Cu<sup>2</sup> (OH)3Cl, Mn2O<sup>3</sup> , Mn2O, MnS<sup>2</sup> , FeO(OH), etc. The content of Cu2S gradually increased with the extension of immersion time. The addition of S2<sup>−</sup> caused a large amount of dissolution of Fe and Ni, and prevented the simultaneous formation of a more protective Cu2O film, which promoted the corrosion process to some extent.

**Keywords:** C71500 copper-nickel alloy; sulfide; immersion test; corrosion behavior; seawater environment
