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Welding Shielding Gas Selection Chart for MIG, TIG and Flux Core

Shielding gas drives penetration, spatter, bead shape and, for stainless and aluminum, weld quality. This chart shows the usual gas for each process and metal, plus the cautions that cause real defects.

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Process	Base metal	Typical gas	Effect	Caution
GMAW short circuit	Carbon steel	75-80% Ar, balance CO2	Stable arc, moderate penetration, low spatter	Lack of fusion risk on thick plate if heat input is low
GMAW spray transfer	Carbon steel	90-98% Ar, balance CO2 or O2	Smooth spray, good bead wetting	Needs sufficient current to reach spray
GMAW	Carbon steel	100% CO2	Deepest penetration, lowest gas cost	More spatter and a rougher bead
GMAW pulsed	Carbon steel	90-98% Ar, balance CO2	Spray quality with lower average heat	Requires a pulse-capable power source
GMAW	Austenitic stainless	98% Ar, 2% CO2 or Ar-O2 mix	Limits carbon pickup and oxidation	High CO2 raises carbon and harms corrosion resistance
GMAW	Austenitic stainless	Tri-mix of He, Ar and a little CO2	Flatter bead, better wetting	Helium costs more
GMAW	Aluminum	100% Ar	Good cleaning action and spray transfer	Add helium blends for thick sections
GMAW	Aluminum, thick	Ar-He mix	Hotter arc, better fusion in thick plate	Higher gas cost and flow rates
GTAW	Carbon and low alloy steel	100% Ar	Stable arc and good control	Use a clean electrode and surface
GTAW	Austenitic stainless	100% Ar	Standard choice for clean root and cap	Pure argon back purge is needed for the root side
GTAW	Austenitic stainless	Ar with a few percent H2	Hotter arc and faster travel	Austenitic only, never on ferritic, martensitic or duplex
GTAW	Aluminum and magnesium	100% Ar or Ar-He, AC current	Arc cleaning of oxide layer	Helium raises arc voltage and heat
GTAW	Titanium	High purity Ar with trailing and back shield	Prevents oxidation and embrittlement	Discoloration of the weld shows contamination
GTAW	Copper	Helium or Ar-He	Needed for the high thermal conductivity of copper	Preheat is usually required
FCAW-G	Carbon steel	100% CO2 or 75-80% Ar, balance CO2	Follow the wire maker's C or M designation	Mix and CO2 wires are not interchangeable without approval
FCAW-S	Carbon steel	None, self-shielded	Works outdoors in wind	More fume and slag to clean
GTAW or PAW	Duplex stainless	Ar, sometimes with a small nitrogen addition	Helps maintain phase balance	Follow the WPS, since gas affects ferrite content
Backing purge	Stainless pipe root	Argon, or nitrogen for some austenitic work	Prevents sugaring and oxide on the root	Check oxygen level before welding
SAW	Carbon and low alloy steel	None, flux protects the weld	High deposition, deep penetration	Flux must be stored dry

Values are typical industry practice, not requirements. Your WPS and the filler maker's data sheet take precedence. Never add hydrogen to carbon or low alloy steel shielding gas because of hydrogen cracking risk.

Cost consumables from work orders

Optional: a review of how gas and filler usage can post to job costs in your ERP.

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How to use this chart

Search by process such as GTAW, by metal such as aluminum, or by gas such as CO2. Compare the Effect and Caution columns before deciding, because the cheapest gas is not always the lowest-cost weld once rework and cleaning are counted. Export the table to put a controlled selection guide beside your gas cylinder storage or in your welding manual.

Why gas choice matters

Argon gives a stable arc and low spatter and supports spray transfer. Carbon dioxide gives deeper penetration but more spatter because it is an active gas. Helium raises arc voltage and heat input, which helps with thick aluminum and copper. Small oxygen or hydrogen additions change wetting and travel speed but must match the base metal. The gas is an essential variable on many WPS forms, so a change usually needs approval.

Common mistakes

Gas problems often show up as porosity or discoloration, which are expensive to find late.

Using a CO2-rich mix on stainless and losing corrosion resistance.
Adding hydrogen to a gas for steel work.
Setting flow too high, which causes turbulence and air entrainment.
Welding in drafts without wind shielding or switching to self-shielded wire.
Skipping the root purge on stainless pipe.

Frequently Asked Questions

What is the best shielding gas for MIG welding mild steel?

A 75-80% argon and balance CO2 mix is the common all-round choice for short circuit transfer, and 90-98% argon works for spray or pulse. Pure CO2 gives more penetration at lower cost but with more spatter. Follow your WPS.

Can I use CO2 on stainless steel?

High CO2 content raises carbon pickup and reduces corrosion resistance, so stainless MIG usually uses 98% argon with 2% CO2 or a tri-mix. For TIG welding, pure argon is standard.

What gas should I use for aluminum?

Pure argon is the default for both MIG and TIG. For thick aluminum, argon-helium mixes give a hotter arc and better fusion. Always weld aluminum with clean material and the correct filler such as ER4043 or ER5356.

Why do I need a back purge on stainless pipe?

Without an inert gas on the inside of the joint, the root oxidizes and forms a rough, sugared surface that loses corrosion resistance. Argon purge, monitored with an oxygen analyzer, keeps the root clean and meets many sanitary and process requirements.

If gas and consumable usage needs to flow from work orders into cost and purchasing in your ERP, Netray can outline how teams model that.

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