Magnesium alloy welding method and joint based on semi-solid intermediate layer and pulse current

Abstract

The invention provides a magnesium alloy welding method based on a semi-solid intermediate layer and pulse current and a connector, and relates to the technical field of material welding, the magnesium alloy diffusion welding method based on the semi-solid intermediate layer comprises the steps that raw materials of a brazing filler metal layer are taken to be smelted, then poured into a mold and cooled to the room temperature, and the solidified brazing filler metal layer is obtained; the solidified brazing filler metal layer is subjected to solution treatment, the brazing filler metal layer subjected to solution treatment is subjected to aging treatment, and a semi-solid brazing filler metal layer is obtained; and the semi-solid brazing filler metal layer is arranged between the two magnesium alloys to serve as a middle layer, pulse current diffusion welding is conducted, and the magnesium alloy connector is obtained. In the welding process, local high temperature of a welding seam is diffused and welded through pulse current to avoid deformation of the magnesium alloy, sharp hard solid-phase particles in the semi-solid middle layer extrude and damage an oxide film existing on the surface of the base metal magnesium alloy, and meanwhile, a liquid phase of the semi-solid middle layer greatly reduces the welding pressure and rapidly fills bonding interface pores; and small-deformation and high-strength metallurgical bonding of the joint is quickly realized.

Description

Technical Field

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

[0002] Magnesium alloy is the lightest commercial metal engineering material and 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 are fusion welding, brazing and diffusion welding. Due to the strong tendency of magnesium alloy to thermal crack, thermal cracks are easily generated during fusion welding. During brazing, the stubborn oxide film on the surface of magnesium alloy easily hinders the spreading and wetting of liquid brazing material, which easily causes local unwelded parts. Therefore, diffusion welding is often used to connect magnesium alloy. However, during the diffusion welding process of magnesium alloy, the stubborn oxide film formed on the surface of magnesium alloy hinders atomic diffusion, interface pore closure and grain boundary migration, resulting in low strength and large deformation of magnesium alloy diffusion welding joints. Summary of the invention

[0003] The problem solved by the invention is how to solve the problem of low strength and large deformation of magnesium alloy diffusion welding joints.

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

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

[0006] S1: Take the raw material of the brazing material layer and smelt it at 670 to 760°C for 25 to 35 minutes, then pour it into a mold and cool it to room temperature to obtain a solidified brazing material layer, place the solidified brazing material layer at 530 to 550°C for 2 to 4 hours for solution treatment, place the brazing material layer after solution treatment at 180 to 220°C for 6 to 8 hours for aging treatment to obtain a semi-solid brazing material layer;

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

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

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

[0010] Optionally, the raw material of the brazing material layer includes 88 to 96 parts of Al and 12 to 4 parts of Si 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, between S1 and S2, the step of placing the magnesium alloy in a CrO 3 and 65% to 75% by weight of H 2 O for 3 to 8 minutes, and then placed in acetone for later 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 ultrasonically cleaning it in acetone for 5 to 10 minutes; then immersing the semi-solid solder layer after alkali washing in a HNO solution with a mass fraction of 18% to 20% 3 The product was pickled in the solution for 5 to 10 minutes, and then ultrasonically cleaned in acetone for more than 30 minutes.

[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 pulse current as described in any one of the above items.

[0016] The beneficial effects of the magnesium alloy welding method and joint based on a semi-solid intermediate layer and pulse current of the present invention are: the solder layer after solid solution is subjected to aging treatment to obtain a semi-solid solder layer with 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 parent magnesium alloy, and at the same time, 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 It 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 is a microscopic magnified image of the interface of the magnesium alloy joint of Example 1;

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

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

[0021] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with 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 interpreted as being limited to the embodiments described herein. On the contrary, 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 only for exemplary purposes 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 specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention;

[0023] The term "including" and its variations used herein are open inclusions, 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 other 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.

[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 breaking of oxide films. In the traditional hot pressing diffusion welding process, deformation and grain growth are prone to occur due to excessively high welding temperatures and long insulation times. Traditional diffusion welding has high requirements on 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 insulation 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 view of 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: Take the raw material of the brazing material layer and smelt it at 670 to 760°C for 25 to 35 minutes, then pour it into a mold and cool it to room temperature to obtain a solidified brazing material layer, place the solidified brazing material layer at 530 to 550°C for 2 to 4 hours for solution treatment, place the brazing material layer after solution treatment at 180 to 220°C for 6 to 8 hours for aging treatment to obtain a semi-solid brazing material layer;

[0028] S2: placing a semi-solid solder layer between two pieces of magnesium alloy as an intermediate layer, placing the semi-solid solder layer and the magnesium alloy in a pulse current diffusion welding device for pulse current diffusion welding, and obtaining 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 having 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 between completely solid and completely liquid under the action of temperature or external force. In terms of microstructure, semi-solid solder presents a spherical or ellipsoidal structure of crystal grains, which makes the material different from the randomness of liquid flow 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, thereby obtaining good processing performance and mechanical properties.

[0032] Semi-solid brazing filler metals have many unique properties. They exhibit good plasticity at high temperatures and can flow like liquids, but exhibit high strength and hardness at low temperatures. In addition, semi-solid brazing filler metals also have good processing properties and can be processed at lower temperatures without worrying about excessive thermal deformation1. These properties make semi-solid brazing filler metals have broad application prospects in many fields.

[0033] The solution treatment in this embodiment refers to a heat treatment process in which the alloy is heated to a high temperature single-phase region and kept at a constant temperature, so that the excess phase is fully dissolved into the solid solution and then rapidly cooled to obtain a supersaturated solid solution. Because the operation process is similar to quenching, it is also called "solution quenching".

[0034] The aging treatment in this embodiment refers to a heat treatment process in which a metal or alloy workpiece is placed at a higher temperature or kept at room temperature after solution treatment, cold plastic deformation or casting or forging, and its performance, shape and size change over time. The purpose of aging treatment includes eliminating internal stress, stabilizing organization and size, improving mechanical properties, etc.

[0035] Pulse current (i.e., spark plasma sintering) diffusion welding is an efficient welding method that uses the material's own resistance and interface contact resistance to quickly heat the interface being connected and achieve interface metallurgical bonding under a certain pressure and time. It has the advantages of fast heating rate, low connection temperature, short connection time and low energy consumption. In addition, the electromigration effect during pulse current diffusion welding can accelerate the efficiency of atomic diffusion, which will further improve the joint performance. The semi-solid interlayer and pulse current technology are combined to diffuse weld the magnesium alloy. During the welding process, the sharp solid phase hard particles of the semi-solid interlayer are used to squeeze and destroy the existing oxide film on the surface of the magnesium alloy parent material. At the same time, the liquid phase in the semi-solid interlayer greatly reduces the welding pressure and fills the pores of the bonding interface, quickly achieving metallurgical bonding of the joint. Since the joint structure composition and performance are similar to those of the parent material, not only can the welding stress be greatly reduced, ensuring that the reliability and electrical properties of the welded joint are similar to those of the parent material, at the same time, pulse current assisted diffusion welding can only heat the area near the weld, and the parent material maintains a strong plastic resistance, avoiding the deformation of the precise structure of the magnesium alloy and the evaporation of magnesium. This precise and reliable welding technology that achieves 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 1, 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 insulation time is 40 to 50 minutes.

[0037] In this optional embodiment, the welding temperature is low, and the temperature during low-temperature welding is low, which can reduce the thermal deformation and deterioration of the material during the welding process, 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, and is not prone to deformation, thereby 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 welding 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 material of the brazing material layer includes 88 to 96 parts of Al and 12 to 4 parts of Si 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. It can also reduce the defect rate of the solder and ensure the quality and stability of the processing.

[0046] Optionally, between S1 and S2, the step of placing the magnesium alloy in a CrO 3 and 65% to 75% by weight of H 2 O for 3 to 8 minutes, and then placed in acetone for later use.

[0047] In this optional embodiment, CrO 3 With H 2 O reacts to form chromic acid, whose chemical formula is H 2 CrO 4 Chromic acid is an inorganic compound. The magnesium alloy is pickled to remove oxides and rust on the surface of the magnesium alloy, and then placed in acetone to further clean the surface impurities and wash away the 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 ultrasonically cleaning it in acetone for 5 to 10 minutes; then immersing the semi-solid solder layer after alkali washing in a HNO solution with a mass fraction of 18% to 20% 3 The product was pickled in the solution for 5 to 10 minutes, and then ultrasonically cleaned in acetone for more than 30 minutes.

[0049] In this optional embodiment, the semi-solid solder layer is alkaline washed 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 acid washed to remove rust and alkaline residue on the surface of the semi-solid solder layer; and the surface impurities are further cleaned in acetone and the acid residue is washed away.

[0050] A joint provided in an embodiment of the present invention is manufactured by the magnesium alloy welding method based on a semi-solid intermediate layer and a pulse current as described in any one of the above items.

[0051] The present invention is further described below in conjunction with specific embodiments.

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

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

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

[0055] (3) placing the Al-Si alloy after solid solution at 200°C for 7 hours for aging treatment to obtain an Al-Si semi-solid intermediate layer;

[0056] (4) The surfaces of the AZ31 magnesium alloy and the Al-Si semi-solid intermediate layer were polished using 80-mesh, 600-mesh, and 1500-mesh sandpapers, and then washed in acetone for 30 min, dried, and set aside;

[0057] (5) AZ31 magnesium alloy is placed in 30% CrO 3 and 70% H 2 O was used for cleaning for 5 min, and then placed in acetone for later use;

[0058] (6) immersing the Al-Si semi-solid intermediate layer in a 10% NaOH solution, alkali washing for 5-10 minutes, and then ultrasonically cleaning it in acetone for 8 minutes;

[0059] (7) The semi-solid Al-Si intermediate layer after alkali washing was immersed in 20% HNO 3 Solution, pickling for 8 min, then ultrasonic cleaning in acetone for 30 min;

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

[0061] The AZ31 magnesium alloy joints were observed under a microscope and the shear strength was tested. Figure 2 As shown in Figure 1, 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.

[0062] Comparative Example 1

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

[0064] (1) The surface of AZ31 magnesium alloy was polished using 80-mesh, 600-mesh, and 1500-mesh sandpapers in sequence, and then washed in acetone for 30 min and dried for later use;

[0065] (2) The surface of the AZ31 magnesium alloy was polished using 80-mesh, 600-mesh, and 1500-mesh sandpapers, and then washed in acetone for 30 min and dried for later use;

[0066] (3) AZ31 magnesium alloy is placed in 30% CrO 3 and 70% H 2 O prepared acid solution for 5 min, and then placed in acetone for later use;

[0067] (4) Two pieces of AZ31 magnesium alloy were placed in a pulse current diffusion welding device for welding, and argon gas was used for protection. During the welding process, the heating rate was 100°C / min, the welding temperature was 430°C, the pressure was 7MPa, and the holding time was 45min. The welded parts were then cooled in the furnace. After cooling, they were taken out to finally obtain the AZ31 magnesium alloy joint.

[0068] Microscope observation of the AZ31 magnesium alloy joint. Figure 4 As shown in the figure, there are still a lot of holes and oxide films in the magnesium alloy joint, and the joint deformation is 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 degree of joint deformation 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 invention is disclosed as above, the protection scope of the present invention is not limited thereto. Those skilled in the art may make various changes and modifications without departing from the spirit and scope of the present invention, and these changes and modifications will fall within the protection scope of the present invention.

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 brazing material layer, smelting it at 670 to 760° C. for 25 to 35 minutes, then pouring it into a mold, cooling it to room temperature to obtain a solidified brazing material layer, placing the solidified brazing material layer at 530 to 550° C. for 2 to 4 hours for solution treatment, placing the brazing material layer after solution treatment at 180 to 220° C. for 6 to 8 hours for aging treatment to obtain a semi-solid brazing material layer; S2: placing the semi-solid solder layer between two pieces of magnesium alloy as an intermediate layer, placing the semi-solid solder layer and the magnesium alloy in a pulse current diffusion welding device for pulse current diffusion welding, and obtaining a magnesium alloy joint.

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 pulse current diffusion welding temperature is 400 to 450° C., the pressure is 2 to 4 MPa, and the pulse current diffusion welding insulation time is 40 to 50 minutes.

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

4. The magnesium alloy welding method based on semi-solid intermediate layer and pulse current according to claim 1, characterized in that: In parts by weight, the raw materials of the brazing material layer include 88 to 96 parts of Al and 12 to 4 parts of Si.

5. The magnesium alloy welding method based on semi-solid intermediate layer and pulse current according to claim 1, characterized in that: In parts by weight, the raw materials of the brazing material layer include 60 to 70 parts of Al, 35 to 15 parts of Mg and 5 to 15 parts of Si.

6. The magnesium alloy welding method based on 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.

7. The magnesium alloy welding method based on semi-solid intermediate layer and pulse current according to claim 1, characterized in that: The steps between S1 and S2 include: washing 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 3 to 8 minutes, and then placing the magnesium alloy in acetone for standby use.

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

9. A joint, characterized in that: The magnesium alloy is manufactured by the magnesium alloy welding method based on a semi-solid intermediate layer and a pulse current as described in any one of claims 1 to 8.

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