how to weld cast to mild steel

I have a 85 amp mig with 75/25 argon/co2 what wire and process

 

chuckyz providing you have enough working amps or you material isn't to thick you must preheat the cast too about 150 to 200 degress which will aid you in your penatration and the cast will except a mild steel wire. weld it like you would mild or A3 steal. OK