Changes

Besides the naturally hard copper materials , precipitation hardening copper alloys play also an important role as carrier materials for electrical contacts. By means of a suitable heat treatment , finely dispersed precipitations of a second phase can be achieved which increase , that increases the mechanical strength of these copper alloys significantly.

The cause for precipitation hardening of CuBe materials , is the rapidly diminishing solubility of beryllium in copper as temperature decreasedecreases. As thephase diagram for CuBe shows, 2.4 wt% of Be are soluble in Cu at 780°C (<xr id="fig:Phase_diagram_of_copperberyllium_with_temperature_ranges_for_brazing_and_annealing_treatments"/><!--(Fig. 5.28)-->). In this temperature range , annealed CuBe alloys are homogeneous(solution annealing). The homogeneous state can be frozen through rapid cooling to room temperature (quenching). Through a subsequent annealing at 325°C , the desired precipitation hardening is achieved , which results in a significant increase in mechanical strength and electrical conductivity of CuBe (<xr id="tab:Physical_Properties_of_Selected_Copper_Beryllium_Alloys"/><!--(Tab. 5.17)-->). The final strength and hardness values depend on the annealing temperature and time , as well as on the initial degree of cold working (<xr id="tab:Mechanical Properties of Selected Copper-Beryllium Alloys"/><!--(Table 5.18)--> and [[#figures7|<xr id="fig:Precipitation_hardening_of_CuBe2_at_325°C_after_different_cold_working"/>, <xr id="fig:Precipitation_hardening_of_CuBe2_(Figs. 43 – 75soft)]]_at_325°C"/>, <!--xr id="fig:Precipitation_hardening_of_CuBe2_(Figs. 5.29 - 5.31half hard)--_at_different_annealing_temperatures"/>).

As precipitation hardening alloys CuBe materials, mainly CuBe2 and CuBe1.7 have gained broad usage as current carrying contact springs because of their outstanding mechanical properties. Besides these , CuCo2Be and CuNi2Be, which have medium mechanical strength and a relatively high electricalconductivity, are also used as contact carrier materials. After stamping and forming into desired contact configurations , these CuBe materials are then precipitation hardened. CuBe alloys are available as semi-finished materials in a variety of cold work conditions. They can also be supplied and used in the already precipitation hardened condition , without significant strength losses. In this case , the hardening was already performed at the alloy producer.

Since Beryllium is rated as a carcinogen by the European regulation EU-67/548, it has been tried to reach the application properties of the well established CuBe1.7 and CuBe2 alloys with a lower Be content. The development Development efforts for alternate alternative precipitation hardening materials without toxic and declaration requiring additive materials, for example CuNiCoSideclarable additives are underway, are aimed at the replacement of CuBee. <div id="figures7"> <xr id="fig:Phase_diagram_of_copperberyllium_with_temperature_ranges_for_brazing_and_annealing_treatments"/><!--Figg. 5.28:--> Phase diagram of copper- beryllium with temperature ranges CuNiCoSi as a substitute for brazing and annealing treatments <xr id="fig:Precipitation_hardening_of_CuBe2_at_325°C_after_different_cold_working"/><!--FigCuBe. 5.29:--> Precipitation hardening of CuBe2 at 325°C after different cold working <xr id="fig:Precipitation_hardening_of_CuBe2_(soft)_at_325°C"/><!--Fig. 5.30:--> Precipitation hardening of CuBe2 (soft) at 325°C <xr id="fig:Precipitation_hardening_of_CuBe2_(half hard)_at_different_annealing_temperatures"/><!--Fig. 5.31:--> Precipitation hardening of CuBe2 (half hard) at different annealing temperatures</div>

|8 - 9[[#text-reference1|^a]]<br />12 - 13[[#text-reference2|^b]]<br />11[[#text-reference3|^c]]

|11 - 12.5[[#text-reference1|^a]]<br />7.7 - 8.3[[#text-reference2|^b<br />]]9.1[[#text-reference3|^c]]

|125[[#text-reference1|^a]]<br />135[[#text-reference2|^b]]

|8 - 9[[#text-reference1|^a]]<br />12 - 13[[#text-reference2|^b]]<br />11[[#text-reference3|^c]]

|11 - 12.5[[#text-reference1|^a]]<br />7.7 - 8.3[[#text-reference2|^b]]<br />9.1[[#text-reference3|^c]]

|125[[#text-reference1|^a]]<br />135[[#text-reference2|^b]]

|11 - 14[[#text-reference1|^a]]<br />25 - 27[[#text-reference2|^b]]<br />27 - 34[[#text-reference3|^c]]

|7.1 - 9.1[[#text-reference1|^a]]<br />3.7 - 4.0[[#text-reference2|^b]]<br />2.9[[#text-reference3|^c]]

|131[[#text-reference1|^a]]<br />138[[#text-reference2|^b]]

|11 - 14[[#text-reference1|^a]]<br />25 - 27[[#text-reference2|^b]]<br />27 - 34[[#text-reference3|^c]]

|7.1 - 9.1[[#text-reference1|^a]]<br />3.7 - 4.0[[#text-reference2|^b]]<br />2.9[[#text-reference3|^c]]

|131[[#text-reference1|^a]]<br />138[[#text-reference2|^b]]

 ^asolution annealed, and cold rolled<br /> ^bsolution annealed, cold rolled, and precipitation hardened<br /> ^csolution annealed, cold rolled, and precipitation hardened at mill (mill hardened) 

!Bend Radius[[#text-reference4|¹⁾]]<br />perpendicular to<br />rolling direction!Bend Radius[[#text-reference4|¹⁾]]<br />parallel to<br />rolling direction

|R 390[[#text-reference5|^a]]<br />R 680[[#text-reference5|^a]]<br />R 1030[[#text-reference6|^b]]<br />R 1240[[#text-reference6|^b]]<br />R 680[[#text-reference7|^c]]<br />R 1100[[#text-reference7|^c]]

|R 410[[#text-reference5|^a]]<br />R 690[[#text-reference5|^a]]<br />R 1140[[#text-reference6|^b]]<br />R 1310[[#text-reference6|^b]]<br />R 690[[#text-reference7|^c]]<br />R 1200[[#text-reference7|^c]]

|R 250[[#text-reference5|^a]]<br />R 550[[#text-reference5|^a]]<br />R 650[[#text-reference6|^b]]<br />R 850[[#text-reference6|^b]]<br />R 520[[#text-reference7|^c]]

</figtablediv id="text-reference4"><supsub>1)</supsub> t: Strip thickness max. 0.5 mm<br /div><supdiv id="text-reference5"><sub>a</supsub>solution annealed, and cold rolled<br /div> <supdiv id="text-reference6"><sub>b</supsub>solution annealed, cold rolled, and precipitation hardened<br /div> <supdiv id="text-reference7"><sub>c</supsub>solution annealed, cold rolled, and precipitation hardened at mill (mill hardened)</div></figtable> <br/><br/>

As the phase diagram shows, copper-chromium has a similar hardening profile compared to CuBe (<xr id="fig:Copper corner of the copper-chromium phase diagram for up to 0.8 wt% chromium"/><!--(Fig. 5.32)-->). In the hardened stage CuCr has limitations to work hardening. Compared to copper it has a better temperature stability with good electrical conductivity. Hardness and electrical conductivity as a function of cold working and precipitation hardening conditions are illustrated in [[#figures8|(Figs. 6 – 9)]]<!--Figs. 5.33-5.35-->, and <xr id="tab:Physical Properties of Other Precipitation Hardening Copper Alloys"/><!--(Tables 5.19)--> and <xr id="tab:Mechanical Properties of Other Precipitation Hardening Copper Alloys"/><!--(Tab. 5.20)-->). Copper-chromium materials are especially suitable for use as electrodes for resistance welding. During brazing the loss in hardness is limited if low melting brazing alloys and reasonably short heating times are used. <div id="figures5"> <xr id="fig:Copper corner of the copper-chromium phase diagram for up to 0.8 wt% chromium"/><!--Fig. 5.32:--> Copper corner of the copper-chromium phase diagram for up to 0.8 wt% chromium <xr id="fig:Softening of precipitation hardened and subsequently cold worked CuCr1"/><!--Fig. 5.33:--> Softening of precipitation-hardened and subsequently cold worked CuCr1 after 4hrs annealing <xr id="fig:Electrical conductivity of precipitation hardened CuCr 0.6"/><!--Fig. 5.34 a:--> Electrical conductivity of precipitation hardened CuCr 0.6 as a function of annealing conditions <xr id="fig:Hardness of precipitation hardened CuCr 0.6"/><!--Fig. 5.34 b:--> Hardness of precipitation hardened CuCr 0.6 as a function of annealing conditions

<xr id="fig:Electrical conductivity and hardness of precipitation hardened CuCr 0.6"/><!Copper--Figchromium materials are especially suitable for use as electrodes for resistance welding. 5.35:--> Electrical conductivity During brazing the loss in hardness is limited, if low melting brazing alloys and hardness of precipitation hardened CuCr 0reasonably short heating times are used.6 after cold working</div>

|26[[#text-reference8|^a]]<br />48[[#text-reference9|^b]]|45[[#text-reference8|^a]]<br />83[[#text-reference9|^b]]|3.8[[#text-reference8|^a]]<br />2.1[[#text-reference9|^b]]|170[[#text-reference8|^a]]<br />315[[#text-reference9|^b]]

|35[[#text-reference8|^a]]<br />52[[#text-reference9|^b]]|60[[#text-reference8|^a]]<br />90[[#text-reference9|^b]]|2.9[[#text-reference8|^a]]<br />1.9[[#text-reference9|^b]]|340[[#text-reference8|^a]]

|20[[#text-reference8|^a]]<br />43[[#text-reference9|^b]]|34[[#text-reference8|^a]]<br />74[[#text-reference9|^b]]|5.0[[#text-reference8|^a]]<br />2.3[[#text-reference9|^b]]|170[[#text-reference8|^a]]<br />310 - 330[[#text-reference9|^b]]

|110[[#text-reference8|^a]]<br />130[[#text-reference9|^b]]

 ^asolution annealed, and cold rolled<br /> ^bsolution annealed, cold rolled, and precipitation hardened<br />  

The solubility of Zirconium in copper is 0.15 wt% Zr at the eutectic temperature of 980°C (<xr id="fig:Copper corner of the copper zirconium for up to 0.5-wt zirconium"/><!--(Fig. 5.36)-->). Copper-zirconium materials have a similar properties spectrum , compared to the one for copper-chromium materials. At room temperature the mechanical properties of copper-zirconium are less suitable than those of copper chromium, its temperature stability is however at least the same.

The earlier used CuCr and CuZr materials have been partially replaced over the years , by the capitation hardening three materials alloy CuCr1Zr. This material exhibits high mechanical strength at elevated temperatures and good oxidation resistance as well as high softening temperatures. In its hardened condition CuCr1Zr has also a high electrical conductivity (<xr id="fig:Softening of CuCr1Zr after 1hr annealing"/><!--(Bild 5.37)-->). Their usage extends from mechanically and thermally highly stressed parts , such as contact tulips in high voltage switchgear to or electrodes for resistance welding. <xr id="fig:Copper corner of the copper zirconium for up to 0.5-wt zirconium"/><!--Fig. 5.36:--> Copper corner of the copper- zirconium for up to 0.5 wt% zirconium <xr id="fig:Softening of CuCr1Zr after 1hr annealing"/><!--Fig. 5.37:--> Softening of CuCr1Zr after 1 hr annealing and after 90% cold working

[[File:Copper corner of the copper zirconium for up to 0.5-wt zirconium.jpg|right|thumb|Figure 10: Copper corner of the copper- zirconium for up to 0.5 wt% zirconium]]

[[File:Softening of CuCr1Zr after 1hr annealing.jpg|right|thumb|Figure 11: Softening of CuCr1Zr after 1 hr annealing and after 90% cold working]]