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Welding of High Copper Alloys |
Welding of High Copper Alloys -
High copper alloys are those of
(i) Cu-Cr
(ii) Cu-Cd
(iii) Cu-Zr
(iv) Cu-Be
Generally the same procedure can be applied to high copper alloys as used for welding coppers. However, extra care must be taken because many high copper alloys are used in the heat treated, age hardened, cold worked or precipitation hardened condition. Specific procedures vary among the alloys although, in general, reduced temperatures and welding currents are possible because high copper alloys are not as thermally conductive as copper. All high copper alloys should .be protected at high temperatures from contact with the surrounding atmosphere to prevent oxidation of alloying elements.
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The arc and gas welding procedures for deoxidized coppers are good starting points for high copper alloys, with the exception of the beryllium coppers.
Beryllium coppers can be successfully welded but adequate ventilation must be insured.
Cu-Be alloys may be classified as
(i) High strength alloys containing 2% Be, 0.25% Co and balance copper.
(ii) High conductivity alloys containing 0.5% Be, 2.5% Co and; balance copper.
Susceptibility to cracking and porosity is greater for welds made in high conductivity than in high strength beryllium copper, especially in multipass welding;
Alloys with higher Be content (i.e., high strength alloys) possess better weldability because Be lowers the melting point, increases fluidity of molten alloy and decreases thermal conductivity.
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The main factors to be kept in mind during TIG and MIG welding of high conductivity Cu-Be alloys are their
(i) High thermal and electrical conductivity.
(ii) Oxide forming characteristics.
(iii) Response to heat treatment.
TIG welding of high conductivity Cu-Be alloys
The maximum thickness that can be TIG welded is about 12.5 mm. Thicker workpieces are welded by MIG process. Shielding gas is usually a mixture of argon and helium to obtain a, hot are, smooth and spatter free welds. The work surfaces should be concept free from beryllium oxide and cuprous oxide during welding.
High-frequency-stabilized A.C., which continually breaks up the oxide coating is preferred. Zirconiated tungsten electrodes are used with A.C. Thoriated tungsten electrodes are used with DCSP when deep penetration is the requirement.
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| To achieve same high electrical conductivity in weld metal as that of base metal, filler rod of same composition as the base metal is generally used. If high electrical conductivity of weld metal is not the major criteria, silicon bronze filler rod is satisfactory. Workpieces above 3 mm thick and requiring multipass welds need to be preheated. Table gives conditions for TIG welding of high conductivity Cu-Be alloys.
TIG welding of High strength Cu-Be Alloys
Contrary to practice with the high conductivity alloys, the TIG process can be used on thicknesses greater than 12.5 mm. Rods or strips of the same composition as the base metal are generally used as filler metal.
Preheating 10150 to 205°C is recommended for welding of metal thicker than 3 mm. Maximum weld strength is obtained by solution annealing and aging after welding. Aging treatment is 3 hours at 316 to 344°C. Nominal conditions for TIG welding of high strength alloys. |
| Plate thickness |
Butt joint groove |
Electrode diameter mm |
Current Amp |
Travel speed cm/min |
No of passes |
Preheat Temp°C |
| High conductivity (96.9% Cu, 0.6% Be, 2.5% Co) alloy |
| 0 to 2 |
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| 2 to 3 |
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| 6 |
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| High strengh (98.3% Cu, 1.7% Be and 98.1% Cu, 1.9% Be) alloys |
| 0 to 2 |
Square |
2.25 |
150 |
12.5-25 |
1 |
None |
| 2 to 3 |
90°Single V, root face 1.5 mm max |
2.25 |
180 |
12.5-25 |
1 |
None |
| 6 to 12.5 |
do |
4.5 |
250 |
12.5-25 |
3-4 |
150 |
| over 12.5 |
do |
4.5 |
250 |
12.5-25 |
5-8 |
205 |
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MIG welding of high conductivity Cu-Be alloys
MIG welding is preferred to TIG welding for joining high conductivity alloys.
The maximum normal thickness joined by MIG process is about 18mm. Filler metal employed is of the same composition as that of base metal. When low conductivity is adequate, Cu-Be high strength alloy filler rods can be used. They provide easier welding.
When (96.9% Cu + 0.6% Be + 2.5% Co) filler metal is used, strength can be increased by aging (treatment at 482°C for 3 hours) after welding. Table gives nominal conditions for MIG welding high conductivity alloys.
MIG welding of high strength alloys
MIG welding is generally preferred for welding precipitation hardened high strength beryllium coppers in thicknesses of more than 6 mm. If heat treatment is to be done after welding, MIG process is preferred for thicknesses down to 2 mm. Table gives nominal conditions for MIG welding high strength alloys.
| Joint |
Plate thickness mm |
Root face mm |
Electrode dia mm |
Shielding Gas |
Gas flow rate lpm |
Current Amp |
No of passes |
Preheat Temp °C |
| 96.9% Cu, 0.6% Be, 2.5% Co high conductivity alloys |
| (a) 90° Single V groove |
6-12.5 |
0.75 |
1.12 |
Argon Helium |
14 |
200-240 |
3-4 |
316 |
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18 |
0.75 |
1.12 |
Argon Helium |
14 |
200-240 |
6 |
482 |
| 98.3% Cu, 1.7% Be/98.1% Cu, 1.9% Be high strength alloys |
| (b) 90° Single V groove |
6-12.5 |
0.75-1.5 |
1.12 |
Argon Helium |
21 |
175-200 |
3-4 |
150-205 |
| 30° Double U groove |
18-37 |
1.5 |
1.5 |
Argon Helium |
28 |
325-350 |
10-20 |
150-205 |
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