Low-stress aluminum-to-steel joint brazing material, method of making and use thereof

Abstract

The application discloses a low-stress green aluminum-steel joint brazing material, which comprises a medicine core and a welding skin. The medicine powder is composed of the following components in percentage by mass: Ag powder 40-50%, Mo powder 10-20%, Cr powder 5-10%, B powder 2-5%, Y2O3+CeO2 powder 0.5-1%, and the balance of Ni powder. The sum of the percentage by mass of the above components is 100%. The material solves the problems of brittle phase generation and large welding residual stress during aluminum-steel butt joint welding. The application further provides a preparation method of the low-stress green aluminum-steel joint brazing material and a method for preparing an aluminum-steel butt joint by using the low-stress green aluminum-steel joint brazing material.

Description

Technical Field

[0001] This invention belongs to the field of metal material welding technology, specifically relating to a low-stress, green and environmentally friendly material for fusion brazing of aluminum-steel joints. This invention also relates to a method for preparing the low-stress, green and environmentally friendly material for fusion brazing of aluminum-steel joints and a method for preparing aluminum-steel butt joints using the low-stress, green and environmentally friendly material for fusion brazing of aluminum-steel joints. Background Technology

[0002] Welding of dissimilar materials has always been a focus of engineering practice because dissimilar material joints combine the superior properties of both materials. For example, aluminum-steel dissimilar material joints possess both the high strength of steel and the low density and excellent corrosion resistance of aluminum alloys. However, welding dissimilar materials often presents several problems. Firstly, some dissimilar material combinations have low solid solubility, leading to the formation of brittle phases during welding. For example, combinations like aluminum-steel, titanium-steel, and titanium-nickel can cause the joint to crack due to the formation of brittle intermetallic compounds, resulting in connection failure. Another reason is the inconsistency in the thermophysical properties of dissimilar materials. For instance, the significant differences in the coefficient of linear expansion and thermal conductivity between aluminum and steel cause residual welding stress to concentrate at the joint. This residual stress, combined with the working stress during subsequent joint operation, can lead to premature structural failure. Currently, for aluminum-steel dissimilar material welding, a galvanized layer is commonly prepared on the steel surface using a galvanizing process to address the issue of brittle phase formation between aluminum and steel. However, when workers are welding galvanized sheets, the galvanized layer produces zinc oxide fumes. If workers inhale these fumes, it can cause metal fume fever and lead to poisoning.

[0003] Therefore, for aluminum-steel joints, which have broad application prospects, in order to achieve large-scale application, it is necessary to solve problems such as the formation of brittle phases and joint stress, as well as green and environmental protection issues. Summary of the Invention

[0004] The purpose of this invention is to provide a low-stress, green, and environmentally friendly material for fusion brazing of aluminum-steel joints, solving the problems of brittle phase formation and high residual stress during aluminum-steel butt joint welding.

[0005] Another objective of this invention is to provide a method for preparing materials for low-stress, green, and environmentally friendly aluminum-steel joint brazing.

[0006] The third objective of this invention is to provide a method for preparing aluminum-steel butt joints using low-stress, green, and environmentally friendly materials for aluminum-steel joint brazing.

[0007] The first technical solution adopted in this invention is a low-stress, green and environmentally friendly material for fusion brazing of aluminum-steel joints, including a flux core and a welding layer, wherein the flux powder is composed of the following components by mass percentage: 40-50% Ag powder, 10-20% Mo powder, 5-10% Cr powder, 2-5% B powder, 0.5-1% Y2O3+CeO2 powder, and the balance is Ni powder, and the sum of the mass percentages of the above components is 100%.

[0008] The invention is further characterized in that,

[0009] The purity of each powder is greater than 99.9%, and the particle size of each powder is 200-300 mesh.

[0010] The solder pad is Inconel 625 tape, which is 0.3mm thick and 7mm wide.

[0011] The material used for low-stress, green and environmentally friendly aluminum-steel joint brazing is flux-cored wire, and the amount of flux-cored powder in the flux-cored wire is controlled at 28wt%~32wt%.

[0012] The second technical solution adopted in this invention is a method for preparing materials for low-stress, green, and environmentally friendly aluminum-steel joint brazing, the specific steps of which are as follows:

[0013] Step 1: Weigh out 40-50% Ag powder, 10-20% Mo powder, 5-10% Cr powder, 2-5% B powder, 0.5-1% Y2O3+CeO2 powder, and the balance is Ni powder, according to the following mass percentages: The sum of the mass percentages of the above components is 100%.

[0014] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 100℃~150℃, and the heat preservation time is 30min~40min. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 30min~40min.

[0015] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, use a flux-cored wire drawing machine to encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die diameter is 2.6 mm. The filling amount of flux powder in the flux-cored wire is controlled between 28 wt% and 32 wt%.

[0016] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0017] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0018] The third technical solution adopted in this invention is a method for preparing aluminum-steel butt joints using the aforementioned low-stress, green, and environmentally friendly aluminum-steel joint brazing material, specifically as follows:

[0019] (1) Open asymmetrical V-shaped bevels on aluminum plates and steel plates, mechanically grind the bevel surfaces of steel plates and aluminum plates to remove oxide scale, and wipe off oil stains with alcohol;

[0020] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.0mm~3.0mm. The welding power source is CMT power source, the welding current is 180A~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2.

[0021] (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used for butt welding of aluminum plate and steel plate. The assembly gap during welding is 0mm~0.5mm. The welding power source is CMT power source, and the welding current is 180A~200A. The shielding gas is a mixed gas, which is composed of the following components by volume percentage: 98%Ar+2%O2. The butt connection of aluminum and steel is completed by multi-layer multi-pass welding.

[0022] The invention is further characterized in that,

[0023] Specifically, the asymmetrical V-shaped bevels on the aluminum and steel plates are made as follows: the bevel angle on the aluminum plate side is 15±5°, and the bevel angle on the steel plate side is 35±5°, without leaving a blunt edge.

[0024] The beneficial effects of this invention are:

[0025] (1) In terms of materials, the material of this invention is nickel-based welding wire, mainly composed of Ni. According to the Ni-Fe binary phase diagram, Ni and Fe have good bonding and their melting points are close, which can ensure good bonding strength. According to the Ni-Al binary phase diagram, up to 11% of Al can be dissolved in Ni. In addition, this invention selects a variety of alloying elements to improve the performance of the weld metal. This invention also adds Ag element with good wettability to the welding wire to improve the wettability of the liquid metal and the Al side steel plate and ensure the forming.

[0026] (2) In terms of process, the method of the present invention selects Ni-based alloy with a large difference in melting point from aluminum as the welding material system, so as to achieve the effect of fusion-brazing during welding; on the other hand, it selects to first deposit Ni-based alloy on the steel side, and then weld the steel (with Ni-based alloy deposited) and aluminum, so as to fully ensure the isolation of Al and Fe elements and suppress the formation of Fe-Al brittle phase.

[0027] (3) In terms of promotion and application, the method of this invention selects nickel-based welding wire, which is green and pollution-free compared with the traditional galvanized plate process, avoiding the risk of zinc oxide poisoning for workers. The welding process selected in this invention is CMT arc fusion welding process, which is simple and flexible to operate. This invention solves the problems of brittle phase, stress concentration and zinc oxide in the welding connection of dissimilar materials such as aluminum and steel by developing a low-stress green and environmentally friendly material for aluminum-steel joint fusion brazing and with reasonable process parameters, thereby achieving high-quality preparation of aluminum-steel joints. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the bevel form of the aluminum-steel butt joint in this invention;

[0029] Figure 2 This is a schematic diagram of the butt welding process of aluminum and steel metal plates according to the present invention;

[0030] Figure 3 The tensile fracture morphology of the aluminum-steel butt joint obtained by welding with the nickel-based flux-cored welding wire prepared in Example 2 is shown in Figure 2.

[0031] Figure 4 Microstructure of the interface between the nickel-based flux-cored wire prepared in Example 2 and the steel plate after the nickel-based weld overlay layer is welded onto the steel plate. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0033] This invention provides a low-stress, green, and environmentally friendly material for fusion brazing of aluminum-steel joints, comprising a flux core and a welding layer. The flux powder is composed of the following components by mass percentage: 40-50% Ag powder, 10-20% Mo powder, 5-10% Cr powder, 2-5% B powder, 0.5-1% Y2O3+CeO2 powder, and the balance being Ni powder. The sum of the mass percentages of the above components is 100%.

[0034] The purity of each powder is greater than 99.9%, and the particle size of each powder is 200-300 mesh.

[0035] The solder pad is Inconel 625 tape, which is 0.3mm thick and 7mm wide.

[0036] The material used for low-stress, green and environmentally friendly aluminum-steel joint brazing is flux-cored wire, and the amount of flux-cored powder in the flux-cored wire is controlled at 28wt%~32wt%.

[0037] The roles and functions of each component in this flux-cored welding wire are as follows:

[0038] (1) Ni is the main component of flux-cored welding wire. Ni is first welded onto the steel plate. As can be seen from the Fe-Ni binary phase diagram, Ni and Fe can be infinitely dissolved in each other, resulting in good weldability. According to the Al-Ni binary phase diagram, although Ni has a very low solid solubility in Al, Al can reach a maximum solid solubility of 11% in Ni. Therefore, when butt welding steel and aluminum with nickel surfacing, using nickel-based welding wire and the fusion-brazing process can ensure excellent metallurgical bonding between the nickel-based weld and the aluminum plate.

[0039] (2) Ag is the main component of the flux powder. According to the Ni-Ag binary phase diagram, the two do not form a brittle phase. According to the Al-Ag binary phase diagram, Al has a high content of Ag that can be dissolved in solids. Therefore, the addition of Ag to the welding wire can play a role in connecting the aluminum and nickel welds. In addition, Ag has a high melting point and good flow properties. Adding Ag to the welding wire can lower the melting point of the welding wire, reduce the melting of the aluminum base material, improve the flowability of the liquid nickel-based weld metal, and ensure the weld formation. In addition, because Ag is relatively soft, it can also play a role in mitigating the residual stress of the joint welding.

[0040] (3) Mo is the main component of the powder. According to the Mo-Ni binary phase diagram, Ni has a high content of Mo that can be dissolved in solids. Therefore, adding Mo to nickel-based welds can improve the strength of the welds. Mo and Fe have good weldability, which can improve the bonding strength between nickel-based welds and steel plates.

[0041] (4) As the main component of the powder, Cr has a high solid solubility in Fe according to the Fe-Cr binary phase diagram. Cr is a commonly used additive element in steel materials. It can not only improve the strength of steel through solid solution strengthening, but also improve the corrosion resistance of welds. However, brittle intermetallic compounds will be formed between Al and Cr. Therefore, it is necessary to control the addition of Cr in the weld.

[0042] (5) As the main component of the powder, the addition of B can further reduce the melting point of the nickel-based weld and improve the fluidity of the liquid metal, thereby reducing the melting of the aluminum side steel plate and inhibiting the formation of the Fe-Al brittle phase.

[0043] (6) A small amount of Y2O3+CeO2 elements were added to the powder. As a composite rare earth oxide, Y2O3+CeO2 effectively refines the grains of nickel-based single-phase welds due to their coarse grains, and also purifies grain boundaries and improves grain boundary bonding strength. In addition, the effect of refining grains is more significant when using composite rare earth oxides compared to adding a single rare earth element.

[0044] This invention also provides a method for preparing a low-stress, green, and environmentally friendly material for fusion brazing of aluminum-steel joints, the specific steps of which are as follows:

[0045] Step 1: Weigh out 40-50% Ag powder, 10-20% Mo powder, 5-10% Cr powder, 2-5% B powder, 0.5-1% Y2O3+CeO2 powder, and the balance is Ni powder, according to the following mass percentages: The sum of the mass percentages of the above components is 100%.

[0046] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 100℃~150℃, and the heat preservation time is 30min~40min. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 30min~40min.

[0047] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, use a flux-cored wire drawing machine to encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die diameter is 2.6 mm. The filling amount of flux powder in the flux-cored wire is controlled between 28 wt% and 32 wt%.

[0048] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0049] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0050] This invention also provides a method for preparing aluminum-steel butt joints using the aforementioned low-stress, environmentally friendly aluminum-steel joint brazing material, specifically as follows:

[0051] (1) Open asymmetrical V-shaped bevels on aluminum plates and steel plates, mechanically grind the bevel surfaces of steel plates and aluminum plates to remove oxide scale, and wipe off oil stains with alcohol;

[0052] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint fusion brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.0mm~3.0mm. The welding power source is selected as CMT power source, and the welding current is 180A~200A. The shielding gas is a mixed gas, which is composed of the following components by volume percentage: 98%Ar+2%O2. (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint fusion brazing material is used to perform butt welding of aluminum plate and steel plate. The assembly gap during welding is 0mm~0.5mm. The welding power source is selected as CMT power source, and the welding current is 180A~200A. The shielding gas is a mixed gas, which is composed of the following components by volume percentage: 98%Ar+2%O2. The butt connection of aluminum and steel is completed by multi-layer multi-pass welding.

[0053] Specifically, the asymmetrical V-shaped bevels on the aluminum and steel plates are made as follows: the bevel angle on the aluminum plate side is 15±5°, and the bevel angle on the steel plate side is 35±5°, without leaving a blunt edge.

[0054] Example 1

[0055] Step 1: Weigh out the following components by mass percentage: 40% Ag powder, 10% Mo powder, 5% Cr powder, 2% B powder, 0.1% Y2O3 powder, 0.4% CeO2 powder, with the remainder being Ni powder. The sum of the mass percentages of the above components is 100%. The purity of each powder is greater than 99.9%, and the particle size of each powder is 300 mesh.

[0056] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 100℃ and the heat preservation time is 30 minutes. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 30 minutes.

[0057] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, using a flux-cored wire drawing machine, encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die bore diameter is 2.6 mm. The flux powder filling amount in the flux-cored wire is controlled at 32 wt%.

[0058] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0059] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0060] When using the nickel-based flux-cored welding wire prepared in Example 1 for aluminum-steel butt welding, the aluminum-steel bevel shape is as follows: Figure 1 As shown: Asymmetrical V-shaped bevels are made, with the bevel size on the aluminum plate side being 10° and the bevel size on the steel plate side being 30°, without leaving blunt edges, and the assembly gap is 0mm during welding.

[0061] The method for preparing aluminum-steel butt joints using the above-mentioned flux-cored welding wire and corresponding beveling pattern is as follows (e.g. Figure 2 (as shown)

[0062] (1) Asymmetrical V-shaped bevels are made on aluminum plates and steel plates. The bevel surfaces of steel plates and aluminum plates are mechanically ground to remove oxide scale and wiped with alcohol to remove oil stains.

[0063] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.0mm. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2.

[0064] (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used for butt welding of aluminum plate and steel plate. The assembly gap is 0mm during welding. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2. The butt connection of aluminum and steel is completed by multi-layer multi-pass welding.

[0065] The structural test results of the aluminum-steel butt joint obtained by the above welding are as follows:

[0066] (1) The joint underwent surface penetration testing and no cracks or defects were found;

[0067] (2) The nickel-based weld is mainly composed of single-phase austenitic structure, and the nickel-based weld has good bonding with the steel matrix and aluminum weld;

[0068] (3) Tensile test specimens of the joint were prepared. The test results showed that the tensile strength of the joint was 221 MPa, the elongation after fracture was 32%, and the fracture location was in the heat-affected zone of Al base material.

[0069] Example 2

[0070] Step 1: Weigh out 50% Ag powder, 20% Mo powder, 10% Cr powder, 5% B powder, 0.5% Y2O3 powder, and 0.5% CeO2 powder by mass percentage, with the remainder being Ni powder. The sum of the mass percentages of the above components is 100%. The purity of each powder is greater than 99.9%, and the particle size of each powder is 200 mesh.

[0071] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 150℃ and the heat preservation time is 40 minutes. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 40 minutes.

[0072] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, use a flux-cored wire drawing machine to encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die diameter is 2.6 mm. The flux powder filling amount in the flux-cored wire is controlled at 28 wt%.

[0073] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0074] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0075] When using the nickel-based flux-cored welding wire prepared in Example 2 for aluminum-steel butt welding, the aluminum-steel bevel shape is as follows: Figure 1-2 As shown: Asymmetrical V-shaped bevels are made, with the bevel size on the aluminum plate side being 20° and the bevel size on the steel plate side being 40°, without leaving blunt edges, and the assembly gap during welding is 0.5mm.

[0076] The method for preparing aluminum-steel butt joints using the above-mentioned flux-cored welding wire and corresponding beveling pattern is as follows (e.g. Figure 2 (as shown)

[0077] (1) Asymmetrical V-shaped bevels are made on aluminum plates and steel plates. The bevel surfaces of steel plates and aluminum plates are mechanically ground to remove oxide scale and wiped with alcohol to remove oil stains.

[0078] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 3.0mm. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2.

[0079] (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used for butt welding of aluminum plate and steel plate. The assembly gap is 0.5mm during welding. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2. The butt connection of aluminum and steel is completed by multi-layer multi-pass welding.

[0080] The structural test results of the aluminum-steel butt joint obtained by the above welding are as follows:

[0081] (1) The joint underwent surface penetration testing and no cracks or defects were found;

[0082] (2) The nickel-based weld is mainly composed of single-phase austenitic structure, and the nickel-based weld has good bonding with the steel matrix and aluminum weld;

[0083] (3) Tensile test specimens of the joint were prepared. The test results showed that the tensile strength of the joint was 201 MPa, the elongation after fracture was 35%, and the fracture location was in the heat-affected zone of the Al base material. This solved the problems of brittle phase formation and large residual stress during welding of aluminum-steel butt joints.

[0084] Figure 3 The figure shows the interface morphology between the nickel-based weld and the steel plate. As can be seen from the figure, the interface is well bonded, and the nickel-based weld is mainly composed of single-phase austenite with fine grains.

[0085] Figure 4 The tensile fracture morphology of the aluminum-steel butt joint (fracture in the heat-affected zone on the aluminum side) is shown in the figure. As can be seen from the figure, the fracture surface is mainly characterized by bremsstrahlung morphology, indicating good toughness.

[0086] Example 3

[0087] Step 1: Weigh out 45% Ag powder, 15% Mo powder, 7% Cr powder, 4% B powder, 0.2% Y2O3 powder, 0.5% CeO2 powder, and the balance is Ni powder according to the following mass percentages. The sum of the mass percentages of the above components is 100%.

[0088] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 130℃ and the heat preservation time is 35 minutes. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 35 minutes.

[0089] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, use a flux-cored wire drawing machine to encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die diameter is 2.6 mm. The flux powder filling amount in the flux-cored wire is controlled at 30 wt%.

[0090] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0091] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0092] When using the nickel-based flux-cored welding wire prepared in Example 3 for aluminum-steel butt welding, the aluminum-steel bevel shape is as follows: Figure 1-2 As shown: Asymmetrical V-shaped bevels are made, with a bevel size of 10° on the aluminum plate side and 40° on the steel plate side, without leaving blunt edges, and the assembly gap is 0.3mm during welding.

[0093] The method for preparing aluminum-steel butt joints using the above-mentioned flux-cored welding wire and corresponding beveling pattern is as follows (e.g. Figure 2 (as shown)

[0094] (1) Asymmetrical V-shaped bevels are made on aluminum plates and steel plates. The bevel surfaces of steel plates and aluminum plates are mechanically ground to remove oxide scale and wiped with alcohol to remove oil stains.

[0095] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.5mm. The welding power source is selected as CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2.

[0096] (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to surfacing and welding on the steel plate. The assembly gap is 0.3mm during welding. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2. The butt joint connection of aluminum and steel is completed by multi-layer and multi-pass welding.

[0097] The structural test results of the aluminum-steel butt joint obtained by the above welding are as follows:

[0098] (1) The joint underwent surface penetration testing and no cracks or defects were found;

[0099] (2) The nickel-based weld is mainly composed of single-phase austenitic structure, and the nickel-based weld has good bonding with the steel matrix and aluminum weld;

[0100] (3) Tensile test specimens of the joint were prepared. The test results showed that the tensile strength of the joint was 208 MPa, the elongation after fracture was 37%, and the fracture location was in the heat-affected zone of Al base material.

[0101] Example 4

[0102] Step 1: Weigh out the following components by mass percentage: 47% Ag powder, 17% Mo powder, 6% Cr powder, 6% B powder, 0.3% Y2O3 powder, 0.3% CeO2 powder, with the remainder being Ni powder. The sum of the mass percentages of the above components is 100%. The purity of each powder is greater than 99.9%, and the particle size of each powder is 300 mesh.

[0103] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 120℃ and the heat preservation time is 31min. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 31min.

[0104] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, use a flux-cored wire drawing machine to encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die diameter is 2.6 mm. The flux powder filling amount in the flux-cored wire is controlled at 31 wt%.

[0105] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0106] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0107] When using the nickel-based flux-cored welding wire prepared in Example 4 for aluminum-steel butt welding, the aluminum-steel bevel shape is as follows: Figure 1-2 As shown: Asymmetrical V-shaped bevels are made, with a bevel size of 20° on the aluminum plate side and 30° on the steel plate side, without leaving blunt edges, and the assembly gap is 0.2mm during welding.

[0108] The method for preparing aluminum-steel butt joints using the above-mentioned flux-cored welding wire and corresponding beveling pattern is as follows (e.g. Figure 2 (as shown)

[0109] (1) Asymmetrical V-shaped bevels are made on aluminum plates and steel plates. The bevel surfaces of steel plates and aluminum plates are mechanically ground to remove oxide scale and wiped with alcohol to remove oil stains.

[0110] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.8mm. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2.

[0111] (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to surfacing and welding on the steel plate. The assembly gap is 0.2mm during welding. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2. The butt joint connection of aluminum and steel is completed by multi-layer and multi-pass welding.

[0112] The structural test results of the aluminum-steel butt joint obtained by the above welding are as follows:

[0113] (1) The joint underwent surface penetration testing and no cracks or defects were found;

[0114] (2) The nickel-based weld is mainly composed of single-phase austenitic structure, and the nickel-based weld has good bonding with the steel matrix and aluminum weld;

[0115] (3) Tensile test specimens of the joint were prepared. The test results showed that the tensile strength of the joint was 227 MPa, the elongation after fracture was 35.5%, and the fracture location was in the heat-affected zone of Al base material.

[0116] Example 5

[0117] Step 1: Weigh out the following components by mass percentage: 42% Ag powder, 11% Mo powder, 9% Cr powder, 4.5% B powder, 0.2% Y₂O₃ powder, 0.35% CeO₂ powder, with the remainder being Ni powder. The sum of the mass percentages of the above components is 100%. The purity of each powder is greater than 99.9%, and the particle size of each powder is 300 mesh.

[0118] Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation to remove the water of crystallization in the powder. The heating temperature in the vacuum heating furnace is 145℃ and the heat preservation time is 39min. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 38min.

[0119] Step 3: Remove the grease from the surface of the Inconel 625 nickel strip using alcohol. Then, use a flux-cored wire drawing machine to encapsulate the flux powder prepared in Step 2 within the Inconel 625 nickel strip. The first drawing die diameter is 2.6 mm. The flux powder filling amount in the flux-cored wire is controlled at 29 wt%.

[0120] Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm.

[0121] Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

[0122] When using the nickel-based flux-cored welding wire prepared in Example 5 for aluminum-steel butt welding, the aluminum-steel bevel shape is as follows: Figure 1 As shown: Asymmetrical V-shaped bevels are made, with the bevel size on the aluminum plate side being 10° and the bevel size on the steel plate side being 30°, without leaving blunt edges, and the assembly gap during welding is 0.4mm.

[0123] The method for preparing aluminum-steel butt joints using the above-mentioned flux-cored welding wire and corresponding beveling pattern is as follows (e.g. Figure 2 (as shown)

[0124] (1) Asymmetrical V-shaped bevels are made on aluminum plates and steel plates. The bevel surfaces of steel plates and aluminum plates are mechanically ground to remove oxide scale and wiped with alcohol to remove oil stains.

[0125] (2) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.9mm. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2.

[0126] (3) The above-mentioned low-stress green and environmentally friendly aluminum-steel joint brazing material is used to surfacing and welding on the steel plate. The assembly gap is 0.4mm during welding. The welding power source is CMT power source, the welding current is 180~200A, and the shielding gas is a mixed gas. The mixed gas is composed of the following components by volume percentage: 98%Ar+2%O2. The butt joint connection of aluminum and steel is completed by multi-layer and multi-pass welding.

[0127] The structural test results of the aluminum-steel butt joint obtained by the above welding are as follows:

[0128] (1) The joint underwent surface penetration testing and no cracks or defects were found;

[0129] (2) The nickel-based weld is mainly composed of single-phase austenitic structure, and the nickel-based weld has good bonding with the steel matrix and aluminum weld;

[0130] (3) Tensile test specimens of the joint were prepared. The test results showed that the tensile strength of the joint was 203 MPa, the elongation after fracture was 39%, and the fracture location was in the heat-affected zone of Al base material.

Claims

1. A material for low-stress aluminum-steel joint brazing, characterized in that, It includes a flux core and a welding layer. The flux powder is composed of the following components by mass percentage: 40-50% Ag powder, 10-20% Mo powder, 5-10% Cr powder, 2-5% B powder, 0.5-1% Y2O3+CeO2 powder, and the balance is Ni powder. The sum of the mass percentages of the above components is 100%. The welding layer is Inconel 625 tape. The material used for low-stress aluminum-steel joint fusion brazing is flux-cored wire, and the filling amount of flux powder in the flux-cored wire is controlled at 28wt%-32wt%.

2. The material for low-stress aluminum-steel joint brazing according to claim 1, characterized in that, The purity of each powder is greater than 99.9%, and the particle size of each powder is 200-300 mesh.

3. The material for low-stress aluminum-steel joint brazing according to claim 1, characterized in that, The weld bead thickness is 0.3mm and the width is 7mm.

4. The method for preparing the material for low-stress aluminum-steel joint brazing according to claim 1, characterized in that, The specific steps are as follows: Step 1: Weigh out 40-50% Ag powder, 10-20% Mo powder, 5-10% Cr powder, 2-5% B powder, 0.5-1% Y2O3+CeO2 powder, and the balance is Ni powder, according to the following mass percentages: The sum of the mass percentages of the above components is 100%. Step 2: Place the powder weighed in Step 1 into a vacuum heating furnace for heating and heat preservation. The heating temperature in the vacuum heating furnace is 100℃~150℃, and the heat preservation time is 30min~40min. After drying, place the powder into a powder mixer for thorough mixing. The mixing time in the powder mixer is 30min~40min. Step 3: The flux-cored wire powder prepared in Step 2 is wrapped in an Inconel 625 nickel strip using a flux-cored wire drawing machine. The diameter of the first drawing die is 2.6 mm. The filling amount of flux-cored wire powder is controlled between 28 wt% and 32 wt%. Step 4: After the first drawing process is completed, the die hole diameter is changed to 2.3mm, 2.0mm, 1.8mm, 1.6mm, 1.4mm and 1.2mm in sequence for drawing. The final diameter of the flux-cored welding wire is 1.2mm. Step 5: After the flux-cored welding wire is drawn, it is wound onto the welding wire spool by a wire winding machine and finally sealed in a flux-cored welding wire vacuum packaging bag for later use.

5. A method for preparing aluminum-steel butt joints using the low-stress aluminum-steel joint brazing material as described in any one of claims 1-3, characterized in that, Specifically: (1) Asymmetrical V-shaped bevels are made on aluminum and steel plates; Specifically, the asymmetrical V-shaped bevels on the aluminum and steel plates are as follows: the bevel angle on one side of the aluminum plate is 15±5°, and the bevel angle on the other side of the steel plate is 35±5°, without leaving a blunt edge. (2) The low-stress aluminum-steel joint brazing material as described in any one of claims 1-3 is used to perform surfacing welding on the steel plate. The thickness of the surfacing layer is 2.0mm~3.0mm. The welding power source is a CMT power source with a welding current of 180A~200A. The shielding gas is a mixed gas, which is composed of the following components by volume percentage: 98%Ar+2%O2. (3) The low-stress aluminum-steel joint brazing material as described in any one of claims 1-3 is used for butt welding of aluminum plates and steel plates. The assembly gap during welding is 0mm~0.5mm. The welding power source is a CMT power source with a welding current of 180A~200A. The shielding gas is a mixed gas, which is composed of the following components by volume percentage: 98%Ar+2%O2. The butt connection of aluminum and steel is completed by multi-layer multi-pass welding.

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