It is tempting to use self-tapping screws into aluminum extrusion, such as mullion/door-frames. However doing so will most likely result in premature failure after repeated use.
The aerospace industry solved this problem by using rivet-nuts as a durable interface between the soft aluminum and hard screw. The rivet-nuts will provide a solid anchor point you can rely on for years to come.
These are rivet nuts:
One of the main advantage of rivet nuts is their ease of installation. No need to access the other side of the mounting surface as shown below.
Here are some photos showing a KRONOS Side-Mount installed using rivet nuts: