MIG vs. MAG Welding – Differences & When To Use Them

Although job sites frequently refer to MIG and MAG as “MIG,” the term “gas metal arc welding” refers to both MIG and MAG welding. Each has aspects better suited for certain welding purposes than the other.

The main difference lies in the shielding gas used. MIG uses an inert gas, while MAG uses active gasses. Both processes have some overlapping procedures and are easily adapted to robotic manufacturing. 

Knowing which process to use is critical to the weld quality of every project.

How do you know whether to use standard MIG (GMAW) or MAG (GMAW-A)?

Let’s take a look at the main differences between them,

How GMAW Works

Before diving into MIG and MAG separately, it’s worth quickly going over how GMAW works.

GMAW means gas metal arc welding. It’s a semi-automatic welding process, feeding a wire electrode into the weld puddle from a motorized feeder.

The electrode feeds through the hollow torch while shielding gas flows through a hose connected to a pressurized bottle.

The torch connects electrically to a welder, which turns the spool when you press the trigger, continuously feeding the wire.

The welder creates the arc, fusing the wire electrode and the base metal. Shielding gas protects the weld puddle from exposure to the air.

MIG Welding (Metal Inert Gas)

MIG welding uses an inert or stable gas, such as argon, nitrogen, helium, or a mixture, that doesn’t engage in chemical reactions.

This blanket of stable gas completely isolates the weld puddle, meaning MIG also delivers great heat control, protecting the weld pool and creating clean, precise welds. 

The inert gas or gas blends allow MIG welding to work on various materials, including carbon steel, stainless steel, and aluminum.

When welding non-ferrous metals or stainless steel, helium helps prevent oxidation. This mix adds helium in ratios of 25-75 percent, blended to argon, which can also vary between 25-75 percent. 

Different ratios of each gas can change the profile and depth of the weld bead. Gas suppliers can recommend the blend for a specific task.

It’s not recommended to use a pure inert gas like argon as you will get weak and brittle welds.

Helium runs the arc at a higher temperature. However, it’s expensive. It costs more than argon, and you also have to run a higher flow rate because it’s a lot lighter than air. 

With MIG stainless steel, running a 3-way blend of helium, argon, and CO2 is common.

Typical Uses for MIG Welding

You would usually choose the MIG process for non-ferrous metals, including aluminum, copper, and magnesium.

MIG is the go-to choice with thin sheet metals because of its fine heat control and easily adjusted wire speed. These advantages lend themselves well to auto body repair, appliance manufacturing, and toolmaking.

The automotive, aircraft, racing, and military industries prefer MIG for its high production rates on aluminum and magnesium parts and its versatility and ease of use.

Advantages of MIG Welding

• Corrosion resistance
• Easy to learn
• Versatile for non-ferrous metals
• Heat control on thin sheet metal
• High production rates
• Clean, precise welds

Disadvantages of MIG Welding

• More expensive than MAG
• Not as many metals as MAG
• Less penetration than MAG on thick pieces

MAG Welding (Metal Active Gas)

MAG welding, known as gas metal arc welding with active gas (GMAW-A), is similar to MIG welding, but different shielding gasses control the weld characteristics. 

Instead of inert gasses like argon, nitrogen, or helium, MAG welding employs a mixture of an active gas such as carbon dioxide (CO2) or oxygen (O2) with an inert gas like argon, making an argon/CO2 mix.

Though not common for DIYers, you can add oxygen to shielding gasses in small amounts, between 1-9%, to make a tri-mix. The purpose is to add heat, provide arc stability, and improve the weld puddle flow when welding steel alloys and carbon steel. 

As most people wouldn’t use O2, it’s more common to use CO2 as a substitute for oxygen. This combination is cheaper than pure argon while providing the benefits of active gas, including better weld cleaning and more precise beads.

Shielding gas providers recommend against using more than 25 percent active gas for MAG to reduce spatter.

Whilst it’s possible to weld with 100% CO2, you’ll get poor arc quality and more spatter.

Active gasses react with the weld pool, producing a more stable arc and enhancing penetration. Different active gasses produce different bead shapes, heat levels, and penetration depths.

The active gasses used in MAG welding offer several advantages over MIG welding. Because active gasses react with both the base metal and the weld, they provide better weld penetration, making MAG suitable for thicker materials.  

Additionally, using active gas reduces the weld’s porosity risk, delivering stronger, more reliable joints. They improve penetration, adding heat on thick pieces to produce rigid welds with better mechanical properties than MIG welds. 

MAG welding is also more versatile than MIG because it can weld a wider range of metals, including stainless steel.

MAG welding can be more difficult to learn than MIG welding, and it can produce more spatter. MAG welding is also more toxic than MIG welding because active gasses are more harmful to breathe.

What Do You Typically Use MAG Typically For?

You typically use MAG welding for ferrous metals such as steel and stainless steel. It’s also a good choice for welding thick metals like structural steel.

Advantages of MAG Welding

• Better mechanical properties than MIG
• More versatile than MIG
• Less costly shielding gasses than MIG

Disadvantages of MAG Welding

• More difficult to learn than MIG
• Produces more spatter
• Not as safe as MIG

Key Differences Between MIG and MAG Welding Techniques

Here are the differences between both processes:

Aspect	MIG	MAG
Shielding gas type	Inert gas	Active gas
Shielding gasses	Argon & Helium	Carbon Dioxide & Oxygen
Gas cost	More expensive	Less expensive
Gas interaction	Does not react with base metal	Reacts with base metal
Common applications	Non-ferrous metals, thin metals	Ferrous metals, thick metals
Arc stability	Good	Excellent
Weld appearance	Smooth, shiny	Matt, textured
Weld penetration	Good	Excellent