Team #75 has been using Aluminum Sprockets and Shafts for many years. The type of Aluminum you specify is important. The application loads, forces and process will dictate the use of these materials. We have also used Titanium (6Al-4V (a/k/a Grade 5)) for shafting. The Aluminum we have used in the past has been 7075 for shafting and sprockets. The Aluminum has held up in most applications but a Slight press fit helps the application. We have also used Lock-tite to help in the assembly. If you are using a set screws or screws during assembly, with aluminum you should size the screws for Course thread pitches. I would also double up on the set screws, as then tend to loosen during use and eventually fall out. Getting back to your original question. These are specialized materials and you would probably have to get a machine shop to fabricate the keyways in the shafts. I’m sure any local shop would help out if you ask.
Place to order Material.
http://www.onlinemetals.com/
Carmine
Team 75 Mentor