Hi,
There is another way to remove stuck screws once you have ruined the heads without any welding/gluing.
You need a tool called a screw extractor, (no suprise there!), lots of places have them.
It is basically a steel cylinder with a bolt type head at one end for your spanner and a tapering cone at the other, having a reverse direction screw thread on it..
You carefully drill a small pilot hole into the centre of the stuck screw head, then thread in the screw extractor. As it is screwing in anti clock wise it will eventually stick fast and the torque applied to it will then undo your stuck screw. This works for aluminium and steel screws, though steel can be hard to drill a good pilot hole into..
Good luck!