TIG (GTAW) of Magnesium — Choose the Correct DC Polarity In gas tungsten arc welding (TIG) of magnesium alloys, when direct current is selected, which polarity is commonly specified for stable arc and adequate penetration?

Introduction / Context:
TIG (GTAW) welding quality depends strongly on polarity. Magnesium forms a refractory oxide (magnesium oxide) that influences arc behavior and heat distribution. Understanding when to use DC straight polarity versus other modes is essential for sound welds.

Given Data / Assumptions:

• Process: TIG (GTAW) on magnesium or its alloys.
• Shielding: inert gas, typically argon or helium, or their mixtures.
• Question focuses on direct current selection, not AC cleaning balance settings.

Concept / Approach:
In DC TIG, heat concentrates at the positive terminal (anode). With straight polarity (DCEN), the electrode is negative and the work is positive, yielding deeper penetration and lower electrode heating. For magnesium, DCEN with appropriate shielding can provide stable welding, whereas DCEP overheats the electrode and gives shallow penetration. AC is widely used for oxide cleaning, but when DC is explicitly chosen, DCEN (straight) is the conventional selection.

Step-by-Step Solution:
Identify intent: DC welding of magnesium.Map definitions: straight polarity = DCEN, reversed polarity = DCEP.Evaluate effects: DCEN → good penetration and electrode life; DCEP → excessive electrode heating.Conclude that straight polarity is the accepted DC choice.

Verification / Alternative check:
Practical guides note AC or DCEN with helium for thicker magnesium; DCEP is rarely preferred due to electrode overheating.

Why Other Options Are Wrong:
Reversed polarity: overheats the electrode and limits penetration.AC only / pulsed DC only: the question explicitly asks for DC choice; these are not mandatory.No current selection required: incorrect; polarity selection is fundamental.

Common Pitfalls:
Assuming aluminum and magnesium always require AC; DCEN can be used in certain magnesium applications.

Final Answer:
straight polarity