Copper versus aluminum-which construction is best? [induction motor rotors]

Many induction motors in service today are running critical processes in which failure at any time can be very costly. Many times, these critical processes will not have a back up. As a result, a large portion of these processes will shut down until the motor is repaired and put back into service. Those aware of this situation will strive to purchase a motor that will maximize reliability. As a result of the strong push for maximum reliability, it is easy to over specify costly components not required for specific applications. These decisions will result in an unnecessarily high motor purchase price. To maximize reliability without overspending, large induction motors need to be properly matched to specific applications. With this consideration, the choice between die cast or fabricated rotor constructions is evaluated, with the conclusion that there are pros and cons to both construction methods