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How to Weld Aluminum: Methodologies and Tips

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worker welding aluminum truss using tig welder

Aluminum is a relatively soft metal in its pure form, with a good strength-to-weight ratio. This metal has ubiquitous applications in the engineering sector because of its many advantages, such as conductivity and corrosion resistance. However, it requires the addition of alloys to increase its strength.

It is challenging to join metal components by melting them together, even for the most experienced welders. But welding lightweight metals such as aluminum necessitates different processes and techniques than welding steel. The process requires extreme accuracy to ensure the strongest possible bond. Since the properties of aluminum vary from that of steel, working with the metal presents unique challenges.

While welding aluminum can be challenging, access to the right information and regular practice can help develop and hone your aluminum welding skills. Read on to find out the different methodologies’ tips and tricks for welding aluminum.


What Makes Aluminum Welding Challenging?

Aluminum is a common metal in fabrication because of its higher corrosion resistance, excellent electrical conductivity, lightweight, and aesthetics. It is used for different types of welding endeavors. Unfortunately, the same traits that make it a suitable welding metal also make it challenging to handle.

Perhaps the major challenge is that it is made from soft material that is highly sensitive and is insulated by a sturdy oxidized layer. In a molten state, the metal is also highly susceptible to impurities such as dirt, air, and water.

These impurities can significantly reduce its ductility, strength, and the formation of oxidation on the weld. This consequently complicates multi-pass welding and distorts the weld’s appearance.

Also, aluminum and its alloys tend to have a high oxygen affinity. In its pure form, aluminum melts at 650 degrees Celsius while the oxidized layer melts at 2,037 degrees Celsius. Since the oxidized layer melts at a higher temperature compared to the pure aluminum itself, you have to clean the surface of the metal thoroughly before attempting any welding.

The other challenge is brought on by the low melting point and high thermal conductivity qualities of the metal. These qualities tend to narrow down the window of workability compared to other metals. This could easily result in a burn-through. In addition, the qualities make it hard to indicate the quality and progress of the weld, making it difficult to work with.

man welding aluminum with MIG

Image Credit: aydngvn, Shutterstock


How Can Aluminum Be Welded?

When it comes to welding aluminum, everything hinges on choosing the right welding method. While there may be numerous methods for welding steel, aluminum requires specialized equipment and techniques. The two main methods used to weld aluminum and its alloys are Metal Inert Gas (MIG) and Tungsten Inert Gas (TIG) welding.

1. TIG Aluminum Welding

Also known as Gas Tungsten Arc Welding (GTAW), this is one of the most popular welding processes often used by professional welders in the automotive industry and car racing enthusiasts. TIG welding can successfully fuse aluminum alloys.

It is particularly suitable for thinner aluminum sheets because it produces a clean weld. A TIG welder requires equipment that can handle Alternating Current (AC) while using 100% argon gas for shielding. 

In addition, TIG does not need mechanical wire feeding, which can potentially bring about feed ability issues. Instead, it directs the filler material into the weld puddle.

Another reason for TIG’s popularity in aluminum welding is the fact that it prevents the contamination of aluminum, which is very sensitive, throughout the process.

Factors to Consider in TIG Aluminum Welding
  • Shielding Gas: You first have to prepare all the equipment that you require for your welding project. Argon gas is the best for shielding because it can stabilize the arc to produce a fusion with better weld geometry. Helium is also a viable option as a shielding gas because it helps clean the oxidized layer from the aluminum surface.
  • Electrode: TIG welding will also require a tungsten electrode. You can use any kind of tungsten electrode. Depending on your budget, you can opt for the cheaper pure tungsten or a pricier thoriated tungsten electrode.
  • AC Power: After choosing an electrode, you need to get a TIG welding machine, preferably one capable of producing a high-frequency alternating current (AC). High-frequency AC is an ideal option because it balances surface cleaning with weld penetration while keeping the tip of the electrode cool.
  • Filler Materials: You can opt to use filler metals or not, depending on the joint design and the thickness of the base metals.
  • Cleaning: After gathering the necessary tools and accessories, prepare the base metal by removing the oxidized layer through wire brushing or grinding. Ensure this process is thorough because the final results are affected by this step.
  • Settings Adjustments: Finally, you can adjust the settings of your TIG welder, such as gas flow and amperage. This depends on your preference and welding environment. Keep in mind that aluminum burns hotter than steel. So, you may have to use a low amperage setting.

Also, modify the electrode to have a ball tip end. This will widen the arc, ensuring the distribution of heat on the surface of the base metal.

After setting up the TIG welder, you can start welding. Start slowly without dabbing the filler metal until the electrode creates a welding pool. Continue welding while occasionally stopping after every 10 to 15 centimeters to allow the base metal to cool down. This prevents issues of burning through.

Tips for TIG Welding
  • While any kind of tungsten can work, the best option for aluminum is the pure tungsten electrode. 
  • Prepare the aluminum for welding by cleaning the oxidized layer and preheating it.
  • If you use argon as a shield, ensure that the torch doesn’t get too much of it because it creates irregular arcs.
  • Use a heat sink to prevent warping.
  • Always keep the filler electrode free from contaminants. Also, melt the rod with the base material to create a constant weld.

2. MIG Aluminum Welding

Also known as Gas Metal Arc Welding (GMAW), this is another common arc welding method used for aluminum welding. It is an ideal process for aluminum because it uses less heat compared to thicker metals. It also produces higher deposition rates and faster speeds compared to TIG, affecting the final weld quality.

It does, however, use a mechanical wire feeding system that uses either a push-pull gun or a spool gun to enable wire feeding.

Factors to Consider in MIG Aluminum Welding
  • Material Thickness: First, you have to consider the material thickness. Aluminum that can be MIG welded should have a gauge of 14 and above. The metal thickness is determined by the output capacity of the TIG welding machine. If you want to weld aluminum with a gauge below 14, you may have to utilize specialized pulse MIG welding equipment.
  • Shielding Gas: Just like TIG welders, MIG welding also requires shielding gas. Since aluminum is a non-ferrous metal, 100% argon is the perfect shielding gas in MIG welding. The best flow rates for argon are 20 to 30 cubic feet per hour.
  • Cleaning: Before embarking on the welding process, you need to thoroughly clean aluminum by removing any debris on the surface, including dirt and lubricants. Proceed to the removal of the oxidizer only after degreasing. You can use either hand wire or cup wire brush, provided they are stainless brushes. In case you opt for a power wire brush, reduce the pressure and RPMs to reduce the smearing of the surface. This could trap impurities and oxides under the surface. Also, clean the base metal with a wire brush that is only designated for aluminum to avoid contamination.
  • The Process to Use: The best process to use in MIG welding of aluminum is spray transfer. It entails the transfer of molten metal droplets from the electrode to a welding pool. This is an ideal process because it reduces short-circuiting while increasing efficiency and deposition rate. However, keep in mind that spray transfer produces a lot of heat which creates a large weld pool that is difficult to control.
  • Gun and Wire Feeding: Before MIG welding aluminum, you need to choose the gun and wire feeding system required. Normally, a spool gun or a push-pull system is used to feed the aluminum wire in MIG welding. The spool gun helps eliminate the likelihood of bird-nesting because it only feeds a few inches. A push-pull system, on the other hand, uses a motor in the gun to pull the wire through the liner while a motor in the feeder assists the feeding. The push-pull system is suitable in situations where you are welding further from the power source. It is also user-friendly and features an ergonomic design.
  • Filler Material: Determine the base aluminum alloy and the conditions the end-product is likely to be subjected to. The ER4043 and ER5356 are the most readily available aluminum filler wires available on the market. For more recommendations on wire alloys, you can use with aluminum, consider contacting your local store.
Tips for MIG Aluminum Welding
  • Always maintain the proper tip-to-work distance. If you can, consider having the contact tip recessed about 1/8 inch inside the nozzle.
  • When MIG welding aluminum, the weld puddle and reflective tend to get very hot. Holding the tip at a favorable distance will prevent the wire from burning back to the contact tip among other feeding problems.
  • Large weave beads are not good for aluminum. If you require larger fillet welds, use multiple pass straight beads. They are less likely to experience burn-through, cold lapping, and other welding issues.
  • When welding MIG aluminum, it’s necessary to ramp up the torch travel speed as the base material gets hot during a weld.

Alternative Methods of Welding Aluminum

TIG and MIG may be the common methods of welding aluminum; however, there are other types of welding processes that can work with this metal, as seen below.

Laser Beam Welding

Similar to other metal fusing processes, laser beams can fuse a variety of aluminum alloys. The laser beam is one of the fastest welding processes owing to a high-power density at the surface of the materials. It is capable of producing high aspect ratio welds that narrow heat-affected zones.

Laser welding can produce fast and clean welds and is ideal for metals susceptible to cracking, such as aluminum. The shielding gasses required for this process depend on the grade of aluminum to be joined.

Electron Beam Welding

This process is also good at producing fast and clean welds, even in very thick sections of aluminum. Unlike other fusion-based welding processes, electron beam welding works in a vacuum. So, a shielding gas is not necessary for the process. This produces very pure welds.

However, you must be careful when choosing the filler and when selecting welding parameters and joint design to minimize the risk of cracking in sensitive materials like aluminum.

Friction Welding

This is a process of metal fusion that happens in the solid-state. The metals don’t have to melt to fuse. Friction welding can fuse all series of aluminum alloys, including the notoriously stubborn 2xxx and 7xxx series.

In addition, the process does not require shielding gas because the materials fuse in a solid-state. Friction welding offers superior mechanical performance compared to other fusion welding methods.


Conclusion

Aluminum has a lot of applications in engineering because of its conductivity and corrosion resistance capabilities. However, you need to fuse the metal with other alloys to make it stronger. As aluminum welding becomes more popular, it is also good to learn the skills to work with the material.

MIG and TIG welding are the most popular methods of welding aluminum. They can produce clean and precise welds. However, there are other alternative processes such as Laser Beam, Electron Beam, and Friction welding processes.

When working with TIG, surface cleaning is the key because it determines the quality of the weld produced. Argon is also the ideal gas to use as a shielding gas because it helps stabilize the arc. Working with MIG on the other hand, use a spool gun to reduce the chances of bird-nesting. Also, use the spray transfer process to increase the welding efficiency and deposition rate. 

Keep in mind that some of these welding methods get too hot, so it is important to have your safety gear on while welding aluminum.


Featured Image Credit: guteksk7, Shutterstock

Cameron Dekker
 

Cameron grew up in Allentown, Pennsylvania, a once-proud steel town on the Lehigh River, where he got a taste of TIG welding in his high school shop class. He holds certificates for Certified WeldingEducator (CWE) and Certified Resistance Welding Technician (CRWT) from the American Welding Institute. His interests include scuba diving, sculpture, and kayaking.