G'day vint_mow,
These plastic welders, just as for the electric pro level units, use a jet of hot air to heat the surface of the workpiece while fusing the filler rod onto/into it.
Soft soldering methods can be executed with a hot air gun, but metal fusion welding/brazing is the domain of flame torch and arc welding methods.
The cheapest really effective option for welding aluminium alloy would be one of the small portable DC output inverter welders, plus a GTA/TIG torch/regulator/gas hose kit, and a CoreGas Size D Argon cylinder from Bunnings. So you'd be looking at setup costs, with new kit, a bit north [depending on the exact torch/reg selection] of $800,including the $200 fully refundable cylinder deposit. That's based on a Lincoln 130A inverter welder kit; $449 in the current Total Tools EOFY flyer.
Oxy/LPG torch brazing of aluminium can be used with special brazing rods, but it's quite a bit more difficult manual technique. And the result always looks lumpy, compared to a well-executed TIG weld.
