Aluminum alloy composite material for brazing and preparation method thereof

Abstract

The invention provides an aluminum alloy composite material for brazing and a preparation method thereof. The preparation method comprises the following steps: preparing a solid coating layer strip coil and a core material alloy solution; liquid-solid casting and rolling compounding: injecting the core material alloy solution into a front box of a double-roller casting and rolling machine, attaching a solid coating layer strip coil to the surface of a casting and rolling roller, synchronously guiding into a roller gap area of the casting and rolling machine, and dynamically adjusting the temperature of the core material solution in the front box, the casting and rolling speed and the cooling water flow according to a model prediction control method, and the liquid core material alloy and the solid coating layer strip coils on the two sides are subjected to metallurgical bonding under the cooling and pressure effects of roller gaps, and the layered composite material blank is prepared. The method solves the technical problems that in the process of preparing the aluminum alloy layered composite material through liquid-solid casting and rolling compounding, a solid coating layer and a liquid core material are difficult to effectively compound, the interface corrosion phenomenon is difficult to restrain, and parameter fluctuation is difficult to deal with through traditional process control.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy composite materials for brazing, and specifically to an aluminum alloy composite material for brazing and its preparation method. Background Technology

[0002] Conventional brazing aluminum alloy composite materials mostly use Al-Mn alloy as the core material, with brazing alloy or other alloys cladding on one or both sides, and are all manufactured using a hot-rolling process. This method uses a semi-continuous casting machine to produce aluminum alloy flat ingots, which are then sawed, homogenized, milled, surface treated, the composite layer and core material are fixed together, heated, and hot-rolled to form a composite billet. The production process includes raw material melting, casting, sawing, homogenization, milling, surface treatment, composite layer fixing, heating, hot rolling, cold rolling, heat treatment, and finished product slitting. Its characteristics include a long production process, uneven composite layer ratio, low yield, and high energy consumption costs.

[0003] Patent document CN103599934A discloses a production process and equipment for continuously cast and rolled aluminum-aluminum metallurgically bonded composite strip. After the core material is melted into aluminum liquid, it is placed in a settling furnace, degassed online, filtered, and then flows into the composite zone through a flow channel. A coiler for coiling the sheet material is set on the casting and rolling equipment. During the composite process, the sheet material on the coiler directly enters the composite zone and contacts the surface of the core material (aluminum liquid). Then, the metallurgically bonded aluminum-aluminum composite strip is continuously rolled by the casting and rolling mill.

[0004] However, the following technical problems still exist in the process of preparing aluminum alloy layered composite materials by liquid-solid casting and rolling: First, it is difficult to achieve effective bonding between the solid cladding layer and the liquid core material during the casting and rolling process, making it difficult to suppress interfacial erosion. In existing production processes, the control of the interfacial bonding quality of aluminum alloy composite materials mainly relies on experience-based setting of process parameters, lacking theoretical guidance and real-time monitoring methods, resulting in unstable interfacial bonding quality and frequent erosion phenomena.

[0005] Secondly, traditional process control relies on the deterministic setting of key parameters such as the temperature of the core material solution in the front box and the casting and rolling speed. However, the impact of process parameter fluctuations and their interactions on the interfacial bonding quality is difficult to quantify. There is a lack of systematic research on the mutual influence between these parameters, and it is impossible to establish a quantitative relationship between parameter fluctuations and interfacial bonding quality.

[0006] Third, control strategies based on fixed thresholds are insufficient to reliably and consistently mitigate the risk of erosion. Current processes primarily rely on offline testing to evaluate the interfacial bonding quality of aluminum alloy composites, lacking online real-time monitoring and feedback control methods. This makes it impossible to promptly detect and adjust process parameters, leading to significant fluctuations in product quality.

[0007] Therefore, there is an urgent need for a method that can monitor and optimize the liquid-solid casting-rolling composite process in real time to improve the interfacial bonding quality and production stability of aluminum alloy layered composite materials. Summary of the Invention

[0008] To address the technical challenges in the preparation of layered aluminum alloy composite materials using liquid-solid casting and rolling processes, such as the difficulty in effectively combining the solid cladding layer and the liquid core material, the difficulty in suppressing interfacial erosion, and the inability of traditional process control to handle parameter fluctuations, this invention provides a method for preparing brazing aluminum alloy composite materials, thus resolving the problems mentioned in the background.

[0009] To achieve the above objectives, the present invention provides a method for preparing an aluminum alloy composite material for brazing, comprising the following steps: Step 1: Preparation of solid cladding layer strips and core alloy solution: Solid cladding layer strips are prepared by aluminum alloy smelting and continuous casting and rolling, respectively, to obtain brazing layer alloy and / or water-contact layer alloy; The core aluminum alloy is smelted, refined, degassed and filtered in the online process to obtain the core solution. Step 2, Liquid-Solid Casting and Rolling Composite: The core material solution is injected into the front box of a twin-roll casting mill. The solid coating layer is rolled and adhered to the surface of the casting rolls, and simultaneously introduced into the roll gap area of ​​the casting mill. A layered composite material billet is obtained through liquid-solid casting and rolling composite. Specifically, the temperature of the core material solution in the front box, the casting speed, and the cooling water flow rate are dynamically adjusted using a model predictive control method. The reference value for the core solution temperature in the front box is set based on the liquidus temperature of the core alloy. The interface temperature between the core solution and the solid coating layer at instantaneous contact is calculated based on the core solution temperature in the front box, the roll speed, and the cooling water flow rate, and is kept below the solidus temperature of the solid coating layer. The rolling force is calculated based on the roll contact area, comprehensive flow stress, and composite layer structural parameters, and the rolling force is ensured to reach the critical value required to achieve interfacial metallurgical bonding. The system collects data on the temperature of the core material solution in the front box, the casting and rolling speed, the cooling water flow rate, and the rolling force in real time by deploying a sensor network. At the same time, it uses an ultrasonic flaw detection system to detect the interface in conjunction with the quality index. A dynamic state-space model of the process is constructed, and the following control loop is executed in each sampling period: the state estimate is updated based on sensor data, the dynamic behavior of the system in the future prediction time domain is predicted, and the optimal control sequence is obtained by rolling optimization calculation so that the interface combined with the quality index approaches the set value and the control variables change smoothly. The first step control increment of this sequence is implemented to adjust the power of the front box heater, the casting and rolling speed and the cooling water flow rate. Step 3: The composite material blank obtained in Step 2 is cold rolled, heat treated and finished to obtain the finished product.

[0010] As a second aspect of the present invention, an aluminum alloy composite material for brazing is provided, the aluminum alloy composite material comprising a core material and a brazing layer alloy and / or a water-contact layer alloy located on at least one side of the core material, and the layers are metallurgically bonded interfaces.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs a liquid-solid casting-rolling composite process, using a model predictive control method to achieve multi-variable collaborative optimization control of the core material solution temperature, casting-rolling speed, and cooling water flow rate in the front box. This control method can precisely regulate the interface temperature state, ensuring that the core material maintains sufficient fluidity while avoiding cladding layer erosion defects caused by excessively high temperature or slow speed. It also prevents poor interface bonding caused by insufficient temperature or excessive speed, achieving ideal composite conditions of rapid contact and rapid solidification, and ensuring the metallurgical bonding quality of the composite interface. 2. This invention systematically quantifies the impact of key process parameter fluctuations and their interactions on interfacial composite quality. It employs an MPC predictive control method based on a state-space model, combined with a Kalman filter to estimate unmeasurable key states (such as interface temperature) in real time, significantly improving the system's robustness to uncertainties in the process. Compared to traditional fixed threshold control methods, this invention can predict future process development trends and take control measures in advance, keeping the interfacial composite quality index stably within the high-quality composite range, greatly improving the stability of process control. 3. This invention achieves stable operation of process parameters within a high-quality composite range by constructing a complete closed-loop control system. In addition, through a full-cycle production data archiving and analysis mechanism, it provides data support for the continuous optimization of process parameters, forming a complete closed loop from quality control to process improvement, which significantly improves product consistency and production efficiency. Attached Figure Description

[0012] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same areas. Wherein: Figure 1 This is a schematic diagram of the aluminum alloy composite material structure in an embodiment of the present invention; Figure 2 This is a schematic diagram of the solution casting and rolling composite process of the coating layer and the core material in an embodiment of the present invention; Figure 3 This is a flowchart of the MPC predictive control model in an embodiment of the present invention. Detailed Implementation

[0013] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0014] The present invention will be further described in detail below with reference to the accompanying drawings, but this is not intended to limit the scope of the invention.

[0015] Combination Figures 1 to 3 The present invention proposes a method for preparing an aluminum alloy composite material for brazing, comprising the following steps: Step 1: Preparation of solid cladding layer strip coils: Aluminum alloy melting and continuous casting rolling are used to prepare brazing layer alloy and / or water-contact layer alloy cast coils, respectively. The cast coils are then cooled and heat-treated to form solid cladding layer strip coils with a thickness of 0.5-2.5 mm and a straight shape. The coils are then trimmed, straightened, and surface cleaned. Specifically, the heat treatment after rolling is an annealing process with an annealing temperature of 250-300℃ and a holding time of 0.5-2h.

[0016] It should be noted that the core material has brazed alloy layers on both the top and bottom, or one side has a brazed alloy layer and the other side has a water-contact alloy layer, or one side of the core material has a brazed alloy layer. Processing the solid cladding strip coil to a specific thickness and shape is to ensure that the solid strip coil has sufficient rigidity, strength, and shape quality, so that it can be stably and smoothly fed into the high-speed rotating casting roll gap, preventing wrinkling or breakage.

[0017] To prevent the solid coating from oxidizing at high temperatures and to avoid poor bonding at the composite interface due to the presence of a surface oxide film, an anti-oxidation protective coating is applied to the side of the brazing layer alloy and the water-contact layer alloy that is bonded to the core material solution. The anti-oxidation protective coating has the characteristic of volatilizing instantly upon contact with the high temperature of the core material solution during casting and rolling, ensuring that the coating itself does not remain at the composite interface and does not affect the metallurgical bond between the liquid core material and the solid coating, thereby improving the cleanliness and bonding strength of the composite interface. Its components, by mass percentage, include: hexanediol 55%–75%, propylene glycol 20%–45%, ethoxypropoxylated fatty alcohol 0.5%–2%, and hydroxypropyl methylcellulose 0.05%–1.5%.

[0018] It should be noted that ethylene glycol and propylene glycol have low boiling points, much lower than the core material solution temperature. When they come into contact with the core material solution, they absorb a large amount of heat and evaporate rapidly. Ethoxypropoxylated fatty alcohols are surfactants that allow the coating to spread quickly and form a film. Hydroxypropyl methylcellulose is a thickener. A small amount of thickener can ensure proper adhesion of the coating during application, but its amount is extremely low and it is an organic substance. When exposed to high temperatures, it will rapidly decompose and carbonize, leaving no residue.

[0019] Specifically, a preferred composition may be 65% hexanediol, 34% propylene glycol, 0.8% ethoxypropoxylated fatty alcohol, and 0.2% hydroxypropyl methylcellulose. Another preferred composition may be 70% hexanediol, 27.5% propylene glycol, 1.5% ethoxypropoxylated fatty alcohol, and 1% hydroxypropyl methylcellulose.

[0020] Step 2: Melt, refine, degas online, and filter the core aluminum alloy to obtain a pure core alloy solution. When refining the core aluminum alloy solution, add an aluminum-titanium-boron wire refiner online to refine the grains and introduce inert gas. The amount of aluminum-titanium-boron wire refiner added is 0.1-0.2% of the weight of the core alloy solution. The refining time is 15-25 minutes and the refining temperature is 720-750℃.

[0021] Step 3, Liquid-solid casting and rolling composite: The core alloy solution obtained in step 2 is injected into the front box of the twin-roll casting and rolling mill. At the same time, the solid coating layer strip prepared in step 1 is attached to the surface of the casting and rolling rolls from both sides and simultaneously introduced into the roll gap area of ​​the casting and rolling mill.

[0022] In this step, the two solid coating layers must be simultaneously, centered, and smoothly adhered to the surface of the casting roll before entering the casting zone. Any deviation, wrinkling, or insufficient adhesion to the roll surface will lead to lamination failure, resulting in problems such as incomplete lamination or tearing. Simultaneously, the width of the solid coating layer must be 2-10mm narrower than the width of the casting roll gap. This is to prevent an excessively wide solid coating layer from being rolled into the solidified shell at the edges during the lamination process, causing edge defects or tearing.

[0023] It is further important to note that during the liquid-solid casting-rolling composite process, if the temperature of the molten aluminum in the foreground is too high when the high-temperature core material solution comes into contact with the room-temperature solid cladding coil, severe interfacial erosion will occur. The overheated core material solution will excessively melt the surface of the solid cladding, leading to excessive mutual solubility of alloying elements and the formation of a coarse, continuous, brittle intermetallic compound layer; it will also disrupt the original composite interface design, causing an uncontrolled composite layer ratio; and it will generate microscopic pores and cracks at the interface. In summary, these erosion defects will significantly reduce the interfacial bonding strength and thermal conductivity, making the material highly susceptible to interfacial cracking during subsequent rolling deformation or high-temperature brazing. Therefore, the key to preparing aluminum alloy layered composite materials lies in precisely controlling process parameters to achieve effective composite of the solid cladding and liquid core material during the casting-rolling process, while simultaneously suppressing interfacial erosion.

[0024] To systematically quantify the impact of fluctuations and interactions of key process parameters in the composite process on the quality of the interface composite, this invention proposes a model predictive control method. Through multivariate collaboration, rolling optimization, and feedforward mechanisms, it anticipates future process trends, achieves global optimal control, and provides a precise theoretical calculation basis for optimizing the production process window. Thus, under real-world fluctuation conditions, it determines the essential process parameters for achieving excellent metallurgical bonding strength and thermal conductivity of the composite interface.

[0025] High-precision sensors are deployed in the casting and rolling production line area to collect real-time process data. Specifically, in the front box area, a non-contact infrared thermometer is used to monitor the core material solution temperature at a preset frequency. In the roll gap area, rolling force sensors and laser velocimeters are installed to monitor the rolling force F and casting speed V in real time, respectively; electromagnetic flowmeters are used inside the casting rolls to monitor the cooling water flow rate. Understandably, the core material solution temperature... Casting and rolling speed and V cooling water flow rate Coordinated regulation of interfacial thermal cycling is a prerequisite for achieving micro-diffusion bonding and suppressing excessive erosion. The rolling force F ensures the breakage of the interfacial oxide film and promotes solid-state plastic bonding, directly determining the interfacial bonding strength. A multi-channel ultrasonic flaw detection system is integrated at the roll exit to scan the composite material interface, quantifying the interface echo characteristics into an interfacial bonding quality index (IBQI) ranging from 0 to 100. Only when the above parameters work synergistically can a dense, stable, and thermally matched metallurgical bonding layer be formed at the composite interface, achieving an ideal IBQI value and thus meeting the requirements for interfacial strength and thermal conductivity during subsequent cold rolling deformation and high-temperature brazing.

[0026] S1. Constructing the interface temperature and rolling force model The front box serves as a storage and conveying device for the core material solution. The liquidus temperature of the core material determines the lower limit of the core material solution temperature in the front box. Taking aluminum alloy AA3003 as an example, its liquidus temperature is approximately 655℃. To ensure good fluidity, a superheat of 30-50℃ is usually set. Therefore, the core material solution temperature in the front box is set at around 690℃. The solidus temperature of the solid coating layer determines the upper limit of the temperature of the core material solution in the front box when it reaches the roll gap area. Taking brazed layer AA4343 as an example, its solidus temperature is approximately 577℃. When the 690℃ core material aluminum liquid reaches the roll gap area and comes into contact with the solid coating layer, heat will be transferred from the core material solution to the coating layer coil at an extremely high rate. At the same time, the cooling water in the casting roll will continuously extract heat from the coating layer. Therefore, the interface bonding temperature is much lower than 690℃.

[0027] Traditional process control relies on the deterministic setting of key parameters such as the temperature of the core material solution in the front box and the casting and rolling speed. However, parameter fluctuations are unavoidable in actual production, such as the natural fluctuations in the temperature of the core material solution in the front box, making it difficult for control strategies based on fixed thresholds to reliably avoid the risk of melting. In particular, the temperature of the core material solution in the front box, which is the starting point of the composite process, is not an independent setpoint, but rather the interface temperature after the core material solution comes into instantaneous contact with the solid coating layer. However, this temperature is affected by the temperature of the core material solution. Casting and rolling speed (V), cooling water flow rate ( The combined influence of parameters such as ( ).

[0028] Furthermore, the interface temperature required for the core solution to reach instantaneous contact with the solid coating layer is calculated. for: In the formula, The temperature of the core material solution in the front chamber. This refers to the instantaneous heat loss temperature; In the formula, The heat loss coefficient of the cooling water. The heat loss coefficient is the coefficient of heat loss due to contact between the roller surfaces. The heat loss coefficient due to environmental convection. Qcool Cooling water flow rate ， V For casting and rolling speed, The characteristic speed is the speed at which the casting and rolling speed affects the heat loss from the roll surface contact. This is the initial temperature of the coating layer (usually room temperature).

[0029] Specifically, interface temperature Temperature of the core material solution in the front chamber With instantaneous heat loss temperature The difference. Among them, the instantaneous heat loss temperature. Quantified as a function of cooling water flow rate A function directly proportional to and inversely proportional to the contact time (inversely proportional to the casting and rolling speed V) is used to accurately calculate the impact of casting and rolling speed and cooling water flow rate on instantaneous heat exchange. Interface temperature As a key process parameter, it is affected by a variety of uncertain factors, such as environmental heat loss, material property fluctuations, and equipment aging.

[0030] Furthermore, based on the combined effects of contact area, comprehensive flow stress, and thickness influence factors, the rolling force F of the roll is calculated using the following formula: In the formula, The contact area is calculated from the roll geometry parameters (casting mill roll diameter and billet width); For the deformation resistance of the solid coating layer, For the flow stress of the solid coating layer; This represents the percentage of the solid coating layer in the total thickness. This is the nonlinear influence index of the material in this layer; Let be the state function of the core material's resistance to deformation. For interface temperature, The average strain rate is proportional to the casting and rolling speed V. ); The interfacial bonding strength coefficient; This serves as a reference thickness and a standard for thickness normalization, used to eliminate the influence of different thickness specifications on rolling force calculations. The total thickness of the composite blank is a preset fixed value, i.e., the roll gap height. This is the thickness influence index.

[0031] It should be noted that the contact area, as a geometrical factor, directly determines the base value of the rolling force, and its magnitude is directly proportional to the rolling force. The overall flow stress consists of three parts: the deformation resistance of the solid cladding layer, the solidification resistance of the core material, and the interfacial bonding strength. The higher the interfacial temperature, the lower the flow stress between the solid cladding layer and the solidified core material, and the smaller the required rolling force. The faster the casting and rolling speed, the more significant the strain rate strengthening effect exhibited by the material, leading to an increase in rolling force. The thickness influence factor is a process calibration constant, and its value is determined by a fixed roll gap height (i.e., the total thickness Ht of the composite billet) and a reference thickness Hr.

[0032] In practical applications, two key constraints must be met to ensure the success of the composite process: First, the interface temperature must not exceed the solidus temperature of the core material and a necessary degree of safe supercooling must be maintained to prevent molten aluminum from flowing out after rolling. This constraint ensures that the interface temperature must be low enough for the core material to solidify before exiting the rolls. If the interface temperature is too high, approaching or exceeding the solidus temperature, the core material cannot form a stable solid structure and will be torn at the roll exit, or even leak out molten aluminum, leading to composite failure. Second, the rolling force must reach the critical value required to achieve the embedding of the solid cladding layer and the metallurgical bonding of the interface. If the critical rolling force is not reached, defects such as incompatibility or composite delamination may occur, making it impossible to form a complete composite plate. These two constraints together determine the stable operating range of the liquid-solid casting-rolling composite process.

[0033] S2, Collect real-time data This step provides a data foundation for model predictive control by building a real-time data acquisition network.

[0034] A dual-redundant high-frequency response infrared thermometer is precisely deployed on the surface of the molten aluminum in the front chamber to monitor the core material solution temperature in real time. ,like =690℃, its instantaneous fluctuation provides a key feedforward signal for predictive control; a high-precision photoelectric encoder is installed at the drive end of the casting roll to directly measure and convert the roll speed V, such as V=1.0m / min; an electromagnetic flow meter and a PT100 temperature sensor are configured in the cooling water circuit to accurately quantify the cooling water flow rate by calculating the heat dissipation in real time. ,like =100L / min. A high-precision piezoelectric force gauge installed on the casting and rolling mill monitors the rolling force F in real time, and its measured value is directly used as the process constraint and status feedback input to the MPC controller. It should be noted that the roll speed V and cooling water flow rate are also important parameters. and core material solution temperature Used to jointly regulate the interface thermal balance; the rolling force F is to ensure that the interface oxide film is broken, and to achieve the strength required for the solid coating layer to be embedded and the interface metallurgically bonded.

[0035] A multi-channel ultrasonic flaw detection system is integrated at the roll exit, with the probe scanning the composite material interface at a frequency of 5MHz and a rate of 1000 times per second. This system comprehensively evaluates the interface bonding state by analyzing various characteristic parameters of the ultrasonic echo signal, including: the echo amplitude of the interface, which is directly related to the sound wave transmittance; a lower echo amplitude indicates a better macroscopic bonding state (e.g., no delamination, unbonded defects); the center frequency shift of the interface echo energy spectrum, caused by the scattering and attenuation of sound waves at the interface; a significant downward shift in the center frequency indicates the presence of microscopic defects at the interface (e.g., micropores, coarse intermetallic compounds in the erosion zone); and a time-frequency domain feature vector constructed based on the echo signal, used to more comprehensively capture the complex influence of the interface microstructure on the ultrasonic waveform, thereby improving the accuracy and robustness of the classification and evaluation of composite interface bonding quality.

[0036] Furthermore, the system uses a pre-trained quantization model to fuse and calculate the aforementioned multi-feature parameters, ultimately outputting an Interface Bond Quality Index (IBQI) within the range of 0-100. The quantization model is established based on a large number of samples with known bonding states, trained through regression analysis or machine learning methods, and its output value is highly positively correlated with the actual bonding strength of the tested interface.

[0037] The IBQI value is used as the quality criterion for composite material preforms, and is directly used as the feedback target and model calibration benchmark for the MPC controller. If IBQI > 90, it is judged as "high-quality bonding", 75 < IBQI ≤ 90 is judged as "acceptable", and IBQI ≤ 75 is judged as "defective (such as melting or lack of bonding)".

[0038] Furthermore, all sensor data is synchronized at the same timestamp via the OPCUA protocol and transmitted to the real-time process database to establish a full-cycle data archive for each composite billet.

[0039] S3. Construct the MPC predictive control model In the traditional liquid-solid casting-rolling composite production process of aluminum alloys, control strategies rely on the deterministic setting of key parameters such as the temperature of the core material solution in the front box and the casting and rolling speed. However, control strategies based on fixed thresholds are difficult to reliably avoid defects such as interface erosion or lack of bonding. The construction of an MPC predictive control model aims to infer and control the intangible critical process states through measurable final product quality indicators, thereby dynamically adjusting the temperature of the core material solution in the front box, the casting and rolling speed, and the cooling water flow rate to form a self-optimizing production closed loop.

[0040] First, based on process experimental data covering interface temperature, casting and rolling speed, cooling water flow rate, rolling force, and corresponding interface comprehensive quality index, a dynamic state-space model of the process is constructed.

[0041] Define the state vector: In the formula, The core material solution temperature; For casting and rolling speed; This refers to the cooling water flow rate; Interface temperature; For rolling force; The interface incorporates a quality index.

[0042] Control vector: In the formula, This refers to the power adjustment amount of the front box heater. For the adjustment of casting and rolling speed, This refers to the cooling water flow rate adjustment.

[0043] Output vector: Therefore, the system dynamic equation is: In the formula, For control vectors, It is a measurable disturbance vector.

[0044] It should be noted that A is the state transition matrix, which characterizes the dynamic characteristics of the liquid-solid casting-rolling composite system itself. For example, if the roll temperature suddenly rises, due to the thermal inertia of the system, the molten aluminum alloy will not increase its temperature instantaneously, but rather according to a specific time delay. The temperature change trend can be predicted through the state transition matrix, thereby optimizing parameters such as heating power and rolling speed. B is the input matrix, which quantifies the influence of each manipulated variable on the liquid-solid casting-rolling composite state. D is the disturbance matrix. For example, in the aluminum alloy composite process, sudden changes in ambient temperature, subtle differences in raw material composition, and mechanical vibrations during equipment operation can all be regarded as disturbance factors of the system. These disturbance factors will affect key indicators such as temperature and casting-rolling speed. C is the output matrix.

[0045] Secondly, based on the requirements for product quality, energy consumption, and equipment operational stability in the liquid-solid casting-rolling composite process, an optimization objective function is constructed: In the formula, The prediction range represents the number of time steps the controller needs to predict the future dynamics of the system. The control range represents the number of time steps the controller takes to calculate future optimized control actions. To set a threshold, such as a threshold of 90, a value greater than 90 indicates good metallurgical bonding quality at the liquid-solid casting-rolling composite interface; To control the increment; This is the weight matrix.

[0046] It should be noted that, Used to measure the importance of different control objectives. Q measures the impact of output value variables deviating from target values. For example, IBQI reflects the importance of interface bonding quality. A larger Q value requires higher IBQI detection accuracy and faster achievement of high-quality bonding standards, while a smaller Q value allows for fluctuations within a certain range, resulting in smoother controller adjustments. R controls the magnitude of changes in manipulated variables, such as the weighting of changes in front box heating power, roll speed adjustment, and cooling water flow. Typically, trial-and-error methods, genetic algorithms, or dynamic programming are used, combined with system simulation and actual process requirements, to iteratively calculate and determine the specific values ​​of the weight matrix to achieve optimal coordinated control of multiple variables.

[0047] In order to limit key parameters such as the front box temperature and casting speed within the range of safe equipment operation and process feasibility, while ensuring that the interface bonding quality meets the standards and effectively suppressing erosion defects, constraints on each parameter are established.

[0048] Manipulation constraints: Specifically including .

[0049] Control Increment Constraints: To prevent drastic changes in the operated variables; Process constraints: The rolling force ensures the appropriate pressure range required for the composite interface; Output constraints: To ensure that the product meets the requirements.

[0050] In this embodiment, the variable constraints are as follows: ; Controlling incremental constraints such as , , .

[0051] In this embodiment, since the critical state (such as interface temperature) at the instantaneous contact interface between the core material solution and the solid coating layer cannot be directly measured, and IBQI measurements may have noise or delay, a Kalman filter is used to fuse real-time sensor data with the process model for state estimation. In the formula, It is the state estimate at time k. yes The predicted state value at time step is used to repeat the above optimization calculation process to achieve rolling range optimization control; A is the state transition matrix, which represents how the state at the previous time step affects the current time step; B is the input matrix, which represents how the manipulated variables affect the changes in the system state. Kalman gain; The actual measured output value; This indicates a predicted value based on the current state.

[0052] It should be noted that MPC updates the state estimate in real time through a Kalman filter, and continuously corrects model prediction errors and suppresses unmeasurable disturbances by utilizing the residual between the actual measured IBQI and the model prediction output. Through a closed-loop mechanism of prediction, optimization, execution, and feedback, it can continuously overcome process disturbances and model errors, ensuring that the liquid-solid casting and rolling composite process remains stable within the optimal operating range while meeting all process constraints.

[0053] Furthermore, a closed-loop control process is constructed. Initially, MPC parameters and constraints are set. At each sampling time K, data is collected in real time through a sensor network and an ultrasonic testing system, including... Update the state estimate using a Kalman filter. The objective function is then solved further to obtain the optimal control sequence. The next step is to implement the first-step control increment based on the optimal control sequence. (The first control increment) adjusts the power of the front box heater, the casting and rolling speed, and the cooling water flow rate. At the next sampling time, the measured values ​​are updated, and the optimization is re-executed. Based on the rolling optimization and feedback correction mechanism, MPC can continuously overcome process disturbances and model errors, keeping the production process stable in the high-quality composite zone.

[0054] If the initial process parameters are set as follows The actual rolling force was F=1480kN, but the produced composite material was tested by ultrasonic testing and showed IBQI=85, which was only qualified.

[0055] Initiating the closed-loop control process: The MPC controller detects the current interface temperature based on state estimation. While 575℃ is within a safe range, the IBQI deviates from the target. The optimal control sequence is calculated through multivariate coordinated optimization, adjusting the power of the front chamber heater. Adjustment of casting and rolling speed =0.08 m / min, cooling water flow rate After execution, the process parameters were adjusted to... The measured rolling force F = 1520 kN, and the interface temperature at this time... Maintaining the temperature within the safe range of 570℃, while improving core material flowability and interfacial bonding conditions, the process parameters stabilized after several control cycles of dynamic adjustment. At this time, the interface temperature At 572℃, the IBQI remained stable at 91.2, meeting the high-quality bonding standard. By implementing this closed-loop process, the yield rate increased from the baseline of 85% to 96%, while ensuring no melting defects at the interface, achieving stable production with high quality and high efficiency.

[0056] The entire process significantly improves the accuracy and robustness of state perception, providing a reliable foundation for MPC optimization calculations. By deeply integrating real-time quality inspection (IBQI), process dynamics models, and model predictive control (MPC), the industry challenge of unmeasurable key process states and low control accuracy in aluminum alloy liquid-solid casting-rolling composite processes is solved. This closed-loop control system not only actively maintains process parameters at optimal operating points but also effectively resists external disturbances, significantly improving the stability of interface bonding quality and product yield.

[0057] S4. Dynamic feedback optimization control of liquid-solid casting and rolling composite process. Understandably, the purpose of this step is to synchronously store all the production process data generated in stages S2 and S3, including process parameters (such as core material solution temperature, casting and rolling speed, cooling water flow rate, and rolling force), model predictions, and the measured interface combined with the Income Quality Index (IBQI) as the ultimate quality feedback, into the historical database, thereby establishing a complete data set for each production batch.

[0058] In practice, the system automatically archives the real-time database established in S2 into a historical database, and extracts data containing { from it weekly. The process involves: 1) compiling production batch data packages for the product's mechanical properties and calculating process parameters in step S3, defining the percentage of time within the high-quality composite zone and quantifying it as a key feature, namely the Process Robustness Index (PRI). 2) Periodically initiating reinforcement learning (RL) optimization tasks using historical data as the environment, fine-tuning the key parameters of the MPC internal prediction model to maximize PRI and average IBQI. 3) Simulating and validating the new model parameters, and then inputting them into the MPC system to update the model. Finally, continuous iteration is performed to improve product quality.

[0059] Based on the above technical concept, it should be noted that the mechanical properties of the product refer to a series of key indicators related to mechanical strength and deformability exhibited by the aluminum alloy composite material after completing all preparation processes (including liquid-solid casting and rolling composite, cold rolling, heat treatment, etc.). These mainly include the following core indicators: Tensile strength: The maximum stress a material can withstand before it breaks in a tensile test.

[0060] Yield strength: The stress at which a material begins to undergo significant plastic deformation.

[0061] Elongation: The percentage of permanent plastic deformation of a material at break to its original length. The higher the elongation, the better the plasticity and toughness of the material, and the stronger its processing and forming ability.

[0062] Collapse resistance: This is a performance metric for specific applications such as ultra-thin fins, used to simulate a material's ability to resist softening and deformation due to its own weight and heat during high-temperature brazing. A lower collapse resistance value indicates better high-temperature shape stability and superior performance.

[0063] Furthermore, based on the above-mentioned MPC predictive control model, its control effect in the liquid-solid casting and rolling composite process was verified through the following specific embodiment: the temperature of the aluminum liquid in the front core material was stably controlled at 695℃, the casting and rolling speed was set to 1050mm / min, and the coolant flow rate was set to 84.6L / min. A three-layer composite material of AA4343 / AA3003 / AA7072 with a dense structure and an interfacial bonding quality index (IBQI) greater than 90 was successfully prepared, effectively suppressing melting defects. Example 1

[0064] (1) Preparation of solid clad strip coils: AA4343 brazing alloy and AA7072 water-contact alloy were melted separately, and then transferred to a holding furnace for refining. Inert gas and refining flux were introduced during refining. The refining time was 15 minutes, the aluminum liquid temperature was 730℃, and the holding time was 20 minutes. After that, continuous casting and rolling were started to produce a cast coil with a thickness of 7mm. Subsequently, it was cold rolled to a thickness of 1mm in multiple passes and annealed at 280℃ / 1h. Finally, it was trimmed, tensioned and degreased with alkali to obtain solid clad strip coils with good shape and clean surface.

[0065] (2) Melting and processing of core alloy: Melt AA3003 aluminum alloy, refine it in a holding furnace at 730°C with argon gas for 20 minutes, and let it stand for 25 minutes. Add Al-Ti-B wire at 0.15% of the weight of aluminum liquid online to refine the grains, and after filtering through a ceramic filter plate, introduce it into the front box of the twin-roll casting mill.

[0066] (3) Liquid-solid casting and rolling composite: The temperature of the core aluminum liquid in the front box is stably controlled at 695℃, the casting and rolling speed is set to 1050mm / min, and the coolant flow rate is set to 84.6L / min. At the same time, the pretreated AA4343 and AA7072 solid strip coils are precisely aligned, tightly adhered to the surface of the casting and rolling rolls, and synchronously introduced into the casting and rolling zone. The process parameters are dynamically adjusted by the MPC control system to stably control the rolling force at 1580kN. At the roll gap, the liquid core material and the solid coating layer are instantly metallurgically bonded under the pressure and cooling of the rolls to produce a three-layer composite material billet with a total thickness of 10mm, the structure of which is AA4343 / AA3003 / AA7072 in sequence.

[0067] (4) Post-processing: The composite material blank is cold rolled to 1 mm thickness through multiple passes, then annealed at 400℃ for 2 hours, and finally cut and packaged.

[0068] Table 1 shows the composite layer ratio of the finished product in Example 1 and a comparison of its mechanical properties before and after simulated brazing:

[0069] Table 1 As shown in Table 1, the AA4343 composite layer ratio fluctuation range of the 1mm thick composite material prepared by the liquid-solid casting-rolling composite process of this invention is strictly controlled within ±0.5% (actually 9.5%-9.8%), with a total fluctuation range of only 0.3%, far lower than the ±1.8% fluctuation of the traditional hot-rolling composite process (total fluctuation 3.3%). This extremely high layer thickness control precision ensures that the composite material can form a uniform, strong, and well-sealed weld during subsequent brazing. Simultaneously, the tensile strength of the material before and after brazing reaches 112 MPa and 135 MPa respectively, both superior to the 98 MPa and 123 MPa of products produced by the traditional process, proving that its casting-rolling structure is superior and its interfacial bonding quality is higher.

[0070] Furthermore, based on the above-mentioned MPC predictive control model, its control effect in the liquid-solid casting and rolling composite process was verified through the following specific embodiment two: the temperature of the aluminum liquid in the front core material was stably controlled at 690℃, the casting and rolling speed was set to 1100mm / min, and the coolant flow rate was set to 86.5L / min. A three-layer composite material of AA4343 / AA3003 / AA7072 with a dense structure and an interfacial bonding quality index (IBQI) greater than 90 was successfully prepared, which effectively suppressed the melting defects. Example 2

[0071] The finished product in this embodiment is an ultra-thin fin with AA4343 brazing alloy bonded to both sides of the core material.

[0072] Preparation of solid-clad strip coils: AA4343 brazing alloy was melted and then transferred to a holding furnace for refining. Inert gas and refining flux were introduced during refining for 20 minutes at a molten aluminum temperature of 750℃. After a holding time of 25 minutes, continuous casting and rolling were started to produce a 6.5mm thick coil. Subsequently, it was cold rolled to a thickness of 0.8mm through multiple passes and annealed at 280℃ / 1h. Finally, edge trimming, tension straightening, and cleaning were performed to obtain solid-clad strip coils with good shape and clean surface.

[0073] (2) Melting and processing of core alloy: Melt AA3003 aluminum alloy, refine it in a holding furnace at 720°C with argon gas for 15 minutes, and let it stand for 20 minutes. Add Al-Ti-B wire accounting for 0.1% of the weight of aluminum liquid online to refine the grains, and after filtering through a ceramic filter plate, introduce it into the front box of the twin-roll casting mill.

[0074] (3) Liquid-solid casting and rolling composite: The temperature of the core aluminum liquid in the front box is stably controlled at 690℃, the casting and rolling speed is set to 1100mm / min, the coolant flow rate is set to 86.5L / min, and the rolling force is 1420kN. At the same time, two AA4343 solid strip coils are precisely aligned, closely adhered to the surface of the casting and rolling rolls, and synchronously introduced into the casting and rolling zone. At the roll gap, the liquid core material and the solid coating layer are instantly metallurgically bonded under the pressure of the rolls and the cooling action, resulting in a three-layer composite material billet with a total thickness of 8mm, with the structure being AA4343 / AA3003 / AA4343 in sequence.

[0075] (4) Post-processing: The composite material blank is cold rolled to an intermediate thickness of 0.13 mm through multiple passes, then annealed at 400℃ for 2 hours, and then finely rolled to a fin thickness of 0.08 mm. Finally, it is slit and packaged.

[0076] Table 2: Performance comparison of the finished product of Example 2 and the traditional hot-rolled composite fins, with simulated brazing conditions of 600℃ / 5min:

[0077] Table 2 As shown in Table 2, this embodiment demonstrates that even at this ultra-thin specification, the ratio of the AA4343 composite layers on both sides is precisely controlled within an extremely narrow range of 9.2%-9.8%, with layer thickness accuracy far exceeding that of traditional processes. This is attributed to the rapid solidification interface bonding mechanism during the liquid-solid casting and rolling process, which effectively inhibits interface erosion and forms a dense metallurgical bond. The direct benefit is that the material's collapse resistance after simulated brazing is significantly reduced from 43mm in the traditional process to 38mm, an improvement of approximately 11.6%. This indicates that the material has stronger creep resistance at high temperatures and better dimensional stability, meeting the requirements of ultra-thin heat exchanger fin applications with extreme demands for weight, reliability, and durability.

[0078] As a second aspect of the present invention, an aluminum alloy composite material for brazing is provided, which is manufactured using the process conditions of the aluminum alloy composite material for brazing of the present invention. The aluminum alloy composite material comprises a core material and a brazing layer alloy located on at least one side of the core material, or both sides of the core material are brazing layer alloys, or one side is a brazing layer alloy and the other side is a water-contact layer alloy, and the layers are metallurgically bonded interfaces.

[0079] Specifically, the core alloy is AA3003 aluminum alloy of the Al-Mn series, the brazing layer alloy is AA4343 or AA4045 aluminum alloy, and the water-contact layer alloy is AA7072 aluminum alloy, AA1050 or AA1070 industrial pure aluminum.

[0080] The aluminum alloy composite material of the present invention, through the full liquid state of the core material and high-speed casting and rolling, can obtain a fine and rapid solidification structure. While ensuring a good composite interface and corrosion resistance, it is more conducive to maintaining the excellent comprehensive performance of the core material, and its low cost advantage makes it have a wider market application potential.

[0081] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A method for preparing an aluminum alloy composite material for brazing, characterized in that: Including the following steps: Step 1: Preparation of solid clad strip and core alloy solution: Solid clad strip is prepared by aluminum alloy smelting and continuous casting and rolling; the core aluminum alloy is smelted, refined, degassed and filtered in the online process to obtain the core solution. Step 2, Liquid-Solid Casting and Rolling Composite: The core material solution is injected into the front box of a twin-roll casting mill. The solid coating layer is rolled and adhered to the surface of the casting rolls, and simultaneously introduced into the roll gap area of ​​the casting mill. A layered composite material billet is obtained through liquid-solid casting and rolling composite. Specifically, the temperature of the core material solution in the front box, the casting speed, and the cooling water flow rate are dynamically adjusted using a model predictive control method. The reference value for the core solution temperature in the front box is set based on the liquidus temperature of the core alloy. The interface temperature between the core solution and the solid coating layer at instantaneous contact is calculated based on the core solution temperature in the front box, the roll speed, and the cooling water flow rate, and is kept below the solidus temperature of the solid coating layer. The rolling force is calculated based on the roll contact area, comprehensive flow stress, and composite layer structural parameters, and the rolling force is ensured to reach the critical value required to achieve interfacial metallurgical bonding. The system collects data on the temperature of the core material solution in the front box, the casting and rolling speed, the cooling water flow rate, and the rolling force in real time by deploying sensors. At the same time, it uses an ultrasonic flaw detection system to detect the interface in conjunction with the quality index. A dynamic state-space model of the process is constructed, and the following control loop is executed in each sampling period: the state estimate is updated based on sensor data, the dynamic behavior of the system in the future prediction time domain is predicted, and the optimal control sequence is obtained by rolling optimization calculation so that the interface combined with the quality index approaches the set value and the control variables change smoothly. The first step control increment of this sequence is implemented to adjust the power of the front box heater, the casting and rolling speed and the cooling water flow rate. Step 3: The composite material blank obtained in Step 2 is cold rolled, heat treated and finished to obtain the finished product.

2. The preparation method according to claim 1, characterized in that: An antioxidant protective coating is applied to the side where the solid coating layer is composite with the core material solution. The antioxidant protective coating can evaporate instantly upon contact with the core material solution during casting and rolling. Its components include, by mass percentage, 55%–75% hexanediol, 20%–45% propylene glycol, 0.5%–2% ethoxypropoxylated fatty alcohol, and 0.05%–1.5% hydroxypropyl methylcellulose.

3. The preparation method according to claim 1, characterized in that: The interface temperature is the difference between the temperature of the core material solution in the front chamber and the instantaneous heat loss temperature at the interface between the core material solution and the solid coating layer. The instantaneous heat loss temperature is: In the formula, The heat loss coefficient of the cooling water. The coefficient of heat loss due to contact between the roller surfaces. The heat loss coefficient due to environmental convection. Qcool Cooling water flow rate ，V For casting and rolling speed, The characteristic speed is the speed at which the casting and rolling speed affects the heat loss from the roll surface contact. The temperature of the core material solution in the front chamber. This represents the initial temperature of the coating layer.

4. The preparation method according to claim 3, characterized in that: The formula for calculating the rolling force F is: In the formula, The contact area is calculated from the roll geometry parameters; For the deformation resistance of the solid coating layer; This is the state function of the core material's deformation resistance; The interfacial bonding strength coefficient; For reference thickness, This represents the total thickness of the composite blank. This is the thickness influence index.

5. The preparation method according to claim 4, characterized in that: The thickness of the layered composite material blank is 3-15 mm, and the solid coating layer accounts for 5-25% of the total thickness of the layered composite material blank.

6. The preparation method according to claim 1, characterized in that: The state-space model includes: Construct a state vector, which includes core material solution temperature, casting and rolling speed, cooling water flow rate, interface temperature, rolling force, and interface bonding quality index; Construct a manipulation vector, which includes the adjustment of the front box heater power, the adjustment of the casting and rolling speed, and the adjustment of the cooling water flow rate; Construct an output vector, which includes core solution temperature, casting and rolling speed, cooling water flow rate, rolling force, and interface bonding quality index.

7. The preparation method according to claim 6, characterized in that: Construct the optimization objective function: In the formula, For the prediction range, To control the scope, Set a threshold for the interface to incorporate a quality index. To control the increment, This is the weight matrix.

8. The preparation method according to claim 6, characterized in that: The real-time state estimation using a Kalman filter includes: based on real-time acquired sensor data and a state-space model, calculating the measurement residual by fusing the actual measured interface with the quality index and model prediction values ​​through Kalman gain fusion; and continuously correcting the system state estimation using the residual to compensate for model prediction errors and suppress unmeasurable disturbances.

9. The preparation method according to claim 1, characterized in that: The width of the solid coating layer roll is 2mm-10mm narrower than the width of the casting roll gap.

10. A brazing aluminum alloy composite material prepared by the preparation method according to any one of claims 1-9, characterized in that: The aluminum alloy composite material comprises a core material and a brazing layer alloy and / or a water-contact layer alloy located on at least one side of the core material, and the layers are metallurgically bonded interfaces.

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