Microstructure and Mechanical Properties of Laser-MIG Hybrid Welding of Invar36 Alloy with Different Grooves

Laser-MIG hybrid welding experiments were performed on 10 mm thick Invar36 alloy plates. The influence of three different types of welding grooves (V-shape, rectangle, and X-shape) on the microstructure and mechanical properties of the welded joints were analyzed. The results indicated that the grain growth morphologies and grain sizes varied among the grooves. The average grain size at the center of the weld seam was 177.97 μm, which was smaller than the top grain size of 317.29 μm and the bottom grain size of 233.59 μm. In V-shape and rectangle grooves, the dimensions of grain the first weld pass was obviously smaller than the top region of the second pass. Microstructural characterization and tensile test showed no vertically columnar grains along the weld centerline in rectangle grooves which significantly affected the mechanical properties of welded joints. As a result of this phenomenon, V-shape groove joints demonstrated better mechanical properties than rectangle groove joints. The highest average tensile strength for V-shape groove, X-shape groove, and rectangle groove joints were 429.0 MPa, 419.3 MPa, and 395.4 MPa, respectively. Based on the Abaqus software, three-dimensional finite element analyses of three groove types were performed to investigate the relationship between microstructure and groove geometries. It was observed that the higher KAM regions in the EBSD results correlated with the higher effective plastic deformation in the finite element analysis. Furthermore, it was inferred from the thermal cycle curves that variations in thermal cycles across different regions resulted differences in grain size and grain growth morphology.