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Welding of Copper and its Alloys |
Welding of Copper and its Alloys -
Introduction
Copper
Copper is second only to iron and steel in commercial importance. It is of brownish red colour and possess the following properties.
(a) Excellent resistance to corrosion.
(b) Non-magnetic properties.
(c) Easy to work, it is ductile and malleable.
(d) Moderate to high hardness and strength.
(e) High thermal and electrical conductivity.
if) It can be easily polished, plated and possesses a pleasing appearance.
(g) Resistance to fatigue and abrasion.
(h).It can be soldered, brazed or welded.
(i) Very good machinability.
(j) Ease of forming alloys with other elements like Zn, Sn, AI, Pb, Si,
(k) Copper has a melting point of 1083°C.
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The main grades of raw copper used for copper base alloys are:
(a) High conductivity Copper (electrolytic) having not less than 99.9% Cu. The oxygen content may be of the order 0.04%, Pb and Fe less than 0.005% each, Ag 0.002% and Bi less than 0.001%. Electrolytic copper is used for electrical purposes.
(b) Deoxidized Copper having not less than 99.85% Cu, less than 0.05% As, 0.03% Fe, and 0.003% Bi. Other elements may be of the order of 0.05% P, 0.01% Pb, 0.10% Ni, 0.003 and 0.005% Ag and Sb respectively,
(c) Arsenical deoxidized copper having 0.4% As, 0.04% P and remaining copper. It is used for welded vessels and tanks.
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(d) Arsenical tough pitch copper containing 0.04% As, 0.065% oxygen, 0.02% Pb, 0.15% Ni, 0.006% Ag, 0.01% Sb and less than 0.005% Bi, less than 0.020% Fe and remaining copper.
(e) oxygen free copper contains 0.05% Pb, 0.001% Ni, 0.001% Ag and less than 0.005% and 0.001 % Fe and Bi respectively. It is melted and cast in non-oxidising atmosphere.
Uses of Copper: Electrical parts, Screw machine products, Heat exchanger components.
Copper Alloys
Copper alloys normally possess excellent corrosion resistance, electrical and thermal conductivities and formability. Some copper alloys combine high strength and corrosion resistance a combination desirable for marine applications.
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| Some copper alloys because of their wearing properties, high hardness or corrosion resistance are used as surfacing metals. Some copper alloys are selected for decorative applications because of appearance. Elements such as aluminium, zinc, tin, beryllium, nickel, silicon, lead etc. form alloys with copper.
Copper alloys may be classified as
(a) High Copper Alloys
High copper alloys possess 96.0 to 99.3% Copper. They possess enhanced mechanical properties due to the addition of small amounts of alloying elements such as chromium, zirconium, beryllium and cadmium. A few typical high copper alloys are
1. Cu, 1% Cd,
2. Cu, 0.8% Cr,
3. Cu, 0.12-0.30% Zr,
4. Cu, 1.5-2.0% Be.
Such alloys are used for electrical and electronic components, as resistance welding electrodes, wire conductors, diaphragms and pump parts. |
(b) Brasses
Brasses contain zinc as the principal alloying element. Brasses are subdivided into three groups:
(i) Cu-Cz alloys,
(ii) Cu-Pb-Zn alloys or leaded brasses,
(iii) Cu-Zn-Sn alloys or tin brasses.
(i) CU-Zn alloys are
| Low (Zinc) Brasses |
|
Cu |
Zn (%) |
| 1. Gilding |
95 |
5 |
| 2. Commercial |
90 |
10 |
| 3. Red Brass |
85 |
15 |
| 4. Low Brass |
80 |
20 |
| High (Zinc) Brasses |
1. Cartridge Brass |
70 |
30 |
| 2. Yellow Brass |
65 |
35 |
| 3. Muntz Metal |
60 |
40 |
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(ii) Cu-Pb-Zn alloys:
1. Lead is added to brass in amounts up to 4% to improve machinability.
2. Lead impairs the weldability.
3. Leaded brasses contain 10 to 45% Zn, up to 4.5% Pb and rest copper.
(iii) Cu-Zn-Sn-alloys:
| |
Cu |
Zn |
Sn (%) |
| 1. Admiralty |
71 |
28 |
1 |
| 2. Naval Brass |
60 |
39.25 |
0.75 |
Uses
Decorative and architectural applications
Screw machine products
Heat Exchanger Components
Pump impellers, dairy equipment etc.
(c) Bronzes
It is a broad term defining an alloy of Copper and elements other than Nickel or Zinc.
Bronzes are subdivided into four groups
1. Cu-Sn-P alloys or phosphor bronzes.
2. Cu-Sn-Pb-P alloys or leaded phosphor bronzes.
3. Cu-AI alloys or aluminium bronzes.
4. Cu-Si alloys or silicon bronzes.
1. Phosphor Bronzes contain
90 to 95% Cu, 10 to 5% Sn and 0.2% P
2. Leaded Phosphor Bronzes contain
1 to 4% Pb, about 5% Sn, some with additions of Zn
3. Aluminium Bronzes
| Cu |
Al |
Fe |
Sn |
Mn (%) |
| 89 |
7 |
3.5 |
0.35 |
- |
| 91 |
6-8 |
1.5-3.5 |
- |
1 (max) |
4. Silicon Bronzes
| |
Cu |
Si (%) |
| Low silicon bronze |
98.5 |
1.5 |
| High silicon bronze |
97 |
3 |
Uses:
1. Bearings,
2. Ways and gibs,
3. Roll mill slippers, screwdown nuts turntable bushings and other steel mill parts.
4. Components in the power generating, petroleum and chemical industries.
(d) Copper Nickels
1. These alloys contain nickel as the main alloying element.
2. Their composition may be
| Cu |
Ni |
Fe |
Mn (%) |
| 88.6 |
9-11 |
1.4 |
1.0 |
| 70.0 |
30.0 |
- |
- |
Uses:
Salt water service. Petrochemical industry applications where corrosion resistance is important.
(e) Nickel Silvers
1. These alloys contain Zinc and Nickel as the principal alloying elements. Silver is not an alloying element.
2. Nickel silvers or formerly known as German Silvers possess nickel which gives silvery appearance for decorative purposes. Nickel also increases strength and corrosion resistance.
3. Given below are some compositions of nickel silvers.
| Cu |
Zn |
Ni |
| 65 |
25 |
10 |
| 65 |
20 |
15 |
| 55 |
27 |
18 |
Uses:
Name plates and Jewelry,
Table flat ware and decorative applications, Optical goods.
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