You will need to do some serious reading on aluminum. If you started with some aluminum chips of say 6061-t6 and melted it down, you would be vaporing off many of the qualities then when ready to pour you'd be dragging off many more qualities in the slag. The actual pour would be something completely different than what you started with. The engineers who do this for a living know what and how much to add to the melt so that they are within limits of what they want. What you would end up with could be considered as "Pot metal" ! If you bought a bag of mix with all the alloys and chemicals pre-mixed for a melt of say 6061 and you controlled your melt and temp perfectly you'd have a chance at ending up with 6061 but no guarantees !
Don
IH v-3 early model owner