Which tungsten types are preferred for AC welding?

• A. Green, Brown
• B. Green and Red
• C. Brown and Red
• D. Pure tungsten and thoriated tungsten

Answer: (A)

For AC TIG welding, you want a tungsten electrode that can handle the alternating polarity and re‑ignite easily after oxide layers form on the workpiece. Green indicates pure tungsten, which provides a clean, stable arc and is a good general choice for AC because it doesn’t introduce alloying elements into the weld.

Brown indicates zirconiated tungsten, which adds a small amount of zirconium oxide to improve arc starting and stability when the current polarity switches and at higher amperages. This makes it particularly helpful for AC welding of aluminum and magnesium, where quick re‑ignition and a steady arc are important.

Thoriated tungsten (red) is more common for DC welding because it helps stabilize the arc with a constant polarity, but it isn’t ideal for AC. The other electrode types (not as commonly used for AC) won’t give the same reliable arc start and stability on AC as pure tungsten or zirconiated tungsten.