Hi James - Brazing is defined as a - group of joining process that that produces coalescence of the materials by heating them to the brazing temperature in the presence of a filler metal having a liquidus above 450°C (840°F) and below the solidus of the base metal. The filler metal is distributed between the closely fitting faying surfaces of the joint by capillary action.
When using GTAW (gas tungsten arc welding) process (TIG) the arc will melt the base metal thus welding. It would not be practical to lower the current so that the aluminum is brought up to a temperature of 1100°F for brazing and not melt the base metal.
The joint surfaces would have an oxide on them and the brazing filler metal would mot flow into the closely fitting joint surfaces.
While BAlSi-4 brazing filler metal and others are sometimes used in gas tungsten arc welding of aluminum, it is a welding process and not a brazing process as the base metal must be melted to form the joint. ----- Bob Peaslee