Microstructure and mechanical properties of laser-welded 30MnB5 via precise Al–Si coating geometry control

During the laser welding of Al–Si–coated 30MnB5 steel, the incorporation of molten coating constituents into the fusion zone (FZ) promotes δ-ferrite formation, Al segregation, and heterogeneous microstructures, undermining the reliability of hot-stamped tailor-welded blanks (TWBs). To address this challenge, the thickness and geometry of the remaining Al–Si coating were precisely tailored using femtosecond laser ablation, providing a controllable pathway for regulating Al incorporation into the molten pool. TWBs with systematically varied coating geometries were fabricated and examined to establish the link between coating control, solidification dynamics, and weld performance. EBSD analysis showed that suppression of Al segregation reduced δ-ferrite content by ~30–40% and promoted a more homogeneous martensitic matrix, while KAM results confirmed higher dislocation density and improved plastic accommodation in coating-minimized conditions. Mechanical testing further demonstrated that when the Al–Si coating was controlled to an Fe 2 SiAl 7 inhibition layer, the welded joints exhibited notable improvements in hardness and strength compared to the intact-coated samples. With progressive coating removal, the hardness of FZ exceeded 550 HV and the tensile strength approached 1.7 GPa, whereas fully de-coated joints achieved performance comparable to the base metal. These findings demonstrate that femtosecond laser tailoring of the Al–Si coating thickness and remaining layer structure is a scientifically grounded and scalable strategy for improving the weldability, microstructural uniformity, and mechanical integrity of advanced high-strength steels, offering new opportunities for the reliable production of hot-stamped automotive components.