TIG/GTA with straight Argon shield gas is the top welding method for Al alloy, particularly cast.
Oxy welding thin section cast alloy tends to be pretty dicey, as the metal will liquefy very suddenly, and fall away in blobs if there isn't a backup plate supporting it.
If you're a dab hand at silver solder, silver brazing and straight brazing, like me :-), then aluminum is no problem. Just have to keep your tip size and flame down to match the metal. But I guess not everyone has done a NASA standards course like I did back in the 70's when oxy was still the predominant method.
