An in-situ nanoparticle reinforced welding wire for aluminum body welding and a welding method thereof

Abstract

The present application belongs to the technical field of aluminum alloy welding wire, and relates to an in-situ nano-particle reinforced welding wire for aluminum body welding and a welding method thereof. The welding wire is prepared into a stir head and embedded into a friction stir welding device; the welding wire and a welding piece are connected with "+" and "-" poles of an electric welding machine respectively to form an arc welding. Through the combination of the friction stir welding and the arc welding, in-situ reaction of the welding wire is promoted, and binary in-situ nano-particles are generated through doping and reaction of mixed salt, rare earth and alloy elements. This method can not only ensure the weldability of the welding wire and the welding piece, but also strengthen and improve the mechanical properties and microstructure of the weld through the binary in-situ nano-particles. The in-situ reaction of the reaction salt and Al has no by-product, in addition, the in-situ reaction is beneficial to the enhancement of the wettability of the endogenous particles and the base material, the addition of the rare earth can also play an obvious grain refinement role, and can overcome the problems of serious crack tendency, alloy element burning loss, coarse structure grain, serious joint performance decline and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy welding wire, and relates to an aluminum alloy flux-cored wire and a welding method thereof, in particular to an in-situ nanoparticle reinforced welding wire for aluminum vehicle body welding and a welding method thereof. TECHNICAL BACKGROUND

[0002] High-speed trains have become the mainstream direction of train development in the world due to high running speed, low energy consumption and other advantages. The application of aluminum alloy in high-speed trains has become a hot research and development topic in the world. The demand for aluminum alloy is increasing. Aluminum alloy has become the most widely used material after steel.

[0003] As a hot topic of the new era, the innovative development of rail transit has gradually been valued by scientific researchers. A7N01 aluminum alloy, as an Al-Mg-Zn alloy, has rapidly developed in the application in high-speed train body structure in recent years due to its light weight, high strength-to-weight ratio, excellent strength and toughness. The main method for connecting and manufacturing aluminum alloy structures of train bodies is welding, which is a high-efficiency connecting means and has advantages such as convenient forming and strong adaptability. However, there are still many problems in its application in industrial production, such as serious tendency of welding hot cracks, coarse grains in the weld, and softening of the mechanical properties of the weld. When LBW welding is performed on the aluminum alloy, there are inevitably defects such as high surface reflectivity and crack solidification. At present, relevant documents point out that adding a certain volume fraction of particles into the aluminum alloy can reduce its macroscopic cracks, equiaxialize dendrites in the weld and effectively refine the grains, and the strength attenuation is also obviously improved.

[0004] Chinese patent application CN202110873399.4 proposes a mixed salt and rare earth filled flux-cored wire for welding 7XXX aluminum alloy. Through direct fusion welding, the mixed salt in the flux-cored wire generates unit reinforcing particles in-situ, thereby improving the performance of the base material. In the trace alloying elements of the flux-cored wire, in addition to 2.5% of metal Cu powder and 0.5% of metal Mn, no alloying elements beneficial to the weldability of aluminum alloy are added. The effect of the in-situ synthesized unit nanoparticles ZrB2 on grain refinement is not obvious, which leads to the inability to effectively improve the strength of the weld. More importantly, the reaction salts K2ZrF6 and KBF4 are not protected and are prone to metamorphism and deliquescence before welding. In addition, the reaction of K2ZrF6, KBF4 mixed salt and Al is easy to generate by-products, which are not easy to remove and are not conducive to the performance of the weld. SUMMARY

[0005] In view of the above technical problems, the patent application embeds a special welding wire into a friction stir welding device to form an arc welding by connecting the welding wire and the welding piece with the "+" and "-" poles of an electric welding machine. This welding method is intended to promote the in-situ reaction of the special welding wire by combining the friction stir welding and the arc welding, and to generate bimetallic in-situ nanoparticles by doping and reacting the mixed salt, rare earth and alloying elements. This method can not only ensure the weldability of the welding wire and the welding piece, but also strengthen and improve the mechanical properties and microstructure of the weld joint by means of the bimetallic in-situ nanoparticles. The in-situ reaction of the reaction salt B2O3, ZrO2 and Al in the patent application has no by-products. In addition, the in-situ reaction is beneficial to enhancing the wettability of the endogenous particles and the base material, and the addition of rare earth can also play a significant grain refinement effect. In summary, the introduction of bimetallic nanoparticles is superior to the introduction of single nanoparticles, and can achieve a strengthening effect of 1+1>2. In addition, the synergistic strengthening of rare earth can overcome the problems of serious crack tendency, alloy element burning loss, coarse grain structure, and serious joint performance degradation.

[0006] The application combines the in-situ nanoparticle reinforcement mechanism and welding technology, designs and prepares a flux-cored wire filled with mixed salt and rare earth suitable for aluminum alloy welding, proposes a new welding idea, and meets the welding performance of aluminum alloy used for high-speed train body manufacturing. The purpose is to solve the problems of porosity, solidification cracks, alloy element burning loss, coarse grain structure, joint performance degradation and other problems that occur during welding of aluminum alloy, especially 7N01 aluminum alloy.

[0007] The aluminum alloy flux-cored wire prepared by the application can generate bimetallic nanoparticles ZrB2 and Al2O3 through in-situ chemical reaction, that is, on the basis of single nanoparticle reinforcement of weldability and mechanical properties, the bimetallic nanoparticle reinforcement mechanism is realized, and by adjusting the proportion of reaction salt in the inner core wire, the adjustment range of the aluminum alloy weld composition can be increased, the 7N01 aluminum alloy weld structure and performance can be optimized, and the welding joint strength can be improved. The welding wire of the application can significantly reduce the hot crack tendency of the weld metal while ensuring that the chemical composition, mechanical properties and corrosion resistance of the weld metal meet the relevant requirements, and obtain a weld joint with good appearance, high strength and excellent performance.

[0008] The application is implemented by the following technical solutions:

[0009] The in-situ nano-particle reinforced welding wire for aluminum body welding comprises, from outside to inside, a wear-resistant layer, an oxidation-resistant layer, a cladding layer, a core layer and three filling wires.

[0010] The above-mentioned engineering ceramic zirconia is used as the wear-resistant layer, the molybdenum disilicide (MoSi2) is used as the oxidation-resistant layer, the Ni-Cr-Co-Al aluminum-based alloy strip is used as the cladding layer, and the 1070 pure aluminum strip is used to coat the reaction salt to form the three filling wires. The three filling wires respectively contain the following components according to the mass percentage: B2O3 5.0-30.0, ZrO2 5.0-30.0 and metal fluoride 1.0-3.0, the filling rate is 20%-30%, and the balance is pure Al; the components of the core layer outside the filling wire are calculated according to the mass percentage: V≤0.1, Mo≤0.2, Mg 1.0-2.0, Zn 4.0-5.0, rare earth≤1.0, binder 0.5-1.0, and the balance is pure Al.

[0011] The above-mentioned reaction salts B2O3 and ZrO2 are synthesized into two filling wires, wherein the B2O3 is a white waxy solid, and the ZrO2 is a white odorless and tasteless crystal. The two salts B2O3 and ZrO2 have a certain proportion relationship, and the mass ratio is 8.7:15.4. Both of them need to be ground to below 200 mesh before adding.

[0012] The in-situ reaction products of the above-mentioned reaction salts B2O3, ZrO2 and Al do not contain impurities and by-products.

[0013] The above-mentioned metal fluoride is AlF3.

[0014] The above-mentioned rare earth is Er.

[0015] The above-mentioned binder is potassium silicate.

[0016] The above-mentioned welding methods are friction stir welding and electric arc welding.

[0017] The above-mentioned chemical composition design is based on the traditional welding substrate 7N01 aluminum alloy, and the harmful elements such as Si, Mn and Cu are removed to further improve the weldability of the alloy. At the same time, Cr, V, Mo, Zr, B, O and Er are added to the alloy to realize in-situ nano-particle reinforcement, rare earth micro-alloying, fine-grain matrix and improved weldability of the alloy.

[0018] The above in-situ nanoparticle strengthening and refining is realized by generating high-hardness, high-thermal-conductivity and low-expansion nanometer ZrB2 and Al2O3 ceramic particles through the reaction of B2O3 and ZrO2 with Al melt. On one hand, the nanometer ceramic particles can be used as heterogeneous nucleation core of α-Al to significantly refine the matrix grain, and are finally distributed in the grain and grain boundary to improve the strength and toughness of the weld through the interaction with dislocation; on the other hand, the in-situ synthesized nanometer ceramic particles can also effectively reduce the grain boundary.

[0019] The components and effects of the alloy elements used are as follows:

[0020] Mg: beneficial to improve the hardness of the weld, and does not significantly reduce the plasticity;

[0021] Zn: forms MgZn2 phase with Mg element, has a dispersion strengthening effect, and has a significant strengthening effect on the alloy;

[0022] Cr: Cr and Al combination and Cr and Ni combination both have high electrical resistance, so the corrosion resistance of the alloy can be improved, and the effect of Cr on improving the corrosion resistance will decrease with the increase of the carbon content;

[0023] Co: Co has good compatibility and almost does not affect the structure of the alloy, and can effectively avoid the generation of brittle intermetallic compounds;

[0024] V: V can refine the grain size of the structure, improve the strength and toughness;

[0025] Ni: the addition of Ni element in the welding wire can be mutually soluble with Co and Cr, and the addition of Ni can improve the compatibility of the weld and the base material, and inhibit the generation of intermetallic compounds;

[0026] Rare earth Er: promotes heterogeneous nucleation, refines the grain, and is easy to promote the formation of stable compounds to inhibit the generation of hydrogen pores;

[0027] The action mode and mechanism of the mixed salt powder are as follows:

[0028] The following metallurgical chemical reactions will occur in the Al-ZrO2-B2O3 ternary system:

[0029] 3ZrO2+4Al+6[B]→2Al2O3+3ZrB2 (1) BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 Fig. 1 shows a schematic diagram of welding aluminum alloy by using the welding wire of the present application.

[0031] Figure 2 Fig. 2 shows a sectional view of the welding wire of the present application.

[0032] Figure 3 Fig. 3 shows an elevation view of the welding wire of the present application.

[0033] Figure 4 Figure 1 shows a cross-sectional view of the welding wire of the present application.

[0034] Figure 5 Figure 2 shows a partial SEM image and corresponding Mapping image of the welded joint. Figure 5 (a) is a SEM image, from which the particle clusters can be seen. Figure 5 (b)-(e) are B, Al, O, Zr element maps, respectively, showing that two kinds of particles, ZrB2 and Al2O3, are successfully prepared.

[0035] Figure legend: 1 - wear-resistant layer, 2 - oxidation-resistant layer, 3 - cladding layer, 4 - gas-permeable hole, 5 - B2O3 filler wire, 6 - ZrO2 filler wire, 7 - metal fluoride filler wire, 8 - core layer, 9 - connecting head, 10 - anti-slip protrusion, 11 - sealing head. DETAILED DESCRIPTION

[0036] The present application will be further described below in conjunction with specific examples.

[0037] Example 1: A in-situ nanoparticle-strengthening welding wire for welding of an aluminum body of a high-speed train, in which the content of generated ZrB2 particles is 8.7 wt%, the content of Al2O3 particles is 5.8 wt%, and the content of rare earth is 0.7 wt%. The outer layer composition and its length x width are as follows: an engineering ceramic zirconia is used as the wear-resistant layer, with a size of 20 x 10 cm, molybdenum disilicide (MoSi2) is used as the oxidation-resistant layer, with a size of 20 x 8 cm, a Ni-Cr-Co-Al system aluminum-based alloy strip is used as the cladding layer of the powder, with a size of 20 x 6 cm, and a 1070 pure aluminum strip is used to coat the reaction salt to form a filler wire, with a diameter of 4 cm; the composition of the filler wire is as follows in terms of mass percentage: the content of mixed salt (B2O3 + ZrO2) is 24.0, in which the mass ratio of B2O3 to ZrO2 is 8.7:15.4, the content of metal fluoride is 1.0, and the balance is pure Al. The filling rate of the welding wire is 20%. The composition of the core layer outside the filler wire is as follows in terms of mass percentage: the content of metal Zn powder is 5.0, the content of metal Mg powder is 2.0, the content of metal V powder is 0.1, the content of metal Mo powder is 0.2, the content of pure Er powder of rare earth is 0.7, the content of adhesive potassium silicate is 0.5, and the balance is pure Al.

[0038] In this embodiment, one end of the prepared welding wire is sealed, and the connecting head at the other end is embedded in a friction stir welding device, and the anti-slip protrusion makes the connection firm, so that the welding wire is prepared into a stirring head. Since the heat input of a single friction stir welding cannot meet the melting point of aluminum, on the one hand, the requirements of fusion welding cannot be met, and on the other hand, the in-situ reaction in the welding wire cannot be carried out, therefore, this embodiment adopts a combination of friction stir welding and arc welding to perform welding.

[0039] The specific experimental steps are as follows: (1) the B2O3, ZrO2 drug powder and metal fluoride are ground, then wrapped by 1070 pure aluminum tape, and then twisted; the binder and alloy elements are added, and mixed into the core layer. (2) the Ni-Cr-Co-Al aluminum-based alloy strip is selected as the cladding layer, and the cladding layer is polished smooth by using a steel wire brush to remove the oxide film on the alloy strip. (3) the engineering ceramic zirconia and molybdenum disilicide (MoSi2) are formed and processed to form a wear-resistant layer and an oxidation-resistant layer wrapped on the surface of the Ni-Cr-Co-Al aluminum-based alloy strip, the wear-resistant layer surface is provided with a plurality of air holes, the air holes penetrate from the surface of the wear-resistant layer to the surface of the oxidation-resistant layer, and the air holes are conical structures, the top diameter of the air holes is larger than the bottom diameter. (4) one end of the welding wire is fixed with a connecting head, a plurality of anti-skid protrusions are fixed on the outer wall of the connecting head, and the other end of the welding wire is fixed with a sealing head. (5) introduce the friction stir welding and arc welding device, the welding wire is connected with the stirrer as the stirrer, and at the same time connected with the "+" pole of the electric welding machine, and the welding piece is connected with the "-" pole of the electric welding machine. (6) start the stirrer, the welding wire rotates at high speed, and the joint of the workpiece and the welding piece moves relatively, the rotating welding wire can not only rub with the welding piece to make it plasticize, but also make the in-situ reaction generated reinforcing particles uniformly distributed in the weld. At the same time, start the electric welding machine, the high temperature generated by the electric arc makes the welding wire and the welding piece melt, and also makes the reaction salt in the welding wire in-situ reaction. In the welding process, the workpiece is rigidly fixed, and the welding seam is formed under the action of the welding wire forging pressure.

Claims

1. An in-situ nanoparticle reinforced welding wire for aluminum vehicle body welding, characterized by, The welding wire structure is sequentially from outside to inside wear-resistant layer, oxidation-resistant layer, cladding layer, core layer and three kinds of filler wires; engineering ceramic zirconia is used as the wear-resistant layer, molybdenum disilicide is used as the oxidation-resistant layer, and Ni-Cr-Co-Al aluminum-based alloy belt is used as the cladding layer; the composition of the core layer outside the filler wire is, according to mass percentage: metal Zn powder content 5.0, metal Mg powder content 2.0, metal V powder content 0.1, metal Mo powder content 0.2, pure Er powder 0.7, adhesive potassium silicate 0.5, and the balance is pure Al; the three kinds of filler wires are respectively B2O3 filler wire, ZrO2 filler wire and metal fluoride filler wire, wherein the metal fluoride does not participate in the reaction, and its function is to improve the forming quality of the weld surface and the deslagging property of the weld surface, and further increase the penetration of the welded part; one end of the welding wire is provided with a connecting head, and the other end is provided with a sealing head.

2. An in situ nanoparticle strengthened welding wire for aluminum vehicle body welding as claimed in claim 1, characterized in that, The wear-resistant layer is provided with a ventilation hole, and the connecting head is provided with an anti-skid protrusion.

3. An in situ nanoparticle strengthened welding wire for aluminum vehicle body welding as claimed in claim 1, characterized in that, Three kinds of filler wires are made by using 1070 pure aluminum belt to coat the reaction salt; the three kinds of filler wires respectively contain the following components according to mass percentage: B2O3 5.0-30.0, ZrO2 5.0-30.0 and metal fluoride 1.0-3.0, and the filling rate is 20%-30%, and the balance is pure Al.

4. An in situ nanoparticle strengthened welding wire for aluminum vehicle body welding as claimed in claim 1 or 3, characterized in that, The two kinds of salts B2O3 and ZrO2 have a certain proportional relationship, and the mass ratio is 8.7:15.4, and they need to be ground to below 200 mesh before adding.

5. An in situ nanoparticle strengthened welding wire for aluminum vehicle body welding as claimed in claim 3, wherein, The in-situ reaction product of the reaction salt B2O3, ZrO2 and Al does not contain impurities and by-products; the metal fluoride is AlF3; the rare earth is Er; and the adhesive is potassium silicate.

6. A method of welding using the in-situ nanoparticle reinforced welding wire as claimed in claim 1, characterized in that, The specific steps are as follows: (1) After the B2O3, ZrO2 and metal fluoride are ground, they are wrapped by 1070 pure aluminum belt, and then twisted; the adhesive and alloy elements are added and mixed into the core layer; (2) The Ni-Cr-Co-Al aluminum-based alloy belt is selected as the cladding layer, and the cladding layer is polished smooth by using a steel wire brush to remove the oxide film on the alloy belt; (3) The engineering ceramic zirconia and molybdenum disilicide are formed and processed to make the wear-resistant layer and the oxidation-resistant layer wrapped on the surface of the Ni-Cr-Co-Al aluminum-based alloy belt, the wear-resistant layer is provided with a ventilation hole, the ventilation hole penetrates from the surface of the wear-resistant layer to the surface of the oxidation-resistant layer, and the ventilation hole is a tapered structure, the top diameter of the ventilation hole is larger than the bottom diameter; (4) One end of the welding wire is connected with the connecting head, the outer wall of the connecting head is fixed with an anti-skid protrusion, and the other end of the welding wire is fixed with a sealing head; (5) The friction stir welding and electric arc welding devices are introduced, the welding wire is connected with the stirrer as the stirring head, and at the same time connected with the "+" pole of the electric welding machine, and the welding part is connected with the "-" pole of the electric welding machine; (6) The stirrer is started, the welding wire rotates at high speed and moves relative to the joint of the workpiece and the welding part, the rotating welding wire and the welding part are plasticized, and the in-situ reaction generated reinforcing particles are uniformly distributed in the weld; at the same time, the electric welding machine is started, the high temperature generated by the electric arc makes the welding wire and the welding part melt, and also makes the reaction salt in the welding wire in-situ reaction; in the welding process, the workpiece is rigidly fixed, and the weld is formed under the action of the welding wire forging pressure.

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