ASTM Copper-Nickel Alloys

The composition of ASTM Copper-Nickel alloys varies depending on their composition. In general, cu-ni alloys contain less than 50% nickel. Some alloys have higher nickel content than others, depending on the application. For example, copper-nickel wire contains only 50% nickel, and a higher percentage contains less than 30% nickel. As a result, this alloy is not recommended for arc-welding.
For marine applications, copper-nickel alloys are widely used in heat exchangers, seawater piping, and boiler feed water. They also have excellent resistance to corrosion and high flow rates. CuNi30Mn alloys contain 23% Ni and 30% Mn. CuNi44 alloy contains 44% Ni and 1% Mn, and is generally used in boat hulls. This alloy is more resistant to high temperatures and can be used in higher temperature applications.
This copper-nickel alloy is commonly called Cast 70-30, and it is a popular metal for a variety of applications. It is also the lowest-cost alloy among cast copper-nickels, but has the lowest electrical conductivity of all types of copper-nickel alloys. However, it is highly ductile, a desirable feature in a pipe or tube. Copper-Nickel Pipes and Tubes have excellent dimensional stability and are rustproof.
Cu-Ni alloys are diamagnetic and show no ferromagnetic properties, but this changes as the nickel content increases. While iron has negligible effect in a solid solution, it is precipitated and causes a macroscopic increase in ferromagnetic properties. Consequently, 20 to 25% Ni and 20% Fe Cu-Ni alloys are considered distinctly magnetic. This makes them suitable for permanent magnets.
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