Microstructure and texture evolution of Ti-6A1-4V alloy T-joint fabricated by dual laser beam bilateral synchronous welding

摘要

The microstructure and microtexture evolution of Ti-6A1-4V T-joints produced by dual laser beam bilateral synchronous welding (DLBSW) were investigated using the optical microscopy (OM) and electron back-scattered diffraction (EBSD) and correlated with the mechanical properties of the joint. We demonstrate important differences in temperature field, grain morphology, misorientation angles and texture intensity between the base material (BM), the skin-side heat-affected zone (SK-HAZ), the stringer-side heat-affected zone (ST-HAZ) and the weld seam (WS). Through in-depth crystallographic analysis, we demonstrate that the kernel average misorientation curve of the WS is steeper and the peak misorientation angle is larger, revealing that the WS has a lower geometrically necessary dislocations density and a smaller residual strain. Due to the different orientation of each a-phase colony at the interface of the two phases, it is not conducive to the deformation mode of dislocation slip, so a large number of twins are generated in the WS. Furthermore, the WS has a strong crystal preferential orientation and the maximum polar density of the pole figure is 17.05, which is significantly higher than the polar density of the base material. It is found that the gradient of microstructure variation in the narrow HAZ is higher than that in the WS, which leads to more heterogeneous properties in the HAZ compared to the weld. This research result is consistent with the phenomenon that all the fractures of the resultant T-joints occurred in the HAZ.