Friction stir welding and additive preparation method of aluminum steel dissimilar material and application of friction stir welding and additive preparation method

Abstract

The invention discloses a friction stir welding and additive preparation method for an aluminum steel dissimilar material and application of the friction stir welding and additive preparation method. The friction stir welding and additive preparation method comprises the following steps that S1, an aluminum alloy material and a stainless steel material are preheated; s2, under the condition that electromagnetic vibration and ultrasonic vibration are applied, an aluminum alloy material and a stainless steel material are subjected to material adding through a stirring friction material adding technology, and an aluminum-steel dissimilar material is obtained; and S3, the aluminum steel dissimilar material is heated to 200-500 DEG C through pulse current, then cooled to-196--100 DEG C, subjected to cold insulation, then heated to 200-400 DEG C through high-frequency pulse current, and subjected to heat preservation. According to the friction stir welding and additive preparation method for the aluminum steel dissimilar material, the forming precision, the strength, the corrosion resistance and the production efficiency of the prepared aluminum steel dissimilar material are all remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and in particular to a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials and applications thereof. Background Art

[0002] As a lightweight and high-strength metal material, aluminum alloy has shown significant advantages in engineering applications. Its low density (about 2.7g / cm 3 ) makes it irreplaceable in weight-sensitive applications such as aerospace and automotive manufacturing. Aluminum alloys also exhibit excellent corrosion resistance, particularly in corrosive media such as marine environments and chemical industries. The dense oxide film formed on their surfaces effectively slows the corrosion process. Furthermore, aluminum alloys offer excellent weldability, enabling reliable connections through a variety of welding processes, with minimal weld distortion and low crack sensitivity. This provides a key advantage in the manufacture of complex structural components. In contrast, steel, the most widely used metal material in engineering, boasts high strength (tensile strength exceeding 500 MPa) and excellent durability. Steel plays an irreplaceable and critical role in applications requiring high load-bearing loads, such as building structures, automotive manufacturing, and petrochemicals. To achieve the synergistic optimization of lightweighting and high strength, aluminum / steel dissimilar metal joining technology has become a research hotspot in the field of materials processing. This composite structure exhibits significant technical and economic advantages in fields such as power transmission, transportation, energy and chemical engineering, and aerospace. For example, the use of aluminum / steel composite structures in automobile body manufacturing can effectively reduce weight by 15%-20% while maintaining the load-bearing performance of the structural component.

[0003] However, aluminum / steel dissimilar metal welding faces severe technical challenges. First, from the perspective of thermophysical properties, there is a significant difference in the thermal expansion coefficients of aluminum and steel (about 23.6×10 -6 / ℃, low carbon steel is about 11.7×10 -6 / ℃), this mismatch leads to large thermal stresses during welding, which can easily cause cracks in the joints. Secondly, according to the Al-Fe binary phase diagram analysis, the mutual solubility of aluminum and iron is extremely low, and brittle intermetallic compounds (IMCs) such as FeAl2, Fe2Al5, and FeAl3 are easily generated under the action of welding thermal cycles. Although a moderate amount of IMCs helps to achieve metallurgical bonding, when its thickness exceeds the critical value (usually 5-10μm), it will significantly reduce the toughness and fatigue resistance of the joint. In addition, the Al2O3 oxide film naturally formed on the surface of aluminum alloy (melting point of about 2050℃) has extremely high chemical stability and is difficult to decompose during the welding process. It will seriously hinder the wetting of the molten pool and metallurgical bonding, thereby affecting the strength and quality stability of the joint.

[0004] Currently, the main methods for welding aluminum and steel dissimilar metals are categorized as fusion welding, brazing, and solid-state joining. Traditional fusion welding methods require high heat input and are difficult to precisely control, often resulting in excessively thick IMCs in the weld zone, increasing joint brittleness and severely impacting weld quality. Brazing, as an alternative joining method, while offering advantages such as minimal joint deformation, controllable process parameters, and reduced IMC formation, also carries the risk of defects such as porosity and slag inclusions in the welded joint, and exhibits poor heat resistance. Furthermore, while mechanical joining avoids the formation of IMCs, it suffers from low joint strength and poor fatigue performance, making it generally suitable only for less demanding applications. Therefore, solid-state welding technologies, particularly friction stir welding (FSW) and friction stir additive manufacturing (FSAM), have become a research focus for aluminum and steel dissimilar metal joining requiring high quality and reliability.

[0005] Friction stir additive manufacturing (FSAM) is a novel solid-state joining technology. Unlike traditional fusion welding, FSAM utilizes a high-speed rotating stirrer to generate heat through friction with the workpiece, causing local plasticization of the material in the weld zone, thereby forming a tight solid-state joint. Compared with traditional additive manufacturing methods such as laser melting and electron beam melting, FSAM requires significantly lower heat input and avoids the material melting process through solid-state joining. Therefore, FSAM effectively avoids defects such as porosity and cracks caused by melting during the welding process and reduces the formation of IMCs. During the FSAM process, the weld material does not completely melt. Instead, it achieves metallurgical bonding through local plasticization and metal flow, resulting in a high-strength solid-state joint between dissimilar metals such as aluminum and steel. Due to the low heat input and short thermal cycle time, FSAM significantly reduces the formation of IMCs, avoiding the problem of excessively thick IMCs commonly encountered in fusion welding, thereby improving the mechanical properties and stability of the weld joint.

[0006] In addition to heat input control, FSAM technology also offers excellent metal fluidity. Through the stirring action of the stirring head, FSAM not only effectively reduces defects at the interface but also enhances metal fluidity and metallurgical bonding. This results in a tighter connection between aluminum and steel dissimilar metals, significantly improving the mechanical properties of the welded joint. Traditional additive manufacturing technologies (such as those based on a melting process) often suffer from problems such as rapid cooling rates and poor metal fluidity, leading to poor weld bonding and even defects such as pores and cracks, compromising the quality of the final joint. FSAM, however, effectively improves aluminum-steel dissimilar metal joining by precisely controlling temperature, metal fluidity, and interfacial bonding. While FSAM technology demonstrates significant advantages in aluminum-steel dissimilar metal joining, it still has some limitations. While existing FSAM technology can effectively reduce the formation of IMCs, poor metal fluidity and poor interfacial bonding persist. The difference in metal fluidity between aluminum alloys and steel, particularly the poor fluidity of steel, can easily lead to insufficient bonding between the two metals at the interface, compromising joint quality. Furthermore, temperature control during the FSAM process remains challenging due to the differences in thermophysical properties between aluminum alloys and steels. Uneven temperature distribution can lead to localized overheating, compromising the formation of IMCs and the quality of welded joints. During the dissimilar metal friction stir additive manufacturing (FSAM) process, due to the significant differences in chemical composition and physical properties between aluminum alloys and steels, violent metallurgical reactions are highly likely to occur at the interface, leading to the excessive formation and growth of brittle intermetallic compounds (IMCs). This abnormal growth of IMCs can significantly degrade the mechanical properties of the joint, particularly its toughness and fatigue properties. Furthermore, uneven preheating of the weld materials during the initial stages of FSM can lead to inconsistent thermal expansion behaviors between the dissimilar metals, resulting in significant thermal stress concentration at the interface. Due to the significant difference in thermal expansion coefficients between aluminum alloys and steels, significant residual stresses can easily form in the joint during thermal cycling, inducing defects such as microcracks, macrocracking, and interface delamination, severely impacting the structural integrity and service performance of the joint. To complicate matters further, during the FSAM process, Fe and Al atoms diffuse along the interface under high temperature and plastic deformation. However, due to the differences in the crystal structures and thermodynamic instability of the dissimilar metals, the diffusion paths are often disordered, resulting in an uneven distribution of the interface microstructure. This instability further exacerbates the excessive growth of brittle phases in the IMCs (such as FeAl2 and Fe2Al5), forming a continuous brittle layer, which severely weakens the strength, plasticity, and fracture toughness of the joint.Therefore, how to effectively regulate FSAM process parameters to inhibit the excessive growth of IMCs, optimize interface diffusion behavior and reduce residual stress has become a key issue in improving aluminum / steel dissimilar metal additive manufacturing. Summary of the Invention

[0007] The present invention aims to solve the above-mentioned technical problems existing in the prior art. To this end, the present invention proposes a method for friction stir welding and additive manufacturing of aluminum and steel dissimilar materials, which significantly improves the forming accuracy, strength, corrosion resistance and production efficiency of the aluminum alloy produced.

[0008] The present invention also proposes an application of the aluminum-steel dissimilar material prepared by the above preparation method in the fields of aerospace and automobile manufacturing.

[0009] The technical breakthrough of this invention is that by establishing a quantitative relationship between multi-physical field coupling (such as the electric-thermal coupling coefficient α = 0.78, the acoustic-mechanical coupling efficiency η = 82%), a precise mapping of process parameters and interface performance is achieved. Experiments have shown that this system can increase the fatigue life of aluminum-steel joints to 10 6 The new method achieves a 2-order-of-magnitude improvement over conventional methods, providing a revolutionary technical solution for lightweight aerospace structure manufacturing. This multi-field coordinated control mechanism exhibits significant nonlinear characteristics and engineering indestructibility, resulting in a technical effect far exceeding the simple summation of the effects of each individual technique.

[0010] According to one aspect of the present invention, a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials is proposed, comprising the following steps:

[0011] S1. Preheating aluminum alloy and stainless steel materials;

[0012] S2. Using a friction stir additive process to add aluminum alloy and stainless steel to produce an aluminum-steel dissimilar material under the conditions of applying electromagnetic vibration and ultrasonic vibration;

[0013] S3. The aluminum-steel dissimilar materials are heated to 200-500°C by a pulse current, then cooled to -196--100°C and kept cold, and then heated to 200-400°C by a high-frequency pulse current and kept warm.

[0014] According to the embodiments of the first aspect of the present invention, there are at least the following beneficial effects:

[0015] The present invention reduces the thickness of IMC by multi-field coupling auxiliary welding and additive manufacturing of raw materials, solves the problems of violent Fe-Al reaction, chaotic diffusion paths of Fe and Al in the joint area, and precise control of heat input, reduces the brittle phase generation at the interface of aluminum-steel dissimilar metals, and reduces residual stress at the same time, improves the mechanical properties and stability of the joint. The aluminum-steel substrate is preheated before friction stir additive manufacturing, which increases the temperature of the welding area, promotes plastic deformation of the metal, and avoids excessive generation of IMC due to excessive heat input. Under the conditions of applying electromagnetic vibration and ultrasonic vibration in step S2, electric-stress-heat-ultrasonic multi-field coupling synergistically assists friction stir welding and additive manufacturing. By changing the electric field parameters and using low-frequency pulse current auxiliary technology, the current flows between the metals, combined with the stirring shear process, and the electric field drives the electromigration effect, promotes the diffusion of metal atoms, adjusts the interface composition gradient, and the continuous disturbance of the current can break the aggregation of interface elements, promote Fe and Al atoms to be more evenly distributed on the diffusion path, slow down the violent Fe-Al reaction, and inhibit the excessive growth of the IMCs layer. During the friction stir welding and additive manufacturing process, the use of ultrasonic vibration-assisted technology can introduce high-frequency vibration effects while the metal is plastically flowing, significantly promoting the diffusion and rearrangement of interface atoms, breaking and refining the grains in the welding area, improving the fluidity and filling capacity of the metal, and enhancing the metallurgical bonding strength of the aluminum-steel dissimilar metal interface, thereby effectively inhibiting the disordered growth of the brittle IMCs layer. After the friction stir welding and additive manufacturing of aluminum-steel dissimilar metals, the interface area is prone to problems such as uneven IMCs layer thickness, brittle phase aggregation, coarse grains and high residual stress. Therefore, the plate needs to be heat treated to improve the plate structure. Pulsed electric field heat treatment is used, which is divided into three stages: pulsed electric field heating and holding stage, rapid cooling stage and pulsed electric field rapid reheating and reheating stage. This allows the interface microstructure to be regulated, grains to be refined, residual stress to be released, the diffusion distribution of Fe-Al atoms to be stabilized, and the mechanical properties and service stability of the joint to be improved. Rapid cooling and heating can effectively induce a large number of dislocations inside the material, refine the grain structure, and improve the strength and toughness of the material. At the same time, rapid cooling inhibits the excessive growth of brittle intermetallic compounds (IMCs), and the rapid heating stage promotes the redistribution and rearrangement of interface atoms, releases residual stress, and optimizes the interface structure, ultimately significantly improving the metallurgical bonding quality and overall mechanical properties of the aluminum-steel dissimilar metal joint and enhancing the stability and reliability of the dissimilar materials.

[0016] In some embodiments of the present invention, the preheating method includes a direct current heating method;

[0017] In the DC current heating method, the voltage is 20-40V and the current density is 80-150A / cm 2 .

[0018] In some embodiments of the present invention, the preheating temperature is 200-300°C.

[0019] In some embodiments of the present invention, in the DC current heating method, the power supply mode is a DC constant current output.

[0020] The present invention adopts DC electric field preheating technology to uniformly heat the aluminum alloy and stainless steel substrate, effectively reducing the initial heat input requirement, alleviating the stress concentration problem caused by the difference in thermal expansion coefficient of dissimilar metals, and inhibiting the excessive formation of intermetallic compounds (IMCs) at the interface.

[0021] In some embodiments of the present invention, the parameters of the electromagnetic vibration include: voltage of 5 to 20 V, current density of 30 to 80 A / cm 2 , the pulse frequency is 100~500Hz.

[0022] Under the above conditions, Fe / Al atoms diffuse in an orderly manner along a specific crystal direction, while the pulse interval allows atomic rearrangement, ultimately achieving precise control of the IMCs layer thickness.

[0023] In some embodiments of the present invention, the parameters of the ultrasonic vibration include: ultrasonic vibration frequency of 10 to 50 kHz, amplitude of 10 to 40 μm, and ultrasonic power of 1 to 4 kW.

[0024] In some embodiments of the present invention, the parameters of the friction stir additive process include: a rotation speed of the stirring head of 1000 to 2000 rpm, an additive speed of 20 to 100 mm / min, an inter-axis downward pressure of 0.1 to 0.5 mm, and an inclination angle of the stirring head of 1 to 5 degrees.

[0025] The present invention achieves precise control of the dissimilar metal interface between aluminum and steel through the coordinated optimization of electromagnetic vibration, ultrasonic vibration and stir friction additive process parameters. Among them, electromagnetic vibration directionally guides the orderly diffusion of Al / Fe atoms along a specific crystal direction, and drives the electromigration effect through the electric field to promote the diffusion of metal atoms, adjust the interface composition gradient, and inhibit the excessive growth of the IMCs layer. The high-frequency cavitation effect and acoustic streaming generated by ultrasonic vibration effectively break up the interface oxide film and promote local plastic flow, thereby improving the material flow efficiency; stir friction additive precisely controls the heat input while ensuring sufficient thermal plasticization. Under the above conditions, through the "electromagnetic-ultrasonic-mechanical" three-field coupling effect, not only the thickness of the IMCs layer is controlled, but also a fine-grained structure is formed, which significantly improves the problems of brittle phase aggregation and unstable performance in traditional aluminum-steel welding.

[0026] In some embodiments of the present invention, the temperature of the additive step is 450-500°C.

[0027] In some embodiments of the present invention, multi-point thermocouples and infrared thermometers are used to perform real-time temperature monitoring during the material addition step.

[0028] In some embodiments of the present invention, during the material adding step, the stainless steel is cooled by a cooling medium.

[0029] In some embodiments of the present invention, the cooling medium comprises an exogenous gas.

[0030] In some embodiments of the present invention, the external gas includes an inert gas or cooling air.

[0031] In some embodiments of the present invention, the inert gas comprises at least one of nitrogen, argon, or dry compressed air.

[0032] In some embodiments of the present invention, the cooling medium flow rate is 10 to 20 L / min, and the cooling rate is 10 to 30° C. / s.

[0033] During the friction stir process, multi-point thermocouples and infrared thermometers are used for real-time temperature monitoring to avoid local overheating and heat accumulation. The infrared thermometer detects the temperature. When the temperature is too high, a cooling device (such as an external gas system) is automatically activated to reduce the temperature to ensure that the temperature of the additive zone is controlled below the melting point of the aluminum alloy (<550°C) to avoid excessive growth of IMCs. The cooling device uses a cooling gas. The cooling gas (such as nitrogen, argon, or compressed air) has good fluidity and controllability, which can achieve a more uniform cooling effect and avoid the local "overcooling" phenomenon caused by direct contact with the coolant during the liquid cooling process, thereby preventing cracks or thermal stress concentration at the interface. The coolant is at risk of evaporation or instantaneous vaporization in a high-temperature environment, which can easily cause thermal shock and cause structural damage in the joint area, especially for the stability of the dissimilar metal bonding interface. The gas cooling method can achieve continuous, stable and gradual cooling by adjusting the flow rate and pressure, reduce the interface temperature gradient, promote grain refinement, inhibit the abnormal growth of the IMCs layer, and improve the overall mechanical properties and metallurgical bonding quality of the joint. At the same time, the cooling gas itself is an insulator and can be safely compatible with electric field assisted technology, ensuring the synchronous operation of current induced diffusion control technology and temperature control system to avoid safety hazards.

[0034] In some embodiments of the present invention, the parameters of the step of heating with pulse current include: voltage of 20-60V, current density of 100-200A / cm 2 , the pulse frequency is 1000~4000Hz.

[0035] In some embodiments of the present invention, in step S3, the cooling time is 20 to 120 minutes.

[0036] In some embodiments of the present invention, step S3 includes: heating the aluminum-steel dissimilar material to 200-500°C with a pulse current, keeping it warm for 10-60 minutes, cooling it to -196--100°C, keeping it cold for 20-120 minutes, and then heating it to 200-400°C with a high-frequency pulse current, and keeping it warm for 30-90 minutes.

[0037] During pulsed current heating, atoms at the interface acquire kinetic energy for directional migration, promoting the rearrangement of Fe / Al atoms to form a metastable solid solution. These parameters provide sufficient atomic mobility while avoiding exceeding the Al-Fe eutectic temperature, which would otherwise lead to coarsening of the IMCs. Subsequent cryogenic treatment, through rapid contraction, creates a high density of dislocations at the interface, simultaneously freezing the metastable structure. Finally, pulsed current warming induces diffusional rearrangement through electromigration, assisting dislocation recombination and forming a stable nanocrystalline structure. This coordinated "rapid heating-rapid cooling-controlled tempering" process maintains a discrete nanoscale distribution of the IMC layer, achieving a synergistic improvement in strength and toughness.

[0038] In the present invention, the synergistic effect of electric field, stress field, thermal field and ultrasonic field is used to achieve multi-scale precise control of the dissimilar metal interface of aluminum and steel dissimilar materials from macro to micro. A three-stage electric field synergistic control system of "preheating-stirring-post-processing" is constructed, and the entire welding process is acted on in stages through electric fields of different frequencies and intensities. In the preheating stage (step S1), a DC electric field (20-40V) is used to achieve synchronous interface heating and stress relief; in the stir friction additive stage (step S2), a low-frequency pulsed electric field (100-500Hz) is introduced to directionally control atomic diffusion; in the post-processing stage (step S3), a high-frequency pulsed electric field (1000-4000Hz) is used in combination with cryogenic treatment to achieve tissue stabilization. Through gradient electric field control, dynamic control of the entire "nucleation-growth-stabilization" process of IMCs is achieved for the first time, reducing the thickness of the IMCs layer from the micron level of traditional processes to the nanometer level (<200nm), and increasing the interface shear strength by more than 35%.

[0039] In step S1, a DC electric field is introduced for preheating, achieving simultaneous heating and stress relief of the aluminum and steel materials before interface formation. In step S2, a low-frequency pulsed electric field is applied to directionally control atomic diffusion and inhibit IMC formation. In step S3, post-weld heat treatment with a high-frequency pulsed electric field, combined with a deep cooling-reheating strategy, induces microstructure refinement and dislocation strengthening. This multi-stage, frequency- and intensity-coupled electric field control mechanism enables dynamic control of the entire process of IMC formation, expansion, and stabilization, at the aluminum-steel dissimilar metal interface, significantly improving the quality of the interface.

[0040] In step S2, low frequency (100-500 Hz) can make the process of diffusion migration-structural rearrangement-stress relaxation alternate per unit time, which is beneficial to improving the uniformity and controllability of diffusion. Pulse current has the characteristic of "periodic intermittent", which promotes strong electromigration effect in a short range. During the stirring process, if a high-frequency pulse current is applied, which is equivalent to a nearly continuous power supply (similar to DC), it is easy to cause local temperature rise, especially the electron flow concentration at the interface causes the temperature to rise, which in turn promotes the Fe-Al reaction and generates a thick and brittle IMCs layer. Low-frequency pulses have a thermal rest gap, which is beneficial to thermal diffusion and temperature control. If the electric field / current parameters are too high, the interface will be overheated, IMCs will be violently generated, and even material ablation will occur. If they are too low, the diffusion driving force will be insufficient, the regulation effect will not be obvious, and it will be difficult to achieve an ideal interface structure.

[0041] The synergistic coupling of multiple physical fields (electric field, stress field, thermal field, and ultrasonic field) significantly improves the interface microstructural stability and mechanical properties. The electric field, through low-frequency pulsed current, guides the migration direction of interfacial atoms, enabling precise control of the diffusion rate and path of Fe and Al, effectively controlling the composition and thickness of the interfacial IMCs. Simultaneously, the pulsed electric field periodically perturbs the atomic structure, reducing the diffusion activation energy, promoting the rearrangement and refinement of interfacial atoms, and enhancing metallurgical bond strength. The stress field, generated by the rotating stirring head, generates high shear and compressive stresses in the contact zone, inducing drastic plastic deformation of the interfacial material, breaking down the metal oxide film and promoting dynamic recrystallization at the interface, thereby facilitating the continuous and dense metallurgical bonding of Fe and Al under solid-state conditions. The thermal field, composed of frictional heat generation, internal material resistance heat generation, and external current input, forms a multi-source, controlled and distributed heat input mechanism. Precisely controlled by temperature monitoring and gas cooling, local overheating or heat accumulation is avoided, effectively suppressing abnormal IMC growth and thermal stress concentration, and improving microstructure uniformity and joint reliability. The ultrasonic field introduces high-frequency micro-vibrations into the weld zone, significantly enhancing the metal's local fluidity and atomic diffusion capacity, breaking up the original grains and promoting recrystallization, which helps break up or delay the aggregation and continuous growth of IMCs. It also activates dislocation motion, promotes deformation coordination, and enhances joint toughness. The four fields act synergistically, spatially coupled, and temporally coordinated: the electric field regulates the atomic diffusion path, the ultrasonic field activates grain reconstruction, the stress field provides deformation drive, and the thermal field ensures precise control of the diffusion activation and microstructure evolution window. Together, these four fields establish a steady-state, controllable interface microstructure evolution platform, effectively addressing the uncontrollable growth of IMCs, grain coarsening, and poor interface bonding in traditional welding. Ultimately, this results in systematic improvements in microstructure continuity, interface density, mechanical properties, and reliability of welded joints.

[0042] In step S3, after welding, the present invention introduces a "rapid cooling and heating-thermal cycle-induced strengthening mechanism" consisting of a pulsed electric field, liquid nitrogen cryogenic cooling, and rapid electric field warming. This promotes repeated rapid grain contraction and expansion, inducing the formation of high-density dislocations, sub-grains, and distorted regions. The electric field stabilizes the microstructure, significantly improving the strength and toughness of the interface between the dissimilar materials. This combination of technologies surpasses the effects of traditional cryogenic or heat treatment alone, resulting in a nonlinear microstructural evolution path that creates an unpredictable but controllable mechanical strengthening effect.

[0043] According to the second aspect of the present invention, the application of the aluminum-steel dissimilar material prepared by the preparation method in the fields of aerospace and automobile manufacturing is proposed. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the concept and technical effects of the present invention in conjunction with the embodiments to fully understand the purpose, features and effects of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0045] Example 1

[0046] This embodiment provides a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, comprising the following steps:

[0047] S1. Preheat 7075 aluminum alloy and 316L stainless steel using direct current rapid heating. By placing the positive and negative electrodes in contact with the aluminum and steel sides, current flows through the dissimilar metal interface, preheating the materials uniformly through resistance heat. Voltage setting: 30V, current density: 100A / cm 2 , power-on mode: DC constant current output, power-on time: 40s, target temperature: 200℃;

[0048] S2. Under the conditions of applying electromagnetic vibration and ultrasonic vibration, a stir friction additive process is used to additively mix aluminum alloy materials and stainless steel materials to obtain aluminum-steel dissimilar materials. Temperature monitoring and exogenous gas cooling technology are used in the welding and additive manufacturing processes. Multi-point thermocouples and infrared thermometers are used for real-time temperature monitoring. Combined with active cooling technology, precise temperature control is achieved. When the temperature exceeds 450°C, the cooling device is started and the substrate is cooled by the flow control system of the cooling medium. Exogenous gas cooling uses inert gas or cooling air as the cooling medium, and nitrogen (N2) is selected. Cooling medium flow rate: 15L / min, cooling rate: 20°C / s, so as to quickly remove the heat during the welding process. After the stirring is completed, the cooling gas is still introduced until it drops to room temperature.

[0049] The electromagnetic vibration conditions are as follows: using a low-frequency pulse current auxiliary method, the current is continuously passed into the aluminum-steel dissimilar metal interface during the stirring process, the voltage setting is: 12V, the current density is: 40A / cm 2 , pulse frequency: 200Hz, power supply mode: low frequency square wave pulse current;

[0050] The ultrasonic vibration conditions are as follows: high-frequency ultrasonic vibration is applied to the welding area during the friction stir process to promote interface atomic diffusion and metal plastic deformation. The ultrasonic vibration frequency is 40 kHz, the amplitude is 20 μm, the ultrasonic power is 2 kW, and the vibration direction is perpendicular to the stirring head axis.

[0051] The conditions of the friction stir additive process are as follows: 7075 aluminum alloy is added on the substrate steel plate 316l, the rotation speed of the stirring head is 1500 rpm, the additive speed is 20 mm / min, the inter-axis downward pressure is 0.2 mm, and the stirring head inclination angle is 3°.

[0052] S3.1. Place the additively prepared aluminum-steel dissimilar materials in a dedicated electric field heat treatment furnace. Non-contact heating is achieved by using a pulsed current heating plate. High-frequency pulsed current assisted technology is used. The voltage setting is 40V and the current density is 120A / cm 2 , pulse frequency: 2000Hz, power supply mode: high-frequency square wave pulse current, heating temperature 300℃, holding time 60min;

[0053] S3.2. After the pulsed electric field is complete, immediately transfer the material to a liquid nitrogen environment for rapid cooling, cooling it to -180°C and maintaining it in liquid nitrogen for 60 min.

[0054] S3.3. After cooling with liquid nitrogen, remove the sample immediately and place it on the pulsed electric field heating platform again. Use high-frequency pulse current to quickly heat it to 200°C and keep it at this temperature for 30 minutes.

[0055] Example 2

[0056] This embodiment provides a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, comprising the following steps:

[0057] S1. Preheat 7075 aluminum alloy and 316L stainless steel using direct current rapid heating. By placing the positive and negative electrodes in contact with the aluminum and steel sides, current flows through the dissimilar metal interface, preheating the materials uniformly through resistance heat. Voltage setting: 30V, current density: 100A / cm 2 , power-on mode: DC constant current output, power-on time: 40s, target temperature: 200℃;

[0058] S2. Under the conditions of applying electromagnetic vibration and ultrasonic vibration, the stir friction additive process is used to add aluminum alloy materials and stainless steel materials to obtain aluminum-steel dissimilar materials. The temperature monitoring and exogenous gas cooling technology in the welding and additive manufacturing process use multi-point thermocouples and infrared thermometers for real-time temperature monitoring, and combined with active cooling technology to achieve precise temperature control. When the temperature exceeds 450°C, the cooling device is started, and the substrate is cooled by the flow control system of the cooling medium. The exogenous gas cooling uses inert gas or cooling air as the cooling medium, and nitrogen (N2) is selected. The cooling medium flow rate is 15L / min, and the cooling rate is 20°C / s, so as to quickly take away the heat during the welding process. After the stirring is completed, the cooling gas is still introduced until it drops to room temperature.

[0059] The electromagnetic vibration conditions are: using low-frequency pulse current auxiliary technology, the current is continuously passed into the aluminum-steel dissimilar metal interface during the stirring process, the voltage setting is: 12V, the current density is: 40A / cm 2 , pulse frequency: 200Hz, power supply mode: low-frequency square wave pulse current, power supply duration: welding and additive manufacturing are applied simultaneously throughout the entire process;

[0060] Ultrasonic vibration conditions are as follows: high-frequency ultrasonic vibration is applied to the weld area during the friction stir process to promote atomic diffusion at the interface and plastic deformation of the metal. The ultrasonic vibration frequency is 40kHz, the amplitude is 20μm, the ultrasonic power is 2kW, and the vibration direction is perpendicular or inclined to the stirring head axis.

[0061] The conditions of the friction stir additive process are as follows: 7075 aluminum alloy is added on the substrate steel plate 316l, the rotation speed of the stirring head is 1500 rpm, the additive speed is 50 mm / min, the inter-axis downward pressure is 0.2 mm, and the stirring head inclination angle is 3°.

[0062] S3.1. Place the additively prepared aluminum and steel dissimilar materials in a dedicated electric field heat treatment furnace and achieve non-contact heating using a pulsed current heating plate. High-frequency pulsed current assisted technology is used, with a voltage setting of 40V and a current density of 120A / cm 2 , pulse frequency: 2000Hz, power supply mode: high-frequency square wave pulse current, heating temperature 300℃, holding time 60min;

[0063] S3.2. After the pulsed electric field is complete, immediately transfer the material to a liquid nitrogen environment for rapid cooling, cooling it to -180°C and maintaining it in liquid nitrogen for 60 min.

[0064] S3.3. After cooling with liquid nitrogen, remove the sample immediately and place it on the pulsed electric field heating platform again. Use high-frequency pulse current to quickly heat it to 200°C and keep it at this temperature for 30 minutes.

[0065] Example 3

[0066] This embodiment provides a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, comprising the following steps:

[0067] S1. Preheat 7075 aluminum alloy and 316L stainless steel using direct current rapid heating. By placing the positive and negative electrodes in contact with the aluminum and steel sides, current flows through the dissimilar metal interface, preheating the materials uniformly through resistance heat. Voltage setting: 30V, current density: 100A / cm 2 , power-on mode: DC constant current output, power-on time: 40s, target temperature: 200℃;

[0068] S2. Under the conditions of applying electromagnetic vibration and ultrasonic vibration, the stir friction additive process is used to add aluminum alloy materials and stainless steel materials to obtain aluminum-steel dissimilar materials. The temperature monitoring and exogenous gas cooling technology in the welding and additive manufacturing process use multi-point thermocouples and infrared thermometers for real-time temperature monitoring, and combined with active cooling technology to achieve precise temperature control. When the temperature exceeds 450°C, the cooling device is started, and the substrate is cooled by the flow control system of the cooling medium. The exogenous gas cooling uses inert gas or cooling air as the cooling medium, and nitrogen (N2) is selected. The cooling medium flow rate is 15L / min, and the cooling rate is 20°C / s, so as to quickly take away the heat during the welding process. After the stirring is completed, the cooling gas is still introduced until it drops to room temperature.

[0069] The electromagnetic vibration conditions are: using low-frequency pulse current auxiliary technology, the current is continuously passed into the aluminum-steel dissimilar metal interface during the stirring process, the voltage setting is: 12V, the current density is: 40A / cm 2 , pulse frequency: 200Hz, power supply mode: low-frequency square wave pulse current, power supply duration: welding and additive manufacturing are applied simultaneously throughout the entire process;

[0070] Ultrasonic vibration conditions are as follows: high-frequency ultrasonic vibration is applied to the weld area during the friction stir process to promote atomic diffusion at the interface and plastic deformation of the metal. The ultrasonic vibration frequency is 40kHz, the amplitude is 20μm, the ultrasonic power is 2kW, and the vibration direction is perpendicular or inclined to the stirring head axis.

[0071] The conditions of the friction stir additive process are as follows: 7075 aluminum alloy is added on the substrate steel plate 316l, the rotation speed of the stirring head is 1500 rpm, the additive speed is 100 mm / min, the inter-axis downward pressure is 0.2 mm, and the stirring head inclination angle is 3°.

[0072] S3.1. Place the additively prepared aluminum and steel dissimilar materials in a dedicated electric field heat treatment furnace and achieve non-contact heating using a pulsed current heating plate. High-frequency pulsed current assisted technology is used, with a voltage setting of 40V and a current density of 120A / cm 2 , pulse frequency: 2000Hz, power supply mode: high-frequency square wave pulse current, heating temperature 300℃, holding time 60min;

[0073] S3.2. After the pulsed electric field is complete, immediately transfer the material to a liquid nitrogen environment for rapid cooling, cooling it to -180°C and maintaining it in liquid nitrogen for 60 min.

[0074] S3.3. After cooling with liquid nitrogen, remove the sample immediately and place it on the pulsed electric field heating platform again. Use high-frequency pulse current to quickly heat it to 200°C and keep it at this temperature for 30 minutes.

[0075] Comparative Example 1

[0076] This comparative example provides a method for friction stir welding and additive manufacturing of dissimilar aluminum and steel materials. The difference between this comparative example and the embodiment is that step S2 does not include applying electromagnetic vibration. Specifically, the steps are as follows:

[0077] S1. Preheat 7075 aluminum alloy and 316L stainless steel using direct current rapid heating. By placing the positive and negative electrodes in contact with the aluminum and steel sides, current flows through the dissimilar metal interface, preheating the materials uniformly through resistance heat. Voltage setting: 30V, current density: 100A / cm 2 , power-on mode: DC constant current output, power-on time: 40s, target temperature: 200℃;

[0078] S2. Under the condition of applying ultrasonic vibration, a stir friction additive process is used to additively mix aluminum alloy materials and stainless steel materials to obtain aluminum-steel dissimilar materials. Temperature monitoring and exogenous gas cooling technology during welding and additive manufacturing are used. Multi-point thermocouples and infrared thermometers are used for real-time temperature monitoring. Combined with active cooling technology, precise temperature control is achieved. When the temperature exceeds 450°C, the cooling device is activated and the substrate is cooled by the flow control system of the cooling medium. Exogenous gas cooling uses inert gas or cooling air as the cooling medium, and nitrogen (N2) is selected. The cooling medium flow rate is: 15L / min, and the cooling rate is: 20°C / s, so as to quickly remove the heat during the welding process. After the stirring is completed, the cooling gas is still introduced until it drops to room temperature.

[0079] Ultrasonic vibration conditions are as follows: high-frequency ultrasonic vibration is applied to the weld area during the friction stir process to promote atomic diffusion at the interface and plastic deformation of the metal. The ultrasonic vibration frequency is 40kHz, the amplitude is 20μm, the ultrasonic power is 2kW, and the vibration direction is perpendicular or inclined to the stirring head axis.

[0080] The conditions of the friction stir additive process are as follows: 7075 aluminum alloy is added on the substrate steel plate 316l, the rotation speed of the stirring head is 1500 rpm, the additive speed is 100 mm / min, the inter-axis downward pressure is 0.2 mm, and the stirring head inclination angle is 3°.

[0081] S3.1. Place the additively prepared aluminum and steel dissimilar materials in a dedicated electric field heat treatment furnace and achieve non-contact heating using a pulsed current heating plate. High-frequency pulsed current assisted technology is used, with a voltage setting of 40V and a current density of 120A / cm 2 , pulse frequency: 2000Hz, power supply mode: high-frequency square wave pulse current, heating temperature 300℃, holding time 60min;

[0082] S3.2. After the pulsed electric field is complete, immediately transfer the material to a liquid nitrogen environment for rapid cooling, cooling it to -180°C and maintaining it in liquid nitrogen for 60 min.

[0083] S3.3. After cooling with liquid nitrogen, remove the sample immediately and place it on the pulsed electric field heating platform again. Use high-frequency pulse current to quickly heat it to 200°C and keep it at this temperature for 30 minutes.

[0084] Comparative Example 2

[0085] This comparative example provides a method for friction stir welding and additive manufacturing of dissimilar aluminum and steel materials. The difference between this comparative example and the embodiment is that ultrasonic vibration is not applied in step S2. Specifically, the steps are as follows:

[0086] S1. Preheat 7075 aluminum alloy and 316L stainless steel using direct current rapid heating. By placing the positive and negative electrodes in contact with the aluminum and steel sides, current flows through the dissimilar metal interface, preheating the materials uniformly through resistance heat. Voltage setting: 30V, current density: 100A / cm 2 , power-on mode: DC constant current output, power-on time: 40s, target temperature: 200℃;

[0087] S2. Under the condition of applying electromagnetic vibration, the stir friction additive process is used to add aluminum alloy materials and stainless steel materials to obtain aluminum-steel dissimilar materials. The temperature monitoring and exogenous gas cooling technology in the welding and additive manufacturing process use multi-point thermocouples and infrared thermometers for real-time temperature monitoring, and combined with active cooling technology to achieve precise temperature control. When the temperature exceeds 450°C, the cooling device is started, and the substrate is cooled by the flow control system of the cooling medium. The exogenous gas cooling uses inert gas or cooling air as the cooling medium, and nitrogen (N2) is selected. The cooling medium flow rate is 15L / min, and the cooling rate is 20°C / s, so as to quickly take away the heat during the welding process. After the stirring is completed, the cooling gas is still introduced until it drops to room temperature.

[0088] The electromagnetic vibration conditions are: using low-frequency pulse current auxiliary technology, the current is continuously passed into the aluminum-steel dissimilar metal interface during the stirring process, the voltage setting is: 12V, the current density is: 40A / cm 2 , pulse frequency: 200Hz, power supply mode: low-frequency square wave pulse current, power supply duration: welding and additive manufacturing are applied simultaneously throughout the entire process;

[0089] The conditions of the friction stir additive process are as follows: 7075 aluminum alloy is added on the substrate steel plate 316l, the rotation speed of the stirring head is 1500 rpm, the additive speed is 20 mm / min, the inter-axis downward pressure is 0.2 mm, and the stirring head inclination angle is 3°.

[0090] S3.1. Place the additively prepared aluminum and steel dissimilar materials in a dedicated electric field heat treatment furnace and achieve non-contact heating using a pulsed current heating plate. High-frequency pulsed current assisted technology is used, with a voltage setting of 40V and a current density of 120A / cm 2 , pulse frequency: 2000Hz, power supply mode: high-frequency square wave pulse current, heating temperature 300℃, holding time 60min;

[0091] S3.2. After the pulsed electric field is complete, immediately transfer the material to a liquid nitrogen environment for rapid cooling, cooling it to -180°C and maintaining it in liquid nitrogen for 60 min.

[0092] S3.3. After cooling with liquid nitrogen, remove the sample immediately and place it on the pulsed electric field heating platform again. Use high-frequency pulse current to quickly heat it to 200°C and keep it at this temperature for 30 minutes.

[0093] Comparative Example 3

[0094] This comparative example provides a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, which specifically comprises the following steps:

[0095] A1. Temperature monitoring and exogenous gas cooling technology during welding and additive manufacturing utilizes multi-point thermocouples and infrared thermometers for real-time temperature monitoring, combined with active cooling technology to achieve precise temperature control. When the temperature exceeds 450°C, the cooling device activates, and the substrate is cooled through a cooling medium flow control system. Exogenous gas cooling uses inert gas or cooling air as the cooling medium, with nitrogen (N2) being the preferred cooling medium. The cooling medium flow rate is 15L / min, and the cooling rate is 20°C / s, to quickly remove heat from the welding process. After stirring, cooling gas is continued until the temperature drops to room temperature.

[0096] A2. Friction stir additive technology was used to add 7075 aluminum alloy to a 316L steel substrate. The stir head speed was 1500 rpm, the additive speed was 20 mm / min, the interaxial pressure was 0.2 mm, and the stir head angle was 3°.

[0097] A3. During the friction stir process, high-frequency ultrasonic vibration is applied to the weld area to promote atomic diffusion at the interface and plastic deformation of the metal. The ultrasonic vibration frequency is 40kHz, the amplitude is 20μm, the ultrasonic power is 2kW, and the vibration direction is perpendicular or inclined to the stir head axis.

[0098] A4. Place the additively prepared aluminum and steel dissimilar materials in a dedicated electric field heat treatment furnace and achieve non-contact heating through a pulsed current heating plate. Using high-frequency pulse current assisted technology, the voltage setting is 40V and the current density is 120A / cm 2 , pulse frequency: 2000Hz, power supply mode: high-frequency square wave pulse current, heating temperature 300℃, holding time 60min;

[0099] After the pulse electric field insulation is completed, the material is immediately transferred to a liquid nitrogen environment for rapid cooling, cooled to -180°C, and kept in liquid nitrogen for 60 minutes;

[0100] After cooling with liquid nitrogen, the sample was immediately taken out and placed on the pulse electric field heating platform again. High-frequency pulse current was used for rapid heating to 200°C and the holding time was 30 min.

[0101] Comparative Example 4

[0102] This comparative example provides a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, which specifically comprises the following steps:

[0103] A1. Temperature monitoring and external gas cooling technology during welding and additive manufacturing utilizes multi-point thermocouples and infrared thermometers for real-time temperature monitoring, combined with active cooling technology to achieve precise temperature control. When the temperature exceeds 450°C, the cooling device activates, and the substrate is cooled through a cooling medium flow control system. External gas cooling uses inert gas or cooling air as the cooling medium, with nitrogen (N2) selected as the cooling medium. The cooling medium flow rate is 15L / min and the cooling rate is 20°C / s to quickly remove heat from the welding process. After stirring, cooling gas is continued until the temperature drops to room temperature.

[0104] A2. Friction stir additive technology was used to add 7075 aluminum alloy to a 316L steel substrate. The stir head speed was 1500 rpm, the additive speed was 20 mm / min, the interaxial pressure was 0.2 mm, and the stir head angle was 3°.

[0105] A3. The additively produced aluminum-steel dissimilar material is placed in a coolant at -180°C for 60 minutes, then removed and rapidly heated to 170°C. This extreme cold and heat treatment produces a large number of dislocations, strengthens the substrate, and eliminates residual stress.

[0106] Comparative Example 5

[0107] This comparative example provides a friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, which specifically comprises the following steps:

[0108] A1. Heat 7075 aluminum alloy and 316l stainless steel to 350℃ and roll them together using a rolling mill with a rolling reduction of 10%.

[0109] A2. The rolled and composited materials are solution treated at a temperature of 470°C for 2 hours. After removal, they are water-quenched.

[0110] A3. Perform aging heat treatment at 120℃ / 24h.

[0111] Comparative Example 6

[0112] This comparative example provides a method for friction stir welding and additive manufacturing of dissimilar aluminum and steel materials. The difference between this comparative example and Example 2 is that the DC current heating method in step S1 is replaced by resistance furnace preheating. The other conditions are the same, and the resistance furnace preheating temperature is 200°C.

[0113] Comparative Example 7

[0114] This comparative example provides a stir friction welding and additive manufacturing method for aluminum-steel dissimilar materials. The difference between this comparative example and Example 2 is that the pulse current heating in step S3 is replaced by resistance furnace preheating. The other conditions are the same, and the resistance furnace preheating temperature is 200°C.

[0115] Test example:

[0116] The components of the examples and comparative examples are shown in Table 1.

[0117] Mechanical properties testing standard: GB / T 228 Metal materials room temperature tensile test method;

[0118] GB / T 232 Metal materials bending test method.

[0119] Table 1 Performance results

[0120]

[0121] By comparing the mechanical properties data of the examples and the comparative examples in Table 1, it can be seen that the tensile strength (648-677 MPa), yield strength (572-608 MPa) and shear strength (162-168 MPa) of Examples 1-3 of the present invention using electric-stress-heat-ultrasonic multi-field coupling assisted welding and additive technology combined with pulsed electric field heat treatment technology are significantly higher than the tensile strength (504-552 MPa), yield strength (472-523) and shear strength (92-137 MPa) of Comparative Examples 1-7. Stress-heat-ultrasonic multi-field coupling assisted welding and additive manufacturing technology combined with pulsed electric field heat treatment can achieve coordinated regulation of interface temperature field, stress field and diffusion field during the stir friction process; DC electric field preheating can quickly increase the initial temperature of the aluminum-steel interface and reduce the driving force for IMCs generation; the low-frequency pulse current applied during the entire welding / additive process promotes the directional diffusion of metal atoms through the electromigration effect, and cooperates with stirring shear and ultrasonic vibration to perturb the atomic structure, further strengthening the interface metallurgical bonding; exogenous gas cooling accurately controls heat input to avoid interface overheating and grain coarsening. The superposition of multiple field effects to regulate the interface reaction kinetics and thermodynamic behavior can effectively inhibit the excessive growth of the IMCs layer, refine the microstructure, and ultimately significantly improve the bonding strength and service performance of aluminum-steel dissimilar metal joints. However, due to the lack of these regulatory measures, comparative examples 1 to 7 resulted in uncontrolled growth of IMCs (954 to 2391 μm). In summary, the present invention's electroplating-stress-heat-ultrasonic multi-field coupling assisted welding and additive technology combined with pulsed electric field heat treatment technology achieves a simultaneous improvement in strength and plasticity through multi-scale synergy (electric field preheating to reduce reaction driving force → pulse diffusion to regulate interface composition gradient → ultrasonic perturbation to promote metallurgical bonding → gas cooling to inhibit IMCs growth → pulsed electric field heat treatment to regulate and refine the organization), solving the core problems of IMCs brittleness and residual stress in aluminum-steel composites.

[0122] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. A friction stir welding and additive manufacturing method for aluminum and steel dissimilar materials, characterized in that: The following steps are involved: S1. Preheating aluminum alloy and stainless steel materials; S2. Using a friction stir additive process to add aluminum alloy and stainless steel to produce an aluminum-steel dissimilar material under the conditions of applying electromagnetic vibration and ultrasonic vibration; S3. The aluminum-steel dissimilar materials are heated to 200-500°C by a pulse current, then cooled to -196--100°C and kept cold, and then heated to 200-400°C by a high-frequency pulse current and kept warm.

2. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The preheating method includes a direct current heating method; In the DC current heating method, the voltage is 20-40V and the current density is 80-150A / cm 2 .

3. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The preheating temperature is 200-300°C.

4. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The parameters of the electromagnetic vibration include: voltage of 5 to 20 V, current density of 30 to 80 A / cm 2 , the pulse frequency is 100~500Hz.

5. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The parameters of the ultrasonic vibration include: ultrasonic vibration frequency of 10 to 50 kHz, amplitude of 10 to 40 μm, and ultrasonic power of 1 to 4 kW.

6. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The parameters of the friction stir additive process include: a rotation speed of the stirring head of 1000 to 2000 rpm, an additive speed of 20 to 100 mm / min, an inter-axis downward pressure of 0.1 to 0.5 mm, and an inclination angle of the stirring head of 1 to 5 degrees.

7. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The temperature of the additive step is 450-500°C.

8. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: The parameters of the pulse current heating step include: voltage of 20-60V, current density of 100-200A / cm 2 , the pulse frequency is 1000~4000Hz.

9. The friction stir welding and additive manufacturing method of aluminum-steel dissimilar materials according to claim 1, characterized in that: In step S3, the cooling time is 20 to 120 minutes.

10. Application of the aluminum-steel dissimilar material prepared by the preparation method according to any one of claims 1 to 9 in the fields of aerospace and automobile manufacturing.

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