Soldering or welding??
Soldering does not require shielding gas. This is a lower temp process that bonds on the surface.
Welding fuses the surfaces and requires higher temps. Atmospheric gases such as nitrogen and oxygen, which can cause fusion defects, porosity, and weld metal embrittlement if they come in contact with the electrode, the arc, or the welding metal. Inert gasses Argon and helium are used for shielding. Excellent welds are often produced using pure argon as a shielding gas. Pure argon is the most popular shielding gas and is often used for both gas metal arc and gas tungsten arc welding of aluminum. Mixing helium and argon have higher heat characteristics but cost more.