Argon is the most common gas used for GTAW because it is both dirt cheap and prevents defects due to varying arc lengths. The downside with using Helium as a shielding gas (besides cost) in GTAW is that the arc length is more difficult to control. This being said, Helium has the advantage of increasing the weld penetration. This can allow increased welding speed and welding between metals with high heat conductivity (such as copper). Helium-Argon gas mixtures are sometimes used in GTAW as they can strike a balance between the properties of both gases.

argon gives deeper penetration than helium, to gtaw on dcep you need a huge tungsten and low amperage...tell me the metal and I will tell you how to weld it..as far as your question, never count on shielding gas or welding current flow for cleaning the material, that is done during prep..so many things to put here, this is the tip of the iceberg

Argon has a higher molecular weight than helium does. So there is more energy imparted to surface of the metal. Thus it will "clean better". I hope this answer helps since the other two answers seem to contradict each other.

Ar is used for good cleaning action and also high Arc stability and good Arc striking capacity.

Also Deeper penetration and narrow weldbead profile made by Argon gas.

due to low ionization potential less voltage is required for intiation of Arcing.also heavy gas so less gas required for welding mainly 2 to 12 litres.where He is 12 to 24 liters used as same welding.He not good only swallow and wider penetration occur.also Helium gas in welding poor cleaning action take place.He good for overhead welding and also used for high speed welding.Please follow if you like it.thanks for your reading.keep it up.

Watch the video in the following link to understand the differences between the two gases

((https://youtu.be/mwdxnBf0ZXg))

Thank you