MIL-101-based composite welding shielding gas, preparation method and application thereof

Abstract

The application discloses a MIL-101-based composite welding protective gas and a preparation method and application thereof, and belongs to the technical field of metal material welding manufacturing. The composite welding protective gas is composed of a reference mixed gas and modified MIL-101(Cr) nanoparticles uniformly suspended and dispersed in the reference mixed gas. The preparation method is as follows: MIL-101(Cr) nanoparticles are synthesized by using a solvothermal method and are loaded with active elements through impregnation adsorption, and then the nanoparticles are injected into a pressure-resistant mixing chamber filled with the reference mixed gas, and a gas-solid suspension system is formed under the dual action of mechanical stirring and ultrasonic fluidization. The application effectively solves the problems of pores associated with high-strength welds and deterioration of toughness, significantly inhibits the weld pores through the dual synergistic effect of channel confined adsorption and in-situ catalytic nucleation, refines the grains, and improves the comprehensive mechanical properties and strength-plasticity product of the joint, and the preparation process is controllable, and can be applied to the welding manufacturing of thick plates, narrow-gap and high-precision structural parts.

Description

Technical Field

[0001] This invention belongs to the field of metal material welding and manufacturing technology, specifically relating to a MIL-101-based composite welding shielding gas, its preparation method, and its application. Background Technology

[0002] In the welding and manufacturing of thick plates, narrow gaps, and high-precision structural components, the narrow gap gas shielded welding (NG-GMAW) process is widely used due to its significant advantages such as concentrated heat input and small welding deformation. However, this process still faces several prominent technical bottlenecks in practical applications: First, the narrow gap groove has a small internal space and complex gas flow, making it easy for air to be entrained by disturbances in the shielding gas flow; at the same time, the high temperature of the arc can cause the decomposition of trace water vapor in the shielding gas and environment, leading to defects such as hydrogen porosity in the weld. Second, thick plate narrow gap welding has a significant heat accumulation effect, and the molten metal in the molten pool cools slowly, causing the formation of coarse columnar crystal structures at the crystallization front, which in turn leads to poor sidewall fusion and a decline in joint strength and toughness.

[0003] Traditional gas shielding processes mainly employ pre-mixed inert / active gases (such as 80% Ar + 20% CO2), but their mechanism of action is limited to "passive physical isolation" of the molten pool. To address the metallurgical defects in the aforementioned high aspect ratio welds, existing technologies primarily focus on improving the welding torch structure or optimizing the power supply waveform. Current shielding gases mainly emphasize physical isolation, with relatively limited active metallurgical control methods.

[0004] Metal-organic frameworks (MOFs) are a new class of porous crystalline materials. Among them, MIL-101(Cr) possesses an extremely high specific surface area (up to 3000 m²). 2 With its abundant porous structure and excellent thermochemical stability, and a decomposition temperature exceeding 300℃, MIL-101(Cr) meets the requirements of the high-temperature environment surrounding the welding arc. Therefore, introducing this porous functional material into the welding shielding gas medium to develop a novel composite shielding gas with active metallurgical functions, breaking through the limitations of existing physical isolation, and solving the technical problems of porosity and coarse grains in thick plate narrow-gap welding from the metallurgical source, has significant scientific and practical value for promoting the engineering application of high-end welding manufacturing. Summary of the Invention

[0005] In view of the above, it is necessary to provide a MIL-101-based composite welding shielding gas, its preparation method and application. The "gas-solid two-phase" composite welding shielding gas is composed of a reference mixed gas and modified MIL-101(Cr) nanoparticles with confined loading of Ti / B active elements. By utilizing the channel confinement effect and high-temperature instantaneous release mechanism of MOF materials, it can simultaneously achieve deep degassing and grain refinement of the molten pool in narrow gap welding, thus solving the industry problem of porosity and toughness deterioration in high-strength welds.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A MIL-101-based composite welding protective gas is composed of a reference mixed gas and modified MIL-101(Cr) nanoparticles uniformly suspended and dispersed in the reference mixed gas. The composite welding protective gas is a gas-solid two-phase suspension system.

[0008] The modified MIL-101(Cr) nanoparticles have a particle size of 50-200 nm and their mass accounts for 0.1 wt%-1.0 wt% of the total mass of the reference mixed gas.

[0009] In this invention, the modified MIL-101(Cr) nanoparticles are further wherein microalloying active elements are confined within the micropores of the nanoparticles, and the microalloying active elements are immobilized in the pores of the nanoparticles through physical adsorption and / or chemical bonding.

[0010] In this invention, the microalloying active element is at least one of Ti or B.

[0011] In this invention, the reference mixed gas is further composed of argon with a volume fraction of 75%-85% and carbon dioxide with a volume fraction of 15%-25%.

[0012] The present invention also proposes a method for preparing the MIL-101-based composite welding shielding gas as described above, comprising the following steps:

[0013] S1. MIL-101(Cr) nanoparticles were prepared by a solvothermal method;

[0014] S2. The nanoparticles obtained in step S1 are immersed in a precursor solution containing microalloying active elements, and after adsorption and drying, modified MIL-101(Cr) nanoparticles are obtained.

[0015] S3. A reference mixed gas is introduced into the pressure-resistant mixing chamber to establish back pressure, and the modified nanoparticles treated in step S2 are injected according to the set mass fraction.

[0016] S4. Turn on the mechanical stirring and ultrasonic fluidization device to make the nanoparticles uniformly suspended in the gaseous medium, thus obtaining the MIL-101-based composite welding protective gas.

[0017] In this invention, further, in step S1, the raw materials used in the solvothermal method include chromium nitrate and terephthalic acid, the solvent is N,N-dimethylformamide, the reaction temperature is 150°C, and the reaction time is 12 hours.

[0018] In this invention, further, in step S2, the precursor solution is a soluble salt aqueous solution containing Ti or B with a concentration of 0.05 mol / L.

[0019] The present invention also proposes an application of the MIL-101-based composite welding shielding gas as described above in gas-solid two-phase narrow gap shielded welding. The modified MIL-101(Cr) nanoparticles suspended in the composite welding shielding gas and their confined loaded microalloying active elements are released under the heat generated by the welding arc and participate in the metallurgical reaction of the molten pool to improve the grain refinement effect of the weld structure.

[0020] In this invention, the gas-solid two-phase narrow gap shielded welding adopts DC reverse polarity, the welding current is 180A-220A, the arc voltage is 22V-28V, and the welding speed is 25cm / min-35cm / min.

[0021] Furthermore, in this invention, the composite welding shielding gas can control the fluctuation range of the arc voltage within 1.5V during the welding process, and the spatter rate is less than 1.5g / min.

[0022] Compared with the prior art, the present invention has at least the following beneficial effects.

[0023] 1. This invention introduces MIL-101(Cr) nanoporous material into the welding shielding gas medium, constructing a novel working mode of "gas-solid two-phase suspension transport—instantaneous fixed-point arc release—in-situ metallurgical control of the molten pool". Experimental data show that when using the composite welding shielding gas of this invention for narrow-gap welding of 10mm thick low-carbon steel plates, the weld porosity can be reduced from 0.82% in conventional processes to below 0.11%, and the defect rate is reduced by more than 86%; the weld solidification structure changes from coarse columnar crystals to fine and uniform equiaxed crystals, and the average grain size is refined from about 25μm to about 15μm, a refinement of 40%; the tensile strength of the weld joint increases from 402MPa to 455MPa, the elongation after fracture increases from 18.2% to 22.5%, and the strength-ductility product jumps from about 7316 MPa·% to over 10237 MPa·%, achieving a simultaneous improvement in the strength and ductility of the weld metal.

[0024] 2. Further analysis revealed that the significant reduction in porosity was due to the active removal of impurity gases by the modified MIL-101(Cr) nanoparticles. Their ultra-high specific surface area and abundant microporous structure exhibit significant confined adsorption capacity for small molecules such as hydrogen and oxygen. When the particles enter the high-temperature arc zone with the gas flow, the adsorbed impurity gases are simultaneously locked in as the framework decomposes, and ultimately float to the surface with the molten slag, effectively suppressing porosity defects. The significant refinement of the weld microstructure is attributed to the "protective transport" and "targeted release" functions of MIL-101(Cr): microalloying active elements such as Ti and B are confined and encapsulated within the nanopores, preventing premature contact and burn-off with oxidizing components such as CO2 during gas flow. When the particles enter the high-temperature arc zone and the framework decomposes within milliseconds, the active elements and Cr... 3+ Ions are released explosively at a fixed point at the molten pool front, instantly forming a large number of dispersed, highly efficient, heterogeneous nucleation particles. This promotes the solidification of the molten pool metal through simultaneous nucleation of multiple particles, resulting in a fine and uniform equiaxed grain structure. This effectively suppresses the formation of coarse columnar crystals in epitaxial growth, which is common in traditional processes. Furthermore, the nanoscale oxide remnants generated by framework decomposition may also have a pinning effect on grain boundary migration at the solidification front, further inhibiting grain growth. The solidification of some active elements in the matrix may also produce a solid solution strengthening effect. The combined effect of these multiple strengthening mechanisms may be the reason for the improved weld performance.

[0025] 3. Regarding welding processability, this invention employs a dual dispersion process of mechanical stirring and ultrasonic fluidization to uniformly suspend nanoparticles in the gaseous medium in the form of primary particles. Within a mass fraction range of 0.1wt%-1.0wt%, the system viscosity increase does not exceed 5%, preventing blockage of the gas supply pipeline and welding torch nozzle, thus ensuring the reliability of continuous industrial welding operations. Arc testing results show that after using the composite welding shielding gas of this invention, the arc voltage fluctuation range is reduced from 3.2V to 1.1V, and the spatter rate decreases from 4.5g / min to 1.2g / min, significantly improving the stability of the welding process. Further advantages include the good controllability of the preparation process, the mature synthesis route of the MIL-101(Cr) nanoparticles, and the readily available raw materials. The preparation process of the gas-solid two-phase suspension system can be completed in conventional high-pressure mixing equipment without large-scale modification of existing welding gas supply systems, demonstrating high engineering practical value and promising prospects for widespread application. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the preparation process of the MIL-101-based composite welding shielding gas and the implementation of narrow-gap gas shielded welding in an embodiment of the present invention.

[0027] Figure 2 This is a microstructure characterization diagram of the modified MIL-101(Cr) nanoparticles in this embodiment of the invention; wherein, Figure 2 a is a high-resolution transmission electron microscope (TEM) image. Figure 2 b is the corresponding EDS energy spectrum.

[0028] Figure 3 These are SEM images comparing the metallographic morphology and grain size distribution of welds under different shielding gas systems in this embodiment of the invention; wherein, Figure 3 a is a SEM image of the traditional protective gas group. Figure 3 b is a high-magnification SEM image of the composite protective gas group of the present invention. Figure 3 c is the histogram of the particle size distribution of the composite protective gas group of the present invention.

[0029] Figure 4 The figures shown are characterization diagrams of the structure and thermal stability of MIL-101(Cr) nanoparticles in the embodiments of the present invention; wherein, Figure 4 a is the XRD diffraction pattern. Figure 4 b is the TGA thermogravimetric analysis curve.

[0030] Figure 5 This is a comparison curve of room temperature tensile stress-strain of welded joints under different protective gas systems in embodiments of the present invention.

[0031] Figure 6 This is a comparison diagram of welding processability under different shielding gas systems in embodiments of the present invention; wherein, Figure 6 a and Figure 6 b is a comparison diagram of arc voltage waveforms. Figure 6 c is a statistical comparison chart of splash rates.

[0032] Figure 7 This is a graph showing the effect of different mass fractions of modified MIL-101(Cr) on the porosity of the weld in an embodiment of the present invention. Detailed Implementation

[0033] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0034] Example 1: Preparation of modified MIL-101(Cr) nanoparticles.

[0035] (1) Preparation of precursor solution and solvothermal synthesis: Weigh 10.0 g of chromium nitrate (Cr(NO3)3·9H2O) and 4.15 g of terephthalic acid, dissolve them in 70 mL of N,N-dimethylformamide (DMF), and sonicate for 30 min until completely dissolved to form a homogeneous precursor solution. Transfer the mixture to a 100 mL stainless steel high-pressure reactor lined with polytetrafluoroethylene, seal it, and place it in an oven at 150 °C for 12 h for solvothermal reaction.

[0036] (2) Washing and deagglomeration: After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting suspension was centrifuged at 8000 rpm for 15 min to collect the precipitate, and then ultrasonically washed three times each with anhydrous ethanol and deionized water. The washed product was dried in a vacuum drying oven at 80℃ for 24 h, and finally controlled by low-temperature planetary ball milling to avoid damaging the crystal structure of MIL-101(Cr). The MIL-101(Cr) nanoparticles with a particle size between 50-200 nm were collected by sieving.

[0037] (3) Pore confined loading: A 0.05 mol / L Ti-containing soluble salt aqueous solution was prepared as a precursor solution. The obtained MIL-101(Cr) powder was immersed in the precursor solution at a solid-liquid ratio of 1 g: 20 mL and magnetically stirred at room temperature for 24 h. Utilizing the ultra-high specific surface area and capillary force of MIL-101(Cr), Ti-containing active ions were confined and immobilized inside the pores through physical adsorption and / or chemical bonding. After adsorption was completed, the mixture was filtered and gently washed with a small amount of deionized water, and then dried in a vacuum drying oven at 60 °C to obtain modified MIL-101(Cr) nanoparticles loaded with the active element Ti.

[0038] Example 2: Preparation of MIL-101-based composite welding shielding gas and preparation of comparative materials.

[0039] In this embodiment, a MIL-101-based composite welding shielding gas is prepared, and comparative materials are also prepared.

[0040] (1) Preparation of the composite protective gas group (the present invention group): In a high-pressure resistant mixing chamber integrated with a mechanical stirring impeller and a bottom ultrasonic fluidization generator, a reference mixed gas consisting of 80% Ar and 20% CO2 by volume was first introduced. Subsequently, the modified MIL-101(Cr) nanopowder prepared in Example 1 was precisely injected into the mixing chamber at a ratio of 0.5 wt% of the total mass of the mixed gas through a sealed powder feeder. At the same time, the mechanical stirring and ultrasonic fluidization devices were turned on to deagglomerate the nanoparticles and uniformly suspend them in the gas phase medium, forming a stable gas-solid two-phase suspension system. After confirming by a laser particle size online monitoring instrument that the main peak of the nanoparticle size distribution in the system was located in the 50-200 nm range and the concentration distribution was uniform, the gas was output to the welding torch under stable pressure and marked as "composite protective gas group".

[0041] (2) Traditional protective gas group: only 80%Ar+20%CO2 reference gas mixture is used, and no nanoparticles are added to the gas path.

[0042] (3) Physical pre-coating control group: The shielding gas used was a standard mixed gas of 80%Ar + 20%CO2, but an equal amount (0.5wt% corresponding amount) of modified MIL-101(Cr) nano powder was pre-physically coated on the bevel surface of the base material to be welded, and conventional gas supply method was used during the welding process.

[0043] Example 3: Stability verification of gas-solid two-phase suspension system.

[0044] To verify the suspension stability of nanoparticles in the composite welding shielding gas of this invention, the composite shielding gas prepared in Example 2 was placed in a mixing chamber for observation. Under static conditions without mechanical stirring or ultrasonic fluidization, the nanoparticles did not show significant sedimentation within 2 hours, and the suspension concentration remained above 95% of the initial value, as measured by an online laser particle size analyzer. After the circulating gas flow was turned on, the system maintained uniform suspension during 8 hours of continuous output. These results indicate that the gas-solid two-phase suspension system of this invention possesses the stability required for continuous industrial welding operations, and the nanoparticles and the reference mixed gas constitute an inseparable, synergistic working whole.

[0045] Furthermore, viscosity and flowability tests were conducted on the composite welding shielding gas with a mass fraction of 0.5 wt%. The results showed that the apparent viscosity of the system increased by only 3.8% compared to the pure reference mixed gas. Under the condition of connecting a standard MIG / MAG welding torch nozzle, continuous output at a conventional flow rate (15-25 L / min) for 8 hours was performed, and no powder accumulation or blockage was observed on the nozzle or the inner wall of the gas pipe, confirming that the gas-solid two-phase suspension system of the present invention has good compatibility and industrial applicability with existing welding gas supply equipment.

[0046] Example 4: Characterization of the microstructure, chemical state and thermal stability of nanoparticles.

[0047] The modified MIL-101(Cr) nanoparticles prepared in Example 1 were characterized using high-resolution transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). The results are as follows: Figure 2 As shown, Figure 2 TEM images of a show that the particles maintain a regular and intact porous framework structure. Figure 2 The EDS surface scan of b confirms that Ti was successfully introduced and uniformly distributed within the pore structure of the particles.

[0048] Further analysis of the chemical bonding state of the active elements using X-ray photoelectron spectroscopy (XPS) revealed that the binding energy of the Ti 2p orbital shifted significantly after loading compared to the pure Ti salt precursor. This indicates that a coordinate bond was formed between the Ti element and the oxygen atom on the MIL-101(Cr) framework, i.e., chemical bonding was achieved, rather than simple physical attachment.

[0049] X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to characterize the phase composition and thermal stability of the products. Figure 4 As shown in a, the XRD results confirm that the product is a pure-phase MIL-101(Cr) structure with good crystallinity. Figure 4 The TGA curve of b shows that the material does not lose significant weight in air up to 350°C, indicating that its thermal stability is sufficient to withstand the high-temperature environment around the welding arc.

[0050] Example 5: Implementation of narrow gap gas shielded welding process.

[0051] Figure 1 This is a schematic diagram illustrating the preparation process of the MIL-101-based composite welding shielding gas and the implementation of narrow-gap gas shielded welding in an embodiment of the present invention. Specifically, this embodiment follows... Figure 1 The welding process is as follows: A 10mm thick low-carbon steel plate is selected as the base material. A narrow-gap I-type bevel with a bevel angle of 5°-8° is machined. Before welding, the bevel and surrounding area are thoroughly cleaned with acetone to remove oil. The shielding gases prepared in Example 2 are connected to the automatic welding machine (NG-GMAW). The uniformly set welding process parameters are: DC reverse polarity, steady-state welding current of 200A, arc voltage of 25V, welding speed of 30cm / min, and constant shielding gas flow rate (e.g., 15-25L / min).

[0052] Example 6: Macroscopic mechanical property test of welded joint.

[0053] According to relevant national standards, tensile specimens were cut from each group of welded test plates and subjected to room temperature tensile tests. The resulting engineering stress-strain curves are shown below. Figure 5 As shown. The test results indicate that:

[0054] The yield strength of conventional shielded gas welds is 315 MPa, the tensile strength is 402 MPa, and the elongation after fracture is 18.2%. Its strength-ductility product (the product of tensile strength and elongation after fracture) is approximately 7316 MPa.

[0055] In comparison, the yield strength of the composite protective gas weld of the present invention is increased to 368 MPa, the tensile strength is as high as 455 MPa, the elongation after fracture is increased to 22.5%, and the strength-ductility product is significantly increased to 10237 MPa.

[0056] This result fully demonstrates that the dual mechanism of confined degassing and catalytic nucleation introduced by the composite protective gas of this invention not only effectively eliminates metallurgical defects, but also successfully achieves simultaneous improvement in the strength and plasticity of weld metal, breaking through the bottleneck that is often difficult to achieve in traditional welding.

[0057] Combination Figure 3 The comparison of weld metallographic structures under different shielding gas systems provides a more intuitive understanding of the microscopic mechanisms underlying the aforementioned performance improvements. Among these, Figure 3 a is an SEM image of a conventional shielded gas weld, which shows that its microstructure is relatively coarse; Figure 3 b is a high-magnification SEM image of the weld seam of the composite protective gas group of the present invention, showing a significantly refined grain structure; Figure 3 c is the histogram of the particle size distribution of the composite protective gas group of the present invention. As can be seen from the figure, the grain size of the weld of the present invention group exhibits a concentrated distribution characteristic, and the overall grain size is small, indicating that the method of the present invention can effectively refine the grain structure of the weld metal.

[0058] The physical metallurgical mechanism behind the aforementioned performance improvement lies in the following: When the MIL-101-based composite welding shielding gas enters the welding arc region, the suspended modified MIL-101(Cr) nanoparticles rapidly decompose under the thermal shock of the arc. Their function is not to maintain structural integrity, but rather to utilize their pores as "micro-release containers," releasing the confined Ti active element and the intrinsic Cr of the MIL-101 framework at specific points during decomposition. 3+ Ions. These released substances then act as highly efficient heterogeneous nucleation sites, promoting the formation of numerous fine equiaxed crystals (such as...) in the molten pool metal during solidification. Figure 3 (as shown in b), thus simultaneously achieving fine-grained strengthening and improved ductility and toughness of the weld metal.

[0059] Example 7: Test on the effect of modified MIL-101(Cr) mass fraction on porosity.

[0060] To investigate the effect of different amounts of modified MIL-101(Cr) addition, composite shielding gases with mass fractions of 0% (traditional group), 0.1%, 0.3%, 0.5%, 0.8%, and 1.0% were prepared, and welding was performed under the same conditions. The porosity of the welds in each group was measured, and the results are as follows: Figure 7 As shown.

[0061] When the mass fraction is 0%, the weld porosity is as high as 0.82%.

[0062] As the mass fraction of nanoparticles increases, the porosity decreases rapidly; when the mass fraction reaches 0.5wt%, the porosity drops to an extremely low 0.11% (the defect rate is reduced by more than 86%), demonstrating the optimal active confined adsorption and degassing effect.

[0063] When the mass fraction is further increased to 1.0 wt%, the porosity tends to stabilize and no longer decreases significantly, but excessively high particle concentration may cause fluctuations in the stability of the protective gas flow. Therefore, 0.1 wt%-1.0 wt% is the effective operating range of this invention, of which 0.5 wt% is a better ratio that combines performance and process stability.

[0064] It should be noted that the weld porosity of the "physical pre-coating control group" in Example 2 rebounded to 0.58%, which strongly proves that the essential difference between the present invention and the prior art (such as simply applying an activator to the surface of the base material) is that the active elements are supplied in situ, in real time and uniformly by using gas-solid two-phase flow. Physical coating alone cannot achieve active adsorption and degassing throughout the welding process. "Transporting modified nanoparticles in a gas-solid two-phase suspension state" is a necessary technical feature for achieving deep degassing.

[0065] Example 8: Testing of welding processability and arc physical properties.

[0066] A high-precision arc parameter acquisition system and a high-speed camera were used to compare and test the arc voltage waveform and spatter rate of each welding process. The results are as follows: Figure 6 As shown.

[0067] Figure 6 a and Figure 6 The arc voltage waveform diagram of b shows that the arc voltage of the traditional protective gas group fluctuates violently, with a waveform range of up to 3.2V; while the voltage waveform of the composite protective gas group of the present invention is very stable, with the fluctuation range significantly reduced to 1.1V.

[0068] Figure 6 The splash rate statistics of c show that the splash rate of the traditional group is as high as 4.5 g / min, while the composite protective gas group of the present invention ( Figure 6 The splash rate of the innovative protective gas group (c) was significantly reduced to 1.2 g / min.

[0069] The above results show that solid MIL-101 nanoparticles uniformly distributed in the protective gas flow change the thermophysical properties of the single gas medium, accelerate the transfer and homogenization of arc heat, thereby balancing the arc physical thermal field and endowing the composite protective gas of the present invention with excellent welding processability.

[0070] Further analysis suggests that the significant reduction in arc voltage fluctuations is not only due to the balancing effect of solid nanoparticles on the arc's thermophysical field, but also closely related to the shielding and protection mechanism of the MIL-101 channels for active elements. Because the Ti active element is confined within the nanopores before entering the arc core region, the porous framework constructs a natural mass transfer and thermal resistance barrier, effectively suppressing its early and severe oxidation and uneven burn-off by CO2 gas at the high-temperature periphery of the arc. This ensures the stability and consistency of the supply of active elements into the molten pool, reducing voltage fluctuations caused by severe disturbances in arc ionization due to localized chemical reactions, ultimately achieving an extremely low spatter rate and an extremely stable welding process.

[0071] Example 9: Verification of welding process parameters and gas composition range.

[0072] To verify the applicability of the composite shielding gas of this invention under different welding process parameters, orthogonal experiments were conducted by adjusting the welding current (180A, 200A, 220A), arc voltage (22V, 25V, 28V), and welding speed (25cm / min, 30cm / min, 35cm / min) while keeping other conditions constant. The results show that within the above parameter range, the weld porosity remained below 0.15%, the tensile strength was above 430MPa, and the elongation after fracture was above 21%, demonstrating that the composite shielding gas of this invention has good adaptability and robustness to welding process parameters and can stably exert its technical effect within the parameter fluctuation range reasonably expected by those skilled in the art.

[0073] Further verification of the applicability of the reference mixed gas components showed that when the argon gas fraction in the reference mixed gas was adjusted to 75% or 85% (corresponding to a CO2 volume fraction of 25% or 15%), the weld porosity remained below 0.14% and the mechanical properties did not decrease significantly when combined with the modified nanoparticles of this invention.

[0074] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A MIL-101-based composite welding shielding gas, characterized in that, It consists of a reference mixed gas and modified MIL-101(Cr) nanoparticles uniformly suspended and dispersed in the reference mixed gas. The composite welding protective gas is a gas-solid two-phase suspension system. The modified MIL-101(Cr) nanoparticles have a particle size of 50-200 nm and their mass accounts for 0.1 wt%-1.0 wt% of the total mass of the reference mixed gas. The modified MIL-101(Cr) nanoparticles have microalloying active elements confined within their micropores. These microalloying active elements are immobilized within the pores of the nanoparticles through physical adsorption and / or chemical bonding. The microalloying active elements are at least one of Ti or B. The reference mixed gas consists of 75%-85% argon and 15%-25% carbon dioxide by volume.

2. A method for preparing the MIL-101-based composite welding shielding gas as described in claim 1, characterized in that, Includes the following steps: S1. MIL-101(Cr) nanoparticles were prepared by a solvothermal method. The raw materials used in the solvothermal method included chromium nitrate and terephthalic acid, the solvent was N,N-dimethylformamide, the reaction temperature was 150℃, and the reaction time was 12 hours. S2. The nanoparticles obtained in step S1 are immersed in a precursor solution containing microalloying active elements, and modified MIL-101(Cr) nanoparticles are obtained after adsorption and drying; the precursor solution is a soluble salt aqueous solution containing Ti or B with a concentration of 0.05 mol / L. S3. A reference mixed gas is introduced into the pressure-resistant mixing chamber to establish back pressure, and the modified nanoparticles treated in step S2 are injected according to the set mass fraction. S4. Turn on the mechanical stirring and ultrasonic fluidization device to make the nanoparticles uniformly suspended in the gaseous medium, thus obtaining the MIL-101-based composite welding protective gas.

3. The application of the MIL-101-based composite welding shielding gas as described in claim 1 in gas-solid two-phase narrow gap shielded welding, characterized in that, Modified MIL-101(Cr) nanoparticles suspended in the composite welding shielding gas and their confined loaded microalloying active elements are released under the heat generated by the welding arc and participate in the metallurgical reaction of the molten pool to improve the grain refinement effect of the weld structure.

4. The application according to claim 3, characterized in that, The gas-solid two-phase narrow gap shielded welding uses DC reverse polarity, with a welding current of 180A-220A, an arc voltage of 22V-28V, and a welding speed of 25cm / min-35cm / min.

5. The application according to claim 3 or 4, characterized in that, The composite welding shielding gas can control the arc voltage fluctuation range within 1.5V during the welding process, and the spatter rate is less than 1.5g / min.

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