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====<!--5.1.4.2 -->Copper-Tin Alloys (Tin Bronze)====

Because of their good elastic spring properties and formability the copper-tin alloys CuSn6 and CuSn8 are standard materials for spring contact elements in electrome-chanical components such as connectors, switches, and relays <xr id="tab:Physical Properties of Copper-Tin Alloys"/> <!--(Tab. 5.9) --> and <xr id="tab:Mechanical Properties of Copper-Tin Alloys"/><!--(Tab.5.10)-->. Besides these other alloys such as CuSn4 and CuSn5 and the multi-metal tin bronze CuSn3Zn9 have significant usage – mainly in North America.<!--Figure 5.10 --> <xr id="fig:Phase diagram of the Cu-Sn system for the range of 0 – 30 wt% Sn"/> shows the copper rich side of the phase diagram for the CuSn system. The mechanical property values achieved by cold forming are superior to these of the brass alloys <xr id="fig:Mechanical properties of tin bronze depending on the tin content (cold working 0 and 50%)"/> <!--(Fig. 5.11)-->. They increase significantly with increasing Sn content. The work hardening and softening behavior are shown for the example of CuSn8 in <xr id="fig:Strain hardening of CuSn8 by cold working"/> <!--Figures 5.12 --> and <xr id="fig:Softening of CuSn8 after 3 hrs annealing after 50% cold working"/> <!--Fig. 5.13-->. The stress relaxation properties for CuSn alloys are good for up to 100°C, deteriorate however quickly for temperatures above 150°C.

<caption>'''<!--Table 5.9: -->Physical Properties of Copper-Tin Alloys'''</caption>

<caption>'''<!--Table 5.10: -->Mechanical Properties of Copper-Tin Alloys'''</caption>

<xr id="fig:Softening of CuZn36 50"/> <!--Fig. 5.9: --> Softening of CuZn36 after 3 hrs annealing after 50% cold working)

<xr id="fig:Phase diagram of the Cu-Sn system for the range of 0 – 30 wt% Sn"/> <!--Fig. 5.10: --> Phase diagram of the Cu-Sn system for the range of 0 – 30 wt% Sn)

<xr id="fig:Mechanical properties of tin bronze depending on the tin content (cold working 0 and 50%)"/> <!--Fig. 5.11: --> Mechanical properties of tin bronze depending on the tin content (cold working 0 and 50%)

<xr id="fig:Strain hardening of CuSn8 by cold working"/> <!--Fig. 5.12: --> Strain hardening of CuSn8 by cold working

<xr id="fig:Softening of CuSn8 after 3 hrs annealing after 50% cold working"/> <!--Fig. 5.13: --> Softening of CuSn8 after 3 hrs annealing after 50% cold working