The role of discontinuous precipitation in the corrosion process of Cu-Ni-Si alloys: Rebar and firewall effects

It is conventionally believed that discontinuous precipitation exacerbates alloy corrosion, but its corrosion behavior remains unclear. This work investigates the influence of discontinuous precipitation on the corrosion behavior of a Cu-5.0Ni-1.2Si alloy through microstructural characterization and electrochemical testing. The results demonstrate that fibrous delta-Ni2Si discontinuous precipitation forms after 4 h of aging at 450(degrees)C, occupies approximately half of the microstructure by 8 h, and nearly fully dominates the alloy after 12 h. The corrosion resistance ranks as follows: 12 h (0.163 mm & sdot;a(-1)) > 4 h (0.169 mm & sdot;a(-1)) > 8 h (0.182 mm & sdot;a(-1)). During the initial corrosion stage, discontinuous precipitation accelerates Cu2O formation, promoting faster and thicker growth of the corrosion product film. In later stages, the larger dimensions of discontinuous precipitation enable it to act as "reinforcing bars" and "firewalls" within the film, inhibiting crack propagation and spallation, which has an unexpected contribution to the corrosion resistance of the alloy.