Effect of aluminum addition on the microstructure and mechanical properties of high-strength steel T-joints in flux bands constricting arc welding

In the context of lightweight manufacturing, High-Strength Low-Alloy (HSLA) steel T-joints have been widely adopted in critical components of advanced equipment. The precise control of alloying elements to synergistically enhance the strength and toughness of HSLA joints remains a pivotal challenge for expanding their applications. Aluminum (Al), recognized as one of the most influential alloying elements affecting the microstructural characteristics of HSLA steels, demonstrates significant metallurgical regulation effects dependent on its content and introduction method. However, conventional welding processes suffer from inherent limitations in Al regulation, including insufficient spatiotemporal control over elemental distribution and restricted process efficiency, while quantitative studies on the complex "process-composition-property" relationships of Al in HSLA joints remain scarce. To address these challenges, this study proposes an innovative in-situ dynamic Al regulation approach via Flux Bands Constricting Arc (FBCA) welding. The effects of Al content (0–0.92 wt%) in flux bands on the microstructural evolution and mechanical properties of HSLA joints including heat-affected zone (HAZ) and welding zone (WZ) were systematically investigated. Results demonstrate that Al addition achieves remarkable synergistic regulation on Q960 steel T-joints: average grain sizes in the welding zone and heat-affected zone were refined by 17 % and 21 %, respectively. With increasing Al content, the average hardness of welding zone and heat-affected zone increased by 35 %. Tensile strength reached 955.7 MPa (0.18 wt% Al) and 1044 MPa (0.92 wt% Al), representing a maximum enhancement of 23.5 %. While welding zone impact toughness slightly improved, heat-affected zone toughness decreased from 94.13 J to 65.77 J. Comprehensive microstructural characterization (Optical Microscope, Energy Dispersive Spectrometer, Electron Back Scatter Diffraction) revealed distinct Al-regulated mechanisms: In the welding zone, fine Al₂O₃ particles (<1 μm) induced acicular ferrite formation, enhancing strength without compromising toughness. In contrast, heat-affected zone refinement originated from arc constriction-induced temperature gradient modulation, which promoted low-angle grain boundary accumulation and increased dislocation density, ultimately reducing toughness through elevated strain energy storage. This work provides novel insights into in-situ elemental regulation during welding and elucidates the synergistic mechanisms of Al on HSLA joint performance, offering theoretical foundations for quantitative studies on complex multi-element interactions in HSLA joints.