Why is an aluminum track not performing as a voltage divider?
Aluminum readily developes a non-conductive coating (oxide?) when exposed to air, so you may not have actually made contact with the actual conductive aluminum.

Aluminum is a very good conductor (if you can get through the oxide) so will not develope a significant voltage - it will just be a short circuit on the battery.

Nichrome is a fairly high resistance material, and a length of wire coiled around a rod will have a much higher resistance than a sheet of aluminum foil, so you can easily measure the voltage developed across part of the coil.