Effect of welding speed on microstructure and mechanical properties of selective laser melting Inconel 625 alloy laser welded joint

The Inconel 625 manufactured by SLM is limited in size and practical application requires advanced welding techniques to join them. In this paper, Inconel 625 fabricated by SLM was laser welded and the effect of welding speed on the microstructure of the joint was investigated. The microstructures were analyzed by SEM, EBSD and TEM. The fusion zone of the joint was mainly columnar dendrites, a large number of equiaxed crystals formed along with the fusion line, and nanoscale carbides and Nb-rich phases precipitated at the grain boundaries can be observed. With increasing welding speed, the grain size and the ratio of high angle grain boundary (HAGB) were decreased, and the tensile strength and elongation are improved. The tensile strength of joints exceeds 875 MPa, joint efficiency reaching 97.8%. Moreover, the elongation of joints is near 39.8%, reaching 94.8% of the base metal. In addition, the cause of softening of the fusion zone was explored， and The fracture method of the joint shows that it is ductile fracture. The material properties for selective laser melting fabrication meet the requirements of the application.