TIG Welding Copper: Preheat, Amperage Settings & Filler Selection

TIG welding copper requires DCEN polarity, preheating to 400-750°F for material thicker than 1/16", and significantly more amperage than steel of the same thickness. Copper’s thermal conductivity is roughly 8 times higher than steel, so heat leaves the weld zone almost as fast as you put it in. You’re fighting the base metal’s ability to conduct heat away from the joint the entire time.

Use ERCu (deoxidized copper) filler rod for pure copper joints, 100% argon or 75/25 argon/helium shielding gas at 20-30 CFH, and a 2% lanthanated tungsten sized one step larger than you’d use on steel of the same thickness.

Why Copper Is Different

Copper’s properties create a unique set of challenges that don’t exist with steel, stainless, or aluminum:

• Thermal conductivity: 226 BTU/hr-ft-°F (steel is 26). Heat disappears into the base metal instantly.
• Melting point: 1,981°F, which is actually lower than steel’s 2,500°F. But you’ll never notice because the heat conducts away before the joint reaches melting temperature.
• Coefficient of expansion: Higher than steel. Copper parts move and warp during welding.
• No color change before melting: Unlike steel, copper gives minimal visual warning before it melts through. The surface goes slightly dull, then suddenly the puddle appears.

These properties mean copper welding is about heat input strategy. You need to overwhelm the base metal’s ability to conduct heat away by preheating, using high amperage, and sometimes switching from pure argon to hotter argon/helium mixes.

Preheat Requirements

Preheat is not optional on copper thicker than about 1/16". Without it, the base metal conducts heat away from the joint faster than the arc can deliver it. You’ll run maximum amperage and still can’t form a puddle.

Use an oxy-acetylene rosebud tip for preheating. Propane torches don’t deliver enough concentrated heat. Verify temperature with a contact pyrometer or temperature-indicating crayons. Heat the area uniformly, not just the weld line. Copper conducts so well that a 6-inch square of preheated copper will cool to below preheat temperature in under a minute if the surrounding material is cold.

On thick copper (1/4"+), you may need an assistant maintaining preheat with a second torch while you weld. The base metal pulls heat out of the weld zone constantly.

Amperage Settings

Copper needs roughly 30-50% more amperage than steel of the same thickness because so much heat conducts away from the joint. These settings assume adequate preheat is maintained.

These amperages push most 200A hobby machines beyond their limits for anything thicker than 1/8". Welding copper thicker than 1/8" typically requires a 250A or larger machine. On 1/4" copper, you need a 350-400A machine running at or near capacity.

Shielding Gas Options

100% Argon

Works fine for thin copper (under 1/8") with proper preheat. Flow rates run 20-25 CFH, slightly higher than for steel because you need consistent coverage over the wide heat-affected zone.

Argon/Helium Mixes

Helium increases arc voltage and total heat input without changing amperage. This extra heat helps overcome copper’s conductivity on thicker sections.

• 75% Ar / 25% He: A mild bump in heat input. Good for 1/8" to 3/16" copper.
• 50% Ar / 50% He: Significant heat increase. Effective for 3/16" to 1/4" copper.
• 25% Ar / 75% He: Maximum practical heat boost. For 1/4"+ copper. The arc becomes harder to control and gas consumption increases significantly.
• 100% He: Rarely used for TIG because the arc becomes very unstable. Sometimes used for automated copper welding.

Helium is expensive compared to argon and requires 2-3 times the flow rate because it’s lighter and disperses faster. Budget helium costs into the job when quoting copper welding work.

Filler Rod Selection

ERCu (Deoxidized Copper)

The standard filler for copper-to-copper joints. Contains small amounts of tin, silicon, and manganese as deoxidizers. These deoxidizers react with oxygen in the puddle and float to the surface as slag, preventing porosity.

Never use bare copper wire (electrical wire, plumbing tube scraps) as TIG filler. It lacks deoxidizers and will produce porous, weak welds full of internal voids.

ERCuSi-A (Silicon Bronze)

A copper-silicon alloy with about 3% silicon. Lower melting point and better flow than ERCu. Silicon bronze is technically a brazing filler when used on copper because it melts below the copper base metal’s melting point.

Use ERCuSi-A for:

• Decorative work and art
• Copper to brass joints
• Situations where lower heat input is critical
• Thin copper sheet where ERCu requires too much heat

The resulting weld has a golden-bronze color instead of copper color. Mechanical properties are lower than ERCu.

ERCuNi (Copper-Nickel)

For welding copper-nickel alloys (CuNi 70/30 and 90/10) commonly used in marine piping and heat exchangers. Don’t use ERCuNi on pure copper unless you’re joining copper to copper-nickel.

ERCuAl-A2 (Aluminum Bronze)

For welding aluminum bronze base metals. Also used for hard-facing and wear surfaces. The high aluminum content makes the weld pool less fluid but creates a harder deposit.

Copper Alloys

Pure copper (C110, C101, C102) is the most common and most difficult to weld because of its extreme thermal conductivity. Copper alloys are generally easier because the alloying elements reduce conductivity and lower the melting range.

Brass (Copper-Zinc)

Welding brass with TIG is problematic because zinc vaporizes at 1,665°F, well below the melting point of the brass itself. The zinc fumes create porosity and a rough, spongy weld surface. Use ERCuSi-A filler and keep heat input as low as possible. Work in a well-ventilated area or under a fume extractor because zinc fumes cause metal fume fever.

Bronze (Copper-Tin)

Easier to weld than pure copper. Phosphor bronze (C510, C521) welds well with ERCuSn-A filler. Silicon bronze (C655) uses ERCuSi-A. The tin content reduces thermal conductivity enough that preheat requirements drop significantly compared to pure copper.

Copper-Nickel

The most weldable copper alloy family. Thermal conductivity is only about 2x steel’s, compared to 8x for pure copper. Preheat is generally not needed. Use ERCuNi filler and 100% argon. Avoid nitrogen contamination (which causes porosity in CuNi welds) by maintaining good gas coverage.

Technique Adjustments for Copper

Travel Speed

Move faster than you would on steel. The puddle on copper is fluid and prone to sagging. A faster travel speed keeps the puddle small and manageable. If you see the puddle growing out of control, speed up rather than reducing amperage. Reducing amperage on copper risks losing the puddle entirely once the base metal heat-sinks it away.

Arc Length

Keep a short arc, 1/8" or less. Copper’s high conductivity means any heat lost to a long arc is heat you can’t afford to waste. A tight arc concentrates energy into the joint.

Filler Rod Feeding

Copper puddles are extremely fluid. The filler rod melts and flows fast once it contacts the molten pool. Use smaller-diameter filler than you would on steel of the same thickness, and feed it quickly. Hesitating with the rod in the puddle adds too much material and creates a humped bead.

Torch Angle

A slightly steeper torch angle (20-25 degrees from vertical) helps drive heat deeper into the joint. On thick copper, some welders point the torch almost straight down to maximize penetration.

Common Problems and Fixes

Can’t Form a Puddle

You’re not getting enough heat into the joint. Solutions in order:

1. Verify preheat temperature is correct and maintained during welding
2. Increase amperage
3. Switch to argon/helium mix for more heat input
4. Check that your machine has enough capacity for the copper thickness
5. Use a larger tungsten to handle higher amperages

Porosity

Copper is highly susceptible to porosity from oxygen and hydrogen. Deoxidized filler (ERCu) helps, but you also need:

• Clean, dry base metal (no fingerprints, no tarnish in the joint area)
• Dry shielding gas (moisture in the gas line creates hydrogen porosity)
• Adequate gas flow (copper’s wide HAZ needs good coverage)
• No drafts

Cracking

Hot cracking in copper welds happens when impurities (phosphorus, sulfur, lead, bismuth) segregate to grain boundaries during solidification. Using high-purity copper base metal and deoxidized filler minimizes this. Free-machining copper alloys containing lead are essentially unweldable.

Discoloration and Oxidation

The weld and HAZ on copper oxidize visibly at welding temperatures. Post-weld cleanup with a scotch-brite pad and copper cleaner restores the surface. For critical applications, welding in a chamber with argon shielding prevents all surface oxidation.

Undercut

Copper’s fluidity combined with high amperage makes undercut common. Slow down slightly at the toes of fillet welds and direct the arc into the thicker member. On butt joints, reduce arc length to concentrate the heat zone.

Safety Considerations

Copper fumes are toxic at high concentrations. Always weld copper with adequate ventilation or a fume extractor positioned close to the arc. Brass welding produces zinc fumes, which are particularly dangerous and cause metal fume fever (chills, fever, nausea) within 4-12 hours of exposure.

Preheat torches running on copper parts create a large area of hot metal with no visible color change until it’s extremely hot. Mark preheated areas and keep flammable materials away. Copper retains heat longer than you’d expect because the entire piece reaches near-preheat temperature.

Wear full-coverage welding gloves when handling preheated copper. Standard welding gloves may not provide enough insulation for extended contact with 600°F+ base metal.