A diffusion welding method for magnesium alloys and a welded joint

Abstract

This invention provides a diffusion welding method and weld joint for magnesium alloys, relating to the field of welding technology. The diffusion welding method includes: Step S1, depositing silver on the surface of the magnesium alloy base material to be welded using magnetron sputtering to form a silver film; Step S2, coating the silver film with a nano-metal particle slurry and drying it to form a nano-metal particle layer, obtaining a workpiece to be welded; Step S3, assembling two workpieces to be welded so that the nano-metal particle layers adhere, obtaining an assembly; Step S4, performing pulsed current-assisted diffusion welding on the assembly under vacuum conditions or an inert gas protective atmosphere to obtain a weld joint. The diffusion welding method for magnesium alloys provided by this invention can avoid defects such as grain growth and large deformation of the base material, and also yields a weld joint with high strength.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically, to a diffusion welding method for magnesium alloys and a welded joint. Background Technology

[0002] Magnesium alloys, as one of the lightest engineering structural metals available today, possess high specific strength, excellent damping and vibration reduction performance, electromagnetic shielding capabilities, and recyclability, making them ideal materials for lightweight upgrades in the automotive, aerospace, and 3C electronics industries. In the automotive industry, they can be used to manufacture components such as dashboard brackets and wheel hubs to reduce vehicle weight and improve energy efficiency; in the aerospace field, they can meet the stringent weight reduction requirements for aircraft seat frames and drone structural components; and in 3C electronic products, they enable the dual goals of thinner and lighter casings and stronger structures.

[0003] Currently, welding methods for magnesium alloys include fusion welding, brazing, and traditional thermo-pressure diffusion welding. Fusion welding requires high-temperature melting of the base material. Magnesium's high chemical reactivity easily triggers severe oxidation, and grain coarsening is prone to occur in the joint area, leading to a significant loss of strength, while defects such as porosity and hot cracking are frequent. Although brazing can reduce heat input, existing brazing filler metals often have poor compatibility with the magnesium matrix, and brittle intermetallic compounds easily form at the interface, resulting in insufficient joint strength and deteriorated corrosion resistance. Traditional thermo-pressure diffusion welding requires high-temperature and high-pressure conditions, which easily leads to defects such as grain growth and deformation in the base material. Moreover, an oxide film easily forms on the surface of magnesium alloys during welding, resulting in low joint strength. Summary of the Invention

[0004] The problem solved by this invention is that, for magnesium alloy welding, traditional hot-press diffusion welding needs to be carried out under high temperature and high pressure conditions, which can easily lead to defects such as grain growth and deformation of the base material. Moreover, an oxide film is easily formed on the surface of magnesium alloy during the welding process, which can easily lead to low strength of the weld joint.

[0005] To address the above problems, this invention provides a diffusion welding method for magnesium alloys, comprising:

[0006] Step S1: Deposit silver on the surface of the magnesium alloy base material to be soldered by magnetron sputtering to form a silver film on the surface of the magnesium alloy base material to be soldered.

[0007] Step S2: Coat the silver film with a nano-metal particle paste and dry it to form a nano-metal particle layer, thereby obtaining the workpiece to be soldered; wherein, the nano-metal particle paste is prepared from nano-silver particles, nano-copper particles and a binder; the mass ratio of the nano-silver particles, the nano-copper particles and the binder in the nano-metal particle paste is (70 to 90): (3 to 5): (10 to 45);

[0008] Step S3: Assemble the two parts to be welded so that the nano-metal particle layers adhere to each other to obtain an assembly.

[0009] Step S4: Under vacuum conditions or an inert gas protective atmosphere, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint.

[0010] Optionally, in step S1, the thickness of the silver film is 1 μm to 5 μm.

[0011] Optionally, in step S2, the adhesive includes at least polyethylene glycol 400.

[0012] Optionally, in step S2, the particle size of the silver nanoparticles is 30 nm to 150 nm, and the particle size of the copper nanoparticles is 20 nm to 80 nm.

[0013] Optionally, in step S2, the thickness of the nano-metal particle layer is 5 μm to 50 μm.

[0014] Optionally, in step S2, the drying process is carried out at a temperature of 40°C to 60°C for 1 hour to 12 hours.

[0015] Optionally, in step S4, the welding temperature of the pulse current assisted diffusion welding is 300°C to 450°C, the pressure is 3MPa to 20MPa, and the time is 15min to 60min.

[0016] Optionally, in step S4, during the pulsed current assisted diffusion welding process, the heating rate is from 50°C / min to 200°C / min.

[0017] Optionally, in step S4, the frequency of the pulse current used in the pulse current assisted diffusion welding process is 20kHz to 40kHz, and the duty cycle is 82% to 84%.

[0018] The present invention also provides a welded joint, which is made by diffusion welding of magnesium alloy as described above.

[0019] Compared with related technologies, this invention avoids the oxidation problem of the magnesium alloy surface during welding by depositing a silver film on the surface to be welded on the magnesium alloy base material. This prevents the oxide film on the magnesium alloy surface from hindering the metallurgical bonding of the weld joint, thus improving the strength of the weld joint. Furthermore, the nano-metal particles in the nano-metal particle layer consist mainly of nano-silver particles and a small amount of nano-copper particles. The coupling of the nano-silver particles with the silver film transforms the traditional "magnesium-magnesium connection" at the magnesium alloy interface into a "silver-silver connection," while the nano-copper particles provide dispersion strengthening, further enhancing the strength of the weld joint. Because the nano-metal particles in the nano-metal particle layer have a high specific surface area, high surface energy, and low sintering activation energy, the heat input required for diffusion welding can be significantly reduced. In addition, the pulsed current assisted diffusion welding method applies pressure and pulsed current to the assembly. The main heat source of pulsed current assisted diffusion welding is Joule heat concentrated in and around the weld, which has a fast heating rate. At the same time, the electroplastic, electrodiffusion and discharge plasma effects work together to activate the interface to be welded. It can achieve good metallurgical bonding of the welded joint at a lower welding temperature, lower pressure and shorter time, which helps to avoid defects such as grain growth and large deformation of the base material. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the diffusion welding method for magnesium alloys in an embodiment of the present invention. Detailed Implementation

[0021] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Although some embodiments of the present invention are shown in the drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0022] Unless otherwise defined, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0023] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to"; the term "based on" means "at least partially based on"; the term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments"; and the term "optionally" means "optional embodiments". Definitions of other terms will be given in the following description. It should be noted that the concepts of "first," "second," etc., mentioned in this invention are used to distinguish different objects, not to describe a specific order or hierarchy. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0024] like Figure 1 As shown in the embodiment of the present invention, a diffusion welding method for magnesium alloys includes:

[0025] Step S1: Deposit silver on the surface of the magnesium alloy base material to be soldered by magnetron sputtering to form a silver film on the surface of the magnesium alloy base material to be soldered.

[0026] Step S2: Coat the silver film with a nano-metal particle paste and dry it to form a nano-metal particle layer, thereby obtaining the workpiece to be soldered; wherein, the nano-metal particle paste is prepared from nano-silver particles, nano-copper particles and a binder; the mass ratio of the nano-silver particles, the nano-copper particles and the binder in the nano-metal particle paste is (70 to 90): (3 to 5): (10 to 45);

[0027] Step S3: Assemble the two parts to be welded so that the nano-metal particle layers adhere to each other to obtain an assembly.

[0028] Step S4: Under vacuum conditions or an inert gas protective atmosphere, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint.

[0029] This invention avoids oxidation of the magnesium alloy surface during welding by depositing a thin silver film on the surface to be welded, thus preventing the oxide film on the magnesium alloy surface from hindering the metallurgical bonding of the weld joint and improving its strength. Furthermore, the nano-metal particles in the nano-metal particle layer consist mainly of nano-silver particles and a small amount of nano-copper particles. The coupling between the nano-silver particles and the silver film transforms the traditional "magnesium-magnesium connection" at the magnesium alloy interface into a "silver-silver connection," while the nano-copper particles provide dispersion strengthening, further enhancing the weld joint's strength. Because the nano-metal particles in the nano-metal particle layer have a high specific surface area, high surface energy, and low sintering activation energy, the heat input required for diffusion welding can be significantly reduced. In addition, the pulsed current assisted diffusion welding method applies pressure and pulsed current to the assembly. The main heat source of pulsed current assisted diffusion welding is Joule heat concentrated in and around the weld, which has a fast heating rate. At the same time, the electroplastic, electrodiffusion and discharge plasma effects work together to activate the interface to be welded. It can achieve good metallurgical bonding of the welded joint at a lower welding temperature, lower pressure and shorter time, which helps to avoid defects such as grain growth and large deformation of the base material.

[0030] In some embodiments of the present invention, in step S1, the thickness of the silver film is 1 μm to 5 μm.

[0031] In some embodiments of the present invention, in step S2, the adhesive includes at least polyethylene glycol 400; preferably, the adhesive includes polyethylene glycol 400 and ethyl cellulose.

[0032] In some embodiments of the present invention, in step S2, the particle size of the silver nanoparticles is 30 nm to 150 nm, and the particle size of the copper nanoparticles is 20 nm to 80 nm. In this embodiment, because the added copper has a small particle size and is added in small amounts, it can prevent the silver nanoparticles from agglomerating, promote the densification of the welding interface, and help to further improve the strength of the welded joint.

[0033] In some embodiments of the present invention, in step S2, the thickness of the nano-metal particle layer is 5 μm to 50 μm.

[0034] In some embodiments of the present invention, in step S2, the drying process is carried out at a temperature of 40°C to 60°C for a time of 1 hour to 12 hours.

[0035] In some embodiments of the present invention, in step S4, the welding temperature of the pulse current assisted diffusion welding is 300°C to 450°C, the pressure is 3MPa to 20MPa, and the time is 15min to 60min.

[0036] In some embodiments of the present invention, in step S4, during the pulsed current assisted diffusion welding process, the heating rate is 50°C / min to 200°C / min.

[0037] In some embodiments of the present invention, in step S4, the frequency of the pulse current used in the pulse current assisted diffusion welding process is 20kHz to 40kHz, and the duty cycle is 82% to 84%.

[0038] This invention also provides a welded joint, which is made using the diffusion welding method for magnesium alloys as described above.

[0039] The present invention will be further described below with reference to specific embodiments.

[0040] Example 1

[0041] A1. Use 240 grit, 600 grit, 1000 grit, 1500 grit and 1500 grit sandpaper to grind the AZ31B magnesium alloy base material in sequence, then polish it, and then place it in anhydrous ethanol for ultrasonic cleaning for 5 minutes, blow dry and set aside.

[0042] A2. Silver is deposited on the solderable surface of the AZ31B magnesium alloy base material by magnetron sputtering to form a silver film on the solderable surface of the AZ31B magnesium alloy base material; wherein the thickness of the silver film is 3μm.

[0043] A3. Coat the silver film with a nano-metal particle slurry and dry it to form a nano-metal particle layer, thus obtaining the workpiece to be welded; wherein, the nano-metal particle slurry is prepared from nano-silver particles, nano-copper particles and a binder; the mass ratio of the nano-silver particles, the nano-copper particles and the binder in the nano-metal particle slurry is 75:5:20; the particle size of the nano-silver particles is 80nm and the particle size of the nano-copper particles is 60nm; the binder is composed of polyethylene glycol 400 and ethyl cellulose in a mass ratio of 95:5; the drying temperature is 50℃ and the time is 6.5h; the thickness of the nano-metal particle layer is 25μm.

[0044] A4. Assemble the two parts to be welded so that the nano-metal particle layers adhere to each other to obtain an assembly;

[0045] A5. Under vacuum conditions, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint; wherein the welding temperature of the pulsed current assisted diffusion welding is 300℃, the pressure is 3MPa, the time is 45min, the heating rate during the pulsed current assisted diffusion welding process is 120℃ / min, and the frequency of the pulsed current used in the pulsed current assisted diffusion welding process is 30kHz with a duty cycle of 83.3%.

[0046] Example 2

[0047] The difference from Example 1 is that the welding temperature of the pulse current assisted diffusion welding is 450°C.

[0048] Example 3

[0049] The difference from Example 1 is that in step A3, the adhesive is polyethylene glycol 400.

[0050] Example 4

[0051] A1. Use 240 grit, 600 grit, 1000 grit, 1500 grit and 1500 grit sandpaper to grind the AZ31B magnesium alloy base material in sequence, then polish it, and then place it in anhydrous ethanol for ultrasonic cleaning for 5 minutes, blow dry and set aside.

[0052] A2. Silver is deposited on the solderable surface of the AZ31B magnesium alloy base material by magnetron sputtering to form a silver film on the solderable surface of the AZ31B magnesium alloy base material; wherein the thickness of the silver film is 5μm.

[0053] A3. Coat the silver film with a nano-metal particle slurry and dry it to form a nano-metal particle layer, thus obtaining the workpiece to be welded; wherein, the nano-metal particle slurry is prepared from nano-silver particles, nano-copper particles and a binder; the mass ratio of the nano-silver particles, the nano-copper particles and the binder in the nano-metal particle slurry is 75:5:20; the particle size of the nano-silver particles is 60nm and the particle size of the nano-copper particles is 20nm; the binder is composed of polyethylene glycol 400 and ethyl cellulose in a mass ratio of 95:5; the drying temperature is 60℃ and the time is 4h; the thickness of the nano-metal particle layer is 50μm.

[0054] A4. Assemble the two parts to be welded so that the nano-metal particle layers adhere to each other to obtain an assembly;

[0055] A5. Under vacuum conditions, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint; wherein the welding temperature of the pulsed current assisted diffusion welding is 365℃, the pressure is 3MPa, the time is 35min, the heating rate during the pulsed current assisted diffusion welding process is 50℃ / min, and the frequency of the pulsed current used in the pulsed current assisted diffusion welding process is 30kHz with a duty cycle of 83.3%.

[0056] Comparative Example 1 (without the introduction of a layer of nano-metal particles)

[0057] The AZ31B magnesium alloy base material was successively polished with 240 grit, 600 grit, 1000 grit, 1500 grit and 1500 grit sandpaper, then polished, and then ultrasonically cleaned in anhydrous ethanol for 5 minutes. After drying, it was ready for use.

[0058] Silver is deposited on the surface of the AZ31B magnesium alloy substrate to be soldered by magnetron sputtering to form a silver film on the surface of the AZ31B magnesium alloy substrate to be soldered, thereby obtaining the workpiece to be soldered; wherein the thickness of the silver film is 3μm.

[0059] The two parts to be welded are assembled so that the silver film adheres to each other, thus obtaining an assembly.

[0060] Under vacuum conditions, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint; wherein the welding temperature of the pulsed current assisted diffusion welding is 450℃, the pressure is 3MPa, the time is 45min, the heating rate during the pulsed current assisted diffusion welding process is 120℃ / min, and the frequency of the pulsed current used in the pulsed current assisted diffusion welding process is 30kHz with a duty cycle of 83.3%.

[0061] Comparative Example 2 (without silver film and nano-metal particle layer)

[0062] The AZ31B magnesium alloy base material was successively polished with 240 grit, 600 grit, 1000 grit, 1500 grit and 1500 grit sandpaper, then polished, and then ultrasonically cleaned in anhydrous ethanol for 5 minutes. After drying, it was ready for use.

[0063] Two AZ31B magnesium alloy base materials are assembled so that their polished surfaces fit together to obtain an assembly.

[0064] Under vacuum conditions, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint; wherein the welding temperature of the pulsed current assisted diffusion welding is 450℃, the pressure is 3MPa, the time is 45min, the heating rate during the pulsed current assisted diffusion welding process is 120℃ / min, and the frequency of the pulsed current used in the pulsed current assisted diffusion welding process is 30kHz with a duty cycle of 83.3%.

[0065] Comparative Example 3 (No copper nanoparticles were introduced into the nano-metal particle layer)

[0066] Compared with Example 2, step A3 is as follows: coating the silver film with a nano-metal particle slurry and drying it to form a nano-metal particle layer, thereby obtaining the workpiece to be welded; wherein, the nano-metal particle slurry is prepared from nano-silver particles and a binder; the mass ratio of the nano-silver particles to the binder in the nano-metal particle slurry is 80:20; the particle size of the nano-silver particles is 60 nm; the binder is composed of polyethylene glycol 400 and ethyl cellulose in a mass ratio of 95:5; the drying temperature is 60°C and the time is 4 h; the thickness of the nano-metal particle layer is 50 μm.

[0067] Effect Example

[0068] The shear strength and deformation rate of the welded joints obtained in Examples 1 to 2 and Comparative Examples 1 to 3 were tested, and the results are shown in Table 1. As can be seen from Table 1, compared with Comparative Example 1, the welded joint obtained in Example 1 has higher shear strength and lower deformation rate. Furthermore, the welding temperature in Example 1 was lower. Compared with Comparative Examples 1 to 3, the welded joint obtained in Example 2 has higher shear strength and lower deformation rate.

[0069] It should be noted that in Comparative Example 1, effective welding could not be achieved at a welding temperature of 450℃, resulting in extremely low strength of the welded joint.

[0070] Table 1

[0071]

[0072] While the present invention has been disclosed above, its scope of protection is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention, and all such changes and modifications will fall within the scope of protection of the present invention.

Claims

1. A diffusion welding method for magnesium alloys, characterized in that, include: Step S1: Deposit silver on the surface of the magnesium alloy base material to be soldered by magnetron sputtering to form a silver film on the surface of the magnesium alloy base material to be soldered. Step S2: Coat the silver film with a nano-metal particle paste and dry it to form a nano-metal particle layer, thereby obtaining the workpiece to be soldered; wherein, the nano-metal particle paste is prepared from nano-silver particles, nano-copper particles and a binder; the mass ratio of the nano-silver particles, the nano-copper particles and the binder in the nano-metal particle paste is (70 to 90): (3 to 5): (10 to 45); Step S3: Assemble the two parts to be welded so that the nano-metal particle layers adhere to each other to obtain an assembly. Step S4: Under vacuum conditions or an inert gas protective atmosphere, the assembly is subjected to pulsed current assisted diffusion welding to obtain a welded joint.

2. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S1, the thickness of the silver film is 1 μm to 5 μm.

3. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S2, the adhesive includes at least polyethylene glycol 400.

4. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S2, the particle size of the silver nanoparticles is 30nm to 150nm, and the particle size of the copper nanoparticles is 20nm to 80nm.

5. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S2, the thickness of the nano-metal particle layer is 5 μm to 50 μm.

6. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S2, the drying process is carried out at a temperature of 40°C to 60°C for 1 hour to 12 hours.

7. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S4, the welding temperature of the pulsed current assisted diffusion welding is 300°C to 450°C, the pressure is 3MPa to 20MPa, and the time is 15min to 60min.

8. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S4, during the pulsed current assisted diffusion welding process, the heating rate is from 50°C / min to 200°C / min.

9. The diffusion welding method for magnesium alloys according to claim 1, characterized in that, In step S4, the frequency of the pulsed current used in the pulsed current assisted diffusion welding process is 20kHz to 40kHz, and the duty cycle is 82% to 84%.

10. A welded joint, characterized in that, It is manufactured using the diffusion welding method for magnesium alloys as described in any one of claims 1 to 9.

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