Welding aluminum is more challenging than welding steel because the material has different characteristics. Aluminum melts at around 1200 degrees, but it’s coated with an oxide layer that melts at around 3700 degrees.
This can be problematic, because if you don’t clean off the oxide layer, the aluminum will melt underneath the oxide and mix with the oxide forming horrible brittle welds.
Aluminum conducts heat much faster than carbon steel, so aluminum electrodes must move faster and supply higher amperage to reach the same temperature. By recognizing these differences, we can adjust accordingly while still maintaining quality control.
MIG Welding Aluminum
To weld aluminum with a MIG welder, you need to attach a spool gun. It’s quite messy and you’ll see sparks flying about. To get the best results, preheat the metal before starting the weld.
What is a Spool Gun?
A spool gun has a spool of wire that’s located in the gun itself, so there’s less distance for the wire to travel before entering the weld pool. You need a spool gun because Aluminum is much softer than steel and won’t travel through the machine as effectively.
Check your welder’s settings to learn how to switch from a spool gun to an MIG gun. You’ll need to unplug your MIG gun and plug in your spool gun. Usually there is a switch on the machine that you can hit to let it know that you’ve changed it over.
Which MIG Wire for Aluminum?
You will need an aluminum wire to weld aluminum. Popular wires include 4043 and 5356; 5554 is also a popular choice. The grade of wire should match the grade of aluminum you’re welding, so make sure you know your alloys. 5356 offers good tensile strength whilst 4043 is a popular silicon alloy that gives you better control over the weld pool and is compatible with a range of base alloys. For welding 5454 or 5154 to themselves use 5554. Use 5356 or 5554 for 5052. For the full chart of specifications see this chart from Hobart.
Clean the Metal
When welding aluminum, you need to make sure that the metal is clean. Remove any oil or other contaminants from the surface, including the thin layer of aluminum oxide that sits on the surface of aluminum. Rubbing with an stainless steel wire brush removes this layer, leaving a shiny surface.
Speed
Aluminum is somewhat more conductive than steel, so you will need to run your spool gun at higher voltage settings. Because of this, you will need to move the spool gun quickly and take care not to burn through the metal, especially on thin aluminum. Use a push technique instead of pulling the bead.
Shielding Gas
When you are welding wrought aluminum, pure argon or an argon/helium mix is needed. Helium is more expensive than argon and can be hard to find, but if you need more heat for thicker metals, you might need this gas added. You won’t be able to use your CO2 gas cylinder or your argon and CO2 mix for MIG welding aluminum because the CO2 will oxidize the aluminum.
TIG welding Aluminum
One of the most challenging methods of welding is TIG welding aluminum. Learning how to TIG weld aluminum can be very difficult, but it is also one of the most rewarding methods of welding. If you are new to welding, learning how to TIG weld steel first will help you get the hang of this process more quickly.
AC Current
When TIG welding aluminum, remember to use alternating current. Alternating current breaks through the oxide layer that covers the aluminum. DC won’t break through the oxide layer and will ruin your weld. You can technically weld with DC but you’ll get in a real mess because you can’t break up the oxide.
Some TIG welders have Square Wave as a function that cleans the metal, but you should still manually clean the metal. It’s really important that you do everything you can to stop the oxide layer from ruining your weld. Use a wire brush to break down the oxide layer and solvents to remove any grease before getting ready to TIG.
Which Tungsten Electrode?
People have their own preferences and different machines work well with different electrodes. If you use an inverter TIG, 100% pure tungsten electrodes won’t give you the best results; instead, try 2% thoriated tungsten electrodes or 2% lanthanated electrodes which perform just as well and can handle higher amperage more effectively.
To prepare your electrode, simply ball the end of it. You can either form the end into a point of a ball. I prefer to have a ball on the end. To ball an electrode, connect it to the machine and let it heat up for a couple of seconds until it turns into a ball. The ball shouldn’t exceed 1.5 times the diameter of the electrode.
Filler Rod
Before you choose a filler rod it’s important to know the specific grade of aluminum you’re using and get the most appropriate. 4043 rods will do the job for most people.
Preheating
Preheat the aluminum before you weld it and it will make your life a lot easier. You’ll get better penetration and find it easier to start and manage the arc.
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Stick Welding Aluminum
You can stick-weld aluminum, but this is a lot messier and less clean than TIG welding. Again, you should preheat the metal before welding and scrape away any debris with a stainless steel brush. Set the welder to DCEP reverse polarity.
It requires a bit of patience starting the arc when stick welding aluminum but you’ll get the hang of it.
Electrode Rods
Remember to buy stick electrodes that are specifically designed for stick welding aluminum, such as 4043s. You’ll find different types of rods perform differently but 4043s are widely used for this application.
Make sure that your work space is well ventilated because the rods give off a lot of smoke.
The electrodes produce a lot of slag, so you need to move them quickly across the joint. Once they’re complete, you’ll need to spend some time chipping off the slag and cleaning the weld.
Manmohan Hebbar
An Industrial Engineer by qualification and a Digital Marketer by profession.
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