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Can I Weld Aluminium with a MIG Welder?

Date: 28-11-2023

Can I Weld Aluminium with a MIG Welder - Alphaweld

With some practice, you can make high-quality welds on aluminium. The MIG welding process is one of the most efficient and easiest welding methods for joining thin and thick aluminium. While MIG welding aluminium is quite different from welding mild steel, modern MIG welders can produce excellent aluminium welds that resemble the TIG welding quality.

What Makes MIG Welding Aluminium Challenging

Unlike steel, aluminium conducts heat rapidly. At the same time, aluminium has a significantly lower melting point than steel and as a result, it becomes challenging to apply the correct heat input. 

You need a high heat input because aluminium will easily conduct the heat away from the weld joint. However, since this material has a low melting point, high heat can quickly result in burning through and distortion, especially when welding thin sections. 

Aluminium is also highly prone to surface oxidation, and this oxide layer has a significantly higher melting point than the base metal. It's vital to clean the oxide layer thoroughly using a dedicated stainless steel wire brush before welding. Otherwise, you'll melt the metal underneath the oxides, while the oxide layer will turn into hard inclusions in the weld, which can lead to cracking.

What Kind of MIG Equipment Do You Need for Aluminium?

You can weld aluminium with most MIG welders, even if they don't support a spool gun connection. However, a spool gun eliminates the chance of the wire from causing a ‘bird nest’ inside the wire-feeding unit. Since the aluminium wire is much softer than steel MIG wire, it can kink in the wire feeder and unroll inside the unit instead of going through the MIG torch. 

But you don't necessarily need a spool gun. If you use a high-quality torch, like the Sumig MIG torches, with a Teflon liner, the chances of birdnesting will be low. Alternatively, you can use a push-pull MIG torch which has a built-in mechanism to pull the wire and prevent the bird nesting effect.

While you can MIG weld aluminium with almost any MIG welder, it's highly beneficial if your welder supports pulsed MIG output. As we noted earlier, aluminium requires high heat input, but it can melt excessively because of it. Pulsed MIG inputs high heat, but it alternates it with a colder phase, which prevents burn-through. 

In other words, pulsed MIG gives you the best of both worlds. Its colder phase makes welding aluminium far easier by preventing excessive heat input, while the hot pulse phase penetrates the joint and provides a high deposition rate.

The Weldmax 225C is a multi-process welder with support for pulsed MIG and TIG welding. In addition, it includes Synergic MIG mode, which makes setting up the welder far more manageable as it auto-sets most of the adjustments for you. The Weldmax 225C also supports a hot start function, which ramps up the current output at the start of the weld. This feature makes aluminium MIG welding easier because cold aluminium can quickly draw out the arc's heat and make weld starting difficult. 

In addition, the Weldmax 225C has a 35% duty cycle at its maximum 200A output, which is vital for welding thick aluminium. Since aluminium conducts heat rapidly, you must apply high amperage for thick pieces. Weldmax's 35% duty cycle will let you weld for 3.5 minutes straight, allowing you to make those long welds in one pass.

How to Set Your MIG Welder For Welding Aluminium

If your MIG welder supports the Synergic MIG, like the previously mentioned Weldmax 225C, the setup process is very simple. Manual settings can be somewhat challenging, but they are also necessary for unorthodox welding scenarios where Synergic settings may need some tweaking. 

You will need to set your MIG welder for spray arc transfer to weld aluminium: short circuit transfer isn't hot enough to keep the weld puddle going on aluminium, so spray transfer is a must. 

To enter spray transfer, you must simultaneously crank up the wire feeding speed (WFS) and voltage, but the exact values vary from brand to brand. You should check your machine's instruction manual to find recommended settings for welding aluminium – this is a great starting point for entering the spray arc transfer. 

You will recognise entering the spray transfer mode by a noticeable spatter reduction and the arc that turns into a stream of droplets deposited in the weld puddle without the wire ever hitting the weld joint. 

Shielding Gas Selection

MIG welding aluminium requires a 100% argon shielding gas. You can’t use the standard 75/25 MIG gas for aluminium because the CO2 will destroy the weld. It's also possible to include helium in the mix with argon when welding very thick sections. Helium amplifies the arc's heat, allowing you to maximise the available amperage from your MIG welder.

Choosing an Aluminium MIG Wire

The two most commonly available aluminium MIG wires are the ER4043 and ER5356:

• ER4043 MIG Wire - A general-purpose aluminium MIG wire with good weld ductility and liquidity. It's used for welding 4000 to 6000 aluminium series.

ER5356 MIG Wire - Has a magnesium addition for improved weld strength and can be used for welding 3000, 5000, and 6000 series aluminium. The ER4043 is softer than the ER5356, making the ER5356 a better choice because it feeds better with a regular MIG gun, thanks to improved rigidity.

MIG vs. TIG Welding Aluminium

TIG welding aluminium can produce better-looking aluminium welds but TIG is a significantly more challenging process to learn and apply. In addition, TIG is far slower than the MIG welding process. MIG welding aluminium provides superior productivity and requires less training to master. 

Modern MIG welders, like the Weldmax 225C, support pulsed MIG, which makes aluminium welding easier and improves the appearance and overall quality of the weld. Some MIG welders also support double-pulsed MIG welding, like the Unimig Razor 200, which allows you to produce a very similar weld appearance to TIG welds on aluminium.

So, unless your application requires TIG welding specifically, MIG welding aluminium is a better choice.

Need More Help with Welding Aluminium?

If you need additional help choosing a suitable MIG welder for aluminium, the experts at Alphaweld are here for you. To speak now with an expert, call (08) 9456 8000 or send us an online enquiry and we'll be happy to assist.