An aluminum alloy-based extruded multi-path flat tube having a multiple number of passageways extending internally through the flat tube in parallel with one another and adapted to be coupled to other such flat tubes to form a heat exchanger after performing a brazing operation with the flat tube having a surface layer extending inwardly from the external surface containing at least 5% non-recrystallized grains and having an inner layer extending from the surface area containing at least 30% recrystallized grains.