A swing laser-mig hybrid welding method of sheet invar alloy with co and cr interlayer

Abstract

This invention relates to the field of metal material welding technology, specifically a method for oscillating laser-MIG composite welding of thin Invar alloy plates with added Co and Cr interlayers. The welding method comprises the following steps: Step 1: Grinding the Invar alloy surfaces to be welded to remove oil and oxides, and wiping them clean with acetone; simultaneously, preparing pure Co foil or Co+Cr composite sheets and cleaning them, using them as the Co interlayer or Co+Cr composite interlayer; Step 2: Placing the Co interlayer or Co+Cr composite interlayer between two Invar alloy surfaces to be welded, and securing them tightly to form a weldment clamped in the order of "Invar alloy / interlayer / Invar alloy"; Step 3: Welding the weldment using an oscillating laser-MIG composite welding system, using inert gas as the shielding gas during welding, and obtaining an Invar alloy welded joint after cooling. This method has advantages such as simplicity, improved ultimate tensile strength and ductility, and corrosion resistance in marine environments.

Description

Technical Field

[0001] This invention relates to the field of metal material welding technology, specifically to a method for oscillating laser-MIG composite welding of thin Invar alloy plates with added Co and Cr interlayers. Background Technology

[0002] Invar alloys (typically Fe-36Ni) are widely used in marine engineering, particularly in the manufacture of membrane-type cargo tank liners for liquefied natural gas (LNG) storage and transportation vessels, due to their extremely low coefficient of thermal expansion at very low temperatures. These applications typically require the efficient and high-quality welding and assembly of large quantities of thin Invar alloy plates.

[0003] Existing welding technologies for thin-plate Invar alloys primarily employ tungsten inert gas (TIG), metal inert gas (MIG), or conventional laser welding processes. Due to the low thermal conductivity and extremely high viscosity of Invar alloys in their molten state, traditional single heat sources easily lead to problems such as poor forming, high porosity sensitivity, and extremely stringent requirements for assembly clearances in thin plates. To expand gap bridging capabilities and attempt to improve molten pool flow behavior through dual heat sources, the industry has recently begun to introduce laser-MIG hybrid welding technology. However, in conventional hybrid welding processes, an intermediate layer is usually not added, or only a conventional welding wire with a composition similar to the base metal is used for filler.

[0004] However, existing thin-plate Invar alloy welded joints exhibit two significant shortcomings in harsh marine service environments: firstly, insufficient mechanical properties, with low strength and ductility, making them unable to withstand complex alternating loads; and secondly, extremely poor corrosion resistance, making them highly susceptible to severe pitting and localized perforation in high-salt-spray environments. Therefore, current technology cannot fully meet the requirements of marine environments. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a simple, corrosion-resistant method for oscillating laser-MIG composite welding of thin Invar alloy plates with added Co and Cr interlayers in marine environments.

[0006] The technical solution adopted by this invention to solve its technical problem is: A method for oscillating laser-MIG hybrid welding of thin Invar alloy plates with added Co and Cr interlayers, characterized by the following steps: Step 1: Grind the Invar alloy surface to be soldered to remove oil and oxides, and wipe it clean with acetone; at the same time, prepare pure Co foil or Co+Cr composite sheet and clean it, and use it as Co intermediate layer or Co+Cr composite intermediate layer. Step 2: Place the Co intermediate layer or Co+Cr composite intermediate layer between the two Invar alloy surfaces to be welded, and secure them tightly to form a weldment clamped in the order of "Invar alloy / intermediate layer / Invar alloy". Step 3: The workpiece is welded using a oscillating laser-MIG hybrid welding system. Inert gas is used as the shielding gas during the welding process, and the Invar alloy welded joint is obtained after cooling.

[0007] In step one of this invention, the thickness of the Invar alloy base material is 3 mm; the purity of the Co foil and Cr foil is 99.99%.

[0008] In step one of this invention, the total thickness of the Co interlayer or Co+Cr composite interlayer is 0.6 mm. The Co+Cr composite interlayer is formed by stacking pure Co foil with a thickness of 0.3 mm and pure Cr foil with a thickness of 0.3 mm in a 1:1 thickness ratio. This equal composite thickness can refine the joint grains to an extreme value, optimize the mechanical properties and corrosion resistance of the joint, and effectively avoid the risk of ferrite embrittlement and excessive thermal expansion caused by the addition of high Cr alone.

[0009] In step one of this invention, the Invar alloy surface to be welded, the pure cobalt (Co) foil, and the pure chromium (Cr) foil are all wiped with acetone or ultrasonically cleaned, and then dried with cold air to obtain dust-free and oil-free materials to be welded.

[0010] In step three of this invention, the spatial attitude parameters for the oscillating laser-MIG composite welding are as follows: the angle between the welding torch and the horizontal plane is set to 70°, the angle between the laser beam and the horizontal plane is set to 85°, and the laser beam is located in front of the welding torch, with the filament spacing between the two maintained at 2mm.

[0011] The core energy and motion parameters of the oscillating laser-MIG composite welding in step three of this invention are as follows: laser power 3500W; laser oscillation mode is circular oscillation, oscillation frequency is 150Hz, and oscillation amplitude is 1.5mm; MIG welding is a unified DC pulse mode, welding current is 140A; welding speed is 1m / min. The specific combined action of the oscillating laser and pulsed arc can improve the fluidity of the molten pool and make the distribution of trace elements more uniform.

[0012] In step three of this invention, the inert protective gas is pure argon with a purity of 99.99%, and the gas flow rate is set to 15 L / min to prevent oxidation of the weld during the cooling process.

[0013] Compared with the prior art, the advantages of the present invention are as follows: 1. This invention uses the combined stirring effect of oscillating laser and pulsed electric arc to reduce the high viscosity of the Invar alloy molten pool, so that the added trace alloying elements (Co or Co+Cr) can achieve uniform solid solution distribution in the weld, completely eliminating the problem of local enrichment of elements at the bottom of the weld and poor back formation caused by excessive addition of Cr. 2. The pure Co or Co+Cr composite used in this invention perfectly balances "high strength" and "high ductility and toughness". Adding pure Co alone effectively refines the weld grains and induces deformation-induced strengthening; while replacing the same thickness with a Co+Cr composite intermediate layer, the extremely low elastic anisotropy index and high Poisson's ratio significantly enhance the strain hardening ability, greatly delay local necking, and enable the joint tensile strength to reach its peak. 3. This invention can significantly improve corrosion resistance without damaging the austenitic matrix structure of Invar alloys. Adding Co alone can stabilize active sites and kinetically inhibit corrosion initiation; while the composite addition of Cr drives rapid nucleation of a dense Cr-based passivation film through strong local polarization and high surface energy, resulting in a significant increase in charge transfer resistance and capacitive arc radius. 4. The method of this invention is based on the scientific logic of first optimizing a single element to determine the optimal thickness (0.6mm), and then performing equal-thickness composite replacement (0.3mmCo+0.3mmCr). The process design is rigorous and efficient, and it can be widely used in marine engineering, especially in LNG storage and transportation systems, for high-quality connection of thin-plate Invar alloys. Attached Figure Description

[0014] Figure 1 The following are EDS distribution diagrams for welds with different Co contents: (a1-a4) are EDS distribution diagrams for welds with 0mm Co content, (b1-b4) are EDS distribution diagrams for welds with 0.3mm Co intermediate layer, (c1-c4) are EDS distribution diagrams for welds with 0.6mm Co intermediate layer, and (d1-d4) are EDS distribution diagrams for welds with 0.9mm Co intermediate layer.

[0015] Figure 2 The following are EDS diagrams of the weld center after adding intermediate layers with different compositions: (a1–a5) are EDS diagrams of the weld center with a 0.6mmCo intermediate layer, (b1–b5) are EDS diagrams of the weld center with a 0.3mmCo+0.3mmCr intermediate layer, and (c1–c5) are EDS diagrams of the weld center with a 0.6mmCr intermediate layer.

[0016] Figure 3The images show the EBSD inverse pole figure (IPF), nucleus average misalignment diagram (KAM), and grain size diagram of the weld center for different Co interlayer thicknesses (0 mm, 0.3 mm, 0.6 mm, 0.9 mm). Specifically, (a) is the EBSD inverse pole figure (IPF) of the weld center with a 0 mm Co interlayer thickness, (b) is the KAM of the weld center with a 0 mm Co interlayer thickness, (c) is the grain size diagram of the weld center with a 0 mm Co interlayer thickness, (d) is the EBSD inverse pole figure (IPF) of the weld center with a 0.3 mm Co interlayer thickness, and (e) is the KAM of the weld center with a 0.3 mm Co interlayer thickness. (f) is the grain size diagram of the weld center with a 0.3 mm Co interlayer thickness, (g) is the EBSD inverse pole figure (IPF) of the weld center with a 0.6 mm Co interlayer thickness, (h) is the nucleus average misalignment diagram (KAM) of the weld center with a 0.6 mm Co interlayer thickness, (i) is the grain size diagram of the weld center with a 0.6 mm Co interlayer thickness, (j) is the EBSD inverse pole figure (IPF) of the weld center with a 0.9 mm Co interlayer thickness, (k) is the nucleus average misalignment diagram (KAM) of the weld center with a 0.9 mm Co interlayer thickness, and (l) is the grain size diagram of the weld center with a 0.9 mm Co interlayer thickness.

[0017] Figure 4 The EBSD inverse pole figure (IPF), core-averaged misalignment diagram (KAM), and phase diagram of the weld center after adding different intermediate layers (0 mm intermediate layer, 0.6 mm Co intermediate layer, 0.3 mm Co + 0.3 mm Cr intermediate layer, 0.6 mm Cr intermediate layer) are shown. Specifically, (a) is the EBSD inverse pole figure (IPF) of the weld center with a 0 mm intermediate layer, (b) is the EBSD inverse pole figure (IPF) of the weld center with a 0.6 mm Co intermediate layer, (c) is the EBSD inverse pole figure (IPF) of the weld center with a 0.3 mm Co + 0.3 mm Cr intermediate layer, and (d) is the EBSD inverse pole figure (IPF) of the weld center with a 0.6 mm Cr intermediate layer. (e) is the core average misalignment diagram (KAM) for the weld center with a 0mm intermediate layer, (f) is the core average misalignment diagram (KAM) for the weld center with a 0.6mm Co intermediate layer, (g) is the core average misalignment diagram (KAM) for the weld center with a 0.3mm Co + 0.3mm Cr intermediate layer, (h) is the core average misalignment diagram (KAM) for the weld center with a 0.6mm Cr intermediate layer, (i) is the phase diagram for the weld center with a 0mm intermediate layer, (j) is the phase diagram for the weld center with a 0.6mm Co intermediate layer, (k) is the phase diagram for the weld center with a 0.3mm Co + 0.3mm Cr intermediate layer, and (l) is the phase diagram for the weld center with a 0.6mm Cr intermediate layer.

[0018] Figure 5 Grain size diagrams of the weld center after adding intermediate layers of different compositions (0mm intermediate layer, 0.6mm Co intermediate layer, 0.3mm Co+0.3mm Cr intermediate layer, 0.6mm Cr intermediate layer); where (a) is the grain size diagram of the 0mm intermediate layer, (b) is the grain size diagram of the 0.6mm Co intermediate layer, (c) is the grain size diagram of the 0.3mm Co+0.3mm Cr intermediate layer, and (d) is the grain size diagram of the 0.6mm Cr intermediate layer.

[0019] Figure 6 Tensile stress-displacement curves and typical fracture microstructures of joints with different Co layer thicknesses are shown. (a) is the tensile stress-displacement curve of the joint with a 0 mm Co intermediate layer, (b) is the tensile stress-displacement curve of the joint with a 0.3 mm Co intermediate layer, (c) is the tensile stress-displacement curve of the joint with a 0.6 mm Co intermediate layer, (d) is the tensile stress-displacement curve of the joint with a 0.9 mm Co intermediate layer, (e, f) are typical fracture microstructures of the joint with a 0.6 mm Co intermediate layer, and (gh) is a typical fracture microstructure of the joint with a 0.9 mm Co intermediate layer.

[0020] Figure 7 Tensile stress-displacement curves of welded joints with different intermediate layer compositions (0mm intermediate layer, 0.6mm Co intermediate layer, 0.3mm Co+0.3mm Cr intermediate layer, 0.6mm Cr intermediate layer) are shown. Among them, (a) is the tensile stress-displacement curve of the joint with 0mm intermediate layer, (b) is the tensile stress-displacement curve of the joint with 0.6mm Co intermediate layer, (c) is the tensile stress-displacement curve of the joint with 0.3mm Co+0.3mm Cr intermediate layer, and (d) is the tensile stress-displacement curve of the joint with 0.6mm Cr intermediate layer.

[0021] Figure 8 The figures show the open circuit potential and potentiodynamic polarization curves of the weld in a 3.5 wt% NaCl solution; where (a) is the open circuit potential curve and (b) is the potentiodynamic polarization curve.

[0022] Figure 9 The figures are electrochemical impedance spectroscopy (EIS) of the weld seam; where (a) is the Nyquist plot and (b) is the Bode plot.

[0023] Figure 10 The figures show the results of the first-principles calculations of surface energy and work function; where (a) is the result of the surface energy calculation and (b) is the result of the work function calculation. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings: As shown in the attached figure, a method for oscillating laser-MIG composite welding of thin Invar alloy plates with added Co and Cr interlayers is characterized by the following steps: Step 1: Grind the Invar alloy surface to be soldered to remove oil and oxides, and wipe it clean with acetone; at the same time, prepare pure Co foil or Co+Cr composite sheet and clean it, and use it as Co intermediate layer or Co+Cr composite intermediate layer. Step 2: Place the Co intermediate layer or Co+Cr composite intermediate layer between the two Invar alloy surfaces to be welded, and secure them tightly to form a weldment clamped in the order of "Invar alloy / intermediate layer / Invar alloy". Step 3: The workpiece is welded using a oscillating laser-MIG hybrid welding system. Inert gas is used as the shielding gas during the welding process, and the Invar alloy welded joint is obtained after cooling.

[0025] In step one of this invention, the thickness of the Invar alloy base material is 3 mm; the purity of the Co foil and Cr foil is 99.99%.

[0026] In step one of this invention, the total thickness of the Co interlayer or Co+Cr composite interlayer is 0.6 mm. The Co+Cr composite interlayer is formed by stacking pure Co foil with a thickness of 0.3 mm and pure Cr foil with a thickness of 0.3 mm in a 1:1 thickness ratio. This equal composite thickness can make the joint grain refinement reach the extreme value, while effectively avoiding the risk of ferrite embrittlement and excessive thermal expansion caused by the addition of high Cr alone.

[0027] In step one of this invention, the Invar alloy surface to be welded, the pure cobalt (Co) foil, and the pure chromium (Cr) foil are all wiped with acetone or ultrasonically cleaned, and then dried with cold air to obtain dust-free and oil-free materials to be welded.

[0028] In step three of this invention, the spatial attitude parameters for the oscillating laser-MIG composite welding are as follows: the angle between the welding torch and the horizontal plane is set to 70°, the angle between the laser beam and the horizontal plane is set to 85°, and the laser beam is located in front of the welding torch, with the filament spacing between the two maintained at 2mm.

[0029] The core energy and motion parameters of the oscillating laser-MIG composite welding in step three of this invention are as follows: laser power 3500W; laser oscillation mode is circular oscillation, oscillation frequency is 150Hz, and oscillation amplitude is 1.5mm; MIG welding is a unified DC pulse mode, welding current is 140A; welding speed is 1m / min. The specific combined action of the oscillating laser and pulsed arc can improve the fluidity of the molten pool and make the distribution of trace elements more uniform.

[0030] In step three of this invention, the inert protective gas is pure argon with a purity of 99.99%, and the gas flow rate is set to 15 L / min to prevent oxidation of the weld during the cooling process.

[0031] The thin-plate Invar alloy welding method of this invention first prepares Invar alloy base material and pure Co foil or Co+Cr composite foil samples, then clamps and splices them in the order of "Invar alloy / intermediate layer / Invar alloy", and performs composite welding under a set oscillating laser and pulsed arc process to obtain an Invar alloy welded joint. After electrochemical corrosion testing, the obtained joint shows a wide and stable passivation range in its polarization curve, and its corrosion resistance in marine environments is significantly improved; at the same time, the joint has extremely high yield strength and ultimate tensile strength, perfectly achieving a simultaneous leap in mechanical properties and corrosion resistance, and has extremely wide engineering applicability.

[0032] Before exploring the optimal composite interlayer process, this invention first conducted optimization experiments on the thickness of a single pure Co interlayer. The experiments showed that when the pure Co interlayer thickness was 0.6 mm, the mechanical tensile properties of the weld reached the peak value of the pure Co group; however, the passivation film of single Co was relatively porous, resulting in limited pitting corrosion resistance. To simultaneously improve corrosion resistance and eliminate the limitations of a single element, this invention directly fixed the interlayer thickness (0.6 mm) and replaced it with a Co and Cr composite foil (i.e., 0.3 mm Co + 0.3 mm Cr) at a 1:1 ratio, thereby implementing the composite strengthening and passivation mechanism.

[0033] Example 1: (The preferred embodiment of the present invention, using a Co+Cr composite interlayer of optimal thickness): Step 1: Take a 100×50×3mm thin Invar alloy plate, grind the surface to be welded to remove oil and oxides, and clean it with acetone. Prepare pure Co foil and pure Cr foil with a thickness of 0.3mm each (the total thickness is the optimal thickness of 0.6mm selected in the previous step), and clean them for later use.

[0034] Step 2: Stack 0.3mm Co foil and 0.3mm Cr foil to form a composite intermediate layer, sandwich it between the mating surfaces of the two base materials and secure it tightly.

[0035] Step 3: Welding is performed using a oscillating laser-MIG hybrid welding system. The filament spacing is set to 2mm, the laser power to be 3500W, the circular oscillation frequency to be 150Hz, the oscillation amplitude to be 1.5mm, the pulsed MIG current to be 140A, and the argon gas protection flow rate to be 15L / min.

[0036] Microstructure: The weld seam is fully formed on both sides. EDS surface scanning shows that Fe, Ni, Co, and Cr elements are highly uniformly distributed with no enrichment of elements at the bottom. Figure 2As shown in the diagram, the EBSD phase diagram indicates that the weld is a fully austenitic structure with no ferrite precipitation. This composite group has the finest grains (average perimeter reduced to 289.28 μm) and a high KAM value, indicating strong solid solution strengthening. Figure 4 , 5 As shown.

[0037] Mechanical properties: Tensile testing shows that this joint possesses both the highest yield strength and ultimate tensile strength, such as Figure 7 As shown in Table 1, DFT calculations reveal that the FeNiCoCr composite system exhibits the lowest elastic modulus (E=151.52 GPa, G=62.38 GPa) and bulk modulus (B=116.64 GPa), indicating a relatively lower atomic bond stiffness. However, it possesses the highest Poisson's ratio (ν=0.30) and a significantly reduced elastic anisotropy index (A=0.08). This demonstrates that the synergistic effect of Co+Cr endows the lattice with excellent plastic deformation capability and isotropic characteristics. Although the stiffness decreases during the elastic stage, the resulting lattice distortion effectively hinders dislocation slip and enhances strain hardening during tensile plastic deformation, thus significantly delaying necking and fracture during macroscopic tension.

[0038] Table 1 Calculation results of alloy elastic properties Corrosion resistance: In the polarization curves, the composite group has the lowest corrosion current density and the highest open-circuit potential, such as... Figure 8 As shown in the Nyquist graph, this group exhibits the largest impedance-capacitive arc resistance, with a significant improvement in corrosion resistance, such as... Figure 9 As shown. The DFT calculation results intuitively reveal the dual mechanism by which the composite intermediate layer improves corrosion resistance: on the one hand, the addition of Co (FeNiCo) significantly increases the work function of the system from 4.80 eV to 4.88 eV, effectively stabilizing the surface active sites and kinetically delaying pitting corrosion initiation; on the other hand, the composite addition of Cr (FeNiCoCr system) causes the surface energy of the system to surge to a maximum of 3.75 J / m². This high surface energy strongly drives Cr atoms to migrate and accumulate on the surface thermodynamically, greatly promoting the rapid nucleation of the dense passivation film. The two work synergistically to endow the joint with excellent corrosion resistance, such as... Figure 10 As shown.

[0039] Example 2 (Pure Co interlayer, establishing the preferred group with optimal thickness): The intermediate layer uses a pure Co foil with a thickness of 0.6 mm, and the other parameters are the same as in Example 1.

[0040] Result: Co was evenly distributed after an appropriate amount was added, such as Figure 1As shown, the grains were effectively refined (average perimeter approximately 291.52 μm), as... Figure 3 As shown. The mechanical strength reaches the maximum value of the pure Co system, such as... Figure 6 As shown in Table 1, the DFT results indicate that its elastic anisotropy index (A=0.35) is significantly better than that of the parent material. This embodiment establishes 0.6 mm as the optimal physical thickness for structural reinforcement.

[0041] Comparative Example 1 (thin pure Co intermediate layer, validation group): The intermediate layer uses a pure Co foil with a thickness of 0.3 mm, and the other parameters are the same as in Example 1.

[0042] Results: Compared to the absence of an intermediate layer, the Co element was more evenly distributed after appropriate addition, such as... Figure 1 As shown, the addition of 0.3 mm pure Co has begun to exert its effects on grain refinement and solid solution strengthening, resulting in improved joint mechanical properties. However, because the amount of Co added did not reach the optimal saturation value, its overall mechanical properties are lower than those of Example 2 (0.6 mm Co). Figure 3 , 6 As shown.

[0043] Comparative Example 2 (no intermediate layer, blank control): Without any intermediate layer, two 3mm thick Invar alloy base materials are directly welded together.

[0044] Results: The grains were the coarsest, and the tensile strength was the lowest among all groups. Figure 3-7 As shown. It rapidly develops pitting and perforation in a 3.5 wt% NaCl solution, exhibiting extremely poor corrosion resistance, such as... Figure 8 , 9 As shown.

[0045] Comparative Example 3 (Pure Cr intermediate layer, single-element drawbacks comparison): The intermediate layer uses a pure Cr foil with a thickness of 0.6 mm, and the other parameters are the same as in Example 1.

[0046] Results: Cr significantly improved corrosion resistance, such as Figure 8 , 9 As shown. However, the addition of a single element of 0.6 mm caused metallurgical defects, resulting in poor weld back formation and localized Cr enrichment at the bottom, such as... Figure 2 As shown. EBSD reveals the precipitation of a brittle ferrite phase, as... Figure 4 The green phase is shown in Table 1. DFT results indicate that the FeNiCr system exhibits extremely high elastic anisotropy (A=0.89), leading to a sharp decrease in plasticity and a risk of brittle fracture.

[0047] Comparative Example 4 (Excess Pure Co Interlayer, Limit Control): The intermediate layer uses a pure Co foil with a thickness of 0.9 mm, and the other parameters are the same as in Example 1.

[0048] Results: Due to excessive Co addition, the metallurgical kinetics of the molten pool deteriorated, leading to element enrichment and stress concentration, such as... Figure 1 As shown, the tensile strength and elongation of the joint decreased significantly compared to Example 2 (0.6 mm Co), and the sample exhibited brittle fracture, proving that 0.6 mm is indeed the critical optimal value for pure Co thickness. Figure 6 As shown.

[0049] The above embodiments target thin-plate Invar alloys and a wobbling laser-MIG composite welding method based on the addition of a Co and Cr interlayer. To address the problem of poor mechanical properties and susceptibility to corrosion in Invar alloy welded joints in humid marine environments, a Co and Cr interlayer is introduced. The synergistic effect of these elements is used to simultaneously improve overall performance. First, a pure Co interlayer experiment established an optimal thickness of 0.6 mm. Subsequently, it was replaced with a 0.3 mm Co + 0.3 mm Cr composite foil. Experimental results show that the addition of both Co and Cr improves the mechanical and corrosion resistance of the alloy. Furthermore, when Co and Cr are added simultaneously... At this time, the weld exhibits the best overall performance. First-principles calculations show that adding Co alone can stabilize the active sites of Fe atoms and reduce surface energy, thereby kinetically inhibiting corrosion initiation. After the composite addition of Cr, the elastic anisotropy index of the system drops to 0.08 and the Poisson's ratio reaches a maximum of 0.30, significantly improving ductility and strain hardening ability. At the same time, the surface energy increases to 3.75 J / m², driving Cr to accumulate on the surface and rapidly nucleate a dense passivation film. The synergy of these two factors enables the joint to exhibit the finest grains, the highest tensile strength, and the best pitting corrosion resistance, perfectly meeting the long-term service requirements in harsh marine environments.

[0050] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for oscillating laser-MIG composite welding of thin Invar alloy plates with added Co and Cr interlayers, characterized in that... The welding method involves the following steps: Step 1: Grind the Invar alloy surface to be soldered to remove oil and oxides, and wipe it clean with acetone; at the same time, prepare pure Co foil or Co+Cr composite sheet and clean it, and use it as Co intermediate layer or Co+Cr composite intermediate layer. Step 2: Place the Co intermediate layer or Co+Cr composite intermediate layer between the two Invar alloy surfaces to be welded, and secure them tightly to form a weldment clamped in the order of "Invar alloy / intermediate layer / Invar alloy". Step 3: The workpiece is welded using a oscillating laser-MIG hybrid welding system. Inert gas is used as the shielding gas during the welding process, and the Invar alloy welded joint is obtained after cooling.

2. The method for oscillating laser-MIG composite welding of thin Invar alloy plates with an intermediate layer containing Co and Cr as described in claim 1, characterized in that... In step one, the thickness of the Invar alloy base material is 3mm; the purity of both the Co foil and the Cr foil is 99.99%.

3. The method for oscillating laser-MIG composite welding of thin Invar alloy plates with an intermediate layer containing Co and Cr as described in claim 1, characterized in that... In step one, the total thickness of the Co interlayer or Co+Cr composite interlayer is 0.6 mm. The Co+Cr composite interlayer is composed of pure Co foil with a thickness of 0.3 mm and pure Cr foil with a thickness of 0.3 mm stacked in a 1:1 thickness ratio. This equal composite thickness can refine the joint grains to an extreme value, while effectively avoiding the risk of ferrite embrittlement and excessive thermal expansion caused by the addition of high Cr alone.

4. The method for oscillating laser-MIG composite welding of thin Invar alloy plates with an intermediate layer containing Co and Cr as described in claim 1, characterized in that... In step one, the Invar alloy surface to be welded, the pure cobalt (Co) foil, and the pure chromium (Cr) foil are all wiped with acetone or ultrasonically cleaned, and then dried with cold air to obtain dust-free and oil-free materials to be welded.

5. The method for oscillating laser-MIG composite welding of thin Invar alloy plates with an intermediate layer containing Co and Cr as described in claim 1, characterized in that... In step three, the spatial attitude parameters for the oscillating laser-MIG hybrid welding are as follows: the angle between the welding torch and the horizontal plane is set to 70°, the angle between the laser beam and the horizontal plane is set to 85°, and the laser beam is located in front of the welding torch, with the filament spacing between the two maintained at 2mm.

6. The method for oscillating laser-MIG composite welding of thin Invar alloy plates with an intermediate layer containing Co and Cr as described in claim 1, characterized in that... The core energy and motion parameters of the oscillating laser-MIG composite welding in step three are as follows: laser power 3500W; laser oscillation mode is circular oscillation, oscillation frequency is 150Hz, and oscillation amplitude is 1.5mm; MIG welding is a unified DC pulse mode, welding current is 140A; welding speed is 1m / min. The specific combined action of oscillating laser and pulsed arc can improve the fluidity of the molten pool and make the distribution of trace elements more uniform.

7. The method for oscillating laser-MIG composite welding of thin Invar alloy plates with an intermediate layer containing Co and Cr as described in claim 1, characterized in that... In step three, the inert protective gas is pure argon with a purity of 99.99%, and the gas flow rate is set to 15 L / min to prevent oxidation of the weld during the cooling process.

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