The effects of the grain boundary precipitation on intergranular corrosion behavior were investigated by exfoliation tests and complementary techniques like scanning electron microscope (SEM), optical profilometry (OP), transmission electron microscope together with energy dispersive spectroscopy (TEM-EDS), and atomic force microscope (AFM). The results reveal the influencing mechanism of intergranular corrosion behavior from grain boundary precipitates (GBPs). The potential discrepancy between GBPs and adjacent areas induces corrosion cavity germination along the grain boundary. Furthermore, the increase of both active Mg and Zn content in GBPs improve the potential difference, which aggravates the intergranular corrosion cavity germination. However, the increment of noble Cu content in GBP is beneficial to reduce the potential difference. On the other side, the distribution of the continuous precipitates in the grain boundary region helps the initial corrosion cavities to connect, which improves the growth of intergranular corrosion cracks. Additionally, discontinuous GBPs and precipitation free zone (PFZ) hinder the spread and connection of intergranular corrosion cavities. Therefore, 7050 aluminum alloy forming different grain boundary precipitation characteristics after different aging treatments shows different resistance to intergranular corrosion: peak-aging < under-aging < over-aging.

The effects of Sn and Nb additions on the corrosion resistance of Cu-2.89Ni-0.61Si-0.14Mg alloy in 3.5 wt% NaCl solution were investigated. The results show that the additions of Sn and Nb can improve the corrosion resistance of Cu-Ni-Si-Mg alloy. The sample with 0.2 wt% Nb exhibits better corrosion resistance than the sample with 0.2 wt% Sn. Compared with the dopant-free sample, for the 0.2Sn-doped sample and 0.2Nb-doped sample, the values of corrosion current densities decrease by 7% and 21%, and the values of polarization resistances increase by 5% and 21%, respectively. The corrosion film of Cu-Ni-Si-Mg alloy is a double-layer structure. The additions of Nb and Sn are helpful to improve the density of the outer layer of corrosion film and increase the charge transfer resistance of the inner layer of corrosion film. The additions of Sn and Nb can refine and uniform the microstructure of alloy, which is helpful to the formation of a more complete corrosion layer. Cu2O and CuO are the corrosion products of alloys, and the content of Cu2O can be increased by the Sn and Nb additions.