I've used 'Lumiweld' successfully on small jobs (filling holes where the thread stripped and so on). I keep a load of rods in readiness as its a useful process.
I also have a MIG and TIG welders. I repaired a Horse Trailer alloy partition with the MIG, using alloy wire, Argon shielding gas and with the polarity reversed (torch is Negative). It was OK but not the greatest weld - pre-heating is essential with MIG, I find.
My TIG welder has both D/C & A/C current options. For Alloy use A/C, Torch is Negative, Argon gas, Zirconiated (white tip) Tungsten and, if possible, adjust the A/C frequency (mine goes up to 200 Hz) to clean the oxide off the alloy ahead of the weld.
Its a whole different world when you get a modern, very complicated, A/C - D/C TIG welder
Which reminds me, I have a pair of Panther crankcases to repair (once I've had more practice)
My avatar shows the late Len Rich in 1970 with the bike I now have - a 1958 Ariel VH