in the USA, co2 mig welding gas is often considered to be inferior to c25.
But it is definitely cheaper.
and if you can dial in that sweet spot setting, it is almost as good as C25 argon/co2.
Is 75/25 ar/co2 welding gas (aka C25) better than straight c02 gas?
Is 75/25 mix smoother than straight co2?
Does straight Co2 penetrate better than 75/25 mix?
Lets find out by some quick down and dirty testing using these 2 shielding gases.
Using a36 hot rolled steel 1/4" thick ...set up for lap joints.
All welds were done using er70s6 .035" wire using about 350 -360 inches per minute.
Voltage was not really known because the IronMan 230 does not read out in voltage numbers.
The click setting number 6 was the voltage setting recommended for 1/4" and my guess is that the # 6 Setting is equivalent to 22-23 volts.
I used a pull angle for both co2 and 75/25....and then a push angle with the 75/25 ar/co2 gas.
I cooled the piece off to barely warm before making the next weld so that preheat would not be a factor.
After welding, I labeled the welds and sectioned them using a horizontal band saw.
Then, using an 80 grit flap disc and a 3m scotch-brite roloc disc, I blended out the saw scratches.
Then I swab etched the weld areas using a diluted acid mixture to reveal the weld penetration.
Co2 pulling angle penetrated into the root plenty deep
75/25 welding gas using a pulling angle penetrated into one leg but the other one showed some uneven penetration.
75/25 gas using a push technique penetrated almost as well as the straight co2.
Here is something to remember...
Anytime you are testing welds done manually...by hand that is... it is possible that the technique used will influence the results.
In order for the test to be conclusive, several welds would need to be done and sectioned several times...preferably set up using an automated process with a stationary torch.
Short circuit mig welding can be done using straight co2 , 75/25 argon/co2, 80/20 argon /co2 and a few others.
Why test straight co2 gas?
Straight co2 welding gas is cheaper than mixed gas.
In some countries, its a whole lot cheaper.
Straight co2 for mig welding has a reputation for producing lots of spatter but if the voltage and wire speed are balanced to find the sweet spot, c02 gas can actually run very smoothly with little or no spatter. Especially when using inverter power sources that have an inductance setting favorable to Co2 shielding gas.
Generally speaking 75/25 is a better choice for thin sheet metal but for general fabrication, co2 gas is fine. exit mig welding gases page and see more welding videos