There are two commercially important groups of copper-nickel alloys in the 90/10 and 70/30 ranges both having exceptional corrosion resistance in sea water. With either, 1 or 2% each of iron and manganese is added for a further improvement in corrosion resistance. In this form they are particularly useful for sea water condenser systems and for cladding off-shore structures. A further group of alloys in commercial use is based on Cu-3% Ni. These alloys are used for electrical connectors and springs.
The Cu: Ni alloys are an example of complete miscibility in the solid and liquid states. All the alloys have identical single-phase structures. In the cast condition the wide freezing range gives rise to heavily cored dendrites and as the two elements inter-diffuse slowly, segregation usually persists.