You can create a folder with your favorite materials and apply a favorite material from the list to multibody parts and assemblies.
Right-click the part icon to apply a material and click Apply Favorite Material. Select a material from the list of favorite materials.
From the materials favorites list, you can quickly apply a material without displaying the Material dialog box.
To manage the material favorites list, right-click
Material 
in the FeatureManager design tree of a part and select
Manage Favorites.