Weldability of Copper and Copper Alloys

weldability of copper alloys-header

Copper and its alloys are widely used in various environments and applications because of their excellent corrosion resistance. Of all common metals, copper also possesses the highest electrical and thermal conductivity. The best known types of copper alloys are bronze, where tin is the alloying element, and brass, in which zinc is is the alloying element.

When welding copper and its alloys, you want to maintain 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-based alloys are categorized into families based on their elemental makeup. These range from C10000 to C99999. Wrought metals fall between C10000 and C7999. Cast metals are between C80000 and C99999. Here is an overview of the of common families. This includes the weldability of copper alloys and common filler metals.

Copper – Wrought: C10100 to C13000 | Cast: C80100 to C81200

A soft metal in its pure, unalloyed state, copper welds fair. Oxygen-free coppers are readily joined by welding. Whereas oxygen-bearing copper is not recommended because high temperatures cause a major reduction in its strength and ductility.

Fusion welding is not recommended for free-machining copper because these alloys are very susceptible to cracking. Nor is it suggested for precipitation-hardenable copper alloys. High temperatures will overage the heat affected zone and lower its mechanical properties. Commonly weldable coppers are typically paired with Cu 1897 and Cu 1898 filler metal.

If you have questions about Soft-Annealed C11000 Pure Copper sheet, check out our blog post about it.

Brass – Wrought: C20500 to C28580 | Cast: C83300 to C85800

With the exception of alloys containing lead, all brasses are weldable. Those with low zinc are the most easily welded. Low-zinc brasses, less than 20% zinc, have good weldability. By comparison, high-zinc brasses, 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.

If you have more questions about it, we made a blog post for Muntz c280 brass. Check it out!

Tin Brass – Wrought: C40400 to C48600 | Cast: C83300 to C84800

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.

Phosphor Bronze – Wrought: C50100 to C52400 | Cast: C90200 to C91700

Unleaded phosphor bronze alloys have fair weldbility. But, under stressed conditions these alloys 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 these alloys decreases as lead content increases. The most frequently used phosphor bronze alloy is best suited to Cu 5180 filler metal.

Aluminum Bronze – Wrought: C60800 to C64210 | Cast: C95200 to C95900

The low electrical and thermal conductivity of aluminum bronze alloys enhances their weldability. However, is it crucial to remove all of the aluminum oxide layer 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. Aluminum silicon bronze, C64200, is best paired with Cu 6100.

Silicon Bronze – Wrought: C64700 to C66100 | Cast: C87000 to C87999

Silicon bronzes 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. These alloys should be stress relieved or annealed prior to welding, slowly heated to the desired temperature, and then rapidly cooled through the critical temperature range. Silicon bronzes are readily weldable with Cu 6560 filler metal.

Copper Nickel – Wrought: C70100 to C72950 | Cast: C96200 to C96900

Copper nickel alloys are the most commonly used in welded fabrication projects. Phosphorus and sulfur levels in these alloys is 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 – Wrought: C73500 to C79900 | Cast: C97300 to C97800

Nickel silver alloys possess a weldability similar to brass. Like brass, the weld quality decreases if lead is present. Unleaded nickel silver alloys are considered suitable to weld. Leaded nickel silver alloys are not. Also similar to brasses, alloys with lower zinc content have better weldability. These low-zinc nickel silver alloys are readily weldable with Cu 6328 and Cu 6560 filler metals.

Welding 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.

Click the charts to make them bigger

fabrication properties of copper alloys

Common Copper Alloy Welding Defects

Welding copper based alloys can be difficult. Let’s explore some of the more common defects and how to avoid them.

welding copper 2

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, autogenous welding, using a matching filler, is not recommended. Instead, a filler wire containing deoxidants, such as Al, Si, Mn, Ti, P, should be used. Phosphor bronzes are best paired with fillers with an especially high level of deoxidants. Copper nickels are best paired with fillers containing 0.2-0.5% titanium.

The risk of porosity in brasses can be reduced by using a zinc-free filler. Either a silicon bronze or an aluminum bronze filler is best suited with brasses. Additionally, higher welding speeds will help to reduce pore size in the weld.

Aluminum bronze alloys have a strong aluminium oxide film that forms on their surface. This film gives them their strong corrosion resistance, but it also gives rise to the issue of oxide film entrapment which increases its risk of porosity. To lower this risk, the film must be eliminated. Rigorous cleaning, such as scraping and wire brushing, of the material surfaces is required before welding these alloys.

LACK OF FUSION

Brasses with a low zinc content, less than 20% zinc, are susceptible to fusion defects because of their high thermal conductivity. Therefore, is it normal practice to preheat low zinc alloys before welding to deter the risk.
Aluminum bronzes are also susceptible to lack of fusion due to the tenacious aluminium oxide film that forms on its surface. Again, it’s crucial to thoroughly clean the surface of the material to remove this film before welding in order to ensure a strong fusion.

HOT CRACKING

Coppers containing chromium or beryllium alloys, brasses, and aluminum bronzes with low aluminum content, less than 8.5%, are susceptible to this weld defect. For coppers with chromium/beryllium and aluminum bronzes, the risk of hot cracking can be reduced by carefully using preheat before welding. Though 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

There are lots of tips and tricks to welding copper, brass and bronze. Check out some of the videos we found from experts on how to weld, solder, and braze copper, brass and bronze. 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.

HOW TO WELD COPPER TO BRASS

Learn about how to weld copper and how to get the best results when welding copper bus bars and other items that require a full penetration weld.

TIG BRAZING COPPER TO BRASS

This video covers cover how to heli-braze Brass to Copper. Working with brass generates a lot of fumes. It is important that your work area is well-ventilated. Or better yet, have ventilation and some sort of fume extraction system. In order to join these two materials, you will 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. It is especially important to not overheat when working with brass. Doing so creates even more fumes than usual.

LEARN MORE ABOUT THE WELDABILITY OF METALS

Explore the weldability of aluminum and stainless steel, plus get tips and tricks for welding various metals.

WELDABILTIY OF ALUMINUM HEADER

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