Acoustic-thermal induced dual-interlayer controllable spreading of dissimilar materials welding device and method

Abstract

The application discloses a kind of sound-thermal induced double intermediate layer controllable spreading of dissimilar material welding device and method, belong to dissimilar metal laser welding technical field.The device includes laser heat source unit, ultrasonic auxiliary unit, workpiece to be welded, aluminum side temperature regulation unit and synchronous control unit.Workpiece to be welded is copper-based material / Ni intermediate layer / Ag intermediate layer / aluminum-based material in turn.Red light laser and blue light laser act on the welding area, so that Ni intermediate layer and Ag intermediate layer reach softened, semi-melting, local melting or liquid phase state constrained by interface.Ultrasonic vibration induces Ag intermediate layer to be controlled spreading along aluminum side interface and form Ag enrichment conductive area, while promoting Ni intermediate layer to form barrier structure.Aluminum side temperature regulation unit carries out local temperature regulation to aluminum-based material, according to temperature feedback control cooling rate and temperature gradient, reduce interface residual stress.The method can obtain high-conductivity, high-strength, low-crack copper-aluminum welded joint.

Description

Technical Field

[0001] This invention belongs to the field of dissimilar metal laser welding technology, specifically relating to a copper-aluminum dissimilar metal laser welding device and method. More particularly, it relates to a copper-aluminum laser welding device and method that uses ultrasonic vibration to induce controlled spreading of a double interlayer at the copper-aluminum interface, regulates the growth of intermetallic compounds at the interface through the double interlayer, and reduces welding residual stress through aluminum-side temperature control. This method is applicable to high-conductivity, high-strength connection structures such as battery tabs, busbars, electrical connectors, conductive connectors in energy storage systems, and copper-aluminum composite conductors for new energy vehicle power batteries. Background Technology

[0002] Copper and copper alloys possess excellent electrical and thermal conductivity and corrosion resistance, while aluminum and aluminum alloys feature low density, high specific strength, good electrical and thermal conductivity, and lower cost. Copper-aluminum dissimilar metal connection structures combine the high conductivity of copper with the lightweight advantages of aluminum, and are widely used in new energy vehicle power batteries, energy storage systems, electrode tabs, busbars, electrical connectors, and copper-aluminum composite conductors. As related products develop towards higher current density, higher reliability, and lighter weight, copper-aluminum connectors need to simultaneously possess high conductivity, high strength, and good service stability.

[0003] Laser welding offers advantages such as high energy density, fast welding speed, small heat-affected zone, and ease of automation integration, making it suitable for efficient and precise joining of dissimilar metals like copper and aluminum. However, in lap-welded structures where the copper-based material is on top and the aluminum-based material is on the bottom, the laser initially acts on the copper side. Copper's absorption of conventional lasers is unstable, and its high thermal conductivity easily leads to unstable energy coupling on the copper side, difficulty in forming the molten pool, and fluctuations in weld depth. Simply increasing the laser power to ensure copper melting can result in over-melting, collapse, or burn-through of the lower aluminum layer due to its lower melting point. Therefore, achieving a balance between stable absorption on the copper side and controlled heat input on the aluminum side is a key issue in copper-aluminum laser lap-welding.

[0004] Besides the difficulty in matching heat input, copper-aluminum welded joints also exhibit high crack susceptibility. Under the welding thermal cycle, copper and aluminum readily interdiffusion, forming intermetallic compounds such as CuAl2, CuAl, and Cu9Al4. A moderate amount and thin layer of these intermetallic compounds is beneficial for metallurgical bonding; however, when the intermetallic compound layer is too thick or continuously distributed, a hard and brittle interfacial reaction layer is formed, easily becoming a weak point for crack initiation and propagation. Furthermore, copper and aluminum differ significantly in melting point, thermal conductivity, coefficient of thermal expansion, and solidification shrinkage behavior, easily leading to residual tensile stress at the copper-aluminum interface and in the heat-affected zone after welding. When a continuous brittle reaction layer coexists with residual tensile stress, interfacial cracks are more likely to initiate and propagate along the interface.

[0005] In existing technologies, methods such as blue laser, red laser, red-blue composite laser, and oscillating laser have been proposed to improve the quality of copper-aluminum laser welding. These methods can improve the laser absorption capacity of the copper side, improve the molten pool formation, and reduce some welding defects. However, they mainly focus on controlling laser energy coupling, keyhole stability, and macroscopic stirring of the molten pool, lacking targeted design for the continuous growth of intermetallic compounds at the copper-aluminum interface, controlled spread of the intermediate layer, barrier layer formation, and post-weld residual stress control.

[0006] Setting up an interlayer is an effective way to regulate the copper-aluminum interfacial reaction. The Ni interlayer possesses good thermal stability and diffusion barrier properties, reducing direct interdiffusion between Cu and Al and inhibiting the continuous growth of brittle intermetallic compounds in copper and aluminum. The Ag interlayer exhibits good conductivity, plasticity, and wetting properties, improving interfacial wetting and spreading while reducing interfacial resistance. Combining the Ni and Ag layers to form a double interlayer can create a composite interface between copper and aluminum that combines diffusion barrier, conductive transition, and stress buffering functions. However, the regulating effect of the double interlayer is affected by welding heat input, the degree of interfacial melting, spreading state, and solidification process. Insufficient heat input can easily lead to incomplete fusion at the interface; excessive heat input may result in localized loss of the Ag layer, weakening of the Ni layer's barrier effect, and uncontrolled Cu-Al reaction.

[0007] Ultrasonic-assisted welding can generate acoustic flow, cavitation, and periodic disturbances through high-frequency mechanical vibration, promoting interfacial wetting, elemental distribution, and microstructure refinement. For copper-aluminum laser welding containing a Ni / Ag double interlayer, ultrasonic vibration can induce controlled propagation of the Ag interlayer along the aluminum side interface and fill micro-gaps during the softening, semi-melting, or localized melting stages of the interlayer. Simultaneously, it promotes the formation of continuous or semi-continuous barrier structures in the Ni interlayer, thereby inhibiting the continuous growth of brittle intermetallic compounds in copper and aluminum. However, relying solely on the laser heat source, ultrasonic vibration, and double interlayer control is insufficient to adequately reduce the residual tensile stress caused by uneven cooling and shrinkage on the aluminum side. Therefore, it is necessary to propose a copper-aluminum laser welding device and method capable of simultaneously controlling the brittle interfacial phase and residual stress. Through the synergistic effect of the Ni / Ag double interlayer, ultrasonically controlled propagation, and aluminum-side temperature control, the electrical conductivity, mechanical strength, and service reliability of the copper-aluminum welded joint can be improved. Summary of the Invention

[0008] To address the problems existing in the current copper-aluminum laser welding process, such as insufficient laser absorption on the copper side, easy overmelting on the aluminum side, difficulty in matching interfacial heat input, easy continuous growth of brittle intermetallic compounds in copper and aluminum, concentration of residual tensile stress, and high sensitivity to joint cracks, this invention provides a dissimilar material welding device and method with controllable spreading of acoustic-thermal induced double intermediate layers.

[0009] This invention aims to establish a controllable heat input window at the copper-aluminum interface by utilizing the synergistic effect of red and blue lasers; to regulate the metallurgical reaction at the copper-aluminum interface using a Ni / Ag double interlayer; to induce controlled spreading of the Ag interlayer and promote the formation of the Ni interlayer barrier by combining ultrasonic vibration; and to adjust the heat-affected zone and cooling rate of the aluminum-based material through an aluminum-side temperature control unit. This will suppress the continuous growth of brittle intermetallic compounds in copper and aluminum while reducing residual stress concentration at the interface, thereby achieving high conductivity, high strength, and low crack connection of the copper-aluminum joint.

[0010] To achieve the above objectives, the present invention provides a copper-aluminum laser welding device, comprising a laser heat source unit, an ultrasonic auxiliary unit, a workpiece to be welded, an aluminum side temperature control unit, a workpiece clamping unit, a protective gas unit, a motion execution unit, and a synchronization control unit.

[0011] The laser heat source unit provides controlled heat input to the copper-aluminum welding area, causing a localized melting zone to form at the welding interface among the copper-based material, Ni interlayer, Ag interlayer, and aluminum-based material in the workpiece. This activates the Ni interlayer, maintaining its continuous or semi-continuous distribution, and allows the Ag interlayer to reach a softened, semi-melted, locally melted, or interface-constrained Ag-rich liquid phase state. The laser heat source unit includes a red laser unit and a blue laser unit. The red laser unit outputs red laser light, and the blue laser unit outputs blue laser light. The red laser provides the main heat input required for welding and controls the weld pool morphology, while the blue laser improves the absorption stability of laser energy on the copper-based material surface. The red and blue lasers work together on the same or nearly the same welding area to form a composite heat input field at the copper-aluminum interface suitable for the activation of the Ni and Ag interlayers and for interfacial metallurgical bonding.

[0012] Preferably, the red and blue lasers are applied to the area to be soldered using a coaxial, paraxial, or spatially adjacent combination. The area of ​​effect of the blue laser at least partially covers the area of ​​effect of the red laser, or is adjacent to or overlaps with the area of ​​effect of the red laser, in order to improve the energy coupling stability on the copper side and reduce the melt depth fluctuation caused by copper side reflection and high thermal conductivity.

[0013] The workpiece to be welded comprises a copper-based material, a Ni interlayer, an Ag interlayer, and an aluminum-based material. The copper-based material is located on the upper layer, the aluminum-based material is located on the lower layer, the Ni interlayer is disposed on the side of the copper-based material near the aluminum-based material, and the Ag interlayer is disposed on the side of the aluminum-based material near the copper-based material, so that the workpiece to be welded is sequentially formed into a stacked structure of copper-based material / Ni interlayer / Ag interlayer / aluminum-based material. The Ni interlayer is used to regulate the heat input transfer on the copper side and form a continuous or semi-continuous diffusion barrier structure during the welding process to suppress the direct interdiffusion between Cu and Al; the Ag interlayer is used to improve the wetting and spreading behavior of the aluminum side interface, fill the interfacial micro-gaps, and improve the interfacial conductivity continuity and plastic transition capability.

[0014] Preferably, the Ni interlayer and Ag interlayer are one or more of the following: foil, plating, pre-coated layer, or composite thin layer. The plating includes electroplating, electroless plating, vapor deposition, magnetron sputtering, or physical vapor deposition. The thicknesses of the Ni and Ag interlayers are matched according to the thicknesses of the copper-based and aluminum-based materials and the welding heat input, so that the Ni interlayer maintains its barrier function during welding and that the Ag interlayer can undergo controlled wetting and spreading along the aluminum side interface under ultrasonic vibration.

[0015] The ultrasonic auxiliary unit is used to apply ultrasonic vibration to the copper-aluminum interface to be welded, causing the Ag interlayer to be controlled-wetted and spread along the aluminum side interface and fill the interfacial micro-gaps, while promoting the formation of a continuous or semi-continuous diffusion barrier structure in the Ni interlayer. The ultrasonic auxiliary unit includes an ultrasonic transducer, an amplitude transformer, and an ultrasonic auxiliary platform. The ultrasonic transducer is connected to the ultrasonic auxiliary platform through the amplitude transformer to transmit ultrasonic vibration to the structure to be welded. The ultrasonic vibration can be applied before the start of laser welding to improve the interlayer adhesion between the copper-based material, Ni interlayer, Ag interlayer, and aluminum-based material; it can be applied during laser welding to induce the Ag interlayer, which is in a softened, semi-melted, partially melted, or interface-constrained Ag-rich liquid phase state, to be controlled-wetted and spread along the aluminum side interface, and to promote the formation of a continuous or semi-continuous barrier structure in the Ni interlayer; it can also be applied in the early stage of post-weld cooling to promote the escape of interfacial bubbles, homogenization of solidification structure, and stable formation of composite transition interface.

[0016] The controlled spreading of the Ag interlayer refers to the softening, semi-melting, partial melting, or formation of an interface-constrained Ag-rich liquid phase under the combined heat input field generated by red and blue lasers. Then, under the influence of periodic pressure, acoustic flow disturbance, and interface micro-vibration generated by ultrasonic vibration, the Ag interlayer wets and spreads along the surface of the aluminum-based material and the micro-gap at the copper-aluminum welding interface, rather than randomly flowing into the aluminum molten pool or locally agglomerating. After cooling and solidification, the Ag interlayer forms a continuous or semi-continuous Ag-rich conductive region at the aluminum side interface.

[0017] The controlled spreading of the Ag intermediate layer satisfies the interface temperature constraint relationship:

[0018] T Ag，act ≤T i ≤T Ag，loss

[0019] Among them, T i The equivalent temperature of the copper-aluminum interface, T, is obtained through interface temperature measurement, numerical conversion, or pre-experimental calibration. Ag，act The interfacial activation temperature required for the Ag interlayer to soften, effectively wet and spread, partially melt, or partially melt; T Ag，loss It is the critical interface temperature at which the Ag intermediate layer undergoes excessive melting, localized loss, disordered diffusion, or entrainment into the molten aluminum pool.

[0020] To characterize the degree of spreading of the Ag intermediate layer, the Ag spreading coefficient K is defined. Ag :

[0021]

[0022] Among them, W Ag The average spreading width of the Ag-rich conductive region on the aluminum side interface after welding is denoted as K, and W0 is the initial width of the Ag intermediate layer before welding or the equivalent width of the region affected by the combined action of red and blue lasers. The Ag spreading coefficient K is adjusted by modifying the red laser power, blue laser power, ultrasonic amplitude, ultrasonic frequency, ultrasonic treatment time, welding speed, and aluminum side cooling intensity. Ag satisfy:

[0023] K1≤K Ag ≤K2

[0024] Wherein, K1 is the lower limit of the spreading coefficient to ensure that the Ag intermediate layer is fully wetted, spread and fills the micro gaps at the interface, and K2 is the upper limit of the spreading coefficient to prevent the Ag intermediate layer from being over-spread, locally lost or randomly diffused into the aluminum molten pool.

[0025] Furthermore, the degree of Ag interlayer spreading is controlled by the following parameters, interface temperature, Ag interlayer thickness, and clamping pressure:

[0026] K Ag =f(A u f u , t u T i h Ag P c )

[0027] Among them, A u f is the ultrasonic amplitude. u t is the ultrasonic frequency. u T represents the duration of ultrasound treatment.i h is the equivalent temperature of the copper-aluminum interface. Ag Where is the thickness of the Ag interlayer, P c The clamping pressure for the workpiece.

[0028] After controlled spreading and cooling solidification, a composite transition interface is formed at the copper-aluminum interface. This composite transition interface includes a continuous or semi-continuous Ni-enriched barrier region on the copper side, a continuous or semi-continuous Ag-enriched conductive region and an Ag-Al interface bonding region on the aluminum side, and a thin-layer Cu-Al reaction region formed in locally discontinuous or weak areas of the Ni-enriched barrier region. Preferably, the average spreading width of the Ag-enriched conductive region along the aluminum side interface is greater than the average width of the Ni-enriched barrier region; after some Ag locally melts or forms an interface-constrained Ag-enriched liquid phase, it solidifies and fills the depressions or micro-gaps at the aluminum side interface, thereby improving the continuity of interfacial conductivity and the plastic transition capability.

[0029] The aluminum-side temperature control unit is used to locally regulate the temperature of the aluminum-based material to control the heat-affected zone and cooling rate on the aluminum side, thereby reducing residual stress concentration at the copper-aluminum interface. The aluminum-side temperature control unit includes a cooling medium circulation mechanism, a cooling channel, a cooling medium inlet, a cooling medium outlet, and a temperature detection device. Preferably, the aluminum-side temperature control unit is at least partially integrated into the ultrasonic-assisted platform. The cooling channel is located inside the ultrasonic-assisted platform and communicates with the cooling medium inlet and outlet. The cooling medium circulation mechanism is used to deliver cooling medium into the cooling channel to locally regulate the temperature of the back side of the aluminum-based material or the ultrasonic-assisted platform.

[0030] Preferably, the cooling medium circulation mechanism is one of a liquid nitrogen cooling device, a cryogenic coolant circulation device, or a cooling water circulation device. The cooling medium can be cooling water, cryogenic coolant, cryogenic nitrogen, or a cryogenic medium after liquid nitrogen heat exchange. The cooling channel can be a serpentine channel, an annular channel, a reciprocating channel, or a zoned channel. More preferably, the cooling channel is arranged around the main ultrasonic vibration transmission area, or avoids the main ultrasonic vibration transmission area, so as to achieve temperature control on the aluminum side while avoiding significantly weakening the transmission effect of ultrasonic vibration to the structure to be welded.

[0031] Preferably, the temperature detection device is disposed on the back side of the aluminum base material, the surface of the ultrasonic auxiliary platform, the area adjacent to the cooling channel, the area adjacent to the area to be welded, and / or the cooling area behind the weld, for detecting the temperature of the back side of the aluminum base material, the temperature of the ultrasonic auxiliary platform, the temperature of the area adjacent to the area to be welded, or the temperature of the cooling area after welding. The temperature detection device can be one or more of the following: an infrared thermometer, a thermocouple, an infrared thermal imager, a contact temperature sensor, or an industrial camera-type temperature monitoring device. The detected temperature obtained by the temperature detection device can be directly used as the aluminum-side feedback temperature, or after pre-test calibration and conversion, it can be used as the aluminum-side equivalent temperature.

[0032] The synchronous control unit adjusts the cooling medium flow rate, cooling medium temperature, red laser power, blue laser power, welding speed, and / or ultrasonic vibration parameters based on the temperature signal fed back by the temperature detection device. The detected temperature obtained by the temperature detection device or the equivalent aluminum side temperature calculated through pre-test calibration is denoted as T. A .

[0033] The synchronization control unit establishes the equivalent temperature T on the aluminum side through pre-testing. A Equivalent temperature T at the copper-aluminum interface i The correspondence between them ensures that when the equivalent temperature on the aluminum side is within the preset control window, the equivalent temperature at the copper-aluminum interface is simultaneously within the interface temperature range required for controlled wetting and spreading of the Ag intermediate layer.

[0034] The aluminum-side temperature control window satisfies:

[0035] T A，L ≤T A ≤T A，H

[0036] And ensure that the equivalent temperature of the copper-aluminum interface meets the following requirements:

[0037] T Ag，act ≤T i ≤T Ag，loss

[0038] Among them, T A，L This corresponds to the lower limit of the equivalent lower temperature of the aluminum side where the Ag interlayer begins to effectively wet and spread and the Ni interlayer forms a barrier structure; T A，H The upper limit of the equivalent temperature of the aluminum side is to address the risks of over-melting of aluminum-based materials and over-melting or localized loss of the Ag interlayer.

[0039] Preferably, the lower limit of the equivalent lower temperature T on the aluminum side A，L satisfy:

[0040] T A，L =T A，act +ΔT2

[0041] The upper limit of the equivalent temperature T on the aluminum side A，H satisfy:

[0042] T A，H =T A，loss -ΔT1

[0043] And satisfy:

[0044] T A，L ≤T A，H

[0045] Among them, T A，actT is the equivalent activation temperature on the aluminum side at which the Ag intermediate layer begins to effectively wet and spread, obtained through preliminary experimental calibration. A，loss ΔT1 and ΔT2 are the equivalent critical temperatures on the aluminum side, obtained through pre-test calibration, at which the corresponding aluminum-based material is at risk of overmelting, collapse, or burn-through, or the Ag intermediate layer is at risk of overmelting, local loss, or disordered diffusion; ΔT1 and ΔT2 are the temperature safety margins, respectively.

[0046] when:

[0047] T L >T A，H

[0048] The synchronous control unit performs at least one cooling regulation, including increasing the cooling medium flow rate, decreasing the cooling medium temperature, increasing the cooling medium circulation speed, decreasing the red laser power, decreasing the blue laser power, and increasing the welding speed, in order to reduce the heat input on the aluminum side, suppress over-melting, collapse, or burn-through of the aluminum-based material, and prevent excessive melting or disordered loss of the Ag intermediate layer.

[0049] when:

[0050] T A >T A，L

[0051] The synchronous control unit performs at least one temperature regulation, including reducing the cooling medium flow rate, increasing the cooling medium temperature, reducing the cooling intensity, increasing the red laser power, increasing the blue laser power, and reducing the welding speed, in order to avoid insufficient interface heat input leading to insufficient Ag interlayer spreading, insufficient Ni interlayer interface bonding, or failure of the interface to be welded to fuse.

[0052] when:

[0053] T A，L ≤T A ≤T A，H

[0054] The synchronous control unit maintains the current cooling medium flow rate, cooling medium temperature, red laser power, blue laser power, welding speed, and ultrasonic vibration parameters, or fine-tunes the above parameters according to the temperature change trend of the aluminum side.

[0055] Furthermore, the synchronization control unit also adjusts the temperature change rate R on the aluminum side according to... A To determine whether the cooling process is too fast or too slow, the following steps are taken:

[0056]

[0057] When R A Greater than the preset cooling rate limit R maxWhen the synchronous control unit reduces the cooling medium flow rate, increases the cooling medium temperature, and / or reduces the cooling medium circulation speed, it avoids uneven shrinkage and concentration of residual tensile stress at the copper-aluminum interface caused by excessively rapid cooling of the aluminum-based material. When R A Less than the preset cooling rate lower limit R min And the aluminum side temperature T A Still close to the upper limit of the equivalent temperature T on the aluminum side A，H At the same time, the synchronous control unit increases the cooling medium flow rate, decreases the cooling medium temperature, and / or increases the cooling medium circulation speed to improve the heat dissipation capacity of the aluminum side.

[0058] Furthermore, when the temperature detection device includes multiple detection points, the synchronous control unit determines the uniformity of the temperature field on the aluminum side based on the temperature difference between different detection points. Let the detected temperature near the welding center area be T1, and the detected temperature far from the welding center area or the cooling area behind the weld be T2, then the temperature gradient judgment value G... A satisfy:

[0059]

[0060] Where L is the distance between the two detection points. When G A Greater than the preset temperature gradient upper limit G max During this process, the synchronous control unit adjusts the cooling medium flow rate, cooling medium temperature, red laser power, blue laser power, and / or welding speed in different cooling zones to reduce the temperature gradient on the aluminum side and minimize uneven cooling shrinkage after welding.

[0061] Preferably, the synchronous control unit adjusts the cooling intensity on the aluminum side using segmented threshold control, proportional-integral-derivative control, or a combination of both. Based on the deviation between the aluminum side temperature and the target temperature and its changing trend, the synchronous control unit continuously or in stages adjusts the cooling medium flow rate and cooling medium temperature to maintain the aluminum side temperature within a preset temperature control window and to keep the aluminum side temperature change rate and temperature gradient within a preset range.

[0062] Furthermore, the aluminum-side temperature control unit adopts a zoned temperature control method. The cooling channel includes multiple cooling zones arranged along the welding direction, and each cooling zone is equipped with a cooling medium inlet, a cooling medium outlet, and / or a flow rate adjustment mechanism. The synchronous control unit adjusts the cooling medium flow rate and cooling intensity of each cooling zone according to the temperature feedback signals from different welding positions to compensate for the differences in heat input during the welding start-up stage, the stable welding stage, and the arc termination stage, thereby improving the consistency of the weld temperature field and the cooling process.

[0063] The workpiece clamping unit is used to position, clamp, and support the copper-based material, Ni interlayer, Ag interlayer, and aluminum-based material. The workpiece clamping unit includes a clamping component, a positioning component, and a supporting component. The clamping component applies a stable clamping force to the structure to be welded, ensuring that the copper-based material, Ni interlayer, Ag interlayer, and aluminum-based material remain in close contact during welding, reducing localized incomplete fusion or uneven interface reactions caused by gap fluctuations.

[0064] The shielding gas unit provides a protective atmosphere to the welding area to reduce the oxidation of copper-based materials, aluminum-based materials, and intermediate layer materials during welding. The shielding gas is argon, helium, or an argon-helium mixture. The motion execution unit is used to achieve positioning and relative movement between the laser heat source and the workpiece to be welded. The motion execution unit may include one or more of the following: a welding worktable, a robotic arm, a linear module, or a galvanometer scanning mechanism.

[0065] The synchronous control unit is connected to the laser heat source unit, ultrasonic auxiliary unit, aluminum-side temperature control unit, shielding gas unit, and motion execution unit, respectively, and is used to coordinate and control laser heat input, ultrasonic vibration, aluminum-side temperature control, shielding gas flow rate, and welding motion parameters. The synchronous control unit can coordinately adjust the red laser power, blue laser power, welding speed, ultrasonic vibration frequency, ultrasonic amplitude, cooling medium flow rate, cooling medium temperature, and shielding gas flow rate according to a preset welding program and / or temperature feedback signal, so that a stable spreading-barrier composite transition interface is formed between the two intermediate layers during the welding process.

[0066] This invention also provides a method for laser welding copper and aluminum, comprising the following steps:

[0067] S1, pre-treat the surfaces of copper-based and aluminum-based materials to be welded, remove oil, oxide film and impurities from the surfaces to be welded, so as to improve the cleanliness and bonding stability of the interface to be welded;

[0068] S2, a double intermediate layer is set between the copper-based material and the aluminum-based material, so that the structure to be welded is in the order of copper-based material / Ni intermediate layer / Ag intermediate layer / aluminum-based material, wherein the Ni intermediate layer is closer to the copper-based material and the Ag intermediate layer is closer to the aluminum-based material.

[0069] S3, the structure to be welded is placed on the ultrasonic-assisted platform and positioned and clamped by the workpiece clamping unit, so that the copper-based material, Ni intermediate layer, Ag intermediate layer and aluminum-based material are stably bonded in the area to be welded;

[0070] S4, activate the shielding gas unit to cover the welding area with shielding gas, thereby reducing oxidation in the welding area and stabilizing the weld pool;

[0071] S5, activate the aluminum side temperature control unit to make the cooling medium flow inside the ultrasonic auxiliary platform, perform local temperature control on the back of the aluminum base material or the ultrasonic auxiliary platform, and obtain the aluminum side temperature, ultrasonic auxiliary platform temperature or temperature of the adjacent position of the area to be welded through the temperature detection device.

[0072] S6, activate the laser heat source unit, so that the red laser and blue laser act together on the area to be welded, establish a controlled composite heat input field, so that the copper-based material and the aluminum-based material form a local melting zone near the interface to be welded, so that the Ni intermediate layer is heated and activated and maintains a continuous or semi-continuous distribution, so that the Ag intermediate layer reaches a softened, semi-melted, locally melted or Ag-enriched liquid phase state constrained by the interface;

[0073] S7, ultrasonic vibration is applied during the period when the Ag intermediate layer is in a softened, semi-melted, partially melted, or Ag-rich liquid phase state constrained by the interface, and the Ag spreading coefficient K is adjusted by regulating the ultrasonic amplitude, ultrasonic frequency, ultrasonic action time, red laser power, blue laser power, welding speed, and aluminum side cooling intensity. Ag satisfy:

[0074] K1≤K Ag ≤K2

[0075] The Ag interlayer is controlled to wet and spread along the aluminum side interface and fill the interface depressions or micro gaps, while the Ni interlayer is kept continuously or semi-continuously distributed on the copper side and forms a diffusion barrier structure.

[0076] S8. After welding, controlled cooling is performed to form a continuous or semi-continuous Ni-enriched barrier region on the copper side of the Ni interlayer, and a continuous or semi-continuous Ag-enriched conductive region and Ag-Al interface bonding region on the aluminum side of the Ag interlayer. The Ag solidifies and fills the interface depressions or micro-gaps on the aluminum side by partially melting or forming a liquid phase constrained by the interface. A thin Cu-Al reaction zone is formed in the local discontinuities or weak areas of the Ni-enriched barrier region, thus forming a composite transition interface.

[0077] Preferably, in steps S5 to S8, the synchronization control unit determines the temperature T on the aluminum side. A The rate of temperature change R on the aluminum side A and temperature gradient judgment value G A The cooling intensity and welding parameters are adjusted to keep the aluminum side temperature within the preset temperature window, maintain the cooling rate within the preset cooling rate range, and keep the temperature gradient below the preset upper limit of the temperature gradient.

[0078] Preferably, in step S6, the blue laser acts on the area to be soldered before the red laser, or acts on the area to be soldered synchronously with the red laser, to improve the laser absorption stability on the copper side. The red and blue lasers act on the area to be soldered in a coaxial, paraxial, or spatially adjacent manner, and the combined heat input of the red and blue lasers improves the energy coupling stability on the copper side and adjusts the heat input distribution at the copper-aluminum interface.

[0079] Preferably, in step S7, the direction of ultrasonic vibration is perpendicular to the interface to be welded, parallel to the interface to be welded, or at a certain angle to the interface to be welded. Ultrasonic vibration causes the Ag interlayer, which is in a softened, semi-molten, or partially molten state, to spread along the aluminum side interface, and causes the Ni interlayer to form a continuous or semi-continuous distribution on the copper side, thereby constructing a composite interface that has the functions of conductive transition, diffusion barrier, and stress buffer.

[0080] Preferably, during the controlled cooling process, after the laser stops, the temperature on the aluminum side is maintained and ultrasonic vibration can continue to be applied for a certain period of time to reduce the uneven cooling shrinkage of the aluminum-based material, reduce the concentration of residual tensile stress at the copper-aluminum interface, and improve the stability of the composite transition interface.

[0081] Compared with the prior art, the present invention has the following beneficial effects:

[0082] 1. This invention employs the synergistic effect of red and blue lasers. On the one hand, blue lasers are used to improve the stability of laser absorption on the copper side, while red lasers are used to provide the main heat input required for welding and control the molten pool morphology. This establishes an interface heat input window suitable for the activation of Ni and Ag interlayers, reducing the fluctuation of copper side melt depth and the risk of overmelting on the aluminum side.

[0083] 2. In this invention, a Ni intermediate layer is disposed on the copper side and an Ag intermediate layer is disposed on the aluminum side. The Ni intermediate layer serves as a diffusion barrier and heat input transition layer, while the Ag intermediate layer serves as a wetting and spreading layer, a conductive transition layer, and a plastic buffer layer. This results in the copper-aluminum welding interface having good metallurgical bonding continuity, conductive continuity, and stress buffering capacity.

[0084] 3. In this invention, ultrasonic vibration is applied to the Ag intermediate layer when it is in a softened, semi-melted, partially melted, or interface-constrained liquid phase state, and the Ag spreading coefficient K is controlled. Ag This allows Ag to spread in a controlled manner along the aluminum side interface. After cooling and solidification, a continuous or semi-continuous Ni-enriched barrier region is formed on the copper side, while a wider Ag-enriched conductive region and Ag-Al interface bonding region are formed on the aluminum side. Some Ag solidifies and fills the micro-gaps at the interface, thereby reducing incomplete fusion, uneven distribution of the intermediate layer, and excessive local reaction, and inhibiting the continuous growth of Cu-Al brittle intermetallic compounds.

[0085] 4. The present invention forms a closed-loop temperature feedback control system by means of an aluminum side temperature control unit, a temperature detection device and a synchronous control unit. The system adjusts the cooling medium flow rate, cooling medium temperature, laser power, welding speed and / or ultrasonic vibration parameters according to the aluminum side temperature, temperature change rate and temperature gradient, so that the aluminum side temperature is kept within the preset temperature window, reducing the risk of aluminum side overmelting, collapse, burn-through and uneven cooling shrinkage after welding.

[0086] This invention achieves a synchronized control of laser heat input, ultrasonic vibration, aluminum side temperature, shielding gas, and welding motion parameters, thereby matching the controlled Ag spreading, Ni barrier forming, and aluminum side cooling processes to form a composite transition interface comprising a Ni-enriched barrier region, an Ag-enriched conductive region, an Ag-Al interface bonding region, and a thin Cu-Al reaction region. This improves the conductivity, strength, and crack resistance of the copper-aluminum joint. Attached Figure Description

[0087] Figure 1 This is a schematic diagram of the overall structure of a dissimilar material welding device with controllable spreading of acoustic-thermal induced double intermediate layers according to the present invention.

[0088] Figure 2 This is a schematic diagram of the clamping and vibration transmission structure of the workpiece to be welded on the ultrasonic-assisted platform according to the present invention.

[0089] Figure 3 This is a schematic diagram of the cooling channel structure of the aluminum-side temperature control unit in the ultrasonic-assisted platform of the present invention.

[0090] Figure 4 A schematic diagram illustrating the controlled spreading process of the Ag intermediate layer and the morphology of the post-weld composite transition interface. Figure 4 (a) is a schematic diagram of the initial state of the double intermediate layer before welding;

[0091] Figure 4 (b) is a schematic diagram of the ultrasound-induced controlled spreading process of the Ag intermediate layer;

[0092] Figure 4 (c) shows the morphology of the Ni-enriched barrier region, Ag-enriched conductive region, and composite transition interface after welding.

[0093] Figure 5 This is a process flow diagram of the copper-aluminum laser welding method of the present invention.

[0094] Figure Labels

[0095] 1-Laser heat source unit; 11-Red laser; 12-Red laser transmission assembly; 13-Red laser head; 14-Blue laser; 15-Blue laser transmission assembly; 16-Blue laser head;

[0096] 2-Ultrasonic Auxiliary Unit: 21-Ultrasonic Generator; 22-Ultrasonic Transducer; 23-Amplitude Transducer; 24-Ultrasonic Auxiliary Platform;

[0097] 3-Workpiece to be welded: 31-Copper-based material; 32-Ni intermediate layer; 33-Ag intermediate layer; 34-Aluminum-based material;

[0098] 4-Aluminum side temperature control unit: 41-External cooling medium circulation mechanism; 42-Cooling flow channel; 43-Cooling medium inlet; 44-Cooling medium outlet; 45-Temperature detection device;

[0099] 5-Workpiece clamping unit;

[0100] 6-Protection gas unit: 61-Protection gas source; 62-Gas regulating device; 63-Gas pipeline; 64-Air nozzle;

[0101] 7-Motion Execution Units: 71-X-axis motion mechanism; 72-Y-axis motion mechanism; 73-Z-axis motion mechanism;

[0102] 8-Synchronization control unit. Detailed Implementation

[0103] The present invention will be further described below with reference to the accompanying drawings and specific structures. It should be understood that the following content is only used to explain the technical solution of the present invention and is not intended to limit the scope of protection of the present invention. Without departing from the technical concept of the present invention, those skilled in the art can make appropriate adjustments, substitutions, or combinations to the specific structures, materials, parameters, and process steps.

[0104] like Figure 1 As shown, this invention provides a schematic diagram of the overall structure of a dissimilar material welding device with controllable spreading of a double intermediate layer induced by acoustic and thermal processes. The device includes a laser heat source unit 1, an ultrasonic auxiliary unit 2, a workpiece to be welded 3, an aluminum-side temperature control unit 4, a workpiece clamping unit 5, a protective gas unit 6, a motion execution unit 7, and a synchronization control unit 8.

[0105] The laser heat source unit 1 is used to provide controlled heat input to the copper-aluminum welding area of ​​the workpiece 3 to be welded, so that the copper-based material 31, Ni intermediate layer 32, Ag intermediate layer 33 and aluminum-based material 34 form a local melting zone at the welding interface, and the Ni intermediate layer 32 is activated by heat and undergoes local diffusion or local dissolution, while maintaining a continuous or semi-continuous distribution; and the Ag intermediate layer 33 reaches a softened, semi-melted, locally melted or Ag-enriched liquid phase state constrained by the interface.

[0106] The laser heat source unit 1 includes a red laser 11, a red laser transmission component 12, a red laser head 13, a blue laser 14, a blue laser transmission component 15, and a blue laser head 16. The red laser head 13 outputs red laser light, which provides the main heat input required for welding and regulates the weld pool morphology and interface heat input distribution. The blue laser head 16 outputs blue laser light, which enhances the absorption capacity of the copper-based material 31 for laser energy, improving the energy coupling stability during the initial and stable welding stages on the copper side.

[0107] The red and blue lasers are applied to the same or nearly the same welding area on the surface of the copper-based material 31 using coaxial, off-axis, or spatially adjacent methods to form a combined red and blue laser heat input field. By adjusting the red laser power, blue laser power, their power ratio, the relative position of the laser spots, the degree of laser spot overlap, and the welding speed, the heat input distribution of the copper-aluminum welding area can be controlled, ensuring that the Ni interlayer 32 and Ag interlayer 33 are in a thermal state suitable for spreading, barrier forming, and interface bonding.

[0108] like Figure 4 (a) shows a schematic diagram of the cooling channel structure of the aluminum-side temperature control unit in the ultrasonic-assisted platform of the present invention. The workpiece 3 to be welded includes a copper-based material 31, a Ni intermediate layer 32, an Ag intermediate layer 33, and an aluminum-based material 34. The copper-based material 31 is located on the upper layer, and the aluminum-based material 34 is located on the lower layer. The Ni intermediate layer 32 is disposed on the side of the copper-based material 31 close to the aluminum-based material 34, and the Ag intermediate layer 33 is disposed on the side of the aluminum-based material 34 close to the copper-based material 31. Before welding, the stacking order of the workpiece 3 to be welded is: copper-based material 31 / Ni intermediate layer 32 / Ag intermediate layer 33 / aluminum-based material 34.

[0109] The copper-based material 31 can be pure copper, copper, or a copper alloy, and the aluminum-based material 34 can be pure aluminum or an aluminum alloy. In one specific embodiment, the copper-based material 31 is a T2 copper plate, and the aluminum-based material 34 is a 1060 aluminum plate. Before welding, the surfaces of the copper-based material 31 and the aluminum-based material 34 to be welded are pretreated. The pretreatment includes mechanical grinding, chemical cleaning, ultrasonic cleaning, plasma cleaning, laser cleaning, or a combination thereof, to remove oil, oxide film, moisture, and surface impurities, thereby improving the cleanliness and bonding stability of the interface to be welded.

[0110] The Ni intermediate layer 32 can be formed by magnetron sputtering, electroplating, electroless plating, vapor deposition, physical vapor deposition, metal foil pre-placement, composite film attachment, or metal paste coating. The Ag intermediate layer 33 can be formed by magnetron sputtering, electroplating, vapor deposition, physical vapor deposition, metal foil pre-placement, composite film attachment, or metal paste coating.

[0111] In one specific fabrication method, a Ni intermediate layer 32 is first deposited on the surface of the copper-based material 31 to be soldered, and then an Ag intermediate layer 33 is deposited on the surface of the Ni intermediate layer 32. During assembly, the Ag intermediate layer 33 is brought into contact with the aluminum-based material 34, thereby forming a stacked structure of copper-based material 31 / Ni intermediate layer 32 / Ag intermediate layer 33 / aluminum-based material 34. In another specific fabrication method, a Ni intermediate layer 32 can also be fabricated on the surface of the copper-based material 31 to be soldered, and an Ag intermediate layer 33 can be fabricated on the surface of the aluminum-based material 34 to be soldered. Then, the Ni intermediate layer 32 and the Ag intermediate layer 33 are bonded together to form a stacked structure of copper-based material 31 / Ni intermediate layer 32 / Ag intermediate layer 33 / aluminum-based material 34.

[0112] Preferably, the thickness of the Ni interlayer 32 is 50 nm to 5 μm, more preferably 0.1 μm to 2 μm. If the Ni interlayer 32 is too thin, it is difficult to form a stable heat input buffer and diffusion barrier; if the Ni interlayer 32 is too thick, it may increase the interface resistance and reduce the conductivity of the joint. The thickness of the Ag interlayer 33 is 100 nm to 10 μm, more preferably 0.3 μm to 5 μm. If the Ag interlayer 33 is too thin, the wetting, spreading, micro-gap filling, and conductive transition effects are insufficient; if the Ag interlayer 33 is too thick, it may undergo local enrichment or loss under laser heat input and ultrasonic vibration, affecting the uniformity of the interface structure. The total thickness of the double interlayer is 0.15 μm to 15 μm, more preferably 0.5 μm to 7 μm.

[0113] like Figure 2 The diagram illustrates the clamping and vibration transmission structure of the workpiece to be welded on the ultrasonic auxiliary platform according to the present invention. The ultrasonic auxiliary unit 2 includes an ultrasonic generator 21, an ultrasonic transducer 22, an amplitude transformer 23, and an ultrasonic auxiliary platform 24. The ultrasonic generator 21 is connected to the ultrasonic transducer 22 via a cable. The ultrasonic transducer 22 is connected to the amplitude transformer 23, and the amplitude transformer 23 is connected to the ultrasonic auxiliary platform 24. The ultrasonic auxiliary platform 24 is located below the aluminum-based material 34, supporting the workpiece 3 to be welded and transmitting ultrasonic vibrations to the aluminum-based material 34 and the copper-aluminum welding interface.

[0114] The ultrasonic vibration can be applied in different sequences depending on the welding stage. Before laser welding begins, ultrasonic vibration can be applied in advance to improve the interlayer adhesion between the copper-based material 31, Ni interlayer 32, Ag interlayer 33, and aluminum-based material 34. During laser welding, ultrasonic vibration is applied when the Ag interlayer 33 reaches a softened, semi-melted, partially melted, or Ag-rich liquid phase state constrained by the interface. The periodic pressure, acoustic flow disturbance, and interfacial micro-vibration generated by the ultrasonic vibration promote controlled wetting and spreading of the Ag interlayer 33 along the surface of the aluminum-based material 34 and the micro-gap at the copper-aluminum welding interface. At the same time, it promotes the formation of a continuous or semi-continuous diffusion barrier structure of the Ni interlayer 32 on the copper side. In the initial cooling stage after laser welding stops, ultrasonic vibration can continue to be applied for a preset time to promote bubble escape, homogenization of solidification structure, and stable formation of composite transition interface.

[0115] like Figure 4 (b) shows a schematic diagram of the ultrasound-induced controlled spreading process of the Ag intermediate layer. g The controlled wetting and spreading of the intermediate layer 33 refers to the softening, semi-melting, partial melting, or formation of an interface-constrained Ag-rich liquid phase by the Ag intermediate layer 33 under the combined heat input of red and blue lasers, and its controlled spreading and filling of interfacial micro-gaps along the aluminum side interface under ultrasonic vibration. After cooling and solidification, a continuous or semi-continuous Ni-rich barrier region is formed on the copper side, and a Ag-rich conductive region with a large spreading width and an Ag-Al interface bonding region are formed on the aluminum side; some Ag solidifies and fills local depressions or micro-gaps, and a thin Cu-Al reaction zone is formed at the local discontinuities in the Ni barrier region.

[0116] To prevent the Ag intermediate layer 33 from insufficiently spreading due to excessively low temperature, or from over-melting, localized loss, or entrapment into the molten aluminum pool due to excessively high temperature, the controlled spreading of the Ag intermediate layer 33 satisfies the following interface temperature constraint relationship:

[0117] T Ag，act ≤T i ≤T Ag,loss

[0118] Among them, T i T is the equivalent temperature of the copper-aluminum interface. Ag,act T is the activation temperature at which the Ag intermediate layer 33 softens, wets, spreads, partially melts, or partially melts. Ag,loss This is the critical temperature at which the Ag intermediate layer 33 over-melts, locally leaks out, or diffuses disorderly into the aluminum molten pool.

[0119] To characterize the spreading degree of the Ag intermediate layer 33, the Ag spreading coefficient K is defined. Ag :

[0120]

[0121] Among them, W Ag W0 represents the average spreading width of the Ag-enriched conductive region at the aluminum side interface after welding, and W0 represents the initial width of the Ag intermediate layer 33 before welding or the equivalent width of the region affected by the combined action of red and blue lasers. The Ag spreading coefficient K is adjusted by modifying the red laser power, blue laser power, ultrasonic amplitude, ultrasonic frequency, ultrasonic treatment time, welding speed, and aluminum side cooling intensity. Ag satisfy:

[0122] K1≤K Ag ≤K2

[0123] Wherein, K1 is the lower limit of the spreading coefficient to ensure that the Ag intermediate layer 33 is fully wetted, spread and fills the micro gaps at the interface, and K2 is the upper limit of the spreading coefficient to prevent the Ag intermediate layer 33 from being over-spread, locally lost or randomly diffused into the aluminum molten pool.

[0124] Furthermore, the degree of spreading of the Ag interlayer 33 is subject to the following control relationship with the ultrasonic parameters, interface temperature, Ag interlayer thickness, and clamping pressure:

[0125] K Ag =f(A u f u , t u T i h Ag P c )

[0126] Among them, A u f is the ultrasonic amplitude. u t is the ultrasonic frequency. u T represents the duration of ultrasound treatment. i h is the equivalent temperature of the copper-aluminum interface. Ag Where is the thickness of Ag intermediate layer 33, P c The clamping pressure of the workpiece is adjusted. Thus, by controlling the laser heat input, ultrasonic vibration parameters, aluminum-side cooling intensity, and clamping pressure, the Ag intermediate layer 33 can form a controlled Ag-rich conductive region, while avoiding insufficient Ag layer spreading or excessive loss.

[0127] The aluminum-side temperature control unit 4 is used to locally control the temperature of the back side of the aluminum-based material 34 or the ultrasonic-assisted platform 24, so as to limit the over-melting of the aluminum side and the expansion of the heat-affected zone, adjust the joint cooling rate and temperature gradient, and reduce the concentration of residual tensile stress at the copper-aluminum interface. The aluminum-side temperature control unit 4 includes an external cooling medium circulation mechanism 41, a cooling channel 42, a cooling medium inlet 43, a cooling medium outlet 44, and a temperature detection device 45.

[0128] The external cooling medium circulation mechanism 41 is preferably a liquid nitrogen cooling device, a cryogenic coolant circulation device, or a cooling water circulation device, used for cooling, storing, and transporting the circulating cooling medium. The cooled medium enters the cooling channel 42 through the cooling medium inlet 43, performs localized heat exchange on the back of the aluminum-based material 34 or the ultrasonic-assisted platform 24, and then flows out through the cooling medium outlet 44 and back to the external cooling medium circulation mechanism 41. The cooling medium can be cooling water, cryogenic coolant, cryogenic nitrogen, or a cryogenic medium after liquid nitrogen heat exchange.

[0129] like Figure 3 The diagram shows the cooling channel structure of the aluminum-side temperature control unit within the ultrasonic-assisted platform of the present invention. The cooling channel 42 is disposed inside the ultrasonic-assisted platform 24, preferably near the back side of the aluminum-based material 34, to improve the control efficiency of the aluminum-side heat-affected zone. The cooling channel 42 can be a serpentine channel, an annular channel, a reciprocating channel, a parallel partitioned channel, or a multi-stage gradient channel. Preferably, the cooling channel 42 is arranged around the main ultrasonic vibration transmission area, or avoids the main ultrasonic vibration transmission area, so as to achieve aluminum-side temperature control while avoiding significantly weakening the transmission effect of ultrasonic vibration to the workpiece 3 to be welded.

[0130] In a preferred configuration, the ultrasonic-assisted platform 24 has a serpentine cooling channel inside, which reciprocates along the platform's interior and avoids the main ultrasonic vibration transmission area. The platform's sidewalls or ends have cooling medium inlets 43 and outlets 44. The cooling medium enters the serpentine cooling channel through the inlet 43, flows through the platform's interior, and exits through the outlet 44. This structure enables aluminum-side temperature control without obstructing the main ultrasonic vibration transmission path, allowing the ultrasonic-assisted unit 2 and the aluminum-side temperature control unit 4 to form an integrated, collaborative structure.

[0131] The temperature detection device 45 is disposed on the back of the aluminum base material 34, the surface of the ultrasonic auxiliary platform 24, the area adjacent to the cooling channel 42, the area adjacent to the welding area, or the cooling area behind the weld. It is used to detect the temperature of the aluminum side, the temperature of the ultrasonic auxiliary platform, the temperature near the welding area, or the temperature of the post-weld cooling zone. The temperature detection device 45 can be one or more of an infrared thermometer, thermocouple, infrared thermal imager, temperature sensor, or industrial camera-type temperature monitoring device. The detected temperature obtained by the temperature detection device 45 is used to characterize the temperature state of the aluminum side, and the equivalent temperature TA of the aluminum side can be obtained through pre-test calibration or numerical conversion. The equivalent temperature TA of the aluminum side and the equivalent temperature T of the copper-aluminum interface are related. i For different temperature parameters, TA is used for the actual feedback control of the synchronous control unit 8, and T... i Used to characterize the controlled wetting and spreading state of Ag intermediate layer 33 at the copper-aluminum interface.

[0132] The synchronous control unit 8 is connected to the temperature detection device 45 and performs closed-loop adjustment of the aluminum-side temperature control unit 4, the laser heat source unit 1, the ultrasonic auxiliary unit 2, and the motion execution unit 7 based on the temperature signal fed back by the temperature detection device 45. The temperature detection device 45 detects the temperature of the back side of the aluminum base material 34, the surface of the ultrasonic auxiliary platform 24, the area adjacent to the area to be welded, or the cooling area behind the weld in real time or intermittently, and records the detected temperature or the equivalent temperature of the aluminum side obtained by pre-test calibration as T. A .

[0133] The synchronous control unit 8 establishes the equivalent temperature TA on the aluminum side and the equivalent temperature T at the copper-aluminum interface through pre-testing. i The correspondence between them makes the equivalent temperature T on the aluminum side... A When in the preset control window, the copper-aluminum interface equivalent temperature Ti simultaneously meets the interface temperature conditions required for the controlled wetting and spreading of the Ag intermediate layer 33.

[0134] The aluminum-side temperature control window satisfies:

[0135] T A，L ≤T A ≤T A，H

[0136] The equivalent temperature of the copper-aluminum interface satisfies:

[0137] T Ag,act ≤T i ≤T Ag,loss

[0138] Among them, T A，L This corresponds to the lower limit of the equivalent lower temperature of the aluminum side where the Ag intermediate layer 33 begins to effectively wet and spread and the Ni intermediate layer 32 forms a barrier structure; T A,H The upper limit of the equivalent temperature of the aluminum side is to address the risk of over-melting of the aluminum-based material 34 and the risk of excessive melting or local loss of the Ag intermediate layer 33.

[0139] Preferably:

[0140] T A，L =T A，act +ΔT2

[0141] T A，H =T A，loss -ΔT1

[0142] And satisfy:

[0143] T A，L <T A，H

[0144] Among them, T A，actT is the equivalent activation temperature on the aluminum side, obtained through preliminary testing and calibration, corresponding to the effective wetting and spreading of the Ag intermediate layer 33. A,loss ΔT1 and ΔT2 are the equivalent critical temperatures on the aluminum side, obtained through pre-test calibration, at which the aluminum-based material 34 is at risk of over-melting, collapse, or burn-through, or the Ag intermediate layer 33 is at risk of over-melting, local loss, or disordered diffusion; ΔT1 and ΔT2 are temperature safety margins.

[0145] When T A >T A，H At the same time, the synchronous control unit 8 performs at least one cooling regulation, including increasing the cooling medium flow rate, decreasing the cooling medium temperature, increasing the cooling medium circulation speed, decreasing the red laser power, decreasing the blue laser power, and increasing the welding speed.

[0146] When T A <T A,L At the same time, the synchronous control unit 8 performs at least one temperature increase regulation, including reducing the cooling medium flow rate, increasing the cooling medium temperature, reducing the cooling intensity, increasing the red laser power, increasing the blue laser power, and reducing the welding speed.

[0147] When T A，L ≤T A ≤T A，H At the same time, the synchronous control unit 8 maintains the current cooling medium flow rate, cooling medium temperature, red laser power, blue laser power, welding speed and ultrasonic vibration parameters, or fine-tunes the above parameters according to the temperature change trend of the aluminum side.

[0148] Furthermore, the synchronous control unit 8 also determines whether the cooling process is too fast or too slow based on the rate of temperature change on the aluminum side. The rate of temperature change on the aluminum side is denoted as R. A It satisfies:

[0149]

[0150] When R A Greater than the preset cooling rate limit R max When the synchronous control unit 8 reduces the cooling medium flow rate, increases the cooling medium temperature, or reduces the cooling intensity, it avoids the rapid contraction of the aluminum-based material 34 leading to residual tensile stress concentration at the copper-aluminum interface; when R A Less than the preset lower limit of cooling rate R min When the aluminum side temperature is still close to the upper temperature limit TH, the synchronous control unit 8 increases the cooling medium flow rate or decreases the cooling medium temperature to improve the heat dissipation capacity of the aluminum side.

[0151] Furthermore, when the temperature detection device 45 includes multiple detection points, the synchronous control unit 8 also determines the uniformity of the temperature field on the aluminum side based on the temperature difference between different detection points. Let the detection temperature near the welding center area be T1, and the detection temperature far from the welding center area or the cooling area behind the weld be T2, then the temperature gradient judgment value G... A satisfy:

[0152]

[0153] Where L is the distance between the two detection points. When G A Greater than the preset temperature gradient upper limit G max At the same time, the synchronous control unit 8 adjusts the zone cooling flow rate, cooling medium temperature, welding speed or laser power to reduce the temperature gradient on the aluminum side and reduce uneven cooling shrinkage after welding.

[0154] Preferably, the synchronous control unit 8 adjusts the cooling intensity using proportional-integral-derivative (PID) control, piecewise threshold control, or a combination of both. Taking PID control as an example, let the target temperature be T0, and the temperature deviation be:

[0155] e(t) = T A (t)-T0

[0156] Then the cooling medium flow rate Q c(t) It can be adjusted as follows:

[0157]

[0158] Among them, Q c0 K represents the initial cooling medium flow rate. p K i K d These are the proportional coefficient, integral coefficient, and differential coefficient, respectively. When e(t) > 0, it indicates that the aluminum side temperature is higher than the target temperature, and the synchronous control unit 8 increases the cooling medium flow rate or decreases the cooling medium temperature; when e(t) < 0, it indicates that the aluminum side temperature is lower than the target temperature, and the synchronous control unit 8 decreases the cooling medium flow rate or increases the cooling medium temperature.

[0159] Furthermore, the aluminum-side temperature control unit 4 can adopt a zoned temperature control method. The cooling channel 42 includes a first cooling zone near the welding start end, a second cooling zone near the stable welding section, and a third cooling zone near the arc termination end. Each cooling zone can be equipped with an independent cooling medium inlet, cooling medium outlet, or flow regulating valve. The synchronous control unit 8 adjusts the cooling medium flow rate and cooling intensity of each cooling zone according to the temperature feedback signals from different welding positions to compensate for the heat input differences during the welding start, stable welding, and arc termination stages, thereby improving the temperature field consistency of the entire weld and the joint formation stability.

[0160] The workpiece clamping unit 5 is used to maintain the copper-based material 31, Ni intermediate layer 32, Ag intermediate layer 33, and aluminum-based material 34 in stable stacking and close contact. The workpiece clamping unit 5 is positioned on both sides of the welding area, avoiding the laser action path, shielding gas blowing path, and ultrasonic vibration transmission path, thereby reducing the interference of the clamping structure on the welding process and ultrasonic vibration transmission. By positioning and clamping the workpiece 3 to be welded through the workpiece clamping unit 5, the interlayer gap fluctuation can be reduced, lowering the risk of local incomplete fusion, uneven spreading, and uneven interface reaction.

[0161] The protective gas unit 6 includes a protective gas source 61, a gas regulating device 62, a gas supply pipeline 63, and a nozzle 64. The protective gas source 61 can be an argon cylinder, a helium cylinder, or an argon-helium mixed gas source. The nozzle 64 is connected to the protective gas source 61 through the gas supply pipeline 63 and is positioned towards the surface of the copper-based material 31 or the weld pool area. During welding, the protective gas is ejected through the nozzle 64, forming a local protective atmosphere in the welding area to reduce the oxidation degree of the copper-based material 31, aluminum-based material 34, Ni intermediate layer 32, and Ag intermediate layer 33 at high temperatures.

[0162] The motion execution unit 7 includes an X-axis motion mechanism 71, a Y-axis motion mechanism 72, and a Z-axis motion mechanism 73. The X-axis and Y-axis motion mechanisms 71 and 72 are used to achieve horizontal relative movement between the laser head and the workpiece 3 to be welded, while the Z-axis motion mechanism 73 is used to adjust the working distance between the laser head and the surface of the copper-based material 31. The red laser head 13 and blue laser head 16 are mounted on the motion execution unit 7 and can move along a preset welding path with the motion execution unit 7. The relative position, incident angle, and beam overlap of the red laser head 13 and blue laser head 16 are adjustable to adapt to copper-aluminum workpieces 3 with different thicknesses and material combinations.

[0163] The synchronous control unit 8 is connected to the laser heat source unit 1, the ultrasonic auxiliary unit 2, the aluminum side temperature control unit 4, the protective gas unit 6, and the motion execution unit 7, respectively. The synchronous control unit 8 is used to control the red laser power, blue laser power, laser action sequence, ultrasonic frequency, ultrasonic amplitude, cooling medium temperature, cooling medium flow rate, protective gas flow rate, welding speed, and motion path. Based on the temperature signal fed back by the temperature detection device 45, it coordinates the above parameters to keep the aluminum side temperature, cooling rate, and temperature gradient within a preset range, thereby reducing the risk of over-melting, collapse, burn-through, and uneven cooling shrinkage of the aluminum base material 34 after welding.

[0164] Figure 5The diagram illustrates the process flow of the copper-aluminum laser welding method of the present invention. When performing copper-aluminum laser welding using the aforementioned apparatus, the surfaces of the copper-based material 31 and the aluminum-based material 34 to be welded are first pretreated to remove oil, oxide film, moisture, and surface impurities. Subsequently, a Ni intermediate layer 32 and an Ag intermediate layer 33 are placed between the copper-based material 31 and the aluminum-based material 34, and the workpieces 3 to be welded are stacked sequentially in the order of copper-based material 31 / Ni intermediate layer 32 / Ag intermediate layer 33 / aluminum-based material 34. The workpieces 3 to be welded are placed on the ultrasonic-assisted platform 24, with the side of the aluminum-based material 34 facing away from the Ag intermediate layer 33 in contact with the ultrasonic-assisted platform 24. The workpiece clamping unit 5 positions and clamps the workpieces 3 to be welded, ensuring close contact between the material layers.

[0165] Before welding, the shielding gas unit 6 is activated, allowing the shielding gas to be blown through the nozzle 64 onto the surface of the copper-based material 31 or the weld pool area, forming a localized protective atmosphere in the area to be welded. Before or during welding, the aluminum-side temperature control unit 4 is activated, allowing the cooling medium to enter the cooling channel 42 inside the ultrasonic-assisted platform 24 through the cooling medium inlet 43 and exit through the cooling medium outlet 44. The cooling medium circulates within the cooling channel 42, providing localized temperature control for the back side of the aluminum-based material 34 or the ultrasonic-assisted platform 24. Preferably, the cooling medium is cooled by liquid nitrogen cooling before entering the cooling channel 42.

[0166] Before welding begins, the synchronous control unit 8 can first activate the aluminum-side temperature control unit 4 to circulate the cooling medium within the cooling channel 42, pre-cooling or isothermizing the back of the ultrasonic-assisted platform 24 and the aluminum-based material 34 to reduce the rapid temperature rise of the aluminum-based material 34 during the laser welding initiation stage. After the pre-cooling or isothermizing treatment is completed, the laser heat source unit 1 is activated to form a localized melting zone at the interface between the copper-based material 31, the Ni intermediate layer 32, the Ag intermediate layer 33, and the aluminum-based material 34.

[0167] During welding, the red and blue laser units are activated. The red laser provides the main heat input required for welding and controls the morphology of the weld pool; the blue laser improves the absorption stability of laser energy on the surface of the copper-based material 31. The red and blue lasers can act together on the same or nearly the same area to be welded on the surface of the copper-based material 31 in a coaxial, off-axis, or spatially adjacent manner. By adjusting the power of the red and blue lasers, the power ratio of the red and blue lasers, the relative position of the laser spots, the degree of laser spot overlap, and the welding speed, a local melting zone is formed near the interface between the copper-based material 31 and the aluminum-based material 34. This activates the Ni intermediate layer 32 and maintains a continuous or semi-continuous distribution, while the Ag intermediate layer 33 reaches a softened, semi-melted, partially melted, or Ag-enriched liquid phase state constrained by the interface.

[0168] Figure 4 (b) is a schematic diagram of the ultrasonic-induced controlled spreading process of the Ag interlayer. Ultrasonic vibration is applied while the Ni interlayer 32 is thermally activated and maintains a continuous or semi-continuous distribution, and the Ag interlayer 33 is in a softened, semi-melted, partially melted, or Ag-rich liquid phase state constrained by the interface. The ultrasonic vibration is transmitted to the aluminum-based material 34 and the copper-aluminum interface to be welded via an ultrasonic auxiliary platform 24. The Ag spreading coefficient K is adjusted by regulating the ultrasonic amplitude, ultrasonic frequency, ultrasonic action time, red laser power, blue laser power, welding speed, and aluminum-side cooling intensity. Ag Within a preset range, the Ag interlayer 33 is controlled to wet and spread along the aluminum side interface, filling the interfacial micro-gaps. After cooling and solidification, the Ag interlayer 33 forms a continuous or semi-continuous Ag-rich conductive region; the Ni interlayer 32 maintains a continuous or semi-continuous distribution on the copper side, forming a thermal buffer and diffusion barrier structure, such as... Figure 4 (c) shows the morphology of the Ni-enriched barrier region, Ag-enriched conductive region, and composite transition interface after welding.

[0169] During welding, the aluminum-side temperature control unit 4 operates continuously or intermittently to locally cool the back side of the aluminum-based material 34 or the ultrasonic-assisted platform 24, limiting over-melting and the expansion of the heat-affected zone on the aluminum side. The synchronous control unit 8 controls the movement of the motion execution unit 7 according to the preset welding path and coordinates the red laser power, blue laser power, ultrasonic vibration parameters, cooling medium flow rate, cooling medium temperature, and shielding gas flow rate. When the temperature detection device 45 detects that the aluminum-side temperature or the ultrasonic-assisted platform temperature deviates from the preset temperature window, the aluminum-side temperature change rate exceeds the preset cooling rate range, or the temperature gradient between different detection points exceeds the preset upper limit of the temperature gradient, the synchronous control unit 8 adjusts the cooling medium flow rate, cooling medium temperature, laser power, welding speed, and / or ultrasonic vibration parameters to keep the aluminum-side temperature, cooling rate, and temperature gradient within the preset range.

[0170] After welding, the red and blue lasers are turned off. The shielding gas unit 6 can be delayed in shutting down to continue protecting the high-temperature welding area. Ultrasonic vibration can be delayed in shutting down after the laser is turned off to promote bubble escape and microstructure refinement during the solidification stage. The aluminum-side temperature control unit 4 can be delayed in shutting down according to a set cooling curve to adjust the joint cooling rate and temperature gradient, reducing residual tensile stress concentration at the copper-aluminum interface. The set cooling curve can be a constant cooling rate curve, a segmented cooling curve, or a stepped cooling curve. In other words, after welding, the synchronous control unit 8 can first turn off the laser heat source unit 1, and then delay the shutdown of the ultrasonic auxiliary unit 2, the aluminum-side temperature control unit 4, and the shielding gas unit 6 to ensure the timing matching between laser heat input, ultrasonic spreading, aluminum-side cooling, and the shielding atmosphere, thereby improving the stability of the joint formation.

[0171] After cooling and solidification, a composite transition interface is formed between the copper-based material 31 and the aluminum-based material 34. This composite transition interface includes a continuous or semi-continuous Ni-enriched barrier region on the copper side, a continuous or semi-continuous Ag-enriched conductive region and Ag-Al interface bonding region on the aluminum side, a locally solidified Ag-filled region, and a thin-layer Cu-Al reaction region. The Ni-enriched barrier region restricts the direct interdiffusion of Cu and Al and inhibits the continuous growth of brittle copper-aluminum intermetallic compounds. The Ag-enriched conductive region is formed by the Ag intermediate layer 33 through local softening, local melting, controlled wetting and spreading, and cooling and solidification; preferably, its average spreading width along the aluminum-side interface is greater than the average width of the Ni-enriched barrier region. Some Ag enters the depressions or micro-gaps of the aluminum-side interface after local melting or the formation of an interface-constrained Ag-enriched liquid phase, and solidifies during cooling to form the Ag-filled region. The thin-layer Cu-Al reaction zone is mainly formed in the local discontinuous parts or local weak areas of the Ni-enriched barrier zone, and is used to achieve local metallurgical bonding under the condition of limiting excessive interdiffusion between Cu and Al.

Claims

1. A dissimilar material welding device with controllable spreading of acoustic-thermal induced double intermediate layers, characterized in that, It includes a laser heat source unit, an ultrasonic auxiliary unit, a workpiece to be welded, an aluminum side temperature control unit, a workpiece clamping unit, a protective gas unit, a motion execution unit, and a synchronization control unit; The laser heat source unit includes a red laser unit and a blue laser unit, which are used together to act on the copper-aluminum area to be welded, forming a composite heat input field. The workpiece to be welded includes a copper-based material, a Ni intermediate layer, an Ag intermediate layer and an aluminum-based material stacked in sequence, wherein the Ni intermediate layer is disposed close to the copper-based material and the Ag intermediate layer is disposed close to the aluminum-based material; The composite heat input field is used to form a local melting zone near the interface between the copper-based material and the aluminum-based material, to activate the Ni interlayer by heat and maintain a continuous or semi-continuous distribution, and to make the Ag interlayer reach a softened, semi-melted, locally melted or Ag-enriched liquid phase state constrained by the interface. The ultrasonic auxiliary unit is used to apply ultrasonic vibration to the copper-aluminum interface to be welded, so that the Ag intermediate layer is controlled to wet and spread along the aluminum side interface and fill the interface depressions or micro gaps, while promoting the formation of a continuous or semi-continuous barrier structure of the Ni intermediate layer on the copper side. The aluminum-side temperature control unit includes a cooling component and a temperature detection device, used for local temperature control of the back side of the aluminum-based material and / or the ultrasonic-assisted platform. The workpiece clamping unit is used to position and clamp the workpiece to be welded, the protective gas unit is used to provide protective gas to the area to be welded, and the motion execution unit is used to realize the relative movement between the laser heat source unit and the workpiece to be welded. The synchronous control unit is connected to the laser heat source unit, the ultrasonic auxiliary unit, the aluminum side temperature control unit, the protective gas unit, and the motion execution unit, respectively, and adjusts the cooling intensity, red laser power, blue laser power, welding speed, and / or ultrasonic vibration parameters in a coordinated manner according to the temperature signal fed back by the temperature detection device.

2. The copper-aluminum laser welding apparatus according to claim 1, characterized in that, The red and blue lasers are applied to the copper-aluminum welding area in a coaxial, off-axis, or spatially adjacent manner. The area of ​​action of the blue laser at least partially covers the area of ​​action of the red laser, or is adjacent to or overlaps with the area of ​​action of the red laser.

3. The copper-aluminum laser welding apparatus according to claim 1, characterized in that, The Ni intermediate layer and the Ag intermediate layer are each one of the following: metal foil, electroplating layer, chemical plating layer, vapor deposition layer, physical vapor deposition layer, magnetron sputtering layer, pre-coated layer, or composite thin layer, or a combination of two or more of them; the thickness of the Ni intermediate layer is 50 nm to 5 μm, and the thickness of the Ag intermediate layer is 100 nm to 10 μm.

4. The copper-aluminum laser welding apparatus according to claim 1, characterized in that, The ultrasonic auxiliary unit includes an ultrasonic generator, an ultrasonic transducer, an amplitude transformer, and an ultrasonic auxiliary platform. The ultrasonic generator is connected to the ultrasonic transducer, and the ultrasonic transducer is connected to the ultrasonic auxiliary platform via the amplitude transformer. The cooling assembly includes a cooling medium circulation mechanism, a cooling channel, a cooling medium inlet, and a cooling medium outlet. The cooling channel is located inside the ultrasonic auxiliary platform and communicates with the cooling medium inlet and outlet. The cooling channel is arranged around or away from the main ultrasonic vibration transmission area to reduce the influence of the cooling channel on the ultrasonic vibration transmission.

5. The copper-aluminum laser welding apparatus according to claim 1, characterized in that, The temperature detection device is located on the back of the aluminum substrate, on the surface of the ultrasonic-assisted platform, in the vicinity of the cooling channel, in the vicinity of the area to be welded, and / or in the cooling area behind the weld. The detected temperature or the temperature obtained through calibration and conversion is taken as the equivalent temperature T on the aluminum side. A ; The synchronization control unit is based on a pre-established aluminum-side equivalent temperature T. A Feedback control is used to establish the correspondence between the effective temperature Ti at the copper-aluminum interface, ensuring that the effective temperature on the aluminum side meets the following requirements: T A，L ≤T A ≤T A，H And ensure that the equivalent temperature of the copper-aluminum interface meets the following requirements: T Ag，act ≤T i ≤T Ag，loss Among them, T A，L To correspond to the lower limit of the effective wetting and spreading temperature of the aluminum side at which the Ag intermediate layer begins to spread, T A，H To address the risk of overmelting in aluminum-based materials or excessive melting and localized loss of the Ag interlayer, T Ag，act T is the interfacial activation temperature at which the Ag interlayer achieves effective wetting and spreading. Ag，loss This is the critical temperature at which the Ag intermediate layer undergoes excessive melting, localized loss, or disordered diffusion. When T A >T A，H At the same time, the synchronous control unit performs at least one of the following cooling adjustments: increasing the cooling medium flow rate, decreasing the cooling medium temperature, increasing the cooling medium circulation speed, decreasing the red laser power, decreasing the blue laser power, and increasing the welding speed. When T A <T A，L At the same time, the synchronous control unit performs at least one of the following temperature-increasing adjustments: reducing the cooling medium flow rate, increasing the cooling medium temperature, increasing the red laser power, increasing the blue laser power, and reducing the welding speed. When T A，L ≤r A ≤T A，H At the same time, the synchronization control unit maintains the current process parameters, or fine-tunes the process parameters according to the changing trend of the equivalent temperature on the aluminum side; The synchronization control unit also adjusts the temperature change rate R on the aluminum side. A and / or temperature gradient judgment value G A Adjust the cooling intensity, where: Where T1 and T2 are the temperatures at two different detection points, and L is the distance between the two detection points; While maintaining T A Under the condition that R is located within the aluminum-side temperature control window, A >R max When R... A <R min And TA is close to T A，H At that time, the synchronous control unit increases the cooling medium flow rate, decreases the cooling medium temperature, and / or increases the cooling medium circulation speed; when G A >G max At the same time, the synchronous control unit adjusts the cooling medium flow rate, cooling medium temperature, red laser power, blue laser power and / or welding speed of different cooling zones; The synchronous control unit uses segmented threshold control, proportional-integral-derivative control, or a combination of both for feedback adjustment; the cooling channel is provided with multiple cooling zones along the welding direction that can independently adjust the cooling intensity; the synchronous control unit adjusts the cooling intensity of each cooling zone according to the temperature feedback signals of the starting welding section, the stable welding section, and the ending welding section.

6. A method for ultrasonically induced double interlayer spreading and aluminum-side temperature-controlled copper-aluminum laser welding, characterized in that, Includes the following steps: S1, Pre-treatment of the surfaces to be welded for copper-based and aluminum-based materials; S2, a Ni interlayer and an Ag interlayer are set between the copper-based material and the aluminum-based material, so that the structure to be welded is in the order of copper-based material / Ni interlayer / Ag interlayer / aluminum-based material; S3, Place the structure to be welded on the ultrasonic-assisted platform and position and clamp it; S4, introduce protective gas into the area to be welded and start aluminum side temperature control; S5 allows red and blue lasers to act together on the area to be welded, forming a composite heat input field. This causes the copper-based and aluminum-based materials to form a local melting zone near the interface to be welded, which activates the Ni interlayer and keeps it continuously or semi-continuously distributed. This allows the Ag interlayer to reach a softened, semi-melted, locally melted, or Ag-enriched liquid phase state constrained by the interface. S6, ultrasonic vibration is applied while the Ag intermediate layer is in the state, causing the Ag intermediate layer to be controlled to wet and spread along the aluminum side interface and fill the interface depressions or micro gaps. S7, based on the temperature signal fed back by the temperature detection device, coordinately adjust the cooling intensity, red laser power, blue laser power, welding speed and / or ultrasonic vibration parameters; S8. After welding, controlled cooling is performed to form a continuous or semi-continuous Ni-enriched barrier region on the copper side of the Ni intermediate layer, and a continuous or semi-continuous Ag-enriched conductive region on the aluminum side of the Ag intermediate layer. An Ag-Al interface bonding region is formed between the Ag-enriched conductive region and the aluminum-based material. Part of the Ag solidifies and fills the interface depressions or micro-gaps on the aluminum side, and a thin Cu-Al reaction region is locally formed at the copper-aluminum interface.

7. The copper-aluminum laser welding method according to claim 6, characterized in that, The controlled wetting and spreading of the Ag intermediate layer is achieved through the Ag spreading coefficient K. Ag Characterization: Among them, W Ag W0 represents the average spread width of the Ag-enriched conductive region on the aluminum side interface after welding, and W0 represents the effective initial width of the Ag intermediate layer participating in the welding reaction before welding in the same measurement direction. By adjusting the red laser power, blue laser power, ultrasonic amplitude, ultrasonic frequency, ultrasonic treatment time, welding speed, and aluminum side cooling intensity, the Ag spreading coefficient is made to meet the following requirements: K1≤K Ag ≤K2 K1 is the lower limit of the spreading coefficient to ensure that the Ag intermediate layer is effectively wetted and spread and fills the interface depressions or micro gaps, and K2 is the upper limit of the spreading coefficient to prevent the Ag intermediate layer from being over-spread, locally lost, or randomly diffused into the aluminum molten pool. The average spreading width of the Ag-enriched conductive region is greater than the average width of the Ni-enriched barrier region.

8. The copper-aluminum laser welding method according to claim 6, characterized in that, Ultrasonic vibration is applied before laser welding begins, during laser welding, and / or in the early stage of post-weld cooling. Ultrasonic vibration applied before laser welding begins is used to improve the interlayer bonding state of the structure to be welded. Ultrasonic vibration applied during laser welding is used to induce controlled wetting and spreading of the Ag intermediate layer. Ultrasonic vibration applied in the early stage of post-weld cooling is used to promote the stable formation of the composite transition interface. After the red and blue lasers stop, the aluminum side temperature is controlled and / or ultrasonic vibration is applied for a preset time to allow the joint to cool according to the preset cooling curve, thereby reducing uneven cooling shrinkage of the aluminum base material and residual stress concentration at the copper-aluminum interface.

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