Achieving high strength of laser welded Al/steel joint by optimized energy distribution with adjustable mode beam heat source

This study investigates the role of ring–beam power (Pr) in adjustable mode beam (AMB) laser welding of dissimilar 6061 Al alloy to DP590 steel, with a focus on the critical balance between porosity suppression and intermetallic compound (IMC) control. Unlike conventional lasers, AMB enables independent modulation of the center and ring beams, providing precise energy distribution essential for dissimilar joining. By integrating high–speed imaging and CFD simulations, we reveal that Pr governs keyhole stability and melt–pool convection. The results show that Pr = 600 W yields the highest mean shear force of 1067 N, with a recommended processing window of 500–700 W, within which mechanical performance is significantly improved over both lower and higher power conditions,the enlarged and stabilised keyhole effectively reduces porosity, while the formation of a ductile Fe 3 Al–rich layer enhances joint ductility and strength. However, when Pr exceeds 800 W, excessive turbulent mixing can lead to an excess of brittle Fe 2 Al 5 and FeAl 3 phases, triggering IMC-induced brittle cracking, severely degrading mechanical performance. This combined experimental–numerical approach provides a quantitative mechanistic framework for optimising Al/steel laser welding and clearly defines the allowable Pr window for achieving sound joints.