Welding aluminum requires specific techniques, shielding gasses, specifications, and pre-weld and post-weld processing compared to other materials. Thankfully through the correct application, aluminum can be welded with ease as long as one ensures they are using the recommended method.
Aluminum can be difficult to weld for various reasons. Alloys such as 6061 experience solidification cracking when welded without a filler metal, for example. Alloys like a 6061 used with a 6061 filler metal can result in weld failure, highlighting the need to select the right filler metal.
Another challenge with aluminum is feeding. When a mechanical wire feeding process is used, additional special drive systems will be needed to ensure the aluminum does not buckle and tangle.
There are also other things to weigh when it comes to how to weld aluminum. Aluminum has greater thermal conductivity than steel which means full penetration may not occur in welding until the weld has progressed far enough from the start, otherwise known as a ‘cold open’. Aluminum is susceptible to crater cracking also requiring craters to be filled in so that failure doesn’t occur at the tail end of a weld.
There are 4 types of welding used for aluminum. There’s GTAW/TIG, GMAW/MIG, laser beam & electron beam welding, and resistance welding.
Gas tungsten arc welding (GTAW), sometimes referred to as ‘tungsten inert gas welding, is the most popular welding process used with aluminum. GTAW is a recommended choice for aluminum as it does not require mechanical wire feeding. In its place, filler material is fed by the welder with his hand. GTAW welding on aluminum is also known as very clean with prevents unintended contamination.
Gas metal arc welding (GMAW), otherwise referred to as ‘metal inert gas’ welding has higher deposition rates and faster travel speeds than GTAW. The drawback is that it does use a mechanical wire feeding system, requiring a push-pull gun or spool gun. It’s key with GMAW aluminum welding not to use 100% CO2 or 75% Argon/25% CO2 shielding gas. Although these gases are excellent for steel, aluminum cannot handle reactivity.
Laser beam and electron beam
Beam welding can handle aluminum, in many cases. The power density of beam welding processes is high, which thankfully means cold starts aren’t usually a concern. With laser welding, material light reflectivity can be something to weigh. Shielding gas optimization is also recommended to eliminate the risk of porosity.
However, in electron beam welding, you don’t encounter the same issues as the process does not use light as an energy medium.
Resistance welding is the least likely method of welding aluminum as difficulties can arise in the electrical and thermal conductivity of the material. Parameter development time can be significant and special resistance welding equipment may be required to overcome these challenges.
Processes not recommended for welding
For welding aluminum, other than the aforementioned 4 processes, it is rare for other welding processes to be recommended. Stick welding, flux cored arc welding, and submerged arc welding are not effective ways of treating aluminum. Oftentimes, these methods create large amounts of porosity which is not preferred.
The type of welding used on aluminum matters a lot. Welding aluminum with the wrong specifications can easily result in failure. Any welder working with aluminum always wants to ensure best practices are being followed.