Effect of Friction Welding Condition and Weld Faying Surface Properties on Tensile Strength of Friction Welded Joint between Pure Titanium and Pure Copper

Abstract

This paper describes the effect of the friction welding condition and the weld faying surface properties on the tensile strength of the friction welded joint between pure titanium (Ti) and pure copper (OFC). The joint strength of the joint, which was made with the weld faying surface of the Ti side specimen finished with a surface grinding machine, was investigated. The joint did not have 100% efficiency and OFC side fracture regardless of the friction welding conditions. When the joint was made with a friction pressure of 75 MPa, the joint efficiency was approximately 64% regardless of the forge pressures, and all joints fractured at the weld interface, although that efficiency exceeded that of the joints made with other friction pressures. To improve the joint efficiency, one was made with a Ti side specimen whose weld faying surface was finished by buff polishing. The joint efficiency was increased to approximately 85%, although the joint fractured at the weld interface. Moreover, a joint at a friction pressure of 75 MPa with a forge pressure of 270 MPa or higher was obtained with an OFC side fracture, although it did not achieve 100% efficiency. The fact that the joint did not fracture at the OFC base metal was due to the mechanically mixed layer at the weld interface that depended on the maximum height of the Ti side weld faying surface. To clarify the reason why the joint did not achieve 100% joint efficiency, the tensile strength of the OFC base metal with the addition of various compressive stresses was investigated. When the compressive stress was higher than the yield stress of the OFC base metal, its tensile strength was lower than that without a compressive load. Moreover, the tensile strength along the radial direction of the OFC base metal was also slightly lower than that of the longitudinal direction. Hence, the fact that the joint did not also achieve 100% efficiency was due to the decrease in the tensile strength of the OFC base metal by the Bauschinger effect and the difference of the anisotropic property with as-manufactured condition.