All aluminum worth machining is going to be a wrought alloy.
Castings are mediocre even when produced by commercial foundries ran by PHD metallurgists.
For everyday machined components find a source for drop offs of 6061-T6 , T651 and T6511. These are all cold rolled, extruded or cold drawn rod, bar and plate. Don't waste anymore time on fire ant alloys.
6061-T6 is a cold worked alloy that has been heat treated. There is zero ways to produce an equivalent alloy at home. 6061-T6 is as strong as mild steel and will have no porosity.
You put 87 octane fuel in your car. 6061-T6 is the 87 octane equivalent in the world of aluminums fit for machining. There are many other alloys but none are remotely as popular as 6061-T6 in rod, bar or plate stock. It does not bend well so sheet metal is usually 5052-H32 or H34.
You can find plenty of references to back up what I say. I have been involved with machined parts for 50 years. That includes thousands of investment castings cast from A356 and millions of parts machined from 6061-T6.
So forget home cast alloys unless you enjoy wasting time.