TIG Welding Guide (GTAW): AC/DC Techniques, Tungsten Selection & Aluminum Welding
TIG welding (GTAW) produces the highest quality, cleanest welds of any arc welding process. It is the preferred method for aerospace, food-grade equipment, motorcycle frames, and any application where weld appearance and integrity are critical.
AC vs. DC TIG: When to Use Which
| Mode | Best For | Key Benefit |
|---|---|---|
| DC TIG (DCEN) | Steel, stainless steel, titanium, copper | Deep penetration, stable arc, 70% heat into work |
| AC TIG | Aluminum, magnesium | Cleaning action removes oxide layer during EN half-cycle; penetration during EP half-cycle |
Aluminum requires AC TIG. The positive half-cycle strips aluminum oxide (which melts at 2,072°C — far above aluminum's 660°C melting point), while the negative half-cycle provides penetration. A standard DC-only TIG machine cannot weld aluminum.
Tungsten Electrode Selection
| Type | Color | Current | Best For |
|---|---|---|---|
| 2% Thoriated (Red) | Red | DC only | Steel, stainless — excellent arc starting |
| 2% Lanthanated (Blue) | Blue | AC & DC | Universal — steel + aluminum, replaces thoriated |
| Pure Tungsten (Green) | Green | AC only | Aluminum on transformer machines (forms balled tip) |
| 2% Ceriated (Grey) | Grey | AC & DC | Low amperage, thin materials — excellent arc stability |
Tungsten Diameter & Amperage Guide
| Diameter | DC Amperage | AC Amperage |
|---|---|---|
| 1/16" (1.6mm) | 30-120A | 20-100A |
| 3/32" (2.4mm) | 80-200A | 70-180A |
| 1/8" (3.2mm) | 150-300A | 130-250A |
Dual Pulse for Aluminum
Modern inverter TIG welders feature dual pulse for aluminum welding. The primary pulse controls heat and penetration, while a secondary, faster pulse agitates the weld puddle to refine grain structure and reduce porosity. Results: smoother bead appearance, reduced heat-affected zone, and better mechanical properties compared to single-pulse or continuous AC.
Filler Rod Selection Quick Guide
| Base Metal | Filler Rod | Notes |
|---|---|---|
| Mild Steel | ER70S-2 / ER70S-6 | General fabrication |
| 304 Stainless | ER308L | Food, medical grade |
| 316 Stainless | ER316L | Marine, chemical environments |
| 6061 Aluminum | ER4043 | General aluminum (reduces cracking risk) |
| 5052/5083 Aluminum | ER5356 | Marine-grade aluminum |
Sources: AWS A5.12 tungsten electrode specification, Miller Welds TIG welding guide, Lincoln Electric GTAW technical resources.
Quick Reference: TIG Welding Parameters
| Parameter | DC TIG (DCEN) | AC TIG |
|---|---|---|
| Best For | Carbon steel, stainless steel, titanium, copper, nickel alloys | Aluminum, magnesium, zinc alloys |
| Tungsten Type | 2% Thoriated (Red) or 2% Lanthanated (Blue) | 2% Lanthanated (Blue) or Pure (Green) |
| Tungsten Tip Prep | Sharp point (20-30deg grind angle) | Slightly blunted ball (forms naturally on pure) |
| Heat Distribution | 70% work, 30% electrode | ~50% work, ~50% electrode (balanced) |
| Cleaning Action | None | Oxide removal during EP half-cycle |
| Gas Flow Rate | 10-20 CFH (5-10 L/min) | 15-25 CFH (7-12 L/min) |
| Post-Flow Time | 5-10 seconds (prevents oxidation) | 8-15 seconds (larger tungsten needs more) |
| AC Balance Control | N/A | 65-75% EN for general aluminum |
Common TIG Welding Mistakes to Avoid
1. Tungsten Contamination — Proper TIG Welding Technique
Contaminating the tungsten with base metal or filler metal is the most common TIG mistake. A dipped tungsten produces an erratic, wandering arc and leaves tungsten inclusions in the weld that act as crack initiation points. The fix: stop immediately, break off the contaminated portion of the tungsten, and re-grind the tip to a fresh point. Keep the tungsten 1/8" to 1/4" above the puddle at all times.
2. Tungsten Grind Angle — Correct Electrode Preparation
Grinding the tungsten lengthwise (parallel to the axis) is essential -- never grind radially (around the circumference). Radial grinding creates ridges that channel the arc to the side, producing an unstable, wandering arc. The fix: use a dedicated tungsten grinding wheel and always grind so the scratch marks run from tip to shank. A 20-30degree included angle works for most DC applications.
3. Insufficient Post-Flow Gas Coverage
Turning off the torch or lifting away immediately after extinguishing the arc leaves the hot tungsten and weld pool exposed to air, causing oxidation, tungsten erosion, and a grey, contaminated weld surface. The fix: always hold the torch over the weld zone for the full post-flow duration (typically 1 second per 10 amps). The post-flow timer on modern inverters handles this automatically -- don't override it.
4. Attempting Aluminum on DC TIG
A DC-only TIG machine cannot weld aluminum. Without the AC cleaning action that strips the aluminum oxide layer (melting point 2,072degC vs. aluminum's 660degC), the oxide remains as a solid crust while the aluminum underneath melts away. The fix: use an AC-capable TIG welder for aluminum. If your machine is DC-only, you need a different process (MIG with spool gun or stick with aluminum electrodes) for aluminum work.
5. Incorrect TIG Filler Rod Feeding Technique
Pulling the filler rod out of the gas shield between dips exposes the hot rod tip to air, forming an oxide layer that contaminates the next dip. The fix: keep the filler rod tip inside the argon shield envelope at all times during welding. If the rod tip oxidizes (turns dark), clip off the contaminated end before continuing.
Related Products from BrightWelding
TIG-200P Pulse TIG Welder -- The go-to machine for precision fabrication, stainless steel work, and thin-gauge welding. 200A DC TIG with pulse function that alternates between high and low current, reducing heat input and distortion on thin materials. Includes HF arc start, 2T/4T torch control, and runs on single-phase 220V.
TIG-315P AC/DC TIG Welder -- Equipped with both AC and DC modes, this machine handles everything from aluminum (AC) to stainless steel (DC). 315A output with 60% duty cycle. Dual pulse capability refines aluminum weld grain structure for superior bead appearance. Features adjustable AC balance, AC frequency control, and pulse frequency up to 500 Hz.
TIG-400 Industrial AC/DC TIG Welder -- Built for heavy production and critical aerospace-grade welding. 400A @ 60% duty cycle on three-phase input. Waveform control (square, sine, triangle, soft square) for application-specific arc characteristics. Water-cooled torch ready, digital memory for 100 welding parameter sets, and interface for automation integration.