Welding Copper & Brass

Copper and its alloys (brass, bronze, copper-nickel) fight you with thermal conductivity. Pure copper pulls heat away from the weld zone 8 times faster than steel, so maintaining a puddle requires either massive amperage or substantial preheat. Thin copper TIG welds fine once you bump the amps up. Thick copper needs preheat to 400-1000F just to get a puddle started.

TIG (GTAW) is the primary process for copper alloys. Use DCEN with 100% argon or argon/helium blends. Helium additions (up to 75%) raise arc voltage and increase heat input, which helps overcome copper’s heat sink effect. ERCu (deoxidized copper) filler matches pure copper. ERCuSi-A (silicon bronze) works on brass, bronze, and dissimilar copper-to-steel joints. ERCuAl-A2 (aluminum bronze) handles high-strength applications and marine hardware.

Brass contains zinc, and zinc vaporizes during welding just like on galvanized steel. Brass welding produces toxic zinc fumes that require proper ventilation and respiratory protection. Silicon bronze MIG brazing at lower temperatures minimizes zinc loss and fume generation compared to fusion welding.

Preheat varies by alloy and thickness. Pure copper over 1/8 inch needs 400-750F. Thick sections over 1/2 inch may need 900-1000F. Brass and bronze alloys need less preheat (200-400F) because their alloying elements reduce thermal conductivity. Copper-nickel alloys (90/10, 70/30) are the easiest copper alloys to weld and often need no preheat at all.

After welding, copper alloys cool slowly and don’t harden in the HAZ like steel. But they’re prone to hot cracking from residual stress, so avoid excessive restraint and use a balanced weld sequence on multi-pass joints.