Enhancing corrosion resistance of nickel-aluminum bronze (NAB) alloys with chromium and silicon additions in marine environments

Nickel-Aluminum bronze (NAB), are widely used in marine applications. However, their performance in chloride-rich environments can be compromised by pitting corrosion. This study investigates the effects of chromium (Cr) and silicon (Si) additions on the corrosion resistance of NAB alloy in a 3.5 % NaCl solution. Electrochemical techniques were analyzed using open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, cyclic polarization, along with surface morphology analysis through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results show that the unmodified NAB alloy exhibited poor corrosion resistance, with an open circuit potential of −308.8 mV, a corrosion current density (I_corr) of 13.014μA/cm², and a 141.6 μm/year corrosion rate. Adding 0.5 % Si significantly improved the alloy performance, shifting the corrosion potential to −272.4 mV, reducing I_corr to 6.282μA/cm², and lowering the corrosion rate to 68.35 μm/year. The 0.5 % Si-modified alloy exhibited the highest charge transfer resistance (R_ct) of 1.312kΩ·cm², the lowest double-layer capacitance (C_dl) of 38.32μF/cm², and no hysteresis loop during cyclic polarization, indicating excellent resistance to pitting corrosion. SEM/EDS analysis confirmed the smooth surface features following the treatment, the presence of silicon and oxygen, indicating the formation of a Si-rich layer, likely SiO₂. The novelty of this study lies in demonstrating the superior corrosion resistance achieved with Si additions, particularly at 0.5 %, making Si-modified Cu-base alloys highly suitable for marine applications.