Can copper be welded?
Yes, with preheat and TIG or MIG using ERCu filler. Oxygen-free C101 or C102 welds best; C110 (ETP) is prone to porosity and brittle welds.
Copper welds, but it fights the arc. C110 conducts heat at about 390 W/m·K, roughly eight times carbon steel and more than twice 6061 aluminum, so the heat of a TIG or MIG arc drains into the part before a puddle forms. Thin sheet under about 1.5 mm (0.06") can be TIG welded with argon and no preheat. From about 3 mm (0.12") up, preheat rises with section size, commonly 200-500 °C (400-930 °F) on heavy bus bar and plate. Helium or a helium-argon mix (for example 75% He, 25% Ar) runs a hotter arc and cuts the preheat needed, and it is the normal choice for thick copper. TIG (DCEN) covers sheet and small parts; MIG in spray transfer covers plate.
The grade matters as much as the process. C110 is electrolytic tough pitch (ETP) copper: 99.90% copper with about 0.02-0.04% oxygen held as cuprous oxide particles. In the weld and heat-affected zone that oxide causes porosity and a brittle oxide network at the grain boundaries. If hydrogen is present (a reducing oxyfuel flame, a damp joint, hydrogen furnace brazing), it reacts with the oxide to form steam that cracks the metal from inside. For parts that will be fusion welded, specify oxygen-free C10100 (OFE) or C10200 (OF), or phosphorus-deoxidized C12200 (DHP), the standard grade for welded and brazed tube. Use a deoxidized filler: ERCu (AWS A5.7) carries small amounts of silicon, tin, manganese and phosphorus to tie up oxygen.
Welding also changes the part. Cold-worked copper anneals in the heat-affected zone, so a half-hard bus bar drops toward the soft condition, around 70 MPa (10 ksi) yield. The weld bead has lower electrical conductivity than the 100% IACS base metal, much lower with silicon bronze filler, which matters on current-carrying joints. For tube, fittings and many electrical joints, brazing is the better answer: copper-phosphorus filler (BCuP alloys per AWS A5.8) is self-fluxing on copper, runs well below the melting point and leaves a sound, conductive joint. Laser welding of copper, common on battery tabs and bus bars, needs green or blue lasers or high-power fiber lasers with beam oscillation, because copper reflects most infrared light.
Welding for C110 parts: where to send them
What to specify
- Base metal for welded parts: C10100 (OFE), C10200 (OF) or C12200 (DHP); avoid C11000 (ETP) where the weld must be sound and ductile
- Filler: ERCu per AWS A5.7 for TIG and MIG; say whether silicon bronze (ERCuSi-A) is acceptable on joints where conductivity does not matter
- Qualified procedure (AWS B2.1 or ASME Section IX) with preheat and shielding gas stated, or ask the shop for its WPS
- Joint conductivity or current rating on bus bars and electrical joints, so the shop picks filler and joint design to suit
- Whether brazing with BCuP filler (AWS A5.8) is an acceptable alternative to fusion welding
- Design strength based on the annealed heat-affected zone, not the cold-worked temper of the bar
- Leak test (helium or pressure) on vacuum, cooling-water and fluid parts
Pitfalls
- Porous, brittle welds on C110 ETP because of its oxygen content; the fix is a deoxidized or oxygen-free base metal
- Too little preheat or argon-only shielding on thick sections, leaving cold laps and lack of fusion that look like a weld
- Hydrogen embrittlement when ETP copper is heated in a reducing flame or hydrogen atmosphere
- Expecting cold-worked strength after welding; the heat-affected zone anneals soft
- Silicon bronze filler on a bus bar joint, cutting its conductivity well below the copper
- Thick-to-thin joints where the heavy side soaks up the heat and the thin side burns through
Frequently asked questions
- Can you TIG weld copper?
- Yes. Use DCEN, ERCu filler, and argon for thin sheet or a helium-argon mix for thicker sections. Sheet under about 1.5 mm needs no preheat; heavier sections are preheated, commonly into the 200-500 °C range depending on thickness and gas.
- Why is copper so hard to weld?
- Its thermal conductivity, about 390 W/m·K, pulls heat out of the joint roughly eight times faster than carbon steel, so the puddle is hard to start and hold. Tough pitch copper (C110) adds porosity and embrittlement from its oxygen content.
- Should copper be welded or brazed?
- Brazing with BCuP filler is standard for tube, fittings and most electrical joints: lower heat, less distortion and a conductive, leak-tight joint. Fusion welding is used for thick bus bar, large structures and joints that must survive temperatures above the braze alloy.
