Corrosion of a Ni-Al Composite Coating in 2 M NaCl Solution

A Ni-Al composite was electrodeposited on a Ni substrate, and its corrosion behavior was observed in 2 M NaCl solution, compared with a pure Ni coating. The Al particles increased the porosity of the composite and encouraged charge percolation, both at the corrosion product layer-solution interface and at the substrate–solution interface, based on EIS characterization. This phenomenon greatly decreased the corrosion potential, and increased both cathodic and anodic current densities in the active region, as well as the passive current density in the passive potential range, during polarization of the composite. Although a continuous Al3+ ions supply to the passivation front was suspected, based on the longer passivation potential of the Ni-Al composite, the simultaneous consumption of the Al products by the chloride ions is the reason for serious cracking and localized collapse of the composite corrosion layer, as confirmed by SEM. This conferred lower corrosion resistance on the Ni–Al composite, compared to the pure Ni coating, in the 2 M NaCl solution.