Use a skill saw with a metal cutting blade.
Also, since its an alloy, a skillsaw with a plastic guard will be ok otherwise if you are cutting steel the steel melts to the plastic and can cause damage to the saw.
Use something straight as a guide for your cuts. Clamp it at both ends and run you skill saw along the guide and you will have very straight cuts. Also remember to let the tool do the work, not your shoulders.
Good luck!