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. 3 – 7)]] (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 <xr id="tab:Physical Properties of Selected Copper-Nickel Alloys"/> (Tab. 5.15) and <xr id="tab:Mechanical Properties of Selected Copper-Nickel Alloys"/> (Tab. 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).