Research on Forming Quality and Microstructure of Laser-MIG Hybrid Welded Joint of Invar Steel

Abstract

In the present study, by using the process of laser-MIG hybrid welding (LMHW) and raw material of invar steel wire, the effect of process parameters of LMHW on the surface macroscopic morphology and the distribution of internal defects of the weld was analyzed and a set of highly fault-tolerant, insensitive to assembly accuracy and stable optimal process parameters were determined. In addition, the microstructural characteristics and mechanical properties of welded joints under optimal parameters were analyzed. The results show that the laser power and arc power are positively and linearly related to the line energy density (LED). As the LED increased, the width and penetration of the weld increased gradually, but the effect on reinforcement was less. With the double-layer welding method, the defocusing distance, laser-arc distance, laser power and arc power were adopted to significantly inhibit the generation of porosity defects in the weld seam. The grains in the weld overheated zone grew in the cooling direction toward the weld zone to form columnar crystals, and the internal austenite organization took the lead. The average tensile strength and elongation of the weld were 422.3 MPa and 44.4%, reaching more than 96.1% and 71.2% of the base material, respectively, making the mechanical properties of the weld close to those of the base material.