Which Gas Do You Need for MIG Welding?

When it comes to MIG welding, choosing the right gas is essential for clean, strong welds whether you’re working with mild steel, stainless, or aluminium the gas you use will impact the arc stability, penetration, spatter, and bead profile.

This guide breaks down everything you need to know about MIG welding gases so you can choose the best one for your needs.

 

What is shielding gas in MIG welding?

Shielding gas protects the weld pool from being contaminated by the atmosphere around it. The contaminants include oxygen, nitrogen, and water vapor – which can cause defects like porosity and weak joints. Without the right shielding gas, you won’t be able to get clean and strong welds.

*This guide does not cover the flux-cored wire.

 

Types of Welding Gases
 

Inert Gases

Inert gases like argon and helium don’t react with the weld pool. They create a stable arc and a clean weld. Argon is the most common inert gas used for MIG welding.

 

Active Gases

Active gases do react with the weld pool. Carbon dioxide is the most commonly used active gas. It’s classified as semi-inert and is less reactive than oxygen but still influences the weld.

 

Common MIG Welding Gases

There are two main gas options for MIG welding

 

• Pure Argon
• Argon/CO2 Mix (commonly 75% argon / 25% CO2)

The blend is often referred to as MIG Gas and is the go-to for most general welding on steel.

 

Best Gases for Different Metals (recommendation)

 

• Mild Steel: Argon/CO2 mix (75/25)
• Stainless Steel: CO2 mix (98% Argon / 2% CO2 or tri-mix
• Aluminium: 100% Argon
• Thick Sections or Deep Penetration: Argon with added helium

 

MIG Welding Gas Comparison

 

 
CO2 Mix (98% Argon / 2% CO2)

Used for stainless steel welding. It offers cleaner results than pure CO2 and is a cost-effective option compared to helium-based mixes.

Spray Transfer Mixes (82-92% Argon / 18-8% CO2)

Ideal for spray transfer methods. Not suitable for short-circuit MIG, which uses a standard 75/25 mix or CO2.

 

Helium Blends

Helium burns hotter, providing deeper penetration – useful for thicker materials, or colder environments. Often blended with Argon or as part of a tr-mix with CO2 or O2 for stainless steel welding.

 

Oxygen additions (1-5%)

Small amounts of oxygen can improve arc stability and penetration on ferrous metals. However, too much of it can damage the weld and increase porosity.

 

What happens if you use the wrong gas?

 

Using the wrong MIG gas can lead to:

• Inconsistent welds
• Increased splatter
• Poor penetration
• Porosity or weak joints

For example, welding mild steel with pure argon will result in poor fusion and messy beads. On the flip side, using hot helium on thin material can burn right through.

Choose the Right MIG Gas for the job.

 

The right shielding gas depends on your metal type, welding process, and material thickness. For most DIY and professional MIG welding, a 75/25 argon/CO2 mix gets the job done. But for aluminium, stainless steel or specialty work, gas selection becomes more critical.

Need help to choose? Get in touch with the team at Gentronics – we’ll make sure you get the right setup for clean, strong, and efficient welds.