How to Weld Deoxidized Copper with ERCu: Complete TIG and MIG Welding Guide

Welding copper is not the same as welding carbon steel, stainless steel, or aluminum. Copper moves heat extremely fast, reacts differently under the arc, and requires careful control of preheat, filler metal, shielding gas, and travel speed. For deoxidized copper, one of the most commonly used filler metals is ERCu, an AWS A5.7 copper filler metal designed for welding high-copper base metals and copper alloys.

ERCu is often used in TIG and MIG welding applications where good electrical conductivity, copper color match, and sound weld deposits are required. It is widely associated with deoxidized copper welding, copper pipe fabrication, copper tank repair, electrical components, bus bars, copper fittings, and copper overlay work. AWS A5.7 covers copper and copper-alloy bare welding rods and electrodes for inert-gas welding processes, and ERCu is one of the classifications used for copper filler metals. 

This guide explains how to weld deoxidized copper with ERCu, including filler selection, TIG and MIG setup, preheat, shielding gas, welding technique, and common defect prevention.

What Is ERCu Welding Wire?

ERCu is a deoxidized copper filler metal used for welding copper and selected copper-related applications. It typically contains a high percentage of copper with small additions such as phosphorus and silicon, which act as deoxidizers and help produce cleaner weld deposits. Some ERCu filler metals may also contain small amounts of tin, manganese, silver, or other controlled elements depending on the specification and manufacturer. 

In practical welding, ERCu is commonly supplied as:

• TIG rods for GTAW welding

• MIG wire for GMAW welding

• Bare copper alloy filler metal under AWS A5.7 classification

ERCu is mainly selected when the base material is deoxidized copper or high-copper material and the weld needs to maintain copper-like color, conductivity, and corrosion resistance.

Why Deoxidized Copper Is Easier to Weld Than ETP Copper

Not all copper grades weld the same way. Deoxidized copper grades are generally more weldable because oxygen has been reduced or removed during processing. This matters because oxygen-containing copper can create porosity, cracking, or embrittlement problems when exposed to welding heat and hydrogen.

Deoxidized copper grades, such as DHP and DLP copper, are often preferred for fusion welding because they respond better to proper preheat, ERCu filler metal, and argon or argon-helium shielding gas. In contrast, electrolytic tough pitch copper can be more difficult to weld reliably because of its oxygen content.

For this reason, before welding copper, always confirm the base metal grade. If the material is deoxidized copper, ERCu is usually a strong filler metal choice. If the material is oxygen-bearing copper, extra care is required, and in some applications another joining process may be more appropriate.

When Should You Use ERCu?

ERCu is suitable for many copper welding and repair applications. Common uses include welding deoxidized copper, joining copper pipes, repairing copper tanks, welding copper fittings, overlaying steel surfaces with copper, and working on electrical or thermal-conductive components. Some suppliers also describe ERCu as usable for copper-to-galvanized steel or copper-to-mild steel joints where high joint strength is not the main requirement. 

Typical ERCu applications include:

• Deoxidized copper pipe welding

• Copper tank fabrication and repair

• Copper fittings and connectors

• Electrical bus bars and conductive parts

• Copper overlay on steel

• Copper casting repair

• Heat exchanger components

• Non-critical copper-to-steel joining

However, ERCu should not be treated as a universal copper alloy filler. If the joint requires high mechanical strength, wear resistance, or compatibility with bronze, brass, nickel-copper, or aluminum bronze, another filler metal may be better.

The Most Important Rule: Preheat the Copper

The biggest mistake in copper welding is using too little heat. Copper has very high thermal conductivity, which means it pulls heat away from the weld zone quickly. Without enough preheat, the arc may look active on the surface but still fail to create proper fusion at the root or sidewalls.

Preheat is especially important for thick copper sections. Some technical guidance lists suitable preheat ranges for copper welding from about 400°F to 1000°F, or 205°C to 540°C, depending on material thickness, joint design, and welding process.

For thin copper, light preheat may be enough. For thick copper, heavy preheat is often essential. The goal is not simply to make the metal hot, but to slow heat loss so the weld pool can form and fuse correctly.

General Preheat Guidance

Use these ranges as practical starting points:

Always follow the project specification, material data sheet, or welding procedure when one is available.

TIG Welding Deoxidized Copper with ERCu

TIG welding is often preferred for precision copper work because it gives better control of the arc, filler addition, and weld pool. When welding deoxidized copper with ERCu TIG rod, the most important factors are clean base metal, adequate preheat, correct shielding gas, and steady travel speed.

Recommended TIG Setup

For TIG welding with ERCu:

• Process: GTAW / TIG

• Filler metal: ERCu TIG rod

• Polarity: DCEN is commonly used for TIG welding copper filler applications

• Shielding gas: Argon or argon-helium mixture

• Tungsten: Use a properly sized tungsten for the amperage

• Technique: Maintain a short arc length and controlled filler addition

ERCu rods and wires are commonly associated with TIG and MIG welding of deoxidized copper, with argon or argon-helium shielding gases used depending on heat input needs. 

TIG Welding Technique

Start by cleaning the copper surface thoroughly. Remove oxides, grease, oil, paint, plating, and contamination. Copper oxides can affect weld quality, and surface contamination can create porosity.

After cleaning, preheat the workpiece. For small parts, localized heating may be enough. For heavier copper, preheat a wider area around the joint so heat does not disappear from the weld zone too quickly.

Once welding begins, keep the arc tight and focused. Add ERCu filler smoothly into the leading edge of the weld pool. Avoid long arc length, excessive weaving, or slow travel that overheats the surface without improving fusion. Copper needs heat, but uncontrolled heat can make the weld pool too fluid and difficult to manage.

MIG Welding Deoxidized Copper with ERCu

MIG welding with ERCu wire is useful for production work, longer seams, thicker sections, or applications where travel speed matters. Compared with TIG, MIG can deposit filler faster, but it also requires more attention to wire feeding, shielding gas coverage, and heat input.

Recommended MIG Setup

For MIG welding with ERCu:

• Process: GMAW / MIG

• Filler metal: ERCu MIG wire

• Polarity: DCEP is commonly used for GMAW

• Transfer mode: Spray transfer is often preferred when suitable

• Shielding gas: Argon or argon-helium mixture

• Joint preparation: Clean, bright copper surface

• Preheat: Required for many copper sections, especially thick parts

Some ERCu product guidance describes use with GMAW using DCEP and spray transfer, with argon or argon-helium shielding gas. 

MIG Welding Technique

Copper MIG welding should be performed with enough heat input to maintain fusion. If the weld bead sits on top of the copper without tying into the sidewalls, the part is probably too cold, the travel speed is too fast, or the voltage and amperage are too low.

Use a push angle where appropriate, maintain consistent stick-out, and avoid erratic travel. If the weld pool becomes unstable or the wire stubs into the workpiece, check wire feed speed, voltage, contact tip condition, liner condition, and ground connection.

Shielding Gas for ERCu Welding

Shielding gas has a major effect on copper welding. Pure argon is commonly used for TIG welding and light to medium copper work. For thicker copper sections, an argon-helium blend can help increase heat input because helium produces a hotter arc.

Argon

Argon is stable, easy to control, and widely available. It is often a good starting point for TIG welding thinner copper sections.

Argon-Helium Mixture

Argon-helium mixtures are useful when more heat is needed. This can help when welding thicker copper, large parts, or joints that cool too quickly.

The shielding gas should provide full coverage of the weld pool. Poor gas coverage can lead to oxidation, contamination, and porosity.

Joint Preparation Before Welding

Good copper welding starts before the arc is struck. ERCu filler metal cannot compensate for dirty, oxidized, or poorly fitted joints.

Before welding:

1. Mechanically clean the joint area.

2. Remove oxide layers with a stainless brush dedicated to copper.

3. Degrease the surface with a suitable cleaner.

4. Make sure the joint fit-up is consistent.

5. Use proper beveling for thick sections.

6. Preheat evenly around the weld zone.

For thicker copper, joint design matters. A narrow joint with poor access may not allow enough heat and filler metal to reach the root. A proper groove angle helps ensure fusion and reduces the risk of trapped defects.

Common Problems When Welding Copper with ERCu

1. Lack of Fusion

Lack of fusion is one of the most common copper welding defects. It usually happens when the copper absorbs heat faster than the arc can supply it.

How to prevent it:

• Increase preheat

• Use higher heat input

• Reduce travel speed

• Use argon-helium shielding gas for thicker parts

• Improve joint preparation

2. Porosity

Porosity may result from contamination, moisture, poor shielding gas coverage, or oxide layers.

How to prevent it:

• Clean the copper thoroughly

• Use dry, clean filler metal

• Check shielding gas flow

• Avoid drafts around the weld area

• Remove oxides before welding

3. Excessive Fluidity

Copper weld pools can become very fluid, especially when overheated.

How to prevent it:

• Control travel speed

• Avoid excessive weaving

• Use correct amperage and voltage

• Maintain a stable arc length

4. Poor Bead Appearance

Poor bead appearance can come from inconsistent travel, unstable arc length, poor filler addition, or inadequate preheat.

How to prevent it:

• Keep a steady torch angle

• Maintain consistent filler feeding

• Use a clean joint

• Keep the arc focused

ERCu vs Other Copper Filler Metals

ERCu is not the only copper alloy filler metal. For example, ERCuSi-A is often used for silicon bronze applications and certain copper-to-steel or copper-zinc work. Aluminum bronze, nickel-copper, and tin bronze fillers may be better for other base metals or mechanical requirements.

Choose ERCu when the goal is to weld deoxidized copper or high-copper base metal while maintaining a copper-like deposit. Choose another filler when the job requires higher strength, different corrosion behavior, or compatibility with a different copper alloy family.

Best Practices for Welding Deoxidized Copper with ERCu

For the best results:

• Confirm that the base metal is deoxidized copper.

• Use ERCu filler metal that meets the required AWS A5.7 classification.

• Clean the joint until the copper is bright and free of oxide.

• Preheat the workpiece, especially for thick copper.

• Use argon for general welding and argon-helium when more heat is needed.

• Use TIG for precision work and MIG for higher deposition or production welding.

• Keep a short, stable arc.

• Avoid excessive weaving.

• Let the weld cool under controlled conditions.

• Inspect for porosity, fusion, and bead consistency.

FAQ: Welding Deoxidized Copper with ERCu

Is ERCu good for welding deoxidized copper?

Yes. ERCu is commonly used for welding deoxidized copper and high-copper base metals. It is designed to produce copper-like weld deposits with good conductivity and color match when used correctly.

Can ERCu be used for TIG welding?

Yes. ERCu is available as TIG rod and is commonly used for GTAW welding of deoxidized copper. Proper preheat and shielding gas are essential.

Can ERCu be used for MIG welding?

Yes. ERCu is also available as MIG wire for GMAW welding. MIG welding is often useful for longer welds, thicker copper, or production applications.

What shielding gas should be used with ERCu?

Argon is commonly used for many TIG and MIG copper welding applications. Argon-helium mixtures can be helpful for thicker copper because they increase heat input.

Does copper need preheat before welding?

In many cases, yes. Copper conducts heat very quickly, so preheat is often required to achieve proper fusion. Thick copper sections usually need more preheat than thin parts.

Can ERCu weld copper to steel?

ERCu may be used for some copper-to-mild steel or copper-to-galvanized steel applications where high joint strength is not required. For structural or high-strength joints, consult a qualified welding engineer or welding procedure.

Conclusion

Welding deoxidized copper with ERCu requires more than simply choosing the right filler metal. The key to a sound weld is controlling heat. Because copper removes heat from the weld zone so quickly, proper preheat, clean joint preparation, suitable shielding gas, and correct TIG or MIG technique are essential.

ERCu is a strong choice for welding deoxidized copper, copper fittings, copper tanks, conductive components, and selected copper overlay applications. When used with the right welding procedure, it can produce clean, conductive, copper-colored weld deposits with reliable fusion and good appearance.

For best results, always match the ERCu filler metal to the base material, confirm the required AWS classification, and develop welding parameters based on copper thickness, joint design, and service requirements.