Low-temperature diffusion welding method for magnesium alloy and magnesium alloy connector

Abstract

The invention relates to the technical field of metal material connection, in particular to a magnesium alloy low-temperature diffusion welding method and a magnesium alloy connector, and the magnesium alloy low-temperature diffusion welding method comprises the steps that metal powder is adopted to conduct cold spraying on the surfaces of two magnesium alloys to be welded, a metal coating is formed on the surface of each magnesium alloy to be welded, and the metal powder comprises at least one of copper powder, nickel powder, titanium powder and silver powder; carrying out surface self-nanocrystallization treatment on the metal coating of each magnesium alloy to be welded; and diffusion welding is conducted on the two to-be-welded magnesium alloys subjected to surface self-nanocrystallization treatment through the spark plasma sintering technology. The method aims at solving the problem that the welding effect of the magnesium alloy is affected due to the existence of an oxidation film.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material connection. Specifically, it relates to a low-temperature diffusion welding method for magnesium alloys and a magnesium alloy connection joint. Background Art

[0002] The mainstream welding methods for magnesium alloys include fusion welding, brazing, and hot pressing connection, etc. Magnesium alloys are prone to form oxide films during the welding process. These oxide films have the characteristics of high melting point and high density. The existence of the oxide films will lead to poor connection between magnesium alloy materials during the welding process, thereby affecting the strength and tightness of the weld.

[0003] Currently, chemical methods or mechanical methods are usually used to remove the oxide films on the surface of magnesium alloys before welding. For example, chemical reagents are used to remove the surface oxide films or the oxide films are removed by mechanical grinding or polishing. However, although cleaning measures are taken before welding, new oxide films will usually be generated within a short time. The main component of the oxide film is magnesium oxide, and the melting point of magnesium oxide is as high as 2800°C. Therefore, if the oxide film is not effectively removed, it will hinder the fusion of liquid metals, causing problems such as pores or inclusions, and further affecting the welding effect. Summary of the Invention

[0004] The present invention aims to improve the problem that the welding effect of magnesium alloys is affected by the existence of oxide films.

[0005] To solve the above problems, as a first aspect, the present invention provides a low-temperature diffusion welding method for magnesium alloys, including: Cold spraying the surfaces of two magnesium alloys to be welded with metal powder respectively to form metal coatings on the surfaces of each of the magnesium alloys to be welded, wherein the metal powder includes at least one of copper powder, nickel powder, titanium powder, and silver powder; Performing surface self-nanocrystallization treatment on the metal coatings of each of the magnesium alloys to be welded; Using spark plasma sintering technology to perform diffusion welding on the two magnesium alloys to be welded after surface self-nanocrystallization treatment.

[0006] Optionally, the step of using spark plasma sintering technology to perform diffusion welding on the two magnesium alloys to be welded after surface self-nanocrystallization treatment includes: Performing single-point diamond cutting on the two magnesium alloys to be welded after surface self-nanocrystallization treatment respectively; Using spark plasma sintering technology to perform diffusion welding on the two magnesium alloys to be welded after single-point diamond cutting.

[0007] Optionally, the diffusion welding of the two magnesium alloys to be welded after single-point diamond cutting by using spark plasma sintering technology includes: the sintering pressure is 3 to 5 MPa, the sintering temperature is 300 to 350 °C, and the heat preservation time is 1 to 1.5 h.

[0008] Optionally, the process parameters of the cold spraying include: the spraying gas is argon, the argon pressure is 3 to 5 MPa, and the argon temperature is 300 to 350 °C.

[0009] Optionally, the process parameters of the cold spraying further include: the spraying distance is 20 to 50 mm, the powder feeding rate is 20 to 30 g·min -1 , and the gun moving speed is 300 to 500 mm·s -1 .

[0010] Optionally, the particle size of the metal powder is 15 to 20 μm.

[0011] Optionally, the thickness of the metal coating is 1 to 10 mm.

[0012] Optionally, the surface self-nanocrystallization treatment of each metal coating of the magnesium alloy to be welded includes: using ultrasonic rolling technology or ultrasonic shot peening technology to perform surface self-nanocrystallization treatment on each metal coating.

[0013] Optionally, the process parameters of the ultrasonic rolling technology include: the static pressure is 0.09 to 0.15 MPa, the rotation speed is 300 to 350 r / min, the feeding speed is 15 to 20 mm / min, and the amplitude is 8 to 10 μm.

[0014] As a second aspect, the present invention also provides a magnesium alloy connection joint, and the magnesium alloy connection joint is prepared by using the low-temperature diffusion welding method of the magnesium alloy as described above.

[0015] The beneficial effects of the present invention compared with the prior art are: First, the present invention sprays metal powders with relatively poor activity on the surface of a magnesium alloy to form a dense metal coating on the surface of the magnesium alloy base material to be welded, thereby alleviating the problem that the oxide film on the surface of the magnesium alloy base material hinders the joint combination. In addition, through the surface self-nanocrystallization technology, the surface of the metal coating is further plastically deformed to prepare a gradient surface structure with "surface nanocrystals → subsurface microcrystals → matrix coarse crystals", thereby significantly refining the grains of the metal coating on the surface of the magnesium alloy. The synergy of cold spraying and surface self-nanocrystallization technology transforms the magnesium-magnesium joint interface during traditional magnesium alloy diffusion welding into a joint interface that is not easily oxidized and has high joint activity, such as a copper-copper joint interface, so that the joint has a very high diffusion coefficient, providing a good basis for metallurgical bonding. Finally, combined with the spark plasma sintering technology, the growth of nanoparticles is effectively prevented, thereby overcoming the characteristics of high welding temperature, long holding time, and large deformation during the traditional diffusion welding process of magnesium alloys due to the presence of oxide films, and achieving high-efficiency, high-strength, and small-deformation welding of magnesium alloys at low temperatures. Brief Description of the Drawings

[0016] Figure 1 It is a schematic flow chart of the low-temperature diffusion welding method for magnesium alloys in the embodiments of the present invention. Detailed Embodiments

[0017] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following detailed description of the specific embodiments of the present invention is provided.

[0018] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application; The term "including" and its variants used herein are open-ended, that is, "including but not limited to"; the term "based on" is "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"; the term "optionally" means "optional embodiments". The relevant definitions of other terms will be given in the following description. It should be noted that the concepts of "first", "second", etc. mentioned in the present invention are used to distinguish different objects and are not used to describe a specific order or primary-secondary relationship. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, unless otherwise stated, the meaning of "a plurality" is two or more.

[0019] At present, the mainstream welding methods for magnesium alloys include fusion welding, brazing, and hot pressing connection, etc., but these technologies all have obvious limitations. Fusion welding requires high temperature to melt the base material, which easily causes severe oxidation and grain coarsening in the joint area, resulting in extremely high strength loss. At the same time, pores and hot cracks occur frequently, seriously affecting the welding quality. Although brazing can reduce the heat input, the compatibility between the filler metal and the magnesium matrix is poor, and brittle intermetallic compounds are easily formed at the interface, resulting in insufficient joint strength and significantly deteriorated corrosion resistance. Moreover, if the activity of the brazing flux is insufficient or the temperature control is improper, it is easy to cause incomplete film breaking, resulting in joint weakening. Hot pressing connection relies on high temperature and high pressure conditions, which easily causes incomplete rupture of the oxide film on the surface of magnesium alloys, resulting in unstable interface bonding strength, and low process efficiency, making it difficult to meet the high-precision connection requirements of complex components.

[0020] An embodiment of the present invention provides a low-temperature diffusion welding method for magnesium alloys. Referring to Figure 1 as shown, the low-temperature diffusion welding method for magnesium alloys includes: Step S1: Cold spray the surfaces of two magnesium alloys to be welded with metal powder respectively, and form metal coatings on the surfaces of each of the magnesium alloys to be welded; wherein, the metal powder includes at least one of copper powder, nickel powder, titanium powder, and silver powder.

[0021] Step S2: Perform surface self-nanocrystallization treatment on the metal coatings of each of the magnesium alloys to be welded.

[0022] Step S3: Use spark plasma sintering technology to perform diffusion welding on the two magnesium alloys to be welded after surface self-nanocrystallization treatment.

[0023] Cold spray technology uses gas flow to accelerate metal powder to high speed and impact the substrate at a temperature below the melting point of the material. The particles break the oxide film on the surface of the magnesium alloy base material through severe plastic deformation and form a dense coating. Since this process is carried out at a relatively low temperature, problems such as oxidation, phase transformation, and thermal stress of the base material will not occur.

[0024] Surface nanocrystallization refers to making the metal surface undergo severe plastic deformation through processing means such as shot peening, surface rolling, and surface mechanical grinding. In this process, a large number of dislocation sources in the grains of the metal surface layer are activated, a large number of dislocations proliferate and form microstructures such as dislocation walls and dislocation cells. Subsequently, structures such as dislocation cells further develop into sub-grain boundaries and grain boundaries, and finally the surface grains are refined. And the plastic deformation weakens with the increase of depth, so the grain size of the metal surface increases with the increase of depth, and finally a gradient grain structure is formed. The nanocrystallized surface has a high density of nanograin boundaries, which can greatly reduce the atomic activation energy, so it has the advantages of low melting point and high diffusion coefficient.

[0025] However, due to the high surface energy of the nanostructured surface itself, during the diffusion welding heating process, it often grows and loses its advantages of low melting point and high diffusion coefficient. Spark plasma sintering utilizes the characteristic that the interface resistance of the welded joint is significantly greater than that of the base material. By applying current and a certain pressure to the base material, the purpose of rapid heating of the welded joint is achieved. This method has a series of advantages such as high heating efficiency, low temperature of the base material except for the joint, and good connection effect. At the same time, the Joule heat and electroplastic effect generated by the current can achieve rapid atomic diffusion at a lower temperature, effectively suppressing the problems of high-temperature oxidation, grain coarsening, and thermal stress deformation of magnesium alloys.

[0026] Therefore, in the embodiments of the present invention, first, metal powder with poor activity is sprayed on the surface of the magnesium alloy to form a dense metal coating on the surface of the magnesium alloy base material to be welded, thereby reducing the problem that the oxide film on the surface of the magnesium alloy base material hinders the joint combination. In addition, through the surface self-nanocrystallization technology, the surface of the metal coating is further plastically deformed to prepare a gradient surface structure with "nanocrystalline surface layer → sub-surface microcrystalline layer → coarse-grained matrix", thereby significantly refining the grains of the metal coating on the surface of the magnesium alloy. The cooperation of cold spraying and surface self-nanocrystallization technology transforms the magnesium-magnesium connection interface during traditional magnesium alloy diffusion welding into a copper-copper connection interface that is not easily oxidized and has high connection activity, making the joint have a high diffusion coefficient and providing a good basis for metallurgical bonding. Finally, combined with the spark plasma sintering technology, the growth of nanoparticles is effectively prevented, thereby overcoming the characteristics of high welding temperature, long holding time, and large deformation during the traditional diffusion welding process of magnesium alloys, and achieving high-efficiency, high-strength, and small-deformation welding of magnesium alloys at low temperature.

[0027] In some alternative embodiments, step S3 further includes: Step S31: Perform single-point diamond cutting on the two magnesium alloys to be welded after surface self-nanocrystallization treatment; Step S32: Perform diffusion welding on the two magnesium alloys to be welded after single-point diamond cutting.

[0028] Since surface self-nanocrystallization treatment increases the surface roughness of the metal, and a rough surface easily leads to a reduction in actual contact points, resulting in a decrease in heat conduction efficiency, which in turn affects the mechanical properties, sealing performance, and reliability of the welded joint. Therefore, in the present invention, a single-point diamond cutting operation is performed on the magnesium alloy to be welded after surface self-nanocrystallization treatment before diffusion welding. The single-point diamond cutting process is a highly precise machining process, that is, using a single diamond tool to perform extremely precise cutting on the material, which can achieve a very smooth surface finish and strict tolerances, thereby achieving a nanoscale surface finish. Specifically, by using a natural single-crystal diamond tool with an edge radius that can reach the nanoscale, through the relative movement of the tool and the workpiece, the material is cut with a very small cutting depth to form a smooth surface. In the embodiments of the present invention, the cutting depth can be 30 to 50 μm.

[0029] In some alternative embodiments, in step S3, the process parameters of spark plasma sintering specifically include: a sintering pressure of 3 to 5 MPa, a sintering temperature of 300 to 350 °C, and a holding time of 1 to 1.5 h.

[0030] Specifically, the spark plasma sintering process in the embodiments of the present invention can be achieved by the following means: stacking two magnesium alloy base materials to be welded into a graphite mold, and using the upper and lower punches of the graphite mold to apply a pressing pressure to the magnesium alloy to be welded in a direction perpendicular to the joint surface of the two magnesium alloys to be welded. At the same time, a pulsed current, direct current, or alternating current is applied to the magnesium alloy base materials by using the energized electrodes in the upper and lower punches. Thus, the diffusion welding of the magnesium alloy base materials to be welded is completed sequentially through discharge activation, thermoplastic deformation, and cooling. By adopting the spark plasma sintering process, the heating efficiency can be improved, and the welding temperature can be controlled within a lower range, effectively suppressing the problems of high-temperature oxidation, grain coarsening, and thermal stress deformation of the magnesium alloy.

[0031] In some alternative embodiments, before step S1, in order to pre-remove the oxide film on the surface of the magnesium alloy base material to be welded and improve the cold spraying effect, the surface of the magnesium alloy base material to be welded can be polished. Specifically, the surface of the magnesium alloy is polished with sandpapers of 240 mesh, 600 mesh, 1000 mesh, 1500 mesh, and 3000 mesh respectively, ultrasonically cleaned in alcohol for 30 min, and then the surface of the magnesium alloy base material to be welded is dried.

[0032] In some alternative embodiments, in step S1, the process parameters of cold spraying include: the spraying gas is selected as argon, the argon pressure is 3 to 5 MPa, the argon temperature is 300 to 350 °C, the spraying angle is 90°, the spraying distance is 20 to 50 mm, the powder feeding rate is 20 to 30 g·min -1 and the moving speed of the spray gun is 300 to 500 mm·s -1 .

[0033] Specifically, in the cold spraying process, particles are accelerated to supersonic speeds (500 to 1200 m / s) by high-pressure gas (argon) inside the spray gun, and a metal coating is formed by high-speed impact on the surface of the magnesium alloy base material in a low-temperature environment. Argon has high chemical stability and is not easily involved in chemical reactions with other substances. This property enables argon to provide a stable protective environment during the cold spraying process, preventing the metal powder from reacting with oxygen, nitrogen, etc. in the air.

[0034] Furthermore, in some alternative embodiments, in step S1, the particle size of the metal powder is 15 to 20 μm, and the thickness of the metal coating formed by the cold spraying process is 1 to 10 mm.

[0035] In the embodiments of the present invention, when selecting metal powder as the cold spraying raw material, micron-sized particles are more easily accelerated to the critical speed in a high-speed gas flow, having higher particle kinetic energy and deposition efficiency. Moreover, micron-sized particles undergo sufficient plastic deformation during impact, filling the pores of the coating, thereby reducing defects (such as cracks and voids), and thus improving the coating density. In addition, the metal coating formed by the present invention has a certain thickness, which is beneficial to the subsequent smooth progress of surface self-nanocrystallization and single-point diamond turning operations.

[0036] In some alternative embodiments, the surface self-nanocrystallization treatment is performed on each of the metal coatings using ultrasonic rolling technology or ultrasonic shot peening technology.

[0037] Specifically, ultrasonic rolling technology refers to the combination of ultrasonic vibration and static pressure, causing the rolling head to generate high-frequency impacts on the surface of the workpiece, resulting in plastic deformation of the surface material and grain refinement to the nanoscale. Optionally, when performing the surface self-nanocrystallization treatment on each of the metal coatings using ultrasonic rolling technology, the process parameters of the ultrasonic rolling technology include: static pressure of 0.09 to 0.15 MPa, rotational speed of 300 to 350 r / min, feed rate of 15 to 20 mm / min, amplitude of 8 to 10 μm, and the number of repeated treatments in the same area is not less than 4 times.

[0038] Ultrasonic shot peening technology, on the other hand, drives the shot to impact the surface of the material through high-frequency vibration, inducing severe plastic deformation to achieve surface nanocrystallization. It refines the surface grains to the nanoscale through the input of mechanical energy, and at the same time introduces residual compressive stress, significantly improving the fatigue strength, wear resistance, and corrosion resistance of the material. Specifically, in the embodiments of the present invention, the process parameters of the ultrasonic shot peening technology include: the shot selected is SiC, WC-Co, or Si3N4, the ultrasonic frequency is 20 to 30 kHz, the amplitude is 10 to 30 μm, and the shot peening pressure is 0.3 to 0.5 MPa.

[0039] Another embodiment of the present invention provides a magnesium alloy connection joint, which is prepared by the low-temperature diffusion welding method of the magnesium alloy as described above.

[0040] The present invention will be described in detail below through specific examples and comparative examples: Example 1 The low-temperature diffusion welding method of the magnesium alloy in this example includes the following steps: Step (1): The surface of the AZ31B magnesium alloy is polished. The surface of the magnesium alloy is polished with sandpapers of 240 mesh, 600 mesh, 1000 mesh, 1500 mesh, and 3000 mesh respectively, and then placed in alcohol and ultrasonically treated for 30 min and then dried.

[0041] Step (2): Pure copper powder with a particle size between 15 and 20 μm is selected to perform cold spraying on the surface of the AZ31B magnesium alloy to be welded. The spraying angle is 90°, the gas is argon, the pressure is 3 MPa, the temperature is 300 °C, the spraying distance is 20 mm, the powder feeding rate is 20 g·min -1 , and the moving speed of the spray gun is 300 mm·s -1 .

[0042] Step (3): After the surface of the magnesium alloy with cold spraying is cleaned with an alcohol solution, a surface self-nanocrystallization treatment is performed on the copper layer on the surface of the AZ31B magnesium alloy to be welded by using an ultrasonic rolling device. The static pressure is 0.09 MPa, the rotation speed is 300 r / min, the feeding speed is 15 mm / min, the amplitude is 8 μm, and the same area is repeatedly treated 4 times.

[0043] Step (4): The AZ31B magnesium alloy to be welded with surface self-nanocrystallization is subjected to single-point diamond cutting operation, wherein the cutting depth is 30 μm.

[0044] Step (5): The cut AZ31B magnesium alloy to be welded is placed in alcohol and ultrasonically treated for 30 min, taken out and dried, then stacked in a graphite mold, and the graphite mold is placed in a spark plasma sintering device for diffusion welding, and argon protection is used during welding. During the welding process, the heating rate is 100 °C / min, the pressure is 3 MPa, the welding temperature is 300 °C, the holding time is 60 min, and the pulse current frequency is 30000 Hz. After the holding is completed, the welded specimen is cooled to room temperature with the furnace, and then the furnace is opened to take samples to obtain the magnesium alloy connection joint.

[0045] Example 2 The difference between this example and Example 1 is that in step (2), pure nickel powder with a particle size between 15 and 20 μm is selected to perform cold spraying on the surface of the AZ31B magnesium alloy to be welded, and in step (5), the welding temperature is 320 °C, and other processes are the same.

[0046] Example 3 The difference between this example and Example 1 is that in step (2), pure titanium powder with a particle size between 15 and 20 μm is selected for cold spraying on the surface of the AZ31B magnesium alloy to be welded. In step (5), the welding temperature is 325 °C, and other processes are the same.

[0047] Example 4 The difference between this example and Example 1 is that in step (3), an ultrasonic shot peening device is used to perform surface self-nanocrystallization treatment on the copper layer on the surface of the AZ31B magnesium alloy to be welded. The shot is selected as Si3N4, the ultrasonic frequency is 20 kHz, the amplitude is 15 μm, and the shot peening pressure is 0.3 MPa. In step (5), the welding temperature is 350 °C.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that the cold spraying process in step (2) is not carried out, and the polished AZ31B magnesium alloy to be welded is directly subjected to surface self-nanocrystallization treatment. In step (5), the welding temperature is 550 °C, and the welding pressure is 5.5 MPa.

[0049] Comparative Example 2 The difference between this comparative example and Example 1 is that the surface self-nanocrystallization treatment in step (3) is not carried out. In step (5), the welding temperature is 500 °C, and the welding pressure is 5.5 MPa.

[0050] Comparative Example 3 The difference between this comparative example and Example 1 is that the machined AZ31B magnesium alloy to be welded is stacked and loaded into a WC cemented carbide mold. Subsequently, the mold is placed between the upper and lower punches in a vacuum hot press furnace, the furnace door is closed, the furnace chamber is evacuated, and heating is carried out using a pre-set temperature program. After the furnace temperature reaches 450 °C, it is kept warm for 1 h, and at the same time, an axial pressure of 5 MPa is applied to perform vacuum diffusion welding.

[0051] The connection temperatures of the AZ31B magnesium alloy to be welded in Examples 1 to 4 and Comparative Examples 1 to 3, as well as the corresponding deformation rates and shear strengths of the magnesium alloy connection joints, are shown in Table 1. It can be seen from Table 1 that compared with the magnesium alloy base materials in Comparative Examples 1 to 3 that need to be welded under high temperature (greater than 430 °C) and high pressure (not less than 5 MPa) conditions and have a large deformation rate (greater than 5%), the examples of the present invention can complete the connection of magnesium alloys under the conditions of 300 °C and 3 MPa, the welding rate can reach 100%, and at the same time, the deformation rate of the magnesium alloy specimen is controlled below 0.15%.

[0052] Table 1 Connection temperatures of the AZ31B magnesium alloy to be welded in Examples 1 to 4 and Comparative Examples 1 to 3, as well as the corresponding deformation rates and shear strengths of the magnesium alloy connection joints

[0053] Although the present invention is disclosed as above, the scope of protection of the present invention 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 these changes and modifications will all fall within the scope of protection of the present invention.

Claims

1. A low-temperature diffusion welding method for a magnesium alloy, characterized in that, Including: Cold spray the surfaces of two magnesium alloys to be welded with metal powder respectively to form metal coatings on the surfaces of each of the magnesium alloys to be welded, wherein the metal powder includes at least one of copper powder, nickel powder, titanium powder and silver powder; Perform surface self-nanocrystallization treatment on the metal coatings of each of the magnesium alloys to be welded; Use spark plasma sintering technology to perform diffusion welding on the two magnesium alloys after surface self-nanocrystallization treatment.

2. The low-temperature diffusion welding method of the magnesium alloy according to claim 1, characterized in that, The use of spark plasma sintering technology to perform diffusion welding on the two magnesium alloys after surface self-nanocrystallization treatment includes: Perform single-point diamond cutting on the two magnesium alloys after surface self-nanocrystallization treatment respectively; Use spark plasma sintering technology to perform diffusion welding on the two magnesium alloys after single-point diamond cutting.

3. The low-temperature diffusion welding method of the magnesium alloy according to claim 2, characterized in that The use of spark plasma sintering technology to perform diffusion welding on the two magnesium alloys after single-point diamond cutting includes: the sintering pressure is 3 to 5 MPa, the sintering temperature is 300 to 350 °C, and the holding time is 1 to 1.5 h.

4. The low-temperature diffusion welding method of the magnesium alloy according to claim 1, wherein, The process parameters of the cold spray include: the spraying gas is argon, the argon pressure is 3 to 5 MPa, and the argon temperature is 300 to 350 °C.

5. The low-temperature diffusion welding method of the magnesium alloy according to claim 4, characterized in that, The process parameters of the cold spraying further include: the spraying distance is 20 to 50 mm, and the powder feeding rate is 20 to 30 g·min -1 , and the moving speed of the spray gun is 300 to 500 mm·s -1 .

6. The low-temperature diffusion welding method of the magnesium alloy according to claim 1, wherein The particle size of the metal powder is 15 to 20 μm.

7. The low-temperature diffusion welding method of the magnesium alloy according to claim 1, characterized in that, The thickness of the metal coating is 1 to 10 mm.

8. The low-temperature diffusion welding method of the magnesium alloy according to claim 1, characterized in that The performing of surface self-nanocrystallization treatment on the metal coating of each of the magnesium alloys to be welded includes: using ultrasonic rolling technology or ultrasonic shot peening technology to perform surface self-nanocrystallization treatment on each of the metal coatings.

9. The low-temperature diffusion welding method of the magnesium alloy according to claim 8, characterized in that, The process parameters of the ultrasonic rolling technology include: the static pressure is 0.09 to 0.15 MPa, the rotation speed is 300 to 350 r / min, the feed speed is 15 to 20 mm / min, and the amplitude is 8 to 10 μm.

10. A magnesium alloy connection joint, characterized in that, The magnesium alloy connection joint is prepared by the low-temperature diffusion welding method of the magnesium alloy according to any one of claims 1 to 9.

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