Naturally Hard Copper Alloys

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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.

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 Table 1 and Table 2, 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 Figure 1. It is important to note the strong dependence of the electrical conductivity and mechanical strength on the zinc content Figure 2.

Table 1: Physical Properties of Selected Copper-Zinc Alloys
Material/
Designation
EN UNS
Composition
[wt%]
Density
[g/cm3]
Electrical
Conductivity
Electrical
Resistivity
[μΩ·cm]
Thermal
Conductivity
[W/(m·K)]
Coeff. of Linear
Thermal
Expansion
[10-6/K]
Modulus of
Elasticity
[GPa]
Softening Temperature
(approx. 10% loss in
strength)
[°C]
Melting
Temp Range
[°C]
[MS/m] [% IACS]
CuZn5
CW500L
C21000
Cu 94 - 96
Zn Rest
8.87 33 57 3.8 243 18.0 127 1055 - 1065
CuZn10
CW501L
C22000
Cu 89 - 91
Zn Rest
8.79 25 43 4.0 184 18.2 125 1030 - 1045
CuZn15
CW502L
C23000
Cu 84 - 86
Zn Rest
8.75 21 36 4.8 159 18.5 122 ca. 250 1005 - 1025
CuZn20
CW503L
C24000
Cu 79 - 81
Zn Rest
8.67 19 33 5.3 142 18.8 120 ca. 240 980 - 1000
CuZn30
CW505L
C26000
Cu 69 - 71
Zn Rest
8.53 16 28 6.3 124 19.8 114 ca. 230 910 - 940
CuZn37
CW508L
C27200
Cu 62 - 64
Zn Rest
8.45 15.5 27 6.5 121 20.2 110 ca. 220 900 - 920
CuZn23Al3Co
CW703R
C68800
Cu 73.5
Al 3.4
Co 0.4
Zn Rest
8.23 9.8 17 10.2 78 18.2 116 ca. 280 950 - 1000


Table 2: Mechanical Properties of Selected Copper-Zinc Alloys
Material Hardness
Condition
Tensile Strength Rm
[MPa]
0,2% YieldStrength
Rp02
[MPa]
Elongation
A50
[%]
Vickers
Hardness
HV
Bend Radius1)
perpendicular to
rolling direction
Bend Radius1)
parallel to
rolling direction
Spring Bending
Limit σFB
[MPa]
Spring Fatigue
Limit σBW
[MPa]
CuZn5 R 230
R 270
R 340
230 - 280
270 -350
340 - 440
≤ 130
≥ 200
≥ 280
36
12
4
45 - 90
70 - 120
110 - 160
0 x t
0 x t
0 x t
0 x t
250 130
CuZn10 R 240
R 280
R 350
240 - 290
280 - 360
350 - 450
≤ 140
≥ 200
≥ 290
36
13
4
50 - 100
80 - 130
110 - 160
0 x t
0 x t
0 x t
0 x t
260 140
CuZn15 R 300
R 350
R 410
R 480
R 550
300 - 370
350 - 420
410 - 490
480 - 560
≥ 550
≤ 150
≥ 270
≥ 360
≥ 420
≥ 480
16
8
3
1
85 - 120
100 - 150
125 - 155
150 - 180
≥ 170
0 x t
0 x t
0 x t
1 x t
0 x t
0 x t
1 x t
3 x t
300 160
CuZn20 R 270
R 320
R 400
R 480
270 - 320
320 - 400
400 - 480
480 - 570
≤ 150
≥ 200
≥ 320
≥ 440
38
20
5
3
55 - 105
95 - 155
120 - 180
≥ 150
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
320 180
CuZn30 R 270
R 350
R 410
R 480
270 - 350
350 - 430
410 - 490
480 - 580
≤ 160
≥ 200
≥ 430
≥ 430
40
21
9
4
95 - 125
120 - 155
150 - 180
170 - 200
0 x t
0 x t
0 x t
1 x t
0 x t
1 x t
2 x t
3 x t
330 180
CuZn37 R 300
R 350
R 410
R 480
R 550
300 - 370
350 - 440
410 - 490
480 - 560
550 - 640
≤ 180
≥ 200
≥ 260
≥ 430
≥ 500
38
19
8
3
55 - 105
95 - 155
120 - 190
≥ 150
≥ 170
0 x t
0 x t
0 x t
0.5 x t
1 x t
0 x t
0 x t
0 x t
1 x t
3 x t
350 190
CuZn23Al3Co R 660
R 740
R 820
660 - 750
740 - 830
≥ 820
≥ 580
≥ 660
≥ 780
10
3
2
190 - 220
210 - 240
≥ 235
0 x t
1 x t
0 x t
2 x t
≥ 400 230

1) t: Strip thickness max. 0.5 mm

The main disadvantages of these alloys are with increasing zinc content the also increasing tendency towards tension crack corrosion and the poorer stress relaxation properties compared to other copper alloys.

One of the special brass alloys used as a contact carrier material is CuSn23Al3Co. This material exhibits significantly higher mechanical strength than the standard brass alloys. Even so this material is a naturally hardening alloy, a suitable heat treatment allows to further increase its strength.

Figure 1 Strain hardening of Ag 99.95 by cold working

Figure 2 Mechanical properties of brass depending on the copper content (after cold working of 0 and 50%)

Figure 3 Strain hardening of CuZn36 by cold forming

Figure 4 Softening of CuZn36 after 3 hrs annealing after 25% cold working

Figure 1: Phase diagram of copper-zinc for the range of 0-60 wt% zinc
Figure 2: Mechanical properties of brass depending on the copper content (after cold working of 0 and 50%)
Figure 3: Strain hardening of CuZn36 by cold forming
Figure 4: Softening of CuZn36 after 3 hrs annealing after 25% cold working

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 Table 3 and Table 4. Besides these other alloys such as CuSn4 and CuSn5 and the multi-metal tin bronze CuSn3Zn9 have significant usage – mainly in North America. Figure 6 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 Figure 7. They increase significantly with increasing Sn content. The work hardening and softening behavior are shown for the example of CuSn8 in Figure 8 and Figure 9. The stress relaxation properties for CuSn alloys are good for up to 100°C, deteriorate however quickly for temperatures above 150°C.


Table 3: Physical Properties of Copper-Tin Alloys
Material
Designation
EN UNS
Composition
[wt%]
Density
[g/cm3]
Electrical
Conductivity
Electrical
Resistivity
[μΩ·cm]
Thermal
Conductivity
[W/(m·K)]
Coeff. of Linear
Thermal
Expansion
[10-6/K]
Modulus of
Elasticity
[GPa]
Softening Temperature
(approx. 10% loss in
strength)
[°C]
Melting
Temp Range
[°C]
[MS/m] [% IACS]
CuSn4
CW450K
C51100
Sn 3.5 - 4.5
P 0.01 - 0.4
Cu Rest
8.85 12.0 20 8.3 118 18.0 120 ca. 260 960 - 1060
CuSn5
CW451K
C51000
Sn 4.5 - 5.5
P 0.01 - 0.4
Cu Rest
8.85 10.0 17 10.0 96 18.0 120 ca. 260 940 - 1050
CuSn6
CW452K
C51900
Sn 5.5 - 7.0
P 0.01 - 0.4
Cu Rest
8.80 9.0 15 11.1 75 18.5 118 ca. 280 910 - 1040
CuSn8
CW453K
C52100
Sn 7.5 - 8.5
P 0.01 - 0.4
Cu Rest
8.80 7.5 13 13.3 67 18.5 115 ca. 320 875 - 1025
CuSn3Zn9
CW454K
C42500
Zn 7.5 - 10
Sn 1.5 - 3.5
P 0.2
Ni 0.2
Cu Rest
8.75 12 28 6.2 120 18.4 126 ca. 250 900 - 1015


Table 4: Mechanical Properties of Copper-Tin Alloys
Material Hardness
Condition
Tensile Strength Rm
[MPa]
0,2% Yield Strength
Rp02
[MPa]
Elongation
A50
[%]
Vickers
Hardness
HV
Bend Radius1)
perpendicular to
rolling direction
Bend Radius1)
parallel to
rolling direction
Spring Bending
Limit σFB
[MPa]
Spring Fatigue
Limit σBW
[MPa]
CuSn4 R 290
R 390
R 480
R 540
R 610
290 - 390
390 - 490
480 - 570
540 - 630
≥ 610
≤ 190
≥ 210
≥ 420
≥ 490
≥ 540
40
13
5
4
2
70 - 100
115 - 155
150 - 180
170 - 200
≥ 190
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
1 x t
420 200
CuSn5 R 310
R 400
R 490
R 550
R 630
R 690
310 - 390
400 - 500
490 - 580
550 - 640
630 - 720
≥ 690
≤ 250
≥ 240
≥ 430
≥ 510
≥ 600
≥ 670
45
17
10
6
3
75 - 105
120 - 160
160 - 190
180 - 210
200 - 230
≥ 220
0 x t
0 x t
0 x t
0 x t
1 x t
0 x t
0 x t
0 x t
1 x t
2 x t
460 220
CuSn6 R 350
R 420
R 500
R 560
R 640
R 720
350 - 420
420 - 520
500 - 590
560 - 650
640 - 730
≥ 720
≤ 300
≥ 260
≥ 450
≥ 500
≥ 600
≥ 690
45
20
10
7
4
80 - 110
125 - 165
160 - 190
180 - 210
200 - 230
≥ 220
0 x t
0 x t
0 x t
0 x t
1 x t
0 x t
0 x t
0 x t
1 x t
2 x t
480 230
CuSn8 R 370
R 450
R 540
R 600
R 660
R 740
370 - 450
450 - 550
540 - 630
600 - 690
660 - 750
≥ 740
≤ 300
≥ 280
≥ 460
≥ 530
≥ 620
≥ 700
50
23
15
7
4
90 - 120
135 - 175
170 - 200
190 - 220
210 - 240
≥ 230
0 x t
0 x t
0 x t
1 x t
2 x t
0 x t
0 x t
0 x t
1 x t
2 x t
520 240
CuSn3Zn9 R 320
R 380
R 430
R 510
R 580
R 660
320 - 380
380 - 430
430 - 520
510 - 600
580 - 690
≥ 660
≤ 230
≥ 200
≥ 330
≥ 430
≥ 520
≥ 610
25
18
6
3
4
80 - 110
110 - 140
140 - 170
160 - 190
180 - 210
≥ 200
0 x t
0 x t
0 x t
0 x t
1 x t
0 x t
0 x t
0 x t
1 x t
2 x t
500 210

1) t: Strip thickness max. 0.5 mm

Figure 5 Softening of CuZn36 after 3 hrs annealing after 50% cold working)

Figure 6 Phase diagram of the Cu-Sn system for the range of 0 – 30 wt% Sn)

Figure 7 Mechanical properties of tin bronze depending on the tin content (cold working 0 and 50%)

Figure 8 Strain hardening of CuSn8 by cold working

Figure 9 Softening of CuSn8 after 3 hrs annealing after 50% cold working

Figure 5: Softening of CuZn36 after 3 hrs annealing after 50% cold working
Figure 6: Phase diagram of the Cu-Sn system for the range of 0 – 30 wt% Sn
Figure 7: Mechanical properties of tin bronze depending on the tin content (cold working 0 and 50%)
Figure 8: Strain hardening of CuSn8 by cold working
Figure 9: Softening of CuSn8 after 3 hrs annealing after 50% cold working

Copper-Nickel-Zinc Alloys (German Silver)

Despite its lower electrical conductivity, the good spring properties, high corrosion resistance, and the good workability make copper-nickel-zinc alloys a frequently used spring contact carrier in switches and relays. As illustrated in the phase diagram the most commonly used materials are in the α -range which means that they are single-phase alloys Figure 10. The formability and strength properties of german silver are comparable to those of the copper-tin alloys. The work hardening and softening behavior is illustrated on the example of CuNi12Zn24 in Figure 11 and Figure 12.

The relaxation behavior of Cu-Ni-Zn alloys is superior to the one for the tin bronzes. Additional advantages are the very good weldability, brazing properties, and the high corrosion resistance of these copper-nickel-zinc alloys.


Table 5: Physical Properties of Copper-Nickel-Zinc Alloys
Material
Designation
EN UNS
Composition
[wt%]
Density
[g/cm3]
Electrical
Conductivity
Electrical
Resistivity
[μΩ·cm]
Thermal
Conductivity
[W/(m·K)]
Coeff. of Linear
Thermal
Expansion
[10-6/K]
Modulus of
Elasticity
[GPa]
Softening Temperature
(approx. 10% loss in
strength)
[°C]
Melting
Temp Range
[°C]
[MS/m] [% IACS]
CuNi12Zn24
CW403J
C75700
Cu 63- 66
Ni 11 - 13
Mn 0.5
Fe 0.3
Zn Rest
8.67 4.4 7 30 42 18 125 ca. 400 1020 - 1065
CuNi18Zn20
CW409J
C76400
Cu 60 - 63
Ni 17 - 19
Mn 0.5
Fe 0.3
Zn Rest
8.73 3.3 5 23 33 17.7 135 ca. 440 1055 - 1105
CuNi18Zn27
CW410J
C77000
Cu 53 - 56
Ni 17 - 19
Mn 0.5
Fe 0.3
Zn Rest
8.70 3.3 5 23 32 17.7 135 ca. 440 1050 - 1100


Table 6: Mechanical Properties of Copper-Nickel-Zinc Alloys
Material Hardness
Condition
Tensile Strength Rm
[MPa]
0,2% Yield Strength
Rp02
[MPa]
Elongation
A50
[%]
Vickers
Hardness
HV
Bend Radius1)
perpendicular to
rolling direction
Bend Radius1)
parallel to
rolling direction
Spring Bending
Limit σFB
[MPa]
Spring Fatigue
Limit σBW
[MPa]
CuNi12Zn24 R 360
R 430
R 490
R 550
R ≥ 610
360 - 430
430 - 510
490 - 580
550 - 640
≥ 580
≤ 230
≥ 230
≥ 400
≥ 480
≥ 580
35
8
6
3
2
80 - 110
110 - 150
150 - 180
170 - 200
≥ 190
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
480 210
CuNi18Zn20 R 380
R 450
R 500
R 580
R ≥ 640
380 - 450
450 - 520
500 - 590
580 - 670
≥ 640
≤ 250
≥ 250
≥ 410
≥ 510
≥ 600
27
9
5
2
85 - 115
115 - 160
160 - 190
180 - 210
≥ 220
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
520 220
CuNi18Zn27 R 390
R 470
R 540
R 600
R ≥ 700
390 - 470
470 - 540
540 - 630
600 - 700
≥ 700
≤ 280
≥ 280
≥ 450
≥ 550
≥ 680
30
11
5
2
90 - 120
120 - 170
170 - 200
190 - 220
≥ 220
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
0 x t
1 x t
550 250

1) t: Strip thickness max. 0.5 mm

Figure 10 Copper rich region of the ternary copper-nickel-zinc phase diagram with indication of the more commonly available german silver materials

Figure 11 Strain hardening of CuNi12Zn24 by cold working

Figure 12 Softening of CuNi12Zn24 after 3 hrs annealing after 50% cold working

Copper rich region of the ternary copper-nickel-zinc phase diagram with indication of the more commonly available german silver materials
Figure 11: Strain hardening of CuNi12Zn24 by cold working
Figure 12: Softening of CuNi12Zn24 after 3 hrs annealing after 50% cold working

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 Figure 13 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 Table 7 and Table 8. 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 (Figs. 13 – 15). 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 under higher current loads. Taking advantage of their high temperature stability they are also used as current carrying contacts in high voltage switchgear and as electrode material for resistance welding.


Table 7: Physical Properties of Selected Copper-Silver-(Cadmium) Alloys
Material
Designation
EN UNS
Composition
[wt%]
Density
[g/cm3]
Electrical
Conductivity
Electrical
Resistivity
[μΩ·cm]
Thermal
Conductivity
[W/(m·K)]
Coeff. of Linear
Thermal
Expansion
[10-6/K]
Modulus of
Elasticity
[GPa]
Softening Temperature
(approx. 10% loss in
strength)
[°C]
Melting
Temp Range
[°C]
[MS/m] [% IACS]
CuAg2
not standardized
Ag 2
Cu Rest
9.0 49 85 2.0 330 17.5 123 ca. 330 1050 - 1075
CuAg2Cd1,5
not standardized
Ag 2
Cd1,5
Cu Rest
9.0 43 74 2.3 260 17.8 121 ca. 350 970 - 1055
CuAg6
not standardized
Ag 6
Cu Rest
9.2 38 66 2.4 270 17.5 120 960 - 1050


Table 8: Mechanical Properties of Selected Copper-Silver-(Cadmium) Alloys
Material Hardness
Condition
Tensile Strength Rm
[MPa]
0,2% Yield Strength
Rp02
[MPa]
Elongation
A50
[%]
Vickers
Hardness
HV
Bend Radius1)
perpendicular to
rolling direction
Bend Radius1)
parallel to
rolling direction
Spring Bending
Limit σFB
[MPa]
Spring Fatigue
Limit σBW
[MPa]
CuAg2 R 280
R 380
R 450
R 550
280 - 380
380 - 460
450 - 570
≥ 550
≤ 180
≥ 300
≥ 420
≥ 500
30
6
3
1
50 - 110
100 - 140
130 - 165
≥ 160
0 x t
0 x t
1 x t
0 x t
0 x t
1 x t
400 190
CuAg2Cd1,5 R 300
R 380
R 480
R 600
300 - 380
380 - 490
480 - 620
≥ 600
≤ 190
≥ 310
≥ 440
≥ 550
30
8
3
1
55 - 110
100 - 145
130 - 170
≥ 160
0 x t
0 x t
1 x t
0 x t
0 x t
1 x t
440 220
CuAg6 R 320
R 400
R 500
R 650
320 - 400
400 - 510
500 - 660
≥ 650
≤ 210
≥ 330
≥ 460
≥ 610
30
6
3
1
70 - 120
110 - 150
145 - 175
≥ 175
0 x t
0 x t
1 x t
0 x t
0 x t
1 x t
460 230

1) t: Strip thickness max. 0.5 mm

Figure 13 Phase diagram of copper-silver for the range of 0 – 40 wt% silver

Figure 14 Strain hardening of CuAg2 by cold working

Figure 15 Softening of CuAg2 after 1 hr annealing after 40% cold working

Figure 16 Softening of CuAg2 after 1 hr annealing after 80% cold working

Figure 13: Phase diagram of copper-silver for the range of 0 – 40 wt% silver
Figure 14: Strain hardening of CuAg2 by cold working
Figure 15: Softening of CuAg2 after 1 hr annealing after 40% cold working
Figure 16: Softening of CuAg2 after 1 hr annealing after 80% cold working

References

References