I want to use a #6 aluminum 3 wire cable (2 conductors sheilded and one bare) that was used to feed a 50 amp oven to feed a sub panel that will supply a 40 amp circuit (20ft.) to a new oven ,1 20amp circuit dedicated to a micro wave, and 2 15 amp circuits to supply lighting (1000 watts per circuit) . The neutral and the ground bar in the sub panel will not be connected. I will be bring a gound from the main panel to the sub panel. My question is: Can I use the bare conductor in the #6 alumium cable as the neutral?
Thanks,
Sal

You CANNOT use that cable for a sub-feed. The ground MUST be part of the cable and cannot be run separately.