Enhanced strength of Al/Ti dissimilar joints via trailing support friction stir welding at high welding velocities

The Al/Ti dissimilar metals were joined by the novel trailing support friction stir welding (TSFSW) technique. A sound joint was produced and a high-strength Al/Ti joint was obtained at a high welding velocity. The trailing support column had a great influence on the temperature field of Al/Ti joint. The temperature of the support column continuously increased (<100 °C) during welding, which made the temperature at the bottom was higher than that at the middle on the Al side. Dynamic recrystallization occurred only on the Al side at the Ti-protrusion location because of the indirect stirring effect. The interface realized mechanical interlocking and metallurgical bonding depending on the tearing zone and mixed zone (adaptive TiAl₃/Ti multilayer structure). The Al/Ti joint strength was determined by the interface metallurgical bonding strength and strengthened by interface mechanical interlocking. Only TiAl₃ phase formed at the bonding interface. At 400 mm/min and 600 mm/min, both joints fractured at Al-HAZ. The maximum joint strength of 230 MPa joint was obtained at 600 mm/min while the maximum interface strength of 251 MPa was achieved at 400 mm/min. The maximum joint and interface strength were 75 % and 82 % compared with the Al-BM strength, respectively. At 700 mm/min, the joint fractured at the Al/Ti bonding interface with the tensile strength of 218 MPa.