A Comparative Study of Friction Stir Brazing and Furnace Brazing of Dissimilar Metal Al and Cu Plates

Abstract

Friction stir brazing of 5-mm-thick Al and Cu plates in simple lap and stepped lap joint configurations was carried out in air as a modified process for friction stir lap welding of dissimilar metals, in which a pin-free tool and a 0.1-mm-thick Zn braze foil were used to eliminate both pin wear and keyhole and to achieve interface mixing by a metallurgical reaction route instead of vertical plastic mixing, respectively. The microstructure distribution features of friction stir brazing were characterized and compared with traditional furnace brazing to confirm the metallurgical advantages of the new process. For traditional furnace brazing, poor wettability at the Al side for lower brazing temperature or solidification cracking within too thick solidified microstructure (~150 µm) at higher brazing temperature was found. For friction stir brazing, oxide film removal could be achieved well in air without flux by rapid dissolution of the base metals into the molten braze; both solidified microstructure and solidification cracking could be eliminated by extruding excessive liquid phase out of the interface.