Okay, so aluminum wires oxidizes when exposed to air long enough, and the alumina oxide is highly resistive- so connections to terminals on switches are prone to heating up and melting. This effect is compounded when accelerated by copper and aluminum conductors being mated.But how come on service panels- the bus bar, and wire lugs are all aluminum, and you screw the copper leads right into those with no worry?
Use a chemical redox (reduction/oxidation) reaction. You need two beakers, one with an aqueous copper solution (such as Copper Nitrate) and the other with something that needs to pick up some electrons, like an NaI solution. Put a cotton rag connecting the two beakers, and then connect the two beakers with your aluminum wire. Electrons will flow from the copper solution to make elemental iodine and elemental copper, which will collect at the electrode (the wire). THe result is that your wire will become coated with copper.
You've only stated part of the problem. Aluminum is also more susceptible to 'thermal creep', in which heat/cool, expansion/contraction cycles 'work' the connection loose. Special lugs connectors rated for 'aluminum and copper clad Al. conductors' + the use of antioxidant compounds have largely solved the problem. The lugs in question are so marked and are designed to maintain the proper pressure.
The screws that hold the wires into the bus bar make an excellent mechanical connection that is almost vibration thermal expansion-proof. The set screws are specially designed to dig into the metal to make a long-lasting electrical connection that resists oxidation. Its the copper to aluminum wire connectors and the outlets that have aluminum wire plugged in, or screwed on that you have to worry about. .
