A shoulder bolt is a good approach in applications with light loading, but it needs to be specified such that it can be fully tightened while still allowing the necessary clearance for movement without binding. Use shims where needed.
You can reduce some of the play in the joint by having the bolt threaded into one of the aluminum pieces (but still backed up with a nut for strength). In other words, only one of the aluminum bars needs to turn freely on the bolt.