I don't usually do deep slots that deep single pass unless using a ripper and even then I'd be very weary with small cutters.! . . .(That thou is mostly down to low torque high speed spindle)

I find air blast and air mist is the best option for cutting aluminium. Unless flood is high pressure and lots of it then it's not as affective at clearing chips so you don't get as good a finish in Ali.
In your case if you can't do the mist I'd just have a constant air stream clearing chips and keep giving odd squirt of WD.