2000 Volume 18 Issue 4 Pages 617-627
In order to clarify the stress/strain distribution across the joint interface of friction weld between pure titanium (Ti) /pure aluminium (Al), the characteristics of the joint interface have been investigated in view of ultrasonic leaky surface acoustic (Rayleigh) wave velocity (VR) and hardness distributions across it. Especially, one of the first efforts is focused on whether a mechanical scanning acoustic microscope (SAM) can be utilized to measure the VR distribution across the interface or not. The effect of tensile/compressive strains on VR of Ti and Al substrates, the relation of crystal direction versus VR for single crystAl pure Al substrate, and VR distribution across as-welded and post-weld heat-treated Ti/Al friction joints have been investigated by using a SAM.
As for Ti and Al substrates, all direction (isotropic) VR (AVR) decreased when the applied tensile strain increased in elastic deformation region, however, they increased as increasing applied strain in plastic one. Compressive strain slightly affected the change of AVR versus in both elastic and plastic deformation regions. Uni direction (anisotropic) VR (UVR) increased as increasing tensile and compressive strains for Ti substrate. While UVR of Al substrate decreased with increasing of tensile strain, it increased for compressive strain. There was clear relation between UVR and crystal direction of single crystal pure Al substrate, and the highest UVR was obtained at the direction parallel to the most close-packed crystal direction of fcc metal ().
In case of as-welded Ti/Al friction joint, the scatter of AVR distribution was relatively high overall the measured region, and AVR of Al substrates adjacent to the joint interface was relatively high. It was thought that this high AVR was resulted from high plastic strain generated during friction weld operation. The scatter of AVR distribution was reduced and the high AVR was not observed when the joint was post-weld heat-treated. While axial direction UVR of Al substrate adjacent to the joint interface was extremely high in as-welded condition, that of radial direction was not high. Those of Ti side were not high in as-welded joint. The VR distributions were relatively similar characteristics to hardness and calculated stress/strain distributions.