Learning how to gas weld aluminum is a valuable skill set utilized by many industries. Aluminum is one of the most flexible, light, and corrosion-resistant metals in the world, so it stands to reason why it is used in just about every scenario where ductile fracture behavior is necessary. But even with aluminum being quite literally everywhere in modern production, learning to gas weld aluminum may require special knowledge, skills, and tools to create a high-quality bond.
Below, we present a how-to guide for gas welding aluminum along with ideal tools/supplies to ensure that your next gas weld project will be nothing but a successful one.
Step One: Preparation
The first step to gas weld aluminum is cracking the oxide layer. The oxide layer has a melting temp of 3722°F (2050°C) and the aluminum on its own melts around 1221°F (660°C), so you must apply a gas welding temp that is 3X hotter than the aluminum can withstand to bust through the oxide layer. With many aluminum welding rods, this step brings the risk of melting the aluminum away as soon as that layer is broken due to the high melting temperature of the welding rod.
To help avoid that risk, this is why preparing your aluminum in advance is vital. To do that, be sure that your welding space is clean of grease, oil, and dirt (left behind dirt can burn). Next, you can start removing the oxide layer using either a brush or synthetic fleece. Keep in mind that aluminum oxidizes again in just a few minutes, so this process may take several tries.
Super Alloy 5 eliminates the need to prepare aluminum altogether. Its powder flux cleans through impurities and oxidation, preparing the aluminum for the gas weld process.
Tip: If you want to gas weld aluminum using thicker sheets, consider preheating your workpiece to avoid too much heat leaving during the welding process.
Step Two: Selecting Your Gas Torch and Rods
Much like anything in life, you have more than one option you can utilize when it comes to gas welding aluminum. Though there are several processes like the MIG welding process and the plasma one, they each entail going with the right rods/equipment to translate your goals into realities. With that being said, the most common rods you can decide between is brazing vs. soldering.
In general, brazing is defined as using a filler metal with a liquidus above 842°F (450°C), and soldering features a filler metal with a liquidus of 842°F (450°C) or less. All in all, choosing the right gas torch and rod all depends on what your gas welding objectives entail. For example, if you need a high-strong joint and/or fatigue resistance, then the Super Alloy 5 brazing rod would be ideal. If you need something lower and easily reversible, then go with the Super Alloy 1 solder.
Step Three: Choosing The Right Shielding Gas
The next thing you will need to consider is your shielding gas. In standard scenarios, argon or argon mixtures are used as a protective gas when gas welding aluminum, depending on the thickness. For instance, pure argon is leveraged when a sheet is about 12.5mm. In the event that a sheet is thicker, helium is typically mixed with the argon to form a higher temp to help the welding process go smoothly. Generally speaking, the mixture of helium can range anywhere from 25% to 75%, depending on your circumstances and goals.
As a final note, keep in mind that you should also check the dew point of your shielding gas. For reference, argon 4.6 is the most common level for welding as it has a purity percentage of 99.996 (dew point of -62°C). Yes, your argon supplier will likely meet these requirements, but it is not uncommon for moisture to find its way into your gas line and raise that dew point. So be sure to do your due diligence and check your gas pipes regularly.
Step Four: After Gas Welding Aluminum
Finally, the aftermath. Once you are finished with your gas weld aluminum project, some alloys may have to proceed through a hardening process that you can influence directly based on the alloy you chose. For some more insight here, the alloys that can be hardened include AlCuMg, AlZnMg, AlMgSi and AlZnMgCu, whereas AlSiCu, AlMgMn, AlMg, AlMn, and AlSi are considered non-hardening aluminum alloys. Based on what you are using will determine the temp you should introduce during the aging process to provoke the lattice structure of the metal changes along with the mechanical properties. If the wrong temp is selected, you could end up dissolving the alloy elements (precipitating too early) and not have proper distribution control.
What is the Difference Between Gas Welding and Brazing?
As defined by the American Welding Society, gas welding is “a group of welding processes wherein coalescence is produced by heating with a gas flame or flames, with or without the application of pressure, and with or without the usage of a filler metal.”
Brazing is defined as “a group of joining processes that produce coalescence of materials by heating them to the brazing temperature in the presence of a filler metal having a liquidus above 840°F (450°C) and below the solidus of the base metal. The filler metal is distributed between the closely fitted faying surfaces of the joint by capillary action.”
The main difference between the two processes is brazing does not melt and fuse the parent metal with the filler rod.
In the end, it is no secret that there is a lot of dexterity, process power, and underlying conditions involved to ensure your gas-welding aluminum project is successful from start to finish. With so many moving factors and considerations to prioritize, it may feel a bit overwhelming at first glance, especially when compared to welding steel which tends to be less complicated. But as long as you follow the right preparation procedures and invest in the right tools, you can be confident that your gas weld aluminum result(s) will not only meet but hopefully exceed your expectations.