Most welders dislike working with aluminum because of the unique challenges it presents. The techniques and processes used are significantly more demanding than steel. Failure to follow these protocols can result in destroyed materials and project delays.
That being said, if a welder has the knowledge and expertise, they can quickly and easily complete excellent, sturdy welds. Read on to learn how to weld cast aluminum, as well as some tips and tricks for beginners. Thanks to this handy guide, you can be making beautiful aluminum welds in no time.
Why Is Welding Cast Aluminum So Difficult?
As one of the most common metals used in fabrication, aluminum is lightweight, non-corrosive and aesthetically pleasing. Fabricators love using it in projects that need to be both strong and eye-catching.
What makes it so difficult to weld? Aluminum is extremely soft, sensitive, and insulated by an oxidized layer. When in a molten state (like welding), aluminum can become porous and absorb impurities. This creates weak welds that won’t hold up under strain, effectively making them both ineffective and unsafe.
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Additionally, aluminum and aluminum alloys love oxygen, and they oxidize very quickly. Pure aluminum has a melting point of 1200 degrees Fahrenheit (650 degrees Celsius), which is about 100 degrees cooler than the melting point of steel. Conversely, the oxide exterior that protects cast aluminum melts at 3700 degrees Fahrenheit (2037 degrees Celsius). To weld aluminum without liquefying it completely, any oxidation must be scrubbed from the surface before welding begins.
Essentially, aluminum’s lower melting point and high thermal conductivity mean it has a shorter working time than other metals. It also means aluminum is prone to burn through while welding due to most builds using thinner sections. Welders must balance penetrating thick material deep enough to create a strong weld without burning through thinner sections. Combined with the difficulty of determining weld progress, aluminum remains one of the most difficult materials to weld.
Types Of Aluminum Welding
There are two types of welding commonly used to work with aluminum. Both are effective, but some welders prefer one over the other depending on the build. Here’s a brief summary of the two:
Gas Tungsten Arc Welding (GTAW), also called Tungsten Inert Gas welding (TIG), is the most popular choice among experienced aluminum welders. Pro racing teams and auto enthusiasts also prefer to use this type of welding in their shops.
Its popularity derives from using AC current to weld metal, rather than mechanical wire feeding prone to malfunctions. GTAW/TIG welding forms the filler material into a puddle so it can be maneuvered across the joint evenly. It’s a cleaner process that also removes the oxidized layer off aluminum as it welds, preventing impurities.
Gas Metal Arc Welding (GMAW), or Metal Inert Gas (MIG) welding, is another popular method for working with aluminum. This method is preferred for its speed and higher deposition rate, as it uses a mechanical wire feed system. The drawback to GMAW/MIG welding is that the mechanical wire feeder may require the operator to use a spool gun or push-pull gun in addition to the welding torch to keep the wire feeding smoothly.
Also Read: Different types of Mig Welding
Additionally, aluminum surfaces and the filler rod must be cleaned thoroughly, dry, and have strong shielding gas coverage (usually pure argon content). The actual welding process may be faster, but thorough cleaning and drying are critical to creating strong welds.
The Best Way To Weld Aluminum
1. Use acetone as a solvent or a mild alkaline solution like heavy-duty soap to remove grease, oil, and water vapor from the aluminum surfaces to be welded.
2. With a stainless steel wire brush designed for use with aluminum, work the aluminum surface over to remove any surface oxides. If you prefer, you can use a strongly alkaline solution or acid. Rinse and fully dry the aluminum before welding if you opt for the second method.
3. Assemble and cover the joining if you won’t be making welds immediately. Storing the joint under a cover prevents dirt, grit, and debris from contaminating the work surfaces.
4. Keep any aluminum to be worked dry and maintain it at room temperature. Cleaned aluminum joints should be welded within a few days. If this isn’t possible, clean the joint again before working on it.
Other Methods For Welding Aluminum
TIG and MIG are not the sole methods for welding aluminum, though the welding equipment for both methods is more widely available. Here are some other methods welders use to work with aluminum for clean, strong welds:
1. Laser Beam And Electron Beam Welding
The most precise method of welding, laser and electron beam welding creates extremely precise heat zones that are ideal for aluminum welding. Thanks to this precision, burn through and cracking are far less common than conventional welding methods. The drawback is that the equipment required is significantly more expensive to buy and maintain than TIG or MIG welding.
2. Resistance Welding
An uncommon but effective method, resistance welding involves pressing the pieces to be joined and running an electrical current through the area where the pieces meet. It can be used for aluminum, but it’s a less popular choice due to the metal’s high thermal and electrical conductivity. Burnthrough and cracking are more likely to occur using this method.
3. Shielded Metal Arc Welding
This method is not recommended for general aluminum welding, though it is sometimes used to repair cast aluminum combined with constant current equipment and an aluminum electrode set to positive electrode polarity. By and large, veteran welders do not use this method, as it tends to be problematic at best and dangerous at worst.
The bottom line, welding aluminum is not much more difficult than welding any other metal. Provided you can account for potential problems like burn through and cracking, welding cast aluminum is no different than welding steel. Remember to clean aluminum surfaces thoroughly to remove oxidation and impurities. Additionally, stick to the TIG or MIG welding since both methods are the top choices of professionals. Once you have your technique down, you will be working with aluminum for your next build in no time.