Need some advice. I have been welding with a Lincoln 110 MIG welder, with gas, since 1993. However, I have never MIG welded al. aly. sheet-metal. How much different are the techniques. Also, what tip size should I use and what type of wire, diameter. Do I use Argon/CO2? I will be welding in small patches on a 50 year old year CA license plate.