A Complete Guide to Welding Gas

What Welding Gas Do I Need? A Complete Guide to Choosing the Right Gas

Choosing the right welding gas can make a significant difference to arc stability, penetration, spatter levels, weld appearance and overall weld quality.

But with Pure Argon, Argon/CO2 mixtures, Carbon Dioxide and other shielding gases available, knowing which cylinder you actually need isn't always straightforward.

One of the questions we're regularly asked at Sphinx Industrial Supplies is simply:

"What welding gas do I need?"

The answer depends mainly on three things:

The welding process you're using, the material you're welding and what you're trying to achieve from the weld.

Whether you're MIG welding mild steel, TIG welding stainless steel or trying to weld aluminium, this guide will help you understand which welding gas to choose and, importantly, why.

Quick Answer: Which Welding Gas Should I Use?

If you just need a quick starting point:

*The exact mixture should be selected for the wire, material and welding requirements.

For many workshops, this means the choice is considerably simpler than it first appears.

MIG/MAG welding mild steel? You're generally looking at an Argon/CO2 mixture.

TIG welding? Pure Argon is the standard choice for a very wide range of applications.

MIG welding aluminium? Pure Argon is commonly used here too.

But why?

What Does Welding Gas Actually Do?

In MIG, MAG and TIG welding, shielding gas protects the molten weld pool and hot electrode from the surrounding atmosphere.

The air around us contains gases including oxygen and nitrogen. If the molten weld pool is inadequately protected, atmospheric contamination can contribute to weld defects and poor results.

The shielding gas creates a protective envelope around the arc and weld pool.

However, the gas isn't just there for protection.

The type and mixture of gas can also influence:

• Arc characteristics
• Penetration profile
• Spatter levels
• Weld-pool behaviour
• Metal transfer
• Travel speed
• Weld appearance
• Arc stability

This is why changing welding gas can noticeably change how a MIG welder behaves even when you're welding the same material.

What Gas Do I Need for MIG Welding Mild Steel?

For general MIG/MAG welding of mild steel, an Argon and CO2 shielding gas mixture is one of the most commonly used options.

Two mixtures you'll frequently come across are:

Argon / 5% CO2

An Argon-rich mixture containing approximately 5% Carbon Dioxide can provide a smooth, stable arc with relatively low levels of spatter.

It is particularly suited to applications where good weld appearance and controlled arc characteristics are desirable.

Argon / 20% CO2

Increasing the COâ'' content changes the characteristics of the arc.

An Argon / 20% CO2 mixture is another option for welding carbon and mild steels and can provide stronger penetration characteristics, making it useful across many general fabrication applications.

So which should you choose?

As a simplified rule:

Lower CO2 → generally smoother arc and lower spatter

Higher CO2 → generally more penetrating/active arc, but potentially more spatter

The correct choice ultimately depends on material thickness, welding position, wire, transfer mode and the characteristics you're looking for.

Can I Use Pure CO2 for MIG Welding?

This is a very common question.

Yes, CO2 can be used for MAG welding mild/carbon steel.

Pure CO2 has been widely used for welding carbon steels and offers some practical advantages, including good penetration and relatively low gas cost.

However, compared with an Argon-rich mixture, pure CO2 generally produces a harsher arc with higher levels of spatter.

An Argon/CO2 mixture will therefore often be preferred where the welder wants:

• A smoother arc
• Reduced spatter
• Better bead appearance
• Greater control

Pure COâ'' can still be perfectly suitable for certain applications, particularly where penetration and economy are more important than minimising spatter.

Can I Use Pure Argon for MIG Welding Mild Steel?

This one causes a surprising amount of confusion.

Pure Argon is generally not the appropriate shielding gas for conventional MIG welding of mild steel.

While you may be able to establish an arc, the resulting weld characteristics and penetration are unlikely to be what you're looking for.

For conventional MIG/MAG welding of mild steel, an Argon/COâ'' mixture is normally the better choice.

This is an important distinction because Pure Argon is absolutely the correct gas for many other welding applications.

Which brings us to TIG.

What Gas Do I Need for TIG Welding?

For the majority of everyday TIG welding applications, the answer is:

Pure Argon

Pure Argon is commonly used when TIG welding:

• Mild steel
• Stainless steel
• Aluminium
• Copper and copper alloys
• Nickel alloys
• Titanium and other reactive metals

It provides excellent shielding and stable TIG arc characteristics.

For someone buying their first TIG welder, a cylinder of Pure Argon will therefore cover a very wide range of common TIG welding jobs.

There are specialist applications where different gases or mixtures, including helium-containing mixtures, may be beneficial, but Pure Argon remains the standard starting point for most TIG welding.

What Gas Do I Need for TIG Welding Stainless Steel?

Pure Argon is commonly used for TIG welding stainless steel.

Good shielding is particularly important when working with stainless because poor gas coverage or excessive heat input can lead to heavy oxidation and discolouration.

If your stainless TIG welds are coming out dark grey, black or heavily oxidised, don't immediately assume the gas itself is wrong.

Check:

• Gas flow rate
• Torch angle
• Cup size
• Gas lens condition
• Tungsten stick-out
• Drafts around the welding area
• Post-flow time
• Material cleanliness

For stainless pipework and applications where the reverse side of the weld needs protection, back purging with Argon may also be required.

What Gas Do I Need for TIG Welding Aluminium?

For most conventional AC TIG welding of aluminium:

Pure Argon

Argon provides the shielding and arc characteristics required for a wide range of aluminium TIG applications.

If you're struggling with aluminium TIG welding, however, don't automatically blame your shielding gas.

Aluminium TIG performance can also be affected by:

• AC balance
• Amperage
• Tungsten selection
• Material cleanliness
• Oxide removal
• Filler-wire selection
• Gas flow
• Torch setup

Aluminium naturally develops an oxide layer, which is one of the reasons AC TIG settings and preparation are particularly important.

What Gas Do I Need for MIG Welding Aluminium?

Pure Argon is also commonly used for MIG welding aluminium.

This is one of the important exceptions to the idea that MIG welding always requires an Argon/COâ'' mixture.

You do not want to use your standard mild-steel Argon/CO2 shielding gas for conventional aluminium MIG welding.

Aluminium MIG also requires attention to other parts of the setup, including:

• Correct aluminium MIG wire
• Suitable drive rolls
• Appropriate liner
• Correct contact tip
• Suitable wire-feeding system
• Correct machine settings

Because aluminium wire is much softer than steel wire, wire feeding can become particularly important.

What Gas Do I Need for Stainless Steel MIG Welding?

This is where we'd recommend being slightly more careful.

Stainless steel MIG welding commonly uses an Argon-rich shielding gas containing a small proportion of active gas, but the ideal mixture depends on the material, wire, transfer mode and application.

Using the same high-CO2 mixture you'd normally use for mild steel isn't automatically the best choice for stainless.

If you're unsure, speak to your welding-gas or welding-equipment supplier with the grade of stainless, wire type and welding machine/process you're using.

What Flow Rate Should I Set My Welding Gas To?

Having the right gas is only half the story.

You also need the correct gas flow rate.

For many workshop MIG and TIG applications, you might see flow rates somewhere around 8–15 litres per minute, but this should never be treated as a universal setting.

The correct flow depends on factors such as:

• MIG or TIG
• Torch and nozzle/cup size
• Welding current
• Joint configuration
• Indoor or outdoor environment
• Draughts
• Tungsten stick-out
• Gas-lens setup

And importantly:

More gas isn't always better.

Excessively high gas flow can create turbulence around the shielding envelope and potentially draw surrounding air towards the weld.

If you're experiencing porosity, don't simply keep turning the regulator up.

Find the cause.

Why Am I Getting Porosity Even Though I'm Using the Right Gas?

If you've selected the correct shielding gas but you're still seeing small holes or cavities in your weld, you may be experiencing weld porosity.

Possible causes include:

Insufficient gas flow
Not enough shielding gas is reaching the weld pool.

Excessive gas flow
High flow can create turbulent shielding.

A gas leak
Check connections, hoses, regulator and torch.

Blocked or contaminated nozzle
Heavy spatter can disrupt shielding-gas coverage.

Drafts
Fans, open doors and outdoor conditions can blow shielding gas away from the weld.

Dirty material
Oil, moisture, rust, paint and other contaminants can contribute to weld problems.

Torch position
Excessive torch angle or distance from the workpiece can reduce effective gas coverage.

Before increasing the flow rate, systematically check the entire gas system.

How Do I Know If My Welding Gas Is Actually Flowing?

If you suspect a shielding-gas problem, don't rely solely on the reading on your regulator.

Check the gas is actually reaching the torch.

Depending on your equipment, you can use a flowmeter or gas-flow tester at the torch nozzle to check actual gas delivery.

This can help identify problems such as leaks, restrictions or incorrect regulator settings.

It's particularly useful when troubleshooting unexplained porosity.

Do I Need Different Gas for MIG and TIG Welding?

Potentially, yes.

If you're welding mild steel with MIG/MAG and also using TIG, you'll commonly have:

MIG/MAG mild steel → Argon/CO2 mixture

TIG → Pure Argon

If you also MIG weld aluminium, your Pure Argon may be suitable for that application too.

This is why workshops operating several welding processes often keep more than one shielding-gas cylinder available.

Welding Gas Quick Reference Guide

Remember that specialist materials, procedures and coded welding applications may have more specific shielding-gas requirements.

Choosing the Right Welding Gas: Don't Just Choose on Price

It's tempting to look at welding gas as simply another consumable.

But your shielding gas has a direct influence on the welding process.

A cheaper gas isn't necessarily cheaper overall if it results in:

• More spatter
• Additional grinding
• Increased clean-up time
• Slower welding
• Poor appearance
• Rework
• Weld defects

For a fabrication business, labour usually costs considerably more than shielding gas.

The best welding gas is therefore the one that provides the required weld quality and productivity for your particular application—not necessarily whichever cylinder has the lowest refill price.

Need Help Choosing Your Welding Gas?

If you're still thinking "What welding gas do I need?", don't guess.

At Sphinx Industrial Supplies, we've specialised in welding equipment and consumables since 1989 and can help you select the appropriate shielding gas for your machine, material and welding process.

We supply welding gases including Pure Argon, Argon/CO2 mixtures and Carbon Dioxide, alongside regulators, flowmeters, MIG and TIG consumables, welding wire and professional welding equipment.

Whether you're MIG welding mild steel, TIG welding stainless, setting up for aluminium or simply trying to solve a shielding-gas problem, our team can help you get the setup right.

Speak to Sphinx Industrial Supplies for welding gas, equipment, consumables and expert technical advice.

Frequently Asked Questions

What is the best gas for MIG welding mild steel?

An Argon/CO2 shielding-gas mixture is commonly used for MIG/MAG welding mild steel. The ideal COâ'' percentage depends on factors including material thickness, transfer mode and the desired arc characteristics.

What gas do I need for TIG welding?

Pure Argon is the standard shielding gas for many common TIG welding applications, including mild steel, stainless steel and aluminium.

Can I use Argon/CO2 for TIG welding?

For conventional TIG welding, Pure Argon is normally used rather than the Argon/CO2 mixtures commonly associated with MAG welding mild steel.

Can I MIG weld with Pure Argon?

It depends on the material. Pure Argon is commonly used for MIG welding aluminium, but it isn't generally the correct choice for conventional MIG/MAG welding of mild steel.

What gas should I use for aluminium welding?

Pure Argon is commonly used for both TIG and MIG welding aluminium.

What gas should I use for stainless steel?

Pure Argon is commonly used for TIG welding stainless steel. MIG welding stainless usually requires a suitable Argon-rich shielding-gas mixture selected for the application.

Why am I getting holes in my weld?

If by "holes" you mean small cavities or pinholes in the weld, you may be experiencing porosity. Possible causes include poor shielding-gas coverage, leaks, drafts, contamination, incorrect flow rate or an unsuitable gas.

Is a higher welding gas flow rate better?

No. Excessively high flow can create turbulence and reduce effective shielding. Set the gas flow appropriately for the torch, process and welding environment rather than simply turning it up.