Coathangers are fine for what you want to do.Just make sure to clean them up good(no paint or other garbage)and have fun.

I have used (metal wire) coathangers for "glueing" exhaust pipes together when I had nothing else available. As suggested already, burn off the paint or coatings before you start, and keep your head out of the plume, it's hard to say what some of those are made of. I would practice with them but not much more than that, I have found them to be very brittle and not ductile enough for much of anything. Here is a link for help in determining fillers for various materials....http://www.jwharris.com/home/
Links are on the left side of the screen to all sorts of info...
Brazing, Soldering, Welding

Hope this helps,
John Wright