Correlation of seawater corrosion and processing of Cu-Ni alloy tubes①
(General Research Institute for Nonferrous Metals, Beijing100088, P.R.China)
Abstract: The investigations on the effect of the initial surface and microstructure on the seawater corrosion of Cu-Ni alloy tubes were carried out by processing, electrochemical methods and natural seawater exposure as well as SEM. Deformation had more impact on the final microstructure of the tubes than the annealing time did, and at the deformation of 32% and annealing temperature 550~600℃for 1h the tubes was completely recrystallized microstructure. As increasing the volume fraction of recrystallization, the homogeneity of microstructure and the corrosion resistance increased. The residual carbon film produced on the inner surface of the tubes during the processing, had higher corrosion potential than the alloy substrate and good electronic conductivity, so accelerating the dissolution of the substrate in seawater, and the non-protective and loose corrosion product film formed. Immersed in natural seawater, the tubes of incomplete recrystallization, consisting of deformed and recrystallized grains, displayed intergranular corrosion, which resulted from corrosion micro-cells built between deformed and recrystallized grains and the preferable transportation of electrons on the boundaries of both the grains. In contrast, the recrystallized alloy tubes formed the uniform and compact corrosion product film under which no corrosion was found.
Key words: Cu-Ni alloy tubes; processing; recrystallization; residual carbon film; seawater corrosion