If so, 1/8" 0.9mm 4043 wire, current setting 1-2, wire feed probably 4-7. 1/4" power setting 3-4, wire feed 5-8 (as far as I can remember).
If it does not get hot, then 5356 0.8 or 0.9mm wire. Wire speed 2.5-4 on 1-2 heat setting.
In either case, weld will start out real cold with no penetration. Will be tall welds. Will tend blow through when reaching end.
What are you going to weld? Mig is fine for doing fab of stock AL. Things like manifolds will require the control of a TIG to get consistent penetration, no gaps and less heat distortion.
After playing with MIG Al welding, I realized I could weld thin, flat stock together, but anything else had marginal results. This is why i got my AC/DC TIG.
Really to do thicker AL with MIG, you need a better welder. Above 1/8" you would want a pulse MIG that can do spray-mode transfer. That will allow high peak currents for penetration and spray mode, but keep the average down so you don't melt the wire back to the gun.
Al takes fiddling with wire speed and current until you have it right. Fine for production work once it is set up, then you can repeat it. For a one-of piece of Al, you don't have anything else to practice on.
Iv only ever used a syngenic mig on ally so can only really speek from a tig prespective, the problem you have with cast ally is most of it is very impure ie masac, nasty stuff, I have done some 1/4" crane castings which as far as i know held, preheat can help as long as you dont get it too hot and i would not consider it nessary to clean ahead of welding. I would say its really only a job for tig but then the only migs that i would consider welding ally with would be a syngenic.
Synergic MIG or a TIG is great, but not everyone has them. Would be possible but less tidy and more tricky with an ordinary MIG depending on the purity of the casting. I'd use a brass backer/heat sink and increase the power setting. Did you find the aluminium tips page?
The power settings for aluminium have always seemed to me to be similar to the equivalent thickness steel settings, and wire speed twice that used for steel. Aluminium does conduct away heat very quickly, but also melts at a lower temperature than steel so it evens out.
You might want to look at Al brazing rods. They are tricky to use but I have hed real good results using them. I used a MAPP torch, but propane can be used also.
yep id go down the gas route would proberbly make a better job than the mig did this on a repair a few years ago as i havent a portable a/c tig set and worked just fine.
I cut it down to the runners, grinded the cast down enough and welded the 1/8" 6061 sheet to it. Seems to have welded pretty good. At the beginning it did start off with tall welds, but i just grinded that part enough and rewelded it. Right now i only have one part welded on there, but later i will be sure to take pictures. I still need a few sides and the elbow but that won't take long.
Looking at it, i could of just made a box plenum for my 2-piece intake instead of hacking this 1-piece. Would of made my life a bit easier, but while i am at it i might aswell finish and see how it will turns out.