Choosing the correct shielding gas is essential for producing clean, strong and consistent welds. The gas you use affects arc stability, penetration, weld appearance, spatter levels and the overall quality of the finished weld.
Whether you are MIG welding mild steel, TIG welding stainless steel or working with aluminium, using the wrong gas can quickly lead to porosity, contamination, poor penetration and unnecessary rework.
In this guide, we explain the most common shielding gases used for MIG and TIG welding, what they are used for and how to choose the right gas for your application.
What Does Shielding Gas Do?
Shielding gas protects the molten weld pool from the atmosphere.
Without proper shielding, oxygen, nitrogen and moisture can contaminate the weld, causing defects such as:
- Porosity
- Oxidation
- Poor weld appearance
- Lack of fusion
- Excessive spatter
- Reduced weld strength
The correct gas helps create a stable arc, improves weld bead shape and protects the weld as it cools.
MIG Welding Shielding Gases
MIG and MAG welding use shielding gas to protect the weld pool and influence weld performance. The correct gas depends on the material, wire type, welding position and required finish.
Argon / CO₂ Mixes for Mild Steel MIG Welding
Argon and carbon dioxide mixed gases are the most common choice for MIG welding mild steel.
Typical mixes include:
- 95% Argon / 5% CO₂
- 93% Argon / 5% CO₂ / 2% Oxygen
- 80% Argon / 20% CO₂
Best suited for:
- Mild steel fabrication
- General workshop welding
- Automotive repairs
- Thin to medium thickness steel
- Clean weld appearance
Advantages:
- Smooth arc
- Reduced spatter compared with pure CO₂
- Good bead appearance
- Better control on thinner materials
- Suitable for dip transfer and spray transfer depending on settings
A 95/5 argon/CO₂ mix is a popular choice for cleaner welds and lower spatter, while higher CO₂ mixes can improve penetration on heavier sections.
Pure CO₂ for MIG Welding
Pure CO₂ can be used for MAG welding mild steel and is often chosen for cost-sensitive applications.
Best suited for:
- Mild steel
- Thicker material
- General fabrication
- Outdoor or less cosmetic work
Advantages:
- Lower gas cost
- Good penetration
- Widely available
Disadvantages:
- More spatter
- Harsher arc
- Rougher weld appearance
- More post-weld clean-up
Pure CO₂ can be useful in some production and repair environments, but most welders prefer argon/CO₂ mixes for cleaner, more controllable results.
Tri-Mix Gases for Stainless Steel MIG Welding
Stainless steel MIG welding usually requires a specialist shielding gas.
Common stainless MIG gases may include:
- Argon
- Helium
- Carbon dioxide
- Oxygen
The exact mixture depends on the wire type, material grade and application.
Best suited for:
- Stainless steel fabrication
- Food industry fabrication
- Architectural stainless
- Thin stainless sheet
- Industrial stainless applications
Advantages:
- Improved arc stability
- Better wetting
- Reduced oxidation
- Improved weld appearance
- Better control of penetration
Using standard mild steel MIG gas on stainless steel can result in poor weld appearance, oxidation and reduced corrosion resistance.
Pure Argon for Aluminium MIG Welding
Aluminium MIG welding typically uses 100% argon shielding gas.
Best suited for:
- Aluminium sheet
- Aluminium fabrication
- Automotive aluminium repairs
- Marine aluminium work
- General aluminium welding
Advantages:
- Stable arc
- Good cleaning characteristics
- Clean weld appearance
- Suitable for most aluminium applications
For thicker aluminium sections, argon/helium mixtures may be used to increase heat input and improve penetration.
Argon / Helium Mixes for MIG Welding
Helium can be added to argon to increase heat input.
Best suited for:
- Thick aluminium
- Copper alloys
- High thermal conductivity materials
- Industrial applications
Advantages:
- Increased penetration
- Faster travel speeds
- Better fusion on thick materials
Disadvantages:
- Higher gas cost
- May require setting adjustments
- Less commonly used in general workshops
TIG Welding Shielding Gases
TIG welding is more sensitive to shielding gas quality than MIG welding. Because TIG produces clean, precise welds, poor gas coverage or contamination can quickly ruin weld appearance and weld integrity.
Pure Argon for TIG Welding
Pure argon is the most commonly used TIG welding gas.
Best suited for:
- Mild steel
- Stainless steel
- Aluminium
- Titanium
- Copper alloys
- General TIG welding
Advantages:
- Excellent arc stability
- Easy arc starts
- Clean weld appearance
- Suitable for AC and DC TIG welding
- Works well on most TIG applications
For most workshops, pure argon is the standard TIG gas.
Typical gas flow rates:
- Standard TIG cup: 6-10 L/min
- Gas lens setup: 8-12 L/min
- Larger cups: 10-14 L/min
Argon / Helium Mixes for TIG Welding
Argon and helium mixtures are used when more heat input is needed.
Best suited for:
- Thick aluminium
- Thick copper
- High thermal conductivity materials
- High-speed welding applications
Advantages:
- Increased heat input
- Improved penetration
- Faster travel speeds
- Better performance on thick sections
Disadvantages:
- More expensive than pure argon
- Can make arc starting slightly harder
- Less common for everyday TIG work
Most general TIG welding can be completed with pure argon, but helium mixes are valuable for specialist industrial applications.
Hydrogen-Containing TIG Gases
Some specialist TIG gases include a small percentage of hydrogen.
Best suited for:
- Austenitic stainless steel
- Mechanised TIG welding
- Specialist production applications
Advantages:
- Increased heat input
- Improved travel speed
- Smooth weld appearance
Important:
Hydrogen-containing gases must not be used on materials where hydrogen cracking is a risk. They are not suitable for all materials and should only be used where the material and welding procedure allow it.
Nitrogen and Specialist Shielding Gases
Specialist gases may be used for certain duplex stainless steels, high-alloy materials and automated welding processes.
These gases are normally selected according to:
- Material grade
- Welding procedure
- Code requirements
- Metallurgical properties
- Manufacturer recommendations
For general fabrication, pure argon or argon-based mixtures are usually sufficient.
Gas Flow Rates Explained
Using the correct gas flow rate is just as important as choosing the right gas.
Too little gas can cause:
- Porosity
- Oxidation
- Poor arc stability
- Contaminated welds
Too much gas can cause:
- Turbulence
- Air being pulled into the shielding gas
- Wasted gas
- Poor weld quality
Typical starting points:
Gas Flow Rate
MIG Welding Mild Steel
10-15 L/min
MIG Welding Stainless Steel
10-16 L/min
MIG Welding Aluminium
12-18 L/min
TIG Welding Standard Cup
6-10 L/min
TIG Welding Gas Lens
8-12 L/min
TIG Welding Large Cup
10-14 L/min
Always adjust gas flow depending on torch size, nozzle size, welding position and environment.
Common Shielding Gas Problems
Porosity
Possible causes:
- Wrong gas type
- Empty gas cylinder
- Low gas flow
- Leaking gas hose
- Contaminated material
- Drafts disrupting gas coverage
Excessive Spatter
Possible causes:
- Incorrect MIG gas mix
- Too much CO₂
- Poor machine settings
- Incorrect wire type
Black Soot on Aluminium TIG Welds
Possible causes:
- Poor gas coverage
- Contaminated aluminium
- Incorrect torch angle
- Excessive arc length
- Incorrect AC balance
Stainless Steel Discolouration
Possible causes:
- Poor shielding gas coverage
- Excessive heat input
- Lack of purge gas on the back of the joint
- Incorrect gas selection
Back Purging for Stainless Steel TIG Welding
When TIG welding stainless steel pipe or critical stainless joints, shielding the outside of the weld is not always enough.
Back purging protects the root side of the weld from oxidation.
Without purging, stainless steel can develop heavy oxidation known as sugaring.
This can reduce corrosion resistance and create weak weld roots.
Common purge gas:
- Pure argon
Back purging is especially important for:
- Stainless pipework
- Food industry fabrication
- Pharmaceutical fabrication
- Hygienic stainless systems
- Pressure pipework
Which Gas Should You Choose?
Mild Steel MIG Welding
Recommended:
- Argon / CO₂ mix
Best general choice:
- 95% Argon / 5% CO₂
- 80% Argon / 20% CO₂ for heavier work
Stainless Steel MIG Welding
Recommended:
- Specialist stainless MIG gas
Avoid using standard mild steel gas unless approved for the wire and application.
Aluminium MIG Welding
Recommended:
- 100% Argon
For thicker aluminium:
- Argon / Helium mix
Mild Steel TIG Welding
Recommended:
- 100% Argon
Stainless Steel TIG Welding
Recommended:
- 100% Argon
For specialist applications:
- Argon / Hydrogen mixes where suitable
- Back purge with argon where required
Aluminium TIG Welding
Recommended:
- 100% Argon
For thicker aluminium:
- Argon / Helium mix
Final Thoughts
Shielding gas has a major influence on weld quality, arc stability, penetration and appearance.
For most general welding applications:
- Mild steel MIG uses an argon/CO₂ mix
- Aluminium MIG uses pure argon
- TIG welding commonly uses pure argon
- Stainless MIG usually requires a specialist stainless gas
- Thick aluminium or copper may benefit from helium mixtures
Choosing the right gas, setting the correct flow rate and protecting the weld from drafts will help reduce porosity, improve weld appearance and produce stronger, cleaner welds.
At WeldAssist, our goal is to make welding knowledge easier to understand and help welders choose the correct settings, consumables and processes for the job.
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