How to Mig Weld Aluminium Using Spool Gun

Mig weld aluminium using spool gun can sometimes be easy and sometimes can be a big difficulty. Read more here to grasp tips of avoiding soot and other helpful tips, know how to smooth this welding process and create the quality welds that you will be proud of.

Specified below are Mig welding tips and techniques that can work best along the way you weld; rather, the information will help you with Mig welding aluminium using spool gun.

The time you start learning about Mig welding aluminium, to get lots of contact tips is one of first things you should do.

This is more significant than you may think as tips suffering from a burn back due to aluminium melting to the tip are inducing to reuse, but can give you more trouble if you do.

To this end, aluminium isn’t similar to steel. Usually, we work on steel reusing Mig tips, which isn’t a big deal. Still, it’s another story as far as aluminium comes. Aluminium Mig wire is far softer and more prone to wire feeding issues.

It doesn’t mean that we can not re-use them. But it would take some more work to get rid of aluminium, drill out the tip, and ensure the hole is evened out without inhibiting wire feeding. To say nothing about the fact that any burr of tip can result in inconsistent arc or burn-back, which just frustrates the whole affair.

Each of contact tips is about one dollar, and that’s not costly enough to need a loan but also not worth the irritating inconvenience they can bring about from trying to re-use them when you have any burn-back.

So you are suggested to save your burn-back tips in times you have no other alternative or when you have time to re-dress them using a drill, sander, or oxy-fuel tip cleaner.

What induces to black soot when Mig welding aluminium?

Mig welding Aluminium - Sooty weld (Photo cr: Jody Collier)

Black soot is aluminium oxide, which is bizarre since aluminium oxide is considered white in colour while something related to small particles of soot makes it change the direction of light in a way that it turns out to look black.

The carburettor set too rich also causes soot. And it’s due to inefficient burn.

The inefficient burn can result from inappropriate settings – for example, excessive wire speed. Also, it can be the consequence of insufficient argon shielding from poor torch angle, a leak or inadequate flow at the flow-meter.

Sometimes, it takes certain trial and error to figure the settings that result in a soot-free weld. 

As seen from the video, the man had some issues with the Hobart spool gun.

After some trouble shooting, he figured that the pattern of gas shielding was bad, which causes the black soot.

It adds up after learning so, and he added a scotch brite piece for a diffuser, and things go better as such.

Helpful Mig welding tips for those that they concern:
9 Helpful Mig Welding Tips for Brand-New Welders from Pros
8 Useful Tips for Mig Welding

Gun angle?

A push angle helps a lot when it comes to Mig welding aluminium.

That is mainly because the push angle would place the argon shielding over the arc as well as other hot puddle areas that will be under oxidization if being improperly shielded from the atmosphere.

Still, what if the weld position or position of other objects inhibit the use of a push angle? Then just pull. But rising a bit the gas flow rate sometimes works.

And sooting isn't a big deal all the time. For multi-pass welds, you will want to brush the soot all over with a stainless wire brush.

Why preheat?

Preheating thick aluminium (Photo cr: Jody Collier)

Aluminium is electrically and thermally conductive, which means it quickly scatters heat.

That isn’t a problem in case of Mig welding aluminium 1/8" (3.2mm) - 1/2" ( 25mm) thick. 

Still, a preheat is highly encouraged for truly thick aluminium. A preheat in the range of 200 to 250f can help a lot this case whether you’re Mig or Tig welding aluminium.

What is the best stick-out when Mig welding aluminium?

Short stick-out would be used for short-circuit Mig. Still, spray transfer is applied in case of Mig welding aluminium. A short stick-out this case can burn up the tips whilst a longer stick-out (about 3/4”) would work better for the spray transfer.

What is the best type and size of wire to use?

4043 is preferred over 5356 when it comes to general work. In most cases, 4043 gives better flow and less sooting.

Still, sometimes, 5356 is called for because of anodization of post weld. Or perhaps this wire is defined on a drawing.

What should be the diameter of wire?

A good rule of thumb is to employ the largest diameter of wire.

In this video, the man was employing .035" ( .9mm) wire as it was the largest size of tip he had. 

But for 1/8" (3.2mm) and above, he often likes to use 3/64" (1.2mm). The wire of this diameter appears to be more consistent and robust for general spool gun work.

(Above information and video are taken with credit from Jody Collier.)