A high-energy precise pulse cold welding method for magnesium-steel sheet welding

Abstract

The present application relates to the field of material processing engineering, and particularly relates to a high-energy precise pulse cold welding method for magnesium-steel sheet welding, the principle of which is to use a high-power capacitor as a welding power source, to release a pulse arc with high energy density and concentration between a tungsten electrode and a welding piece in an instant during welding, and to realize the connection of the workpiece. In view of the poor interface metallurgical compatibility existing in the welding of magnesium-steel dissimilar metals, the high-energy precise pulse cold welding method is adopted to precisely control the pulse current, pulse time and pulse interval in the order of ms, to optimize the energy distribution of the joint, to accurately control the interface temperature of the magnesium-steel dissimilar metals, to regulate the characteristics of the intermetallic compounds of the interface, and to obtain a high-quality magnesium-steel fusion-brazing joint. Moreover, the welding device used in the welding method is simple in equipment, convenient in operation, low in welding cost and high in efficiency.

Description

Technical Field

[0001] This invention relates to the field of materials processing technology, specifically to the field of magnesium-steel thin plate welding technology, and particularly to a high-energy precision pulse cold welding method for magnesium-steel thin plate welding. Background Technology

[0002] Magnesium alloys, due to their low density, high specific strength, high rigidity, good electromagnetic shielding performance, and good thermal conductivity, are widely used in transportation, electronics, aerospace, and chemical industries. Steel, a structural material with high strength, high plasticity, and good weldability, is the most widely used metallic structural material in society today. Magnesium and steel have broad and overlapping applications; using magnesium-steel composite structures to replace steel can improve material utilization, reduce structural weight, and lower costs. However, magnesium and steel have significant differences in their thermal and physical properties. The melting point of iron (1811K) is much higher than the boiling point of magnesium (1363K), and the two cannot coexist in the liquid state. Furthermore, magnesium and iron have extremely poor metallurgical compatibility, very low miscibility, and no intermetallic compounds are formed. Therefore, welding dissimilar metals like magnesium and steel is very difficult.

[0003] Fusion-brazing is one of the most promising methods for joining dissimilar metals. When welding magnesium and steel dissimilar metal joints using this method, the magnesium side undergoes fusion welding and the steel side undergoes brazing. This avoids excessive evaporation and spattering of the magnesium alloy during welding, reduces defects such as porosity and cracks in the welded joint, and achieves effective bonding of the magnesium-steel joint. Current research on fusion-brazing of magnesium and steel dissimilar metals mainly uses methods such as adding metal interlayers, coatings, and filler wires to improve the metallurgical environment of the joint and promote metallurgical bonding at the magnesium-steel interface. Based on this, further controlling the joining temperature and precisely controlling the interface characteristics (type, morphology, and thickness of intermetallic compounds) is key to obtaining excellent magnesium-steel dissimilar metal joints. A magnesium-steel MIG fusion-brazing method disclosed in Chinese patent application "CN103495796A" controls the intermetallic compound characteristics at the magnesium-steel joint interface by optimizing the magnesium alloy welding wire composition and welding process parameters to obtain magnesium-steel welded joints. However, traditional MIG welding methods have a large heat input, making it difficult to control the welding heat input, and are also difficult to weld thin plates with a thickness of less than 2 mm. Chinese patent application CN108188582A discloses a method for butt welding magnesium alloy plates and steel plates using a laser-arc composite filler wire welding process. This method controls the energy matching of the laser and arc heat sources, regulates the temperature during the instantaneous coexistence of gas and liquid at the magnesium / steel interface, and modulates the characteristics of the intermetallic compounds to obtain a welded joint with high interfacial bonding performance. However, this method is mainly for magnesium-steel butt joints, and the welding process is complex and costly. Summary of the Invention

[0004] To address the aforementioned technical problems, a high-energy precision pulsed cold welding method for magnesium-steel thin plate welding is provided. The principle of this invention lies in using a high-power capacitor as the welding power source, and releasing a high-energy-density, concentrated pulsed arc instantaneously between the tungsten electrode and the workpiece during the welding process to achieve workpiece connection. To address the problem of poor interfacial metallurgical compatibility in magnesium-steel dissimilar metal welding, a high-energy precision pulsed welding method is employed. This method precisely controls the welding energy parameters—pulse current, pulse time, and pulse interval—at the millisecond level, optimizing the joint energy distribution and precisely controlling the magnesium-steel dissimilar metal interface temperature to regulate the intermetallic compound characteristics, thereby obtaining a high-quality magnesium-steel fusion-brazing joint.

[0005] The technical means employed in this invention are as follows:

[0006] A high-energy precision pulse cold welding method for welding magnesium-steel thin plates includes:

[0007] Step 1: Before welding, pre-treat the weld edges of magnesium and steel thin plates by grinding the weld edges to expose the metallic luster and removing the oxide film on the surface of the material. Then, clean the weld edges to remove the grease and dust on the surface and finally dry them for welding.

[0008] Step 2: Butt or overlap magnesium or steel sheets, place the parts to be welded between the upper and lower backing plates in a parallel manner, and use clamps to clamp the upper and lower backing plates to fix the weldment;

[0009] Step 3: Adjust the position of the welding torch according to the welding method of magnesium and steel thin plates, so that the tip of the tungsten electrode is placed vertically above the part to be welded, and the torch tip is pointing towards the workpiece; connect the welding torch to the high-energy precision pulse cold welding device, which uses a capacitor as the welding power source and releases a pulsed arc instantaneously between the tungsten electrode and the part to be welded during the welding process.

[0010] Step 4: Set the welding energy parameters of the high-energy precision pulse cold welding device according to the thickness of the magnesium and steel sheets;

[0011] Step 5: Turn on the high-energy precision pulse cold welding device. The welding torch will automatically complete the welding process according to the preset program of the high-energy precision pulse cold welding device's walking mechanism.

[0012] Furthermore, the welding energy parameters include pulse current of 50–150 A, pulse interval of 100–500 ms, pulse time of 300–800 ms, welding speed of 3.6–36 m / min, and argon flow rate of 5–20 L / min.

[0013] Furthermore, the high-energy precision pulse cold welding device melts the magnesium sheet and wets the steel sheet during the welding process to obtain a magnesium-steel fusion-brazing joint.

[0014] Furthermore, the high-energy precision pulse cold welding device employs filler wire, plating, and metal interlayer addition during the welding process to add alloying elements between dissimilar metals such as magnesium and steel, thereby improving the metallurgical environment of the joint and promoting the metallurgical bonding of the magnesium-steel interface.

[0015] Furthermore, when magnesium and steel sheets are butt-welded, the tungsten electrode should be offset 0.1 to 0.5 mm towards the steel sheet to increase the temperature of the steel sheet during welding, enhance the wettability of molten magnesium on the surface of the steel sheet, and ensure the weld formation of the joint.

[0016] Furthermore, when the magnesium and steel plates are joined in an overlapping manner, the magnesium sheet is on the upper layer and the steel sheet is on the lower layer, with an overlap of 10-20 mm. The tungsten electrode is perpendicular to the magnesium sheet and 5-10 mm away from the edge of the overlap. During welding, the magnesium sheet is melted to wet the steel sheet, ensuring the weld formation of the joint.

[0017] Furthermore, the thickness of the magnesium sheet and steel sheet is 0.2–2 mm.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. This invention uses a high-power (500-2000W) capacitor as the welding power source. During the welding process, the electrical energy stored in the capacitor can be released instantaneously (on the order of milliseconds) between the tungsten electrode and the workpiece in the form of a pulsed arc. A single discharge process can release a large current (50-200A), with high and concentrated energy density. This can melt the magnesium base material, wet the steel base material, and promote the metallurgical reaction between the alloying elements in the base material and the magnesium and iron elements to generate intermetallic compounds, thus enabling the magnesium-steel dissimilar metals to be metallurgically joined.

[0020] 2. This invention uses a high-power capacitor as the welding power source. There is an interval between the discharge time and the next discharge time, which allows sufficient time for heat to diffuse through the workpiece substrate. Heat will not accumulate in the molten pool, which helps to reduce the heat-affected zone and welding deformation. It is suitable for thin plate welding.

[0021] 3. This invention uses a high-energy precision pulse cold welding process, which can precisely control the energy parameters of the pulsed arc released by the welding heat source: pulse current, pulse time, and pulse interval at the millisecond level. It can accurately control the temperature of the magnesium-steel dissimilar metal interface, regulate the intermetallic compound characteristics, and obtain a high-quality magnesium-steel welded joint.

[0022] 4. The high-energy precision pulse cold welding process used in this invention belongs to the electric arc welding method. The welding equipment is simple, easy to operate, precise to control, low in welding cost, and high in efficiency. It is suitable for the actual production of magnesium-steel dissimilar metal welding joints.

[0023] Based on the above reasons, this invention can be widely applied in fields such as magnesium-steel dissimilar metals. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the high-energy precision pulse cold welding method for lap joint of magnesium-steel thin plates in a specific embodiment of the present invention.

[0026] Figure 2 This is the macroscopic morphology of the lap joint between a 1mm thick AZ31B magnesium alloy sheet and a 430 ferritic stainless steel sheet in a specific embodiment of the present invention.

[0027] In the diagram: 1. Welding torch; 2. Tungsten electrode; 3. Upper backing plate; 4. AZ31B magnesium alloy sheet; 5. Lower backing plate; 6. Industrial pure aluminum foil; 7. 430 ferritic stainless steel sheet. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0031] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0032] In the description of this invention, it should be understood that the orientation or positional relationship indicated by directional terms such as "front, back, up, down, left, right", "horizontal, vertical, horizontal" and "top, bottom" is generally based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing this invention and simplifying the description. Unless otherwise stated, these directional terms do not indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the scope of protection of this invention. The directional terms "inner" and "outer" refer to the inner and outer contours relative to the outline of each component itself.

[0033] For ease of description, spatial relative terms such as "above," "over," "on the upper surface of," "above," etc., are used herein to describe the spatial positional relationship of a device or feature as shown in the figures to other devices or features. It should be understood that spatial relative terms are intended to encompass different orientations in use or operation besides the orientation of the device as described in the figures. For example, if the device in the figures is inverted, a device described as "above" or "above" other devices or structures would subsequently be positioned as "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below." The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein will be interpreted accordingly.

[0034] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore should not be construed as limiting the scope of protection of this invention.

[0035] like Figures 1-2As shown, a high-energy precision pulse cold welding method for welding magnesium-steel thin plates is described. This method employs a high-energy precision pulse cold welding device, with the Hengrui HR-05 high-intensity laser welding machine as the heat source. During welding, the pulse current, pulse time, and pulse interval can be adjusted according to the plate thickness. The traveling device in the high-energy precision pulse cold welding device uses a Shanghai Huwei CG1-30 semi-automatic gas cutting machine. The magnesium thin plate is a 1mm thick AZ31B magnesium alloy thin plate 4, and the steel thin plate is a 1mm thick 430 ferritic stainless steel thin plate 7.

[0036] Includes the following steps:

[0037] Step 1: Before welding, the weld edges of AZ31B magnesium alloy sheet 4 and 430 ferritic stainless steel sheet 7 are pretreated by grinding the weld edges to expose the metallic luster and removing the oxide film on the surface of the material. Then, the weld edges are cleaned with petroleum ether to remove the grease and dust on the surface. Finally, they are dried with a hot air blower in preparation for welding.

[0038] Step 2: Butt or lap the AZ31B magnesium alloy sheet 4 and the 430 ferritic stainless steel sheet 7. When butt welding, the tungsten electrode should be offset 0.1 to 0.5 mm towards the steel sheet to increase the temperature of the steel sheet during welding, enhance the wettability of molten magnesium on the surface of the steel sheet, and ensure the weld formation of the joint.

[0039] In this specific embodiment, an overlapping method is adopted. The AZ31B magnesium alloy sheet 4 is placed on the upper layer, and the 430 ferritic stainless steel sheet 7 is placed on the lower layer. Industrial pure aluminum foil 6 is added in the middle as an intermediate layer and overlapped together. The overlap is 15mm. The part to be welded is placed on the fixture pad in a parallel manner. The magnesium-steel overlapping structure is clamped by the two upper pads 3 and the two lower pads 5 of the fixture device. The distance between the two upper pads 3 is 10mm, exposing the magnesium-steel overlapping weld seam to be welded.

[0040] Step 3: Position the welding torch 1 so that the tip of the tungsten electrode 2 is placed vertically 0.5mm above the front of the workpiece and 8mm away from the overlapping edge, with the torch tip pointing towards the workpiece.

[0041] Step 4: Based on the selected AZ31B magnesium alloy sheet and 430 ferritic stainless steel sheet, both with a thickness of 1mm, set the welding process parameters for the cold welding device and its traveling device: pulse current 150A; pulse interval 150ms; pulse time 800ms; welding speed 10.8m / min; argon flow rate: 15L / min;

[0042] Step 5: Turn on the high-energy precision pulse cold welding device and the walking device. The welding torch 1 will automatically complete the welding process according to the preset program of the walking device.

[0043] The macroscopic morphology of the obtained magnesium-steel lap joint is as follows Figure 2 As shown, the welded joint is free of welding defects such as cracks and deformation. A high-energy precision pulse cold welding method was used to achieve a fusion-brazing connection between magnesium and steel dissimilar metals. Compositional analysis of the interface layer in the cross-section of the magnesium-steel welded joint revealed the presence of a Mg-Al compound layer that wets the steel base material surface, enabling the welded joint to complete the metallurgical connection. Furthermore, the absence of an Fe-Al compound layer that would degrade the welded joint's performance resulted in an effective welded joint. The welded joint achieved a maximum shear strength of 142 MPa. Compared to existing magnesium-steel dissimilar metal welding methods, the high-energy precision pulse cold welding method of this invention can precisely control the welding heat input, thereby controlling the formation and thickness of the intermetallic compound layer at the magnesium-steel interface. Moreover, the welding equipment is simple, easy to operate, and has high welding efficiency.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-energy precision pulse cold welding method for welding magnesium-steel thin plates, characterized in that, include: Step 1: Before welding, pre-treat the weld edges of the magnesium and steel thin plates to expose the metallic luster. Step 2: Butt or overlap magnesium and steel sheets. Place the parts to be welded in a parallel manner and fix them. When the magnesium and steel sheets are butt-jointed, the tungsten electrode should be offset towards the steel sheet by 0.1~0.5mm. When the magnesium and steel sheets are overlapped, the magnesium sheet should be on the upper layer and the steel sheet on the lower layer, with an overlap of 10~20mm. Step 3: Adjust the position of the welding torch according to the welding method of magnesium and steel thin plates, so that the tip of the tungsten electrode is placed vertically above the part to be welded, and the torch head points towards the workpiece. When the magnesium and steel thin plates are butt-jointed, the tungsten electrode is shifted towards the steel plate to increase the temperature of the steel plate during welding, enhance the wettability of molten magnesium on the surface of the steel plate, and ensure the weld formation of the joint. When the magnesium and steel plates are lap-jointed, the tungsten electrode is pointed vertically towards the magnesium plate and 5-10 mm away from the lap edge. During welding, the molten magnesium plate wets the steel plate, ensuring the weld formation of the joint. The welding torch is connected to a high-energy precision pulse cold welding device. The high-energy precision pulse cold welding device uses a capacitor as the welding power source and releases a pulsed arc instantaneously between the tungsten electrode and the part to be welded during the welding process. Step 4: Set the welding energy parameters of the high-energy precision pulse cold welding device according to the thickness of the magnesium and steel sheets; Welding energy parameters include pulse current 50~150A, pulse interval 100~500ms, pulse time 300~800ms, welding speed 3.6~36m / min, and argon flow rate 5~20L / min; Step 5: Turn on the high-energy precision pulse cold welding device. The welding torch will automatically complete the welding process according to the preset program of the high-energy precision pulse cold welding device's walking mechanism. In the cross-sectional interface layer of the magnesium-steel lap joint obtained after welding, there is a Mg-Al compound layer that wets the surface of the steel base material, enabling the welded joint to complete the metallurgical connection, and there is no Fe-Al compound layer that would reduce the performance of the welded joint.

2. The high-energy precision pulse cold welding method for magnesium-steel thin plate welding according to claim 1, characterized in that, The high-energy precision pulse cold welding device melts magnesium sheet and wets steel sheet during the welding process to obtain magnesium-steel fusion-brazing joint.

3. The high-energy precision pulse cold welding method for magnesium-steel thin plate welding according to claim 2, characterized in that, The high-energy precision pulse cold welding device uses filler wire, plating, and metal interlayer addition during the welding process to add alloying elements between dissimilar metals such as magnesium and steel, improve the metallurgical environment of the joint, and promote the metallurgical bonding of the magnesium-steel interface.

4. The high-energy precision pulse cold welding method for welding magnesium-steel thin plates according to claim 1, wherein the thickness of the magnesium thin plate and the steel thin plate is 0.2~2mm.

Images