<p>The Cu–15Ni–8Sn alloy is widely utilized in marine applications due to its excellent mechanical strength, thermal conductivity, and resistance to seawater and microbiologically influenced corrosion. The addition of yttrium (Y) to the Cu–15Ni–8Sn alloy has been shown to refine the grain structure and enhance mechanical properties, however, its effects on corrosion resistance remain unclear. In this study, the corrosion behavior of a Cu–15Ni–8Sn–0.2Y alloy, fabricated via powder metallurgy, was systematically investigated to assess the influence of Y on seawater corrosion resistance. Multi-scale characterization techniques, including scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and electrochemical testing, were employed. After 30&#xa0;days of immersion in seawater, the measured corrosion rates for Cu–15Ni–8Sn–0.2Y and Cu–15Ni–8Sn alloys were 0.00416 and 0.00498&#xa0;mm/year, respectively. The Cu–15Ni–8Sn–0.2Y alloy exhibited the lowest corrosion rate, indicating its superior corrosion resistance. Analysis of the corrosion products revealed the presence of metal oxides, including Cu₂O, CuO, NiO, SnO₂, and Y₂O₃. The incorporation of Y promoted the formation of Y₂O₃, which contributed to the development of a denser and more protective passivation film. This film effectively inhibited the adsorption of chloride ions (Cl⁻), thereby enhancing the overall corrosion resistance of the alloy.</p> Graphical Abstract <p></p>