TIG welding electrodes are a ‘non consumable’ as it is not melted into the weld pool and great care should be taken not to let the electrode contact the welding pool to avoid weld contamination. This would be referred to as tungsten inclusion and may result in weld failure. Electrodes will often contain small quantities of metallic oxides which can offer the following benefits:
• Assist in arc starting • Improve current carrying capacity of the electrode • Reduce the risk of weld contamination • Increase electrode life • Increase arc stability
Oxides used are primarily zirconium, thorium, lanthanum or cerium.
These are added usually 1% - 4%.
Pure Tungsten (Green) AWS A5.12 EWP, ISO 6848 WP
These TIG electrodes are unalloyed, ‘pure’ tungsten with a 99.5% tungsten minimum and are relatively low cost. They provide good arc stability when using AC current, with either balanced wave or unbalanced wave and continuous high-frequency stabilization.
Pure tungsten electrodes are preferred for AC sine wave welding of aluminium and magnesium because they provide good arc stability with both argon and helium shielding gas.
The pure tungsten electrode easily forms a balled end but has a tendency to spit at higher currents and this should be considered when making critical welds.
Ceriated 2% (Grey) AWS A5.12 EWCe-2, ISO 6848 WC20
These TIG electrodes are alloyed with about 2% ceria, a non-radioactive material and the most abundant of the rare earth elements. The addition of this small percentage of cerium oxide increases the electron emission qualities of the electrode which gives them a better starting characteristic and a higher current carrying capacity with no spitting.
These are all-purpose electrodes that will operate successfully with AC or DC electrode negative. Compared with pure tungsten, the ceriated tungsten electrodes provide for greater arc stability. They have excellent arc starting properties at low current. If used on higher current applications the cerium oxide may be concentrated to the excessively hot tip of the electrode.
This condition and oxide change will remove the benefits of the cerium. The non radioactive cerium oxide has slightly different electrical properties as compared to the thoriated tungsten electrodes. The cerium electrodes work well with the Advanced Squarewave power sources and should be ground to a modified point.
Lanthanated (1% Lanthanum, Black), (1.5% Lanthanum, Gold), (2% Lanthanum, Blue) AWS A5.12 EWLa-, ISO 6848 WL
These TIG electrodes are alloyed with non radioactive lanthanum oxide, often referred to as lanthana, another of the rare earth elements. These electrodes have excellent arc starting, low erosion rate, arc stability and excellent re-ignition characteristics.
The addition of 1 – 2% lanthana increases the maximum current carrying capacity by approximately 50% for a given size electrode using alternating current compared to pure tungsten. The higher the percentage of lanthana, the more expensive the electrode. Since lanthana electrodes can operate at slightly different arc voltages than thoriated or ceriated tungsten electrodes these slight changes may require welding parameters and procedures to be adjusted.
The 1.5% content appears to most closely match the conductivity properties of 2% thoriated tungsten. Compared to cerium and thorium the lanthana electrodes had less tip wear at given current levels. Lanthanum electrodes generally have longer life and provide greater resistance to tungsten contamination of the weld.
The lanthana is dispersed evenly throughout the entire length of the electrode and it maintains a sharpened point well, which is an advantage for welding steel and stainless steel on DC or the AC from Advanced Squarewave power sources. Thus the lanthana electrodes work well on AC or DC electrode negative with a pointed end or they can be balled for use with AC sine wave power sources.
Thoriated (2% Thorium, Red) AWS A5.12 EWTh-2, ISO 6848 WT20
Thoriated electrodes both 1 and 2% are very commonly used electrodes since they were the first to show better arc performance over pure tungsten for DC TIG welding. However, thoria is a low-level radioactive material, thus vapours, grinding dust and disposal of thorium raises health, safety and environmental concerns.
The relatively small amount present has not been found to represent a health hazard. But if welding will be done in confined spaces for prolonged periods of time, or if electrode grinding dust might be ingested, special precautions should be taken concerning proper ventilation. The welder should consult informed safety personnel and take the appropriate steps to avoid the thoria.
The thoriated electrode does not ball as does the pure tungsten, cerium or lanthana electrodes. Instead, it forms several small projections across the face of the electrode when used on alternating current. When used on AC sine wave machines, the arc wanders between the multiple projections and is often undesirable for proper welding. Should it be absolutely necessary to weld with these type machines, the higher content lanthana or thoria electrodes should be used. The thoriated electrodes work well with the Advanced Squarewave power sources and should be ground to a modified point.
These electrodes are usually preferred for direct current applications. In many DC applications, the electrode is ground to a taper or pointed. The thorium electrode will retain the desired shape in those applications where the pure tungsten would melt back and form the ball end. The thoria content in the electrode is responsible for increasing the life of this type over the pure tungsten.
Zirconiated (1% Zirconium, White) AWS A5.12 NONE, ISO 6848 WZ8
This TIG tungsten is alloyed with zirconium oxide (zirconia) and is preferred for AC TIG welding when the highest quality work is necessary and where even the smallest amounts of weld pool contamination cannot be tolerated. This is accomplished because the zirconium alloyed tungsten produces an extremely stable arc which resists tungsten spitting in the arc.
The current carrying capability is equal to or slightly greater than an equal sized cerium, lanthana or thorium alloyed electrode. Zirconium electrodes are typically used only for AC welding with a balled end.
The tungsten electrodes come in a variety of diameters and you would select the appropriate diameter for the current to be used and type for the process mode. To physically identify the tungsten type the end is dipped with a colour. Take care to grind the non coloured end for welding.