I've used aluminum before. Nothing wrong with how it
functions but it does oxidize after a while and then it looks bad and, of course, it is soft.
The choice is not simply aluminum or brass, many metals can be used as guards. I use a lot of 416 or 410 stainless for guards, a much better choice than aluminum.
As for soldering, there are some who successfully solder their guards and more power to them but personally I think they might be masochists
Use JB Weld and save your sanity ...