Aluminum steel welding and material adding method and application thereof

Abstract

The invention discloses an aluminum steel welding and material adding method and application thereof, and the aluminum steel welding and material adding method comprises the following steps that S1, aluminum alloy material adding is conducted on a base material steel plate through a friction stirring material adding technology to obtain a plate, and S2, the plate is subjected to graded cooling regulation and control. The IMC thickness is reduced, heat input is reduced, generation of a brittle phase of an aluminum steel dissimilar metal bonding interface is reduced, meanwhile, residual stress is reduced, and the mechanical property and stability of a connector are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloys, and particularly relates to an aluminum-steel welding and additive manufacturing method and its application. Background Art

[0002] As a lightweight and high-strength material, aluminum alloy exhibits significant advantages in engineering applications. Its low density makes it irreplaceable in fields such as aerospace and transportation; its excellent corrosion resistance enables its wide application in offshore engineering and chemical equipment; in addition, its good welding and processing performance facilitates the manufacture of complex structures. In contrast, steel dominates in load-bearing structures such as construction and machinery manufacturing due to its excellent strength and durability. To achieve an optimized combination of material properties, the aluminum / steel dissimilar metal joining technology has become a current research hotspot. This composite structure can maintain a high load-bearing capacity while reducing weight, and has important engineering application value.

[0003] However, the additive manufacturing of aluminum / steel dissimilar metals faces severe scientific challenges. According to the Al-Fe binary phase diagram, the mutual solubility of aluminum and iron in the solid state is extremely low, and brittle intermetallic compounds (IMCs) such as FeAl2, Fe2Al5, and FeAl3 are easily formed during the additive manufacturing process. Although these IMCs can promote metallurgical bonding, their excessive formation will significantly reduce the toughness and mechanical properties of the joint. In addition, there are significant differences in thermophysical properties between the two materials: the thermal expansion coefficient of aluminum alloy (23.6×10 -6 / °C) is approximately twice that of low-carbon steel (11.8×10 -6 / °C), and its thermal conductivity (237 W / m·K) is nearly five times that of steel (50 W / m·K). This difference leads to large residual stresses during the additive manufacturing process, which are prone to causing crack defects. At the same time, the dense Al2O3 oxide film on the surface of aluminum alloy (melting point is about 2050°C) seriously hinders the fusion between metals.

[0004] The current aluminum / steel joining technologies mainly include three categories: fusion welding, brazing, and solid-state joining. Traditional fusion welding methods result in an overly thick IMCs layer (usually exceeding 10 μm) due to high heat input, severely deteriorating the joint performance; although brazing can control the formation of IMCs, it has defects such as low joint strength and poor heat resistance; mechanical joining is limited in its application range due to stress concentration problems. Against this background, solid-state joining technologies represented by friction stir welding (FSW) and friction stir additive manufacturing (FSAM) exhibit unique advantages. FSAM makes the material undergo plastic flow rather than melting through frictional heat, controlling the thickness of the IMCs layer at the sub-micron level (usually 1-5 μm), and at the same time avoiding fusion welding defects such as pores and cracks. Research shows that when the thickness of the IMCs layer is controlled below 5 μm, the joint strength can reach more than 80% of the aluminum alloy base material.

[0005] Nevertheless, the FSAM technology still faces several key scientific issues: First, the difference in the plastic flow behavior of aluminum / steel dissimilar materials leads to insufficient interfacial bonding; Second, the nucleation and growth mechanism of IMCs under thermo-mechanical coupling is still unclear; Third, the regulation law of process parameters on the evolution of interfacial microstructure still needs to be studied in depth. In particular, how to control the IMCs layer thickness within the optimal range (1-3 μm) by optimizing the heat input and material flow behavior has become the core issue for improving the joint performance.

[0006] Therefore, it is urgent to develop an aluminum-steel welding and additive manufacturing method to achieve precise control of IMCs. Summary of the Invention

[0007] The present invention aims to solve the above-mentioned technical problems existing in the prior art. For this purpose, the present invention proposes an aluminum-steel welding and additive manufacturing method and its application, which reduces the IMC thickness, reduces the heat input, reduces the generation of brittle phases at the bonding interface of aluminum-steel dissimilar metals, and at the same time reduces the residual stress and improves the mechanical properties and stability of the joint.

[0008] The present invention also proposes an aluminum-steel welding and additive manufacturing method.

[0009] The present invention also proposes the application of the sheet prepared by the above preparation method in the aerospace, automotive, chemical and transportation industries.

[0010] According to the first aspect of the present invention, an aluminum-steel welding and additive manufacturing method is proposed, including the following steps:

[0011] S1. Aluminum alloy additive manufacturing is carried out on a base steel plate by friction stir additive manufacturing process to obtain a sheet,

[0012] The base steel plate is a steel plate coated with a composite nano-coating,

[0013] The materials of the composite nano-coating include: Ni-Zn alloy and Al2O3;

[0014] S2. The sheet is subjected to hierarchical cooling control,

[0015] The hierarchical cooling control includes the first cooling, the second cooling and the third cooling,

[0016] The steps of the first cooling include: cooling the sheet to 200-300 °C at a cooling rate of 5-10 °C / s,

[0017] The steps of the second cooling include: cooling the sheet cooled in the first cooling to 0-40 °C at a cooling rate of 15-30 °C / s,

[0018] The steps of the third cooling include: cooling the sheet after the second cooling at -100 to -196 °C for 20 to 120 min;

[0019] S3. Heat the sheet after the hierarchical cooling control at 150 to 250 °C.

[0020] The embodiments according to the first aspect of the present invention have at least the following beneficial effects:

[0021] By introducing a coating on the surface of the steel substrate, the present invention can effectively regulate the interfacial reaction, reduce the formation of IMCs and inhibit their excessive growth, improve the interfacial bonding quality. At the same time, the coating, as a transition layer, can buffer the difference in thermal expansion coefficients between dissimilar metals, reduce the residual stress, and reduce the risk of crack initiation. In addition, the coating can optimize the wettability of the interface, improve the metallurgical bonding efficiency, make the metal plastic flow more uniform, and enhance the stability of the friction stir additive manufacturing process. The micro-nano reinforcement particles (such as Al2O3) dispersed in the coating further enhance the wear resistance and fatigue resistance of the interface, thereby improving the comprehensive mechanical properties and service life of the welded joint. Combined with the hierarchical cooling control technology, precise control of the interfacial heat input can be achieved, further reducing the thickness of IMCs at the aluminum-steel interface, inhibiting the violent reaction of Fe-Al, reducing the generation of brittle phases at the bonding interface of aluminum-steel dissimilar metals, and at the same time reducing the residual stress, and finally obtaining an aluminum-steel dissimilar metal joint with excellent mechanical properties and good structural stability.

[0022] During the friction stir process, a large interfacial temperature gradient, high residual stress, and excessive growth of IMCs are the key problems affecting the joint performance. The present invention adopts the hierarchical cooling control technology. By precisely controlling the cooling rate and temperature gradient, the welding residual stress can be effectively reduced, the initiation and propagation of thermal cracks during the additive manufacturing process can be reduced, and at the same time, the excessive growth of IMCs at the interface can be inhibited, and the interfacial microstructure of the joint can be optimized. In the third stage of the cooling control, cryogenic treatment and subsequent rapid heating and tempering process are implemented, which can introduce a large number of dislocations and form a dislocation strengthening mechanism, thereby further improving the mechanical properties and stability of the joint, and endowing it with better bonding strength and durability.

[0023] In some embodiments of the present invention, the aluminum alloy includes a preheated aluminum alloy;

[0024] The preheating method includes: preheating the aluminum alloy with a plasma having a power of 1 to 4 kW for 5 to 20 s,

[0025] The preheating temperature is 200 to 300 °C.

[0026] Under the conditions of the above preheating step: Preheating can significantly reduce the flow stress of high-strength aluminum alloy, improve the plastic deformation ability of the material by promoting dynamic recovery, and thus ensure the full flow of aluminum and the mechanical interlocking at the interface during the friction stir process. Secondly, uniform preheating can balance the heat input at the aluminum / steel interface, control the peak temperature below 450 °C, and cooperate with the diffusion barrier effect of the Ni-Zn-Al2O3 coating to effectively control the growth of brittle intermetallic compounds (IMCs). The preheating treatment optimizes the rheological behavior of the material, inhibits the formation of harmful phases, and reduces thermal stress.

[0027] In some embodiments of the present invention, the plasma flow of the plasma includes at least one of argon, nitrogen, or an argon-hydrogen mixed gas.

[0028] In some embodiments of the present invention, the gas flow rate of the plasma is 5-15 L / min.

[0029] The highly active particles (such as electrons, ions, and excited atoms) generated by local ionization of the gas in the plasma can effectively break the Al2O3 oxide film on the surface of the aluminum alloy, reduce its chemical stability, thereby improving the interfacial wettability (the contact angle can be reduced by 15-25°), and promoting the metallurgical bonding between metals. Secondly, plasma-assisted heating can achieve precise preheating control (200-300 °C), form a gradient temperature field by adjusting the plasma power (1-4 kW) and gas flow rate (5-15 L / min), make the substrate reach the best plastic state before friction stir, and avoid excessive growth of IMCs caused by local overheating (>550 °C). More importantly, the active hydrogen atoms in the argon-hydrogen mixed plasma can penetrate into the metal grain boundaries, inhibit the diffusion of Fe-Al atoms through the "hydrogen shield effect", and control the thickness of the IMCs layer at the submicron level (1-3 μm). Experimental results show that this technology can reduce the generation amount of interfacial IMCs by 40-60%, and improve the tensile strength of the joint by 25-35%. In addition, the surface activation effect induced by the plasma can also promote the metallurgical bonding between the Ni-Zn intermediate layer and the substrate, and improve the dispersion uniformity of the nano-Al2O3 particles, thereby further improving the interfacial bonding strength and fatigue resistance.

[0030] In some embodiments of the present invention, in step S1, the temperature of the additive manufacturing step is controlled at 450-500 °C.

[0031] In some embodiments of the present invention, the method for controlling the temperature of the additive manufacturing step includes: performing real-time temperature monitoring and active cooling during the additive manufacturing process.

[0032] The method for active cooling includes: cooling through a cooling medium, the flow rate of the cooling medium is 2-10 L / min, and the cooling rate is 10-30 °C / s.

[0033] In some embodiments of the present invention, the process parameters of friction stir additive manufacturing include: the rotation speed of the stirring head: 1000 - 2000 rpm, the additive manufacturing speed: 20 - 100 mm / min, the axial downward pressure: 0.1 - 0.5 mm, and the inclination angle of the composite stirring head: 1 - 5°.

[0034] In some embodiments of the present invention, the process parameters of friction stir additive manufacturing include: the rotation speed of the stirring head: 1400 - 1600 rpm, the additive manufacturing speed: 40 - 60 mm / min, the axial downward pressure: 0.1 - 0.3 mm, and the inclination angle of the composite stirring head: 1 - 4°.

[0035] Under the above conditions, the rotation speed of the stirring head (1000 - 2000 rpm) can ensure moderate frictional heat input, enabling the material to reach a fully plastic flow state (the peak temperature is controlled at 450 - 500 °C). An excessively high rotation speed (>2000 rpm) will lead to heat accumulation and excessive growth of IMCs. Under the coordinated regulation of the additive manufacturing speed (20 - 100 mm / min), the plastic deformation time of the material can be extended, improving the diffusion bonding between the coating and the substrate; at the same time, defect formation is avoided: too low a speed (<20 mm / min) is likely to cause excessive heat input and interface embrittlement; too high a speed (>100 mm / min) may result in lack of fusion defects due to insufficient plastic flow. The axial downward pressure can ensure that the stirring pin fully embeds into the lower layer of the material, realizing mechanical interlocking and metallurgical bonding at the aluminum / steel interface, while avoiding substrate deformation or stirring head wear caused by an excessive downward pressure (>0.5 mm). The inclination angle of the stirring head (1 - 5°) can form an axial-radial composite flow field, promoting the backward filling of plastic metal and avoiding hole defects; at the same time, reducing the generation of flash and improving the forming accuracy (surface roughness Ra < 5 μm).

[0036] In some embodiments of the present invention, the thickness of the composite nano-coating is 300 - 500 nm.

[0037] This thickness range can effectively block the direct contact between Fe and Al, inhibit the excessive growth of brittle intermetallic compounds (IMCs), limit the thickness of the harmful phase within 1 - 3 μm, and at the same time ensure that the Ni-Zn coating does not crack or peel off during the friction stir process. At the same time, the nano-coating with a thickness of 300 - 500 nm can act as a thermal expansion coefficient gradient transition layer, alleviating the thermal mismatch between aluminum and steel and reducing the residual stress. This thickness can maintain the structural integrity under the shearing action of friction stir, avoiding local penetration caused by being too thin (<300 nm) or plastic flow hindrance caused by being too thick (>500 nm).

[0038] In some embodiments of the present invention, the heating time is 10 - 60 min.

[0039] According to the second aspect of the present invention, there is provided an application of the plate prepared by the described preparation method in the aerospace, automotive, chemical, and transportation industries. Detailed implementation manners

[0040] The following will clearly and completely describe the concept of the present invention and the technical effects produced in combination with embodiments, so as 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. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative efforts shall fall within the scope of protection of the present invention.

[0041] Example 1

[0042] This example provides an aluminum-steel welding and additive manufacturing method, which comprises the following steps:

[0043] S1. Friction stir additive manufacturing is adopted to perform 7075 aluminum alloy additive manufacturing on the substrate steel plate 316l. The rotation speed of the stirring head is 1500 rpm, the additive manufacturing speed is 20 mm / min, the axial downward pressure is 0.2 mm, and the inclination angle of the stirring head is 3°.

[0044] During the additive manufacturing process of the above friction stir additive manufacturing technology, multi-point thermocouples and an infrared thermometer are used for real-time temperature monitoring, and combined with the active cooling technology, precise temperature control is achieved. When the temperature exceeds 450 °C, the cooling device is started, the coolant is selected, the flow rate is set to 10 L / min, and the cooling rate is controlled at 15 °C / s to quickly remove the heat generated during the additive manufacturing process;

[0045] S2. After the additive manufacturing is completed, a temperature-controlled cooling medium (gas cooling) is used to preliminarily cool the composite plate obtained after additive manufacturing, the flow rate is controlled at 10 L / min, and the cooling rate is maintained at 5 °C / s. Subsequently, rapid cooling is carried out. After the temperature drops to 200 °C, spray cooling is adopted to further accelerate the cooling, and the cooling rate is 20 °C / s. When the temperature drops to room temperature, the aluminum-steel composite material prepared by additive manufacturing is placed in liquid nitrogen for cryogenic treatment, the placement time is 60 min, the cooling temperature is -160 °C, and then it is taken out for rapid heating, the heating temperature is 200 °C, and the heating time is 30 min;

[0046] Among them, the substrate steel plate in step S1 is a steel plate with a surface-coated composite nano-coating. The specific preparation method is as follows: The nano-scale intermediate layer is coated on the steel substrate surface by electroplating. The coating uses a Ni-Zn alloy, and nano-reinforcing particles Al2O3 are added to the coating to improve wear resistance and interfacial bonding performance. The coating thickness is 400 nm, and the coating composition is adjusted as follows: Ni content: 50 wt.%, Zn content: 30 wt.%, and the addition amount of Al2O3 nano-particles: 3 wt.%;

[0047] The 7075 aluminum alloy in step S1 is a preheated aluminum alloy. The specific steps are as follows: Use a plasma generator to preheat the 7075 aluminum alloy. Plasma power: 2 kW. Use argon gas (Ar). Plasma heating time: 15 s. Gas flow rate: 10 L / min. Nozzle diameter: 3 mm. Preheating temperature: 300 °C.

[0048] Example 2

[0049] This example provides an aluminum-steel welding and additive manufacturing method, which includes the following steps:

[0050] S1. Perform 7075 aluminum alloy additive manufacturing on the substrate steel plate 316l. The rotation speed of the stirring head is 1500 rpm, the additive manufacturing speed is 50 mm / min, the axial downward pressure is 0.2 mm, and the inclination angle of the stirring head is 3°.

[0051] In the additive manufacturing steps of the above friction stir additive manufacturing technology, a multi-point thermocouple and an infrared thermometer are used for real-time temperature monitoring, and combined with an active cooling technology to achieve precise temperature control. When the temperature exceeds 450 °C, the cooling device starts. The coolant is selected as water, the flow rate is set to 10 L / min, and the cooling rate is controlled at 15 °C / s to quickly remove the heat during the additive manufacturing process.

[0052] S2. After the additive manufacturing is completed, use a temperature-controlled cooling medium (water-based coolant) for preliminary cooling. The flow rate is controlled at 10 L / min, and the cooling rate is maintained at 5 °C / s. Subsequently, rapid cooling is carried out. After the temperature drops to 200 °C, spray cooling or low-temperature gas cooling (nitrogen) is used to further accelerate the cooling. Cooling rate: 20 °C / s. When the temperature drops to room temperature, the aluminum-steel composite material prepared by additive manufacturing is placed in liquid nitrogen for cryogenic treatment. Placement time: 60 min. Cooling temperature: -160 °C. Then take it out and perform rapid heating. Heating temperature: 200 °C. Heating time: 30 min. Cooling temperature: -160 °C. Then take it out and perform rapid heating. Heating temperature: 200 °C. Heating time: 30 min.

[0053] Among them, the substrate steel plate in step S1 is a steel plate with a surface-coated composite nano-coating. The specific preparation method is as follows: Use electroplating to coat a nano-level intermediate layer on the steel substrate. The coating uses a Ni-Zn alloy. Nano-enhanced particles Al2O3 are added to the coating to improve wear resistance and interfacial bonding performance. Coating thickness: 400 nm. Coating composition regulation: Ni content: 50 wt.%, Zn content: 30 wt.%, Al2O3 nano-particle addition amount: 3 wt.%.

[0054] The 7075 aluminum alloy in step S1 is a preheated aluminum alloy. The specific steps are as follows: The 7075 aluminum alloy is preheated using a plasma generator. Plasma power: 2 kW, argon gas is used, the plasma heating time is 15 s, gas flow rate: 10 L / min, nozzle diameter: 3 mm, preheating temperature: 300 °C.

[0055] Example 3

[0056] This example provides an aluminum-steel welding and additive manufacturing method, which is as follows:

[0057] S1. Perform 7075 aluminum alloy additive manufacturing on the substrate steel plate 316l. The rotation speed of the stirring head is 1500 rpm, the additive manufacturing speed is 50 mm / min, the axial downward pressure is 0.2 mm, and the inclination angle of the stirring head is 3°.

[0058] In the additive manufacturing step of the above friction stir additive manufacturing technology, a multi-point thermocouple and an infrared thermometer are used for real-time temperature monitoring, and combined with an active cooling technology to achieve precise temperature control. When the temperature exceeds 450 °C, the cooling device starts. The coolant is selected as water or a water-based coolant, the flow rate is set to 10 L / min, and the cooling rate is controlled at 15 °C / s to quickly remove the heat during the additive manufacturing process;

[0059] S2. After the additive manufacturing is completed, use a temperature-controlled cooling medium (water-based coolant) for preliminary cooling. The flow rate is controlled at 10 L / min, and the cooling rate is maintained at 5 °C / s. Then, rapid cooling is carried out. After the temperature drops to 200 °C, spray cooling or low-temperature gas cooling (nitrogen) is used to further accelerate the cooling. Cooling rate: 20 °C / s. When the temperature drops to room temperature, the aluminum-steel composite material prepared by additive manufacturing is placed in liquid nitrogen for cryogenic treatment. Placement time: 60 min, cooling temperature: -160 °C, and then taken out for rapid heating. Heating temperature: 200 °C, heating time: 30 min;

[0060] Among them, the substrate steel plate in step S1 is a steel plate with a surface-coated composite nano-coating. The specific preparation method is as follows: Use electroplating to coat a nano-level intermediate layer on the steel substrate. The coating is a Ni-Zn alloy, and nano-reinforcing particles Al2O3 are added to the coating to improve wear resistance and interface bonding performance. The coating thickness is 400 nm, and the coating composition is regulated: Ni content: 50 wt.%, Zn content: 30 wt.%, Al2O3 nano-particle addition amount: 3 wt.%;

[0061] The 7075 aluminum alloy in step S1 is a preheated aluminum alloy. The specific steps are as follows: Use a plasma generator to preheat the 7075 aluminum alloy. Plasma power: 2 kW. Use a gas mixture of argon and hydrogen (Ar-H2). Plasma heating time: 15 s. Gas flow rate: 10 L / min. Nozzle diameter: 3 mm. Preheating temperature: 300 °C.

[0062] Comparative Example 1

[0063] This comparative example provides an aluminum-steel welding and additive manufacturing method. The difference between this comparative example and the embodiment is that the surface of the base steel plate in S1 is not coated with a composite nano-coating. The steps are as follows:

[0064] S1. Perform 7075 aluminum alloy additive manufacturing on the base steel plate 316l. The rotation speed of the stirring head is 1500 rpm, the additive manufacturing speed is 100 mm / min, the axial downward pressure is 0.2 mm, and the inclination angle of the stirring head is 3°.

[0065] In the additive manufacturing steps of the above friction stir additive manufacturing technology, a multi-point thermocouple and an infrared thermometer are used for real-time temperature monitoring, and combined with an active cooling technology to achieve precise temperature control. When the temperature exceeds 450 °C, the cooling device is started. The coolant is selected as water or a water-based coolant, the flow rate is set to 10 L / min, and the cooling rate is controlled at 15 °C / s to quickly remove the heat during the additive manufacturing process.

[0066] S2. After the additive manufacturing is completed, use a temperature-controlled cooling medium (such as a water-based coolant or gas cooling) for preliminary cooling, with the flow rate controlled at 10 L / min and the cooling rate maintained at 5 °C / s. Subsequently, perform rapid cooling. After the temperature drops to 200 °C, use spray cooling or low-temperature gas cooling (such as nitrogen, argon) to further accelerate the cooling, with a cooling rate of 20 °C / s. When the temperature drops to room temperature, place the aluminum-steel composite material prepared by additive manufacturing in liquid nitrogen cryogenic treatment for 60 min, with a cooling temperature of -160 °C, and then take it out for rapid heating, with a heating temperature of 200 °C and a heating time of 30 min.

[0067] The 7075 aluminum alloy in step S1 is a preheated aluminum alloy. The specific steps are as follows: Use a plasma generator to preheat the 7075 aluminum alloy. Plasma power: 2 kW. Use argon gas (Ar). Plasma heating time: 15 s. Gas flow rate: 10 L / min. Nozzle diameter: 3 mm. Preheating temperature: 300 °C.

[0068] Comparative Example 2

[0069] This comparative example provides an aluminum-steel welding and additive manufacturing method. The steps of this comparative example are as follows:

[0070] S1. Conduct 7075 aluminum alloy additive manufacturing on the surface of the base material steel plate 316l. The rotation speed of the stirring head is 1500 rpm, the additive manufacturing speed is 100 mm / min, the downward pressure between axes is 0.2 mm, and the inclination angle of the stirring head is 3°;

[0071] S2. After the additive manufacturing is completed, use a temperature-controlled cooling medium (gas cooling) for preliminary cooling. The flow rate is controlled at 10 L / min, and the cooling rate is maintained at 5 °C / s. Subsequently, perform rapid cooling. After the temperature drops to 200 °C, use spray cooling to further accelerate the cooling. The cooling rate is 20 °C / s. When the temperature drops to room temperature, place the aluminum-steel composite material prepared by additive manufacturing in liquid nitrogen for cryogenic treatment. The placement time is 60 min, the cooling temperature is -160 °C, and then take it out for rapid heating. The heating temperature is 200 °C, and the heating time is 30 min.

[0072] Comparative Example 3

[0073] This comparative example provides a method for aluminum-steel welding and additive manufacturing, and the steps are as follows:

[0074] 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%. After compounding, the material is subjected to solution treatment. The solution temperature is 470 °C, the holding time is 2 h. After taking it out, perform water quenching and then perform aging heat treatment at 120 °C / 24 h.

[0075] Comparative Example 4

[0076] This comparative example provides a method for aluminum-steel welding and additive manufacturing. The difference between this comparative example and Example 1 is that the base material steel plate is coated with a composite nano-coating of Ni-Cu alloy and Al2O3, and the other conditions are the same.

[0077] Comparative Example 5

[0078] This comparative example provides a method for aluminum-steel welding and additive manufacturing. The difference between this comparative example and Example 1 is that in step S2, single water cooling is directly used to reduce the temperature to room temperature, and the other conditions are the same.

[0079] Comparative Example 6

[0080] This comparative example provides a method for aluminum-steel welding and additive manufacturing. The difference between this comparative example and Example 1 is that in step S2, the stepwise cooling is adjusted as follows: after the additive manufacturing is completed, when the composite plate obtained after additive manufacturing is cooled to room temperature at a cooling rate of 20 °C / s, place the aluminum-steel composite material prepared by additive manufacturing in liquid nitrogen for cryogenic treatment. The placement time is 60 min, the cooling temperature is -160 °C, and then take it out for rapid heating. The heating temperature is 200 °C, and the heating time is 30 min; the other conditions are the same.

[0081] Test Example

[0082] The components of the examples and comparative examples are shown in Table 1.

[0083] Mechanical property testing standard: GB / T 228 Test method for tensile properties of metallic materials at room temperature;

[0084] Table 1 Performance test results

[0085]

[0086]

[0087] By comparing and analyzing the mechanical property data of the examples and comparative examples in Table 1, it can be seen that in Examples 1-3 of the present invention, the Ni-Zn-Al2O3 composite coating combined with the hierarchical cooling control technology is adopted, and its tensile strength (663-694 MPa), yield strength (596-624 MPa) and shear strength (172-183 MPa) are all significantly higher than those of Comparative Examples 1-3 (tensile strength 504-541 MPa, shear strength 92-102 MPa), and the elongation rate (12-14%). First of all, in the Ni-Zn coating, the Zn element forms an Fe-Zn phase by preferentially reacting with Fe, strictly controlling the thickness of the IMCs and avoiding interface failure caused by brittle phases; secondly, hierarchical cooling (5°C / s → 20°C / s → cryogenic cooling) suppresses the Fe-Al diffusion kinetics through gradient temperature control. At the same time, the cryogenic treatment (-160°C) induces dislocation proliferation to refine the aluminum-based grains to the sub-micron level (0.15-0.3 μm). However, traditional rolling (Comparative Example 3) and uncoated processes (Comparative Examples 1-2) lack these control means, resulting in grain coarsening (13-64 μm) and out-of-control growth of IMCs. Although Comparative Example 4 (Ni-Cu-Al2O3 coating) retains the Al2O3 strengthening phase, Cu has a higher atomic diffusion rate than Zn, is highly soluble in aluminum alloys, and easily diffuses to the aluminum side, and will promote the reaction at the Fe-Al interface, and is instead prone to form a thick brittle IMCs layer, resulting in a decrease in strength and an increase in the thickness of the IMCs (514 mm), proving the irreplaceability of Zn in interface control; the single water cooling in Comparative Example 5 increases the residual stress due to the quenching stress, fails to effectively control the temperature gradient and cooling rate, resulting in greater thermal stress and crack risk at the aluminum-steel interface, grain coarsening, and strength reduction, leading to performance deterioration. Although Comparative Example 6 adopts rapid cooling and rapid heat treatment, due to the lack of hierarchical cooling control, the thermal stress is not effectively controlled, and the intermetallic compounds grow excessively, resulting in a decrease in joint strength, indicating that the lack of precise temperature control leads to performance instability and decline. In summary, the coating design and hierarchical cooling technology of the present invention achieve the synchronous improvement of strength and plasticity through multi-scale synergistic effects (nano-coating blocks diffusion → gradient cooling inhibits IMCs → cryogenic cooling refines the microstructure), and solve the core problems of IMCs brittleness and residual stress in aluminum-steel composite.

[0088] 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 art. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. An aluminum-steel welding and additive manufacturing method, characterized in that: It includes the following steps: S1. Aluminum alloy is added on the base steel plate by friction stir additive manufacturing process to obtain a plate. The base steel plate is a steel plate with a composite nano - coating on its surface. The materials of the composite nano - coating include: Ni - Zn alloy and Al2O3. S2. The plate is subjected to hierarchical cooling regulation. The hierarchical cooling regulation includes the first cooling, the second cooling and the third cooling. The step of the first cooling includes: cooling the plate at a cooling rate of 5 - 10°C / s to 200 - 300°C. The step of the second cooling includes: cooling the plate after the first cooling at a cooling rate of 15 - 30°C / s to 0 - 40°C. The step of the third cooling includes: cooling the plate after the second cooling at - 100 - 196°C for 20 - 120 min. S3. The plate after hierarchical cooling regulation is heated at 150 - 250°C.

2. The aluminum-steel welding and additive manufacturing method according to claim 1, characterized in that: The aluminum alloy includes pre - heated aluminum alloy. The pre - heating method includes: pre - heating the aluminum alloy with a plasma of 1 - 4 kW for 5 - 20 s. The pre - heating temperature is 200 - 300°C.

3. The aluminum-steel welding and additive manufacturing method according to claim 2, characterized in that: The plasma flow of the plasma includes at least one of argon, nitrogen or argon - hydrogen mixed gas.

4. The aluminum-steel welding and additive manufacturing method according to claim 2, wherein: The gas flow of the plasma is 5 - 15 L / min.

5. The aluminum-steel welding and additive manufacturing method according to claim 2, wherein: In step S1, the temperature of the additive manufacturing step is controlled at 450 - 500°C.

6. The aluminum-steel welding and additive manufacturing method according to claim 5, characterized in that: The method for controlling the temperature of the additive manufacturing step includes: real - time temperature monitoring and active cooling during the additive manufacturing process. The method of active cooling includes: cooling through a cooling medium, the flow rate of the cooling medium is 2 - 10 L / min, and the cooling rate is 10 - 30°C / s.

7. The aluminum-steel welding and additive method according to claim 1, characterized in that: The process parameters of the friction stir additive manufacturing include: the rotation speed of the stirring head: 1000 - 2000 rpm, the additive manufacturing speed: 20 - 100 mm / min, the axial downward pressure: 0.1 - 0.5 mm, and the inclination angle of the composite stirring head is 1 - 5°.

8. The aluminum-steel welding and additive manufacturing method according to claim 1, characterized in that: The thickness of the composite nano - coating is 300 - 500 nm.

9. The aluminum-steel welding and additive manufacturing method according to claim 1, wherein: The heating time is 10 - 60 min.

10. Application of a plate prepared by the preparation method according to any one of claims 1 - 9 in aerospace, automotive, chemical and transportation industries.

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