Effect of annealing on microstructure and properties of Cu–30Ni alloy tube

The microstructure, mechanical properties and seawater corrosion resistance of annealed Cu–30Ni alloy tube were investigated using mechanical test, optical microscope, scanning electronic microscope and electrochemical measurement system, respectively. The recrystallizations gradually increased with the increase of annealing temperature and holding time. The hardness and tensile strength, which maintained invariability with annealing temperature at 680–720 °C, dramatically decreased with annealing temperature at 720–770 °C. As annealing temperature and holding time increase, corrosion potential (EC) increased while corrosion rate (iC) decreased at the beginning of seawater immersion. But after 15 days’ seawater immersion, as annealing temperature and holding time increase, EC firstly increased and then decreased, on the contrary, iC firstly decreased and then increased. The Ni-rich surface film and the Ni-rich sub-grains were responsible for the initial and extended immersion, respectively. It was found that the Cu–30Ni alloy tube annealed at 720 °C for 30 min exhibited favorable comprehensive mechanical properties and seawater corrosion resistance.