Aluminum comes in many alloys.
Your heat sinks and hard drive bodies should be the same type,
at least at the scrap yard level. It tends to be purer than most alloys.
Extruded aluminum is the most common type I find in scrap.
It has the classic aluminum color to it and bends relatively easily if you hit it.
Cast aluminum usually has a bit of a dull finish, or may be powder coated, like BBQ grills.
It will usually break if hit with a hammer. It can be doped with small amounts of impurities
and some yards pay slightly less for it.
Painted aluminum, like screen doors and siding trim pieces, is a different alloy
and can contain a small amount of copper or other metal that helps the paint stick.
Some yards pay slightly more for it.
Food container aluminum (pie plates, foil, pop and food cans)
is a ferro-silicate alloy that is doped with carbon, iron, and sand.
It usually goes for slightly less than plain aluminum.
Die cast metal (with zinc) usually has a shiny finish, like plating.
It comes in a variety of alloy percentages and will contain a small amount of aluminum, if at all.
I've seen some that deforms when hammered, and some that shatters.
This usually goes for quite a bit less than aluminum.
Aluminum that you cannot remove other metals from will sometimes have it's own pricing.
If it has steel or iron in it, it will be worth considerably less.
But if it is just aluminum and brass, you may get a good price for it
and save a lot of work in trying to separate it.
The best advice I've seen in this thread is to ask your local yard how they want it sorted.