The Weldability of Copper and its Alloys

Copper and its alloys of Brass and Bronze are widely used. Because of their excellent corrosion resistance and ability to be strengthened, they are extremely versatile and used in many different environments. Also, Copper possesses exceptional electrical and thermal conductivity. 

Bronzes are mostly copper with tin as main alloying element, while brass has zinc as the alloying element. But more recently chemists and metallurgists have preferred to call this family of metals Copper and Copper alloys instead of copper, brass, and bronze. Although these terms are old and well known, there is no distinct line between where one metal ends and the other begins.

When welding copper and its alloys, you want to maintain the desirable corrosion resistance, mechanical properties, and to avoid introducing defects to the welds. Therefore, the first step to success is familiarizing yourself with the various alloys, their properties, and the considerations in choosing filler metal for each.

Copper Alloys

Copper-based alloys are categorized into families based on their chemical makeup. UNS assigns a number designation based on this. These numbers range from 10000 to 99999. Also these alloys often have a C in their name, for example, C11000. Wrought metals fall between 10000 and 7999. Cast metals are between 80000 and 99999.

These numbers are often stylized by dropping the last two zeroes off. This makes them easier to read and take up less space in writing. Online Metals follows this convention. As an example, we have Copper C10100 listed as Copper 101. For consistency’s sake, the rest of this article will also follow this format.

Wrought 101 to 130 | Cast: 801 to 812

These alloys are functionally pure copper. Because of this they are soft and weld fair. Oxygen-free coppers, such as 101, are easily welded. However, oxygen-bearing copper should not be welded as high temperatures seriously reduce the metal’s strength and ductility.

Fusion welding is not recommended for free-machining copper because they are prone to cracking. Nor is it suggested for precipitation-hardenable copper alloys. High temperatures will weaken the heat affected zone.

Commonly weldable coppers are typically paired with Cu 1897 and Cu 1898 filler metal.

Brass Alloys

Wrought: 205 to 28580 | Cast: 833 to 858

All brasses are weldable except the alloys containing lead. However, the lower the zinc content, the more easily welded it is. Low-zinc brasses with less than 20% zinc have good weldability. By comparison, high-zinc brasses with over 20%, have only fair weldability. Lastly, cast brasses are only marginally weldable.

The recommended fillers for low-zinc brasses are Cu 6328 and Cu 6560.

Wrought: 404 to 486 | Cast: 833 to 848 “Tin Brass”

Unleaded tin brass alloys have fair weldability. However, they are prone to hot cracking and forming oxide films on the weld pool. Therefore, high welding heat inputs, high preheat, and slow cooling rates should be avoided. Leaded tin brass alloys are generally considered unweldable.

Bronze Alloys

Wrought: 501 to 524 | Cast: 902 to 917 “Phosphor Bronze”

Unleaded Phosphor Bronze alloys have fair weldbility. But, under stressed conditions they are subject to hot cracking. So like Tin Brass, high heat inputs, high preheat, and slow cooling rates should be avoided. You can carefully weld leaded Phosphor Bronze using SMAW. Keep in mind that weldability of copper alloys decreases as lead content increases.

The most frequently used phosphor bronze alloy is best suited to Cu 5180 filler metal.

Wrought: 608 to 64210 | Cast: 952 to 959 “Aluminum Bronze”

These metals have low electrical and thermal conductivity, which improves weldability. However, is it crucial to remove all aluminum oxide on the surface of the material before welding.

For Aluminum Bronze alloys with less than 7.8% aluminum, Cu 6240 and Cu 6100 are ideal filler metals. While alloys with aluminum content greater than 7.8% are better suited with Cu 6180 and Cu 6100. 642 Aluminum Silicon Bronze is best paired with Cu 6100.

Wrought: 647 to 661 | Cast: 870 to 87999 “Silicon Bronze”

These are arguably the easiest of all the bronzes to weld. Unlike many other copper alloys, their thermal conductivity is relatively low and you can use high welding speeds. Silicon Bronze alloys should be stress relieved or annealed prior to welding. Next, they should be slowly heated to the desired temperature. Then rapidly cooled through the critical temperature range.

Silicon bronzes are readily weldable with Cu 6560 filler metal.

Wrought: 701 to 72950 | Cast: 962 to 969 “Copper Nickel”

These alloys are commonly used in welded fabrication projects. Phosphorus and sulfur levels must be less than 0.02% to ensure good welds. Most Copper Nickel alloys do not contain a deoxidizer. Therefore, fusion welding requires the addition of a deoxodized filler metal. This lowers the risk of porosity in the weld.

For copper nickel with a 10% nickel composition, Cu 7071 or Cu 7158 fillers are recommended. For copper nickel with a 30% nickel composition, a Cu 7158 filler is recommended.

Nickel Silver Alloys

Nickel Silver is neither nickel nor silver. Actually, it is a brass alloy. But because people often list Nickel Silver as its own category, we are doing the same here.

Wrought: 735 to 799 | Cast: 973 to 978 “Nickel Silver”

These alloys possess a weldability similar to other brasses. Also, the weld quality decreases if lead is present. Unleaded Nickel Silver alloys are considered suitable to weld. But leaded alloys are not. Also similar to other brasses, alloys with lower zinc content have better weldability.

These low-zinc alloys are readily weldable with Cu 6328 and Cu 6560 filler metals.

Weldability of Copper, Brass and Bronze

You can connect copper and its alloys by various methods of welding, brazing and soldering. In order to help you find the right one, here’s a breakdown of the weldability ratings and fabrication properties for the most common copper, brass, and bronze alloys.

weldability of copper

weldability of copper

Common Copper Alloy Welding Defects

Because the weldability of copper alloys changes so much, it can be intimidating. Let’s explore some of the more common defects and how to avoid them.

Porosity

Copper and its alloys are most susceptible to this defect. Pure coppers, brasses, phosphor bronzes, copper nickels, and aluminum bronzes are particularly so.

In order to combat porosity in coppers, phosphor bronzes, and copper nickels, do not use autogenous welding with a matching filler. Instead, use filler wire containing deoxidants, such as aluminum, silicon, manganese, titanium, or phosphorous.

Phosphor bronzes are best paired to fillers with a high level of deoxidants.

Copper nickels are best paired with fillers containing 0.2-0.5% titanium.

Reduce the risk of porosity in brasses by using a zinc-free filler. Either a silicon bronze or an aluminum bronze filler is best suited with brasses. Additionally, higher welding speeds reduces pore size in the weld.

Aluminum bronze alloys have a strong aluminium oxide film that forms on their surface. This film gives them strong corrosion resistance. But it also causes oxide film entrapment which increases its risk of porosity. Remove the film to prevent this. Rigorously clean the material surface with wire brushes or scrapers before welding these alloys.

Lack of Fusion

Brasses with less than 20% zinc are vulnerable to fusion defects because of their high thermal conductivity. Therefore, preheat low-zinc alloys before welding.

Aluminum bronzes are also susceptible to lack of fusion due to the aforementioned aluminium oxide film. Again, it’s crucial to thoroughly clean the surface to remove this film before welding.

Hot Cracking

Coppers containing chromium or beryllium alloys, brasses, and aluminum bronzes with low aluminum content, less than 8.5%, are susceptible to hot cracking. Carefully preheat coppers with chromium/beryllium and aluminum bronzes to reduce the risk. However, brasses containing high levels of zinc don’t require preheating. Unlike their low-zinc counterparts, slow cooling rates can reduce their cracking risk.

Tips and Tricks Videos

There are lots of tips and tricks when dealing with the weldability of copper alloys. Check out some videos we liked from experts on how to weld, solder, and braze copper alloys.

If you want even more information on how to weld copper alloys, the Copper Development Association Inc. has put out an in-depth handbook on welding copper and copper alloys. We also have product guides with much more technical information about all of the metals we carry.

How to Weld Copper to Brass

Get the best results when welding copper to brass and other items that require a full penetration welds.

TIG Brazing Copper to Brass

This video covers cover how to heli-braze brass to copper. In order to join these two materials, use silicon bronze filler material. It is important to remember that you are not trying to melt the base material, which you do in traditional welding. Instead, you are creating a puddle from the filler material.

SAFETY NOTE: Working with brass generates a lot of fumes. Therefore, it is important that your work area is well-ventilated. Ideally, have ventilation and some sort of fume extraction system. It is especially important to not overheat when working with brass. Doing so creates even more fumes than usual.

Would you like to know more about the weldability of metals?

Now that you’re more informed on the weldability of copper and its alloys, explore the weldability of other materials plus get tips and tricks!