Nickel-copper alloys have excellent saltwater corrosion and fouling resistance. For that reason, they are used extensively in the marine industry. Iron, tin, and manganese are sometimes added to further improve corrosion resistance. The copper content can be anywhere from 55 to 91.5%, with nickel being the next largest alloying element. The other alloying elements make up a small percentage of the total weight. Monel® is considered a nickel-copper alloy.