Copper–nickel

Cupronickel (also known as copper-nickel) is an alloy of copper that contains nickel and strengthening elements, such as iron and manganese. Despite its high copper content, cupronickel is silver in colour.

Due to the specific properties of nickel and copper alloys, they are applied in various domains of industry e.g. mint industry, armaments industry, desalination industry, marine engineering, extensively used in the chemical, petrochemical and electrical industries.

Cupronickel is highly resistant to corrosion in seawater because its electrode potential is adjusted to be neutral with regard to seawater. For this reason, it is used for piping, heat exchangers and condensers in seawater systems, marine hardware, and sometimes for the propellers, crankshafts and hulls of premium tugboats, fishing boats and other working boats.

Another common use of cupronickel is in silver-coloured modern-circulated coins. A typical mix is 75% copper, 25% nickel, and a trace amount of manganese. In the past, true silver coins were debased with cupronickel.

Aside from the terms cupronickel and copper-nickel, several other terms have been used to describe the material: the tradenames Alpaka or Alpacca, Argentan Minargent, and the French term cuivre blanc ("white copper") are still registered; cupronickel is also occasionally referred to as hotel silver, plata alemana (Spanish for "German silver"), German silver, and Chinese silver.

Cupronickel alloys are used for marine applications due to their resistance to seawater corrosion, good fabricability, and their effectiveness in lowering macrofouling levels. Alloys ranging in composition from 90% Cu–10% Ni to 70% Cu–30% Ni are commonly specified in heat exchanger or condenser tubes in a wide variety of marine applications.

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