... i.e. a furnace), flux is required to prevent oxides from forming while the metal is heated. The flux also serves ... of forms including flux paste, liquid, powder or pre-made brazing pastes that combine flux with filler metal powder. ... or application method. In general, braze alloys are made up of 3 or more metals to form an ... iron, copper, silicon, boron, phosphorus, etc. Welding Tips: What Is Brazing?