Because of its light weight and corrosion resistance, aluminum is commonly used for aircraft and vehicle components, as well as marine hulls, machine frames, wind turbines and more. However, due to aluminum’s high conductivity and its surface oxide layer, this material can pose challenges during welding. Most frequently, lack of fusion and porosity can occur, which negatively impacts weld quality and leads to rework.

Along with following best practices for cleaning and using proper welding techniques, shielding gas plays a role in helping to prevent these issues and create sound welds.

Argon

Argon is the most commonly used shielding gas when welding aluminum. Like other shielding gases, argon protects the weld pool from atmospheric contamination, such as oxygen, nitrogen and moisture. This shielding gas is readily available in the marketplace and is inexpensive. Especially compared to helium, which can also be used to weld aluminum.

Argon also offers excellent arc initiation and stability. It is also operator-friendly and easy to weld with in both MIG and TIG welding processes. Due to its low heat input, argon is well-suited for thinner aluminum (around 1/4 inch or less). This is because it reduces the risk of burn-through.

When MIG welding with argon, use a flow rate of 40 to 50 cubic feet per hour (CFH). This ensures coverage of the weld pool. Depending on the cup size when TIG welding, a range of 15 to 30 CFH works well.

Helium

If instances of porosity or lack of fusion have become a problem when welding aluminum, switching to an argon/helium blend using a spray transfer mode is recommended. While it is a non-renewable resource and therefore much more expensive than argon, helium offers the benefit of higher heat input. This is due to its ionization potential (the amount of voltage it takes to ionize the shielding gas) and higher thermal conductivity (10 times greater than argon), resulting in greater penetration. This helps fuse the weld better, especially on thicker sections of aluminum (usually 1/2 inch and above). The hotter arc also helps drive hydrogen out of the weld pool to reduce instances of porosity.

It is common to use a blend of 75% argon with 25% helium. However, it can be beneficial to increase to a 50/50 blend or even a 75% helium with 25% argon mixture. This higher helium percentage increases penetration and can improve weld quality for applications like castings and thick plates. Higher helium content also provides faster travel speeds. But due to the cost, it is not the first choice for improving productivity.

Because helium has a low density, it must be used at a much higher flow rate than argon. For a mix of 75% helium and 25% argon, 100 to 110 CFH works well when MIG welding aluminum. When TIG welding with a 50/50 blend, 50 CFH is recommended.

If problems occur with welding aluminum or if there are questions about which shielding gas to use, Hobart has resources to help. Contact our Applications Engineers at 800-532-2618 or by email at [email protected].