For making an electrical connection to a large mass I would do one of the following:
1) Larger soldering iron
2) Torch (used for plumbing and roofs, for example)
3) Drill, tap, and use a screw
4) Sheetmetal screw
5) A compression fitting/connector
6) A screw-type compression fitting (as on large power leads)
7) "Something else" that exerts continuous mechanical pressure so that the two electrically important parts stay in good contact.
Without further information on what is being attempted, that's the best I can do.