With measurements outside it (using a microscope, etc.). A standard measure of tool life is the time to develop a flank wear length VBB of 0.3 mm or VBBmax of 0.6 mm.
You need to use the ISO 3685 standard as reference.
I think that depends the level of Si (low content), you can have serious problems with the wear of the tool edge, because the aluminum alloys normally, no wear the tool.
Recommendations: high Si level, and high cutting speed to this work.