You might want to check the temperature of the aluminum surrounding the cut. Aluminum usually comes heat treated or strain hardened (or a combination), but additional (especially prolonged) heat can affect those properties. Consider using an IR thermometer or a thermocouple to check that you're not exceeding 350°C in the surrounding metal for very long—this will tend to anneal the material, leaving it much softer and weaker. You need to consult a graph of temperature vs. time to see if what you're doing will remove the heat treatment.
Maybe this isn't a big deal; you could conceivably not need the extra strength from hardening. That depends on the loads on the sprocket. Also, the heat treatment
could be restored, even if it was changed by the cutting. While it isn't difficult, you'd need an couple of temperature-controlled heat treating ovens to do it.
The ASM handbook will have all the necessary temperature and hardening data for any given grade of aluminum. Also, try
the aerospace materials handbook.