Preparation method and brazing method of silicon carbide reinforced magnesium-zinc brazing filler metal

Abstract

The invention discloses a preparation method of silicon carbide reinforced magnesium-zinc brazing filler metal and a brazing method, belongs to the technical field of magnesium alloy welding materials, solves the technical problem of insufficient welding strength of the magnesium alloy brazing filler metal, and adopts the technical scheme that clean magnesium foils and zinc foils are sequentially staggered and stacked from bottom to top in a mode of one layer of zinc foil and one layer of magnesium foil, a silicon carbide-alcohol solution is evenly sprayed and deposited on the surface of each layer of magnesium foil or zinc foil, then the magnesium foil or zinc foil is put into a resistance furnace to be heated, a silicon carbide reinforced magnesium-zinc brazing filler metal blank is prepared and then fed into a cold rolling unit to be rolled, the silicon carbide reinforced magnesium-zinc brazing filler metal with the thickness not larger than 500 micrometers is prepared and used for magnesium alloy material brazing, the final brazing temperature is 380-420 DEG C, and the final brazing time is 2-3 hours. The heat preservation time is 30 to 120 minutes. The preparation process is simple, silicon carbide is uniformly distributed among layers and is not obviously agglomerated, an eutectic structure at a brazing seam can be obviously refined, and the shearing strength of a welded joint is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of magnesium alloy welding materials, and particularly relates to a preparation method and a brazing method of a silicon carbide reinforced magnesium-zinc brazing filler metal. Background Art

[0002] Magnesium alloys have the advantages of low density, high specific strength and stiffness, good electrical and thermal conductivity, excellent damping and shock absorption performance, good electromagnetic shielding effect, good mechanical processing performance, and easy recycling. As the lightest metal structural material applicable in industry, it has important application value and broad application prospects in the fields of aerospace, national defense, automobile manufacturing, and electronic products. Due to the demand for lightweight products, there is an urgent need to braze some widely used magnesium alloys, which requires research and development of the brazing filler metals required for magnesium alloy brazing.

[0003] At present, the performance of the joints brazed with magnesium alloy brazing filler metals is poor, far lower than the performance of the magnesium alloy matrix material (strength greater than 200MPa). In addition, in the prior art, the strength and heat resistance of magnesium alloy brazing filler metals can be improved by adding rare earth elements to the magnesium alloy brazing filler metal matrix. For example, patent document with application number 201110205638.5 discloses a Mg-Zn-Al-Er magnesium alloy brazing filler metal with added rare earth element Er, and the welding strength can reach 49.2~58.9 MPa. However, rare earth elements are expensive, which limits the application of brazing filler metals; patent document with application number 202210278121.7 discloses a silicon carbide particle-reinforced magnesium alloy brazing filler metal and its preparation method and application, and for the first time proposes to use silicon carbide as a reinforcement to improve the brazing strength of magnesium alloys. However, the brazing shear strength of this brazing filler metal is only 30~36MPa, and the reinforcing particles (silicon carbide, titanium particles, aluminum oxide, boron nitride, etc.) added during the smelting process are very likely to agglomerate, resulting in a decrease in brazing strength, and the particle-reinforced magnesium alloy brazing filler metal prepared by smelting is difficult to thin in secondary processing, making it difficult to achieve industrial application. Summary of the invention

[0004] The main purpose of the present invention is to overcome the deficiencies in the prior art and solve the technical problem of insufficient welding strength of magnesium alloy brazing filler metal. The present invention provides a preparation method and brazing method of silicon carbide reinforced magnesium zinc brazing filler metal. The melting temperature range of silicon carbide reinforced magnesium zinc brazing filler metal is 330℃~380℃, and the welding temperature range is 370℃~420℃, which is suitable for brazing magnesium zinc alloy with a solidus temperature above 420℃.

[0005] The design concept of the present invention is as follows: magnesium foil and zinc foil are alternately stacked from bottom to top in the form of a layer of zinc foil and a layer of magnesium foil, and silicon carbide particles are introduced on the surface of each layer by a spray deposition method, and then a silicon carbide reinforced magnesium-zinc solder with a thickness of less than 500 μm is prepared by a composite rolling method. Silicon carbide is evenly distributed between layers without obvious agglomeration, and the eutectic structure at the brazing seam can be significantly refined. The method has a simple process and does not require secondary processing before brazing. The brazing temperature of the solder is appropriate, the process is simple, and the brazing performance is significantly improved, and the industrial production of magnesium alloy solder can be realized.

[0006] The present invention is achieved through the following technical solutions: A method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.03-0.1 mm into 6-10 pieces, and cut the zinc foil with a thickness of 0.03-0.07 mm into 7-11 pieces, clean them with ultrasonic wave, blow dry them with cold wind, and keep them for later use; S2, prepare silicon carbide-alcohol solution, the particle size of silicon carbide particles is 1~10μm, the mass fraction of silicon carbide particles in alcohol is 0.1%~10%, stir evenly and keep it for use in the next step; S3, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in the manner of a layer of zinc foil and a layer of magnesium foil, with the outermost layer being zinc foil, and spraying and depositing the silicon carbide-alcohol solution prepared in step S2 evenly on the surface of each layer of magnesium foil or zinc foil, and then placing them in a resistance furnace for heating at a heating temperature of 250° C. to 320° C. for a holding time of 5 to 10 minutes, to obtain a silicon carbide reinforced magnesium-zinc solder blank; S3, rolling forming: the silicon carbide reinforced magnesium-zinc solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 15% to 30% per pass and a total reduction of 50% to 70%, to obtain a silicon carbide reinforced magnesium-zinc solder with a thickness of no more than 500 μm.

[0007] Preferably, the number of cross-laminated magnesium foil layers is 8 to 10, the number of zinc foil layers is 9 to 11, the thickness of each magnesium foil layer is 0.05 to 0.1 mm, the thickness of each zinc foil layer is 0.03 to 0.05 mm, the particle size of silicon carbide particles is 3 to 8 μm, and the mass fraction of silicon carbide particles in alcohol is 0.1 to 9%.

[0008] Preferably, the melting temperature range of the prepared silicon carbide reinforced Mg-Zn brazing filler metal is 330°C-380°C, and the welding temperature range is 370°C-420°C, and it is used for brazing Mg-Zn alloys with a solidus temperature above 420°C.

[0009] A brazing method for silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. First, clean the surface of the magnesium alloy to be brazed to remove impurities, oil stains and oxide film on the surface; then use 80 and 600 mesh metallographic sandpaper to grind the surface to be brazed smooth; finally, rinse the magnesium alloy to be brazed and the silicon carbide reinforced magnesium-zinc brazing material with alcohol and blow dry with cold air, and leave them for later use; S2, placing the cleaned silicon carbide reinforced magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold. In order to improve the efficiency of diffusion of the silicon carbide reinforced magnesium-zinc brazing filler metal to form a eutectic structure and the connection accuracy, a constant vertical pressure of 1-5 MPa is applied to the brazing mold; S3. Place the brazing mold assembled in step S2 as a whole in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 0-10Pa. Then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure. Finally, a step-by-step heating method is used to promote the formation of eutectic structure. The heating rate of the vacuum hot pressing welding furnace is set to 1°C / min-10°C / min, and the temperature is kept for 5-10 minutes every time the temperature is increased by 30°C-50°C. The final brazing temperature is 370-420°C, and the insulation time is 30-120 minutes. Cool to room temperature to complete the brazing of magnesium alloy materials.

[0010] Preferably, in step S2, the brazing mold applies a constant vertical pressure of 2-3 MPa.

[0011] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses a spray deposition method to introduce silicon carbide particles on the surface of magnesium foil and zinc foil. The silicon carbide is evenly distributed between the layers without obvious agglomeration, and can significantly refine the eutectic structure at the brazing seam. When the brazing filler metal is used to weld magnesium-zinc alloy, no brazing flux is required, and the shear strength of the welded joint is between 87 and 100 MPa; The melting temperature of the magnesium alloy brazing filler metal of the present invention is 330-380°C, the brazing temperature is 370-420°C, the brazing filler metal thickness is less than 500 μm, and no secondary processing and thinning is required; the brazing filler metal is prepared by a rolling method with mature technology, which is convenient for the industrial transformation of the enterprise, and does not require the purchase of new equipment, and mass production can be realized simply and conveniently. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a low-magnification OM photograph of the silicon carbide reinforced magnesium-zinc solder prepared in Example 1; Figure 2 This is a low-magnification OM photograph of magnesium alloy brazing using the silicon carbide reinforced magnesium-zinc brazing filler metal prepared in Example 1. DETAILED DESCRIPTION

[0013] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. Example 1

[0014] A method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.1 mm into 10 pieces, and cut the zinc foil with a thickness of 0.03 mm into 11 pieces, clean them by ultrasonic wave, blow dry them with cold wind and keep them for later use; wherein the purity of the magnesium foil and the zinc foil is above 99.9%; S2, prepare a silicon carbide-alcohol solution, the particle size of the silicon carbide particles is 5 μm, the mass fraction of the silicon carbide particles in the alcohol is 0.1%, stir evenly and keep it for use in the next step; S3, taking the magnesium foil and zinc foil prepared in step S1, stacking them alternately from bottom to top in the manner of a layer of zinc foil and a layer of magnesium foil, with the outermost layer being zinc foil, and spraying and depositing the silicon carbide-alcohol solution prepared in step S2 evenly on the surface of each layer of magnesium foil or zinc foil, and then placing them in a resistance furnace for heating at a heating temperature of 300° C. and a holding time of 10 min, to obtain a silicon carbide reinforced magnesium-zinc solder blank; S3, rolling forming: the silicon carbide reinforced magnesium zinc solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 26% per pass and a total reduction of 62% to obtain a silicon carbide reinforced magnesium zinc solder with a thickness of 493 μm. The microstructure of the solder is as follows: Figure 1 The melting temperature range of the prepared silicon carbide reinforced magnesium-zinc brazing filler metal is 330℃~380℃, and the welding temperature range is 370~420℃, which is used for brazing magnesium-zinc alloys with solidus temperature above 420℃.

[0015] A brazing method for silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. The size of the magnesium alloy to be brazed in this embodiment 1 is 50 mm in length × 30 mm in width × 5.7 mm in thickness. First, the surface to be brazed of the magnesium alloy to be brazed is cleaned to remove impurities, oil stains and oxide films on the surface; then, the surface to be brazed is polished smooth using 80 and 600 mesh metallographic sandpapers in turn; finally, the magnesium alloy to be brazed and the silicon carbide reinforced magnesium-zinc brazing filler metal are rinsed with alcohol and blown dry with cold air for later use; S2, placing the cleaned silicon carbide reinforced magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 2 MPa to the brazing mold; S3, the brazing mold assembled in step S2 is placed in a vacuum hot pressing welding furnace. First, the vacuum hot pressing welding furnace is evacuated to a vacuum degree of 10Pa; then, argon gas is filled into the vacuum hot pressing welding furnace for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, the vacuum hot pressing welding furnace is set to have a heating rate of 10°C / min, and the temperature is kept for 5 minutes every time the temperature is increased by 50°C. The final brazing temperature is 390°C, the temperature is kept for 60 minutes, and the brazing is completed after cooling to room temperature. The brazing of the magnesium alloy material is completed, and the microstructure of the brazing seam is as follows: Figure 2 As shown in the figure, the magnesium-zinc alloy joint obtained by brazing is well connected, and metallographic observation shows no obvious defects such as cracks and pores. The metallurgical bonding of the welding interface is tight, and the room temperature shear strength is 87.3MPa. Example 2

[0016] A method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.1 mm into 10 pieces, and cut the zinc foil with a thickness of 0.03 mm into 11 pieces, clean them by ultrasonic wave, blow dry them with cold wind and keep them for later use; wherein the purity of the magnesium foil and the zinc foil is above 99.9%; S2, prepare a silicon carbide-alcohol solution, the particle size of the silicon carbide particles is 5 μm, the mass fraction of the silicon carbide particles in the alcohol is 3%, stir evenly and keep it for use in the next step; S3, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in the manner of a layer of zinc foil and a layer of magnesium foil, with the outermost layer being zinc foil, and spraying and depositing the silicon carbide-alcohol solution prepared in step S2 evenly on the surface of each layer of magnesium foil or zinc foil, and then putting them in a resistance furnace for heating at a heating temperature of 310° C. and a holding time of 8 min, to obtain a silicon carbide reinforced magnesium-zinc solder blank; S3, rolling forming: the silicon carbide reinforced magnesium zinc solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 30% per pass and a total reduction of 70%, to obtain a silicon carbide reinforced magnesium zinc solder with a thickness of 480 μm.

[0017] A brazing method for silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. The size of the magnesium alloy to be brazed in Example 2 is 50 mm in length × 30 mm in width × 5.7 mm in thickness. First, the surface to be brazed of the magnesium alloy to be brazed is cleaned to remove impurities, oil stains and oxide films on the surface; then, the surface to be brazed is polished smooth using 80 and 600 mesh metallographic sandpapers in turn; finally, the magnesium alloy to be brazed and the silicon carbide reinforced magnesium-zinc brazing filler metal are rinsed with alcohol and blown dry with cold air for later use; S2, placing the cleaned silicon carbide reinforced magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 2 MPa to the brazing mold; S3. Place the brazing mold assembled in step S2 as a whole in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 9Pa; then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, set the heating rate of the vacuum hot pressing welding furnace to 9°C / min, keep warm for 5 minutes every time the temperature rises by 50°C, the final brazing temperature is 390°C, the insulation time is 60 minutes, and the brazing is completed to room temperature. The brazing of the magnesium alloy material is completed, and the magnesium-zinc alloy joint obtained by brazing is well connected, and the room temperature shear strength is 95.6MPa. Example 3

[0018] A method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. Cut the magnesium foil with a thickness of 0.1 mm into 10 pieces, and cut the zinc foil with a thickness of 0.03 mm into 11 pieces, clean them by ultrasonic wave, blow dry them with cold wind and keep them for later use; wherein the purity of the magnesium foil and the zinc foil is above 99.9%; S2. Prepare a silicon carbide-alcohol solution, wherein the particle size of the silicon carbide particles is 5 μm and the mass fraction of the silicon carbide particles in the alcohol is 9%. Stir evenly and keep it for use in the next step; S3, taking the magnesium foil and zinc foil prepared in step S1, stacking them alternately from bottom to top in the manner of a layer of zinc foil and a layer of magnesium foil, with the outermost layer being zinc foil, and spraying and depositing the silicon carbide-alcohol solution prepared in step S2 evenly on the surface of each layer of magnesium foil or zinc foil, and then placing them in a resistance furnace for heating at a heating temperature of 300° C. and a holding time of 10 min, to obtain a silicon carbide reinforced magnesium-zinc solder blank; S3, rolling forming: the silicon carbide reinforced magnesium zinc solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 22% per pass and a total reduction of 56%, to obtain a silicon carbide reinforced magnesium zinc solder with a thickness of 495 μm.

[0019] A brazing method for silicon carbide reinforced magnesium-zinc brazing filler metal comprises the following steps: S1. The size of the magnesium alloy to be brazed in Example 3 is 50 mm in length × 30 mm in width × 5.7 mm in thickness. First, the surface to be brazed of the magnesium alloy to be brazed is cleaned to remove impurities, oil stains and oxide films on the surface; then, the surface to be brazed is polished smooth using 80 and 600 mesh metallographic sandpapers in turn; finally, the magnesium alloy to be brazed and the silicon carbide reinforced magnesium-zinc brazing filler metal are rinsed with alcohol and blown dry with cold air for later use; S2, placing the cleaned silicon carbide reinforced magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy to be brazed, and then placing it in a brazing mold, and applying a constant vertical pressure of 2 MPa to the brazing mold; S3. Place the brazing mold assembled in step S2 as a whole in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 10Pa; then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, set the vacuum hot pressing welding furnace to a heating rate of 8°C / min, and keep warm for 5 minutes every time the temperature rises by 50°C. The final brazing temperature is 390°C, the insulation time is 60 minutes, and the brazing is completed to room temperature. The brazing of the magnesium alloy material is completed, and the brazing of the magnesium-zinc alloy joint is well connected, and the room temperature shear strength is 99.3MPa.

[0020] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal, characterized in that: The following steps are involved: S1. Cut the magnesium foil with a thickness of 0.03-0.1 mm into 6-10 pieces, and cut the zinc foil with a thickness of 0.03-0.07 mm into 7-11 pieces, clean them with ultrasonic wave, blow dry them with cold wind, and keep them for later use; S2. Prepare a silicon carbide-alcohol solution, wherein the particle size of the silicon carbide particles is 1-10 μm, and the mass fraction of the silicon carbide particles in the alcohol is 0.1%-10%. Stir evenly and keep it for use in the next step; S3, taking the magnesium foil and zinc foil prepared in step S1 and stacking them alternately from bottom to top in the manner of a layer of zinc foil and a layer of magnesium foil, with the outermost layer being zinc foil, and spraying and depositing the silicon carbide-alcohol solution prepared in step S2 evenly on the surface of each layer of magnesium foil or zinc foil, and then placing them in a resistance furnace for heating at a heating temperature of 250° C. to 320° C. for a holding time of 5 to 10 minutes, to obtain a silicon carbide reinforced magnesium-zinc solder blank; S3, rolling forming: the silicon carbide reinforced magnesium-zinc solder blank prepared in step S2 is sent to a cold rolling unit, with a reduction of 15% to 30% per pass and a total reduction of 50% to 70%, to obtain a silicon carbide reinforced magnesium-zinc solder with a thickness of no more than 500 μm.

2. The method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal according to claim 1, characterized in that: The number of cross-laminated magnesium foil layers is 8 to 10, the number of zinc foil layers is 9 to 11, the thickness of each magnesium foil layer is 0.05 to 0.1 mm, the thickness of each zinc foil layer is 0.03 to 0.05 mm, the particle size of silicon carbide particles is 3 to 8 μm, and the mass fraction of silicon carbide particles in alcohol is 0.1 to 9%.

3. The method for preparing a silicon carbide reinforced magnesium-zinc brazing filler metal according to claim 1, characterized in that: The melting temperature range of the prepared silicon carbide reinforced magnesium-zinc brazing filler metal is 330°C-380°C, and the welding temperature range is 370°C-420°C. It is used for brazing magnesium-zinc alloys with a solidus temperature above 420°C.

4. A brazing method using the silicon carbide reinforced magnesium zinc brazing filler metal prepared by the preparation method according to claim 1, characterized in that: The following steps are involved: S1. First, clean the surface of the magnesium alloy to be brazed to remove impurities, oil stains and oxide film on the surface; then use 80 and 600 mesh metallographic sandpaper to grind the surface to be brazed smooth; finally, rinse the magnesium alloy to be brazed and the silicon carbide reinforced magnesium-zinc brazing material with alcohol and blow dry with cold air, and leave them for later use; S2, placing the cleaned silicon carbide reinforced magnesium-zinc brazing filler metal between the surfaces to be brazed of the magnesium alloy, and then placing it in a brazing mold, and applying a constant vertical pressure of 1-5 MPa to the brazing mold; S3. Place the brazing mold assembled in step S2 as a whole in a vacuum hot pressing welding furnace. First, evacuate the vacuum hot pressing welding furnace to a vacuum degree of 0-10Pa; then, fill the vacuum hot pressing welding furnace with argon gas for protection, and the argon gas pressure is not less than the standard atmospheric pressure; finally, set the heating rate of the vacuum hot pressing welding furnace to 1°C / min-10°C / min, and keep warm for 5-10 minutes every time the temperature rises by 30°C-50°C. The final brazing temperature is 370-420°C, and the insulation time is 30-120 minutes. Cool to room temperature to complete the brazing of the magnesium alloy material.

5. A brazing method for silicon carbide reinforced magnesium zinc brazing filler metal according to claim 4, characterized in that: In step S2, the brazing mold applies a constant vertical pressure of 2-3 MPa.

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