GH3536 is a nickel-base superalloy with outstanding oxidation resistance. It has good metallurgical properties and forming ability. For the 3D printing process superalloy, it has become the preferred material of choice. Rolled solid solution GH3128 (R-GH3128) has the benefits of strong corrosion resistance, oxidation resistance, and high fatigue strength. The two materials are extensively employed in the manufacture of high-temperature parts in the aerospace field. 3D printing can rapidly and accurately prepare complex geometric structures, which are challenging to achieve by traditional forging, casting, and other approaches. However, because of the travel limitations of printing equipment, the size of parts manufactured using the 3D printing process is restricted, which is challenging to meet the demands of large-size precision components manufacturing in the aerospace field. Laser welding technology has the benefits of small heat input, and adjustable beam transformation and being implemented in the atmospheric environment. It has developed into a crucial superalloy connection technology. In this study, the butt welding process test is conducted, the impact of fiber laser welding parameters on the weld morphology is investigated, and the structure and properties of the 3D-GH3536/R-GH3128 joint are examined.

The welding equipment uses a fiber laser, with a wavelength of 1060-1070 nm and a transmission fiber core diameter of 200 μm. The collimator’s focal length is 200 mm, the focusing lens’ focal length is 300 mm, and the focal spot diameter is 0.3 mm. The test materials are 3D printed GH3536 and rolled solid solution GH3128 flat plates, and the specification of the butt sample is 60 mm×40 mm×4 mm. In the welding process, the laser beam is incident perpendicular to the plate surface, and the focus is on the plate’s upper surface. The argon lateral protection is used. The circular nozzle’s inner diameter is 10 mm, the gas flow is 10 L/min, the included angle between the protective gas nozzle’s axis and the plate surface is 50°, the phosgene spacing is 2 mm, and the protective gas’ output length is 6 mm. The welding test is conducted using drag welding. In the welding process, a special fixture is employed to keep the sample plate’s butt joint in good condition, and the welding direction is perpendicular to the 3D printing forming direction. Maintaining a 2 m/min welding speed, while changing the laser’s defocus and power for welding. After welding, the sample’s cross-section is cut to prepare the metallographic sample. The joint’s microstructure is observed using a metallographic microscope, and the tensile fracture sample’s cross-section morphology is observed using a scanning electron microscope. The joint’s microhardness is tested using a hardness tester. The hardness tester’s indenter load is 100 g and the loading time is 15 s. With the tensile testing machine, tensile samples are prepared and the welds’ tensile properties are evaluated.

Using the 3D-GH3536/R-GH3128 butt welding test, it is discovered that when the speed is constant, the weld depth is positively correlated with the welding power; however, when the power is 3800 W and the defocus is -5-+ 5 mm, concave defects develop on the back of the weld (Fig. 5). Employing the defocus of 0 mm, welding speed of 2 m/min, and laser power of 3800 W, the well-generated weld is created, and the butt welding test of a 4 mm thick 3D-GH3536/R-GH3128 plate is conducted under these parameters. The butt joint presents a typical nail head weld shape. The joint structure is primarily made of columnar and equiaxed crystals. The joint structure’s columnar crystals are essentially symmetrically distributed along the weld center and converge at the weld center [Fig. 8(b)]. On the weld side near the fusion line of R-GH3128 [ Fig. 8(c)], there is no visible equiaxed fine-grained region, demonstrating a mixed region of columnar and equiaxed grains with shorter lengths. On the weld side near the fusion line of 3D-GH3536, the weld structure is followed by a fine-grained region and a mixed-grain region made of equiaxed and columnar crystals [Fig. 8(d)]. The average grain size at the weld center is 58.11 μm [Fig. 10(b)], the number proportion of grains with a weld size less than 50 μm is 62.2%, and the number proportion of grains with a weld size of 50-100 μm is 18.8%. The number proportion of grains with a grain boundary dislocation angle of less than 15° is 61.8% [Fig. 10(c)]. The tensile test findings demonstrate that the average tensile strength of the upper part of the welded joint is 722.3 MPa, and the average tensile strength of the lower part is 723.1 MPa (Fig. 13). The tensile strength of the upper and lower parts of the welded joint is essentially the same, which is 93% of that of the 3D-GH3536 base metal. The fracture mode is the ductile fracture.

The 4-mm thick 3D-GH3536/R-GH3128 dissimilar alloy butt joint is successfully obtained by laser welding. The welded joint exhibits nail head morphology. The welded structure is primarily columnar crystal and equiaxed crystal. The number proportion of grains with a weld size less than 50 μm is 62.2%. The tensile test findings demonstrate that the sample’s fracture occurs at the weld position, and the upper tensile strength and lower tensile strength are essentially the same, about 93% of that of the 3D-GH3536 base metal. The fracture mode is the ductile fracture.