Welding method for magnesium alloy and stainless steel

Abstract

The invention discloses a welding method for a magnesium alloy and stainless steel, and belongs to the technical field of dissimilar material welding, an ultrasonic-assisted contact reaction brazing process is adopted, ultrasonic vibration is transmitted into a zinc layer through the magnesium alloy, the ultrasonic vibration is indirectly applied to the surface of the stainless steel, and proceeding of a magnesium-zinc eutectic reaction is guaranteed; the brazing temperature is selected to be higher than the magnesium-zinc eutectic reaction temperature and lower than the zinc melting point, the contact eutectic reaction of the magnesium alloy and zinc is achieved, meanwhile, the integrity of a zinc layer is guaranteed, formation of magnesium-zinc brittle compounds is controlled, the strength of a connector is improved, the welding temperature is low, energy is saved, environment friendliness is achieved, and the welding efficiency is high; the ultrasonic-assisted contact reaction brazing method for the magnesium alloy and the stainless steel is provided for the first time, low-temperature welding of the magnesium alloy and the stainless steel in the atmospheric environment is achieved, cost is low, operation is easy, and energy conservation and emission reduction are achieved.

Description

Technical Field

[0001] The present application belongs to the technical field of welding of dissimilar materials, and in particular, relates to a welding method of magnesium alloy and stainless steel. Background Art

[0002] With the emphasis on resource conservation and environmental protection, lightweighting has become a key development trend in the fields of automobiles, rail transit, etc.; magnesium alloys are widely used in the automotive manufacturing industry due to their low density, excellent shock absorption performance and superior processability, which helps to achieve vehicle weight reduction and achieve economic and environmental protection goals; magnesium alloys also have high elastic modulus, good heat dissipation, impact resistance and excellent chemical corrosion resistance, which also makes them widely used in aerospace and military industries; stainless steel occupies an important position in industrial manufacturing due to its low cost and stable performance; the combination of magnesium alloys and stainless steel can make full use of the advantages of both materials, further reduce the weight of the structure and achieve resource conservation.

[0003] However, the joining process of magnesium alloy and stainless steel faces a series of challenges. Magnesium and iron have almost no miscibility in metallurgy, and there are significant differences in their physical, chemical and mechanical properties, which makes traditional melting or solid-state joining technology difficult to apply. The problems of the existing technology are: the melting point and boiling point of magnesium and stainless steel are significantly different. When the stainless steel is melted, magnesium has already reached its boiling point, resulting in severe evaporation of magnesium, which in turn affects the performance of the welded joint; the thermal conductivity and thermal expansion coefficient of magnesium and stainless steel are quite different, which leads to large residual stress during the joining process and increases the risk of welding cracks; the solid solubility between magnesium and stainless steel is extremely low, and almost no metallurgical reaction occurs, which limits the bonding strength between them.

[0004] When welding magnesium alloy and stainless steel by conventional brazing method, a brazing filler metal with a lower melting point is generally used, such as A1-based brazing filler metal or Zn-based brazing filler metal. The brazing joint is obtained by heating and heat preservation, and the brazing filler metal is melted, wetted and spread, and then reacts with the base material to produce metallurgical reaction. Since magnesium alloy is easily oxidized during welding, a brazing flux is generally required during welding, and cleaning is required after welding. In addition, there are welding defects such as pores and microcracks, and the joint density is poor, making it difficult to achieve a high-density connection. Patent CN104084658B provides a contact reaction diffusion brazing method for magnesium alloy and stainless steel, which prepares a pure copper intermediate layer on the surface of the magnesium alloy to form a magnesium alloy / Cu / stainless steel structure, and then heats and heats in a vacuum diffusion furnace to achieve a high-quality connection between the magnesium alloy and the stainless steel. This method is not suitable for welding magnesium alloy and stainless steel in an atmospheric environment. The welding environment requires a vacuum environment, and the welding production cost is high. Summary of the invention

[0005] The purpose of the present application is to provide a method for welding magnesium alloy and stainless steel, so as to solve the technical problems that the welding temperature of traditional magnesium alloy and stainless steel is high, a vacuum environment or a brazing material is required to remove the oxide film on the surface of the magnesium alloy, and the welding efficiency is low, the quality is poor, and the cost is high.

[0006] To achieve the above purpose, the technical solution adopted in this application is: to provide a method for welding magnesium alloy and stainless steel, which specifically includes the following steps:

[0007] (I) Surface pretreatment of the base material: grinding and ultrasonic cleaning the surfaces of the magnesium alloy base material and the stainless steel base material to be welded to obtain pretreated magnesium alloy and pretreated stainless steel;

[0008] (ii) pre-treating the stainless steel surface with an intermediate layer by hot-dip plating a zinc intermediate layer plating solution on the pre-treated stainless steel surface, and cooling the surface to obtain a galvanized stainless steel with a zinc intermediate layer;

[0009] (III) Assembling a welding assembly: placing the pretreated magnesium alloy on top of the galvanized stainless steel, with the zinc intermediate layer on the surface of the galvanized stainless steel in contact with the surface to be welded of the pretreated magnesium alloy, to form an assembly to be welded;

[0010] (IV) Ultrasonic assisted brazing: The components to be welded are fixed on a heating device, and pressure is applied to the assembled workpieces. An ultrasonic device is used to apply ultrasonic vibration to the surface of the pretreated magnesium alloy. After brazing is completed, the ultrasonic device and the heating device are turned off, the temperature is lowered, and the pressure is removed to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0011] In one embodiment,

[0012] The specific steps of the grinding in step (a) are as follows: grinding is performed using #180, #300 and #500 sandpaper or sand trays in sequence.

[0013] In one embodiment,

[0014] The solvent for ultrasonic cleaning in step (a) is acetone, and the ultrasonic cleaning time is 15 minutes.

[0015] In one embodiment,

[0016] The preparation method of the zinc intermediate layer plating solution in step (ii) is as follows: a clean zinc block is placed in a dry graphite crucible, the zinc block is heated to 550° C. in a box-type resistance furnace, and the heat is maintained until the zinc block is completely melted to obtain a zinc intermediate layer plating solution.

[0017] In one embodiment,

[0018] In step (ii), the immersion temperature of the hot dip coating is about 520°C, the removal temperature is about 430°C, the immersion time is 80-120s, preferably, the immersion time is 100s; the cooling temperature is room temperature.

[0019] In one embodiment,

[0020] In step (ii), the surface zinc intermediate layer has a thickness of 150-250 um and an area of ​​20 mm*10 mm. The surface zinc intermediate layer is equal to the area to be welded of the pretreated stainless steel. Preferably, the thickness of the zinc intermediate layer is 200 um.

[0021] In one embodiment,

[0022] The size of the pretreated magnesium alloy is 10*10*5 mm, and the size of the galvanized stainless steel is 20*10*5 mm; the position of the pretreated magnesium alloy is at the center of the galvanized stainless steel.

[0023] In one embodiment,

[0024] The pressure applied to the assembly to be welded in step (iv) is 0.1-0.3 MPa.

[0025] In one embodiment,

[0026] In step (iv), the temperature of the heating device is 360-380°C, the ultrasonic power of the ultrasonic vibration applied is 50180W, the ultrasonic frequency is 20kHz, the time is 410s, and the cooling temperature is room temperature. Preferably, the temperature of the heating device is 370°C, the ultrasonic power of the ultrasonic vibration applied is 50W, and the time is 4s.

[0027] In one embodiment,

[0028] The ultrasonic vibration in step (iv) is applied continuously, and the direction of the ultrasonic vibration is perpendicular to the component to be welded.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present application applies ultrasonic vibration to the magnesium alloy by adopting an ultrasonic assisted contact reaction brazing process. The ultrasonic vibration is transmitted through the magnesium alloy to the zinc layer, and indirectly applies ultrasonic vibration to the surface of the stainless steel. The oxide film on the surface of the magnesium alloy is destroyed by the ultrasonic cavitation effect, so that magnesium and zinc form good contact and ensure the progress of the magnesium-zinc eutectic reaction. No brazing flux is required during the brazing process, which avoids the residue of brazing flux after welding and improves the connection quality of the joint. The brazing temperature is selected to be above the magnesium-zinc eutectic reaction temperature and below the melting point of zinc. While achieving the contact eutectic reaction between the magnesium alloy and zinc, the integrity of the zinc layer is ensured, the formation of magnesium-zinc brittle compounds is controlled, and the strength of the joint is improved. The welding temperature is low, energy-saving and environmentally friendly, and the welding efficiency is high. The present application proposes for the first time a brazing method for magnesium alloy and stainless steel by ultrasonic assisted contact reaction, which realizes low-temperature welding of magnesium alloy and stainless steel under atmospheric environment. The ultrasonic assisted brazing device is adopted, which has low cost, simple operation, and energy saving and emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0032] Figure 1 A schematic diagram of the ultrasonic-assisted contact reaction brazing method of magnesium alloy and stainless steel of the present application;

[0033] Figure 2 This is a diagram of the device for magnesium alloy and stainless steel with hot-dip zinc coating in this application;

[0034] Figure 3 This is a typical interface microstructure diagram of the ultrasonic assisted contact reaction brazing joint in the embodiment of the present application.

[0035] Explanation of symbols in the figure:

[0036] 1. AZ31B magnesium alloy; 2. Zinc intermediate layer; 3. 316 stainless steel; 4. Ultrasonic head; 5. Limit block; 6. Cover plate; 7. Base; 8. Components to be welded. DETAILED DESCRIPTION

[0037] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clear, the present application is further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0038] Example 1

[0039] A method for welding a magnesium alloy and stainless steel comprises the following steps:

[0040] (i) Surface pretreatment of the parent material: The surfaces to be welded of the AZ31B magnesium alloy parent material and the 316 stainless steel parent material are polished with #180, #300, and #500 sandpaper or sand tray in turn, and then the parent materials to be welded are placed in acetone, ultrasonically cleaned at room temperature for 15 minutes, and then dried for standby use, thereby obtaining the pretreated magnesium alloy and pretreated stainless steel;

[0041] (ii) Pre-treatment of the stainless steel surface by dipping the intermediate layer: in a graphite crucible, the zinc intermediate layer plating solution is hot-dip plated on the surface of the pre-treatment stainless steel by hot-dip plating, the immersion temperature is about 520°C, the removal temperature is about 430°C, the dipping time is 100s, and the pre-treatment stainless steel after the zinc intermediate layer is dipped is air-cooled to room temperature to obtain galvanized stainless steel with a zinc intermediate layer on the surface, the thickness of the surface zinc intermediate layer is 200um, the area is 20mm*10mm, and the area of ​​the zinc intermediate layer is equal to the area of ​​the pre-treatment stainless steel to be welded;

[0042] The preparation method of the zinc intermediate layer plating solution is as follows: a cleaned zinc block is placed in a dry graphite crucible, the zinc block is heated to 550° C. in a box-type resistance furnace, and the temperature is kept for 5 minutes until the zinc block is completely melted, thereby obtaining the zinc intermediate layer plating solution;

[0043] (iii) assembling the welding assembly: placing the pretreated magnesium alloy on the galvanized stainless steel, the zinc intermediate layer on the surface of the galvanized stainless steel and the surface to be welded of the pretreated magnesium alloy are in contact with each other, forming the assembly to be welded 8;

[0044] (IV) Ultrasonic assisted brazing: Fix the assembly 8 to be welded on the heating device, and apply a pressure of 0.1-0.3MPa to the assembly 8 to be welded to ensure that the assembly 8 to be welded is always in a compressed state. When the temperature of the heating device rises to 370°C, start the ultrasonic device, set the ultrasonic power to 50W, and the ultrasonic frequency to 20kHz, apply ultrasonic vibration to the surface of the pretreated magnesium alloy, turn off the ultrasonic device and the heating device after the ultrasonic action for 4s, remove the pressure after cooling to room temperature, and obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint;

[0045] In this embodiment, the heating device includes but is not limited to a hot table and a high-frequency induction device; the size of the pretreated magnesium alloy is set to 10*10*5mm, the size of the galvanized stainless steel is set to 20*10*5mm, the position of the pretreated magnesium alloy is at the center of the galvanized stainless steel, and the deviation of the center positions of the two is less than 0.5mm; the end of the ultrasonic head 4 of the ultrasonic device is a circle with a radius of 5mm, the ultrasonic vibration is applied continuously, and the direction of the ultrasonic vibration is perpendicular to the component 8 to be welded.

[0046] Example 2

[0047] The present embodiment differs from Example 1 in that the hot-dip plating time in step (ii) is 80 seconds, and the other steps are the same, thereby obtaining a magnesium alloy-stainless steel ultrasonic-assisted contact reaction brazing joint.

[0048] Example 3

[0049] The present embodiment differs from Example 1 in that the hot-dip plating time in step (ii) is 120 seconds, and the other steps are the same, thereby obtaining a magnesium alloy-stainless steel ultrasonic-assisted contact reaction brazing joint.

[0050] Example 4

[0051] The present implementation method is different from Example 1 in that the thickness of the intermediate layer of the pre-treated stainless steel surface by immersion plating in step (ii) is 150 um, and the other steps are the same to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0052] Example 5

[0053] The present implementation method is different from Example 1 in that the thickness of the intermediate layer of the pre-treated stainless steel surface by immersion plating in step (ii) is 250 um, and the other steps are the same to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0054] Example 6

[0055] The difference between this embodiment and Example 1 is that the temperature of the heating device in step (iv) is 360° C., and the other steps are the same, to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0056] Example 7

[0057] The difference between this embodiment and Example 1 is that the temperature of the heating device in step (iv) is 380° C., and the other steps are the same, to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0058] Example 8

[0059] The present embodiment differs from Example 1 in that the ultrasonic power of the ultrasonic vibration applied in step (iv) is 100 W, and the other steps are the same, thereby obtaining a magnesium alloy-stainless steel ultrasonic-assisted contact reaction brazing joint.

[0060] Example 9

[0061] The present embodiment differs from Example 1 in that the ultrasonic power of the ultrasonic vibration applied in step (iv) is 150 W, and the other steps are the same, thereby obtaining a magnesium alloy-stainless steel ultrasonic-assisted contact reaction brazing joint.

[0062] Example 10

[0063] The present embodiment differs from Example 1 in that the ultrasonic power of the ultrasonic vibration applied in step (iv) is 180 W, and the other steps are the same, thereby obtaining a magnesium alloy-stainless steel ultrasonic-assisted contact reaction brazing joint.

[0064] Embodiment 11

[0065] The difference between this embodiment and Example 1 is that the ultrasonic vibration is applied for 6 seconds in step (iv), and the other steps are the same to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0066] Example 12

[0067] The difference between this embodiment and Example 1 is that the ultrasonic vibration is applied for 8 seconds in step (iv), and the other steps are the same to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0068] Embodiment 13

[0069] The difference between this embodiment and Example 1 is that the ultrasonic vibration is applied for 10 seconds in step (iv), and the other steps are the same to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

[0070] The present application provides a method for welding magnesium alloy and stainless steel, which specifically includes the following steps: pretreatment of the surface of the base material: grinding and ultrasonic cleaning the surfaces to be welded of the magnesium alloy base material and the stainless steel base material to obtain the pretreated magnesium alloy and the pretreated stainless steel; immersion plating of the intermediate layer on the surface of the pretreated stainless steel: hot-dip plating of the zinc intermediate layer plating solution on the surface of the pretreated stainless steel, cooling to obtain the galvanized stainless steel with the surface galvanized intermediate layer; assembling the welding assembly: placing the pretreated magnesium alloy on top of the galvanized stainless steel, the surface zinc intermediate layer of the galvanized stainless steel and the surface to be welded of the pretreated magnesium alloy are in contact with each other to form an assembly to be welded; ultrasonic assisted brazing: fixing the assembly to be welded on a heating device, applying pressure to the assembled workpiece, applying ultrasonic vibration to the surface of the pretreated magnesium alloy by an ultrasonic device, closing the ultrasonic device and the heating device after brazing, cooling, and removing the pressure to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint; the present application hot-dip galvanizing the stainless steel surface, and then using contact reaction brazing to make the zinc at 360-380°C At a temperature of about 100°C, the zinc alloy is brazed with magnesium for contact reaction to form a magnesium-zinc compound, thereby realizing low-temperature metallurgical bonding of zinc and magnesium alloy; ultrasonic vibration is applied to the magnesium alloy, and ultrasonic vibration is indirectly applied to the hot-dip galvanized stainless steel surface, so that ultrasonic cavitation bubbles are generated at the contact surface of zinc and stainless steel, and these bubbles are formed, grown and burst at the interface. The bursting of the bubbles causes the surface energy and liquid kinetic energy to be converted into thermal energy and chemical energy, and the local high temperature and high pressure generated at the interface between zinc and stainless steel promote the low-temperature wetting of zinc on stainless steel and the metallurgical bonding of the Zn element in the zinc layer with the Fe element in the stainless steel, thereby realizing the metallurgical bonding of the zinc layer and the stainless steel, and finally realizing low-temperature welding of magnesium alloy and stainless steel under atmospheric environment; the oxide film on the surface of the magnesium alloy is removed by applying ultrasonic vibration, and no brazing agent is required during the brazing process, which is energy-saving and environmentally friendly; the present application proposes for the first time an ultrasonic-assisted contact reaction brazing method for magnesium alloy and stainless steel, and adopts an ultrasonic-assisted brazing device, which is low in cost, simple in operation, energy-saving and emission-reducing, and can be widely used in the field of welding technology of dissimilar materials.

[0071] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0072] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for welding magnesium alloy and stainless steel, characterized in that: The specific steps include: (1) Surface pretreatment of the base material: grinding and ultrasonic cleaning the surfaces to be welded of the magnesium alloy base material and the stainless steel base material to obtain pretreated magnesium alloy and pretreated stainless steel; (ii) pre-treating the stainless steel surface with an intermediate layer by hot-dip plating a zinc intermediate layer plating solution on the pre-treated stainless steel surface, and cooling the surface to obtain a galvanized stainless steel with a zinc intermediate layer; (III) Assembling a welding assembly: placing the pretreated magnesium alloy on top of the galvanized stainless steel, with the zinc intermediate layer on the surface of the galvanized stainless steel in contact with the surface to be welded of the pretreated magnesium alloy, to form an assembly to be welded; (IV) Ultrasonic assisted brazing: The components to be welded are fixed on a heating device, and pressure is applied to the components to be welded. An ultrasonic device is used to apply ultrasonic vibration to the surface of the pretreated magnesium alloy. After brazing is completed, the ultrasonic device and the heating device are turned off, the temperature is lowered, and the pressure is removed to obtain a magnesium alloy-stainless steel ultrasonic assisted contact reaction brazing joint.

2. A method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: The specific steps of the grinding in step (a) are as follows: grinding is performed using #180, #300 and #500 sandpaper or sand tray in sequence.

3. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: The solvent for ultrasonic cleaning in step (a) is acetone, and the ultrasonic cleaning time is 15 minutes.

4. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: The preparation method of the zinc intermediate layer plating solution in step (ii) is as follows: a clean zinc block is placed in a dry graphite crucible, the zinc block is heated to 550° C. in a box-type resistance furnace, and the heat is maintained until the zinc block is completely melted to obtain a zinc intermediate layer plating solution.

5. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: In step (ii), the immersion temperature of the hot dip coating is about 520°C, the removal temperature is about 430°C, and the immersion time is 80-120s; the cooling temperature is room temperature.

6. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: In step (ii), the thickness of the surface zinc intermediate layer is 150-250um, and the area is 20mm*10mm. The surface zinc intermediate layer is equal to the area to be welded of the pretreated stainless steel.

7. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: The size of the pretreated magnesium alloy is 10*10*5 mm, and the size of the galvanized stainless steel is 20*10*5 mm; the position of the pretreated magnesium alloy is at the center of the galvanized stainless steel.

8. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: The pressure applied to the assembly to be welded in step (iv) is 0.1-0.3 MPa.

9. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: In step (iv), the temperature of the heating device is 360-380°C, the ultrasonic power of the ultrasonic vibration is 50180W, the ultrasonic frequency is 20kHz, the time is 410s, and the cooling temperature is room temperature.

10. The method for welding magnesium alloy and stainless steel according to claim 1, characterized in that: The ultrasonic vibration in step (iv) is applied continuously, and the direction of the ultrasonic vibration is perpendicular to the component to be welded.

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