Welding of Copper Alloys JABIN MATHEW BENJAMIN 13MY04
Jun 22, 2015
Welding of Copper AlloysJABIN MATHEW BENJAMIN
13MY04
04/13/2023Dept. of Metallurgical Enng
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Copper And Copper Alloys
• Excellent electrical and thermal conductivities
• Outstanding resistance to corrosion
• Ease of fabrication
• Good strength and fatigue resistance
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Copper Alloys
• COPPERS, WHICH CONTAIN A MINIMUM OF 99.3% CU
• HIGH-COPPER ALLOYS, WHICH CONTAIN UP TO 5% ALLOYING ELEMENTS
• COPPER-ZINC ALLOYS (BRASSES), WHICH CONTAIN UP TO 40% ZN
• COPPER-TIN ALLOYS (PHOSPHOR BRONZES), WHICH CONTAIN UP TO 10% SN AND 0.2% P
• COPPER-ALUMINUM ALLOYS (ALUMINUM BRONZES), WHICH CONTAIN UP TO 10% AL
• COPPER-SILICON ALLOYS (SILICON BRONZES), WHICH CONTAIN UP TO 3% SI
• COPPER-NICKEL ALLOYS, WHICH CONTAIN UP TO 30% NI
• COPPER-ZINC-NICKEL ALLOYS (NICKEL SILVERS), WHICH CONTAIN UP TO 27% ZN AND 18% NI
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Alloying Elements and weldability
• Zinc
• reduces the weldability of all brasses
• Tin
• increases the hot-crack susceptibility
• Beryllium, aluminum, and nickel
• Oxide entrapment, which may reduce the strength of the weldment.
• Formation of these oxides prevented by shielding gas or by fluxing
• Silicon
• beneficial because of its deoxidizing and fluxing actions.
• Low thermal conductivity makes silicon bronzes the most weldable of the copper alloys for any arc process.
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• Phosphorus
• does not adversely affect or hinder welding
• Chromium
• inert protective atmosphere to prevent formation of chromium oxides.
• Cadmium
• no serious effect on the weldability of copper
• Oxygen
• cause porosity and reduce the strength of welds
• Deoxidizing elements--usually phosphorus, silicon, aluminum, iron, or manganese.
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Factors Affecting Weldability
Effect of Thermal Conductivity.
Cu has high thermal conductivities
the type of current and shielding gas must be selected to provide maximum heat input to the joint
preheating may be decided based on thickness
Counteracts the rapid head dissipation
Cold worked Cu alloys tend to become weaker and softer at HAZhot cracking may occur in heavily cold worked
Welding Position
highly fluid nature
flat position is used whenever possible
Vertical, overhead and the horizontal position- seldom used
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Precipitation-Hardenable Alloys Beryllium, chromium, boron, nickel, silicon, and zirconium.
Care must be taken to avoid oxidation and incomplete fusion.
Reduction in mechanical properties due to overageing
Should be welded in the annealed condition, followed by precipitation hardening treatment
Hot Cracking copper-tin and copper-nickel, are susceptible to hot cracking
wide liquidus-to-solidus temperature range
Severe shrinkage stresses produce interdendritic separation during metal solidification
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Porosity
zinc, cadmium, and phosphorus have low boiling points.
Vaporization of these elements during welding may result in porosity.
Higher travel speed and filler metals with less volatile element content
Surface Condition
Oxides formed are difficult to remove
Cleaning and shielding helps to avoid oxide formation
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Welding of Cu
Difficulties: High oxygen content and impurities
Electrode: Ecu and filler: ERCu
Preheating : thickness, conductivity
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Preheating
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Effect of shielding gas
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GTAW Upto 3.2mm thickness but more for flat position
Shielding: upto 1.6mm Ar and over 1.6mm He, deeper penetration
Pulsed current can be used
GMAW Shielding: Ar or mixture of Ar and He
Filler: ERCu
Spray transfer and pulsed current
SMAW ECuSi, ECuSn-A
DCEP
Flat position
04/13/2023Dept. of Metallurgical Enng
13Welding of Copper-Zinc Alloys (Brass)
• C20500, C49080, C83300
• Evolution of zinc fumes is a problem
• Low-zinc brasses are shown to have good weldability using GTAW
• High-zinc brasses, tin brasses, special brasses, and nickel silvers have only fair weldability
• Preheating is not normally required
• Leaded brasses are unweldable
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• Shielding: He-for alloys having higher thermal conductivities.
• Filler should not contain zinc
• Low zinc- ERCuSn-A
GMAW
• Unleaded brasses can be welded using GMAW.- low-zinc alloys (red brasses) and the high zinc alloys
• Filler should not contain copper-zinc- Silicon bronze (ERCuSi-A)- good fluidity
• DCEP
• Preheat: 95 to 315 °C- low zinc alloys
• High zinc alloys- more porosities
• Filler ERCuAl-A2 strength or ERCuSn-A colour match
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• SMAW
• Covered electrodes- ECuSi, ECuSn-A, ECuSn-C, ECuAl-A2, ECuAl-B
• Low zinc- ECu-Sn-A and ECuSn-C
• Preheating of the base metal from 200 to 260 °C
• High zinc copper alloys can be welded with aluminum bronze (ECuAl-A2) electrodes
• Preheat and interpass temperatures are 260 to 370 °C
04/13/2023Dept. of Metallurgical Enng
16Welding of Copper-Tin alloys (Phosphor Bronzes)
• C50100-C52400
• GTAW• Up to approximately 13 mm
• DCEN or a stabilized alternating current
• Shot peening each layer of multi-pass welds reduces cracking and stresses
• Shielding- Argon- restricts the size of the HAZ.
• Thicker sections, helium shielding gas
• Filler metal- ERCuSn-A
• Preheating: not required for thin sections, Thick sections require preheating to 175 or 200 °C
• Interpass temperature should not exceed 200 °C
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• GMAW
• Thicknesses of 9.5 to 13 mm.
• 90° single-V grooves are used
• Filler Metal- ERCuSn-A
• Preheating of the phosphor bronzes helps in obtaining complete fusion, less porosity, but columnar grains and hot cracking
• SMAW
• Covered electrodes: ECuSn-A and ECu-Sn-C
• Preheating is required in the range of 150 to 200 °C
• Maximum ductility, the welded assembly should be postweld heat treated to 480 °C (900 °F) and cooled rapidly.
04/13/2023Dept. of Metallurgical Enng
18Welding of Copper-Nickel Alloys (C70000-C79900)
• GTAW
• Preferred for copper-nickel alloys with section thicknesses up to 1.6 mm
• Electrode- EWTH-2
• Ar shielding gas- provides better arc control and stability,
• DCEN, Alternating current can be employed for automatic welding
• Preheating is not necessary and backing strips or rings can be used
• Filler Metals: Deoxidized- ERCuNi- minimize porosity and the possibility of oxygen embrittlement
• Autogenous welds can sometimes be made on sheet thicknesses up to 1.6 mm
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• GMAW
• Preferred welding process for non-leaded copper-nickel alloys thicker than approximately1.6 mm (0.06 in.).
• Preferred welding position: Flat position
• Preferred shielding gas: Ar
• Argon-helium mixes give better penetration on thick sections.
• Direct current electrode positive is recommended.
• Spray or short-circuiting transfer
• Filler Metals. ERCuNi- 0.15 to 1.00% Ti, which serves as a deoxidizer
• No preheating or postheating
• Interpass temperatures should be maintained below 65 °C
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• SMAW
• Both wrought and cast forms
• Copper-nickel electrode- ECuNi
• DCEP
• Special care is needed to ensure complete slag removal
• Vertical and overhead positions
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Other processes for welding of Cu
Laser beam welding
Difficulties: high reflection of laser beam and high thermal conductivity
Absorption increases with temperature
Shorter wavelength has better welding
Electron beam welding
Thin and thick sections
Resistance spot welding
Lower conductivity alloys readily spot welded
Not practical for unalloyed Cu
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Flash welding
Leaded Cu (upto 1% Pb) can be flash welded
Rapid upsetting at minimum pressure
Low melting point and narrow plastic range
Premature termination of current: lack of fusion
Delayed termination: over heating
Solid state welding
Annealed Cu can be welded at room temperature: good malleability
Diffusion welded or explosive welding
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Reference
Welding of copper and copper alloys, AWS welding handbook, Volume 3, Ed. 8, 1997
ASM metal handbook, volume 6, 1993
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