High Temperature Mechanical Properties and Microstructure Evolution of Ti-6Al-4V Alloy Linear FrictionWelding Joints

The combination of linear friction welding (LFW) and hot forming processes is limited due to a lack of research on the high-temperature flow behavior and microstructure evolution of welded joints. In this paper, an electric-assisted high-temperature uniaxial tensile test platform based on digital image correlation (DIC) is built, and uniaxial tensile tests of Ti-6Al-4V alloy with LFW joints are performed at different temperatures (923–1023 K) and different strain rates (0.001 s−1–0.01 s−1). Then the microstructure of the LFW joints under different hot deformation conditions have been analyzed by scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results indicate that the high-temperature flow behavior of LFW joints shows an obvious correlation between temperature and strain rate: The yield stress decreases from 203 MPa at 923 K to 105 MPa at 1023 K, and increases from 85 MPa to 130 MPa when the strain rate increases from 0.001 s−1 to 0.01 s−1 at 973 K. The hot deformation mechanisms with deformation conditions have been characterized, which changes from the mechanism of dislocation creep to the mechanism of self-diffusion as the deformation temperature increases from 923 to 1023 K. Especially, the fraction of high angle boundaries (HABs) rapidly rise from 49.2% to 64.1% with the increasing temperatures, the discontinuous dynamic recrystallization (DDRX) become the primary mechanism of nucleation during high-temperature deformation of LFW joints.