Properties of powdered metals
Let me try to answer the part 1. of your question.
The process of compacting powdered Aluminium is also called Sintering. And as you can guess, the thin oxide layer of Alumina inhibits the binding of Aluminium grains between the powder particles.

So, while sintering, we need to either:
1) Break part of the Alumina film or,
2) Reduce part of it to Aluminium,
 in order to facilitate formation of a metallic bond between the powder particles.

For 1), we use a nitrogen atmosphere as it enhances the destruction of Alumina.
For 2), we use because magnesium as a alloying element because magnesium, even in small amounts, concentrates on the surface of powder particles
and supports sintering by local reduction of Alumina.


In conclusion, I would say that compacted Aluminium does have Alumina inside the molded object. But metallic bonds between powders are formed after partly removing the oxide film by the above mentioned methods.