Pure argon is the standard shielding gas for TIG welding and covers the vast majority of applications. It works on every weldable metal, produces a stable and precise arc, and is widely available at reasonable cost. For thicker materials or specialized work, helium, argon-helium blends, and small hydrogen additions each have a role, but argon alone handles most jobs a TIG welder will encounter.
Why Pure Argon Is the Default Choice
Argon is an inert gas, meaning it doesn’t react with hot metal, the filler rod, or the tungsten electrode. That chemical inertness is exactly what TIG welding demands. The process exposes a non-consumable tungsten electrode to extreme heat for extended periods, and any reactive gas in the shielding envelope would oxidize and destroy it. Argon’s low ionization potential (the energy needed to create an arc) makes it easy to start and maintain a smooth, focused arc column. The result is a narrow, deep penetration profile that gives you precise control over the weld puddle.
This is why argon works across the full range of TIG-welded metals: mild steel, stainless steel, aluminum, magnesium, nickel alloys, copper, and titanium. Miller Electric’s guidelines recommend argon as the primary gas for both AC TIG (used for aluminum and magnesium) and DC TIG (used for stainless steel, nickel alloys, copper, titanium, and other exotic metals). If you’re setting up a TIG torch for the first time, a cylinder of 100% welding-grade argon is the place to start.
When Helium or Argon-Helium Blends Make Sense
Helium has a much higher thermal conductivity and ionization potential than argon. In practical terms, that means a helium-rich arc dumps more heat into the workpiece and produces a wider, shallower bead profile compared to argon’s narrow, deep one. The tradeoff is that helium makes arc starting more difficult and costs significantly more per cubic foot. You also burn through it faster because helium is much lighter than argon and disperses quickly.
Rather than choosing one or the other, most welders use blends tuned to the job:
- 75% argon / 25% helium: A common starting blend for aluminum. It increases penetration and improves bead appearance compared to pure argon while keeping the arc easy to manage.
- 25% argon / 75% helium: Used for mechanized welding on aluminum thicker than 1 inch and for copper work, where the extra heat input reduces porosity and ensures full fusion.
- 10% argon / 90% helium: Reserved for the thickest copper and aluminum sections, where maximum heat input is needed to get adequate weld coalescence.
The pattern is straightforward: the thicker or more thermally conductive the material, the more helium you add. Thin aluminum sheet needs only pure argon. A 2-inch-thick aluminum plate benefits from a helium-heavy mix.
Hydrogen Additions for Stainless Steel
Small amounts of hydrogen, typically between 1% and 5% mixed with argon, are sometimes used when TIG welding austenitic stainless steels. Hydrogen is a diatomic molecule, and when it splits apart in the arc, it releases extra energy that creates a hotter, wider bead with better wetting at the edges. This can let you increase travel speed on stainless while keeping full penetration.
Research on stainless steel welded with 1% to 5% hydrogen in argon showed defect-free joints with slightly increased bead size. The welds also had reduced hardness compared to pure argon shielding, which can be desirable in certain applications. Hydrogen additions are limited to stainless and some nickel alloys. On carbon steel or aluminum, hydrogen causes porosity and cracking, so it’s strictly off-limits for those metals.
Gases You Should Never Use for TIG
CO2 and oxygen-containing mixtures are common in MIG welding but will ruin a TIG setup. The issue is the tungsten electrode. In MIG, the wire electrode is consumed and constantly replaced, so a little oxidation doesn’t matter. In TIG, the tungsten sits in the arc for minutes at a time. CO2 breaks down into carbon and oxygen at arc temperatures, and that oxygen reacts directly with the tungsten, contaminating it. The result is a degraded electrode, an unstable arc, porosity, and blowholes in the weld. Even a standard argon/CO2 MIG blend will not work in a TIG torch.
Flow Rates and Gas Coverage
Typical TIG setups run shielding gas at 15 to 25 cubic feet per hour (CFH). The right setting depends mainly on your nozzle size. Smaller cups concentrate the gas flow, so you can run at the lower end. Larger cups need higher flow to maintain adequate coverage over the wider area. Setting the flow too high actually hurts coverage by creating turbulence that pulls surrounding air into the gas stream, so more is not always better.
A gas lens significantly improves how efficiently your shielding gas protects the weld. Standard collet bodies force gas through a 90-degree turn inside the torch, creating turbulent, uneven flow out of the nozzle. A gas lens uses a series of fine mesh screens to straighten that flow into a smooth, laminar column, similar to the screen on a kitchen faucet that turns a choppy stream into an even one. The practical benefits are better gas coverage at the same flow rate, the ability to extend your tungsten farther out of the cup for better visibility in tight joints, and improved protection on oxidation-sensitive metals like stainless steel and titanium.
Back Purging: Protecting the Other Side
Shielding gas from the torch only protects the top of the weld. When you’re welding pipe or tubing with a single-sided root pass, the inside surface is exposed to air at extreme temperatures. Without protection, the root side oxidizes into a rough, brittle, sugar-like formation that weakens the joint and is grounds for rejection on any code work.
The solution is back purging: flooding the inside of the pipe with inert gas before and during welding. The standard back purge gas is 100% welding-grade argon. You seal off a section of pipe around the joint, flow argon through it to displace the air, and maintain the purge until the root pass cools enough that oxidation is no longer a risk. This step is essential on stainless steel, nickel alloys, and titanium pipe work.
Quick Reference by Metal
- Mild steel: Pure argon.
- Stainless steel: Pure argon for most work. Argon with 1% to 5% hydrogen for faster travel on austenitic grades.
- Aluminum (thin): Pure argon.
- Aluminum (thick): Argon-helium blend, with helium percentage increasing with material thickness.
- Copper: Argon-helium blend (75% helium or higher) to overcome copper’s rapid heat dissipation.
- Titanium: Pure argon with thorough shielding, including a trailing shield and back purge. Titanium is extremely reactive when hot.
- Magnesium: Pure argon.
For most hobbyists and shops, a single cylinder of pure argon handles every metal on this list. Helium and hydrogen blends become relevant when you’re chasing productivity on thick sections or specific alloys, but they’re additions to a setup that already starts with argon.