Cupronickel or copper-nickel (CuNi) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. The copper contents typically vary from 70 to 90 percent.
Despite its high copper content, cupronickel is silver in colour. Cupronickel is highly resistant to corrosion by salt water. It is therefore used for piping, heat exchangers and condensers in seawater systems, as well as for marine hardware. It is sometimes used for the propellers, propeller shafts, and hulls of high-quality boats. Other uses include military equipment and chemical, petrochemical, and electrical industries. Aside from being very corrosion resistant to sea water, copper nickel alloys are very thermally stable.