How does a big heavy aluminium aircraft or airplane flies in the sky in so high ?

Question

but a piece of aluminium doesn't

Answer 1

A piece of aluminum isn't shaped for lift and doesn't have any mode of propulsion to create the wind necessary for lift to take place.

Answer 2

As the velocity of a liquid or gas is increased, the pressure perpendicular to the direction of flow is decreased.  The hydrofoil design of an aircraft wing allows the air below the wing to remain relatively unchanged while it speeds up the air above it, creating "lift".  The engines create thrust to move the plane forward and the wings create lift to move it upwards. The combination of the two, thrust plus lift, equals flight.  A piece of Aluminum can have thrust simply by you throwing it but it doesn't have the shape to create lift.   You have to have thrust and lift for flight.