Comparative investigation of laser welded joint properties between rolled-state and additively manufactured TC4 titanium alloys

As the global manufacturing industry facing an urgent demand for transformative technologies, the hybrid manufacturing method of multi-material structures is essential to achieve optimal production efficiency. This study compares the weld morphology and mechanical properties of the rolled and laser power bed fusion fabricated (LPBFed) TC4 titanium alloy joints in adjustable mode laser welding. The influence of critical welding parameters (e.g. laser power and core-ring ratio) on weld geometry and microstructure was systematically analyzed. The results indicate that the variations in welding parameters have a significant effect on weld width, melt depth, and microstructural characteristics. Notably, the LPBFed-LPBFed combination exhibited the highest sensitivity to variations in laser power and core-ring ratio. The discrepancy in thermal conductivity of the different base materials resulted in distinct heat-affected zone (HAZ) characteristics. The LPBFed state exhibited finer and more homogeneous grain structures (6.9 μm at top and 7.2 μm at bottom) due to slower cooling rates, whereas the rolled state showed larger, more oriented columnar crystals due to higher thermal conductivity. At the same process level, Mechanical testing revealed that the Rolled-Rolled combination exhibited the highest tensile strength (6200 N), while the LPBFed-LPBFed combination displayed the lowest (5230 N), mainly attributed to the increased porosity and coarser grain sizes. It also reveals that, although the fracture in all combinations occurs at the interface on a macroscopic scale, there are notable differences in the fracture behavior at the microscopic level.