Magnesium alloy welding method and joint based on semi-solid interlayer and pulsed current

Abstract

The application provides a magnesium alloy welding method based on a semi-solid intermediate layer and pulse current and a joint, relates to the technical field of material welding, and discloses a magnesium alloy diffusion welding method based on a semi-solid intermediate layer, which comprises the following steps: melting raw materials of a filler layer, then pouring the raw materials into a mold, cooling to room temperature, obtaining a solidified filler layer, solid solution treatment of the solidified filler layer, aging treatment of the filler layer after the solid solution treatment, and obtaining a semi-solid filler layer; placing the semi-solid filler layer between two magnesium alloys as an intermediate layer, and performing pulse current diffusion welding to obtain a magnesium alloy joint. In the welding process, the pulse current diffusion welding is used to avoid magnesium alloy deformation caused by local high temperature of a weld seam, sharp hard solid phase particles in the semi-solid intermediate layer extrude and destroy an existing oxide film on a surface of a base metal magnesium alloy, meanwhile, a liquid phase of the semi-solid intermediate layer greatly reduces welding pressure and rapidly fills pores of a bonding interface, and small deformation and high strength metallurgical bonding of the joint are rapidly realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material welding, in particular to a magnesium alloy welding method based on a semi-solid intermediate layer and pulse current and a joint. BACKGROUND

[0002] Magnesium alloy is the lightest commercial metal engineering material and is an ideal modern structural material. In the application process of magnesium alloy, the connection of magnesium alloy is inevitably involved. At present, the commonly used connection methods of magnesium alloy include fusion welding, brazing and diffusion welding. Since magnesium alloy has a large tendency of thermal cracking, thermal cracks are easily generated in the fusion welding process. In the brazing process, the stubborn oxide film on the surface of magnesium alloy easily hinders the spreading and wetting of liquid filler metal, and local incomplete welding is easily caused. Therefore, diffusion welding is often used for the connection of magnesium alloy. However, in the diffusion welding process of magnesium alloy, the stubborn oxide film formed on the surface of magnesium alloy hinders atomic diffusion, interface hole closure and grain boundary migration, resulting in low strength and large deformation of the magnesium alloy diffusion welded joint. SUMMARY

[0003] The problem solved by the present application is how to solve the problems of low strength and large deformation of the magnesium alloy diffusion welded joint.

[0004] To solve the above problems, the present application provides a magnesium alloy welding method based on a semi-solid intermediate layer and pulse current and a joint.

[0005] In a first aspect, the present application provides a magnesium alloy welding method based on a semi-solid intermediate layer and pulse current, comprising the following steps:

[0006] S1: taking the raw material of the filler layer, melting at a temperature of 670 to 760 DEG C for 25 to 35 min, then pouring into a mold, cooling to room temperature to obtain a solidified filler layer, placing the solidified filler layer in 530 to 550 DEG C for 2 to 4 h for solid solution treatment, and placing the solid solution treated filler layer in 180 to 220 DEG C for 6 to 8 h for aging treatment to obtain a semi-solid filler layer;

[0007] S2: placing the semi-solid filler layer between two pieces of magnesium alloy as an intermediate layer, placing the semi-solid filler layer and magnesium alloy in a pulse current diffusion welding equipment for pulse current diffusion welding to obtain a magnesium alloy joint.

[0008] Optionally, in S2, the welding temperature is 400 to 450 DEG C, the pressure is 2 to 4 MPa, and the welding holding time is 40 to 50 min.

[0009] Optionally, in S2, the heating rate during welding is 80 to 120 DEG C / min.

[0010] Optionally, the raw materials of the solder layer include 88 to 96 parts of Al and 12-4 parts of Si in parts by weight.

[0011] Optionally, the raw materials of the brazing material layer include 60 to 70 parts of Al, 35 to 15 parts of Mg and 5-15 parts of Si in parts by weight.

[0012] Optionally, in S1 , the mold is preheated to a temperature of 300 to 350° C.

[0013] Optionally, the step between S1 and S2 includes: placing the magnesium alloy in an acid solution prepared by 25% to 35% by weight of CrO3 and 65% to 75% by weight of H2O for cleaning for 3 to 8 minutes, and then placing it in acetone for standby use.

[0014] Optionally, the steps between S1 and S2 include: immersing the semi-solid solder layer in a NaOH solution with a mass fraction of 8% to 11% for alkali washing for 5 to 10 minutes, and then placing it in acetone for ultrasonic cleaning for 5 to 10 minutes after alkali washing; then immersing the semi-solid solder layer after alkali washing in an HNO3 solution with a mass fraction of 18% to 20% for pickling for 5 to 10 minutes, and then placing it in acetone for ultrasonic cleaning for more than 30 minutes after pickling.

[0015] In a second aspect, the present invention provides a joint made by the magnesium alloy welding method based on a semi-solid intermediate layer and pulsed current as described in any one of the above items.

[0016] The beneficial effects of the magnesium alloy welding method and joint based on the semi-solid intermediate layer and pulse current of the present invention are: the solder layer after solid solution is aged to obtain a semi-solid solder layer containing hard solid phase particles and liquid phase during the diffusion welding process; during the welding process, the sharp hard solid phase particles in the semi-solid intermediate layer are used to squeeze and destroy the existing oxide film on the surface of the base material magnesium alloy, while the liquid phase of the semi-solid intermediate layer greatly reduces the welding pressure and quickly fills the pores at the bonding interface, thereby quickly achieving metallurgical bonding of the joint. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a flow chart of a magnesium alloy welding method based on a semi-solid intermediate layer and pulse current according to an embodiment of the present invention;

[0018] Figure 2 This is a microscopic magnified image of the interface of the magnesium alloy joint of Example 1;

[0019] Figure 3 is a graph showing the tensile strength of the magnesium alloy joint of Example 1;

[0020] Figure 4 This is a magnified microscopic image of the interface of the magnesium alloy joint of Comparative Example 1. DETAILED DESCRIPTION

[0021] To make the above-mentioned objects, features, and advantages of the present invention more clearly understood, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein. Instead, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the 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 the present invention have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs. The terms used in the present invention description are only for the purpose of describing specific embodiments and are not intended to limit the present invention;

[0023] As used herein, the term "including" and its variations are open-ended, i.e., "including but not limited to"; the term "based on" means "based at least in part 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 are provided in the following description.

[0024] In the relevant technology, AZ31 magnesium alloy belongs to deformable magnesium alloy, which has the advantages of high specific strength and high specific stiffness, and has broad application potential in aerospace, transportation, electronics and other fields. Traditional brazing filler metals are mostly single liquid filler metals that spread, wet and solidify, and have inherent problems of difficult spreading and wetting and difficult to break the oxide film. In the traditional hot pressing diffusion welding process, deformation and grain growth are prone to occur due to excessively high welding temperature and long holding time. Traditional diffusion welding has high requirements for the surface state of magnesium alloys, which increases the cost and difficulty of processing. Traditional diffusion welding has a slow heating rate and requires long-term holding at high temperature and high pressure to ensure sufficient diffusion of elements and break the oxide film, which leads to defects such as grain growth and deformation in the parent material, reducing the performance of the parent material.

[0025] In response to the problems existing in the above-mentioned related technologies, this embodiment provides a magnesium alloy welding method and joint based on a semi-solid intermediate layer and pulse current.

[0026] like Figure 1 As shown, an embodiment of the present invention provides a magnesium alloy welding method based on a semi-solid intermediate layer and a pulse current, comprising the following steps:

[0027] S1: The raw material of the solder layer is smelted at 670 to 760°C for 25 to 35 minutes, then poured into a mold and cooled to room temperature to obtain a solidified solder layer. The solidified solder layer is placed at 530 to 550°C for 2 to 4 hours for solution treatment, and the solidified solder layer is placed at 180 to 220°C for 6 to 8 hours for aging treatment to obtain a semi-solid solder layer.

[0028] S2: placing a semi-solid brazing material layer between two pieces of magnesium alloy as an intermediate layer, placing the semi-solid brazing material layer and the magnesium alloy in a pulse current diffusion welding device for pulse current diffusion welding to obtain a magnesium alloy joint.

[0029] In this embodiment, the solder layer after solid solution is subjected to aging treatment to obtain a semi-solid solder layer containing hard solid phase particles and liquid phase during the diffusion welding process; during the welding process, the sharp hard solid phase particles in the semi-solid intermediate layer are used to squeeze and destroy the existing oxide film on the surface of the base material magnesium alloy, while the liquid phase of the semi-solid intermediate layer greatly reduces the welding pressure and quickly fills the pores at the bonding interface, thereby quickly achieving metallurgical bonding of the joint.

[0030] Specifically, semi-solid solder is a material state that, under the influence of temperature or external forces, is between a completely solid and a completely liquid state. Microstructurally, semi-solid solder exhibits a spherical or ellipsoidal structure of grains, which distinguishes it from both the random flow of liquids and the orderly arrangement of solid crystals.

[0031] The formation of semi-solid brazing filler metal usually requires special processing methods, such as high-temperature plastic deformation, rapid solidification, etc. These methods can keep the brazing filler metal in a semi-solid state with stable spherical or ellipsoidal grains, thus obtaining good processing performance and mechanical properties.

[0032] Semi-solid brazing filler metals possess many unique properties. They exhibit excellent plasticity at high temperatures, flowing like liquids, yet exhibit high strength and hardness at low temperatures. Furthermore, they exhibit excellent processability, allowing them to be processed at lower temperatures without excessive thermal deformation. 1 These properties make semi-solid brazing filler metals promising for broad application in a wide range of fields.

[0033] Solution treatment in this example involves heating the alloy to a high-temperature, single-phase region and maintaining the temperature constant to allow the excess phase to fully dissolve into the solid solution, followed by rapid cooling to produce a supersaturated solid solution. Because the process is similar to quenching, it is also called "solution quenching."

[0034] Aging, as used in this example, refers to a heat treatment process in which a metal or alloy workpiece undergoes solution treatment, cold plastic deformation, casting, or forging, then is placed at a higher temperature or maintained at room temperature, causing its properties, shape, and dimensions to change over time. The objectives of aging treatment include eliminating internal stress, stabilizing microstructure and dimensions, and improving mechanical properties.

[0035] Pulsed current (i.e., spark plasma sintering) diffusion welding is a highly efficient welding method that utilizes the inherent resistance of the materials and the interfacial contact resistance to rapidly heat the interface being joined and achieve metallurgical bonding under a specific pressure and time. It offers the advantages of fast heating rates, low joining temperatures, short joining times, and low energy consumption. Furthermore, the electromigration effect during pulsed current diffusion welding can accelerate atomic diffusion efficiency, further improving joint performance. Magnesium alloys are diffusion welded using a combination of a semi-solid interlayer and pulsed current technology. During welding, the sharp, solid, hard particles in the semi-solid interlayer crush and destroy the existing oxide film on the surface of the magnesium alloy parent material. Simultaneously, the liquid phase in the semi-solid interlayer significantly reduces welding pressure and fills the pores at the bonding interface, rapidly achieving metallurgical bonding. Because the microstructure and properties of the joint are similar to those of the parent material, not only can weld stress be significantly reduced, ensuring the reliability and electrical properties of the welded joint are similar to those of the parent material, but pulsed current-assisted diffusion welding also reduces heating to the area near the weld, maintaining a strong plastic resistance in the parent material and preventing deformation of the magnesium alloy's delicate structure and magnesium evaporation. This precise and reliable welding technology, which can achieve the synergistic improvement of small deformation, high strength and high welding rate of magnesium alloy joints, has outstanding advantages for magnesium alloy thin-walled complex multi-weld structures, such as Figure 2 As shown in Figure 2, the magnesium alloy joint is a joint without interface gaps, and the joint deformation is less than 2%. Figure 3 The shear strength of the prepared magnesium alloy joint is as high as 89.15MPa.

[0036] Optionally, in S2, the welding temperature is 400 to 450°C, the pressure is 2 to 4 MPa, and the welding holding time is 40 to 50 minutes.

[0037] In this optional embodiment, the welding temperature is low, and the temperature is low during low-temperature welding, which can reduce thermal deformation and deterioration of the material during welding, thereby ensuring the quality of the product after welding; it is energy-saving and environmentally friendly, and can effectively reduce carbon dioxide emissions during the production process; low-temperature welding can reduce the thermal stress and cooling shrinkage rate of the welding material, making it less likely to deform, avoiding problems such as loose welding and product deformation, thereby improving the reliability of welding and the yield rate of the product.

[0038] Optionally, in S2 , the heating rate during the welding process is 80 to 120° C. / min.

[0039] In this optional embodiment, the heating rate is fast, which accelerates the atomic diffusion efficiency and further improves the joint performance.

[0040] Optionally, the raw materials of the solder layer include 88 to 96 parts of Al and 12-4 parts of Si in parts by weight.

[0041] In this optional embodiment, the raw material of the solder layer is simple and easy to prepare.

[0042] Optionally, the raw materials of the brazing material layer include 60 to 70 parts of Al, 35 to 15 parts of Mg and 5-15 parts of Si in parts by weight.

[0043] In this optional embodiment, the raw material of the solder layer is simple and easy to prepare.

[0044] Optionally, in S1 , the mold is preheated to a temperature of 300 to 350° C.

[0045] In this optional embodiment, preheating the mold can increase the service life of the mold and reduce the crack rate of the mold. At the same time, it can also reduce the defect rate of the solder and ensure the quality and stability of the processing.

[0046] Optionally, the step between S1 and S2 includes: placing the magnesium alloy in an acid solution prepared by 25% to 35% by weight of CrO3 and 65% to 75% by weight of H2O for cleaning for 3 to 8 minutes, and then placing it in acetone for standby use.

[0047] In this optional embodiment, CrO3 reacts with H2O to form chromic acid, which has the chemical formula H2CrO4. Chromic acid is an inorganic compound. The magnesium alloy is pickled to remove oxides and rust from its surface, and then placed in acetone to further clean surface impurities and remove acid residue.

[0048] Optionally, the steps between S1 and S2 include: immersing the semi-solid solder layer in a NaOH solution with a mass fraction of 8% to 11% for alkali washing for 5 to 10 minutes, and then placing it in acetone for ultrasonic cleaning for 5 to 10 minutes after alkali washing; then immersing the semi-solid solder layer after alkali washing in an HNO3 solution with a mass fraction of 18% to 20% for pickling for 5 to 10 minutes, and then placing it in acetone for ultrasonic cleaning for more than 30 minutes after pickling.

[0049] In this optional embodiment, the semi-solid solder layer is subjected to alkaline washing to remove oil, grease, dirt and other impurities on the surface of the semi-solid solder layer, while minimizing metal dust and rust on the surface; the semi-solid solder layer is subjected to acid washing to remove rust and alkaline solution residues on the surface of the semi-solid solder layer; and the semi-solid solder layer is placed in acetone to further clean surface impurities and wash away acid solution residues.

[0050] An embodiment of the present invention provides a joint, which is manufactured by using any of the above magnesium alloy welding methods based on a semi-solid intermediate layer and a pulse current.

[0051] The application will be further described in connection with specific examples.

[0052] Example 1, magnesium alloy joint prepared by magnesium alloy welding method based on semi-solid intermediate layer and pulse current.

[0053] (1) 90% aluminum and 10% Si by mass were placed in 700°C for 30 min, then poured into a preheated to 320°C mold, and finally air-cooled to room temperature;

[0054] (2) The solidified Al-Si alloy was placed in 540°C for 3 h for solid solution treatment;

[0055] (3) The solid-solutioned Al-Si alloy was placed in 200°C for 7 h for aging treatment, to obtain an Al-Si semi-solid intermediate layer;

[0056] (4) The surface of the AZ31 magnesium alloy and the Al-Si semi-solid intermediate layer was polished in turn using 80 mesh, 600 mesh, and 1500 mesh sandpaper, then cleaned in acetone for 30 min, and dried for standby;

[0057] (5) The AZ31 magnesium alloy was cleaned in an acid solution prepared from 30% CrO3 and 70% H2O for 5 min, and then placed in acetone for standby;

[0058] (6) The Al-Si semi-solid intermediate layer was immersed in 10% NaOH solution for 5-10 min for alkali cleaning, and then ultrasonically cleaned in acetone for 8 min;

[0059] (7) The alkali-cleaned Al-Si semi-solid intermediate layer was immersed in 20% HNO3 solution for 8 min for acid cleaning, and then ultrasonically cleaned in acetone for 30 min;

[0060] (8) The Al-Si semi-solid intermediate layer was placed between two pieces of AZ31 magnesium alloy, and placed in a pulse current diffusion welding device for welding, with argon protection during welding. The heating rate during welding was 100°C / min, the welding temperature was 430°C, the pressure was 3 MPa, the holding time was 45 min, and then the welded piece was cooled with the furnace. After cooling, it was taken out, and finally a high-quality AZ31 magnesium alloy joint was obtained.

[0061] The AZ31 magnesium alloy joint was observed by microscope and the shear strength was detected, as shown in Figure 2 , the magnesium alloy joint was an interface gap-free joint, and the joint deformation was less than 2%; as Figure 3 , the shear strength of the prepared magnesium alloy joint was as high as 89.15 MPa.

[0062] Comparative Example 1

[0063] Preparation of magnesium alloy joint based on pulse current diffusion welding method.

[0064] (1) The surface of AZ31 magnesium alloy was polished with 80 mesh, 600 mesh and 1500 mesh sandpaper in turn, and then cleaned in acetone for 30 min, and dried for standby;

[0065] (2) The surface of AZ31 magnesium alloy was polished with 80 mesh, 600 mesh and 1500 mesh sandpaper in turn, and then cleaned in acetone for 30 min, and dried for standby;

[0066] (3) The AZ31 magnesium alloy was cleaned in an acid solution prepared from 30% CrO3 and 70% H2O for 5 min, and then placed in acetone for standby;

[0067] (4) Two pieces of AZ31 magnesium alloy were placed in a pulse current diffusion welding device for welding, and argon was used for protection during welding. The heating rate was 100℃ / min, the welding temperature was 430℃, the pressure was 7 MPa, the holding time was 45 min, and then the welded piece was cooled in the furnace. After cooling, it was taken out, and finally the AZ31 magnesium alloy joint was obtained.

[0068] The AZ31 magnesium alloy joint was observed by microscope, as shown in Figure 4 , there were still a large number of holes and oxide films in the magnesium alloy joint, and the joint deformation was 16%.

[0069] It can be seen that the quality of the magnesium alloy joint of Example 1 is much better than that of Comparative Example 1, and the joint deformation degree of the magnesium alloy joint of Example 1 is much smaller than that of the magnesium alloy joint of Comparative Example 1.

[0070] Although the present application is disclosed as above, the protection scope of the present application is not limited to this. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application, and these changes and modifications will fall within the protection scope of the present application.

Claims

1. A magnesium alloy welding method based on a semi-solid intermediate layer and pulse current, characterized in that: The following steps are involved: S1: taking the raw material of the solder layer and smelting it at a temperature of 670 to 760°C for 25 to 35 minutes, then pouring it into a mold and cooling it to room temperature to obtain a solidified solder layer, placing the solidified solder layer at 530 to 550°C and keeping it for 2 to 4 hours for solution treatment, and placing the solder layer after solution treatment at 180 to 220°C and keeping it for 6 to 8 hours for aging treatment to obtain a solder layer; S2: placing the brazing material layer between two pieces of magnesium alloy as an intermediate layer, placing the brazing material layer and the magnesium alloy in a pulse current diffusion welding device for pulse current diffusion welding to obtain a magnesium alloy joint; In S2, the pulse current diffusion welding temperature is 400 to 450° C., the pressure is 2 to 4 MPa, and the pulse current diffusion welding holding time is 40 to 50 minutes; The raw materials of the solder layer include 88 to 96 parts of Al and 12-4 parts of Si by weight, or, by weight, the raw materials of the solder layer include 60 to 70 parts of Al, 35 to 15 parts of Mg and 5-15 parts of Si.

2. The magnesium alloy welding method based on a semi-solid intermediate layer and pulse current according to claim 1, characterized in that: In S2, the heating rate during the pulse current diffusion welding process is 80 to 120°C / min.

3. The magnesium alloy welding method based on a semi-solid intermediate layer and pulse current according to claim 1, characterized in that: In S1, the mold is preheated to a temperature of 300 to 350°C.

4. The magnesium alloy welding method based on a semi-solid intermediate layer and pulse current according to claim 1, characterized in that: The steps between S1 and S2 include: placing the magnesium alloy in an acid solution prepared by 25% to 35% by weight of CrO3 and 65% to 75% by weight of H2O for cleaning for 3 to 8 minutes, and then placing it in acetone for standby use.

5. The magnesium alloy welding method based on a semi-solid intermediate layer and pulse current according to claim 1, characterized in that: The steps between S1 and S2 include: immersing the solder layer in a NaOH solution with a mass fraction of 8% to 11% for alkali washing for 5 to 10 minutes, and then placing it in acetone for ultrasonic cleaning for 5 to 10 minutes; then immersing the solder layer after alkali washing in an HNO3 solution with a mass fraction of 18% to 20% for pickling for 5 to 10 minutes, and then placing it in acetone for ultrasonic cleaning for more than 30 minutes.

6. A joint, characterized in that: The magnesium alloy is manufactured by the magnesium alloy welding method based on a semi-solid intermediate layer and pulse current as described in any one of claims 1 to 5.

Images