It's generally accepted to be be a bad idea to fusion weld a guard on. The weld zone will have highly enlarged grain, as well as bits of martensite and other unintended microstructures. Another issue is stress locked up in the steel from welding... long story short, the whole joint area will be significantly weakened and prone to cracking.
If you absolutely had to do it this way, you'd want to find a better filler match than er-70-s6 or whatever your spool is running... the best might be to tig weld it using a thin strip of 1084 as filler. Then you'd want to carefully thermal cycle it for grain reduction and stress relief, in a forge or better yet a digital oven.
By the time you get done with that, you'll have a possibly decent yet still fundamentally questionable blade/guard to finish out, with more trouble and time invested than solder or a press fit with epoxy would have cost you.
