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Choosing the right tungsten for aluminum TIG welding

Q: I am just getting into aluminum GTAW and I have heard many recommendations about which tungsten electrode I should use. Can you tell me how to make the right choice?

A: I will certainly try. First, let’s look at the commonly available tungsten electrodes (see Figure 1). Each type is given an AWS classification and includes a painted stripe around one end so you can easily identify the type.

The various additions to the tungsten electrode serve two purposes. First, it makes the tungsten less likely to sag or droop at high temperatures. Second, it makes it easier for the tungsten to emit electrons, which gives it a higher current-carrying capacity compared to pure tungsten.

Almost all direct current electrode negative (DCEN) welding that has been done in the past was with 2 percent thoriated electrodes, although more recently lanthanated and ceriated electrodes have become more popular for this type of welding.

However, when people started to aluminum GTAW using alternating current (AC), they found out thoriated electrodes really weren’t well-suited for that type of welding. In AC GTAW, much more energy is taken up by the tungsten than is taken up in DCEN welding. In the past the electrode choices were limited to pure tungsten or zirconiated tungsten, which could carry more current than a pure tungsten electrode of the same size. Neither of these electrodes was used with a sharpened tip. Instead, they were allowed to form a round ball on the end.

Thoriated tungsten did not form a nice round ball, but became very irregular in geometry, which produced a fluttery, irregular arc. So pure and zirconiated electrodes were preferred, and still are if your GTAW machine is an SCR/transformer type, especially an older model.

Inverter Machines and Tungsten TIG Welding

When inverter GTAW machines came on the scene, they changed everything. The balance control can be set much further toward electrode negative (EN) while still getting good arc cleaning action. Since only a little electrode positive (EP) is used, the tungsten electrode stays much cooler. In fact, the best electrodes for AC inverter GTAW machines are generally ceriated, lanthanated, and rare-earth electrodes, which are all sharpened to a point and can retain the point very well during use. Thoriated, zirconiated, and pure tungsten electrodes are not often used with AC inverter machines.

Figure 1

About the Author
Aluminum Consulting Inc.

Frank Armao

President

Aluminum Consulting Inc.

440-479-0239

Frank Armao was an active member of the AWS D1 Committee, chairman of the AWS D1 Aluminum Subcommittee, and member of the Aluminum Association Committee on Welding and Joining. He also was the author of The WELDER's "Aluminum Workshop" column from 2001 to 2020.