Welding Bronze and Brass: Filler Matching by Alloy Type

Bronze and brass cover a wide family of copper alloys, each with different welding characteristics and filler requirements. Silicon bronze (ERCuSi-A) is the universal repair filler and the go-to for MIG brazing steel. Phosphor bronze (ERCuSn-A) handles bearing and bushing repair. Aluminum bronze (ERCuAl-A2) welds marine hardware and industrial components. Getting the filler match right is the single most important decision on any bronze or brass welding job.

The common theme across all these alloys: TIG on DCEN with 100% argon is the primary process, preheat varies by alloy and thickness, and cleanliness determines whether you get a sound weld or a porous mess.

Bronze and Brass Alloy Families

Silicon Bronze (ERCuSi-A)

Silicon bronze is the most versatile filler in the copper alloy family. It works on silicon bronze base metal, brass, mild steel, galvanized steel, and as a dissimilar-metal filler between copper alloys and steel.

Composition and Properties

ERCuSi-A contains approximately 97% copper, 3% silicon, with traces of manganese and tin. The silicon acts as a deoxidizer and provides excellent fluidity. The deposit is soft (roughly 70-80 Brinell) with good corrosion resistance.

TIG Welding Silicon Bronze

Run DCEN with 100% argon at 15-20 CFH. Silicon bronze flows extremely well and produces a shiny, golden bead that’s easy to read. Use 3/32 or 1/8 inch rod for most work.

Silicon bronze base metal has lower thermal conductivity than pure copper, so preheat requirements are less aggressive. Thin sections often need no preheat at all.

MIG Brazing with ERCuSi-A

This is where silicon bronze really shines for fabrication shops. Running ERCuSi-A wire through a standard MIG gun with 100% argon produces a braze weld on mild steel at temperatures below the steel’s melting point. Benefits include:

• Minimal distortion on thin gauge steel and auto body panels
• Low spatter compared to steel MIG welding
• Zinc-friendly on galvanized steel because the lower temperature reduces zinc burn-off
• Corrosion-resistant deposit that doesn’t rust
• Easy to grind and finish for appearance work

MIG brazing settings for ERCuSi-A on steel:

Short-circuit transfer works well for MIG brazing because you want lower heat input. The silicon bronze wets and flows on the steel surface without deep penetration. This is fundamentally different from fusion welding; you’re creating a capillary bond similar to brazing, just using the MIG process.

Important limitation: MIG brazed joints with ERCuSi-A on steel are braze welds, not fusion welds. Joint strength is lower than a fusion weld, and the joint shouldn’t be used for structural applications governed by AWS D1.1 unless specifically qualified.

Phosphor Bronze (ERCuSn-A)

Phosphor bronze alloys (C51000, C52100, C54400) contain 5-10% tin and a small amount of phosphorus. They’re the standard bearing, bushing, and spring alloys. Welding is primarily for repair: building up worn surfaces, fixing casting defects, or joining broken components.

Filler and Process

ERCuSn-A (approximately 92% Cu, 8% Sn) is the matching filler. TIG on DCEN with 100% argon. The puddle is stiffer than silicon bronze and doesn’t flow as freely.

Bearing Repair Technique

When rebuilding a worn phosphor bronze bearing:

1. Clean the bearing surface thoroughly. Remove all oil, grease, and contamination. Solvent clean, then grind to bright metal.
2. Preheat to 300-400F.
3. TIG weld the buildup layer using ERCuSn-A filler. Use narrow stringer beads with low amperage to minimize dilution and heat input.
4. Build up to 1/16 to 1/8 inch over final dimension.
5. Cool slowly (wrap in insulating blanket).
6. Machine to final dimension using carbide tooling.

The as-welded deposit is softer than the original work-hardened bearing surface. For non-critical bearings, this is acceptable. For precision applications, the machined surface may need additional finishing (honing or burnishing).

Aluminum Bronze (ERCuAl-A2)

Aluminum bronze alloys (C95200 through C95800) contain 9-12% aluminum and produce some of the strongest non-ferrous castings available. They’re used for marine propellers, pump impellers, valve bodies, and heavy-duty bearings in corrosive environments.

Why Aluminum Bronze Is Tricky

Aluminum bronze forms a tenacious aluminum oxide layer (just like aluminum does) that must be removed before welding. Unlike aluminum, you don’t use AC to clean it; the oxide layer is thin enough to manage with mechanical cleaning and flux or gas coverage.

The bigger issue is hot cracking. Aluminum bronze alloys with more than 9% aluminum have a two-phase microstructure (alpha + beta or alpha + kappa) that’s susceptible to cracking during solidification. Tight heat input control and proper filler selection are the countermeasures.

Filler Selection

Welding Procedure

TIG on DCEN with argon or argon-helium. Preheat 200-400F for sections over 1/2 inch. Interpass temperature maximum 350F. Clean the oxide layer immediately before welding with a stainless steel brush and acetone wipe.

Aluminum bronze has good thermal conductivity (lower than pure copper but higher than steel), so preheat is necessary for heavy castings. After welding, cool slowly to prevent cracking. Don’t quench.

For nickel-aluminum bronze (NAB) propeller and marine component repair, the welding procedure typically requires a WPS qualified per AWS D3.7 or classification society rules. Post-weld stress relief at 1100-1200F may be specified for propeller repairs.

Welding Brass (Cu-Zn Alloys)

Yellow brass (30-40% zinc) is better brazed than welded because the zinc vaporizes during fusion welding, creating porosity and toxic fumes. If you must fusion weld brass, ERCuSi-A is the filler of choice. The silicon bronze deposit doesn’t need zinc, so the loss of zinc from the base metal doesn’t affect the weld chemistry.

Red brass (15% zinc) welds more easily because there’s less zinc to vaporize. ERCuSi-A still works, or you can use ERCu for a closer color match.

Fume management is critical on all brass welding. Zinc fumes cause metal fume fever. See the brazing brass fittings guide for detailed safety information.

Tips for minimizing zinc loss on brass:

• Use the lowest heat input that produces good fusion
• Move fast; don’t linger
• Push the torch to keep shielding gas coverage over the hot zone
• Use helium-free shielding (100% argon) to keep arc temperature lower
• Consider MIG brazing with ERCuSi-A for thinner brass

Quick Filler Selection Summary

Post-Weld Finishing

Bronze and brass welds often serve decorative or visible functions where appearance matters. Post-weld finishing options:

• Wire brush with a stainless steel brush for a satin finish. Brush in one direction for a consistent grain pattern.
• Grinding and polishing with progressively finer grits (80, 120, 220, 400) followed by buffing compound for a mirror finish on silicon bronze sculpture and hardware.
• Patina application on bronze sculpture and architectural work. Chemical patinas (liver of sulfur, ferric nitrate, cupric sulfate) create controlled color variations from brown to green to black.
• Clear coat to preserve the polished or natural bronze color. Lacquer or wax prevents oxidation and tarnishing.

Silicon bronze welds polish beautifully and develop a warm golden patina over time. Phosphor bronze is slightly harder to polish but takes a good finish. Aluminum bronze polishes to a pale gold color that’s different from silicon bronze.

For pure copper welding procedures (DHP, OFHC), see the deoxidized copper filler guide. For CuNi marine pipe, see the copper-nickel pipe welding guide. For brass brazing procedures and fume safety details, check the brazing brass fittings article.

Back to the copper and brass welding category.