Is it a good idea to connect aluminum AC mains wires by soldering
Provided I have an appropriate flux for aluminum and I'm able to solder the wires will this connection be durable? 


That's nearly impossible. You can weld aluminium under protective atmosphere (inert gas welding), but you cannot solder it with normal solder. Or at least, I've never seen anyone succeed (and by god, I tried to use alu sheet metal as ground planes). I've heard it's possible, but you'll need a special solder, which seems to be very expensive.


  will this connection be durable? 


If you used the right solder and technique, probably, yes. But since that would be your first alu solder joints: No. Good soldering takes practice, even on much simpler materials like copper. Don't expect good results on your first try :)

Also, other aluminium connections won't be durable: read the comments, it creeps, and that's not a good property for a wire that you want to screw in or stick in to some locking connector.

But: don't use aluminium wires. There's a reason they aren't used anymore today, and it's very simple, and physically inevitable:


Aluminium doesn't like being bent as much as e.g. copper does. You don't want your wire to slightly break when installing it, because that breaking point will have a higher resistance, and get hot, and burn your house down.
Aluminium generally has a much higher resistance than copper. You just convert your electrical energy to heat. Using copper-clad aluminium wire does make sense in some cases, but that cable needs to be thicker than a copper cable carrying the same current (and usually isn't even cheaper, in the end, for installation cables). You find these types of cables in free-hanging high-voltage supply lines – they aren't good for installation, because you can't bend them as much as copper cable (see 1.), and because they are bigger than their copper alternatives. 


In other words, don't use aluminium cabling.