Copper and nickel are in their solid and liquid phase completely soluble in each other <xr id="fig:Phase diagram of copper-nickel for the range of 0 – 50 wt% nickel"/> (Fig. 5.21). Because of their very low electrical conductivity they are mainly used as resistance alloys <xr id="fig:Electrical conductivity of copper-nickel alloys as a function of nickel content"/> (Fig. 5.22). The work hardening and softening behavior of CuNi alloys and CuNi9Sn2 are shown in [[#figures6|(Figs. 43 3 – 757)]]Figs. 5.23 – 5.27. Coppernickel alloys exhibit high corrosion resistance, good weldabilty, and the suitability for cladding to other materials. Because of these and their other properties (Tables 5.15 and 5.16) they are, with and without additives of iron or manganese, widely used as good weldable backing layers on weld buttons and weld profiles (weld tapes).