Joining phenomena and tensile strength of friction welded joint between pure titanium and low carbon steel

Abstract

This paper describes the effect of the friction welding condition on the joining phenomena and the tensile strength of friction welded joint between pure titanium (P-Ti) and low carbon steel (LCS). The adjacent region of the weld interface at the P-Ti side was intensely upsetting with accompanied large deformation of itself when the joint had sparkle at both applied friction pressures of 30 and 90MPa, although that of the LCS side was hardly upset. The temperature of the whole weld interface at a friction pressure of 30MPa reached to 1150K or over at a friction time of 3.0s or longer. However, the half radius and centreline portion temperatures of the weld interface at a friction pressure of 90MPa was not reached to 1150K, although the periphery portion of that was reached to its temperature. The central portion of the weld interface at a friction pressure of 90MPa was deformed to a convex shape from the viewpoint of the P-Ti side, although that of 30MPa remained almost flat after when the friction torque reached the initial peak. When the joint was made at a friction pressure of 30MPa, a friction time of 3.0s or longer, and a forge pressure of 270MPa or higher, it achieved 100% joint efficiency and the P-Ti base metal fracture with no crack at the weld interface. However, many joints at friction times of 1.2 and 1.5s fractured at the weld interface, although those achieved 100% joint efficiency, because whole weld interface temperature was below 1150K. On the other hand, many joints at a friction pressure of 90MPa with high forge pressure also fractured at the weld interface, although those achieved 100% joint efficiency, because the weld interface temperature at the half radius and periphery portions was below 1150K. Those joints did not have the intermetallic compound layer at the weld interface. The difference of the fractured portion of the joint in both applied friction pressures was due to the difference between the maximum temperature at the weld interface during the friction process and the deformation amount of the LCS side caused by applied forge pressure. To obtain 100% joint efficiency with the P-Ti base metal fracture with no crack at the weld interface, the joint should be made with high forge pressure, low friction pressure, and with opportune friction time at which the temperature at whole weld interface reached around 1150K.