Hi morley bill 1.
The motor you have is a very good quality industrial type motor.
Running the motor on 6 volts will take less current than 12 volts. You do not decide what current a motor takes. It depends on the load the motor places on the circuit.
The motor is (loosely) like a variable resistance. It will take most current when the motor spindle is held stationary with the battery connected. ( best not to do this) When it is free running it will take the lowest current.
So if the motor is able to drive what you want on 6 volts that is fine. If necessary it will run at much lower votages probably down to 2 volts, if you try this you will see it runs slower and cannot do as much work as running on a higher voltage.
Hope this helps,
regards Roy