Extrusion method for recycled aluminium alloy profiles for anodizing and electrophoretic painting

Abstract

The present application relates to the technical field of metal pressure processing, and discloses an extrusion method for recycled aluminum alloy profiles for anodic oxidation and electrophoretic spraying, which comprises the following steps: adding strontium and boron into recycled aluminum melt, controlling the mass ratio with iron, forming an interface enrichment layer with shear sensitivity on the surface of the iron-containing impurity phase by using strontium; establishing an ingot axial temperature gradient, and controlling the average equivalent strain rate in the extrusion process to be maintained in the critical rheological interval, and physically activating the interface enrichment layer to produce shear thinning; and implementing online gradient freezing quenching after the profile leaves the die. Through the synergy of the critical strain rate and the interface modification, the present application builds an in-situ lubricating layer between the hard impurity phase and the aluminum matrix, eliminates the microscopic tearing caused by the rheological mismatch, and solves the color difference problem of the recycled aluminum surface treatment.

Description

Technical Field

[0001] This invention relates to a method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying, belonging to the field of metal pressure processing technology. Background Technology

[0002] Currently, using recycled aluminum scrap to produce 6xxx series aluminum alloy profiles is an industry trend. Because recycled aluminum raw materials often contain high levels of iron impurities, the industry standard method is to add manganese to neutralize the iron and combine this with high-temperature homogenization to transform needle-like or sheet-like materials. -AlFeSi phase transformation into a rounded morphology - The AlFeSi phase or Chinese character-shaped phase is used to improve processing performance. This static metallographic structure control method can meet the basic needs of building structural parts or general industrial materials with low surface quality requirements. However, it is applied to scenarios with high surface quality requirements, such as consumer electronics shells and high-end decorative building materials. Especially when anodizing or electrophoretic spraying is required, although the melting heat treatment improves the static morphology of the iron-rich phase, there is a difference in rheological rate between the hard iron-rich phase particles and the soft aluminum matrix when passing through the high temperature and high pressure deformation zone of the die sizing zone. The rheological mismatch between the matrix and the inclusions makes it difficult for the aluminum matrix to tightly wrap the hard particles when flowing at high speed. Microscopic cavities are easily formed on the back flow surface of the particles or dislocation pile-up is generated at the interface. Such microscopic physical defects are difficult to detect with the naked eye under the extrusion state, but in the subsequent anodizing process, the microscopic cavities become acid retention bags. Due to the difference in internal energy, the local oxide film growth rate is abnormal in the dislocation pile-up area, which eventually forms visible black streaks, gray spots or pinholes on the profile surface, which seriously affects the product's appearance consistency and corrosion resistance.

[0003] Existing technological improvements mainly focus on the static heat treatment process during the ingot preparation stage, neglecting the dynamic rheological compatibility between the hard phase and the matrix during subsequent extrusion deformation. For example, Chinese invention patent application CN120249846A discloses a homogenization heat treatment process for recycled aluminum alloys. Although it improves the static morphology of the iron-rich phase and eliminates some casting defects through high-temperature long-term heat preservation combined with water quenching, it is essentially still a static optimization of the initial state of the material. When subjected to high temperature, high pressure and severe shearing in the die sizing zone, this process cannot eliminate the inherent rheological rate difference between the hard iron-rich phase particles and the soft aluminum matrix. Under high-speed flow dynamic conditions, such statically excellent microstructures are prone to microcracks at the interface where hard particles hinder the flow of the matrix. Microscopic physical defects are difficult to detect with the naked eye under extrusion. In the subsequent anodizing process, microscopic cavities become acid retention pockets, and the dislocation pile-up area causes abnormal local oxide film growth rate due to internal energy differences. Finally, visible black streaks, gray spots or pinholes are formed on the surface of the profile.

[0004] Therefore, the technical problem to be solved by this invention is how to eliminate interface damage during the extrusion and rheological process of hard impurity phases and achieve electrochemical uniformity of the surface of recycled aluminum profiles with high impurity content, without increasing the cost of raw material purification and ensuring production efficiency. Summary of the Invention

[0005] To address the problems mentioned in the background art, the technical solution of the present invention is as follows: a method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying, comprising the following steps:

[0006] Step S1, ingot interface chemical pre-setting, providing a homogenized recycled aluminum ingot, the matrix of which contains iron-containing impurity phases, controlling the mass ratio of strontium to iron in the recycled aluminum ingot to 0.15 to 0.25 through smelting batching, and controlling the mass percentage of boron to 0.01% to 0.03%, using strontium atoms to form an interface enrichment layer with strain rate sensitivity on the surface of the iron-containing impurity phase;

[0007] Step S2, axial thermodynamic gradient construction: The recycled aluminum ingot is heated to an initial temperature range of 460°C to 480°C, and a temperature gradient of 15°C to 20°C is established along the axial direction so that the extrusion front end temperature of the recycled aluminum ingot is higher than the extrusion back end temperature, thus compensating for the deformation heat during the extrusion process.

[0008] Step S3, critical strain rate rheological extrusion, the recycled aluminum ingot after the thermodynamic gradient is constructed is sent into a split combination die with an extrusion ratio of 40:1 to 60:1. By coordinating the main cylinder propulsion speed and die geometry parameters, the average equivalent strain rate of the metal flowing through the die deformation zone is maintained in the critical rheological range of 15 to 25 seconds. The physical activation of the interface enrichment layer produces shear thinning, eliminates the rigid rheological resistance between the iron impurity phase and the aluminum matrix, and drives the iron impurity phase to undergo adaptive rotation and rearrangement in the flow field.

[0009] Step S4, online gradient freezing quenching: within 0.5 seconds after the profile leaves the mold exit, apply a combination of strong wind and water mist cooling at a cooling rate greater than or equal to 300 degrees Celsius per minute to the profile until the temperature drops below 200 degrees Celsius to freeze it into a high-temperature solution state.

[0010] Preferably, in step S1, the mass percentage of iron in the recycled aluminum ingot is 0.3% to 0.6%; the smelting batching includes: adding an aluminum-strontium master alloy to the recycled aluminum melt to introduce strontium, adding an aluminum-boron master alloy to introduce boron, and electromagnetic stirring at 720°C to 740°C; the process parameters for homogenization are set as follows: heating to 540°C to 550°C at a heating rate of 200°C per hour, holding at that temperature for 4 to 6 hours, and cooling to room temperature using strong air to solidify the segregated state of strontium atoms at the iron-containing impurity phase interface and induce the transformation of the needle-like β phase to the spherical α phase.

[0011] Preferably, in step S3, the sizing zone region of the splitting combination mold is constructed to have specific rheological resistance characteristics, and the ratio of the length of the sizing zone to the wall thickness of the profile is set to 0.8 to 1.2; the rheological resistance characteristics are coordinated with the propulsion speed of the main cylinder to establish a hydrostatic pressure field in the deformation zone that is sufficient to suppress the nucleation of micro-cavities; the hydrostatic pressure field and shear thinning work together to maintain the continuity and compactness of the physical interface between the iron-containing impurity phase and the aluminum matrix during the extrusion deformation process, and prevent interface tearing.

[0012] Preferably, in step S3, the average equivalent strain rate is a single control variable determined based on the rheological properties of the recycled aluminum ingot and the geometric constraints of the splitting die. Step S3 specifically includes: real-time monitoring of the main cylinder pressure and extrusion outlet speed of the extruder, and dynamic fine-tuning of the main cylinder advance speed according to the monitoring results, so as to ensure that the average equivalent strain rate is always not less than 15 seconds and not more than 25 seconds during the extrusion process of the recycled aluminum ingot throughout its entire length, thereby preventing abrupt changes in the viscosity of the interface enrichment layer caused by strain rate fluctuations.

[0013] Preferably, in step S3, the average equivalent rate of change... As a core process control parameter, the extrusion ratio of the split-flow combination die is... Extrusion exit speed of profiles and the equivalent diameter of recycled aluminum ingots Based on the following rheological relationships, the following is jointly determined: Among them, the extrusion exit speed Controlled between 12 and 18 meters per minute, equivalent diameter The geometric diameter of the cross-section of the recycled aluminum ingot is given; step S3 ensures that the interface enrichment layer is in a quasi-liquid sliding state by locking the above parameter combination, so that the micro-roughness of the profile surface reaches the level of primary aluminum.

[0014] Preferably, the online gradient freeze-quenching in step S4 includes a first cooling stage and a second cooling stage; the first cooling stage uses high-pressure water mist with a pressure of 0.5 MPa to 0.8 MPa, which is directly sprayed onto the surface of the profile, so that the surface temperature of the profile drops to below 350 degrees Celsius within 0.2 seconds, in order to freeze the high-temperature solid solution state between the iron-containing impurity phase and the aluminum matrix; the second cooling stage uses strong cold air with a flow rate of 15 m / s to 20 m / s to cool the entire profile to below 200 degrees Celsius, suppressing the non-uniform precipitation of the strengthening phase around the iron-containing impurity phase.

[0015] Preferably, in step S1, boron is dispersed in the aluminum matrix in the form of aluminum diboride or aluminum dodecylboride particles. The particles serve as heterogeneous nucleation sites for the iron-containing impurity phase during the solidification stage of step S1, and as micro-pinning points during the extrusion deformation stage of step S3. Together with the interfacial modification effect of strontium, they limit the excessive growth or merging of the iron-containing impurity phase in the shear flow field, ensuring that the extruded iron-containing impurity phase maintains a spherical or short rod-shaped morphology with an aspect ratio of less than 3.0.

[0016] Preferably, the method eliminates microscopic tearing defects and potential unevenness regions on the profile surface through the synergistic effect of shear thinning in step S3 and gradient freezing quenching in step S4. When the profile prepared by the method undergoes subsequent anodizing treatment, the growth rate of the oxide film on the surface remains consistent in the aluminum matrix region and the iron-containing impurity phase region, the thickness difference of the formed oxide film is less than 1.5 micrometers, and there are no black stripes or gray spots defects under visual observation, thus achieving electrochemical homogenization of the recycled aluminum surface.

[0017] Preferably, the temperature gradient in step S2 is pre-calculated and set based on the deformation heat data generated by the extrusion ratio and the main cylinder propulsion speed; the temperature gradient is used to offset the adiabatic temperature rise caused by the high strain rate in step S3, so that the actual deformation temperature of the recycled aluminum ingot flowing through the deformation zone is kept constant within the range of 500 degrees Celsius to 520 degrees Celsius, preventing the interface enrichment layer from desorption or redissolution due to local overheating.

[0018] Preferably, in step S3, the inner wall surface of the diversion combination mold is coated with a boron nitride lubricating coating; the boron nitride lubricating coating interacts tribologically with the oxide layer on the surface of the recycled aluminum ingot, and in conjunction with the internal lubrication effect of the interface enrichment layer, the friction coefficient of the profile surface is reduced to below 0.1, and the number of iron-rich phase particles with an equivalent diameter greater than 5 micrometers on the profile cross section is reduced to no more than 3 per square millimeter.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. Establish a specific average equivalent rheological rate field in the mold deformation zone, physically activate the chemically modified layer pre-placed on the iron-rich phase surface, causing a sudden drop in viscosity under strong shearing action, forming a dynamic lubrication channel between hard impurity particles and soft aluminum matrix, enabling hard particles to adaptively rotate and rearrange in intense plastic flow, avoiding cutting the matrix, eliminating microscopic tearing sources caused by the mismatch of two-phase rheological rates, and achieving matrix continuity and integrity of high impurity content recycled aluminum profiles under extrusion state.

[0021] 2. The rheological slip mechanism obtains a dense physical interface to cut off the microscopic channels through which the electrolyte penetrates deep into the particles during subsequent surface treatment, suppressing local high-energy regions caused by lattice distortion. The atomically dense interface bonding state ensures a uniform distribution of current density on the profile surface, blocking the path of acid retention corrosion and pinhole nucleation evolution, so that the recycled aluminum profile exhibits the same uniform luster and film adhesion as the original aluminum material after anodizing and electrophoretic coating.

[0022] 3. By utilizing the interface softening effect induced by high strain rate, the frictional resistance and deformation power consumption of the metal flow through the die sizing zone are reduced, offsetting the tendency of adiabatic temperature rise caused by high extrusion ratio. Thermodynamic and kinetic balance control avoids the generation of hot cracks on the profile surface, enabling the production line to stably produce thin-walled or complex cross-section profiles with demanding surface quality without reducing the extrusion speed, thus improving the engineering stability and production efficiency of recycled aluminum processing. The traditional impurity removal path that relies on high-cost melt purification or long-term high-temperature homogenization is abandoned. By using rheological control methods to utilize and transform the physical behavior of impurity phases, recycled aluminum raw materials with high iron content can be directly used to produce high-value-added decorative profiles, reducing raw material costs and energy consumption. Attached Figure Description

[0023] Figure 1 This is a flowchart of the recycled aluminum extrusion molding process with integrated feedback adjustment mechanism of the present invention;

[0024] Figure 2 This is a comparison diagram of the time-domain response of the extrusion master cylinder pressure under different process conditions of the present invention;

[0025] Figure 3 This is a schematic diagram of the principle of the multi-dimensional key process parameter collaborative control system of the present invention. Detailed Implementation

[0026] The embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of the invention. Those skilled in the art can make various modifications or substitutions based on the technical solutions and embodiments of the invention without departing from the scope of protection of the claims, and all such modifications or substitutions fall within the scope of protection of the invention.

[0027] This invention proposes a method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying. It comprises four core process stages: recycled aluminum melt composition control and ingot preparation, ingot thermodynamic gradient construction, critical rheological extrusion forming, and online gradient freeze-quenching. Each stage, through specific chemical component pre-setting and physical field control, synergistically addresses the rheological mismatch between hard impurity phases and the soft aluminum matrix in recycled aluminum during deformation. Furthermore, it addresses the issue of high iron content and the tendency for needle-like structures to form in recycled aluminum raw materials. The AlFeSi phase leads to the engineering problem of microscopic tearing on the extruded surface. This invention implements a chemical pre-setting process at the ingot interface, selecting an iron element mass percentage of [missing information]. to Using recycled aluminum melt as the base material, aluminum-strontium master alloy and aluminum-boron master alloy are added to the melt, and the mass ratio of strontium to iron in the melt is controlled at [value missing]. to Within the range, and control the mass percentage of boron within to Boron is dispersed as aluminum diboride or aluminum dodecaboride particles, serving as a heterogeneous nucleation core for the iron-containing impurity phase during solidification. Strontium atoms adsorb onto the surface of the iron-containing impurity phase, forming a strain-rate-sensitive interfacial enrichment layer. Heating the ingot to [the desired temperature]... Celsius Temperature and insulation Hours to After hours, the mixture was cooled to room temperature using strong winds. This homogenization process caused strontium atoms to diffuse to the iron-rich phase interface in the solid state, inducing needle-like structures. Phase transformation to aspect ratio less than spherical or short rod-shaped The phase is solidified, and the strontium enrichment state at the interface is solidified.

[0028] To address the thermodynamic problem of excessively high ingot tail temperature caused by heat accumulation during extrusion, leading to desorption of the interfacial enrichment layer or grain coarsening, this invention implements an axial thermodynamic gradient construction process. An induction heating device is used to heat the homogenized recycled aluminum ingot in stages, ensuring the initial temperature of the ingot is within a certain range. Celsius Within a Celsius range, the power distribution of the induction coil is adjusted to establish [something] along the axial direction of the ingot. Celsius The temperature gradient in degrees Celsius, where the temperature at the front end of the ingot extrusion is higher than that at the rear end, is calculated based on the deformation heat data generated by the extrusion ratio and the preset master cylinder propulsion speed. This gradient is used to offset the adiabatic temperature rise generated during subsequent high-strain-rate extrusion, ensuring that the actual deformation temperature of the ingot remains constant throughout its entire length as it flows through the die deformation zone. Celsius Within the temperature range of degrees Celsius; and addressing the dynamic challenge of hard iron-containing impurity phases cutting the matrix and generating micro-voids due to excessive rheological resistance during intense plastic flow in an aluminum matrix, this invention implements a critical strain rate rheological extrusion process. The ingot, after establishing a thermodynamic gradient, is fed into a split-flow die for extrusion. The extrusion ratio of this die... Set as to Length of sizing belt With profile wall thickness The ratio is set as to This is combined with a boron nitride lubricating coating applied to the inner wall of the mold.

[0029] A high hydrostatic pressure field is established in the deformation zone, and the main cylinder pressure and extrusion outlet speed of the extruder are monitored in real time. The main cylinder feed speed is dynamically adjusted, and the average equivalent deformation rate of the metal flow through the die deformation zone is measured. Always maintained at to The critical rheological range, the average equivalent strain rate The determination follows the following rheological relationship: ,in, The extrusion exit speed of the profile, its value range is: to ; This refers to the extrusion ratio; Let be the equivalent diameter of the cross-section of the recycled aluminum ingot. In the calculation, The unit is converted to meters per second. The unit is meters. Under the coupled effect of this strain rate and temperature window, the strontium interface enrichment layer pre-placed on the surface of the iron-containing impurity phase undergoes shear thinning with non-Newtonian fluid characteristics. The interface viscosity decreases and a quasi-liquid slip shell is formed, eliminating rigid friction between hard particles and the aluminum matrix, and driving the iron-containing impurity phase particles to undergo adaptive rotation and rearrangement in the flow field. To prevent the formation of a local potential difference due to non-uniform precipitation of the reinforcing phase around the iron-rich phase caused by slow cooling after profile extrusion, this invention implements an online gradient freeze-quenching process. Within seconds, it enters the first cooling stage, utilizing pressure... Megapascal to High-pressure water mist at megapascals is directly sprayed onto the profile surface, raising the surface temperature of the profile to [temperature range missing]. Dropped to within seconds Below 100 degrees Celsius, it freezes into a high-temperature solid solution state and enters the second cooling stage, using a flow rate of to The strong cold air cooled the entire profile to Below Celsius.

[0030] Example 1: This example focuses on the high-speed extrusion molding scenario of exterior parts for consumer electronics products, specifically demonstrating the process implementation of the method of the present invention when processing recycled aluminum with high iron content. The product being manufactured has a wall thickness of [missing information]. The tablet computer casing uses recycled aluminum raw materials with a high iron content (by weight). This raw material is difficult to extrude at high speed under conventional processes due to scratches from hard, iron-containing impurities on the matrix. Reducing the extrusion speed would result in insufficient production efficiency to meet cost requirements, while increasing the speed would easily lead to micro-tears and black streaks during anodizing. In the smelting stage, this invention establishes a chemical basis for interface modification targeting the iron-containing impurity phase by adding aluminum-strontium master alloys and aluminum-boron master alloys to the recycled aluminum melt, thereby controlling the strontium content in the melt to a specific level. This locks the mass ratio of strontium to iron at a certain value. And control the boron content at At this point, the diffusely distributed aluminum diboride particles act as heterogeneous nucleation sites for the iron-containing impurity phase during solidification. Combined with the interfacial adsorption of strontium atoms, this process further enhances the formation of the ingot. -AlFeSi phase transformation to aspect ratio less than spherical The process involves heating the ingot and establishing an axial thermodynamic gradient, then using an induction heating device to bring the ingot extrusion tip temperature to [a certain level]. The temperature at the extrusion end is [temperature value missing]. Celsius, forming An axial temperature difference of 10 degrees Celsius is used to pre-compensate for the heat of extrusion deformation.

[0031] In the extrusion molding stage, the ingot with a temperature gradient is fed into the extrusion ratio. for In the flow splitting and combination model, based on the rheological relationship disclosed in the aforementioned specific embodiments... The extrusion process is controlled in a closed loop, where the equivalent diameter of the ingot is... for To stimulate the shear-thinning properties of the interface enrichment layer, the extrusion exit speed is increased. Set and maintain at The calculated velocity parameter results in the average equivalent strain rate of the metal flowing through the deformation zone of the mold. Stable at Nearby, this value is within the range defined by the claims of this invention. to Within the critical rheological range, under a high strontium-iron ratio, a strontium-enriched layer coating the surface of the iron-containing impurity phase is induced to produce a non-Newtonian fluid response, resulting in a sharp decrease in viscosity and the formation of a quasi-liquid slip shell. Under this critical rheological state, the hard iron-containing impurity phase particles undergo adaptive rotation and rearrangement in the intense plastic flow of the aluminum matrix through the interfacial slip shell, conforming to the matrix streamlines and ensuring the continuity and integrity of the aluminum matrix at the microscale. After the profile leaves the mold, it undergoes a two-stage intense cooling system. The surface temperature will drop to zero within seconds. Below 100 degrees Celsius, eventually cooled to Below 100 degrees Celsius, a dense interface structure formed by rheological control is solidified. After anodizing, the oxide film growth rate of the profile made with high-impurity recycled aluminum is uniform, with no visible color difference or gray spots. The surface gloss is consistent with that of the benchmark sample made with virgin aluminum.

[0032] Example 2: This example systematically verifies the decisive influence of the process parameters of the present invention on the rheological behavior of iron-containing impurity phases and the final profile surface quality by constructing a multi-dimensional control system and presenting quantitative data. In the experimental design, to ensure the consistency of the benchmark, all sample groups were selected with an iron content of [missing information]. The same recycled aluminum ingots are used as the base material, and the same die structure (extrusion ratio) is used. The experiment included three core sample groups for the cooling system: the sample group of this invention, which fully implemented the process flow of Example 1, i.e., the mass ratio of strontium iron in melt modification was [missing information]. Axial gradient heating temperature difference is Temperature (°C) and extrusion exit speed controlled at [value missing] degrees Celsius. The corresponding average equivalent rate of change is Control group A, as a partially missing control group, had melt modification parameters consistent with the sample group of this invention (Sr / Fe=0.20), but used conventional uniform heating (480 degrees Celsius) and reduced the extrusion speed to [missing information]. This makes the average equivalent rate of change only This simulates a common low-speed preservation strategy in the industry, a rate lower than that defined in this invention. Lower limit; Control group B, as the out-of-range control group, although gradient heating was performed, strontium was not added during the melt modification stage (Sr / Fe=0), but the same method as the sample group of this invention was forcibly used. The compression is performed at high speed.

[0033] After the experiment started, the fluctuation of the main cylinder pressure of the extruder was recorded in real time through a high-frequency data acquisition system. The sample of this invention showed a smooth main cylinder pressure curve throughout the steady-state extrusion phase, with a standard deviation of only [missing information]. This indicates that the flow resistance of the metal within the mold is constant and uniform. In contrast, control group B exhibits severe pressure oscillations in the initial stage of extrusion, with a standard deviation as high as [missing value]. Furthermore, intermittent sharp frictional noise was observed at the die exit, reflecting dry friction and mechanical engagement between the unmodified hard particles and the die sizing zone. To quantitatively evaluate the surface quality and microstructure characteristics of each sample group, extrusion was performed until the sample reached a steady state. After cutting the profile samples, the surface roughness (Ra) was measured using a white light interferometer, and the surface microstructure was observed using a scanning electron microscope (SEM). All samples underwent standard sulfuric acid DC anodizing treatment (film thickness...). The breakdown voltage of the oxide film was tested to characterize its compactness and electrochemical uniformity. Table 1 summarizes the key process parameters and measured performance data of each sample group.

[0034] Table 1: Comparison of Surface Quality and Rheological Characteristics of Extruded Profiles

[0035]

[0036] Referring to Table 1, the Ra value of the sample group of this invention is the lowest, only [value missing]. And the breakdown voltage is as high as This indicates that both the surface physical smoothness and chemical homogeneity have reached their optimal state. Although control group A achieved this through sacrifice... Production efficiency (speed is only that of the sample of this invention) To avoid large-scale physical tearing, but the Ra value still reached Furthermore, gray spots appear after anodizing, and the breakdown voltage drops to [a certain value]. When the strain rate is lower than At that time, the shear force is insufficient to induce sufficient thinning of the interfacial layer, even after chemical modification is completed, for large-sized [structures / products]. AlFeSi particles still microscopically plough the matrix, while the data for control group B is even more extreme, with its Ra value soaring to [value missing]. The breakdown voltage is only Furthermore, its surface is covered with visible black stripes.

[0037] Example 3: This example combines Figures 1 to 3 The extrusion method for recycled aluminum alloy profiles oriented towards anodizing and electrophoretic spraying is described, such as... Figure 1As shown, the process begins with recycled aluminum melt containing iron impurity phases, and proceeds sequentially through step S1, ingot interface chemical pre-setting. In this stage, the synergistic effect of strontium and boron is controlled to form an interface enrichment layer with strain rate sensitivity. Step S2, axial thermodynamic gradient construction, is then carried out to compensate for extrusion deformation heat by establishing an axial temperature gradient. Next, step S3, critical strain rate rheological extrusion, is performed. On the one hand, shear thinning is generated by physically activating the interface enrichment layer and eliminating rheological resistance. On the other hand, a closed-loop feedback control loop is connected, which dynamically fine-tunes the main cylinder advance speed by monitoring the main cylinder pressure and extrusion outlet speed, thereby maintaining the critical rheological range. Finally, step S4, online gradient freeze quenching, utilizes the freezing high-temperature solid solution state and the mechanism of inhibiting non-uniform precipitation of strengthening phases to finally produce highly adaptable recycled aluminum profiles.

[0038] like Figure 2 As shown in the figure, the graph illustrates the dynamic relationship between the extrusion time (in seconds) and the main cylinder pressure (in MPa). The solid line represents the sample group of this invention, whose pressure curve remains highly stable throughout the entire test cycle, demonstrating stable pressure characteristics. The dashed line represents control group B, whose pressure curve exhibits large-scale up-and-down oscillations, showing drastic pressure fluctuation characteristics. Figure 3 As shown, the process control system serves as the core hub, coordinating four key modules: the ingot interface chemical pre-setting module, which sets and controls the Sr / Fe mass ratio between 0.15 and 0.25 to form an interface enrichment layer; the axial thermodynamic gradient construction module, which is responsible for establishing an axial temperature gradient of 15°C to 20°C to compensate for deformation heat; the critical strain rate rheological extrusion module, which aims to maintain the average equivalent strain rate between 15 / s and 25 / s to physically activate shear thinning; and finally, the online gradient freeze-quenching module, which performs the operation of rapidly cooling to below 350°C within 0.5 seconds to freeze the high-temperature solution state. Furthermore, this system performs dynamic fine-tuning of the main cylinder propulsion speed through the dashed path, triggered based on real-time monitoring feedback of the main cylinder pressure and outlet speed.

[0039] Example 4: This example addresses the problem of determining the ratio of die sizing band length to profile wall thickness during the extrusion of recycled aluminum profiles. It provides a systematic engineering calibration procedure. During the design and manufacturing stages of the diversion die, although it is known that a certain sizing band length needs to be maintained to establish back pressure, the ratio of sizing band length to wall thickness significantly impacts the interfacial compactness and extrusion pressure energy consumption—two mutually constraining performance indicators. Therefore, an optimal rheological resistance window needs to be calibrated. To determine this optimal ratio, this example employs a calibration process combining numerical simulation and physical die testing. A rheological constitutive model of recycled aluminum is established, and a series of models with different sizing band lengths are constructed in finite element analysis software. With profile wall thickness The ratio of the mold geometry model, the ratio range is set to to ,by The gradient is used, and the initial boundary condition is set to the ingot temperature. Celsius, extrusion exit speed The extrusion process was simulated, and the hydrostatic pressure distribution data and metal velocity variance at the inlet of the sizing zone were extracted from the simulation results.

[0040] Simulation results show that when the ratio is lower than At that time, the hydrostatic pressure at the inlet of the sizing belt was insufficient to completely suppress... - Cavity nucleation on the back surface of AlFeSi particles and a large velocity variance indicate uneven metal flow; when the ratio is higher than At the same time, although the hydrostatic pressure increases, the main cylinder pressure demand of the extruder increases exponentially, leading to excessive energy consumption and easily causing elastic deformation of the die, affecting the dimensional accuracy of the profile. Considering both interface density and energy consumption indicators, the optimal ratio range is preliminarily determined to be... to A quantitative criterion for hydrostatic pressure field suppression of microscopic holes was established, and the hydrostatic stress tensor trace along the traces of iron-containing phase particles was extracted in the finite element post-processing. Define the critical inhibition threshold ,in For aluminum substrate at 500 Yield strength below To determine the equilibrium partial pressure of hydrogen gas precipitated at the interface, we eliminate those that cannot be established within the first 30% of the sizing zone. The geometric configuration under 240MPa pressure conditions ensures the closure of interfacial micro-gaps before severe shear deformation occurs, preventing crack nucleation caused by rheological mismatch. Based on simulation results, three sets with ratios of [missing information] were manufactured. , and Physical mold testing was conducted on the test molds. During actual extrusion, the main cylinder pressure was monitored, and the cross-sectional microscopic analysis of the extruded profile was performed. The test data showed that all three sets of molds could operate stably within the rated extrusion pressure range, and the microscopic interface of the extruded profile was tightly bonded without microscopic tearing defects. Finally, based on the equipment capacity margin and product wall thickness tolerance requirements in actual production, the engineering setting value of the ratio of sizing band length to profile wall thickness was locked at [value missing]. to Within the range.

[0041] Example 5: This implementation provides a systematic on-site deployment pre-calibration and engineering debugging procedure. To ensure stable activation of the interfacial shear thinning mechanism in different batches of raw materials or different furnace production, a dynamic compensation logic based on microstructure feedback is established. Before formal mass production, a standardized rapid inspection and compensation procedure for the first furnace melt quality must be executed. Standard metallographic samples are prepared by randomly sampling aluminum liquid from the smelting furnace. Rapid cooling and polishing are completed within minutes, using a portable metallographic microscope. Observe the core field of view of the sample at magnification, and statistically analyze the average aspect ratio and roundness of the iron-rich phase within the field of view. If an aspect ratio greater than 1 is detected, The proportion of needle-like phases exceeds If the initial strontium content is insufficient or the reaction is incomplete, then according to the preset compensation model, the calculated amount of aluminum-strontium master alloy is added to the melt, and electromagnetic stirring is started. Minutes were taken until a second sample was taken and tested. This procedure eliminates the interference of raw material fluctuations on the interface preset effect by establishing a closed-loop feedback of metallographic morphology-composition compensation. A shear thinning threshold calibration procedure is executed to lock the physical process window. A standard test mold with an integrated rheological sensor is installed, and a pressure transmitter is placed at the inlet of the mold sizing zone. A stepped speed extrusion test is performed, with the main cylinder speed increment set to 0.5 mm / s. The steady-state extrusion pressure at each speed step is recorded. With the corresponding average strain rate , build Logarithmic constitutive curves, calculating the instantaneous strain rate sensitivity index Locate rheological inflection points and identify them. The critical velocity at which the value suddenly drops from 0.15 (matrix viscosity-dominated) to 0.05 (interfacial slip-dominated) is set as the lower limit of the critical rheological range. This will cause an adiabatic temperature rise. The rate is set to the upper limit at 30°C. This allows the measured physical values ​​to cover the empirical theoretical values.

[0042] In addition, to address the issue of actual strain rates deviating from set values ​​during extrusion due to die wear or equipment aging, this embodiment also constructs a real-time process fine-tuning procedure based on exit surface quality. An online surface defect detection system is deployed at the extruder exit to monitor the micro-tear density and gloss of the profile surface in real time. When a decrease in surface gloss or a micro-tear density exceeding one square millimeter is detected, the system will take action. When the warning threshold is reached, the control system automatically determines that the current strain rate has deviated from the critical shear thinning range, and the system then initiates adaptive adjustment logic to... To fine-tune the extrusion exit speed by step size Simultaneously monitor the master cylinder pressure change rate; when the master cylinder pressure fluctuation rate drops to... Once the surface gloss returns to the baseline value, the current speed is locked as the optimal process parameter for this batch of production. This dynamic debugging procedure ensures that the system always operates within the effective window of the interface sliding mechanism, regardless of changes in equipment status or environmental disturbances.

[0043] Example 6: This example addresses the issue of online quantitative detection and process adaptive feedback of surface micro-quality during the extrusion of recycled aluminum profiles. It provides a systematic engineering calibration procedure. In actual production, although online visual inspection systems are deployed, their sensitivity to different material reflectivity and changes in ambient light can lead to misjudgments or omissions of micro-tear features. Therefore, a defect feature extraction and threshold calibration process needs to be calibrated. To solve this problem, this example constructs an offline calibration and data filling procedure based on physical samples. By controlling extrusion process parameters, a series of standard recycled aluminum profile samples with different degrees of surface defects are intentionally prepared, covering five quality levels from defect-free to micro-tears. A laser confocal microscope is used to scan the micro-morphology of each level of sample, measuring the average depth, length, and distribution density of tears, establishing a physical defect database. These standard samples are then placed at the visual inspection station on the production line, under simulated light intensities (…). to ) and different extrusion speeds ( to Image acquisition is performed under specific conditions. By comparing feature values ​​extracted by image processing algorithms, such as grayscale variance and texture entropy, with measured data in the physical database, a multi-dimensional feature mapping model is constructed and trained. Based on the real-time acquired image features, the actual micro-tear density of the profile surface is calculated in reverse, and errors caused by ambient lighting and motion blur are automatically compensated. On this basis, an image feature threshold for triggering adaptive process adjustment is determined to strictly correspond to the per square millimeter in physical inspection. The critical state of a microscopic tear point.

[0044] In addition to addressing the differences in dynamic response characteristics of extruder hydraulic systems, this embodiment also establishes a pre-deployment calibration procedure. Before the system is officially put into closed-loop control, a step response test is performed: under both no-load and load conditions, a step signal is input to the main cylinder speed control valve, and the response time and overshoot of the main cylinder pressure are recorded. Based on the test results, the proportional, integral, and derivative coefficients of the controller are automatically calculated and updated using a preset PID parameter tuning algorithm to ensure that the system can respond quickly enough to the speed fine-tuning command. Speed ​​adjustment and pressure fluctuation suppression are completed within seconds.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the present invention.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying, characterized in that, Includes the following steps: Step S1, ingot interface chemical pre-setting, providing a homogenized recycled aluminum ingot, the matrix of which contains iron-containing impurity phases, controlling the mass ratio of strontium to iron in the recycled aluminum ingot to 0.15 to 0.25 through smelting batching, and controlling the mass percentage of boron to 0.01% to 0.03%, using strontium atoms to form an interface enrichment layer with strain rate sensitivity on the surface of the iron-containing impurity phase; Step S2, axial thermodynamic gradient construction: The recycled aluminum ingot is heated to an initial temperature range of 460°C to 480°C, and a temperature gradient of 15°C to 20°C is established along the axial direction so that the extrusion front end temperature of the recycled aluminum ingot is higher than the extrusion back end temperature, thus compensating for the deformation heat during the extrusion process. Step S3, critical strain rate rheological extrusion, the recycled aluminum ingot after the thermodynamic gradient is constructed is sent into a split combination die with an extrusion ratio of 40:1 to 60:

1. By coordinating the main cylinder propulsion speed and die geometry parameters, the average equivalent strain rate of the metal flowing through the die deformation zone is maintained in the critical rheological range of 15 to 25 seconds. The physical activation of the interface enrichment layer produces shear thinning, eliminates the rigid rheological resistance between the iron impurity phase and the aluminum matrix, and drives the iron impurity phase to undergo adaptive rotation and rearrangement in the flow field. Step S4, online gradient freezing quenching: within 0.5 seconds after the profile leaves the mold exit, apply a combination of strong wind and water mist cooling at a cooling rate greater than or equal to 300 degrees Celsius per minute to the profile until the temperature drops below 200 degrees Celsius to freeze it into a high-temperature solution state.

2. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, In step S1, the mass percentage of iron in the recycled aluminum ingot is 0.3% to 0.6%; the smelting batching includes: adding an aluminum-strontium master alloy to the recycled aluminum melt to introduce strontium, adding an aluminum-boron master alloy to introduce boron, and electromagnetic stirring at 720°C to 740°C; the process parameters for homogenization are set as follows: heating to 540°C to 550°C at a heating rate of 200°C per hour, holding at that temperature for 4 to 6 hours, and cooling to room temperature using strong air to solidify the segregated state of strontium atoms at the iron-containing impurity phase interface and induce the transformation of the needle-like β phase to the spherical α phase.

3. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, In step S3, the sizing zone region of the splitting combination mold is constructed to have specific rheological resistance characteristics. The ratio of the length of the sizing zone to the wall thickness of the profile is set to 0.8 to 1.

2. The rheological resistance characteristics are coordinated with the propulsion speed of the main cylinder to establish a hydrostatic pressure field in the deformation zone that is sufficient to suppress the nucleation of micro-cavities. The hydrostatic pressure field and shear thinning work together to maintain the continuity and compactness of the physical interface between the iron-containing impurity phase and the aluminum matrix during the extrusion deformation process, and prevent interface tearing.

4. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, In step S3, the average equivalent strain rate is a single control variable determined based on the rheological properties of the recycled aluminum ingot and the geometric constraints of the splitting combination die. Step S3 specifically includes: real-time monitoring of the main cylinder pressure and extrusion outlet speed of the extruder, and dynamic fine-tuning of the main cylinder advance speed according to the monitoring results, so as to ensure that the average equivalent strain rate is always not less than 15 seconds and not more than 25 seconds during the extrusion process of the recycled aluminum ingot throughout its entire length.

5. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, In step S3, the average equivalent rate of change As a core process control parameter, the extrusion ratio of the split-flow combination die is... Extrusion exit speed of profiles and the equivalent diameter of recycled aluminum ingots Based on the following rheological relationships, the following is jointly determined: Among them, the extrusion exit speed Controlled between 12 and 18 meters per minute, equivalent diameter The geometric diameter of the cross-section of the recycled aluminum ingot is given; step S3 ensures that the interface enrichment layer is in a quasi-liquid sliding state by locking the above parameter combination, so that the micro-roughness of the profile surface reaches the level of primary aluminum.

6. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, The online gradient freeze-quenching in step S4 includes a first cooling stage and a second cooling stage. In the first cooling stage, high-pressure water mist with a pressure of 0.5 MPa to 0.8 MPa is sprayed directly onto the surface of the profile, so that the surface temperature of the profile drops to below 350 degrees Celsius within 0.2 seconds, in order to freeze the high-temperature solid solution state between the iron impurity phase and the aluminum matrix. In the second cooling stage, strong cold air with a flow rate of 15 m / s to 20 m / s is used to cool the entire profile to below 200 degrees Celsius.

7. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, In step S1, boron is dispersed in the aluminum matrix in the form of aluminum diboride or aluminum dodecylboride particles. These particles serve as heterogeneous nucleation sites for the iron-containing impurity phase during the solidification stage of step S1, and as micro-pinning points during the extrusion deformation stage of step S3. Together with the interfacial modification effect of strontium, they limit the excessive growth or merging of the iron-containing impurity phase in the shear flow field, ensuring that the extruded iron-containing impurity phase maintains a spherical or short rod-shaped morphology with an aspect ratio of less than 3.

0.

8. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, The method eliminates microscopic tearing defects and potential unevenness regions on the profile surface through the synergistic effect of shear thinning in step S3 and gradient freezing quenching in step S4. When the profile prepared by the method is subsequently anodized, the growth rate of the oxide film on the surface is consistent in the aluminum matrix region and the iron-containing impurity phase region, the thickness difference of the formed oxide film is less than 1.5 micrometers, and there are no black stripes or gray spots defects under visual observation.

9. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, The temperature gradient in step S2 is pre-calculated and set based on the deformation heat data generated by the extrusion ratio and the main cylinder propulsion speed; the temperature gradient is used to offset the adiabatic temperature rise caused by the high strain rate in step S3, so that the actual deformation temperature of the recycled aluminum ingot flowing through the deformation zone is kept constant within the range of 500 degrees Celsius to 520 degrees Celsius.

10. The method for extruding recycled aluminum alloy profiles for anodizing and electrophoretic spraying according to claim 1, characterized in that, In step S3, the inner wall surface of the diversion combination mold is coated with a boron nitride lubricating coating; the boron nitride lubricating coating interacts tribologically with the oxide layer on the surface of the recycled aluminum ingot, and in conjunction with the internal lubrication effect of the interface enrichment layer, the friction coefficient of the profile surface is reduced to below 0.1, and the number of iron-rich phase particles with an equivalent diameter greater than 5 micrometers on the profile cross section is reduced to no more than 3 per square millimeter.

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