When are pure tungsten or zirconiated electrodes used in GTAW?

When are pure tungsten or zirconiated electrodes used in GTAW?

• A. On DC with a tapered point
• B. On AC, with a hemispherical tip that grows with current
• C. On AC with a pointed tip
• D. Only when high frequency start is unavailable

Answer: (B)

In GTAW, the electrode type and its tip shape are chosen to suit the welding current and the workpiece. For nonferrous metals like aluminum, you typically use a non-consumable tungsten electrode (pure tungsten or zirconiated) with alternating current. The AC reversals cause the electrode tip to heat and form a rounded ball, a hemispherical shape, rather than a sharp point. As current increases, this ball tends to grow, which helps stabilize the arc and maintains a clean, continuous arc when the workpiece surface is oxidized or cleaned by the arc. Pure tungsten or zirconiated electrodes are favored here because they resist contamination and provide reliable arc starting and stability under AC. Zirconium offers improved life and easier starting for AC GTAW, which is why this combination is commonly recommended for AC welding of aluminum. The other scenarios aren’t as representative of how pure tungsten or zirconiated electrodes are typically used. A tapered or pointed tip is more associated with DC welding of steels and uses a different polarity strategy, while a pointed tip on AC would not offer the same stable, self-cleaning behavior that a hemispherical tip provides. And arc start conditions like high-frequency starters change initiation but don’t alone define the electrode tip shape or material choice.

In GTAW, the electrode type and its tip shape are chosen to suit the welding current and the workpiece. For nonferrous metals like aluminum, you typically use a non-consumable tungsten electrode (pure tungsten or zirconiated) with alternating current. The AC reversals cause the electrode tip to heat and form a rounded ball, a hemispherical shape, rather than a sharp point. As current increases, this ball tends to grow, which helps stabilize the arc and maintains a clean, continuous arc when the workpiece surface is oxidized or cleaned by the arc.

Pure tungsten or zirconiated electrodes are favored here because they resist contamination and provide reliable arc starting and stability under AC. Zirconium offers improved life and easier starting for AC GTAW, which is why this combination is commonly recommended for AC welding of aluminum.

The other scenarios aren’t as representative of how pure tungsten or zirconiated electrodes are typically used. A tapered or pointed tip is more associated with DC welding of steels and uses a different polarity strategy, while a pointed tip on AC would not offer the same stable, self-cleaning behavior that a hemispherical tip provides. And arc start conditions like high-frequency starters change initiation but don’t alone define the electrode tip shape or material choice.