Re: what kind of metals can i
2 Door, Sorry, I actually don't really text and just make the stuff up; kind o' foolish to think that people will know what I'm talkin about (I suck at typing ironically and that's why I abreviate).
GLO=Good Lookin' Out
I'm no welder (dabble a little) and not a metalurgist (unless you count back yard heat treat and stove top tempering). However I do have first hand knowledge of many material characteristics through my experience machining and fabricating from composites to metals to plastics.
I used to know a bit more about the brands and their metal choices. Much of the chromoly frames are 4130. Most of the frames will say if they have their original labeling.
Aluminum frames and chromoly frames are heat treated and welding will upset that normalization. Brazing is better but will still affect the heat treat. Best practice is to re heat treat after welding. Not always necessary but good to know when and why (if not just knowing that if it fails it won't be catastrophic).
Mild steel frames are not heat treated and thus can be welded on more reliably and easilly!