Aluminium is probably a bad idea, for two reasons:
Firstly, aluminium oxidizes on contact with air. This is good because it forms a protective patina preventing further oxidization of the metal (unlike iron, which just keeps rusting), but it's bad because aluminium oxide is an excellent insulator. It's not impossible to make a good electrical connection to aluminium, but it takes some care. Ordinary electrical solder is not designed for bonding aluminium.
Secondly, aluminium in contact with copper is subject to significant galvanic corrosion, probably causing your connections to fail prematurely.
In the 60s, copper was very expensive and some people had the great idea of using aluminium for home electrical wiring instead of copper. You can read about all the problems that caused.
You can use copper just fine, though. As long as your wire is thick enough to have low enough resistance that running 2A through it won't waste too much energy (or worse, catch fire), then the particular geometry of the wire doesn't matter much as long as everything is touching the same piece of copper. Take a look at a wire gauge chart: anything less than 18 AWG is probably not a great idea for 2A.
Of course, if the wire is bare you should be confident that nothing will come in contact with it and do bad things. It would be bad, for example, if a metal object touched both at once, since this would short the power supply. At the voltages you are probably using for LEDs (I'm guessing 12V), it's unlikely to present any severe safety hazard, but there's easily the potential for some everyday occurrence to break your device.
If you don't have heavy enough wire, you can always run multiple wires in parallel and the current will split between them, just as current splits between parallel resistors. Remember, wire is just a very small valued resistor.