only low co2 content mixed gas is any good for light miging (light ie sub 6mm) as you go up in thickness its better to up the co2 content a little
the co2 effects the arc stablity
somtimes even other gasses can be added in the mix like helium and others
its a real complex affair but all we need to know here is low co2/argon mixed gas for light mild steels and pure argon for stainless and alloy
only thing i would use co2 for is realy thick plate on realy thick wire and a realy big welder otherwise its not nice to use
see below