Al wire is prone to oxidation and thus needs an antioxidant paste applied at connection points.

Hasn't anyone tried using silver wires?

Silver wire is used for some things, but it is a lot more expensive than copper which rules it out for most applications.

Here is a table of the conductivity (in units of 10^7 S/m), the density, and the cost of copper (Cu), aluminum (Al), silver (Ag), and gold (Au).

               Cu    Al      Ag       Au
  Conductivity 5.96  3.5     6.3      4.1
  g/cm^3       8.96  2.6    10.5     19.3
  $/kg         9.03  1.2  1030    92100

If we had a copper wire with a specified capacity in amps, here is what aluminum, silver, and gold wires of the same length and capacity would weigh and cost as a percentage of the weight and cost of the copper wire, and what their diameter would be as a percentage of the diameter of the copper wire.

      Weight  Cost  Diameter
  Al    49       7    139
  Ag   110   12646     97
  Au   310 3190000    121

Suppose Ag was as cheap as, or even cheaper than Al, would it be more useful?

Sure, we could alloy and/or plate it. You have a source on Ag cheaper than Al you'd like to disclose to the class?

Silver and gold could be a lot more useful to society if they weren't so expensive. Plenty of asteroids out there to mine.