A flux for laser welding of aluminum and steel dissimilar materials and its preparation method and application

Abstract

The present invention relates to the field of welding technology, and discloses a flux for laser welding of aluminum and steel dissimilar materials, and a preparation method and application thereof. The flux for laser welding of aluminum and steel dissimilar materials comprises a main material and an auxiliary material, wherein the main material comprises, by mass percentage, 40%-50% of a wetting agent, 5%-10% of an arc stabilizer, and 40%-55% of a composite high-entropy solder, and the auxiliary material comprises polyethylene glycol and alcohol; the wetting agent is a mixture of KAlF4, K3AlF6 and Zn, with a mass ratio of 2-4:1:1; the arc stabilizer is a mixture of potassium oxide, barium carbonate and rubidium oxide, with a mass ratio of 1-2:1-2:1-2; the composite high-entropy solder comprises, by mass percentage, Al8%-14%, Co 16%-22%, Cr 16%-22%, Ni 16%-22%, and the rest is Fe. The present invention can significantly improve the stability of welding and reduce the generation of intermetallic compounds.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, and in particular to a flux for laser welding of dissimilar aluminum and steel materials, and a preparation method and application thereof. Background Art

[0002] Aluminum / steel dissimilar metal joining has a wide range of application prospects in many important industrial fields, such as aerospace, ships and ships, and rail vehicles. Common aluminum / steel metal welding is often limited by assembly accuracy and other requirements. Laser arc hybrid welding has the advantages of fast welding speed, high production efficiency, and high assembly tolerance, providing a high-quality solution for achieving high-efficiency, low-cost, and high-quality connections. However, due to the large differences in the physical and chemical properties of aluminum / steel, liquid aluminum cannot effectively wet the steel surface, resulting in many joint defects and subsequently reducing the mechanical properties. In addition, during the welding process of aluminum / steel, intermetallic compounds (IMCs) such as Fe3Al, FeAl, FeAl2, FeAl3, and Fe2Al5 are generated, which also have adverse effects on the joints due to their high hardness, high brittleness, and low force bearing capacity.

[0003] The formation of aluminum / steel intermetallic compounds (IMCs) is currently mainly addressed by improving welding process parameters and adding intermediate layers. Since the formation of intermetallic compounds (IMCs) is significantly affected by diffusion, it is often necessary to reduce heat input during welding. In addition, the addition of Zn, Si, Ni, etc. has a certain inhibitory effect on the formation of intermetallic compounds (IMCs), but the intermediate products also have the characteristics of high hardness and high brittleness, making it difficult to fundamentally improve the joint performance. Therefore, how to intrinsically inhibit the formation of IMCs has become one of the urgent problems to be solved in order to obtain high-quality aluminum / steel joints.

[0004] Patent application document CN202310223741.5 discloses a composite brazing flux and brazing method for steel / aluminum dissimilar metal brazing / melting brazing, which utilizes KBF4 and molten liquid Al to undergo an in-situ substitution reaction (KBF4+Al=KAlF4+[B]) to transition free B into the weld. The free B enters the atomic gap of the intermetallic compound, thereby improving the intrinsic brittleness of the Fe / Al intermetallic compound, thereby improving the strength and toughness of the joint. However, this application still cannot solve the problem of Fe / FeAl3 or Fe / FeAl x Welding cold cracks.

[0005] Patent application document CN202110895432.3 discloses a dual-beam laser welding method for aluminum / steel dissimilar metals based on a high-entropy alloy intermediate layer. The incomplete melting of the high-entropy alloy layer avoids the mutual diffusion of Fe / Al elements and reduces the formation of Fe / Al intermetallic compounds. However, the dual-beam laser welding process and equipment are relatively complex and cannot meet large-scale production applications. At the same time, it does not solve the many problems caused by the difference in wettability of aluminum / steel.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The purpose of the present invention is to provide a flux for laser welding of dissimilar aluminum and steel materials, and a preparation method and application thereof.

[0008] The present invention is achieved in that:

[0009] In a first aspect, the present invention provides a flux for laser welding of dissimilar aluminum and steel materials, comprising a main material and auxiliary materials, wherein the main material comprises, by mass percentage, 40%-50% of a wetting agent, 5%-10% of an arc stabilizer, and 40%-55% of a composite high-entropy solder, and the auxiliary materials comprise polyethylene glycol and alcohol; the wetting agent is a mixture of KAlF4, K3AlF6, and Zn in a mass ratio of 2-4:1:1; the arc stabilizer is a mixture of potassium oxide, barium carbonate, and rubidium oxide in a mass ratio of 1-2:1-2:1-2; the composite high-entropy solder comprises, by mass percentage, 8%-14% of Al, 16%-22% of Co, 16%-22% of Cr, 16%-22% of Ni, and the remainder is Fe.

[0010] In an optional embodiment, the mass ratio of the KAlF4, the K3AlF6 and the Zn is 3:1:1.

[0011] In an optional embodiment, the mass ratio of the potassium oxide, the barium carbonate and the rubidium oxide is 1:1:1.

[0012] In an optional embodiment, the mass percentage of Al in the composite high-entropy solder is 10-12% in terms of the mass percentage of the flux for laser welding of aluminum and steel dissimilar materials.

[0013] In a second aspect, the present invention provides a method for preparing a flux for laser welding of dissimilar aluminum and steel materials, which comprises uniformly mixing the main material and the auxiliary material of the flux for laser welding of dissimilar aluminum and steel materials as described in any one of the aforementioned embodiments.

[0014] In a third aspect, the present invention provides the use of the flux for laser welding of dissimilar aluminum and steel materials as described in any one of the aforementioned embodiments in welding.

[0015] In a fourth aspect, the present invention provides a laser welding method for aluminum and steel dissimilar materials, which comprises applying the flux for laser welding of aluminum and steel dissimilar materials as described in any of the aforementioned embodiments to the area to be overlapped and the epitaxial area thereof of the aluminum material or the steel material, followed by overlapping and performing laser-arc composite welding.

[0016] In an optional embodiment, the width of the area to be overlapped is 8-12 mm, the coating width of the flux for laser welding of dissimilar aluminum and steel materials is 15-25 mm, the coating length is the same as the length of the area to be overlapped, and the coating thickness is 2.0-3.0 mm.

[0017] In an optional embodiment, the laser-arc hybrid welding is performed by laser-guided arc, and the plane where the laser and arc are located is always kept deflected 15-45° to the left along the plane perpendicular to the workpiece, and the angle between the welding gun and the laser head is 30°.

[0018] In an optional embodiment, the control parameters in the laser-arc hybrid welding process are: laser wavelength is 1000-1100nm, laser power is 1100-1300W, defocus is 0mm, filament spacing is 1-3mm, beam quality is 6-10mm·mrad, optical fiber is LLK-1 type, diameter is 300-500μm; the welding wire during arc welding extends 10-15mm and keeps 1-3mm away from the overlapping edge, the welding speed is 1.8-3.0m / min, the wire feeding speed is 5-7m / min, the arc voltage is 16.9-18.3V, and the current is 84-121A; the material of the welding wire is AlMg5;

[0019] and / or, the welding laser is a Trumpf Trudisk 10002 model;

[0020] And / or, the arc machine is a Fronius TPS5000 model.

[0021] The present invention has the following beneficial effects:

[0022] The flux for laser welding of aluminum and steel dissimilar materials provided by the present invention is formed by mixing a wetting agent, an arc stabilizer and a composite high entropy solder in a specific ratio, wherein a Zn element is added to the wetting agent, and the added Zn element reacts with KAlF4 and K3AlF6 to form an Al(Zn) solid solution during melt-brazing, which is beneficial to reducing the surface tension of the liquid aluminum solder, and then the Zn element volatilizes at high temperature, and the liquid aluminum further combines with the steel under the action of KAlF4 and K3AlF6. Potassium oxide, barium carbonate and rubidium oxide are mixed in a specific ratio to play the role of arc starting and stable arc combustion, improve the stability of the composite arc, facilitate the welding process, increase the welding speed, and improve the quality of the weld, and improve the strength and toughness of the weld. The high entropy effect of the composite high entropy solder makes it difficult for atoms to diffuse, so that the generation of intermetallic compounds can be suppressed; the slow diffusion effect of the composite high entropy solder can prevent the elements in the parent material from diffusing in large quantities into the weld, thereby further suppressing the generation of intermetallic compounds. By combining the above-mentioned wetting agent, arc stabilizer and composite high-entropy solder, the stability of welding can be significantly improved and the formation of intermetallic compounds can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0024] Figure 1 A welding schematic diagram of the laser welding method for aluminum-steel dissimilar materials provided by the present invention;

[0025] Figure 2 The weld surface and joint cross-section morphology of Example 1 in the experimental example provided by the present invention;

[0026] Figure 3 The weld surface and joint cross-section morphology of Example 2 in the experimental example provided by the present invention;

[0027] Figure 4 The weld surface and joint cross-section morphology of Example 3 in the experimental example provided by the present invention;

[0028] Figure 5 A micrograph of the weld center of Example 1 in the experimental example provided by the present invention;

[0029] Figure 6 A micrograph of the weld center of Example 2 in the experimental example provided by the present invention;

[0030] Figure 7A micrograph of the weld center of Example 3 in the experimental example provided by the present invention;

[0031] Figure 8 A micrograph of the brazing area of ​​Example 1 in the experimental example provided by the present invention;

[0032] Fig. 9 A micrograph of the brazing area of ​​Example 2 in the experimental example provided by the present invention;

[0033] Fig.10 A micrograph of the brazing area of ​​Example 3 in the experimental example provided by the present invention;

[0034] Fig.11 The microhardness cloud diagram of Example 1 in the experimental example provided by the present invention;

[0035] Fig.12 The microhardness cloud diagram of Example 2 in the experimental example provided by the present invention;

[0036] Fig.13 The microhardness cloud diagram of Example 3 in the experimental example provided by the present invention;

[0037] Fig.14 The weld surface and joint cross-section morphology of Comparative Example 1 in the experimental example provided by the present invention;

[0038] Fig.15 The weld surface and joint cross-section morphology of Comparative Example 2 in the experimental example provided by the present invention;

[0039] Fig.16 The weld surface and joint cross-section morphology of Comparative Example 3 in the experimental example provided by the present invention;

[0040] Fig.17 The weld surface and joint cross-section morphology of Comparative Example 4 in the experimental example provided by the present invention;

[0041] Fig.18 The weld surface and joint cross-section morphology of comparative example 5 in the experimental example provided by the present invention;

[0042] Fig.19 This is a bar graph of the joint shear strength of Examples 1-3 and Comparative Examples 1-5 in the experimental examples provided by the present invention.

[0043] Icons: 1-aluminum plate; 2-steel plate; 3-laser head; 4-arc welding gun; 10-weld seam. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0045] The invention provides a flux for laser welding of aluminum and steel dissimilar materials, which comprises a main material and auxiliary materials. The main material comprises, by mass percentage, 40%-50% of a wetting agent, 5%-10% of an arc stabilizer and 40%-55% of a composite high-entropy solder, and the auxiliary materials comprise polyethylene glycol and alcohol.

[0046] Wherein, the wetting agent is a mixture of KAlF4, K3AlF6 and Zn, and the mass ratio is 2-4:1:1; preferably, the mass ratio is 2-4:1:1, and KAlF4, K3AlF6 and Zn are mixed as the wetting agent, wherein, because KAlF4 and K3AlF6 have the advantages of low melting point, non-hygroscopicity, good fluidity, convenient preparation, no welding defects in the brazing seam, and no need for cleaning after welding. It has been widely used in the fields of automobile industry, aerospace industry, chemical industry, machinery manufacturing, military industry, instrumentation and electrical industry. However, KAlF4 and K3AlF6 are expensive and the preparation process is complicated, which limits their large-scale application. In the present invention, by adding Zn, the cost of the Zn element is low and the refining process is simple. In addition, the added Zn element will react with KAlF4 and K3AlF6 to form Al(Zn) solid solution during melt-brazing, which is beneficial to reduce the surface tension of liquid aluminum brazing material. Subsequently, the Zn element volatilizes at high temperature, and the liquid aluminum further combines with steel under the action of KAlF4 and K3AlF6.

[0047] The arc stabilizer is a mixture of potassium oxide, barium carbonate and rubidium oxide, with a mass ratio of 1-2:1-2:1-2; preferably, the mass ratio is 1:1:1. In the present invention, potassium oxide, barium carbonate and rubidium oxide are mixed in a specific ratio to play the role of arc initiation and stable arc combustion. Substances containing low ionization potential elements have different degrees of arc stabilization, and the most commonly used material is potassium oxide. Since the arc is extremely unstable during steel / aluminum laser-arc composite welding, BaCO3 and Rb2O with lower potential elements are added to the arc stabilizer in the present invention, which improves the stability of the composite arc to a certain extent, is conducive to the welding process, and increases the welding speed. At the same time, it can also improve the quality of the weld and improve the strength and toughness of the weld. The arc stabilizer can maintain the stability of the arc, prevent the arc from breaking or tripping, and ensure the stability and reliability of the welding process. The arc stabilizer can protect the arc, reduce the generation of oxidation and impurities, thereby reducing the generation of welding defects and cracks. The arc stabilizer can reduce smoke and odor during welding, improve the working environment, and reduce the health risks of workers. The addition of arc stabilizer can reduce oxidation and corrosion of welding rods, thereby extending the service life of welding rods and reducing welding costs.

[0048] The composite high entropy solder comprises, by mass percentage, 8%-14% Al, 16%-22% Co, 16%-22% Cr, 16%-22% Ni, and the remainder is Fe. Preferably, the composite high entropy solder comprises 10%-12% Al, 18-20% Co, 18-20% Cr, 18-20% Ni, and the remainder is Fe.

[0049] The composite high entropy solder in the present invention is composed of five or more elements in an equiatomic ratio or a nearly equiatomic ratio, each element exists in a ratio of 5%-35% and forms a simple solid solution. The composite high entropy solder with multiple components has good plasticity and toughness. The high entropy effect of the composite high entropy solder makes it difficult for atoms to diffuse, so the formation of intermetallic compounds can be suppressed; the slow diffusion effect of the composite high entropy solder can prevent the elements in the base material from diffusing into the weld in large quantities, thereby further suppressing the formation of intermetallic compounds. In particular, the Al content in the present invention can be significantly reduced, specifically 10%-12%. At this time, the reduction of the aluminum element is conducive to reducing the formation of IMCs between the aluminum element and the Fe element at high temperature. Thereby improving the mechanical properties of the joint.

[0050] Furthermore, the present invention also provides a method for preparing a flux for laser welding of aluminum and steel dissimilar materials, which comprises uniformly mixing the main material and auxiliary material of the flux for laser welding of aluminum and steel dissimilar materials.

[0051] The above-mentioned flux for laser welding of dissimilar aluminum and steel materials can be widely used in welding.

[0052] Specifically, see Figure 1The present invention provides a laser welding method for aluminum-steel dissimilar materials, which comprises the following steps:

[0053] S1. Preprocessing.

[0054] The surfaces of the aluminum plate 1 and the steel plate 2 to be welded are cleaned, wherein the surface oxide film of the aluminum plate 1 is removed by using a short pulse laser, and the steel plate 2 is lightly polished by using 2000-grit sandpaper, and the treated plates are wiped with acetone to prevent oxidation.

[0055] S2. Select the overlap mode.

[0056] The overlap mode adopts the steel-on-aluminum-on-bottom mode, in which the steel plate 2 is on the top and the aluminum plate 1 is on the bottom; or the aluminum-on-steel-on-bottom mode, in which the aluminum plate 1 is on the top and the steel plate 2 is on the bottom. When the aluminum plate 1 is on the bottom, the flux for laser welding of aluminum and steel dissimilar materials is applied to the surface of the aluminum plate 1. When the steel plate 2 is on the bottom, the flux for laser welding of aluminum and steel dissimilar materials is applied to the surface of the steel plate 2.

[0057] S3, flux for laser welding of dissimilar materials of aluminum and steel.

[0058] The flux for laser welding of dissimilar aluminum and steel is applied to the overlapping area and the extension area of ​​the lower plate in the aluminum plate 1 or the steel plate 2.

[0059] When coating, use a brush to evenly distribute it. The width of the overlapped area is 8-12mm. The coating width of the flux for laser welding of aluminum and steel dissimilar materials is 15-25mm. The coating length is the same as the length of the overlapped area. The coating thickness is 3mm. After coating, place the upper plate on the coating layer to form a sandwich structure.

[0060] S4, laser-arc hybrid welding.

[0061] Laser-arc hybrid welding is carried out by laser-guided arc, and the plane where the laser head 3 and the arc welding gun 4 are located is always kept deflected 15-45° to the left along the plane perpendicular to the workpiece, the angle between the arc welding gun 4 and the laser head 3 is 30°, and the working direction of the laser head 3 and the arc welding gun 4 is perpendicular to the direction of the weld 10.

[0062] The control parameters during the laser-arc hybrid welding process are as follows: laser wavelength is 1000-1100nm, laser power is 1100-1300W, defocus is 0mm, filament spacing is 1-3mm, beam quality is 6-10mm·mrad, optical fiber is LLK-1 type, diameter is 300-500μm; the welding wire during arc welding extends 10-15mm and is kept 1-3mm away from the overlapping edge, the welding speed is 1.8-3.0m / min, the wire feeding speed is 5-7m / min, the arc voltage is 16.9-18.3V, and the current is 84-121A; the material of the welding wire is AlMg5; the welding laser is Trumpf Trudisk 10002 type; and the arc machine is Fronius TPS5000 type.

[0063] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0064] Example 1

[0065] This embodiment provides a flux for laser welding of aluminum and steel dissimilar materials, which includes 40% wetting agent, 10% arc stabilizer and 50% composite high entropy solder. The wetting agent includes 2.4g KAlF4, 0.8g K3AlF6, and 0.8g Zn; the arc stabilizer includes 0.33g potassium oxide, 0.33g barium carbonate, and 0.33g rubidium oxide; the composite high entropy solder includes 0.6g Al, 1g Co, 1g Cr, 1g Ni, and 1.4g Fe.

[0066] The preparation method of flux for laser welding of aluminum and steel dissimilar materials includes: mixing the above-mentioned wetting agent, arc stabilizer and composite high-entropy solder in proportion, and then adding 5 ml of alcohol to prepare a suspension. In order to ensure a smooth coating process, it is preferable to have a flowing state and maintain a certain shape.

[0067] Example 2

[0068] This embodiment provides a flux for laser welding of aluminum and steel dissimilar materials, which includes 40% wetting agent, 5% arc stabilizer and 55% composite high entropy solder. The wetting agent includes 2g KAlF4, 1g K3AlF6 and 1g Zn; the arc stabilizer includes 0.4g potassium oxide, 0.4g barium carbonate and 0.2g rubidium oxide; the composite high entropy solder includes 0.55g Al, 0.99g Co, 0.99g Cr, 0.99g Ni and 1.98g Fe.

[0069] Example 3

[0070] This embodiment provides a flux for laser welding of aluminum and steel dissimilar materials, which includes 45% wetting agent, 8% arc stabilizer and 47% composite high entropy solder. The wetting agent includes 3g KAlF4, 0.75g K3AlF6 and 0.75g Zn; the arc stabilizer includes 0.2g potassium oxide, 0.2g barium carbonate and 0.4g rubidium oxide; the composite high entropy solder includes 0.66g Al, 1.03g Co, 1.03g Cr, 1.03g Ni and 0.95g Fe.

[0071] Comparative Example 1

[0072] This comparative example is basically the same as Example 1, except that this comparative example does not contain a wetting agent. Specifically, this comparative example provides a flux for laser welding of aluminum and steel dissimilar materials, which includes 16.7% arc stabilizer and 83.3% composite high entropy solder. Among them, the arc stabilizer includes 0.33g potassium oxide, 0.33g barium carbonate and 0.33g rubidium oxide; the composite high entropy solder includes 0.6g Al, 1g Co, 1g Cr, 1g Ni, and 1.4g Fe.

[0073] Comparative Example 2

[0074] This comparative example is basically the same as Example 1, except that the composite high entropy solder is not contained in this comparative example. Specifically, this comparative example provides a flux for laser welding of aluminum and steel dissimilar materials, which includes 80% of a wetting agent and 20% of an arc stabilizer. The wetting agent includes 2.4g of KAlF4, 0.8g of K3AlF6, and 0.8g of Zn; the arc stabilizer includes 0.33g of potassium oxide, 0.33g of barium carbonate, and 0.33g of rubidium oxide.

[0075] Comparative Example 3

[0076] This comparative example is basically the same as Example 1, except that the wetting agent in this comparative example does not contain Zn. Specifically, this comparative example provides a flux for laser welding of aluminum and steel dissimilar materials, which includes 40% wetting agent, 10% arc stabilizer and 50% composite high entropy solder. Among them, the wetting agent includes 3.2g of KAlF4 and 0.8g of K3AlF6; the arc stabilizer includes 0.33g of potassium oxide, 0.33g of barium carbonate and 0.33g of rubidium oxide; the composite high entropy solder includes 0.6g of Al, 1g of Co, 1g of Cr, 1g of Ni and 1.4g of Fe.

[0077] Comparative Example 4

[0078] This comparative example is basically the same as Example 1, except that the arc stabilizer in this comparative example omits barium carbonate and rubidium oxide. Specifically, this comparative example provides a flux for laser welding of aluminum-steel dissimilar materials, which includes 40% wetting agent, 10% arc stabilizer and 50% composite high entropy solder. Among them, the wetting agent includes KAlF4 2.4g, K3AlF6 0.8g, Zn0.8g; the arc stabilizer includes potassium oxide 1g; the composite high entropy solder includes Al 0.6g, Co 1g, Cr 1g, Ni 1g, Fe 1.4g.

[0079] Comparative Example 5

[0080] This comparative example is basically the same as Example 1, except that the content of Al in the composite high entropy solder of this comparative example is 15%. Specifically, this comparative example provides a flux for laser welding of aluminum-steel dissimilar materials, which includes 40% wetting agent, 10% arc stabilizer and 50% composite high entropy solder. Among them, the wetting agent includes 2.4g KAlF4, 0.8g K3AlF6, and 0.8g Zn; the arc stabilizer includes 0.33g potassium oxide, 0.33g barium carbonate, and 0.33g rubidium oxide; the composite high entropy solder includes 0.6g Al, 1g Co, 1g Cr, 1g Ni, and 1.4g Fe.

[0081] Experimental example

[0082] The flux for laser welding of aluminum-steel dissimilar materials provided in the above-mentioned Examples 1-3 and Comparative Examples 1-5 is applied to laser welding of aluminum-steel dissimilar materials. The specific welding method comprises the following steps:

[0083] S1. Preprocessing.

[0084] The surfaces of the aluminum plate and steel plate to be welded are cleaned. The surface oxide film of the aluminum plate is removed by short-pulse laser, and the steel plate is lightly polished with 2000-grit sandpaper. The treated plates are wiped with acetone to prevent oxidation.

[0085] S2. Select the overlap mode.

[0086] The overlapping method adopts the steel-on-aluminum-on-bottom mode, in which the steel plate is on the top and the aluminum plate is on the bottom; the flux used for laser welding of aluminum and steel dissimilar materials is coated on the surface of the aluminum plate.

[0087] S3, flux for laser welding of dissimilar materials of aluminum and steel.

[0088] The flux for laser welding of dissimilar materials of aluminum and steel is applied to the overlapping area and the extension area of ​​the lower plate in the aluminum material or the steel material.

[0089] When coating, a brush is used to evenly distribute the coating. The width of the overlapped area is 10 mm. The coating width of the flux for laser welding of aluminum and steel dissimilar materials is 20 mm. The coating length is the same as the length of the overlapped area. After coating, the upper plate is placed on the coating layer to form a sandwich structure.

[0090] S4, laser-arc hybrid welding.

[0091] Laser-arc hybrid welding is carried out by laser-guided arc, and the laser and arc are always kept in the same plane, which is deflected 30° to the left. The laser beam is irradiated vertically to the workpiece surface through the laser gun head. The angle between the welding gun and the laser head is 30°, and compressed air is used as the shielding gas of the laser welding gun.

[0092] The welding laser is Trumpf Trudisk 10002, and the arc machine is Fronius TPS5000. The control parameters during the laser-arc hybrid welding process are: laser wavelength is 1030nm, laser power is 1100-1300W, welding speed is 1.8-3.0m / min, wire feeding speed is 6.0m / min, defocus is 0mm, wire spacing is 2mm, arc wire dry extension is 12mm, and it is kept 2mm away from the overlap edge. The beam quality is 8mm·mrad, the optical fiber is LLK-1 type, with a diameter of 400 microns; the arc voltage is 16.9V, the current is 97A; the material of the welding wire is AlMg5.

[0093] S5. After completing the above welding, perform subsequent cleaning.

[0094] from Figure 2-Figure 13 and Fig.19 It can be seen that the weld bead morphology with bright surface, no cracks and no spatter is obtained by using composite fluxes of different components in Examples 1-3, indicating that the molten droplet transition is stable during welding, and the AlMg5 welding wire forms an effective spread on the surface of the dual-phase steel. It is conducive to the continuous welding process. From the cross-sectional morphology, it can be seen that the joint has a large molten width and depth at the same time, which effectively avoids the formation of finger-shaped welds and is conducive to improving the mechanical properties of the joint.

[0095] Comparative Example 1 is a composite flux weld surface image. Fig.14 and Fig.19 It can be seen that at this time, the steel / aluminum did not form an effective connection, the AlMg5 welding wire did not form an effective spread in the overlap area, and the cross-sectional image could not be obtained by cutting.

[0096] Comparative Example 2 is the weld surface morphology without high entropy component, and the joint morphology is molten-brazed. Fig.15 and Fig.19It can be seen that a certain amount of spatter was observed on the weld surface, indicating that the stability of the welding process decreased. At the same time, a certain amount of pores was observed in the cross section.

[0097] Comparative Example 3 is the microscopic morphology of the weld bead when there is no Zn component brazing filler metal. At this time, the joint is mainly fused-brazed. Fig.16 It can be seen that a large number of pores are observed on the weld surface and in the cross-sectional image. The cross-sectional image shows that the forming angle at the weld toe is significantly increased, indicating that the wettability is reduced and the welding wire does not form effective spreading in the overlap area.

[0098] Comparative Example 4 shows the surface morphology of the weld bead when a single arc stabilizer is used. Fig.17 and Fig.19 It can be seen that the continuity of the weld surface is significantly reduced, and there are many unwelded areas on the weld surface. This indicates that the welding process is less stable. The aluminum welding wire does not spread effectively in the overlap area.

[0099] Comparative Example 5 is the surface morphology of the weld bead when the Al content is high. Fig.18 and Fig.19 It can be seen that the aluminum element in the brazing filler metal is relatively high at this time, which is conducive to the spreading of the aluminum welding wire on the surface of the duplex steel and significantly reduces the joint angle. However, the excessive aluminum element leads to the generation of a large number of brittle IMCs in the joint, which reduces the mechanical properties of the joint.

[0100] In summary, the flux for laser welding of aluminum and steel dissimilar materials provided by the present invention is formed by mixing a wetting agent, an arc stabilizer and a composite high entropy solder in a specific ratio, wherein a Zn element is added to the wetting agent, and the added Zn element reacts with KAlF4 and K3AlF6 during melt-brazing to form an Al(Zn) solid solution, which is beneficial to reducing the surface tension of the liquid aluminum solder, and then the Zn element volatilizes at high temperature, and the liquid aluminum further combines with the steel under the action of KAlF4 and K3AlF6. Potassium oxide, barium carbonate and rubidium oxide are mixed in a specific ratio to play the role of arc initiation and stable arc combustion, improve the stability of the composite arc, facilitate the welding process, increase the welding speed, and at the same time improve the quality of the weld, and improve the strength and toughness of the weld. The high entropy effect of the composite high entropy solder makes it difficult for atoms to diffuse, thus inhibiting the formation of intermetallic compounds; the slow diffusion effect of the composite high entropy solder can prevent the elements in the base material from diffusing into the weld in large quantities, thus further inhibiting the formation of intermetallic compounds. The combination of the above-mentioned wetting agent, arc stabilizer and composite high entropy solder can significantly improve the stability of welding and reduce the formation of intermetallic compounds.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A flux for laser welding of dissimilar aluminum and steel, characterized in that: The invention is composed of main materials and auxiliary materials. The main materials include, by mass percentage, 40%-50% of a wetting agent, 5%-10% of an arc stabilizer and 40%-55% of a composite high-entropy solder. The auxiliary materials include polyethylene glycol and alcohol. The wetting agent is a mixture of KAlF4, K3AlF6 and Zn in a mass ratio of 2-4:1:

1. The arc stabilizer is a mixture of potassium oxide, barium carbonate and rubidium oxide in a mass ratio of 1-2:1-2:1-2. The composite high-entropy solder includes, by mass percentage, 8%-14% of Al, 16%-22% of Co, 16%-22% of Cr and 16%-22% of Ni, and the rest is Fe.

2. The flux for laser welding of aluminum and steel dissimilar materials according to claim 1, characterized in that: The mass ratio of the KAlF4, the K3AlF6 and the Zn is 3:1:

1.

3. The flux for laser welding of aluminum and steel dissimilar materials according to claim 1, characterized in that: The mass ratio of the potassium oxide, the barium carbonate and the rubidium oxide is 1:1:

1.

4. The flux for laser welding of aluminum and steel dissimilar materials according to claim 1, characterized in that: Calculated by the mass percentage of the flux for laser welding of aluminum and steel dissimilar materials, the mass percentage of Al in the composite high entropy solder is 10-12%.

5. A method for preparing a flux for laser welding of aluminum and steel dissimilar materials, characterized in that: The method comprises uniformly mixing the main material and the auxiliary material of the flux for laser welding of dissimilar aluminum and steel materials as described in any one of claims 1 to 4.

6. Use of the flux for laser welding of dissimilar aluminum and steel materials as described in any one of claims 1 to 4 in welding.

7. A laser welding method for aluminum and steel dissimilar materials, characterized in that: The method comprises applying the flux for laser welding of aluminum and steel dissimilar materials as described in any one of claims 1 to 4 to the area to be overlapped and the epitaxial area thereof of the aluminum material or the steel material, then overlapping and performing laser-arc hybrid welding.

8. The laser welding method of aluminum and steel dissimilar materials according to claim 7, characterized in that: The width of the area to be overlapped is 8-12 mm, the coating width of the flux for laser welding of aluminum-steel dissimilar materials is 15-25 mm, the coating length is the same as the length of the area to be overlapped, and the coating thickness is 2.0-3.0 mm.

9. The laser welding method of aluminum and steel dissimilar materials according to claim 7, characterized in that: The laser-arc hybrid welding is performed by laser-guided arc, and the plane where the laser and arc are located is always kept deflected to the left by 15-45° along the plane perpendicular to the workpiece, and the angle between the welding gun and the laser head is 30°.

10. The laser welding method of aluminum and steel dissimilar materials according to claim 9, characterized in that: The control parameters in the laser-arc hybrid welding process are: laser wavelength is 1000-1100nm, laser power is 1100-1300W, defocus is 0mm, filament spacing is 1-3mm, beam quality is 6-10mm·mrad, optical fiber is LLK-1 type, diameter is 300-500μm; welding wire during arc welding extends 10-15mm and keeps 1-3mm away from the overlapping edge, welding speed is 1.8-3.0m / min, wire feeding speed is 5-7m / min, arc voltage is 16.9-18.3V, current is 84-121A; the material of the welding wire is AlMg5; and / or, the welding laser is a Trumpf Trudisk 10002 model; And / or, the arc machine is a Fronius TPS5000 model.

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