Tags and keywords
The difference between Dependency and Usage in UML (and as available for general domain modelling in SysML) is notoriously vague:
UML-2.5.1: 'A Dependency is a Relationship that signifies that a single model Element or a set of model Elements requires other model Elements for their specification or implementation. This means that the complete semantics of the client Element(s) are either semantically or structurally dependent on the definition of the supplier Element(s).'
Don't fuss too much about which one you use where; try to choose a convention that makes sense for your model, and remember you can always convert between them easily in the tool. Also:
MagicDraw/Cameo: If you can't find Usage on a particular diagram just use a Dependency then the refactor context menu item.But note carefully: