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→5.1.4.2 Copper-Tin Alloys (Tin Bronze)
====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:tab5.9"/> (Tables Tab. 5.9 ) and <xr id="tab:tab5.10"/>(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"/> 5.13. The stress relaxation properties for CuSn alloys are good for up to 100°C, deteriorate however quickly for temperatures above 150°C.
</figure>
<figtable id="tab:tab5.9">
'''Table 5.9: Physical Properties of Copper-Tin Alloys'''
{| class="twocolortable" style="text-align: left; font-size: 12px"|-!Material<br />Designation<br />EN UNS !Composition<br />[wt%]!Density<br />[g/cm<sup>3</sup>]!colspan="2 teile" style="text-align:center"|Electrical<br />Conductivity<br />[MS/m] [% IACS] !Electrical<br />Resistivity<br />[μΩ·cm]!Thermal<br />Conductivity<br />[W/(m·K)]!Coeff. of Linear<br />Thermal<br />Expansion<br />[10<sup>-6</sup>/K]!Modulus of<br />Elasticity<br />[GPa]!Softening Temperature<br />(approx. 10% loss in<br />strength)<br />[°C]! Melting<br />Temp Range<br />[°C]|-|CuSn4<br />CW450K<br />C51100|Sn 3.5 - 4.5<br />P 0.01 - 0.4<br />Cu Rest|8.85|12.0|20|8.3|118|18.0|120|ca. 260|960 - 1060|}</figtable>
'''Table 5.10: Mechanical Properties of Copper-Tin Alloys'''
