Skip to content
Why Is Copper Difficult to Weld and How to Do It?
Copper is a highly versatile metal renowned for its exceptional electrical and thermal conductivity, malleability, and natural antimicrobial properties. Due to its benefits, it is used across building construction, electrical infrastructure, and clean technology.
Since it is so widespread, you will need to weld copper from time to time. The most common copper welding applications include joining pipes and components used in plumbing, HVAC, electronics, and automotive industries.
But for many welders, especially those less experienced, welding copper can be challenging. That's why we decided to answer the questions: why is copper difficult to weld, and help you understand how to do it.
TIG Welding on Copper Pipe
Photo by @sethburpee (TikTok)
Why Is Copper so Valuable?
Copper is considered the backbone of modern civilization due to its unmatched physical properties. People often call it "red gold", and we can find it in almost all technology and infrastructure.
Copper Rods for Modern Industry
What makes copper highly valuable across nearly all industries worldwide is its unique set of properties. The crucial properties that make copper so invaluable include:
-
High conductivity: Copper is the best electrical and heat conductor among the non-precious metals. Its conductivity is critical in wiring, motors, transformers, and electronics.
-
High malleability: Copper has a high ability to deform without breaking (malleability). You can easily stretch it into wires or hammer it into sheets without breaking, making it crucial in manufacturing.
-
Corrosion resistance: Copper does not rust, making it the industry standard for plumbing pipes and roofing.
-
Highly sanitary: Copper has naturally antimicrobial properties. It can actively kill or inactivate up to 99.9% of harmful bacteria, which is why it remains a plumbing standard.
-
Highly recyclable: You can repeatedly recycle copper without losing its physical or chemical properties.
Core Strengths of Copper
All of the properties mentioned make copper an essential commodity that is continuously traded and tracked globally. For you, as a welder, it means you will eventually need to weld copper pieces in your everyday work.
Although copper is weldable, many welders consider it challenging to weld. Less experienced welders who lack an understanding of copper's properties can struggle, so let's explain everything.
TIG Welding a Copper Mug
Source: https://www.youtube.com/watch?v=2bsyDYscR8I
The Most Common Types of Copper and Copper Alloys
As with many metals, manufacturers use copper in both pure form and in alloys. Using alloying elements alters certain properties of the base copper, such as strength, machinability, and corrosion resistance.
Pure Copper and Copper Alloys
However, adding alloying elements can also affect weldability (improving it or making it impossible to weld). Understanding the composition of the metal you are welding is crucial, so below is a quick chart of the most commonly used types of copper and copper alloys:
| Type | Composition | Properties | Weldability |
|---|---|---|---|
| Pure Copper | At least 99.3% copper | High conductivity, moderate strength, and corrosion resistance | Difficult to weld due to high conductivity |
| Free-Machining Copper | High copper with low additions of sulfur or tellurium | High conductivity with improved machinability | Impossible to weld due to cracking |
| Precipitation-Hardenable Copper Alloys | High copper with low additions of beryllium, chromium, or zirconium | Improved mechanical properties of copper | Welding can degrade the mechanical properties of joints |
| Brass (Copper-Zinc) Alloys | Low zinc: up to 20% zinc High zinc: 30–40% zinc |
Improved strength, hardness, and ductility, with reduced melting temperature, density, and electrical and thermal conductivity | Burning zinc creates toxic fumes and can create porosity |
| Phosphor-Bronze (Copper-Tin) | 1–10% tin | High strength and spring qualities | Susceptible to hot cracking in the stressed condition |
| Aluminum-Bronze (Copper-Aluminum) | 3–15% aluminum with additions of iron, nickel, and manganese | High strength and superior wear resistance | Highly weldable |
| Silicon-Bronze (Copper-Silicon) | Low-silicon bronze: 1.5% Si High-silicon bronze: 3% Si |
High strength and excellent corrosion resistance | Good weldability |
| Cupronickel Alloys (Copper-Nickel) | 10–30% Ni | Moderate strength with improved oxidation and corrosion resistance | Highly weldable |
Why Is Copper Difficult to Weld?
The favorable properties of copper that make it widely used can also affect its weldability, making it notoriously challenging to weld. In addition, there are dozens of copper alloys, each with distinct properties and requiring different approaches to welding.
Welding Copper Nuts
Photo by @ninalv01 (TikTok)
The crucial factors that make copper so challenging to weld include:
-
High thermal conductivity: Copper quickly dissipates heat from the joint, making it hard to achieve proper penetration without overheating.
-
Low melting point: Copper has a lower melting point than steel, but not as low as aluminum. Overheating can easily cause burn-through.
-
High coefficient of thermal expansion: Heating and cooling cause expansion and contraction, which can distort thin copper in particular.
-
Reactive when heated: Copper reacts vigorously with oxygen and other atmospheric gases at high temperatures. Reactivity can cause porosity or oxidation.
-
Releasing toxic fumes and steam: Burning alloying elements such as zinc, cadmium, arsenic, or chromium produces toxic fumes. Oxygen in copper reacts with hydrogen, producing steam that may cause severe microfissuring.
-
Highly reflective: Laser-welding copper without specialized beams can be highly inefficient.
Understanding these will help you prepare and use the right approach. That's why we'll explain each in detail.
Copper Welding Challenges
How Does the High Thermal Conductivity Affect Copper Weldability?
Copper conducts heat roughly 15 times better than steel. While conductivity can be advantageous in many applications, it can make copper, especially pure copper, notoriously difficult to weld.
TIG Welding on Pure Copper
Source: https://www.youtube.com/watch?v=gSHM7eVCTvg&t
The high thermal conductivity of copper helps dissipate heat away from the joint. When welding, you can have a hard time reaching the required heat and maintaining the puddle.
In addition, copper has a lower melting point than steel. Copper melts at 1084°C (1983°F), so that is the temperature you're aiming for. But, since copper acts as a heat sink, it can quickly dissipate the heat from the joint, causing the puddle to solidify.
To deal with copper's high conductivity, most welders preheat the pieces. Raising the temperature of the copper pieces before welding helps you maintain a weld puddle.
Heating Copper Pipe for Welding
Source: https://www.youtube.com/watch?v=raEldIPChdA
Thermal Expansion Causes Distortion
Metals change size when heated or cooled, and the magnitude of this change is measured by the coefficient of thermal expansion (CTE). Copper has a CTE of 17 x10⁻⁶/K, which is considered high.
When exposed to the high heat of an arc, copper can expand. But because it acts as a heat sink, copper can also cool quickly, leading to structural deformation, called distortion, or warping.
To prevent distortion when welding copper, welders clamp the pieces to reduce the deformation. Preheating also helps by reducing thermal stress and slowing the cooling rate.
Clamping Copper Welding
Photo by @heathens.garage3(TikTok)
Reactivity of Copper
While copper is originally highly sanitary and safe, it becomes reactive when heated by a welding arc. Heated copper reacts aggressively with atmospheric gases, leading to porosity and oxidation.
Aluminum bronze is particularly fond of oxidation. But silicon bronze also tends to develop mill scale.
Porosity appears as small bubbles in the joint, caused by atmospheric contamination and by gases that escape from it. Although molten copper is corrosion-resistant, it can react with oxygen, leading to oxidation.
Porosity in Copper Welding
Photo by @kraz999(TikTok)
Copper oxidation creates brittle oxide layers and traps gases in the molten pool. This occurrence leads to severe weld porosity and brittle layers, so shielding the welds is crucial.
Reactivity solutions are simple. You should thoroughly clean the joints and copper pieces, and use the proper shielding gas to protect the welds.
Cleaning Copper Before Welding
Photo by @dr.weldz(TikTok)
Toxic Fumes Caused By Copper Alloys
Adding alloying elements to pure copper improves mechanical properties and affects weldability, but it can also have downsides. Burning alloying elements such as zinc, cadmium, arsenic, or chromium forms toxic fumes that can affect your health.
As noted, copper alloys, such as brass or precipitation-hardenable copper alloys, contain elements that can cause severe health issues. So, you need to be extra careful when welding these.
The good practice is to follow OSHA rules for controlling hazardous welding fumes. These sheets contain useful information and recommended safety practices for welding potentially hazardous copper alloys.
Respiratory Protection for Copper Welding
Source: https://www.youtube.com/shorts/lbCSIwCGddo
How Reflectivity Affects Laser Welding Copper?
Laser Beam Welding (LBW) is a modern welding method that uses a focused laser beam to melt and fuse the parts. A laser beam is fundamentally an amplified light, and when it hits a reflective surface, it bounces.
Laser Welding on Copper
Source: https://www.youtube.com/shorts/PhLu5iivuzA
Copper reflects roughly 90% of visible, IR, and UV wavelengths, making laser welding copper highly challenging. Most of the beam's energy is reflected from the surface, while a fraction of the heat enters the joint.
Therefore, attempting to laser-weld copper at these wavelengths results in significant energy loss. You would need powerful lasers to weld thin pieces, which can be highly inefficient.
However, unlike most metals, copper reflects only some wavelengths. You can efficiently laser-weld copper using blue and green wavelengths. Copper efficiently absorbs blue and green laser light, making it a suitable solution.
Pure Copper Absorptivity at Different Wavelengths
Source: https://www.researchgate.net/figure/Absorptivity-of-pure-copper-at-different-wavelengths_fig4_374167351
How to Weld Copper: Quick and Comprehensive Guide
Understanding the challenges is the first step in knowing how to weld copper. Knowledge helps you prepare and adjust to the challenges of copper welding, but you will also need some practical tips.
To successfully weld copper, you will need to:
-
Choose the suitable welding process (MIG, TIG, or Stick).
-
Match the filler to the copper or alloy you are welding.
-
Clean and prepare the pieces.
-
Preheat the metal.
-
Apply the right welding technique.
-
Post-weld treatment.
-
Consider alternatives.
Let's further explain each. If you wish to learn more, check out our detailed guide to welding copper.
TIG Welding a Bespoke Copper Sink
Source: https://www.youtube.com/shorts/Axd54FuBTcI
What Is the Best Welding Method for Copper?
Most welders prefer to braze or solder copper, but you can also arc-weld the pieces using TIG, MIG, or even Stick welding. The choice will mostly depend on the copper parts and applications, and here are the common uses:
TIG welding copper: We recommend using GTAW (TIG) to join thin to medium copper pieces. TIG produces clean, high-quality welds and provides outstanding heat control, which is crucial in copper welding. With all parameters optimized and high-inert-gas shielding (100% helium or 75/25% helium/argon), TIG can produce highly aesthetic welds with minimal rework. However, remember that TIG is slow, and it requires a lot of skill to master.
Crafting a Copper Rose with TIG Welding
Source: https://www.youtube.com/watch?v=zf2N-y2LQpE&t
MIG welding copper: MIG welding is better suited for quick welds on medium to thick copper. Due to lower heat control, TIG takes the edge on thin pieces, but MIG is significantly easier to use. In some automotive applications, you will MIG-braze copper using silicone bronze MIG wire that melts without melting the base metal. High-purity inert shielding is a must, while MIG pulse machines, such as the YesWelder DP200, can help control the puddle.
Firstess DP200 Multi-Process DualPulse™ MIG Welder
Stick welding copper: We recommend Stick welding primarily for outdoor work and when no other copper welding options are available. With self-shielded electrodes, Stick is perfect for outdoor work. However, Stick is messy, and it lacks heat control. As a result, you can hardly control the puddle, leading to a lot of spatter or burn-through.
Stick Welding on Copper
Source: https://www.youtube.com/watch?v=QZUfpAQ7zAM
Matching the Filler With Copper Alloy
Regardless of the welding method, you must match the filler metal composition to the copper or copper alloy being welded. Composition matching is essential for anyone trying to achieve strong copper welds.
Here are the most commonly used copper fillers:
-
ERCu (Pure copper): Fillers with 98% copper composition, designed for pure copper welding. Heavily deoxidized to reduce the risk of steam formation.
-
ERCuSi (Silicon bronze): Copper filler alloyed with silicon, ideal for welding brass (copper-zinc) alloys, and dissimilar metals.
-
ERCuAl (Aluminum bronze): Copper-aluminum fillers with high strength, wear, and corrosion resistance.
-
ERCuSn (Phosphor bronze): Copper-tin filler used primarily for joining phosphor bronzes and brasses.
-
ERCuNi (Copper nickel): Approximately 70% copper and 30% nickel. Designed specifically for welding copper-nickel alloys and widely used in marine environments.
In addition to composition, don't forget to match the filler thickness to the base metal. Fillers come in the form of TIG rods, MIG wires, Stick electrodes, or brazing and soldering rods; use the one appropriate for your application.
Pure Copper TIG Welding at 180A AC
Source: https://www.youtube.com/watch?v=gSHM7eVCTvg
Cleaning and Preparing Copper Before Welding
As noted, heated copper reacts with atmospheric gases and contamination. Therefore, you will need to thoroughly clean the pieces before welding to reduce the risk of porosity or oxidation.
Before welding, make sure you remove oil, paint, grease, dust, or other contaminants from the surface. If you are using tools to do it, make sure they are designed for copper, so they don't contaminate or damage the surface.
Brushing Copper Before Welding
Source: https://www.youtube.com/watch?v=gSHM7eVCTvg
Keep in mind that copper alloys, such as copper-aluminum, copper-nickel, or copper-beryllium, create a surface oxide. As with aluminum welding, these oxides have much higher melting points than the base metal beneath them. So, you will have to remove them before welding to avoid burning through metal.
Don't forget to fit up the pieces and clamp them if needed. Joint fit-up with an even gap is essential for even results. Clamp thin copper if there is a risk of distortion.
Clamping Thin Copper for Welding
Source: https://www.youtube.com/watch?v=lFe1EbcHpF0
Do You Need to Preheat Copper Before Welding?
To deal with copper's high thermal conductivity, you should preheat the surfaces before welding. Preheating the surfaces to 500-750°F stops the surrounding metal from acting like a heatsink, allowing you to establish a proper welding puddle.
Raising the temperature of the copper pieces also reduces the thermal stress. The pieces will cool more slowly, reducing the risk of distortion or cracking.
Thermal Stress in Welding
The optimal preheat temperature depends primarily on the copper thickness. The thicker the base metal is, the higher the temperature you'll need to address thermal conductivity.
Alloys with high conductivity and pure copper are prime candidates for preheating. However, some alloys, such as aluminum-bronze, phosphor-bronze, and copper-nickel alloys, usually don't require preheating due to their properties.
Preheating Copper Before Welding
Photo by @aprenderplomeriaconmigo(TikTok)
Using the Right Welding Technique
Consistency is crucial when welding copper. Since the copper puddle gets very fluid when melted, you will need perfect control.
Failing to control the puddle will cause uneven beads, as the copper solidifies quickly. You'll have to work fast, but make sure you get proper penetration and fusion across the bead.
When welding thin pieces, adjust the technique to avoid distortion or burn-through. Consider using stitch welds and clamping the thin pieces to prevent them from warping.
Clamping Thin Copper to Prevent Warping
Source: https://www.youtube.com/watch?v=8JmQjc4cYmY&t
Post-Weld Copper Treatment
Clean and visually inspect copper welds after welding. Remove any spatter and residuals using a wire brush or sanding pad. If there are inconsistencies or defects, like cracks, incomplete penetration, or porosity, grind out the defective area and re-weld.
Pure copper and copper-nickel alloys usually do not require post-weld heat treatment (PWHT). However, some alloys, such as precipitation-hardened and high-zinc alloys, require a stress-relief bake or post-weld aging.
TIG Welding Copper-Nickel Pipe
Source: https://www.youtube.com/watch?v=NBS7BF_iE_k
Copper Welding Alternatives
Besides arc welding, there are many ways to join copper parts. The most common copper welding alternatives include:
-
Brazing/soldering copper: Joining copper at much lower temperatures than with welding. In fact, the base copper never melts; only the filler rods do. Capillary attraction pulls the molten filler inside a joint, creating fusion. These are very common copper joining methods used in plumbing, HVAC/refrigeration lines, and medical gas piping.
Heating and Soldering Copper Pipe
Source: https://www.youtube.com/watch?v=JyVbjDsric4
-
Resistance spot welding copper: Although notoriously difficult, it is ideal for high-volume production applications. It produces spot-like welds without filler, but it has equipment and joint configuration limitations.
-
Laser welding copper: A fast and precise method, with excellent heat control. It produces narrow, clean, high-quality welds, but it requires specialized equipment to handle copper's reflectivity.
-
Oxyacetylene welding copper: A traditional, cheap, and easy method for copper joining. Equipment is affordable and portable, but it requires very high operator skill, and it is slower than other methods.
Oxy-Acetylene Welding Copper Pipe
Source: https://www.youtube.com/watch?v=aMNIWw4VfYA
Final Thoughts
Copper is an amazing metal widely used for its valuable properties. However, its high thermal conductivity and reactivity make it notoriously difficult to weld.
Understanding the challenges is the first step in successful welding. Knowledge helps you understand that you need the right process, filler, and preparation for the job.
Once you master everything, you can weld copper and various copper alloys with ease.
TIG Brazing for Copper Frame Repair
Source: https://www.youtube.com/watch?v=EOeL7XC-eZg
🧐 Why is Copper Difficult to Weld and How to Do it? FAQ
1. Is copper difficult to weld?
Yes. Copper is difficult to weld because it conducts heat very quickly, reacts with oxygen when heated, and can distort or burn through if the heat is not controlled properly.
2. What is the best welding method for copper?
TIG welding is usually the best choice for thin to medium copper because it gives better heat control and cleaner welds. MIG welding can work better for thicker copper or faster production work.
3. Do you need to preheat copper before welding?
In many cases, yes. Preheating helps reduce copper’s heat-sink effect, makes it easier to form a weld puddle, and lowers the risk of cracking or distortion.
4. Can you weld copper with a MIG welder?
Yes, you can MIG weld copper, especially medium to thick copper parts. You need the right filler wire, proper shielding gas, and enough machine output to overcome copper’s high thermal conductivity.
5. What filler metal should be used for copper welding?
The filler should match the copper or copper alloy being welded. Common options include ERCu for pure copper, ERCuSi for silicon bronze, ERCuAl for aluminum bronze, ERCuSn for phosphor bronze, and ERCuNi for copper-nickel alloys.
6. Why does copper welding cause porosity?
Porosity can happen when oxygen, moisture, oil, dirt, or other contaminants enter the molten weld pool. Cleaning the copper surface and using proper shielding gas help reduce this problem.
7. What are the alternatives to welding copper?
Common alternatives include brazing, soldering, resistance spot welding, laser welding, and oxyacetylene welding. Brazing and soldering are especially common for plumbing, HVAC, and refrigeration work because they join copper without melting the base metal.
👏 You may be interested in the following:
- How To Weld Copper - MIG, TIG, And Stick Welding Copper Overview
- How To TIG Weld
- How To TIG Weld Different Thickness Metals
Leave a comment