Feasibility of Efficiently Fabricating Al/Steel Bimetal Composite by Friction Stir Brazing

To verify the feasibility of efficiently fabricating Al/steel corrosion-resistant bimetal composite by the authors' friction stir brazing (FSB) process, in which a tool without probe is used to eliminate severe wear of probe by steel, the characteristics of bead surface forming, interfacial microstructure and property of FSB joint of Al/steel were investigated with tools of different sizes. For small tool of a diameter less than 20 mm, rough bead surface forming tended to occur at the just starting portion, simultaneously, joints fractured along initial interface under low load. For medium tool of 20 mm diameter, both dense interfacial structure and excellent bonding were obtained at medium traverse speed (150 mm/min). For larger tool of 40 mm diameter, flash became extremely obvious. In this case, the flash could be reduced by decreasing plunge depth or increasing traverse speed, while dense interfacial structure with little filler metal of Zn and excellent bonding could still be obtained even at high traverse speed (300 mm/min) due to the combination of enhanced heating and forging force. Therefore, Al/steel metallic layered composite can be effectively fabricated by FSB with larger tool and higher traverse speed.