How to MIG Weld Aluminum, a Home Welder Tips for Success

By Bill Byers / April 24, 2019
How To MIG Weld Aluminum

Can I weld Aluminum with a MIG welder?

Yes, and welding Aluminum with a MIG welder is well within the scope of a home hobby welder.

With a good understanding of the metal, a bit of practice, a good welder and a spool gun should see you well on your way to some good looking welds.

Here are my Aluminum MIG welding tips for success on how to MIG weld Aluminum for the home hobby welder.

First things first, it pays to understand exactly what you are dealing with.

Understanding Aluminum

When you weld Aluminum at home it is worth knowing how different welding Aluminum is compared to welding mild steel.

Aluminum is very different to steel. It is a relatively softer metal that is sensitive to heat.

Aluminum draws any heat that is applied to it into the metal and has a comparatively low melting point. Aluminum has the tendency to melt when you least expect it.

Before you know it you have bubbles of Aluminum dropping out the bottom of your weld. This is known as burn through. (The weld turns to smush and holes appear).

Example of Aluminum Weld

Example of Good Aluminum Weld

Now you may appreciate why I suggest when you MIG weld Aluminum you do it with a spool gun.

Understanding the different types of Aluminum

The Aluminum you have around the home and out in industry is combined with other metals to form an alloy. These alloys improve the casting ability and strength of Aluminum, as pure metal would be far too soft to use.

The types of Aluminum alloy you would encounter around the home are the;

  • 4000 series Aluminum which has Silicon added to it
  • the 5000 series has Magnesium added to it
  • the 6000 series has Silicon and also Magnesium added to it.

Aluminum MIG Welding Tips

Aluminum is no different to welding any other type of metal in that it is best to know the base metal/alloy you plan to weld and match suitable Aluminum filler metal (welding wire).

Be it 4000, 5000 or 6000 series.

Source an Aluminum wire compatible with your base alloy as then your filler wire will have a similar melting point to your welding project. There are two common types of Aluminum wire for a MIG welder.

4043 has Silicon added to it and should be matched with 4000 and 6000 series Aluminum. Known as a general purpose wire it produces a weld less prone to cracking. The wire leaves a shiny bright finish.

5356 has Magnesium added to it. It is a stronger wire and considered more difficult to weld with. This wire is matched with 5000 series Aluminum alloy and is particularly suited to marine conditions as it is more resistant to salt water affects.

Should you be also looking for Aluminum welding wire, it is worth having a look at my document here on the site.

Aluminum MIG welding Tips: Choosing a MIG Welder

I’m concentrating here on the home hobby welder.

To weld well you need the right equipment. You’ll need to have or buy yourself a MIG welder for Aluminum.

An Aluminum welding MIG welder is firstly a welder that is capable of using shielding gas.

Certainly a welder for home hobby use will need to run on the electrical power you have available at home 120 volt or if you can get a suitable power point put in, run 220 volts.

Certainly you’ll have an easier time with a more powerful MIG welder run on 220 volts.

Make your life easier by choosing a welder that is spool gun capable.

Then you know the manufacturer has designed and built a machine with that capability in mind. A spool gun means you are feeding the Aluminum wire a short distance 6 to 8 inches from the spool as opposed to eight to ten feet up a MIG welder hose.

Spool Gun For Aluminum Welding

Spool Gun For Aluminum Welding

A 115 volt or 120 volt MIG welding machine will be using its maximum volt output to weld Aluminum which means you will have a much shorter duty cycle at that output (this means a shorter welding time before you risk overheating your welder).

This size of MIG welder is for light occasional Aluminum welds only.

MIG Welding Aluminum Without Gas

You will not be able to weld Aluminum with a flux core only welder. I have a document that explains why there is no flux core Aluminum wire should you want to take a look.

Aluminum MIG Welding Tips: Choosing Your Contact Tip

Aluminum as it heats up expands.

A normal contact may well jam the Aluminum wire. And you get a bird nest of wire.

I highly recommend you choose contact tips that say they are suitable for Aluminum. They will either expand on heating to accommodate the Aluminum wire or have holes that are just a shade bigger to fit the hot Aluminum wire yet not be so wide that they loose electrical conductivity.

What’s this thing I’ve head about Spray Transfer

A MIG welder welding Aluminum correctly, spray transfers the wire into the weld.

This means that minute particles of the Aluminum welding wire is sprayed into the weld puddle.

A MIG welder for Aluminum will do this automatically when;

  • the voltage is increased,
  • Aluminum wire is used and
  • Argon gas (or Argon Helium mix) is the shielding gas.

Spray transfer means the tip of the wire never goes into the weld puddle.

It is important to understand this as this is different to welding mild steel and to allow this process to happen you need to retain the correct distance (approx 1/8th inch) from the weld puddle.

A Pulse Spray Machine

I mention this here as you may have heard of this as an alternative to a MIG welder. Pulse Spray Welding varies the voltage to prevent the arc getting too hot or too cold, a bit like spot welding. A machine that does this is quite pricey for the hobby welder but if your job is welding Aluminum then this type of welder is for you.

It is also the machine to have for welding out of position welds.

A Pulse spray welder is used for welding of thin Aluminum 18 gauge or less.

Just as TIG welding is used for thin gauge Aluminum.

A MIG welder just produces too much constant heat to weld thinner gauges of Aluminum.

What Shielding Gas do I use to Weld Aluminum

You will need a tank or cylinder of shielding gas. If you only weld occasionally try and get hold of a small tank.

The typical gas you will need to weld Aluminum is 100% Argon gas.

If you normally MIG weld mild steel using C25 gas, don’t worry you can use the same gas hose and your regulator designed for Argon gas.

Welding thicker pieces of Aluminum 1/4 inch to 1/2 inch then you may well find a mix of Argon and Helium better for deeper penetration. Typically 25% to 75% Helium is used but check the data sheet of the welding wire you plan to use and what mix the manufacturer recommends for that thickness of wire and Aluminum alloy.

The flow rate to use with 100% Argon is 20 to 30 cubic feet per hour.

Note you may need to go higher if you find you are getting lots of soot deposit on your weld or the location you are welding in is affecting the gas coverage of your weld.

Example of Dirty Aluminum

Example of Dirty Aluminum

Aluminum MIG Welding Tips: Metal Preparation

Clean your Aluminum before you start.

It is really a must. Aluminum is prone to oxidation on its surface and that oxidation is a contaminant when you MIG weld.

Clean with a solvent to get rid of any oils. Acetone is the oil remover of choice on Aluminum as it leaves no residue.

Use a wire brush in one direction back and forth not in circles until you take the sheen off the Aluminum.

The wire brush should be reserved for use on Aluminum only.

Hop over to my post all about wire brushes for Aluminum to find out why and how to use, along with a selection of the ones I think are the best.

Otherwise this soft metal would pick up minute specks of contamination from the piece you previously used your brush on.

If you are using a power brush keep the speed low in consideration of the soft metal and use a fresh pad.

A flap disc and a grinder can also be to clean off your Aluminum metal. Look for a flap disc that is designed for welding on Aluminum.

Even with clean Aluminum, soot is formed on and around the weld. Should you observe excess soot then you haven’t cleaned your metal well enough.

Aluminum MIG Welding Tips: MIG Welding Aluminum Polarity

Aluminum welding needs DCEP (direct current electrode positive). This means your MIG gun (spool gun) connected to the positive terminal. Check your MIG welder and ensure your using the right polarity.

Finding the Settings for Aluminum Welding on Your MIG

You should first check your MIG welder’s manual or if there is one, the settings chart on your MIG welder itself.

If neither of those options are available to you or you just want another option then, to get started you can use an online welding calculator.

Miller Welds has a good one.

To use you

  1. Enter the material you are welding : Aluminum
  2. Then how thick the material is say: 1/8th

And it will tell you its recommendations

  • 0.035 wire is suggested with 350 to 440 inches per minute wire feed.
  • Argon gas needs to be used
  • 21-22 volts set on your welder.
  • Amperage range 110 to 130 Amp

It’s not perfect and you’ll probably need to adjust for your particular circumstances though it does give you a good starting point.

How to MIG Weld Aluminum at Home, Tips for the Hobby Welder

Before you Start welding with your Spool Gun

The tension setting on the Aluminum wire in the spool gun needs to be not so loose that you get a nest of wire and not so tight you squash the Aluminum wire.

The drive roller is built into the spool gun and has grooves that are U shaped to help feed the soft Aluminum.

Aluminum Wire and Drive Roll

Aluminum Wire and Drive Roll

Once you have attached your spool gun to your welder there is usually a switch you flip on your welder to tell the welder you are using the spool gun and the wire is fed from there.

Your Argon gas feeds up though the spool gun hose to the spool gun so make sure the connections are properly seated inside your machine so that you get a good feed of gas.

Weld in the flat or slightly down hill horizontal position.

Vertical and overhead welding of Aluminum is challenging to say the least for a beginner and takes a lot of skill.

Just before you Weld

You will need a longer stick out when welding Aluminum 3/8th to 1 inch to allow the spray transfer mechanism required for welding Aluminum to work.

Welding Wire Stickout

Welding Wire Stickout

Keep a pack of contact tips to hand as even when everything is going smoothly when welding Aluminum you can burn out a contact tip.

Set your wire speed: Aluminum needs high heat/Amp and high wire speed 300 to 450 inches per minute.

Set your gas: 20 to 30 cubit feet per hour.

Aluminum Welding With Spool Gun

How do you Weld Aluminum with a MIG welder

  • Hold your spool gun tip at an angle of 10 to 15 degrees from straight up.
  • Use a push technique when Aluminum welding with a MIG welder. This means you hold the spool gun’s tip, nozzle and wire pointed in and moved in the direction you are welding. This allows for the maximum coverage of your shielding gas onto the weld pool.
  • Doing the opposite – a drag technique produces porosity on Aluminum alloy because the Argon gas isn’t able to cover your weld sufficiently.
  • Aluminum reflects back the heat from the weld puddle and working with the tip of the filler wire too close to the base metal will cause feeding problems because of burn back of the wire onto the contact tip. Maintain a 1/8th inch distance from your project piece.
  • The normal crackle you hear when welding mild steel shouldn’t be heard when welding Aluminum. If you do hear excess crackle then it is likely your wire feed setting is set too high or too low or you are welding to close to the base metal and the spray transfer isn’t taking place.
  • When you start welding non preheated Aluminum you will feel like the heat is too low but as you advance you will think its fine as Aluminum doesn’t glow like steel does as it get hotter.
  • The weld puddle looks the same a bit like molten tin foil but in fact it is getting hotter and hotter until suddenly you have burnt through.

Aluminum MIG Welding Tips To Prevent this;

  • You start slower when the piece is cold and move faster as the base metal heats up.
  • Though to be honest compared to welding mild steel, welding Aluminum is going to feel like you are zipping through uncomfortably fast. You should be moving about twice the speed compared to welding mild steel to prevent burn through.
  • What ever you do don’t weave too much side to side as that risks over heating the metal. Keep the circles small and tight about a dime in size so that you get a little overlap as you push forward.

Your aiming for your welds to look like this

Aluminum Weld With Soot

Aluminum Weld With Soot

The problem of burn through is why some people use a series of spot tacks so that overheating the base metal isn’t so much of a problem.

And you may have to on an underpowered welder where you may only have a short duty cycle available to you.

YouTube Video How to MIG Weld Aluminum

I found this video particularly useful. It takes you through the procedure along with some hints and Aluminum MIG welding tips. Yes it is based on an Eastwood MIG welder but the principals are applicable to any MIG welder for Aluminum that uses a spool gun.

How to MIG Aluminum – Pointers and Troubleshooting With Eastwood

Video Credit : Eastwood Company

There is another YouTube video worth checking out. The video is put together by Weld.com – the tutors of Cowley College, their MIG welding with a Spool gun video is sublime. I have a link to it on my Best Wire for MIG welding Aluminum, the Which, Why and When article you can take a look at it there.

Aluminum MIG Welding Tips: After a weld Pass

Clip off the end of the wire after each weld. Aluminum wire produces a ball on the end of the wire. This ball on the end will cause you issues when you start to weld again. Feed the wire to the right stick out length and you are ready to weld.

After the Weld

Brush excess soot and any spatter off. With practice you should have a weld like this one.

Aluminum Weld that has been brushed

Aluminum Weld that has been brushed

MIG Welding Thick Aluminum with an Underpowered Welder

Here are some things to do that can help you when you are MIG welding thick Aluminum and your welder isn’t quite up to it.

Pre heat your project piece.

Let’s assume we are talking about 1/4 inch to half inch Aluminum.

Pre heat the base metal with a hand torch before you weld.

Particularly if you are using small diameter wire (cause it is all you have), on thicker Aluminum,

using a welder that is underpowered for the job.

Get yourself and use a temperature gauge to be sure you don’t go over 230 degrees F.

– you want to pre-heat not melt your project piece.

Pre heating is also useful if you are MIG welding thick Aluminum to a thinner piece of Aluminum.

Advantages and Disadvantages of MIG welding Aluminum

Advantages

  • Can produce good quality welds with time and skill spent on preparation, the correct set up and equipment.
  • Able to weld 14 gauge to 1/4 inch Aluminum depending on the capabilities of your welder and preparation
  • No need to buy a TIG welder and learn those skills and have that expense or pay an expert TIG welder to weld some Aluminum for you.

Disadvantages

  • Needs practice around the correct set up of your MIG welder to weld well.
  • Only have a home 115v or 140 volt welder then you’ll only be able weld up to 1/8th of an inch thick Aluminum without needing a 220 volt welder. With a 220 volt welder you can go up to 3/8th of an inch.
  • 1/4 inch thick Aluminum will need pre-heating before welding.
  • Particularly with an underpowered welder.
  • Welding thinner than 18 gauge Aluminum needs a specialized set up
  • Any other position other than flat or mild down hill horizontal is out. Overhead welding of Aluminum needs special skills.

MIG Weld Aluminum without a Spool Gun

Some claim to have success welding Aluminum without a spool gun …

And you could try, by getting yourself the shortest cable to your MIG gun you can find. This cuts down on the length the Aluminum wire has to travel,

Putting on drive rollers that are U shaped so as not to distort the Aluminum wire as it feeds.

Playing around with your drive roll and tension.

However,

You may do all of that and not be successful feeding any wire at all without bird nesting the wire.

Birds Nest of Wire

Birds Nest of Wire

Aluminum wire isn’t as strong as mild steel and tends to bend and curl and wind back on itself at the slightest provocation.

And when that happens poor wire feed means you blow through a few contact tips if not worse.

And you will have spend time and money, not getting anywhere fast. Because doing all the above is not without cost.

Believe me

If you have a few projects to weld, the willingness to do a bit of practice and limited budget to spend then adding a spool gun to your welder could well be cost effective compared to risking breaking your welder or paying some one to TIG weld your projects for you.

Last Words

Armed with the advice in this article ‘How to MIG Weld Aluminum, a Home Welder Tips for Success’, a good welder and a little practice should see you well on the way to producing some good strong welds when you weld Aluminum at home.

 

Other Resources

Aluminum: A guide to Aluminum GMAW Welding

 

 

 

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