A flux and welding process for laser welding hot-formed steel with Al-Si coating on the surface

Abstract

The present invention discloses a flux and a welding process for laser welding hot-formed steel with an Al-Si coating on the surface, belonging to the field of welding and connection technology. Molten salt, metal oxides and trace alloying elements are used as flux, and the mass percentage (Wt / %) is: niobium pentoxide (Nb2O5) 5-10%, calcium oxide (CaO) 15-20%, manganese oxide (MnO) 35-40%, magnesium oxide (MgO) 5-15%, pure metal copper (Cu) 1-5%, pure metal nickel (Ni) 0.1-1.0%, potassium fluoroaluminate (K3AlF6) remainder. Under the same laser power, the laser welding joint penetration can be increased, and the joint penetration increases by an average of 16-20%, and the tensile strength of the 22MnB5 laser welded blank welded joint is obtained to be ≥1500Mpa and the elongation is ≥4.5%.

Description

Technical Field

[0001] The present invention relates to a flux and a welding process for laser welding hot-formed steel coated with an Al-Si coating. The flux, composed of molten salt, metal oxides and trace alloying elements, undergoes a physical and chemical reaction with the Al-Si coating on the surface of the hot-formed steel plate during a metallurgical process. This reduces the risk of Al elements dissolving or penetrating into the weld after the Al-Si coating on the hot-formed steel surface melts during laser welding, forming Fe-Al intermetallic compounds with Fe elements. At the same time, it reduces laser reflection and increases laser heat input, thereby improving the mechanical properties of laser welded joints. The invention belongs to the field of welding and connection technology. Background Art

[0002] The combination of hot-formed steel and laser welding technology allows for a closer integration of material and component structural design with forming technology. It is widely used in the manufacture of a range of safety components, including A-pillars, B-pillars, and front and rear longitudinal beams. This improves the strength, bending, and torsional rigidity, and other crash safety indicators of these components, enabling lightweighting of vehicle bodies, with weight reductions reaching up to 20%. Hot-formed steel is engineered to enhance hardenability through the addition of trace alloying elements such as boron, manganese, and chromium. Prior to hot-forming, the sheet consists of a ferrite and pearlite microstructure. The steel is then heated to 910-950°C to uniformly austenitize the pearlite and ferrite. The steel is then stamped into shape within a die. Cooling channels within the die provide rapid and uniform cooling of the stamped parts, transforming the austenite into martensite. This results in higher yield strength and tensile strength for high-strength automotive steel, effectively improving overall vehicle performance and safety. Hot-formed steel offers excellent forming accuracy, eliminates the effects of springback, and allows for the creation of complex shapes. Due to the special properties of hot-formed steel sheets and the fact that they are formed after heating, complex shapes that would require multiple steps with conventional cold stamping can be achieved in a single process. The advantage of this single-step forming process is that it protects the steel's internal fiber flow from secondary stresses during processing, ensuring optimal strength and toughness. Furthermore, rapid cooling after forming minimizes springback, significantly improving forming accuracy and ensuring dimensional precision, paving the way for subsequent body welding. During the hot-forming process, hot-formed steel surfaces oxidize due to high temperatures, forming a scale that impairs subsequent processing and reduces weldability and coating performance. Furthermore, surface oxidation can cause decarburization, further compromising strength. Therefore, hot-formed steel requires shot peening or pickling after hot forming to remove surface oxides generated during heating before welding and coating. This process increases production costs, reduces efficiency, and significantly pollutes the surrounding environment. Applying Al-Si coatings to hot-formed steel effectively addresses these process challenges. Hot-formed steel coated with Al-Si coating does not require the addition of protective gas during the hot forming process, and no oxides are generated on the surface, eliminating the need for subsequent surface shot peening, improving the processing environment, and increasing the manufacturing dimensional accuracy of parts and assembly components. Hot-formed steel coated with Al-Si coating is widely used in hot stamping processes. However, when hot-formed steel plates coated with Al-Si coating are laser welded, the Al-Si coating on the surface seriously affects the weldability of the plate. After the Al-Si coating melts, the Al element will dissolve or penetrate into the weld and form a variety of brittle Fe-Al intermetallic compounds with the Fe element. It will also promote the production of δ-ferrite, resulting in reduced mechanical properties of the joint. The technical solution is usually to remove the Al-Si coating before welding.Currently, various removal techniques, including mechanical or physical removal, pulsed laser ablation, wire filling, and flux addition, are available both domestically and internationally. Mechanical removal is mostly contact-based, making it difficult to control the thickness of Al-Si removal. The flatness of the sheet material also impacts the removal results. Furthermore, mechanical removal techniques involve numerous steps, resulting in low production efficiency and significant environmental pollution. Pulsed laser ablation can remove metallic or non-metallic coatings. When the parameters are appropriately selected, it can partially remove Al-Si coatings. However, picosecond or femtosecond pulsed lasers are expensive, increasing equipment investment. Fluctuations in pulsed laser parameters can lead to suboptimal ablation results. In recent years, wire filling and flux addition techniques have garnered significant industry attention. These techniques eliminate the need to remove the Al-Si coating prior to welding, allowing for direct laser welding. The basic principle of wire filling is to add a ferrite-stabilizing element to the welding wire. Through a combination of element transition and dilution, this technique mitigates the effects of the Al-Si coating on weld properties, reducing the amount of ferrite and pearlite in the weld and resulting in a more dispersed martensite structure. The flux addition technique uses chemical reactions to remove the effects of surface aluminum. A literature search reveals dozens of related patents, such as Patent 201380001259.1, which discloses a method for laser welding without removing the Al-Si coating using a filler wire (containing 0.1%-0.8% by weight of C and 1.5%-7.0% by weight of Mn compared to the base material). Patent 201510165732.0 discloses a method for laser welding without removing the Al-Si coating using a filler wire (containing 0.6-0.9% by weight of C, 0.3-0.9% by weight of Mn, 1.6-3.0% by weight of Ni, and the remainder of Fe and other unavoidable impurities). Patent 201611036496.3 discloses a method using a mixture of one or both of oxygen and carbon dioxide with an inert gas (nitrogen, argon, etc.) as a shielding gas to increase the oxygen partial pressure in the weld pool. Oxygen combines with aluminum to form Al2O3, which does not affect the strength and toughness of the weld. This inhibits the formation of intermetallic compounds between Al and Fe and the austenite transformation, ultimately resulting in a fully lath martensite structure in the weld zone. Patent 202010755474.2 discloses a solder paste and process for improving the plasticity of welded joints of hot-formed steel tailor-welded blanks with aluminum-silicon coatings. The alloy powder is pre-mixed with a binder and then applied to the laser weld on the hot-formed steel side. The weld is then preheated and welded. Patent 202210230859.6 discloses a method for removing the surface oxide layer of coated hot-formed steel and a hot-forming method. The surface oxide layer is removed by blowing gas onto the surface of the coated hot-formed steel. While the aforementioned technologies have certain benefits, they also have corresponding shortcomings. How to improve the influence of surface Al-Si coating on the weldability of hot-formed steel during laser welding and improve the strength and toughness of welded joints is a technical problem that researchers urgently need to solve. Summary of the Invention

[0003] In response to the deficiencies in the prior art, the present invention provides a flux and a welding process for laser welding hot-formed steel with an Al-Si coating on its surface. A layer of flux composed of molten salt, metal oxides and trace alloying elements is coated on the surface of the plate to be laser welded, and the flux undergoes a physical and chemical reaction with the Al-Si coating on the surface of the hot-formed steel plate during a metallurgical process, dissolving the Al-Si coating at the weld, thereby reducing the risk of Al elements dissolving or penetrating into the weld after the Al-Si coating on the surface of the hot-formed steel melts during laser welding, and forming Fe-Al intermetallic compounds with Fe elements. At the same time, laser reflection is reduced and laser heat input is increased, thereby increasing the penetration depth of the laser welded joint and improving the mechanical properties of the laser welded joint.

[0004] The core technology of the present invention is that the Al-Si coating does not need to be removed before welding. By adjusting the composition ratio of the molten salt, metal oxides and trace alloying elements in the flux, the penetration depth of the laser welded joint is increased and the Al-Si coating on the surface is melted during laser welding of hot-formed steel. After the Al element dissolves or penetrates into the weld and forms an Fe-Al intermetallic compound with the Fe element, the strength, plasticity and toughness of the laser welded joint are improved.

[0005] The above-mentioned object of the present invention is achieved by a flux and welding process for laser welding hot-formed steel coated with an Al-Si coating. A layer of flux composed of molten salt, metal oxide, and trace alloying elements is sprayed on the weld surface of the hot-formed steel weld joint coated with the Al-Si coating. The molten salt, metal oxide, and trace alloying elements in the flux react with the Al-Si coating on the surface of the hot-formed steel sheet in a metallurgical physical and chemical process, dissolving aluminum into the flux and finally solidifying to form slag. The flux for laser welding hot-formed steel coated with an Al-Si coating of the present invention comprises the following components, by weight percentage (wt / %): niobium pentoxide (Nb2O5) 5-10%, calcium oxide (CaO) 15-20%, manganese oxide (MnO) 35-40%, magnesium oxide (MgO) 5-15%, pure copper (Cu) 1-5%, pure nickel (Ni) 0.1-1.0%, and the balance potassium fluoroaluminate (K3AlF6).

[0006] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage Wt / %, 5% niobium pentoxide Nb2O5, 15% calcium oxide CaO, 35% manganese oxide MnO, 15% magnesium oxide MgO, 5% pure metal copper Cu, 0.1% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

[0007] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage (Wt / %): 6% niobium pentoxide (Nb2O5), 16% calcium oxide (CaO), 36% manganese oxide (MnO), 14% magnesium oxide (MgO), 3% pure metal copper (Cu), 0.3% pure metal nickel (Ni), and the balance potassium fluoroaluminate (K3AlF6).

[0008] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage (Wt / %): 7% niobium pentoxide (Nb2O5), 18% calcium oxide (CaO), 37% manganese oxide (MnO), 13% magnesium oxide (MgO), 3% pure metal copper (Cu), 0.4% pure metal nickel (Ni), and the balance (potassium fluoroaluminate (K3AlF6)).

[0009] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage Wt / %, 8% niobium pentoxide Nb2O5, 15% calcium oxide CaO, 39% manganese oxide MnO, 10% magnesium oxide MgO1, 3% pure metal copper Cu, 0.6% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

[0010] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage (Wt / %): 9% niobium pentoxide (Nb2O5), 16% calcium oxide (CaO), 40% manganese oxide (MnO), 8% magnesium oxide (MgO), 2% pure metal copper (Cu), 0.6% pure metal nickel (Ni), and the balance (potassium fluoroaluminate (K3AlF6)).

[0011] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage (Wt / %): 10% niobium pentoxide (Nb2O5), 17% calcium oxide (CaO), 38% manganese oxide (MnO), 7% magnesium oxide (MgO), 4% pure metal copper (Cu), 0.5% pure metal nickel (Ni), and the balance (potassium fluoroaluminate (K3AlF6)).

[0012] Furthermore, a flux for laser welding hot-formed steel coated with an Al-Si coating is provided, wherein the flux comprises, by mass percentage (Wt / %): 8% niobium pentoxide (Nb2O5), 20% calcium oxide (CaO), 40% manganese oxide (MnO), 5% magnesium oxide (MgO), 1% pure metal copper (Cu), 1.0% pure metal nickel (Ni), and the balance (potassium fluoroaluminate (K3AlF6).

[0013] The above-mentioned flux is used in a laser welding process for hot-formed steel coated with an Al-Si coating, which includes the following process steps:

[0014] In the first step, according to conventional flux smelting technology, the powdered molten salt and metal oxide are dried and dehydrated at a drying temperature of 200-250° C. and a drying time of 30-50 minutes. After drying, the molten salt and metal oxide are cooled and crushed.

[0015] In the second step, according to conventional flux smelting technology, the molten salt and metal oxides in the distribution ratio designed according to the present invention are uniformly mixed, stirred, granulated and dried at low temperature (300-400°C), and then crushed and ground into powder particles with a size of 20-50μm.

[0016] The third step is to mix the crushed and ground molten salt and metal oxides with pure copper and nickel to prepare the flux. The pure copper and nickel are in granular form with a particle size of 20-50 μm.

[0017] In the fourth step, an appropriate amount of flux and adhesive are thoroughly mixed and evenly applied to the welded portion of the hot-formed steel, which has been coated with an Al-Si coating. The adhesive described in this invention is commercially available and commonly used in various fluxes or solder pastes. The adhesive is a transparent plastic with a certain viscosity, made from polystyrene as a solute and trichloroethylene as a solvent. The adhesive completely evaporates when heated between 150°C and 370°C, leaving no residue that could affect subsequent laser welding.

[0018] The fifth step is laser welding, which is used to weld the hot-formed steel tailor-welded blanks coated with an Al-Si coating. The hot-formed steel plate is the most commonly used 22MnB5 steel, with a plate thickness of 1.0 mm and an Al-Si coating thickness of 20-30 μm. Laser welding is used for the plate welding. The laser welder is a CO2 laser with a welding power of P = 0.8-1.3 kW, a welding speed of V = 6 mm / s, a defocus of F = 0 mm, and a side-blown gas flow of 20 L / min. The joint is a butt joint, using a central focusing method, and the weld length is 1000 mm. The plate is laser welded before hot forming. Then, simulating the hot forming process, the welded specimen is heated to 910°C, held at this temperature for 5 minutes, and then cooled and quenched in water to obtain the hot-formed laser-welded blank specimen.

[0019] The surface Al-Si coating seriously affects the weldability of the plate. For hot-formed steel tailor-welded plates coated with Al-Si coating, the Al-Si coating has extremely high initial surface reflectivity and low absorption rate of radiation energy to the laser beam, which will affect the penetration depth of the weld during laser welding. At the same time, after the Al-Si coating melts, the Al element will dissolve or penetrate into the weld and form a variety of brittle Fe-Al intermetallic compounds with the Fe element, and will also promote the production of δ-ferrite, resulting in reduced mechanical properties of the joint. Based on the above reasons, the present invention uses a flux composed of molten salts, metal oxides and trace alloying elements for laser welding. Numerous literature reports show that various molten salts and metal oxide materials have a high absorption rate for lasers at room temperature. There are many types of molten salts and metal oxides, and there are only a handful of molten salts and metal oxides suitable for use as fluxes. The selection criteria are firstly heat absorption to increase the penetration depth of the laser welded joint, secondly the ability to dissolve aluminum, and thirdly the ability to reduce the surface tension of the liquid metal to improve the formation of the laser weld. The melting temperature of K3AlF6 is 560-580℃. It reacts with aluminum and also removes the oxide film. There are two main reaction modes: (1) chemical reaction to generate low-valent aluminum ions: 2Al+Al 3+ =3Al + , (2) a chemical replacement reaction occurs to generate potassium: Al + 3KF = 3K + AlF3; CaO can accelerate the dissolution rate of Al2O3 in the slag and has a decisive influence on the dissolution rate of Al2O3; MgO can reduce the melting temperature of the molten salt and increase the dissolution rate of Al2O3. Based on the MnO-CaO-Al2O3 ternary phase diagram, it can be seen that as the MnO content increases, the area of ​​the low-temperature region of the liquidus becomes larger. Cu, as a trace element, can reduce the mutual diffusion of Fe and Al. Cu and Al react eutectically to form a low-melting-point Al-Cu eutectic structure, which dissolves into the molten salt and reduces the formation of Fe-Al brittle metal compounds; Ni and Al can also react eutectic. The addition of Ni can reduce the formation of Fe2Al5 metal compound layer. The content of Cu and Ni should not be too much, otherwise CuAl2 and Ni-Fe compounds will be formed, which are more brittle. Therefore, the total amount of Cu-Ni is controlled within 5%.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention discloses a flux and a welding process for laser welding hot-formed steel coated with an Al-Si coating. The flux is composed of molten salt, metal oxides and trace alloying elements and is applied to joint welding. The process is simple, has little pollution to the environment, and can increase the penetration depth of the laser welded joint under the same laser power. At the same time, the influence of the Al-Si coating on the mechanical properties of the weld is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Figure 2 is the penetration depth of laser welded joints of hot-formed steel plates with and without flux (P = 900 W, v = 6 mm / s, F = 0 mm), where: (a) penetration depth with flux; (b) penetration depth without flux.

[0023] Figure 2 is the tensile fracture curve of laser welded joints of hot-formed steel plates with and without flux;

[0024] (P=900W, v=6mm / s, F=0mm) DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are part of the embodiments of the present invention, rather than all of the embodiments. The embodiments listed below are only for further understanding and implementation of the technical solution of the present invention, and do not constitute further limitations on the claims of the present invention. Therefore, based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] The flux of the present invention and the welding process using the flux are further described in detail with reference to the following examples.

[0027] The invention discloses a flux for laser welding hot-formed steel coated with an Al-Si coating. The flux comprises molten salt, metal oxides and trace alloying elements in the following composition by mass percentage (Wt / %): niobium pentoxide (Nb2O5) 5-10%, calcium oxide (CaO) 15-20%, manganese oxide (MnO) 35-40%, magnesium oxide (MgO) 5-15%, pure metallic copper (Cu) 1-5%, pure metallic nickel (Ni) 0.1-1.0%, and the balance potassium fluoroaluminate (K3AlF6).

[0028] The present invention adopts the above-mentioned flux for the laser welding process of hot-formed steel with an Al-Si coating on the surface. A layer of flux composed of molten salt, metal oxide and trace alloy elements is coated on the surface of the plate to be laser welded, and the flux undergoes a physical and chemical reaction with the Al-Si coating on the surface of the hot-formed steel plate during the metallurgical process, dissolving the Al-Si coating at the weld, reducing the Al element from dissolving or penetrating into the weld after the Al-Si coating on the surface of the hot-formed steel melts during the laser welding process, and forming an Fe-Al intermetallic compound with the Fe element. At the same time, the laser reflection is reduced and the laser heat input is increased, thereby increasing the penetration depth of the laser welded joint and improving the mechanical properties of the laser welded joint.

[0029] The welding process of the present invention comprises the following steps:

[0030] In the first step, according to conventional flux smelting technology, the powdered molten salt and metal oxide are dried and dehydrated at a drying temperature of 200-250° C. and a drying time of 30-50 minutes. After drying, the molten salt and metal oxide are cooled and crushed.

[0031] In the second step, conventional flux melting technology is used to uniformly mix and stir the molten salt and metal oxide in the distribution ratio designed according to the present invention, granulate them, and dry them at a low temperature (300-400°C). The mixture is then crushed and ground into powder particles with a size of 20-50 μm. The flux and process for laser welding hot-formed steel coated with an Al-Si coating disclosed herein comprises the following components, by weight percentage (wt%): niobium pentoxide (Nb2O5) 5-10%, calcium oxide (CaO) 15-20%, manganese oxide (MnO) 35-40%, magnesium oxide (MgO) 5-15%, pure copper (Cu) 1-5%, pure nickel (Ni) 0.1-1.0%, and the balance potassium fluoroaluminate (K3AlF6).

[0032] The third step is to mix the crushed and ground molten salt and metal oxides with pure copper and nickel to prepare the flux. The pure copper and nickel are in granular form with a particle size of 20-50 μm.

[0033] In the fourth step, an appropriate amount of flux and adhesive are thoroughly mixed and evenly applied to the welded portion of the hot-formed steel, which has been coated with an Al-Si coating. The adhesive described in this invention is commercially available and commonly used in various fluxes or solder pastes. The adhesive is a transparent plastic with a certain viscosity, made from polystyrene as a solute and trichloroethylene as a solvent. The adhesive completely evaporates when heated between 150°C and 370°C, leaving no residue that could affect subsequent laser welding.

[0034] The fifth step is laser welding, which is used to weld the hot-formed steel tailor-welded blanks coated with an Al-Si coating. The hot-formed steel plate is the most commonly used 22MnB5 steel, with a plate thickness of 1.0 mm and an Al-Si coating thickness of 20-30 μm. Laser welding is used for the plate welding. The laser welder is a CO2 laser with a welding power of P = 0.8-1.3 kW, a welding speed of V = 6 mm / s, a defocus of F = 0 mm, and a side-blown gas flow of 20 L / min. The joint is a butt joint, using a central focusing method, and the weld length is 1000 mm. The plate is laser welded before hot forming. Then, simulating the hot forming process, the welded specimen is heated to 910°C, held at this temperature for 5 minutes, and then cooled and quenched in water to obtain the hot-formed laser-welded blank specimen.

[0035] All the following examples were laser welded according to the above process steps and process parameters. The examples are shown in Table 1.

[0036] Table 1 Flux composition and performance of hot-formed steel laser welding joint

[0037]

[0038] The flux and welding process for laser welding hot-formed steel coated with an Al-Si coating described in the present invention achieve the following technical indicators when laser welding the joint of hot-formed steel coated with an Al-Si coating according to the above process steps and components:

[0039] (1) Under the same laser power, the penetration depth of laser welding joints can be increased, and the average penetration depth of the joints increases by 16-20%.

[0040] (2) Through the hot forming process, under the same technical parameter conditions, the sample with a gauge length of 100 mm was prepared in accordance with the national standard "GB / T2651-2008 Tensile Test Method for Welded Joints", and the tensile strength of the welded joint of 22MnB5 laser welded blanks was obtained to be ≥1500 MPa and the elongation was ≥4.5%.

[0041] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and exemplary embodiments. They can be applied to a variety of fields suitable for the present invention. Further modifications will be readily apparent to those skilled in the art. Therefore, the present invention is not limited to the specific details and illustrations shown and described herein without departing from the general concept defined by the claims and their equivalents.

Claims

1. A laser welding process for hot-formed steel coated with an Al-Si coating, the welding process using a flux composed of molten salt, metal oxides, and trace alloying elements, wherein the flux, in mass percentage (Wt / %), is as follows: niobium pentoxide (Nb2O5) 5-10%, calcium oxide (CaO) 15-20%, manganese oxide (MnO3) 5-40%, magnesium oxide (MgO) 5-15%, pure copper (Cu) 1-5%, pure nickel (Ni) 0.1-1.0%, and the balance (potassium fluoroaluminate (K3AlF6)). The process of welding using the above-mentioned flux includes the following steps: In the first step, the powdered molten salt and metal oxide are dried, dehydrated, and crushed; In the second step, the molten salt and metal oxides in the designed distribution ratio are uniformly mixed, granulated and dried at a low temperature of 300-400℃, and then crushed and ground into powder particles with a size of 20-50μm; In the third step, the crushed and ground molten salt and metal oxides are fully mixed with pure metal copper and nickel to prepare a flux; The fourth step is to fully mix an appropriate amount of flux and binder and evenly apply them to the welded area of ​​the hot-formed steel with the Al-Si coating on the surface; The fifth step is to perform laser welding. Laser welding is used to weld the hot-formed steel tailor-welded plates with Al-Si coating on the surface. The hot-formed steel plates are made of the most commonly used 22MnB5 steel. The plate thickness is 1.0mm, and the Al-Si coating thickness is measured to be 20-30μm. Laser welding is used for plate welding. The laser welding machine is a CO2 laser. The welding power P=0.8-1.3kw, the welding speed V=6mm / s, the defocus amount F=0mm, the side blowing gas is pure Ar, the flow rate is 20L / min, the joint form is butt-jointing, and the center focusing method is used. The weld length is 1000mm. The plates are laser welded before hot forming, and then the hot forming process is simulated. The welded specimen is heated to 910℃, kept warm for 5min, and placed in water for cooling and quenching to obtain a hot-formed laser-welded plate specimen.

2. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 5% niobium pentoxide Nb2O5, 15% calcium oxide CaO, 35% manganese oxide MnO, 15% magnesium oxide MgO, 5% pure metal copper Cu, 0.1% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

3. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 6% niobium pentoxide Nb2O5, 16% calcium oxide CaO, 36% manganese oxide MnO, 14% magnesium oxide MgO, 3% pure metal copper Cu, 0.3% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

4. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 7% niobium pentoxide Nb2O5, 18% calcium oxide CaO, 37% manganese oxide MnO, 13% magnesium oxide MgO, 3% pure metal copper Cu, 0.4% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

5. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 8% niobium pentoxide Nb2O5, 15% calcium oxide CaO, 39% manganese oxide MnO, 10% magnesium oxide MgO1, 3% pure metal copper Cu, 0.6% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

6. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 9% niobium pentoxide Nb2O5, 16% calcium oxide CaO, 40% manganese oxide MnO, 8% magnesium oxide MgO, 2% pure metal copper Cu, 0.6% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

7. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 10% niobium pentoxide Nb2O5, 17% calcium oxide CaO, 38% manganese oxide MnO, 7% magnesium oxide MgO, 4% pure metal copper Cu, 0.5% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

8. A welding process according to claim 1, characterized in that: The flux comprises, by mass percentage (Wt / %): 8% niobium pentoxide Nb2O5, 20% calcium oxide CaO, 40% manganese oxide MnO, 5% magnesium oxide MgO, 1% pure metal copper Cu, 1.0% pure metal nickel Ni, and the balance potassium fluoroaluminate K3AlF6.

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