Method for inducing strengthening and toughening of magnesium / stainless steel flexible heat source lap welding interface through rare earth elements

Abstract

The invention provides a method for inducing strengthening and toughening of a magnesium / stainless steel flexible heat source lap welding interface through rare earth elements. The problem that in a magnesium alloy / stainless steel lap welding structure with magnesium on the upper portion and steel on the lower portion, in the traditional welding process, brittle Mg-based eutectic compounds are likely to be generated on an Mg-Fe interface, and therefore the performance of a connector is degraded is solved. According to the method, the welding thought that the energy gradient of a welding seam is regulated and controlled through the spatial domain division effect of the laser-induced arc flexible heat source and the interface structure is regulated and controlled through filling of magnesium-rare earth welding wires is provided; the Mg-Fe interface has a larger metallurgical bonding area, a tough interface compound and a wider strong diffusion solid solution layer, the joint performance is improved by 1.5 times compared with that of a traditional welding method, and the interface energy gradient and the interface structure of the magnesium / stainless steel dissimilar metal lap welding joint are accurately regulated and controlled. And the industrial application process of the magnesium / stainless steel dissimilar metal key structure is promoted.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of processing engineering, in particular, especially relates to a method for strengthening and toughening the interface of a magnesium / stainless steel flexible heat source lap joint induced by rare earth elements. BACKGROUND

[0002] Under the dual drive of green development strategy, energy conservation and environmental protection and lightweight design have become the core direction of transformation and upgrading of various industries. As the lightest "21st century green engineering metal structural material", magnesium alloy has attracted widespread attention in key engineering fields. In the field of vehicle transportation, every 1 kg of automobile weight reduction can reduce carbon emissions by 4 g per kilometer. Data shows that by 2035, the lightweight coefficient of fuel passenger cars will be reduced by 25%, and the lightweight coefficient of pure electric passenger cars will be reduced by 35%, and the proportion of magnesium alloy in the whole vehicle will increase from the current 1% to 4%. Therefore, it is urgent to realize the mass application of lightweight materials and promote the development of energy conservation and environmental protection and the national economy.

[0003] Hybrid material design is an important way to achieve automobile lightweight. Steel is still the main material of automobile, and realizing high-strength welding of magnesium alloy and steel dissimilar metal lap joint structure is the future trend of automobile lightweight structure design. However, magnesium-steel belongs to a difficult solid solution and non-reactive system, and there are many challenges such as large difference in melting point, different crystal structure, and no connecting medium, etc. Therefore, domestic and foreign scholars have made breakthrough progress in magnesium / ordinary carbon steel and magnesium / high-strength steel lap joint structure connection through heat source optimization and interface alloying strategy (such as CN102528286A, CN102091872A, CN103551759A, etc.), so that the tensile strength of the joint reaches more than 85% of the magnesium matrix. However, there are few studies on magnesium / stainless steel, because the content of alloying elements in stainless steel is more than 20wt.%, the interface energy is very high, which leads to the accumulation of Mg / Fe interface elements, and it is very difficult to diffuse into the stainless steel matrix, so that a large number of low-temperature hard and brittle Mg-based eutectic compounds (such as Mg-Al, Mg-Zn, etc.) are formed at the interface, which greatly deteriorates the joint performance (under the same process, the performance of magnesium / stainless steel lap welded joint is only 1 / 3 of that of magnesium / ordinary carbon steel or high-strength steel joint). Therefore, it is urgent to develop a welding method that can form strong diffusion and firm metallurgical bonding at the interface of magnesium / stainless steel lap welded joint, in order to realize automobile lightweight structure design and energy conservation and environmental protection development. SUMMARY

[0004] According to the Mg / Fe interface element accumulation of the traditional Mg / stainless steel lap joint proposed above, it is extremely difficult to diffuse into the stainless steel matrix, so that a large number of low-temperature hard and brittle Mg-based eutectic compounds are formed at the interface, which greatly deteriorates the joint performance. The present application proposes a welding idea of laser-induced arc flexible heat source space domain action to regulate the weld energy gradient and fill the magnesium rare earth welding wire to regulate the interface structure. By using the principle of laser-induced arc directional energy transfer, through laser-arc-wire space phase design (offset, misplacement, D la etc.), the weld energy gradient distribution is regulated, and then the interface metallurgical reaction kinetics process is optimized, and the interface structure is improved. Secondly, by using the micro-alloying effect of rare earth elements, through filling the magnesium rare earth welding wire, the strong diffusion behavior of the magnesium / stainless steel lap joint interface is induced and the strong and tough Mg-RE, Fe-RE interface compounds are formed, so that it forms a firm semi-coherent or full-coherent combination with the matrix on both sides, and finally realizes the good forming and high performance welding of the magnesium alloy / stainless steel lap joint structure, and the joint performance is improved by more than 1.5 times (from 115N / mm to 290N / mm).

[0005] The technical means adopted by the present application are as follows: A rare earth element induced magnesium / stainless steel flexible heat source lap welding interface strengthening method is provided for the lap welding structure of magnesium alloy on the top and stainless steel on the bottom. Laser-induced arc flexible heat source space domain action is used to regulate the weld energy gradient, and magnesium rare earth welding wire is filled to regulate the interface structure. By using the principle of laser-induced arc directional energy deflection and the micro-alloying effect of rare earth elements, a larger metallurgical bonding area, strong and tough interface compounds and a wide range of strong diffusion solid solution layer are formed at the Mg-Fe interface to improve the joint performance, Specifically, the steps include the following steps: S1. Lap assembly: assemble the magnesium alloy plate and the stainless steel plate into a lap structure with magnesium on top and steel on bottom, ensure that the lap area is tightly attached, and the thickness of the magnesium alloy and the stainless steel plate ranges from 0.1 to 3mm, which can be equal or unequal thickness; S2. Heat source arrangement: the laser and the arc heat source are located above the stainless steel matrix, and the two heat sources are in a non-overlapping XOZ plane along the welding direction. The heat source sequence is laser heat source first and arc heat source second. The welding wire and the arc heat source are in an overlapping XOZ plane along the welding direction; S3. Parameter setting: design the spatial relative position of the laser beam and the arc and the welding wire, including the horizontal offset of the tungsten tip from the edge of the magnesium alloy to be welded perpendicular to the welding direction, the horizontal misplacement of the tungsten tip from the laser beam perpendicular to the welding direction, and the horizontal distance Dla of the tungsten tip from the laser beam along the welding direction; S4. Lap welding: laser-induced arc flexible heat source welding is carried out with the set parameters, magnesium rare earth welding wire is filled, and lap welding is completed; S5. Post-weld cooling: naturally cooling to room temperature to obtain a high-performance magnesium / stainless steel lap welded joint.

[0006] Further, the laser heat source is selected from a solid laser or a fiber laser, and the laser mode is a pulse mode; the arc heat source is selected from a GTA arc or a GMA arc, and the heat source mode is an alternating current mode.

[0007] Further, the offset amount, the misalignment amount and the Dla in step S3 are all in the range of 0-5 mm.

[0008] Further, the magnesium-rare earth welding wire is selected from a WE series magnesium-rare earth welding wire or a VW series magnesium-rare earth welding wire, and the rare earth element promotes strong diffusion behavior and a metallurgical reaction with the base element during the welding process to generate Mg-RE and Fe-RE interface compounds.

[0009] Further, the welding parameters in step S4 further include: a laser power of 200-500 W, an arc current of 60-100 A, a welding speed of 500-700 mm / min, and a laser defocusing amount of -1-1 mm.

[0010] Further, the method is applicable to not only the lap welding of magnesium alloy and stainless steel, but also the butt welding structure of magnesium alloy and stainless steel, specifically, the magnesium alloy plate and the stainless steel plate are arranged in butt joint, a butt joint gap is reserved, and the offset amount, the misalignment amount and the Dla in step S3 are dynamically adjusted according to the butt joint gap to ensure that the laser and the arc energy are concentrated on the butt joint gap area. The specific gap is 0-2 mm.

[0011] Further, the welding mode can be selected from a single-sided welding and double-sided forming mode or a double-sided welding forming mode. In the double-sided welding forming mode, one side is welded first, and then the other side is welded after cooling, and the welding parameters of the two sides can remain the same.

[0012] Compared with the prior art, the present application has the following advantages: 1. The present application can realize strong diffusion behavior of rare earth elements in the stainless steel base to form a Fe (RE) solid solution with a diffusion scale of up to hundreds of microns; 2. The present application can make the laser keyhole move flexibly and directionally to the tail of the weld, and the moving range can reach 0-5 mm, which greatly widens the process window and improves the interface metallurgical bonding area and the joint carrying capacity; 3. The present application can flexibly control the weld energy gradient distribution and accurately control the metallurgical reaction kinetics process to form a strong and tough Mg-RE and Fe-RE intermetallic compound interface layer to strengthen the joint performance.

[0013] The present application is based on the principle of laser-induced arc directional energy transfer, and through the spatial phase design (offset amount, misalignment amount, D laThe first is to control the energy gradient distribution of the welding seam by using the flexible heat source, so as to optimize the interface metallurgical reaction kinetics process and improve the interface structure. The second is to use the micro-alloying effect of the rare earth element, to induce the strong diffusion behavior of the magnesium / stainless steel lap joint interface and form the strong and tough Mg-RE, Fe-RE interface compound, so that the interface compound forms a firm semi-coherent or full-coherent combination with the two sides of the matrix, and finally realizes the good forming and high-performance welding of the magnesium alloy / steel lap welding structure.

[0014] The present application is suitable for different steel grades and different plate thicknesses of magnesium alloy / steel dissimilar metal lap welding structure, and can solve the problems of non-spreading, difficult solid solution and non-reaction of the welding seam caused by the large difference in physical and chemical properties of magnesium alloy and steel, and the post-welding deformation and crack problems caused by traditional arc welding. In particular, the problem of element accumulation at the Mg / Fe interface of the traditional lap welded joint of magnesium / stainless steel, which is extremely difficult to diffuse into the stainless steel matrix, so that a large number of low-temperature hard and brittle Mg-based eutectic compounds are formed at the interface, greatly deteriorating the performance of the joint. BRIEF DESCRIPTION OF DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0016] Figure 1 It is a welding schematic diagram of the present application of a method for inducing magnesium / stainless steel flexible heat source lap welding interface strengthening by rare earth elements, wherein the heat sources are located above the steel side, Do represents the offset amount of the arc heat source from the edge of the magnesium alloy, and Malp represents the misalignment amount of the laser beam and the tungsten tip.

[0017] Figure 2 It is a 1.5mm thick AZ31B magnesium alloy plate and 1.0mm thick steel after pulse solid laser-TIG arc composite direct lap welding in the method for inducing magnesium / stainless steel flexible heat source lap welding interface strengthening by rare earth elements.

[0018] Figure 3 It is the lap shear strength of the 1.5mm thick AZ31B magnesium alloy plate and 1.0mm thick steel after pulse solid laser-TIG arc composite direct lap welding in the method for inducing magnesium / stainless steel flexible heat source lap welding interface strengthening by rare earth elements.

[0019] Figure 4The contrast chart of the 1.5 mm thick AZ31B magnesium alloy plate and the 1.0 mm thick S316 stainless steel in the magnesium / steel dissimilar metal automobile door lap welding method of the present application and the pulse solid laser-TIG arc composite filling Mg-Al, Mg-Gd-Y-Zr welding wire lap welding: (a) AZ31B / AZ61 / S316 and (b) AZ31B / Mg-RE / S316; (c) cross-sectional morphology; (d) tensile test results; (e) fracture path; (f) fracture surface morphology. DETAILED DESCRIPTION

[0020] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0022] It should be noted that the terms used herein are only for describing specific embodiments, and are not intended to limit the exemplary embodiments according to the present application. As used herein, the singular form is intended to include the plural form, unless the context clearly indicates otherwise, and it should also be understood that when the terms "comprise" and / or "include" are used in the specification, there is a reference to the presence of a feature, step, operation, device, component and / or combinations thereof.

[0023] Unless specifically stated otherwise, the relative arrangement of components and steps, numerical expressions, and numerical values set forth in the various examples herein are not limiting of the scope of the application. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and not of limitation. The detailed description of the exemplary embodiments should be considered in connection with the accompanying drawings, and not in a isolation. Techniques, methods, and apparatuses known to those of ordinary skill in the art can not be discussed in detail but can be assumed and / or considered known in the field. In the description herein, numerous specific examples are set forth to provide a thorough understanding of the present application. However, it should be understood that the application can be practiced without these specific details. In other instances, well-known methods, procedures, and techniques have not been described in detail so as not to unnecessarily obscure the present application. Some features, structures, or aspects can be shown in exaggerated scale, or in plan schematic, sectional, or patent-like form, and in some instances, several elements can be shown as blocks typically to avoid confusion. Certain terminology can also be used in the description for the purpose of reference only.

[0024] In the description of the application, it should be understood that the orientation words such as "front, back, up, down, left, right", "transverse, vertical, perpendicular, horizontal" and "top, bottom" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the application and simplifying the description, and do not indicate and imply that the devices or elements referred to must have a specific orientation or be constructed and operated in a specific orientation, therefore cannot be understood as a limitation on the scope of protection of the application: the orientation words "inner, outer" refer to the inner and outer of the contour of each component itself.

[0025] For the convenience of description, spatial relative terms such as "on", "above", "upper surface", "upper" and the like can be used herein to describe the spatial positional relationship of one device or feature with other devices or features as shown in the drawings. It should be understood that the spatial relative terms are intended to include different orientations in use or operation in addition to the orientation of the devices described in the drawings. For example, if the devices in the drawings are inverted, the device described as "above" or "on" other devices or structures will be positioned "below" or "under" other devices or structures. Thus, the exemplary term "above" can include both "above" and "below" orientations. The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatial relative descriptions used herein are interpreted accordingly.

[0026] In addition, it should be noted that the use of "first", "second" and the like to define parts is only for the convenience of distinguishing the corresponding parts, and the above words have no special meaning unless otherwise stated, and therefore cannot be understood as a limitation on the scope of protection of the application.

[0027] A rare earth element-induced magnesium / stainless steel flexible heat source lap welding interface toughening method, for the lap welding structure of magnesium alloy on top and stainless steel on bottom, laser-induced electric arc flexible heat source spatial domain action is used to control the weld energy gradient, combined with magnesium rare earth welding wire filling to control the interface structure, using laser-induced electric arc directional energy deflection and rare earth element micro-alloying effect, to form a larger metallurgical bonding area, strong and tough interface compounds and wide amplitude strong diffusion solid solution layer at the Mg-Fe interface, to improve the joint performance, Specifically including the following steps: S1. Lap assembly: assemble the magnesium alloy plate and the stainless steel plate into a lap structure with magnesium on top and steel on bottom, ensure that the lap area is tightly attached, and the thickness of the magnesium alloy and the stainless steel plate ranges from 0.1 to 3mm, which can be equal or unequal thickness; S2. Heat source arrangement: both laser and arc heat sources are located above the stainless steel base, and the two heat sources are in non-overlapping XOZ planes along the welding direction, the heat source sequence is laser heat source first and arc heat source second, and the welding wire is in overlapping XOZ plane with the arc heat source along the welding direction; S3. Parameter setting: design the spatial relative position of the laser beam and the arc and the welding wire, including the horizontal offset amount of the tungsten tip from the edge of the magnesium alloy to be welded perpendicular to the welding direction, the horizontal misalignment amount of the tungsten tip from the laser beam perpendicular to the welding direction, and the horizontal distance Dla of the tungsten tip from the laser beam along the welding direction; S4. Lap welding: laser-induced arc flexible heat source welding is performed using the set parameters, a magnesium rare earth welding wire is used for filling, and the lap welding operation is completed; S5. Post-weld cooling: natural cooling to room temperature to obtain a high-performance magnesium / stainless steel lap welded joint.

[0028] Further, the laser heat source is selected from a solid laser or a fiber laser, and the laser mode is a pulse mode; the arc heat source is selected from a GTA arc or a GMA arc, and the heat source mode is an alternating current mode.

[0029] Further, the offset amount, the misalignment amount, and Dla in step S3 all have a value range of 0-5 mm.

[0030] Further, the magnesium rare earth welding wire is selected from a WE series magnesium rare earth welding wire or a VW series magnesium rare earth welding wire, and the rare earth element promotes strong diffusion behavior and metallurgical reaction with the base element during the welding process to generate Mg-RE and Fe-RE interface compounds.

[0031] Further, the welding parameters in step S4 further include: laser power 200-500 W, arc current 60-100 A, welding speed 500-700 mm / min, and laser defocusing amount -1-1 mm.

[0032] Further, the method is applicable not only to the lap welding of magnesium alloy and stainless steel, but also to the butt welding structure of magnesium alloy and stainless steel. Specifically, the magnesium alloy plate and the stainless steel plate are arranged in butt joint, and a butt joint gap is reserved. The offset amount, the misalignment amount, and Dla in step S3 are dynamically adjusted according to the butt joint gap to ensure that the laser and the arc energy are concentrated on the butt joint gap area.

[0033] Further, the welding mode can be selected from a single-sided welding and double-sided forming mode or a double-sided welding forming mode.

[0034] In summary, for the magnesium alloy / stainless steel lap welding structure with magnesium on top and steel on bottom, the traditional welding process is prone to produce brittle Mg-based eutectic compounds at the Mg-Fe interface, thereby deteriorating the joint performance. The present method proposes a welding idea of laser-induced arc flexible heat source spatial domain action to regulate the weld energy gradient and fill magnesium rare earth welding wire to regulate the interface structure. The directional energy deflection of the laser-induced arc heat source and the micro-alloying effect of rare earth elements make the Mg-Fe interface have a larger metallurgical bonding area, stronger interface compounds and a wider strong diffusion solid solution layer. The joint performance is improved by more than 1.5 times compared with the traditional welding method, and the interface energy gradient and interface structure of the magnesium / stainless steel heterogeneous metal lap welded joint are accurately regulated.

[0035] The present application proposes a welding idea of flexible heat source spatial domain action to regulate the weld energy gradient, and utilizes the laser-induced arc enhancement effect to realize directional energy deflection and aggregation. The specific steps include the following steps: S1, during welding, the magnesium alloy is located on top and the stainless steel is located on bottom. The laser and arc welding heat sources are both located above the stainless steel base, but the two heat sources are in a non-overlapping XOZ plane along the welding direction. That is, from the edge of the magnesium to be welded to the stainless steel base, the heat source sequence is laser heat source first and arc heat source second, and the welding wire and the arc heat source are in an overlapping XOZ plane along the welding direction; S2, during welding, the spatial relative positions of the laser beam, the arc and the welding wire are designed, including but not limited to: the horizontal distance (offset) of the tungsten tip to the edge of the magnesium alloy to be welded perpendicular to the welding direction; the horizontal distance (misalignment) of the tungsten tip to the laser beam perpendicular to the welding direction; the horizontal distance (D la ).

[0036] The present application proposes a welding idea of filling magnesium rare earth welding wire (Mg-RE) to regulate the interface structure. The micro-alloying effect of rare earth elements is utilized to promote the strong diffusion behavior and metallurgical reaction between rare earth elements and base elements, generate strong and tough Mg-RE and Fe-RE interface compounds, and form semi-coherent or fully coherent bonding between the interface compounds and the base on both sides.

[0037] The laser heat source of the present application can be selected from solid laser, fiber laser, etc., and the laser mode is pulse mode. The arc heat source can be selected from GTA arc or GMA arc heat source, and the heat source mode is alternating current mode.

[0038] The thickness range of the magnesium alloy and the stainless steel plate of the present application is 0.1-3mm, which can be equal or unequal thickness.

[0039] The offset, misalignment and D la range in step S2 of the present application are all 0-5mm.

[0040] The filled magnesium rare earth welding wire of the present application can be selected from WE and VW series magnesium rare earth welding wire.

[0041] Example 1 1.5mm thick AZ31B magnesium alloy plate and 1.0mm thick Q235 / DP980 / S316 / S443 steel pulsed solid laser induced TIG arc flexible heat source direct lap welding example A Nd:YAG pulsed solid laser with a maximum power of 1 kW was selected as the laser heat source, and an alternating current non-consumable electrode inert gas welding (TIG) with a maximum current of 500 A was selected as the arc heat source. The magnesium alloy was on the magnesium / steel plate lap joint structure, and the laser and arc were both applied to the magnesium alloy substrate. The lap width was 10 mm. The laser power was set to 300 W, the TIG current was 80 A, the arc heat source was offset to the magnesium alloy side, the offset amount was 3 mm, the laser defocusing amount was 0 mm, the misalignment amount was 2.0 mm, the D la The welding speed was 600 mm / min, no filler wire and no metal interlayer or metal plating treatment was added, and argon (Ar) inert gas with a purity of 99.99% was selected as the welding protective gas, and the gas flow was adjusted to 15 L / min.

[0042] The joint post-weld appearance is shown in Figure 2 Compared with the post-weld joint of Q235 and DP980, the post-weld joint of the two stainless steels has a smaller wetting angle and a larger weld spread width. The post-weld joint of Q235 and DP980 has a larger wetting angle, which is 82° and 77°, respectively, and the weld spread width is 5.5 mm and 6.0 mm, respectively. The wetting angles of the joints of S316 and S443 stainless steels are the same, which are both 65°, and the weld spread widths are 6.1 mm and 6.6 mm, respectively. The joint performance after welding is shown in Figure 3 The tensile shear strength values of the joints of the two stainless steels are close (about 111 N / mm on average), but are significantly lower than the tensile shear strength of the joints of Q235 and DP980 (about 246 N / mm on average).

[0043] Example 2 1.5mm thick AZ31B magnesium alloy plate and 1.0mm thick S316 stainless steel pulsed solid laser induced TIG arc flexible heat source Mg-Al, Mg-Gd-Y-Zr filler wire lap welding comparison example The welding process is as follows Figure 1As shown, the Nd:YAG pulse solid laser with maximum power of 1 kW is selected as the laser heat source, the alternating current non-consumable inert gas welding (TIG) with maximum current of 500 A is selected as the arc heat source, the magnesium alloy is used on the magnesium / steel flat lap joint structure, the lap width is 10 mm, and the heat sources are all located above the steel substrate. The laser power is set to 300 W, the TIG current is 80 A, the arc heat source is offset from the edge of the magnesium alloy by 0.5 mm, the offset amount is 1.5 mm, the laser defocusing amount is 0 mm, the tungsten tip is 1.5 mm above the upper surface of the magnesium alloy, D la The welding speed is 600 mm / min, the Mg-Al (AZ61) and Mg-Gd-Y-Zr (Mg-RE) welding wires with a filling diameter of 1.2 mm are used, the argon (Ar) inert gas with a purity of 99.99% is selected as the welding protection gas, and the gas flow is adjusted to 15 L / min.

[0044] The post-weld appearance, performance and fracture path are shown in Figure 4 The two welds both show good forming continuity and smoothness, the weld width is about 6.3 mm, the height is about 1.5 mm, and the wetting angle is 55°. The maximum tensile shear strength of the AZ31B / AZ61 / S316 lap welded joint is only 115 N / mm, the joint is cracked and failed along the Mg / Fe interface, and the fracture surface morphology shows three different metallurgical bonding areas: FRA, WRA, and KRA, which are closely related to the energy gradient distribution in the joint; the maximum tensile shear strength of the AZ31B / Mg-RE / S316 lap welded joint reaches 290 N / mm, which is about 2.5 times that of the AZ31B / AZ61 / S316 lap welded joint. In this case, the joint crack propagates vertically along the top of the crater to the fusion zone.

[0045] The present application provides a rare earth element induced magnesium / stainless steel flexible heat source lap welding interface strengthening method. For the magnesium alloy / stainless steel lap welding structure with magnesium on top and steel below, the Mg-Fe interface is prone to produce brittle Mg-based eutectic compounds during traditional welding, thereby deteriorating the joint performance. The present method proposes a welding idea of regulating the weld energy gradient by laser-induced arc flexible heat source spatial domain action and regulating the interface structure by filling magnesium rare earth welding wire, utilizes the laser-induced arc heat source directional energy deflection and the rare earth element micro-alloying effect, so that the Mg-Fe interface has a larger metallurgical bonding area, a stronger interface compound and a wider strong diffusion solid solution layer, the joint performance is improved by more than 1.5 times compared with the traditional welding method, the interface energy gradient and interface structure of the magnesium / stainless steel heterogeneous metal lap welded joint are accurately regulated, and the industrial application process of the magnesium / stainless steel heterogeneous metal key structure is promoted.

[0046] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for strengthening and toughening the lap weld interface of magnesium / stainless steel flexible heat source induced by rare earth elements, characterized in that, For lap weld structures with magnesium alloy on top and stainless steel on the bottom, a laser-induced arc flexible heat source is used to spatially regulate the weld energy gradient. Combined with magnesium rare earth welding wire filling to regulate the interface structure, the laser-induced arc directional energy deflection and the micro-alloying effect of rare earth elements are utilized to form a larger metallurgical bonding area, a strong and tough interface compound, and a wide-area, highly diffused solid solution layer at the Mg-Fe interface, thereby improving joint performance. Specifically, the steps include the following: S1. Overlap assembly: The magnesium alloy plate and the stainless steel plate are assembled into an overlap structure with magnesium on top and steel on the bottom to ensure that the overlap area is tightly fitted. The thickness range of the magnesium alloy and stainless steel plates is 0.1~3mm, and they can be of equal or unequal thickness. S2. Heat source arrangement: Both the laser and electric arc heat sources are located above the stainless steel substrate. The two heat sources are in a non-overlapping XOZ plane along the welding direction. The heat source sequence is first the laser heat source and then the electric arc heat source. The welding wire and the electric arc heat source are in an overlapping XOZ plane along the welding direction. S3. Parameter settings: Design the spatial relative positions of the laser beam, the electric arc, and the welding wire, including the horizontal offset of the tungsten electrode tip from the edge of the magnesium alloy to be welded perpendicular to the welding direction, the horizontal misalignment of the tungsten electrode tip from the laser beam perpendicular to the welding direction, and the horizontal distance Dla between the tungsten electrode tip and the laser beam along the welding direction; S4. Lap welding: Laser-induced arc flexible heat source welding is performed using set parameters, and magnesium rare earth welding wire is used to complete the lap welding operation; S5. Post-weld cooling: Allow to cool naturally to room temperature to obtain a high-performance magnesium / stainless steel lap weld joint.

2. The interface toughening method according to claim 1, characterized in that, The laser heat source is a solid-state laser or a fiber laser, and the laser mode is pulsed mode; the electric arc heat source is a GTA electric arc or a GMA electric arc, and the heat source mode is AC mode.

3. The interface toughening method according to claim 1, characterized in that, The values ​​of offset, misalignment, and Dla mentioned in step S3 are all in the range of 0~5mm.

4. The interface toughening method according to claim 1, characterized in that, The magnesium rare earth welding wire is selected from WE series magnesium rare earth welding wire or VW series magnesium rare earth welding wire. During the welding process, rare earth elements promote strong diffusion behavior and metallurgical reaction with matrix elements, generating Mg-RE and Fe-RE interface compounds.

5. The interface toughening method according to claim 1, characterized in that, The welding parameters in step S4 also include: laser power 200~500W, arc current 60~100A, welding speed 500~700mm / min, and laser defocusing amount -1~1mm.

6. The interface toughening method according to claim 1, characterized in that, The method is applicable not only to lap welding of magnesium alloy and stainless steel, but also to butt welding of magnesium alloy and stainless steel. Specifically, the magnesium alloy plate and the stainless steel plate are arranged in a butt joint with a reserved butt gap. The offset, misalignment, and Dla mentioned in step S3 are dynamically adjusted according to the butt gap to ensure that the laser and arc energy are concentrated on the butt gap area.

7. The interface toughening method according to claim 6, characterized in that, The welding mode can be selected as either single-sided welding with double-sided forming mode or double-sided welding with forming mode.

Images