TIG (GTAW) of aluminium — choice of current for oxide cleaning and arc stability When welding aluminium using TIG (gas tungsten arc welding), is alternating current (AC) commonly employed to obtain cathodic cleaning and a stable arc?

Introduction / Context:
Gas tungsten arc welding (TIG/GTAW) of aluminium requires special attention to the refractory oxide film (alumina) that forms instantly on the surface. This oxide has a much higher melting temperature than the base aluminium and can prevent wetting and fusion unless properly managed.

Given Data / Assumptions:

• Base metal: aluminium and its common alloys.
• Process: TIG (GTAW) with inert gas shielding (typically argon or argon–helium blends).
• Objective: select the appropriate current type to achieve cleaning and stable puddle control.

Concept / Approach:
Alternating current is widely used in TIG welding of aluminium because the electrode-positive half-cycle provides cathodic cleaning (oxide disruption), while the electrode-negative half-cycle concentrates heat in the work for penetration and keeps the tungsten from overheating excessively. Modern power sources add balance control and high-frequency stabilization, improving arc initiation and bead quality on both thin and thick sections.

Step-by-Step Solution:

Verification / Alternative check:
Production practice confirms AC as the standard for most aluminium TIG work; DCEN is reserved for special conditions with helium shielding on thick sections and meticulous pre-cleaning.

Why Other Options Are Wrong:

• “Incorrect” or “only for foils”: AC is broadly applicable, not limited to thin stock.
• “Only with helium”: argon is common; helium mixtures are optional for heat input.
• “DCEN is always preferred”: DCEN lacks inherent oxide cleaning and risks lack of fusion without extensive prep.

Common Pitfalls:
Misadjusting AC balance leading to excessive tungsten balling (too much EP) or poor cleaning (too little EP). Also neglecting solvent and stainless-brush cleaning prior to welding.

Final Answer: