Tailoring microstructure and interface integrity in Ti–316L dissimilar keyhole laser welding using controlled 3d magnetic field stimulation

This study investigates the influence of externally applied magnetic fields—both alternating and rotating—on the microstructural evolution and interface integrity of laser-welded dissimilar joints between titanium and 316 L stainless steel. A fiber laser system was employed to perform keyhole-mode lap welding, with various magnetic field orientations introduced to actively manipulate the melt pool dynamics. Alternating fields (Bx, By, Bz) promoted grain refinement (reducing average grain size from 51.8 ± 4.1 µm to 36.2 ± 3.1 µm) and enhanced recrystallization (increasing the recrystallized fraction to ∼0.69), resulting in a finer microstructure and more discrete intermetallic compound (IMC) formation at the Ti–316 L interface. In contrast, rotating magnetic fields (Bxy, Byz, Bxz) encouraged coarser grain growth (increasing average grain size up to 80.1 ± 4.5 µm) and increased the presence of unrecrystallized regions (up to 0.484 fraction) due to stabilized melt flow and slower cooling rates. These conditions facilitated deeper interdiffusion and led to thicker, more continuous IMC layers, correlating with a peak microhardness of 576 ± 8 HV, potentially compromising joint integrity. The findings demonstrate that precise control of magnetic field configuration during laser processing offers a powerful tool to tailor interfacial microstructures and minimize brittle phase formation. This approach provides new opportunities to enhance the performance and reliability of dissimilar metal joints in critical structural applications.