Final thickness of a hard copper sheet = 1.0 mm
25% deformed
Suppose, x = 0.25
So that 0.75x = 1
x = 1/0.75 = 1.33
To decrease the hardness, we will do further normalising.
Naturally Hard Copper Alloys
Alloys such as brass (CuZn), tin bronze (CuSN) and German silver (CuNiZn), for which the required hardness is obtained from cold working, are defined as naturally hardened alloys. This group also includes silver bronze (CuAg) with 2 - 6 wt% of Ag.
Hard Copper-Zinc Alloy Test (Brass)
Copper-zinc alloys are widely used as contact carrier materials in switching materials for electrical power engineering because of their high electrical conductivity, high mechanical strength combined with good elongation compared to pure hard copper and As well as their reasonable economic costs. Particularly suitable are brass with 37 wt% Zn content. It is important to note the strong dependence of electrical conductivity and mechanical strength on the zinc material.
The main disadvantage of these alloys is with the increasing content of zinc, which is an increasing tendency towards stress crack corrosion and poor stress relaxation properties compared to other copper.
One of the special brass alloys used as contact carrier material is CuSn23Al3Co. This material exhibits significantly higher mechanical strength than standard brass alloys. Even as this material is a naturally hardening alloy, a suitable heat treatment allows its strength to be further enhanced.
Hard Copper-tin alloy (tin bronze)
Copper-tin alloys CuSn6 and CuSn8 are standard materials for electrical contact elements such as connectors, switches and tables of spring 3 because of their good elastic spring properties and formability. Table 3 and Table 4. Also these alloys such as CuSn4 and CuSn5 and multi-metal tin bronze CuSn3Zn9 have significant use - mainly in North America. The mechanical property values obtained by cold forming are superior to brass alloys. They increase considerably as Sn content increases. Work hardening and soft behavior have been shown for examples of CuSn8. The stress relaxation properties for CuSn alloys are good for up to 100 ° C, although temperatures quickly deteriorate to temperatures above 150 ° C.
Hard Copper-Nickel-Zinc Alloy (German Silver)
Despite its low electrical conductivity, good spring properties, high corrosion resistance, and good work capacity make copper-nickel-zinc alloys a frequently used spring contact carrier in switches and relays. The most commonly used materials are in the α-arrangement, which means that they are single-phase alloys. German silver has structure and strength properties compared to hard copper silver tin alloys. The work hardening and softening behavior is illustrated at the example of CuNi12Zn24.
The relaxation behavior of Cu – Ni – Zn alloys is superior for tin – cans. Additional benefits are the very good weldability, brazing properties and high corrosion resistance of these copper-nickel-zinc alloys.
Hard Copper-silver- (cadmium) alloy (silver bronze)
Other copper materials with a higher silver content (2–6 wt%) in addition to low-allowed CuAg0.1 are also used as contact carrier materials. Some of them contain 1.5 wt% Cd. But the potential increase in mechanical strength is small.
Copper-silver alloys have good spring properties and have a higher electrical conductivity Table 7 and Table 8 than other spring materials. In strongly worked conditions the mechanical strength values are similar to those of hard copper – tin alloys. Work hardening and softening behavior have been shown for the example of CuAg2. Silver bronzes are better than German silver and tin bronze for relaxation behavior.
Silver bronze are suitable for contact springs used in relays under high current loads due to their good spring properties combined with high electrical conductivity. Taking advantage of their high temperature stability they are also used as current carrying contacts in high voltage switchgear and as electrode materials for resistance welding.
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