OT question on metal forming

[monte55]

I have an old chaise lounge piece of outside patio furniture. It is made of round formed aluminum tubing and has plastic strap webbing attatched for the body to rest against. My question: The aluminum is 7/8" OD and .070" wall, .740" ID. OK...
The 90 degree bends seem to be mandrel bent from the reduced diameter at the bend but to my surprise........inside the aluminum tube(not all) is a steel 1/2 " x
.050" tube inside which is a very sloppy fit. What is this about? Would it be to help the aluminum to not collapse but like I said it's looks mandrel bent. I am tearing it apart because I need the tube for my heli project. We don't use it and it's been in my junk pile for years. No.........I don't use present deck furniture for my projects.