Effects on microstructural refinement of mechanical properties in steel‑copper joints laser welded with alternating magnetic field augmentation

In this research project, pure copper and stainless steel were joined using laser beam welding in the presence of an alternating magnetic field. The microstructure, element distribution and mechanical properties of the welded joints were then analyzed using optical microscopy, scanning electron microscopy, energy dispersive X-ray spectrometry and other methods. We determined that the microstructure in the fusion zone transformed in the alternating magnetic field improved laser welding process from bulky banded and spherical structures to fine blocky and granular structures. Grain refinement and inhibition of composition segregation were achieved with the addition of electromagnetic force generated by alternating current, reducing susceptibility to solidification cracking. During the metallurgical interaction, diffusion of solute atoms decreased the microstructure gradient significantly, reducing thermal stress and improving the mechanical properties of the welded joints. The emergence of an increased number of shear dimples in the fracture confirmed improvement in ductility. A physical model is proposed to validate the strengthening and toughening mechanisms of the laser welded joints augmented by alternating magnetic force. •Alternating magnetic field assisted laser welding is used for joining of steel/copper.•Microstructural evolution and composition segregetion have been deeply investigated.•A physical model was proposed to clarify the strengthening and toughening mechanism.•It may be a means to improve joint quality of dissimilar metals in manufacturing.