I would suggest that your using the wrong cutter. In alloy you want either a single flute or 2 flute cutter. There are software tools to help with feeds and speeds. The one I use suggests for a 3mm dia 2 flute cutter with a cut depth of 1.5mm the spindle speed should be 16,000 rpm and feed rate 950mm/min for roughing (notice I'm European and don't use inches) and 14,600 rpm and 485mm/min for finishing. The most important thing I've found is chip clearance. You have to be completely paranoid about re-cutting chips, so you need good coolant flood or high pressure mist to blow the chips away otherwise they get stuck to the cutter and it'll break. I generally use a single flute cutter with all aluminium alloys and can still have chip clearance issues if my misters are not getting the chips away. With a 4 flute cutter they will always get stuck because they get trapped in the flute even if you've got good coolant.
If your machine can't go that fast, and you mentioned 8,000 rpm, then the feed rate for roughing should be about 460mm/min and for finishing 265mm/min at 8,000 rpm.