Hi Mick,
Lumi weld is one, I have used it a few times the last job was to restore the threads in the alloy sump of a GT550 Kawasaki.
Time before that an alloy front brake lever from the same machine.
Using a virgin stainless steel brush clean the piece to want to “Braze” then warm up the workpiece until it’s hot enough to melt the filler rod (but dont apply direct heat to the filler rod) keep dabbing it on all the while using the supplied stainless rod to “scratch” the edges of the alloy until it forms a skin with it.
Once cooled the filler rod is about as hard as mild steel to file dril tap etc.
The stuff I have is not the latest technology but I bought quite a bit of it cheap and am only now getting down to the last bits of it.
Paul