Copper and nickel are in their solid and liquid phase completely soluble in each other ''(Fig. 5.21)''. Because of their very low electrical conductivity they are mainly used as resistance alloys ''(Fig. 5.22)''. The work hardening and softening behavior of CuNi alloys and CuNi9Sn2 are shown in 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). =====5.1.5.2 Copper-Nickel-Tin Alloys===== Copper-Nickel- multi component alloys with 9 wt% Ni and 2 wt% Sn are used mainly as connector materials because of their suitable mechanical properties, their excellent relaxation behavior, and their high corrosion resistance. Other advantages include their high temperature stability and the good solderability even after longer storage. They are also used as base materials for clad profiles and tapes. Fig. 5.21: Phase diagram of copper-nickelfor the range of 0 – 50 wt% nickel Fig. 5.22: Electrical conductivityof copper-nickel alloys as a functionof nickel content Table 5.15: Physical Properties of Selected Copper-Nickel Alloys (2 Teile!) Table 5.16: Mechanical Properties of Selected Copper-Nickel Alloys (2 Teile!) Fig. 5.23:Strain hardeningof copper-nickel alloysas a function of nickel content Fig. 5.24:Strain hardeningof CuNi25 by cold working Fig. 5.25:Softening of CuNi25 after 1 hrannealing after 50% cold working Fig. 5.26:Strain hardeningof CuNi9Sn2by cold working(Wieland) Fig. 5.27:Softening of CuNi9Sn2after 1 hr annealing after 60%cold working (Wieland)