The weldability of copper and nickel mainly includes the following points:

(1) The atomic radius, lattice type, density and specific heat capacity of copper and nickel are close to each other. Copper and nickel can form infinite mutual solution in both solid and liquid state, and have good plasticity, which is beneficial to the welding of copper and nickel.

(2) Copper and nickel have large differences in chemical composition, thermal conductivity, linear expansion coefficient and resistivity, which brings great difficulties to welding.

(3) Because the action of copper with nickel and oxygen can form an oxide film, especially in the metal side of the copper base material is easy to form copper oxide or cuprous oxide, serious lead to welding difficult.

(4) The melting point of nickel is 378℃ higher than that of copper. When the copper melts, the nickel has not melted yet. When the nickel melts, the liquid copper overheats, resulting in the burning, evaporation and loss of the alloy elements at low melting points, resulting in the reduction of the weld mechanical properties.

(5) During welding, low-melting eutectic crystals of copper and lead, copper and bismuth, copper and cuprous oxide are easily formed on the metal side of the copper base material. The metal side of nickel base metal is easy to form the eutectic low melting point of nickel and sulfur, nickel and phosphorus, nickel and arsenic, nickel and lead. These eutectic causes cracks in the weld.

(6) When copper and nickel are welded, the solubility of oxygen and hydrogen in liquid nickel is very high, and the solubility decreases when cooling, resulting in a large amount of gas escape. In addition, the base metal is not clean, the filling material is wet, the welding zone protection is not strict and the molten pool cooling speed is fast, etc., can make the welding seam porosity.