proper gas

Mig weld with .035 ER70S-6 wire.12Ga. to 1/2" carbon steel. What gas should I use? I've been using 100% argon, but in some of your video's I've heard you mention a 75 25 mix. What should I use, and what are the differences?

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wtt response,

you can either use straight C02 or a mix if ar/c02

75/25 .

pure argon does not give you a very pretty bead because it needs some reactive gas mixed in.