Composite stirring head for friction stir welding and material adding and application of composite stirring head

Abstract

The invention discloses a composite stirring head for friction stir welding and material increase and application of the composite stirring head. The composite stirring head comprises a top shaft shoulder and a stirring needle coaxially fixed to the shaft shoulder. A spiral groove is formed in the surface of the stirring needle; the surface of the stirring needle is coated with a composite nano-plating layer; and the material of the composite nano plating layer comprises TiB2 and Al2O3. According to the composite stirring head for friction stir welding and material adding and the application of the composite stirring head, heat input is dispersed, a spiral groove stirring needle is combined to promote material flowing, friction heat is reduced in cooperation with a bottom nano-plating layer, and IMC overgrowth is restrained.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and particularly relates to a composite stirring head for friction stir welding and additive manufacturing and its application. Background Art

[0002] Compared with other commonly used metal materials, aluminum alloys have many outstanding advantages. First of all, the density of aluminum alloys is relatively low, which enables them to be widely used in projects with high weight requirements, such as the aerospace and automotive manufacturing industries. Secondly, aluminum alloys have excellent corrosion resistance and can maintain good durability in harsh environments, especially in industries such as marine and chemical engineering. In addition, aluminum alloys also have good welding and processing performance, can be effectively connected through various welding methods, and are not prone to problems such as cracks and deformation, which makes aluminum alloys have strong flexibility in the manufacturing and processing processes. In contrast, steel, as the most widely used metal material globally, its main advantages lie in high strength and high durability. Steel is widely used in fields such as construction, automotive, petrochemical, etc. Especially in structures with high load-bearing capacity requirements, steel plays a crucial role as a basic material. In order to make full use of the advantages of these two materials and achieve the ideal combination of low weight and high strength, the dissimilar metal welding technology of aluminum alloy and steel has become a research hotspot. This kind of welded structure has significant economic benefits and performance improvement in fields such as power, automotive, petrochemical, and aerospace. For example, using aluminum-steel composite materials can effectively reduce the structural weight while improving corrosion resistance and load-bearing capacity, so its application prospect is broad. However, the welded connection of aluminum alloy and steel faces great technical challenges. The differences in thermophysical properties and chemical properties greatly increase the welding difficulty of aluminum and steel. According to the Al-Fe binary phase diagram, the mutual solubility between aluminum and steel is relatively low, and brittle intermetallic compounds (IMCs), such as FeAl2, Fe2Al5, and FeAl3, are easily formed during the welding process. Although these IMCs contribute to the metallurgical bonding between aluminum and steel to a certain extent, when too many of them are generated, it will increase the brittleness of the joint, thereby reducing the mechanical properties and crack resistance of the joint. In addition, the thermal expansion coefficients and thermal conductivities of aluminum and steel are quite different, and large residual stresses are easily generated during the welding process, which makes the aluminum-steel connection prone to cracks, especially in the joint area. Moreover, an Al2O3 oxide film that is difficult to melt is easily formed on the surface of aluminum alloys, which not only affects the fusion degree of aluminum-steel welding but also reduces the welding quality and joint strength. At present, the welding methods for dissimilar aluminum-steel metals are mainly divided into fusion welding, brazing, and solid-state connection, etc. Traditional fusion welding methods have a large heat input and are difficult to accurately control. Usually, too thick IMCs are generated in the welding area, resulting in an increase in joint brittleness and seriously affecting the welding quality. As another connection method, brazing has the advantages of small joint deformation and adjustable process parameters, and less IMCs are generated. However, it has defects such as porosity and slag inclusion easily generated in the welded joint and poor heat resistance. In addition, although mechanical connection avoids the formation of IMCs, the joint strength is low and the fatigue performance is poor, and it is usually only applicable to occasions with low requirements.Therefore, in the joining of dissimilar aluminum and steel metals with high quality and reliability requirements, solid-state welding techniques, especially friction stir welding (FSW) and friction stir additive manufacturing (FSAM), have become the focus of research. Friction stir additive manufacturing (FSAM) is a new type of solid-phase joining technology. Different from traditional fusion welding, FSAM uses a high-speed rotating stirring head to generate heat by friction with the workpiece, making the material in the welding area locally plasticized, and then forming a tight solid-phase joint. Compared with traditional additive manufacturing methods, such as laser melting and electron beam melting, FSAM has significantly lower heat input and avoids the melting process of materials through solid-phase joining. Therefore, FSAM can effectively avoid defects such as pores and cracks caused by melting during the welding process and reduce the formation of IMCs. During the FSAM process, the welding material does not completely melt, but achieves metallurgical bonding through local plasticization and metal flow, enabling the formation of high-strength solid-phase joints between dissimilar aluminum and steel metals. Due to the low heat input and short heat cycle time, FSAM significantly reduces the formation of IMCs and avoids the common problem of excessive IMC thickness during fusion welding, thereby improving the mechanical properties and stability of the welded joint. In addition to heat input control, FSAM technology also has good 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 makes the connection between dissimilar aluminum and steel metals tighter, and the mechanical properties of the welded joint are significantly improved. Traditional additive manufacturing technologies (such as additive manufacturing based on the melting process) often suffer from problems such as too fast cooling rate and poor metal fluidity, resulting in poor bonding of the welded joint and even defects such as pores and cracks, affecting the quality of the final joint. However, FSAM effectively improves the joining of dissimilar aluminum and steel metals through precise control of temperature, metal fluidity, and interface bonding. Although FSAM technology has shown great advantages in the joining of dissimilar aluminum and steel metals, there are still some limitations. Although the existing FSAM technology can effectively reduce the formation of IMCs, the problems of poor metal fluidity and poor interface bonding still exist. The difference in metal fluidity between aluminum alloy and steel, especially the poor fluidity of steel, easily leads to insufficient bonding of the two metals at the interface, affecting the quality of the joint. In addition, due to the difference in thermophysical properties between aluminum alloy and steel, the difficulty of temperature control during the FSAM process is still relatively large, and uneven temperature distribution may cause local overheating, thus affecting the formation of IMCs and the quality of the welded joint.

[0003] Therefore, it is urgent to provide an effective method to reduce the thickness of IMC. Summary of the Invention

[0004] The present invention aims to solve the above-mentioned technical problems existing in the prior art. To this end, the present invention provides a composite stirring head for friction stir welding and additive manufacturing, which promotes material flow by dispersing heat input and combining a spiral groove stirring pin, and cooperates with a bottom nano-coating to reduce frictional heat and inhibit the excessive growth of IMCs.

[0005] The present invention also provides a method for preparing an aluminum-steel composite plate.

[0006] The present invention also provides the application of the plate prepared by the above-mentioned preparation method in the aerospace, automotive, chemical and transportation industries.

[0007] According to the first aspect of the present invention, a composite stirring head is provided, which includes a top shoulder and a stirring pin coaxially fixed to the shoulder;

[0008] The surface of the stirring pin is provided with spiral grooves;

[0009] The surface of the stirring pin is coated with a composite nano-coating;

[0010] The material of the composite nano-coating includes TiB2 and Al2O3.

[0011] The inventive concept of the present invention is as follows:

[0012] The top shoulder of the composite stirring head of the present invention reduces the surface heat input by increasing the contact area, avoiding the coarsening of material grains caused by local overheating, especially for aluminum alloy materials. The lower heat input helps to reduce the generation of IMCs and maintain the good fluidity and properties of the material. The spiral grooves provided on the surface of the stirring pin help the material to flow better, optimize the heat distribution, avoid the problem of heat accumulation, further control the temperature gradient, and prevent the emergence of heat overload areas. During the friction stir process, the high-hardness TiB2 particles in the coating are uniformly dispersed in the Al matrix. As a coating, it reduces the friction coefficient and the frictional heat input, suppressing welding overheating from the source; at the same time, the chemical inertness of TiB2 effectively hinders the interdiffusion of Fe-Al atoms, greatly reducing the thickness of the intermetallic compound (IMC) layer. The unique heat conduction network of the coating (the combination of Al matrix and TiB2) realizes the rapid lateral diffusion and longitudinal barrier of heat, stably controlling the welding temperature within the optimized range. In addition, the pinning effect of nano-TiB2 particles refines the dynamically recrystallized grains of aluminum alloy, improves the tensile strength of the joint, and prolongs the service life of the stirring pin.

[0013] In some embodiments of the present invention, the diameter of the top shoulder is 15-20 mm.

[0014] Within the above diameter range, on the one hand, it avoids the situation that when the diameter of the stirring head is too large, the larger the contact area with the material during the welding process, the greater the energy input, which helps to improve the plastic deformation ability of the material, enhance the metal flow, and improve the welding quality. However, if the diameter is too large, the heat input is excessive, which may lead to too high an interface temperature, accelerate the growth of interfacial intermetallic compounds (IMCs), and reduce the joint performance. Therefore, the range of 15 - 20 mm can provide sufficient heat input while avoiding excessive growth of IMCs. At the same time, when the diameter is small, the range of the stirring zone becomes smaller, and the material is not stirred sufficiently, which may lead to poor interfacial bonding or weld defects (such as tunnel defects, pores, etc.). When the diameter is large, the stirring energy is enhanced, which helps to improve the material fluidity and optimize the interfacial bonding, but being too large may cause local overheating and increased tool wear. The range of 15 - 20 mm can ensure an appropriate material flow state while improving the stirring efficiency.

[0015] In some embodiments of the present invention, the length of the stirring pin is 4 - 8 mm.

[0016] The length of the stirring head determines the depth of the stirring layer. In the dissimilar metal welding of aluminum / steel, it is necessary to ensure sufficient stirring of the aluminum layer and the steel layer while avoiding over-stirring that may damage the steel layer.

[0017] With the above length of the stirring pin, on the one hand, it avoids the problems that when the length is too short (<4 mm), it may not be able to fully penetrate the aluminum layer to reach the interface, resulting in insufficient interfacial bonding, reduced weld strength, pores or tunnel defects, etc. On the other hand, it avoids the situation that when the length is too long (>8 mm), it may over-stir the steel layer, leading to an increase in the plastic deformation of the steel, and even excessive wear and heat input, thereby promoting the growth of the thickness of interfacial intermetallic compounds (IMCs) and reducing the joint performance.

[0018] In some embodiments of the present invention, the coating thickness of the composite nano - coating is 100 - 500 nm.

[0019] With the above coating thickness, it avoids insufficient wear resistance that may be caused by too thin a coating, which affects the tool life; at the same time, it avoids that too thick a coating may increase the weight and inertia of the stirring head, affecting the flexibility and control accuracy of the equipment.

[0020] In some embodiments of the present invention, a thermocouple sensor and a cooling chamber are arranged inside the composite stirring head.

[0021] A thermocouple sensor and a cooling chamber are arranged inside the composite stirring head to monitor the temperature of the stirring head in real - time; the cooling chamber is provided with dense micro - channels preset inside the stirring head to connect the coolant, and the coolant flow rate is set to 2 - 10 L / min. The heat of the stirring head is carried away by the coolant, and the temperature of the stirring head is kept stable at 450 - 500 °C.

[0022] According to the second aspect of the present invention, a method for preparing an aluminum-steel composite plate is provided, comprising the following steps:

[0023] S1. Preheat the aluminum alloy with a plasma having a power of 1-4 kW for 5-20 seconds;

[0024] S2. Under the condition of applying electromagnetic vibration, perform aluminum alloy additive manufacturing on a base steel plate by friction stir additive manufacturing process to obtain a plate;

[0025] The process parameters of the friction stir additive manufacturing include: the rotation speed of the composite stirring head is 1000-2000 rpm;

[0026] The composite stirring head is the aforementioned composite stirring head.

[0027] Aiming at the defects of the prior art, the present invention will solve the problems of precise control of the IMC thickness and heat input at the aluminum-steel interface by designing a composite stirring head, adding real-time temperature field control and cooling technology to the stirring head, exogenous plasma-assisted technology and electromagnetic vibration-assisted technology, reducing the IMC thickness, lowering the heat input, improving the metal fluidity, and reducing the wear of the stirring pin. Setting the structure of the composite stirring head can well optimize the heat input control, improve the metal fluidity and interface bonding. The top shoulder of the three-stage composite stirring head structure reduces the surface heat input by increasing the contact area, avoiding the coarsening of material grains caused by local overheating, especially for aluminum alloy materials. The lower heat input helps to reduce the generation of IMCs and maintain the good fluidity and performance of the material. The middle spiral groove stirring pin helps the material to flow better, optimizes the heat distribution, avoids the problem of heat accumulation, further controls the temperature gradient, and prevents the appearance of heat overload areas. During the friction stir process, real-time temperature field control and cooling technology can be added to the stirring head. The temperature is detected by a thermocouple. When the temperature is too high, the cooling device (such as a cooling water system) is automatically started to reduce the temperature, ensuring that the temperature in the welding area is controlled below the melting point of the aluminum alloy (<550 °C), avoiding the excessive growth of IMCs. By synchronously introducing the exogenous plasma-assisted technology into the friction stir welding / additive manufacturing process, the metal fluidity can be improved. Plasma-assisted heating can increase the temperature in the welding area, promote the plastic deformation of the metal. The most crucial thing is to control the growth of IMCs (intermetallic compounds). The plasma can effectively regulate the temperature field during the welding process through precise heating area control, avoiding the excessive generation of IMCs caused by too high temperature. The electromagnetic vibration-assisted technology directly vibrates the IMC layer in the aluminum-steel interface area by applying periodic electromagnetic field vibration, which helps to break and homogenize the IMC layer, reduce the thickness of the IMC, inhibit the excessive growth of the IMC, and at the same time improve the metal fluidity and interface bonding, thereby improving the mechanical properties and stability of the interface.

[0028] In some embodiments of the present invention, the plasma flow of the plasma includes at least one of argon, nitrogen, or an argon-hydrogen mixture gas.

[0029] In some embodiments of the present invention, the gas flow rate of the plasma is 5 - 15 L / min.

[0030] To provide a stable plasma flow, with a gas flow rate of 5 - 15 L / min, ensuring a stable plasma jet.

[0031] In some embodiments of the present invention, the temperature of the preheating treatment is 200 - 300 °C.

[0032] In some embodiments of the present invention, the process parameters of the electromagnetic vibration include: an electromagnetic field vibration frequency of 10 - 50 Hz, an amplitude range of 10 - 40 μm, and an electromagnetic field intensity of 0.1 - 1.5 T.

[0033] In some embodiments of the present invention, the process parameters of the friction stir additive manufacturing further include: an additive speed of 100 - 400 mm / min, an axial downward pressure of 0.1 - 0.5 mm, and an inclination angle of the composite stirring head of 1 - 5°.

[0034] According to the third aspect of the present invention, there is provided an application of a sheet prepared by the described preparation method in the aerospace, automotive, chemical, and transportation industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the following description of the embodiments in conjunction with the accompanying drawings, wherein:

[0036] Figure 1 It is the composite stirring head in the embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] The following will clearly and completely describe the concept of the present invention and the technical effects produced in combination with the embodiments to fully understand the purpose, features, and effects of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0038] Example 1

[0039] This example provides a composite stirring head for friction stir welding and additive manufacturing and a preparation method for an aluminum-steel composite sheet, which are as follows:

[0040] The composite stirring head is:

[0041] The composite stirring head consists of a top shoulder and a stirring pin coaxially fixed to the shoulder. The diameter of the top enlarged shoulder is 18 mm, the length of the middle spiral groove stirring pin is 6 mm, and the surface of the stirring pin is coated with a TiB2 / Al2O3 composite nano - coating with a coating thickness of 300 nm;

[0042] A thermocouple sensor and a cooling chamber are arranged inside the stirring head. The thermocouple sensor is integrated into the stirring head or directly in contact with the welding area to monitor the temperature change during the welding process in real - time. When the temperature exceeds 450 °C, the cooling device starts. The coolant is selected as water or water - based coolant, and the flow rate is set to 20 L / min to quickly remove the heat generated during the welding process. The structure is as Figure 1 shown.

[0043] A preparation method for an aluminum - steel composite plate is as follows:

[0044] S1. Pre - heat the 7075 aluminum alloy raw material using a plasma generator. Set the plasma power to 2 kW, use argon (Ar), nitrogen (N2), or argon - hydrogen mixed gas (Ar - H2) as the shielding gas, control the gas flow rate to 10 L / min, and heat the material through a 3 - mm - diameter nozzle for 15 seconds to uniformly raise the surface temperature of the aluminum alloy to 300 °C;

[0045] S2. Implement the friction stir additive manufacturing process on the base steel plate. Control the stirring head to rotate at a speed of 1500 r / min, move along a predetermined path at an additive speed of 100 mm / min, keep the stirring head at an inclination angle of 3°, set the downward pressure between the plates along the axis to 0.2 mm, and apply electromagnetic vibration assistance synchronously during the additive process. Set the electromagnetic field strength to 0.3 T, the vibration frequency to 30 Hz, and the amplitude to 20 μm. Effectively optimize the metal fluidity and break the interfacial intermetallic compounds through periodic electromagnetic vibration.

[0046] Example 2

[0047] This example provides a composite stirring head for friction stir welding and additive manufacturing and a preparation method for an aluminum - steel composite plate, which are as follows:

[0048] The composite stirring head consists of a top shoulder and a stirring pin coaxially fixed to the shoulder. The diameter of the top enlarged shoulder is 18 mm, the length of the middle spiral groove stirring pin is 6 mm, and the surface of the stirring pin is coated with a TiB2 / Al2O3 composite nano - coating with a coating thickness of 300 nm;

[0049] The stirring head is internally provided with a thermocouple sensor and a cooling chamber. The thermocouple sensor is integrated into the stirring head or directly contacts the welding area to monitor the temperature change during the welding process in real time. When the temperature exceeds 450 °C, the cooling device is activated. The coolant is selected from water or water-based coolant, and the flow rate is set to 20 L / min to quickly remove the heat generated during the welding process.

[0050] A method for preparing an aluminum-steel composite plate comprises the following steps:

[0051] S1. Preheat the 7075 aluminum alloy raw material using a plasma generator. Set the plasma power to 2 kW, use argon (Ar), nitrogen (N2), or argon-hydrogen mixed gas (Ar-H2) as the shielding gas, control the gas flow rate to 10 L / min, and heat the material through a nozzle with a diameter of 3 mm for 15 seconds to evenly raise the surface temperature of the aluminum alloy to 300 °C.

[0052] S2. Implement the friction stir additive manufacturing process on the base steel plate. Control the stirring head to rotate at a speed of 1500 r / min, move along a predetermined path at an additive speed of 200 mm / min, keep the stirring head at an inclination angle of 3°, set the downward pressure between the axes of the plate to 0.2 mm, and apply electromagnetic vibration assistance synchronously during the additive process. Set the electromagnetic field strength to 0.3 T, the vibration frequency to 30 Hz, and the amplitude to 20 μm to effectively optimize the metal fluidity and break the interfacial intermetallic compounds through periodic electromagnetic vibration.

[0053] Example 3

[0054] This example provides a composite stirring head for friction stir welding and additive manufacturing and a method for preparing an aluminum-steel composite plate, which comprises the following steps:

[0055] The composite stirring head consists of a top shoulder and a stirring pin coaxially fixed to the shoulder. The diameter of the enlarged top shoulder is 18 mm, the length of the middle spiral groove stirring pin is 6 mm, and the surface of the stirring pin is coated with a TiB2 / Al2O3 composite nano-coating with a coating thickness of 300 nm.

[0056] The stirring head is internally provided with a thermocouple sensor and a cooling chamber. The thermocouple sensor is integrated into the stirring head or directly contacts the welding area to monitor the temperature change during the welding process in real time. When the temperature exceeds 450 °C, the cooling device is activated. The coolant is selected from water or water-based coolant, and the flow rate is set to 20 L / min to quickly remove the heat generated during the welding process.

[0057] A method for preparing an aluminum-steel composite plate comprises the following steps:

[0058] S1. Preheat the 7075 aluminum alloy raw material using a plasma generator. Set the plasma power to 2 kW, use argon (Ar), nitrogen (N2), or argon-hydrogen mixed gas (Ar-H2) as the protective gas, control the gas flow rate to 10 L / min, and heat the material through a nozzle with a diameter of 3 mm for 15 seconds to evenly raise the surface temperature of the aluminum alloy to 300 °C;

[0059] S2. Implement the friction stir additive manufacturing process on the substrate steel plate. Control the rotation speed of the stirring head to 1500 r / min, move along the predetermined path at an additive manufacturing speed of 300 mm / min, keep the stirring head at a 3° inclination angle, set the downward pressure between the plates to 0.2 mm, and apply electromagnetic vibration assistance synchronously during the additive manufacturing process. Set the electromagnetic field strength to 0.3 T, the vibration frequency to 30 Hz, and the amplitude to 20 μm to effectively optimize the metal fluidity and break the interfacial intermetallic compounds through periodic electromagnetic vibration.

[0060] Comparative Example 1

[0061] This comparative example provides a method for preparing an aluminum-steel composite plate, which is as follows:

[0062] S1. Preheat the 7075 aluminum alloy raw material using a plasma generator. Set the plasma power to 2 kW, use argon (Ar), nitrogen (N2), or argon-hydrogen mixed gas (Ar-H2) as the protective gas, control the gas flow rate to 10 L / min, and heat the material through a nozzle with a diameter of 3 mm for 15 seconds to evenly raise the surface temperature of the aluminum alloy to 300 °C;

[0063] S2. Implement the friction stir additive manufacturing process on the substrate steel plate. The stirring head uses an ordinary threaded conical stirring pin, the shoulder diameter: 12 mm, the stirring pin length 6 mm. Control the rotation speed of the stirring head to 1500 r / min, move along the predetermined path at an additive manufacturing speed of 100 mm / min, keep the stirring head at a 3° inclination angle, and set the downward pressure between the plates to 0.2 mm;

[0064] S3. Implement real-time temperature control during the additive manufacturing process. Integrate the thermocouple sensor inside the stirring head to monitor the temperature change in the welding area in real time. When the temperature exceeds 450 °C, automatically start the cooling system and use water or water-based coolant to quickly cool down at a flow rate of 20 L / min;

[0065] S4. Apply electromagnetic vibration assistance synchronously during the additive manufacturing process. Set the electromagnetic field strength to 0.3 T, the vibration frequency to 30 Hz, and the amplitude to 20 μm to optimize the metal fluidity through periodic electromagnetic vibration.

[0066] Comparative Example 2

[0067] This comparative example provides a method for preparing an aluminum-steel composite plate, which comprises the following steps:

[0068] S1. On the base steel plate, an ordinary threaded conical stirring pin is used for processing, where the shoulder diameter is 12 mm, the length of the stirring pin is 6 mm, and the friction stir additive manufacturing technology is used for adding 7075 aluminum alloy. The stirring head is controlled to rotate at a speed of 1500 r / min and move along a predetermined path at an additive speed of 100 mm / min. The stirring head maintains an inclination angle of 3°, and the downward pressure between the axes of the plate is set to 0.2 mm;

[0069] S2. Implement real-time temperature control. Integrate the thermocouple sensor inside the stirring head to monitor the temperature change in the welding area in real time. When the temperature exceeds 450 °C, automatically start the cooling system and use water or water-based coolant to quickly cool down at a flow rate of 20 L / min.

[0070] Comparative Example 3

[0071] This comparative example provides a method for preparing an aluminum-steel composite plate, which comprises the following steps:

[0072] Heat 7075 aluminum alloy and 316l stainless steel to 350 °C, and use a rolling mill for rolling and compounding. The rolling reduction is 10%. The composite material is subjected to solution treatment, the solution temperature is 470 °C, the holding time is 2 h, and after taking out, it is water-cooled and quenched, and then subjected to aging heat treatment at 120 °C / 24 h.

[0073] Comparative Example 4

[0074] The difference between this comparative example and Example 1 is that a resistance furnace preheating is used to replace the preheating treatment of the 7075 aluminum alloy raw material by the plasma generator in step S1 of Example 1, and the other conditions are the same.

[0075] The main reason for the decline in the preheating effect of the resistance furnace lies in the essential differences in its heating mechanism and process characteristics compared to plasma preheating. The resistance furnace conducts overall slow heating through conduction and convection, causing the surface of the aluminum alloy to be exposed to air during the long-term temperature rise process, inevitably forming a relatively thick oxide layer (Al2O3). This oxide film will hinder the atomic diffusion at the aluminum / steel interface, increase the resistance to the formation of intermetallic compounds (IMCs), and at the same time, the residual oxide inclusions will weaken the interface bonding strength. In contrast, plasma preheating achieves local rapid heating through high-energy ion flows, and with the protection of inert gases (such as Ar), it can effectively inhibit oxidation and clean the surface. In addition, the highly active hydrogen components of the plasma (such as the Ar-H2 mixture) can partially reduce the formed oxide film, and the electromagnetic vibration assistance further breaks the oxide layer, jointly promoting interfacial metallurgical bonding. The slow thermal cycle of the resistance furnace also leads to grain coarsening in the heat-affected zone, while the instantaneous high-temperature concentrated input of the plasma can refine the dynamically recrystallized grains. These factors comprehensively result in the IMC thickness of the resistance furnace preheating (200 - significantly higher than that of plasma preheating, and finally manifested as a decrease in the tensile strength and shear strength by about 10% - 20%.

[0076] Comparative Example 5

[0077] The difference between this comparative example and Example 1 is that ultrasonic vibration assistance is used to replace the electromagnetic vibration assistance in Example 1, and the other conditions are the same.

[0078] Replacing electromagnetic vibration assistance with ultrasonic vibration will lead to a decline in the effect. The main reason is that although the ultrasonic vibration (20 - 40 kHz) has a higher frequency, its mechanical wave energy is mainly concentrated on the surface layer of the material (depth < 1 mm), making it difficult to fully penetrate to the aluminum-steel interface, resulting in a weakened IMC inhibition effect (the thickness increases to 180 - 300 nm). In addition, the non-contact characteristic of electromagnetic vibration can avoid interface contamination, while ultrasonic waves need to be transmitted through a horn contact, which may introduce mechanical interference. More importantly, electromagnetic vibration forms a synergy with plasma preheating and the nano-coated stirring head: after the plasma cleans the surface, electromagnetic vibration further optimizes the atomic-level bonding, while ultrasonic waves lack this systematic cooperation, ultimately leading to a decrease in the tensile strength and a reduction in the interfacial shear strength.

[0079] Comparative Example 6

[0080] The difference between this comparative example and Example 1 is that a CrN coating is used to replace the TiB2 / Al2O3 composite nano-coating in Example 1, and the other conditions are the same.

[0081] CrN cannot form a surface activation synergy with plasma preheating like the TiB2 / Al2O3 coating, nor can it cooperate with electromagnetic vibration to achieve grain refinement, ultimately resulting in a decrease in the tensile strength and a reduction in the interfacial shear strength.

[0082] Test Example

[0083] The components of the examples and comparative examples are shown in Table 1.

[0084] Mechanical property testing standard: GB / T 228 Test method for tensile properties of metallic materials at room temperature;

[0085] Table 1 Performance test results

[0086]

[0087]

[0088] In the examples of the present invention, through the collaborative use of multiple technologies such as composite stirring head design, plasma preheating, and electromagnetic vibration, low heat input, high fluidity, fine grains, and thin IMC layers are achieved, thereby comprehensively improving the mechanical properties. In Comparative Example 1, the ordinary stirring pin lacks spiral grooves and nano-coatings, resulting in poor heat input control, a significant increase in the IMC thickness (648 nm), and grain coarsening (3 μm), leading to a decrease in strength (556 MPa) and ductility (8%). In Comparative Example 2, the material has poor fluidity, a thicker IMC layer (865 nm), larger grain size (5 μm), and further deteriorated mechanical properties (tensile strength 548 MPa); in Comparative Example 3, high temperature (350 °C) and rolling pressure result in an extremely thick IMC layer (3645 nm), large grains (64 μm), and the solution aging treatment cannot repair the interface defects, with the worst performance (tensile strength 504 MPa); in Comparative Example 4, the heating of the resistance furnace causes a relatively thick oxide layer (Al2O3) to form on the surface of the aluminum alloy, hindering the atomic diffusion at the aluminum / steel interface, resulting in difficulty in forming the IMC layer (227 nm), grain coarsening (2 μm), and a reduction in mechanical properties (tensile strength 589 MPa); in Comparative Example 5, the ultrasonic vibration has less obvious auxiliary effect compared to electromagnetic vibration, the IMC layer increases slightly (247 nm), and the tensile strength (643 MPa) and yield strength (563 MPa) decrease slightly; in Comparative Example 6, the coating of the stirring head is changed to CrN, and CrN cannot form surface activation synergy with plasma preheating, resulting in a decrease in tensile strength (553 MPa) and a reduction in interface shear strength (116 MPa).

[0089] The above has described the embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the relevant art. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A composite stirring head for friction stir welding and additive manufacturing, characterized in that: It includes a top shoulder and a stirring pin coaxially fixed to the shoulder; The surface of the stirring pin is provided with a spiral groove; The surface of the stirring pin is coated with a composite nano-coating; The material of the composite nano-coating includes TiB2 and Al2O3.

2. The composite stirring head according to claim 1, wherein: The diameter of the top shoulder is 15 - 20 mm.

3. The composite stirring head according to claim 1, characterized in that: The length of the stirring pin is 4 - 8 mm.

4. The composite stirring head according to claim 1, wherein: The coating thickness of the composite nano-coating is 100 - 500 nm.

5. The composite stirring head according to claim 1, wherein: A thermocouple sensor and a cooling chamber are arranged in the composite stirring head.

6. A preparation method of an aluminum-steel composite plate, characterized in that: It includes the following steps: S1. Preheat the aluminum alloy for 5 - 20 seconds by using a plasma with a power of 1 - 4 kW; S2. Under the condition of applying electromagnetic vibration, use the friction stir additive manufacturing process to perform aluminum alloy additive manufacturing on a base steel plate to obtain a plate; The process parameters of the friction stir additive manufacturing include: the rotation speed of the composite stirring head is 1000 - 2000 rpm; The composite stirring head is the composite stirring head according to any one of claims 1 - 5.

7. The preparation method of the aluminum-steel composite sheet according to claim 6, characterized in that: The temperature of the preheating treatment is 200 - 300 °C.

8. The preparation method of the aluminum-steel composite plate according to claim 6, characterized in that: The process parameters of the electromagnetic vibration include: the electromagnetic field vibration frequency is 10 - 50 Hz, the amplitude range is 10 - 40 μm, and the electromagnetic field strength is 0.1 - 1.5 T.

9. The manufacturing method of the aluminum-steel composite sheet according to claim 6, characterized in that: The process parameters of the friction stir additive manufacturing further include: the additive manufacturing speed: 100 - 400 mm / min, the axial downward pressure is: 0.1 - 0.5 mm, and the inclination angle of the composite stirring head is 1 - 5°.

10. The application of a plate prepared by the preparation method according to any one of claims 6 - 9 in the aerospace, automotive, chemical, and transportation industries.

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