An assembly, by definition is composed of Components, which in turn contain bodies and their corresponding sketches. In the assembly you sent, you did not maintain this structure. You need to create the component first, make sure it is active, create your body sketches and then create bodies and features. Using this method, the sketches and bodies, related to the components, all appear UNDER the component. You then GROUND one component, that makes sense, and then use Joints to assembly all the components together. You use a Rigid Group which may be fine for this assembly but others that have to move, change position, etc. you will want to use Joints.
So the answer to your question is YES, all your bodies should be components if you want to assign Materials. Using the Create Components from Bodies command will not give you proper assembly structure.
Now that you have your answer, please do not forget to Accept Solution to close your question and allow others to find it easily.
John Hackney, Retired
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