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.
For instance, getting rid of a hole or a crack on aluminum pipe.
I have this thought : as applying open fire always causes metal oxidation (and the oxide is especially adverse for soldering aluminium) may it be possible to heat the pipe with a resistance soldering tool (pliers with graphite plates passing high current at low voltage.) When the place get heated, blowing some argon over it clean the surface with a burst and immediately apply the solder (without flux)? An advantage - no flux messing the repaired pipe.
