Shielding gas

[White7]

its either co2, or argon co2 mix Question is why not just straight argon?

[jasonmt]

Short answer would be that straight Argon shielding gas with short circuit transfer will have a narrow, constricted arc which leads to a deep, narrow root that freezes very fast that leads to undercut and cracking in the weld. With a CO2/Ar mix the CO2 disassociates to CO and O, the O superheats the puddle which adds fluidity, flattens the root profile and allows the puddle to “wet out” and reduces/eliminates undercut.

[1bille1]

better/broader penetration