Werowance, I have recently changed from zinc-based soldering of aluminium to some 95% aluminium rods (Cheap from China!). They solder aluminium really well - flux free - so if they do that with aluminium, they may just work on aluminium bronze?
Back in the 1970s, I worked on Aluminium busbars... MIG welded aluminium mostly. But in some instances, we needed to convert from Al to Copper, or steel. Most of the "conversion plates" that we welded to the aluminium assemblies were made by explosion bonding an aluminium plate to a chemically cleaned copper or steel block. (I think some may have been "friction welded"?). But a (cost saving) development proved that the application of MIG-welder-applied aluminium onto a copper surface could give the required mechanical and electrical and durability properties, as the MIG arc "abraded and eroded" the "foreign" material surface so the aluminium spray (from the arc) could adhere to the "foreign" surface. NOT a weld, but an effective friction bonded joint for electrical purposes. Possibly wire brushing (stainless steel wire brush required) the molten aluminium soldering rod onto the surface of the Aluiminium bronze will "tin" the surface, then 2 "tinned" surfaces can be brought together and the aluminium solder melted and allowed to fuse and cool to form the require joint? I may have a bit of Al-Brz. to try... as soon as I get some "experimental time"!
K2