11.3 GTAW Electrodes & Filler Rods
Karl Fulton
Electrode Classification
The tungsten electrode has many different alloys that affect the arc starting, stability, and longevity. These tungstens are color-coded for ease of identification. This section covers a few of the main alloys of tungsten you will see and use. It is important to be aware that new alloys are still being developed for specific purposes, such as for stainless steel, aluminum, and robotic welding. Let’s discuss old and new tungsten.
The Old Guard: Green and Red Tungsten
Green
The color green indicates that the tungsten electrodes are 99% pure. Green tungsten is used in AC welding of aluminum and magnesium. The end of the tungsten will ball as you weld, giving good arc stability and relatively good resistance to contaminating the weld. Green tungsten is to be used with transformer machines only.
Red: 2% Thoriated
The color red indicates that the tungsten contains 2% thorium. For a number of years, this was the most commonly used tungsten because of its versatility. It has a long service life, easy arc starting, high current capacity, and good resistance to contaminating the weld.
Red 2% thoriated tungsten is used for welding carbon steel, stainless steel, nickel alloy, titanium, and copper. However, it cannot be used for AC welding. The tungsten will not ball and it will contaminate the weld. Proper caution should be taken when using this tungsten because thorium is radioactive.
New and Improved Tungsten
Gold:1.5% Lanthanated and Blue: 2% Lanthanated
Gold and blue tungsten are alloyed with lanthanum, giving them very strong characteristics such as easy arc starting, reignition, and arc stability. Gold 1.5% and Blue 2% tungsten each have a long service life and resistance to thermal shock when pulse welding. They have high resistance to contamination and will maintain an arc at a very low current. These can be used in DC and AC welding, making them incredibly versatile.
Gray: 2% Ceriated
Gray tungsten contains 2% cerium. It is excellent for very low amperage starting, and it has good arc stability and a long life. This tungsten performs very well with both AC and DC welding.
White: 0.8% Zirconiated
White tungsten produces an extremely stable arc, maintains a balled end, and is highly resistant to contamination and spitting. White 0.8% zirconiated tungsten is used for AC welding when contamination is intolerable. This tungsten handles high amperage for welding aluminum and magnesium alloys. It is a good replacement for green (pure) tungsten if needed.
Purple: Rare Earth Trimix
Purple tungsten contains some lanthanum, zirconium, and yttrium. It is a good substitute for red 2% thoriated tungsten. It is very durable and produces reliable arc starts, and performs well in both AC and DC welding applications. Purple tungsten is used for welding aluminum alloys, magnesium alloys, titanium alloys, nickel alloys, copper alloys, low-alloyed steels, and non-corrosive steels.
Maintaining Tungst