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TIG power setting for aluminum and magnesium

Aviation Mechanic Airframe (AMA) practice question 2 of 20 on Metallic Structures. ACS element AM.II.A.K12 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA mechanic is setting up a gas tungsten arc welder to weld aluminum and magnesium. Which power setting is selected?

  1. ADC straight polarity
  2. BDC reverse polarity for aluminum
  3. CAlternating current (AC)
Show the answer and explanation

Correct answer: C. Alternating current (AC)

  • A — incorrect Straight polarity, with the work positive and the torch negative, is the setting listed for mild steel, stainless steel, and titanium.
  • B — incorrect Aluminum work is set to an AC output waveform, which breaks up surface oxides, so no direct current setting applies to it.
  • C — correct The setup instructions direct that AC be selected on the welder when welding aluminum and magnesium.

BACKGROUND

Gas tungsten arc welding, more commonly called TIG welding, fills most of the needs in aircraft maintenance and repair and is the preferred method for stainless steel, magnesium, and most forms of thick aluminum. The electrode is a tungsten rod that carries the high-amperage arc and is not consumed, so filler rod is fed into the puddle by hand much as it is with an oxy-acetylene torch. A stream of inert gas such as argon or helium flows around the electrode and envelopes the arc, preventing oxides from forming in the molten puddle. Much of the versatility of a TIG welder comes from the choice of power supply, since direct current of either polarity or alternating current may be used. The welder is set to DC straight polarity for mild steel, stainless steel, and titanium, and to AC for aluminum and magnesium, and the AC waveform on aluminum also breaks up surface oxides.

STUDY TIP

Group the metals by power setting rather than memorizing them one at a time: steels and titanium take DC straight polarity, the light alloys take AC.

KEY POINTS

  • TIG welding of aluminum and magnesium uses alternating current.
  • DC straight polarity, work positive and torch negative, is used for mild steel, stainless steel, and titanium.
  • The tungsten electrode is not consumed, so filler rod is fed in by hand.

SOURCES

  • sources/ama-airframe/ch05.txt "Gas Tungsten Arc Welding (GTAW)"
  • sources/ama-airframe/ch05.txt "TIG Welding Aluminum"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.