FAA Aviation Mechanic General (AMG)Materials, Hardware and ProcessesMedium
A technician is preparing to weld an aluminum alloy component. To prevent the formation of aluminum oxide, which has a much higher melting point than aluminum itself, what type of welding current is typically used for aluminum and why?
- AAlternating Current (AC) because it provides a self-cleaning action during the reverse polarity half-cycle.
- BDirect Current Electrode Positive (DCEP) because it provides a cleaning action.
- CAlternating Current (AC) because it offers a more stable arc for aluminum.
- DDirect Current Electrode Negative (DCEN) because it provides better penetration.
Show answer & explanationAnswer & explanation
Correct answer: A. Alternating Current (AC) because it provides a self-cleaning action during the reverse polarity half-cycle.
Alternating Current (AC) is typically used for welding aluminum because the reverse polarity (electrode positive) half-cycle provides a cathodic cleaning action that breaks up the aluminum oxide layer, which has a very high melting point and would otherwise interfere with the weld.
Why the other options are wrong
- B. DCEP (reverse polarity) provides excellent cleaning but tends to overheat the electrode and results in a shallow, wide bead, making it unsuitable for most aluminum welding.
- C. While AC provides a stable arc, its primary advantage for aluminum is the cleaning action, not just stability.
- D. DCEN (straight polarity) provides deep penetration but does not effectively break up the oxide layer, leading to poor welds on aluminum.
Aluminum Welding Current
Alternating Current (AC) is the preferred welding current for aluminum due to its ability to break up the tenacious aluminum oxide layer during the reverse polarity half-cycle, ensuring a clean and strong weld.
- Aluminum oxide has a much higher melting point (3700°F) than aluminum (1220°F).
- AC provides a 'self-cleaning' action.
- DCEN (straight polarity) is generally not used for aluminum due to lack of oxide cleaning.
Memory trick: AC's dual nature cleans and penetrates for aluminum's tough skin.