WELD 121 Practice Test

Aluminum welds are highly affected by a thin, rapidly forming oxide layer that blocks proper bonding. Using TIG welding with alternating current is ideal because the AC arc naturally helps break up and sweep away that oxide while maintaining a stable, clean weld pool. The positive half-cycle aids oxide disruption and surface cleaning, while the negative half-cycle helps containment and root penetration, all under a protective argon shield. This combination gives excellent control of heat input, which is crucial for aluminum’s high thermal conductivity and tendency to burn through or warp if overheated. Direct current can be used for some alloys with the right filler, but it doesn’t remove oxide as effectively and can lead to porosity or poor wetting. That’s why AC TIG is the commonly used method for aluminum welding, with other processes being less reliable for producing clean, high-quality aluminum welds.