Which Copper Alloy Your Welding Electrode Should Be
September 25, 2026
Resistance welding electrodes are a corner of copper machining with its own classification system, and it is more useful on a drawing than an ASTM number. If you are buying electrodes or electrode blanks, this is the vocabulary.
Why there is a separate system
An electrode has to do two things that fight each other. It has to conduct current and heat away from the weld, which wants pure copper. It has to resist deformation, sticking and softening at the tip under repeated load and heat, which wants a hard, strong alloy.
Pure copper is superb at the first and useless at the second. The alloys in this family are all different compromises along that line, and the Resistance Welding Manufacturers Alliance classes are how the industry names the compromise.
Group A: copper based alloys
These get their properties from alloying, heat treatment and cold work. They are the classes you will actually machine.
Class 1. The highest conductivity in the group and the lowest strength. Copper zirconium, typically C15000. Recommended for welding aluminum and magnesium alloys, and widely used on coated and galvanized material where minimising sticking matters. Around 93 percent IACS.
Class 2. The general purpose class, and the one most electrodes are made from. Chromium copper C18200 or chromium zirconium copper C18150. Lower conductivity than Class 1, around 80 percent IACS, with higher hardness and better resistance to mushrooming. This is the default for welding steel.
Class 3. Higher strength again, lower conductivity again. Nickel beryllium copper such as C17510. Used for electrode holders, backing material, and applications where the part carries mechanical load as well as current.
Class 4. Beryllium copper C17200. The strength end of the group, at roughly 22 percent IACS. It is chosen when the component is primarily structural, and it carries the handling considerations covered in machining beryllium copper C17200.
Group B: refractory materials
Copper tungsten composites and the refractory metals, used where the face has to survive conditions no copper alloy will. Classes 10, 11 and 12 are copper tungsten with increasing tungsten content and decreasing conductivity. Class 13 is tungsten and Class 14 is molybdenum.
These are sintered or infiltrated materials rather than wrought alloys. They machine differently, they cost considerably more, and they are usually bought as inserts brazed into a copper alloy body rather than as whole electrodes.
Choosing in one pass
| What you are welding or doing | Class | Usual alloy |
|---|---|---|
| Aluminum, magnesium, coated or galvanized material | 1 | C15000 zirconium copper |
| Steel, general purpose production welding | 2 | C18200 or C18150 |
| Electrode holders, backing, load bearing parts | 3 | C17510 |
| Structural components where strength dominates | 4 | C17200 |
| Faces that stick, deform or run very hot | Group B | Copper tungsten |
Specifying it on a drawing
An electrode material callout wants three things.
Chromium copper, UNS C18200,
RWMA Group A Class 2,
temper TH04 (cold worked and precipitation hardened)The RWMA class is the line that communicates intent. The UNS number fixes the chemistry. The temper is not optional, because these are age hardening alloys and the hardness that stops a tip mushrooming only exists after the heat treatment.
Note what is missing: an ASTM specification. For the chromium and zirconium coppers the applicable standard depends on product form and supplier, so we do not print one we are not certain of. Confirm it with your stockist. Our rules on this are on the editorial standards page.
Machining these alloys
None of them cut quickly. All the Group A alloys above Class 1 sit near the pure copper end of the machinability scale, around 20 against free-cutting brass at 100, and the hardened tempers are abrasive on tooling as well.
The practical decisions are the same as for any age hardening copper:
- Machine at TB00 and age afterwards for an easier cut, accepting a small dimensional movement
- Machine at TH04 for final dimensions off the machine, accepting slower cycles
- Say which dimensions must survive heat treatment
Everything in copper temper codes explained applies directly.
Two things buyers get wrong
Specifying Class 1 for steel welding. Zirconium copper is softer and will deform sooner under the load and heat of steel welding. It exists for aluminum and coated material.
Ordering electrodes without a temper. An unhardened Class 2 electrode looks correct on the receiving dock and mushrooms in a shift. The temper is the property you are buying.
Where this sits in the wider grade family
Welding electrode alloys are the high strength corner of a bigger family. The copper grade reference puts them next to the pure and free-machining grades with conductivity, machinability and usual temper side by side, which is the fastest way to see what a class costs you in conductivity.
Frequently asked questions
What is the difference between RWMA Class 1 and Class 2?
Class 1 has higher electrical conductivity and lower strength, and suits welding aluminum and coated materials. Class 2 trades some conductivity for higher hardness and strength, which makes it the general purpose choice for steel. Class 1 is typically zirconium copper and Class 2 is chromium or chromium zirconium copper.
Can I just specify C18200 and leave it there?
For a general purpose electrode, often yes. Add the temper, because these are age hardening alloys and an unhardened electrode will mushroom quickly in service. TH04 is the usual delivery condition.
When do I need a refractory electrode instead of a copper alloy?
When the welding face has to resist sticking, deformation and heat beyond what an age hardened copper can take. That is RWMA Group B, the copper tungsten and refractory classes, and they cost considerably more.
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