A lot of alum casting are A356. Not knowing what you've got I would try 4043, as it will give good results on a large number of alloys. Are you sure it's alum? It's common to find mag alloys on 2 Stroke Cycle engs . Find or make a bare spot and apply a mild acid like lemond juice if it's...
I've had good results with 2024 Alclad, 6061T6,and 7075.
The finish of the part is the most important aspect.
I'f you like black for a color then 40 series like 4043is
what you'll get. Something to remember if your welding useing 4043 filler rod.
