Effects of beam oscillation on microstructural characteristics and mechanical properties in laser welded steel-copper joints

In this project, we present experimental laser welding of pure copper to stainless steel in the presence of beam oscillation. The microstructure, element distribution and mechanical properties of joints welded with and without exposure to beam oscillation were contrastively investigated employing scanning electron microscopy, energy dispersive X-ray spectrometry and other methodologies. The results showed that joint microstructure subjected to beam oscillation changed from massive and columnar structures to granular and globular structures. The driven force of circular oscillating beam on the molten pool produced a vortex flow, which promoted heat and mass transfer during laser welding. Moreover, it also led to the refinement of grains and discrete distribution of precipitated phases (rich-Fe α phase and rich-Cu ε phase), thereby reducing microstructural segregation and improving the resistance to crack in welds. The hardness gradient in joints suffered from beam oscillation was significantly reduced because of improvement in microstructural homogenization. The tensile strength and elongation of welded joints subjected to beam oscillation were 282.82 MPa and 2.68 mm respectively, 110.41% of strength and 153.14% of elongation compared to that of joints welded without exposure to beam oscillation. Joint improvement in strength and plasticity was attributive to microstructural refinement and compositional homogeneity.