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

Abstract

A Ni–Al composite was electrodeposited on Ni substrate and its corrosion characteristic was investigated after 72 hr. immersion in 2M NaCl solution, compared with a pure Ni coating. A corrosion product layer could be formed on Ni–Al composite surface during this immersion time which, however, was characterized by high porosity and charge percolation both at the corrosion product layer–solution interface and 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 longer passivation potential of the Ni–Al composite, the chloride ions simultaneously adsorb and consume the Al2O3 leading to serious cracking and localized collapse of the corrosion product layer, as confirmed by SEM. This conferred lower corrosion resistance on the Ni–Al composite, relative to the pure Ni coating, in the 2M NaCl solution.