Welding of copper alloys

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


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


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.


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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Engineering

Welding of copper alloys