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Alloys like brasses (CuZn), tin bronzes (CuSN), and German silver (CuNiZn), for which the required hardness is achieved by cold working are defined as naturally hard alloys. Included in this group are also the silver bronzes (CuAg) with 2 – 6 wt% of Ag.
====<!--5.1.4.1-->Copper-Zinc Alloys Test (Brasses)====
Copper-zinc alloys are widely used as contact carrier materials in switching devices for electrical power engineering because of their high electrical conductivity, the higher mechanical strength combined with good formability compared to pure copper <xr id="tab:Physical_Properties_of_ Selected_Copper_Zinc_Alloys"/><!--(Tab. 5.7)--> and <xr id="tab:Mechanical_Properties_of_Selected_Copper_Zinc_Alloys"/><!--(Tab. 5.8)-->, and at the same time their reasonable economic costs. Especially suitable are the brasses with up to 37 wt% Zn content which are according to the phase diagram all made up from the α -phase of the CuZn system <xr id="fig:Phase_diagram_of_copper_zinc_for_the_range_of_0_60_wt_zinc"/><!--(Fig. 5.5)-->. It is important to note the strong dependence of the electrical conductivity and mechanical strength on the zinc content <xr id="fig:Mechanical_properties_of_brass_ depending_on_the_copper_content_after_cold_working_of_0_and_50"/><!--(Fig. 5.6)-->.
<div class="clear"></div>
====<!--5.1.4.4 -->Copper-Silver-(Cadmium) Alloys (Silver Bronze)====
Besides the low-allowed CuAg0.1 other copper materials with higher silver contents (2-6 wt%) are also used as contacts carrier materials. Some of them contain additionally 1.5 wt% Cd. The phase diagram <xr id="fig:Phase diagram of copper-silver for the range of 0 – 40 wt% silver"/> <!--(Fig. 5.17) --> shows that in principle the CuAg alloys can be precipitation hardened, but the possible increase in mechanical strength is rather small.
Copper-silver alloys have good spring properties and compared to other spring materials have a high electrical conductivity <xr id="tab:tab5.13"/> <!--(Tab. 5.13) --> and <xr id="tab:tab5.14"/> <!--(Tab. 5.14)-->. The mechanical strength values in the strongly worked condition are comparable to those of the copper-tin alloys. Work hardening and softening behavior are shown for the example of CuAg2 [[#figures5|(Figs. 13 – 15)]]<!--(Figs. 5.18 – 5.20)-->. For the relaxation behavior the silver bronzes are superior to German silver and tin bronze.
Because of their good spring properties combined with high electrical conductivity silver bronzes are suitable for the use contact springs in relays
<figtable id="tab:tab5.13">
<caption>'''<!--Table 5.13: -->Physical Properties of Selected Copper-Silver-(Cadmium) Alloys'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<figtable id="tab:tab5.14">
<caption>'''<!--Table 5.14: -->Mechanical Properties of Selected Copper-Silver-(Cadmium) Alloys'''</caption>
{| class="twocolortable" style="text-align: left; font-size: 12px"
<div id="figures5">
<xr id="fig:Phase diagram of copper-silver for the range of 0 – 40 wt% silver"/> <!--Fig. 5.17: --> Phase diagram of copper-silver for the range of 0 – 40 wt% silver
<xr id="fig:Strain hardening of CuAg2 by cold working"/> <!--Fig. 5.18: --> Strain hardening of CuAg2 by cold working
<xr id="fig:Softening of CuAg2 after 1 hr annealing after 40% cold working"/> <!--Fig. 5.19: --> Softening of CuAg2 after 1 hr annealing after 40% cold working
<xr id="fig:Softening of CuAg2 after 1 hr annealing after 80% cold working"/> <!--Fig. 5.20: --> Softening of CuAg2 after 1 hr annealing after 80% cold working
</div>
==References==
[[Contact Carrier Materials#References|References]]
[[de:Naturharte_Kupfer-Legierungen]]
