Shaft Nut, Navy Ship Marine Nickel Copper, cupronickel Self Locking Nut 1-1/2? Despite its high copper content, cupronickel is silver in colour. Cupronickel is highly resistant to corrosion by salt water. Cupronickel or copper?nickel (CuNi) is an alloy of copper with nickel, usually along with small quantities of other elements added for strength, such as iron and manganese. The copper content typically varies from 60 to 90 percent. (Monel is a nickel?copper alloy that contains a minimum of 52 percent nickel.)