Replaceable Rear Derailleur Hanger

[Batbike]

Mechanical engineering question:

Is the hanger on a carbon fiber bike made made of aluminum so that the aluminum will fail rather than sending the stress into the delicate carbon fiber?

Sort of a 'sacrifice the hanger to save the frame" situation?

My cheap-o aluminum frame bike has a steel hanger. (magnet sticks to it, so I assume it's steel)

I believe that is true ... instead of having to replace the entire frame, you end-up saving frame and replacing hanger.