Microstructure evolution and mechanical properties of Ti-15-3 alloy joint fabricated by submerged friction stir welding

In this work, the Ti-15-3 alloy joints were successfully prepared via submerged friction stir welding (SFSW) for the first time. The microstructure evolutions and mechanical properties of the SFSW joints were characterized by electron backscattering diffraction, finite element simulation, microhardness, and tensile tests. The results revealed that the joint included three distinct zones, named as stirring zone (SZ), thermo-mechanically affected zone (TMAZ), and base metal (BM), respectively. During SFSW, the peak temperature (similar to 808 degrees C) and strain in SZ gradually decreased from the upper surface to the bottom surface along the thickness of the as-received plate. Meanwhile, the temperature and strain on the advancing side (AS) were higher than that of the retreating side (RS) within SZ. Comparatively, a slightly low temperature (similar to 480 degrees C) and strain occurred in TMAZ. Due to the high temperature and large strain during SFSW, the grains were significantly refined, and the major grain refinement mechanism of SZ was continuous dynamic recrystallization, while that of TMAZ was coupled by continuous and discontinuous dynamic recrystallization. Note that the ideal shear texture formed in SZ. The shear textures components at the top, center, and bottom of SZ center were D-2(11 (2) over bar)[111], while that of AS and RS within SZ was D-1(11 (2) over bar)[111]. Finally, the ultimate tensile strengths of SZ and TMAZ were 854 MPa and 816 MPa, which reached that of 103% and 96% of BM, respectively. In summary, it was an effective method to prepare a uniform and high-performance Ti-15-3 alloy joint through SFSW.