Can brass be welded?
Not well. Zinc boils out of the weld and the lead in C360 cracks it. Braze or solder brass instead; unleaded C260 can be TIG welded with care.
Brass is copper with 30-40% zinc, and zinc boils at 907 °C (1665 °F), below the melting point of the alloy. Any fusion weld therefore boils zinc out of the pool: the weld is porous, the arc is unstable, the surface is covered with white zinc oxide, and the fumes cause metal fume fever. Free-machining C360 (Cu-Zn-3% Pb) makes it worse. Lead is insoluble in the copper matrix and sits at grain boundaries, where it forms low-melting films that crack the weld and the heat-affected zone as they solidify. C360 is rated as not weldable by the copper alloy producers, and few shops will attempt it beyond a cosmetic tack.
Joining brass is done by brazing and soldering. Silver brazing (AWS BAg-5 or BAg-7 filler, with a flux) at 620-760 °C (1150-1400 °F) gives a strong joint on any brass, including C360, without melting the base metal or boiling off the zinc; it is the standard for plumbing fittings, instrument parts and assemblies. Soft soldering (tin-based, Sn-Ag or Sn-Cu, at 230-260 °C) works for low-load and electrical joints. Both need the surface clean and the lead smeared by machining removed with a light pickle or abrasive; lead-rich surfaces do not wet well. Brazed brass joints can be as strong as the brass itself and are easy to inspect.
When a fused joint is genuinely required, the unleaded alloys are the candidates: C260 cartridge brass (70/30) and C230 red brass can be TIG welded with a silicon bronze (ERCuSi-A) or aluminum bronze (ERCuAl-A2) filler, which does not add zinc, using low heat input, high travel speed and good fume extraction. The result is a weld that is bronze-coloured, porous and lower in strength than the base metal, so it is used for repairs and non-structural attachments. A better option for many parts is to design the assembly so the free-machining brass is joined mechanically (thread, press fit, rivet) or switch the welded component to silicon bronze (C655), which welds well and machines acceptably.
Welding for C360 parts: where to send them
What to specify
- Join by silver brazing (AWS A5.8 BAg-5 or BAg-7 with flux) or soft solder; note that fusion welding of C360 is not permitted
- Braze joint clearance of 0.05-0.13 mm (0.002-0.005") and joint design (lap or socket) on the drawing
- If a fusion weld is unavoidable, change that component to C260 or C655 silicon bronze and specify ERCuSi-A filler, low heat input and fume extraction
- Surface preparation before brazing: degrease, remove lead smear (light pickle or abrasive), flux immediately
- Post-braze flux removal (hot water, mild acid dip) to stop later corrosion under the residue
- Lead content requirements (NSF/ANSI 372 for potable water) if the assembly is a plumbing part; C360 is not compliant
Pitfalls
- Trying to TIG weld C360 and getting a porous, cracked, white-crusted joint
- Welding brass without fume extraction; zinc oxide fumes cause metal fume fever
- Brazing onto a machined lead-smeared surface that will not wet; clean it first
- Leaving brazing flux on the part, which corrodes the joint over months
- Substituting mild-steel welding practice (high heat, slow travel) on C260 and boiling the zinc anyway
- Choosing C360 for a part because it machines well, then discovering it must be welded to something
Frequently asked questions
- Why can't brass be welded?
- Zinc boils at 907 °C, below the melting point of brass, so a fusion weld boils it out of the pool and leaves porosity and white oxide. In C360 the 3% lead also forms low-melting films that crack the weld. Brazing avoids both problems by never melting the base metal.
- How do you join brass parts?
- Silver brazing with an AWS BAg filler and flux is the standard and gives a joint as strong as the brass. Soft solder works for light loads and electrical joints. Threads, press fits and rivets are the mechanical alternatives.
- Which brass alloys can be welded?
- Unleaded alloys like C260 (70/30) and C230 red brass can be TIG welded with silicon bronze filler, with porosity and lower strength. Silicon bronze C655 welds well and is the usual substitute for a welded copper-alloy part. Leaded C360 should not be fusion welded.
