A dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles

Abstract

This application relates to the field of aluminum alloy processing and forming technology, and discloses a dynamic extrusion forming process for large-section thin-walled aluminum alloy profiles. The process includes a composite quenching medium composed of deionized water, temperature-sensitive polyether polyol, liquid sodium silicate, and diethylene glycol butyl ether. A preheated aluminum alloy ingot is hot-extruded to create an asymmetric frictional thermal gradient across the cross-section, resulting in a surface temperature of 520-540°C in the thin-walled region and 470-480°C in the thick-walled region. The medium is then sprayed with quenching fluid at a pressure of 0.15-0.25 MPa. Utilizing the difference in heat flux, the medium undergoes in-situ dehydration and expansion in the thin-walled region, along with phase segregation, to form a composite insulating microporous film for slow cooling. In the thick-walled region, a brittle shell is formed and peeled off by the fluid, achieving rapid cooling. This process achieves simultaneous cooling of the cross-section, eliminates internal residual thermal stress, and avoids macroscopic deformation and microscopic tearing defects in the profile.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy processing and forming technology, specifically to a dynamic extrusion forming process for large-section thin-walled aluminum alloy profiles. Background Technology

[0002] Large-section, thin-walled aluminum alloy profiles are widely used in aerospace, rail transportation, and industrial manufacturing, and are typically made from heat-treatable aluminum alloys such as the 6000 or 7000 series. After extrusion molding, in-line quenching is necessary to obtain the required mechanical properties, suppressing the precipitation of alloying elements and retaining supersaturated solid solutions. Because these aluminum alloy profiles have varying wall thicknesses across their cross-sections, the heat capacity and specific surface area differ significantly between the thick-walled and thin-walled regions. In existing conventional continuous quenching processes, the entire profile is usually subjected to the same cooling flow field or spray medium for heat exchange and cooling.

[0003] This indiscriminate heat transfer method results in rapid cooling of thin-walled regions, while heat dissipation is slow in the large-mass, thick-walled regions. Due to the severe mismatch in cooling rates across the cross-section, a huge temperature gradient is generated within the profile. This temperature difference causes asynchronous volume contraction of the metal matrix, leading to the accumulation of significant residual thermal stress at the interface between thick and thin walls and within the profile. When local thermal stress exceeds the material's high-temperature yield strength, it macroscopically causes severe longitudinal bending and torsional distortion in the profile, increasing the difficulty of subsequent straightening processes and even leading to product scrap. Simultaneously, when the thin-walled regions are subjected to severe thermal shock from conventional liquid cooling media, the surface metal instantly generates large tensile stresses due to cold contraction, easily inducing surface mechanical tearing and microcracks at the microscopic level. Existing technologies typically only passively mitigate deformation by reducing the overall quenching strength or employing complex localized shielding and air-cooling devices. However, the former leads to insufficient cooling in the thick-walled regions, sacrificing final mechanical properties, while the latter presents challenges due to complex equipment structures and difficulties in dynamic control, making it difficult to achieve adaptive differentiated cooling for different wall thicknesses within the same cross-section from a heat transfer mechanism perspective. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a dynamic extrusion forming process for large-section thin-walled aluminum alloy profiles. This process solves the problem that during the extrusion and quenching process of existing large-section aluminum alloy profiles, the severe mismatch between the cooling rates of the thick-walled and thin-walled regions leads to the accumulation of huge thermal stress inside, which in turn causes macroscopic bending distortion and microscopic tearing defects in the profiles.

[0005] To achieve the above objectives, the present invention provides a dynamic extrusion forming process for large-section thin-walled aluminum alloy profiles, comprising the following steps: This invention provides a dynamic extrusion molding process for large-section thin-walled aluminum alloy profiles, employing the following technical solution: A dynamic extrusion molding process for large-section thin-walled aluminum alloy profiles includes the following steps: preparing a composite quenching medium composed of 770-825g deionized water, 120-150g temperature-sensitive polyether polyol, 40-60g liquid sodium silicate, and 15-20g diethylene glycol butyl ether; feeding a preheated aluminum alloy ingot into a preheated extrusion die for hot extrusion, adjusting the extrusion speed to construct an asymmetric frictional thermal gradient across the cross-section. The surface temperature of the thin-walled region at the moment of extrusion die opening is 520-540℃, and the surface temperature of the thick-walled region is 470-480℃. A composite quenching medium with a system spray pressure of 0.15-0.25MPa is used to spray and quench the profile surface. By utilizing the difference in heat flux between the thin and thick walls, the composite quenching medium causes the inorganic salt dehydration and expansion and the polymer phase segregation in situ in the thin-walled region to form a composite heat-insulating microporous film for slow cooling. In the thick-walled region, a brittle shell is formed and peeled off by the fluid to achieve rapid cooling. After cooling, a large-section thin-walled aluminum alloy profile is obtained.

[0006] By adopting the above technical solution, due to the use of a quenching medium composed of temperature-sensitive polyether polyol and liquid sodium silicate, combined with a specific temperature gradient constructed at the extrusion die exit and low-pressure flow field control, adaptive binary phase change heat transfer boundaries are induced on the surfaces of different thickness regions of the profile. Therefore, the effects of synchronous cooling of the cross-section and elimination of residual thermal stress are achieved. The specific in-situ reaction and heat transfer regulation mechanism steps are as follows: Step 1, Construction and triggering conditions preparation of the asymmetric thermal gradient. Through die design and extrusion speed control, a high-temperature state in the thin-walled region and a medium-temperature state in the thick-walled region are artificially created at the moment of extrusion through the die orifice. The surface temperature of 520-540℃ in the thin-walled region exceeds the dehydration and foaming critical point of liquid sodium silicate and the thermodynamic cloud point of polyether polyol; the surface temperature of 470-480℃ in the thick-walled region is in the triggering trough range of the phase change between inorganic materials and polymers. Step 2, In-situ assembly and slow cooling control of the composite insulating microporous membrane in the thin-walled region. When a low-pressure spray liquid flow of 0.15-0.25 MPa contacts the surface of a thin-walled region at 520-540 °C, a simultaneous and synergistic phase change reaction occurs: First, the liquid sodium silicate component undergoes rapid interfacial dehydration under high heat flux, as shown in the following reaction formula: ; The water vapor generated during dehydration causes the silicate framework to expand and foam, forming an inorganic rigid porous layer with numerous closed micropores. Simultaneously, at the interface, the temperature of the thermosensitive polyether polyol aqueous solution far exceeds its cloud point, disrupting the hydrogen bonds between the polymer chains and water molecules, resulting in a reverse solubility phase segregation precipitation reaction. ; The precipitated high-viscosity polymer droplets rapidly penetrate and fill the pores of the inorganic silicate framework. The porous silicate framework provides mechanical stiffness to resist the physical shear of the liquid flow, while the polymer filling phase provides interfacial bonding and extreme pressure lubrication. The two cross-link and bond together to form a stable, adhered composite insulating microporous membrane on the thin-walled surface. This microporous membrane impedes convective heat transfer between the cooling fluid and the thin-walled metal substrate, transforming the intense nucleation boiling in the thin-walled region into slow film boiling, thus reducing the cooling rate of the thin-walled region. Step three: peeling and rapid cooling control of the brittle inorganic shell in the thick-walled region. At the surface of the thick-walled region (470-480℃), the heat flux is insufficient to maintain the high-temperature stable phase segregation of the polymer, and incomplete dehydration and foaming of liquid sodium silicate mainly occurs. The resulting single inorganic silicate framework lacks flexible polymer filling and exhibits a highly brittle structure. Under the physical kinetic energy scouring of a cold fluid of 0.15-0.25 MPa, the brittle inorganic porous shell develops microcracks and undergoes pulverizing peeling. The thick-walled substrate surface continuously exposes fresh metal contact liquid phase, maintaining efficient nucleation boiling heat conduction and achieving rapid cooling of the large-mass thick-walled region. Step four: Mechanical equilibrium is achieved. The cooling rate of the thin-walled region decreases due to physical adiabatic resistance, while the thick-walled region maintains high heat flux for rapid heat dissipation. The volume shrinkage rates of both regions during cooling are synchronized. This eliminates the stress accumulation within the cross-section caused by cooling rate mismatch, suppresses macroscopic bending and torsion of the profile, and simultaneously, the composite film cuts off the initiation and propagation path of thermal stress microcracks on the surface of the thin-walled working zone.

[0007] Preferably, the thermosensitive polyether polyol is a random copolymer formed by copolymerizing ethylene oxide and propylene oxide with n-butanol as the initiator, and the polymerization mass ratio of ethylene oxide to propylene oxide is 1:1.0-1.4. By adopting the above technical solution, using n-butanol as the initiator to initiate the copolymerization of ethylene oxide and propylene oxide, and randomly arranging the hydrophilic ethylene oxide segments and hydrophobic propylene oxide segments at a specific mass ratio of 1:1.0-1.4, the hydration capacity of the polymer molecular chains is adjusted. This polymerization structure establishes a specific thermodynamic cloud point boundary for the polymer, ensuring that it exhibits sharp phase segregation behavior when in contact with the high-temperature surface of the thin-walled region, generating a liquid polymer-rich phase with high adhesion, and guaranteeing the film-forming kinetic response speed of the composite film.

[0008] Preferably, the preparation method of the thermosensitive polyether polyol includes: mixing n-butanol and potassium hydroxide and then performing vacuum dehydration at a temperature of 105-115°C; subsequently, continuously adding a mixture of ethylene oxide and propylene oxide monomers in a mass ratio of 1:1.0-1.4; and carrying out a constant-temperature ripening reaction at a reaction temperature of 115-125°C and a reaction pressure of 0.2-0.4 MPa, followed by cooling and neutralization to obtain the final product. By adopting the above technical solution, setting the constant-temperature reaction temperature of 115-125°C and the reaction pressure of 0.2-0.4 MPa ensures that the chain growth reaction rate of the ring-opening copolymerization of epoxy monomers is uniform and stable. The cooling and neutralization step removes residual alkaline catalytic active centers, maintains the stability of the end structure of the polymer chain, and enables the obtained polyether polyol to have long-term physical stability when subsequently compounded into an aqueous quenching medium.

[0009] Preferably, in the vacuum dehydration step of preparing the temperature-sensitive polyether polyol, the absolute pressure of vacuum dehydration is controlled at 0.05-0.09 MPa, and the water content of the dehydrated system is controlled at 0.01-0.05% by mass. By adopting the above technical solution, the trace free water content in the initial system is controlled before the addition of the comonomer, avoiding water molecules acting as competitive bifunctional initiators to trigger side reactions that generate polyethylene glycol or polypropylene glycol homopolymers. This ensures the uniformity of the copolymer's molecular weight distribution and guarantees the concentration of precipitation temperature of the temperature-sensitive polyether polyol during the quenching and cooling process.

[0010] Preferably, in the step of preparing the composite quenching medium, each component is added sequentially at a temperature of 25-35°C and continuously stirred at a mechanical stirring speed of 300-500 rpm for 50-70 minutes until a homogeneous transparent solution is formed. By adopting the above technical solution, the continuous stirring action of a specific mechanical shear flow field within the room temperature range enables the inorganic silicate oligomers and high molecular weight polyether segments of different molecular weights to achieve micro-dispersion and hydration coating in the aqueous system, preventing phase separation during storage and transportation, and ensuring the uniformity of composition of the quenching medium reaching the profile surface.

[0011] Preferably, before the hot extrusion step, the aluminum alloy ingot is preheated to 450-480°C, and the extrusion die is preheated to 445-455°C. By adopting the above technical solution, the ingot preheating temperature is limited to 450-480°C, providing the basic thermodynamic conditions necessary for alloy solution treatment; the extrusion die is preheated to 445-455°C, reducing the initial temperature drop when the ingot contacts the die, and providing a set initial temperature platform for subsequently using the frictional work of extrusion deformation to build a cross-sectional thermal gradient.

[0012] Preferably, the cross-sectional dimensions of the aluminum alloy profile are as follows: the thickness of the thin-walled region ranges from 1.5 to 2.0 mm, and the thickness of the thick-walled region ranges from 20 to 25 mm. By adopting the above technical solution, the thickness dimension boundary where severe cooling mismatch occurs is defined. Profile cross-sections with this ratio will undergo macroscopic deformation under convective heat transfer. The phase change heat transfer control mechanism of this application has intervention effectiveness for reducing residual stress under this type of geometry.

[0013] Preferably, in the spray quenching step, an annular spray tank is set within a distance of 450-550mm from the extrusion die outlet to deliver the composite quenching medium to the nozzle for uniform spraying. By adopting the above technical solution and setting a spray buffer distance of 450-550mm, a time window is provided for the conduction of frictional heat generated during extrusion to the profile surface, ensuring that the surfaces of the thin-walled and thick-walled areas of the profile reach the set temperature difference boundary before contacting the liquid medium, thus laying the spatial conditions for the subsequent triggering of binary phase change heat transfer.

[0014] Preferably, after the spray quenching step, a media recycling step is included: the quenching reflux liquid is introduced into a gravity settling tank and held for 40-60 minutes, then pumped into a centrifuge at 3000-4000 rpm for slag removal. The purified liquid is cooled to 28-32°C and then recycled. By adopting the above technical solution, the quenching reflux liquid carries brittle inorganic silicate fragments washed away from the thick-walled region. Gravity settling combined with centrifugal separation removes solid residues, preventing fragments from clogging the nozzles and interfering with subsequent spray film formation. Cooling the purified liquid to 28-32°C restores the homogeneous dissolution state of the polyether polyol, achieving a closed-loop recycling of the media system.

[0015] Preferably, the aluminum alloy ingot is selected from an alloy system containing 95.0-99.0% aluminum by mass, specifically 6000 series or 7000 series aluminum alloys. By adopting the above technical solution, 6000 series and 7000 series aluminum alloys contain specific strengthening phase solid solutions, exhibiting high sensitivity to quenching cooling rates and thermal stress. The combined slow cooling and rapid cooling control mechanism provided by this process meets the metallurgical heat treatment requirements of this type of alloy, balancing high solid solubility maintenance with low deformation residual stress release.

[0016] This invention provides a dynamic extrusion forming process for large-section, thin-walled aluminum alloy profiles. It offers the following advantages: 1. This invention constructs an asymmetric frictional thermal gradient in the profile cross-section by controlling the extrusion speed, and uses a composite quenching medium containing temperature-sensitive polyether polyol and liquid sodium silicate to achieve adaptive differentiated cooling for different wall thicknesses in a single flow field. The high temperature in the thin-walled region triggers the dehydration expansion of inorganic salts and the segregation of polymer phases, generating a composite insulating microporous membrane in situ to reduce the heat transfer rate. The medium temperature in the thick-walled region only generates a brittle shell layer, which is eroded and peeled off by the low-pressure fluid, maintaining efficient heat dissipation. This allows the volume shrinkage rate of different thickness areas of the cross-section to be synchronized, eliminating internal residual thermal stress from a mechanical perspective and avoiding macroscopic longitudinal bending and torsional distortion of unstraightened profiles.

[0017] 2. The composite thermal insulation microporous membrane generated in situ on the surface of the thin-walled region in this invention has the dual physical functions of heat transfer inhibition and interfacial extreme pressure lubrication. The high-viscosity polyether polyol droplets that are precipitated permeate and fill the rigid silicate porous framework, maintaining the structural continuity of the membrane layer under the flushing of low-pressure cold fluid, constructing a stable physical barrier, blocking the high-frequency alternating hot and cold impact of aqueous fluid on the high-temperature thin-walled substrate, reducing the local cold shrinkage tensile stress amplitude of the surface metal, and effectively suppressing the initiation of mechanical tearing and thermal stress microcrack defects on the surface of the thin-walled working zone.

[0018] 3. This process incorporates a media circulation and recovery step, which removes the brittle inorganic silicate residue stripped from the thick-walled region along with the quenching reflux liquid. The residue is then purified by gravity settling and centrifugal separation. After the clarified liquid is cooled to below the thermodynamic cloud point of the polyether polyol, the polymer chains return to a homogeneous dissolved state and are pumped back to the spray tank for recycling. This eliminates the risk of solid debris clogging the nozzles and interfering with the subsequent film-forming process, enabling continuous closed-loop operation of the composite quenching liquid and meeting the requirements for long-term material stability and continuous extrusion under large-scale industrial production conditions. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Preparation Examples 1-3: Preparation Example 1: This preparation example provides a method for preparing a thermosensitive polyether polyol, including the following steps: In a stainless steel high-pressure reactor equipped with a temperature control and vacuum system, add 74g of n-butanol as an initiator and 58g of potassium hydroxide as a catalyst. Heat the reactor to 110°C, turn on the vacuum pump to evacuate to an absolute pressure of less than or equal to 0.09MPa, and dehydrate for 2 hours until the water content of the system is less than 0.05%.

[0021] The pressure inside the reactor was purged to 0.1 MPa using nitrogen gas. 1330 g of ethylene oxide and 1596 g of propylene oxide were mixed thoroughly and then continuously added dropwise into the reactor using a metering pump. The reaction temperature was controlled at 120°C, and the reaction pressure inside the reactor was maintained at 0.3 MPa by adjusting the dropping rate.

[0022] After the monomer was added, the reaction was aged at 120°C for 3 hours until the pressure inside the reactor stopped decreasing. The temperature was then lowered to 80°C, and glacial acetic acid was added to neutralize the catalyst until the system pH reached 7.0. Subsequently, magnesium silicate adsorbent was added, and the mixture was vacuum dehydrated at 110°C for 1 hour. Finally, the mixture was filtered through a 5μm pore size filter bag to obtain the target temperature-sensitive polyether polyol.

[0023] Testing revealed that the thermosensitive polyether polyol prepared in this example is a random copolymer of ethylene oxide and propylene oxide, with a number-average molecular weight (Mn) of 3000, a molecular weight distribution coefficient (Mw / Mn) of 1.15, and a kinematic viscosity of 280 mmHg at 40°C. 2 / s, and the thermodynamic cloud point of its aqueous solution was measured to be 70℃.

[0024] Preparation Example 2: This preparation example provides a method for preparing a thermosensitive polyether polyol, including the following steps: In a stainless steel high-pressure reactor equipped with a temperature control and vacuum system, add 74g of n-butanol as an initiator and 5.4g of potassium hydroxide as a catalyst. Heat the reactor to 110°C, turn on the vacuum pump to evacuate to an absolute pressure of less than or equal to 0.09MPa, and dehydrate for 2 hours until the water content of the system is less than 0.05%.

[0025] The pressure inside the reactor was purged to 0.1 MPa using nitrogen gas. 1136 g of ethylene oxide and 1590 g of propylene oxide were mixed thoroughly and then continuously added dropwise into the reactor using a metering pump. The reaction temperature was controlled at 115°C, and the reaction pressure inside the reactor was maintained at 0.2 MPa by adjusting the dropping rate.

[0026] After the monomer was added, the reaction was aged at 115°C for 3 hours until the pressure inside the reactor stopped decreasing. The temperature was then lowered to 80°C, and glacial acetic acid was added to neutralize the catalyst until the system pH reached 6.8. Subsequently, magnesium silicate adsorbent was added, and the mixture was vacuum dehydrated at 110°C for 1 hour. Finally, the mixture was filtered through a 5μm pore size filter bag to obtain the target temperature-sensitive polyether polyol.

[0027] Testing revealed that the thermosensitive polyether polyol prepared in this example is a random copolymer of ethylene oxide and propylene oxide, with a number-average molecular weight (Mn) of 2800, a molecular weight distribution coefficient (Mw / Mn) of 1.12, and a kinematic viscosity of 250 mmHg at 40°C. 2 / s, and the thermodynamic cloud point of its aqueous solution was measured to be 65℃.

[0028] Preparation Example 3: This preparation example provides a method for preparing a thermosensitive polyether polyol, including the following steps: In a stainless steel high-pressure reactor equipped with a temperature control and vacuum system, add 74g of n-butanol as an initiator and 6.2g of potassium hydroxide as a catalyst. Heat the reactor to 110°C, turn on the vacuum pump to evacuate to an absolute pressure of less than or equal to 0.09MPa, and dehydrate for 2 hours until the water content of the system is less than 0.05%.

[0029] The pressure inside the reactor was purged to 0.1 MPa using nitrogen gas. 1563 g of ethylene oxide and 1563 g of propylene oxide were mixed thoroughly and then continuously added dropwise into the reactor using a metering pump. The reaction temperature was controlled at 125°C, and the reaction pressure inside the reactor was maintained at 0.4 MPa by adjusting the dropping rate.

[0030] After the monomer was added, the reaction was aged at 125°C for 3 hours until the pressure inside the reactor stopped decreasing. The temperature was then lowered to 80°C, and glacial acetic acid was added to neutralize the catalyst until the system pH reached 7.2. Subsequently, magnesium silicate adsorbent was added, and the mixture was vacuum dehydrated at 110°C for 1 hour. Finally, the mixture was filtered through a 5μm pore size filter bag to obtain the target temperature-sensitive polyether polyol.

[0031] Testing revealed that the thermosensitive polyether polyol prepared in this example is a random copolymer of ethylene oxide and propylene oxide, with a number-average molecular weight (Mn) of 3200, a molecular weight distribution coefficient (Mw / Mn) of 1.18, and a kinematic viscosity of 300 mmHg at 40°C. 2 / s, and the thermodynamic cloud point of its aqueous solution was measured to be 75℃.

[0032] Examples 1-4: Example 1: This example provides a dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles, including the following steps: (1) 797g of deionized water was injected into the mixing tank. Under mechanical stirring at 400rpm, 135g of the thermosensitive polyether polyol prepared in Preparation Example 1, 50g of liquid sodium silicate, and 18g of diethylene glycol butyl ether were added slowly in sequence. The mixture was stirred continuously at room temperature of 30°C for 60 minutes to form a homogeneous transparent solution. The cloud point of the system was determined to be 70°C.

[0033] (2) Place the 6061 aluminum alloy round ingot in an induction heating furnace and heat it to 465°C. Preheat the split-flow combined extrusion die to 450°C. Start the hot extrusion press to extrude the metal through the die orifice. By adjusting the advance speed of the extrusion shaft, the surface temperature of the 1.8mm thick thin-walled metal flowing out of the die orifice reaches 530°C at the instant, while the surface temperature of the 22mm thick thick-walled metal flowing out of the die orifice is maintained at 475°C at the instant.

[0034] (3) A ring-shaped spray tank is set up 500mm away from the mold outlet. The prepared composite quenching medium is transported to the nozzle through a fluid pump and sprayed evenly onto the profile surface at a system spray pressure of 0.20MPa. The thin-walled area generates a silicate and polyether polyol composite heat-insulating microporous membrane in situ to achieve slow cooling, while the thick-walled area forms a brittle glass shell layer and is continuously peeled off under the scouring of the fluid to achieve rapid cooling.

[0035] (4) The quenching reflux liquid flows into the gravity settling tank and stays for 50 minutes, and then is pumped into a centrifuge with a speed of 3500 rpm for slag removal. The purified liquid flows through a plate heat exchanger to be cooled to 30°C and then pumped back to the water storage tank for recycling.

[0036] Example 2: This example provides a dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles, including the following steps: (1) 825g of deionized water was injected into the mixing tank. Under mechanical stirring at 300rpm, 120g of the thermosensitive polyether polyol prepared in Preparation Example 2, 40g of liquid sodium silicate, and 15g of diethylene glycol butyl ether were added slowly in sequence. The mixture was stirred continuously at room temperature of 25°C for 60 minutes to form a homogeneous transparent solution. The cloud point of the system was determined to be 65°C.

[0037] (2) Place the 6061 aluminum alloy round ingot in an induction heating furnace and heat it to 450°C. Preheat the split-flow combined extrusion die to 450°C. Start the hot extrusion press to extrude the metal through the die orifice. By adjusting the advance speed of the extrusion shaft, the surface temperature of the thin-walled area with a thickness of 2.0 mm flowing out of the die orifice reaches 520°C at the instant, while the surface temperature of the thick-walled area with a thickness of 25 mm flowing out of the die orifice is maintained at 470°C at the instant.

[0038] (3) A ring-shaped spray tank is set up 500mm away from the mold outlet. The above-prepared composite quenching medium is transported to the nozzle through a fluid pump and sprayed evenly onto the surface of the profile at a system spray pressure of 0.15MPa. The thin-walled area generates a silicate and polyether polyol composite heat-insulating microporous membrane in situ to achieve slow cooling, while the thick-walled area forms a brittle glass shell layer and is continuously peeled off under the scouring of the fluid to achieve rapid cooling.

[0039] (4) The quenching reflux liquid flows into the gravity settling tank and stays for 60 minutes, and then is pumped into a centrifuge with a speed of 3000 rpm for slag removal. The purified liquid flows through a plate heat exchanger to be cooled to 28°C and then pumped back to the water storage tank for recycling.

[0040] Example 3: This example provides a dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles, including the following steps: (1) 770g of deionized water was injected into the mixing tank. Under mechanical stirring at 500rpm, 150g of the thermosensitive polyether polyol prepared in Preparation Example 3, 60g of liquid sodium silicate, and 20g of diethylene glycol butyl ether were added slowly in sequence. The mixture was stirred continuously at room temperature of 35°C for 60 minutes to form a homogeneous transparent solution. The cloud point of the system was determined to be 75°C.

[0041] (2) Place the 6061 aluminum alloy round ingot in an induction heating furnace and heat it to 480°C. Preheat the split-flow combined extrusion die to 450°C. Start the hot extrusion press to extrude the metal through the die orifice. By adjusting the advance speed of the extrusion shaft, the surface temperature of the 1.5mm thick thin-walled metal flowing out of the die orifice reaches 540°C at the instant, while the surface temperature of the 20mm thick thick-walled metal flowing out of the die orifice is maintained at 480°C at the instant.

[0042] (3) A ring-shaped spray tank is set up 500mm away from the mold outlet. The prepared composite quenching medium is transported to the nozzle by a fluid pump and sprayed evenly onto the surface of the profile at a system spray pressure of 0.25MPa. The thin-walled area generates a silicate and polyether polyol composite heat-insulating microporous membrane in situ to achieve slow cooling, while the thick-walled area forms a brittle glass shell layer and is continuously peeled off under the scouring of the fluid to achieve rapid cooling.

[0043] (4) The quenching reflux liquid flows into the gravity settling tank and stays for 40 minutes, and then is pumped into a centrifuge with a speed of 4000 rpm for slag removal. The purified liquid flows through a plate heat exchanger to be cooled to 32°C and then pumped back to the water storage tank for recycling.

[0044] Example 4: This example provides a dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles, including the following steps: (1) 789 g of deionized water was injected into the mixing tank. Under mechanical stirring at 400 rpm, 140 g of the thermosensitive polyether polyol prepared in Preparation Example 1, 55 g of liquid sodium silicate, and 16 g of diethylene glycol butyl ether were added slowly in sequence. The mixture was stirred continuously at room temperature of 30 °C for 60 minutes to form a homogeneous transparent solution. The cloud point of the system was measured to be 69 °C.

[0045] (2) Place the 7075 aluminum alloy round ingot in an induction heating furnace and heat it to 470°C. Preheat the split-flow combined extrusion die to 450°C. Start the hot extrusion press to extrude the metal through the die orifice. By adjusting the advance speed of the extrusion shaft, the surface temperature of the thin-walled area with a thickness of 1.8 mm flowing out of the die orifice reaches 535°C, while the surface temperature of the thick-walled area with a thickness of 22 mm flowing out of the die orifice is maintained at 478°C.

[0046] (3) A ring-shaped spray tank is set up 500mm away from the mold outlet. The prepared composite quenching medium is transported to the nozzle by a fluid pump and sprayed evenly onto the surface of the profile at a system spray pressure of 0.22MPa. The thin-walled area generates a silicate and polyether polyol composite heat-insulating microporous membrane in situ to achieve slow cooling, while the thick-walled area forms a brittle glass shell layer and is continuously peeled off under the scouring of the fluid to achieve rapid cooling.

[0047] (4) The quenching reflux liquid flows into the gravity settling tank and stays for 50 minutes, and then is pumped into a centrifuge with a speed of 3500 rpm for slag removal. The purified liquid flows through a plate heat exchanger to be cooled to 30°C and then pumped back to the water storage tank for recycling.

[0048] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference is that liquid sodium silicate was not added in the preparation of the composite quenching medium, and 50g of liquid sodium silicate was replaced with an equal mass of deionized water, while the rest were the same.

[0049] Comparative Example 2: Compared with Example 1, the difference is that the temperature-sensitive polyether polyol was not added in the preparation of the composite quenching medium, and 135g of the temperature-sensitive polyether polyol prepared in Example 1 was replaced with an equal mass of deionized water, while the rest were the same.

[0050] Comparative Example 3: Compared with Example 1, the difference is that in the low-pressure, high-flow-rate interface adaptive quenching step, the system spray pressure is adjusted to 1.0 MPa, while the rest are the same.

[0051] Comparative Example 4: Compared with Example 1, the difference lies in that in the ingot preheating and asymmetric frictional heat gradient construction steps, by adjusting the pushing speed of the extrusion shaft, the surface temperature of the thin-walled region with a thickness of 1.8 mm flowing out of the die hole and the surface temperature of the thick-walled region with a thickness of 22 mm flowing out of the die hole are both maintained at 475°C, and the rest are the same.

[0052] Comparative Example 5: Compared with Example 1, the difference lies in the fact that in the ingot preheating and asymmetric frictional heat gradient construction steps, by adjusting the pushing speed of the extrusion shaft, the surface temperature of the thin-walled region with a thickness of 1.8 mm flowing out of the die hole and the surface temperature of the thick-walled region with a thickness of 22 mm flowing out of the die hole both reach 530°C, and the rest are the same.

[0053] Test Examples 1-5: Test Example 1: Calibration Test of Heat Flux and Dynamic Heat Transfer Coefficient Based on Variable Temperature Interface This test case uses a standard interface heat transfer calibration method based on the reverse heat conduction problem to quantitatively evaluate the dynamic heat transfer behavior of the quenching medium at different initial surface temperatures in the examples and comparative examples.

[0054] The experiment used a standard cylindrical temperature probe made of 6061 aluminum alloy with a built-in multi-channel K-type thermocouple array. The surface roughness Ra of the probe was polished to 1.6μm.

[0055] The temperature probe was placed in the induction heating tube, and the initial surface temperature of the probe was precisely heated and kept constant at 475℃ and 530℃ respectively, to simulate the temperature boundary conditions of the thick-walled area and the thin-walled area at the moment of material discharge during the actual extrusion process.

[0056] The fluid spray system was activated, and the quenching media of Example 1 and Comparative Examples 1 to 3 were extracted respectively. According to the system spray pressure set for each scheme, the probe surface at high temperature was cooled by constant pressure spray through a standard solid conical nozzle.

[0057] The data acquisition system synchronously records the temperature-time cooling curves of each measuring point inside the probe at a sampling frequency of 1000Hz. After the test, the acquired temperature data is imported into calculation software based on a nonlinear reverse heat conduction algorithm to inversely solve for the transient surface heat flux density and macroscopic convective heat transfer coefficient of the solid-liquid interface. The maximum heat flux density peak value and the average heat transfer coefficient within the first 2 seconds after spray contact are extracted as evaluation indicators.

[0058] Test results: Table 1. Test results of maximum heat flux density and heat transfer coefficient at the initial cooling stage of the variable temperature interface.

[0059] Results analysis: According to the data in Table 1, Example 1 exhibits drastically different heat transfer parameters at initial interface temperatures of 475°C and 530°C. When the initial interface temperature is 475°C, the maximum heat flux density at the interface reaches 4.21 MW / m². 2 The average heat transfer coefficient is as high as 18543 W / (m²). 2 • K). This numerical range indicates that at this temperature, sodium silicate did not undergo significant dehydration and expansion. The brittle glassy thin shell formed on the surface physically peeled off under the scouring of 0.20 MPa fluid, and the solid-liquid interface was in the nucleation boiling stage with high heat transfer efficiency. When the initial interface temperature rose to 530 °C, the maximum heat flux density of Example 1 sharply decreased to 0.89 MW / m³. 2 The average heat transfer coefficient decreased to 3217 W / (m²). 2The precipitous drop in heat transfer capacity confirms that after crossing the critical point of 500℃, the intense dehydration and expansion reaction of sodium silicate and the phase segregation precipitation process of polyether polyol were coupled in situ, forming a porous composite thermal insulation microporous membrane with mechanical strength on the metal surface. This membrane forcibly blocked the convective heat transfer of the fluid, keeping the system stably maintained in the film boiling heat transfer zone.

[0060] Comparative Example 1, due to the absence of the inorganic expanding film-forming agent liquid sodium silicate in its formulation, saw its heat transfer coefficient at 530℃ recover to 9842 W / (m²). 2 • K). The polymeric liquid film formed by the precipitation of pure polyether polyol lacks rigid framework support at high temperatures, and part of the liquid film undergoes turbulent delamination under the action of fluid shear force, failing to form a continuous and stable thermal barrier. Comparative Example 2, due to the absence of thermosensitive polyether polyol, has a heat transfer coefficient that further increases to 13105 W / (m). 2 ·K). Although sodium silicate alone can expand and foam at 530℃, the resulting inorganic framework lacks the coating and pore filling of high-viscosity polymers, and the structure is brittle. Under the combined effects of thermal shock from spray cooling and fluid kinetic energy, it is easy to break and fall off, causing the matrix to be re-exposed to a high heat flux density heat exchange environment.

[0061] In Comparative Example 3, after increasing the injection pressure to 1.0 MPa, the maximum heat flux density at the interface at 530℃ reached 4.67 MW / m³. 2 The heat transfer coefficient reaches 19680 W / (m²). 2 The heat transfer level, exceeding even the nucleate boiling state at 475°C in Example 1, was significantly higher than that achieved by the high-pressure fluid. The extremely high shear kinetic energy generated by the high-pressure fluid completely destroyed the composite insulating microporous membrane structure generated in situ at the interface, allowing the medium to directly scour the high-temperature metal surface and rendering the membrane temperature control mechanism against thermal stress distortion completely ineffective. The test data objectively verified the synergistic necessity of low-pressure, high-flow-rate flow field control and specific interfacial chemical reactions in the construction of adaptive heat transfer boundaries.

[0062] Test Example 2: Dynamic Adhesion and Fluid Erosion Retention Test This test case uses a weighing analysis method under simulated thermal shock and fluid scouring conditions to quantitatively determine the anti-peeling ability of the solid-liquid interface film layer generated under different formulations and process parameters.

[0063] A standard 6061 aluminum alloy test block with dimensions of 100mm×100mm×5mm was cut, and the surface oil was cleaned with anhydrous ethanol by ultrasonic cleaning and then dried. The initial mass of the test block was weighed and recorded using an analytical balance with an accuracy of 0.1mg.

[0064] The test block was placed in a resistance heating furnace, heated and kept at a constant temperature of 530°C to simulate the high-temperature surface state of the thin-walled section of the profile at the moment of material discharge.

[0065] The high-temperature test block was quickly moved to the testing station, the spray system was started, and the media of Examples 1 to 4 and Comparative Examples 1 to 3 were extracted respectively. The central area of ​​the test block was continuously sprayed with constant pressure through standard nozzles with fixed angle and distance, and the rinsing time was set to 10 seconds.

[0066] After spraying, immediately stop the fluid supply and collect the aluminum alloy test blocks with residue on their surfaces. Place them in a vacuum oven at 120°C and dry for 4 hours until constant weight. After removing and cooling to room temperature, weigh the total mass of the test blocks again. Subtract the initial mass from the total mass after drying to calculate the total mass of residue on the test block surface, and convert it to the film adhesion amount per unit area.

[0067] Test results: Table 2. Test results of dynamic adhesion of high-temperature interfacial film under different media and scouring pressures

[0068] Results analysis: According to the data in Table 2, under high temperature of 530°C and spray pressure of 0.15 to 0.25 MPa, the surface residue mass distribution per unit area in Examples 1 to 4 ranged from 15.27 to 21.64 g / m². 2 Between these temperatures, a relatively thick solid residue layer remained on the surface of the test block. This test result indicates that within this temperature range, the volume expansion reaction of sodium silicate beyond its dehydration expansion critical point resulted in in-situ recombination with the phase segregation precipitation process of polyether polyol due to its temperature exceeding its cloud point. The precipitated high-viscosity polymer filled and encapsulated the porous inorganic silicate framework, forming a composite microporous membrane with mechanical strength and adhesion, capable of resisting the physical shear erosion of low-pressure fluids and achieving stable adhesion of the membrane layer to high-temperature surfaces.

[0069] In Comparative Example 1, the liquid sodium silicate component was removed, and the surface residue mass was reduced to 1.22 g / m³. 2 In a pure polymer system, the liquid polymer film formed by the precipitation of polyether polyols above their cloud point lacks the support of an inorganic rigid framework. Under the combined action of bubble disturbance generated by nucleation boiling on the substrate surface and the external shear force of the 0.20 MPa fluid, the liquid polymer film undergoes turbulent shearing and cannot maintain a continuous physical coverage on the metal surface.

[0070] In Comparative Example 2, the thermosensitive polyether polyol component was removed, and the surface residue mass was 3.86 g / m³. 2While liquid sodium silicate undergoes dehydration and expansion upon contact with a 530°C surface, the resulting inorganic silicate framework's internal pores remain unfilled by the polymer, resulting in a brittle structure. Under continuous cold fluid thermal shock and mechanical erosion, the brittle inorganic porous layer develops microcracks and undergoes pulverizing peeling, leading to low adhesion. This data confirms the structural coupling effect between inorganic salts and polymers in constructing an erosion-resistant insulation layer.

[0071] Comparative Example 3 used the composite medium from Example 1, but increased the spray pressure to 1.0 MPa; the measured surface residue mass was only 2.11 g / m³. 2 The high system fluid pressure is converted into high-speed shear kinetic energy acting directly on the interfacial film. This shear stress exceeds the mechanical yield limit of the silicate-polyether polyol composite structure, causing the insulating foam membrane, which was originally formed in the thin-walled high-temperature region, to be forcibly destroyed by the fluid and peeled off from the substrate surface. The disruption of mechanical equilibrium leads to the failure of the in-situ self-assembled film structure, demonstrating that the low-pressure, high-flow-rate flow field control conditions have a physical constraint effect on maintaining the adaptive binary heat transfer boundary.

[0072] Test Example 3: Online Cooling Rate and Dynamic Temperature Difference of Profiles This test case relies on the extrusion production line and adopts online drag-and-drop temperature measurement technology to measure the real internal cooling curve of large-section aluminum alloy profiles during the quenching process under various formulas and process control parameters in real time.

[0073] Cut a K-type armored thermocouple probe with a high-temperature resistant compensation wire. At the extruder outlet, before the aluminum alloy profile is extruded from the die and enters the spray tank, quickly drill temperature measurement blind holes in the center area of ​​the thin wall (thickness median line) and the center area of ​​the thick wall (thickness median line) of the profile cross-section. Rigidly fix the thermocouple probe to the bottom of the hole to ensure that the probe is in close contact with the metal substrate.

[0074] The extrusion and spray quenching process is initiated, and continuous production is carried out according to the process parameters set in Examples 1 to 4 and Comparative Examples 1 to 5. Thermocouples are synchronously passed through a multi-stage annular spray water cooling zone with a length of 500mm along with the profile. The data acquisition module records the temperature change data of two measuring points over time at a frequency of 100Hz in real time until the temperature of both measuring points drops below 200℃ and then stops the acquisition.

[0075] The collected cooling curve data were imported into the processing terminal, and the temperature range from 400℃ to 200℃ was selected to calculate the average cooling rate of the thin-walled and thick-walled regions. Throughout the entire quenching process data, the maximum instantaneous temperature difference between the thick-walled and thin-walled regions on the same cross-section was extracted by point-by-point subtraction. Test results: Table 3. Test data of average cooling rate and maximum dynamic temperature difference of profiles in each group during quenching.

[0076] Results analysis: According to the data in Table 3, the average cooling rate of the thin-walled region in Examples 1 to 4 ranged from 38.67 to 45.28 °C / s, while the average cooling rate of the thick-walled region ranged from 39.41 to 43.86 °C / s. The maximum instantaneous temperature difference across the cross-section was controlled within 22 °C. The data indicates that, relying on the transverse temperature difference established by the extrusion of the profile itself, the quenching medium spontaneously constructed a binary heat transfer boundary in the same flow field. In the thin-walled region above 520 °C, the dehydration and expansion of sodium silicate and the phase segregation of polyether polyol were triggered. The resulting composite microporous membrane impeded convective heat transfer, causing the cooling rate of the thin-walled region to decrease to a level matching that of the thick-walled region. The thick-walled region remained below 480 °C, not reaching the critical condition for violent foaming of inorganic salts. The brittle shell formed was peeled off under the scouring of water flow, maintaining the high heat flux of nucleation boiling. The synchronicity of the cross-sectional cooling rate eliminated the residual thermal stress caused by uneven volume shrinkage.

[0077] In Comparative Example 1, without the addition of sodium silicate, the cooling rate in the thin-walled region surged to 125.46℃ / s, with a cross-sectional temperature difference reaching 184.6℃. Due to the lack of an inorganic expansion framework, the polymer liquid film could not exist stably in the thin-walled region, and local metal was directly exposed to the aqueous phase, resulting in intense nucleation boiling heat transfer and large cold contraction stress in the thin wall. In Comparative Example 2, without the addition of polyether polyol, the foamed layer generated by pure sodium silicate was brittle and fractured and peeled under thermal shock, also failing to hinder heat transfer, with a cooling rate in the thin-walled region reaching 132.18℃ / s. Comparative Example 3 used 1.0MPa high-pressure spraying. The mechanical shear force of the high-pressure jet directly destroyed the interfacial insulation film structure, and the thin-walled region lost its slow cooling barrier, with the cooling rate rising back to 110.52℃ / s and the cross-sectional temperature difference expanding to 156.2℃, confirming the impact of disrupted hydrodynamic conditions on the stability of the interfacial film.

[0078] Comparative Example 4 eliminated the initial temperature gradient, resulting in a uniform discharge temperature of 475℃ across the cross-section. Neither the thin-walled nor the thick-walled sections could trigger the silicate phase change foaming mechanism. Due to its large specific surface area, the thin-walled region experienced a cooling rate of 115.81℃ / s, with a cross-sectional temperature difference of 142.1℃. Comparative Example 5 achieved a discharge temperature of 530℃, at which point the thick-walled region also exceeded the inorganic foaming critical point, and a composite insulating microporous film was also formed on the thick-walled surface. The cooling rate in the thick-walled region sharply decreased to 28.47℃ / s. Although the cross-sectional temperature difference narrowed to 45.8℃, the overall cooling rate of the large-section metal was significantly lower than the critical quenching rate required for alloy solution treatment. The lack of a thermodynamic triggering gradient prevented the medium from undergoing spatially adaptive phase change differentiation.

[0079] Test Example 4: Determination of Macroscopic Geometric Tolerances and Residual Stress This test case measures the macroscopic physical dimensional deformation and internal mechanical state of aluminum alloy profiles after extrusion and quenching and cooling to room temperature under different process parameters, in order to evaluate the actual suppression effect of composite medium and temperature control process on thermal stress distortion.

[0080] On the cooling bed at the back end of the extrusion production line, aluminum alloy profiles of a fixed length that have undergone quenching processes in Examples 1 to 4 and Comparative Examples 1 to 5 and have not undergone any manual mechanical stretching and straightening processes are randomly selected as test samples. The length of each sample is uniformly 3000 mm.

[0081] Place the sample on a large cast iron inspection platform with an accuracy grade of 0. Establish a measurement baseline along the length of the profile. Use a feeler gauge and a knife-edge ruler to measure the maximum vertical gap between the bottom surface of the sample and the platform surface, calculate and convert it to longitudinal curvature per meter. Use a high-precision digital inclinometer to measure the deflection angles of the sample's two ends relative to the reference horizontal plane, and calculate the difference, converting it to torsion per meter.

[0082] The transition fillet area where a 1.8mm thick thin wall and a 22mm thick thick wall meet on the cross-section of the profile is selected as the stress test target area. The oxide layer and residual deposits on the surface of the target area are removed using a grinder, with the grinding depth controlled within 0.1mm. The area is then cleaned with anhydrous ethanol and dried.

[0083] A resistance strain gauge was attached to the center of the target area, and a high-precision static strain gauge was connected to complete the bridge balance and zeroing. A blind hole with a diameter of 1.5 mm and a depth of 2.0 mm was drilled in the center of the strain gauge using a miniature drilling device. After drilling, the micro-strain values ​​released in each channel were read, and the macroscopic residual tensile stress in the interface region of the cross section was calculated based on the elastoplastic mechanics theoretical model. Five independent specimens were tested in each group, and the arithmetic mean of the data was taken.

[0084] Test results: Table 4. Test results of macroscopic form and position tolerances and residual stress of aluminum alloy profiles

[0085] Results analysis: According to the data in Table 4, the longitudinal curvature of Examples 1 to 4 was controlled between 0.51 and 0.87 mm / m, the torsion was distributed between 0.12 and 0.25° / m, and the residual tensile stress at the interface between the thin and thick walls was maintained between 32.7 and 45.2 MPa. Test values ​​show that the formulations in these examples, combined with the set temperature boundary conditions and fluid pressure, achieved adaptive adjustment of heat transfer flux on the profile cross-section. The inorganic porous skeleton generated in situ on the high-temperature surface of the thin wall and the cross-linking of the polymer segregated droplets formed a composite insulating microporous membrane that effectively suppressed localized supercooling shrinkage in the thin-walled region. The brittle inorganic shell formed on the thick-walled surface continuously peeled off under the action of low-pressure fluid, maintaining efficient heat conduction from the internal metal to the external cold fluid. The volume shrinkage rate of each region of the profile cross-section reached synchronization during the cooling process, eliminating the internal stress accumulation caused by the temperature gradient from a physical and mechanical perspective, and ensuring the original dimensional accuracy of the extruded aluminum profile without mechanical straightening.

[0086] In Comparative Example 1, the liquid sodium silicate in the formulation was replaced with deionized water. Due to the lack of an inorganic expansion film-forming mechanism, the residual tensile stress measured increased sharply to 218.6 MPa, and the macroscopic longitudinal curvature reached 9.42 mm / m. The thin-walled region experienced intense nucleation boiling heat transfer in the single polyether polyol aqueous solution, resulting in instantaneous material contraction. This generated a huge mutual attraction between the material and the relatively slow-cooling thick-walled, large-volume metal, leading to severe bending and torsional deformation of the profile. In Comparative Example 2, without the addition of temperature-sensitive polyether polyol, the single silicate foam layer underwent brittle fracture and peeling under the thermal shock of cooling water. The thin-walled region also lost its thermal insulation barrier, and the residual tensile stress rose to 195.3 MPa.

[0087] Comparative Example 3 increased the system injection pressure to 1.0 MPa. The strong physical shear force generated by the high-pressure fluid destroyed the composite insulation layer structure formed on the thin-walled surface, allowing the cooling fluid to directly penetrate the film and contact the thin-walled metal substrate, inducing a residual tensile stress as high as 163.8 MPa. Comparative Example 4 eliminated the extreme temperature difference at the outlet. Neither the thin-walled nor the thick-walled temperatures reached the critical point for triggering the inorganic salt dehydration phase transformation. The cross-sectional cooling process was entirely controlled by the difference in heat capacity caused by the metal's own wall thickness, generating an extreme thermal stress of 241.5 MPa, resulting in the most severe deformation in the test group. Comparative Example 5 increased the outlet temperature of the entire cross-section above the foaming trigger point. Although the overall cooling difference was reduced, the full-surface composite insulation layer coverage disrupted the normal quenching cooling process required for alloy solidification. The slow internal heat conduction prevented the residual stress from being released through a rapid and uniform phase transformation process. The measured data confirmed the synergistic limiting relationship between polymer reverse solubility thermodynamics, inorganic salt phase transformation kinetics, and fluid physical parameters in controlling aluminum alloy distortion.

[0088] Test Example 5: Statistical Analysis of Detection Rate of Microcracks and Tearing Defects on the Surface of Thin-Walled Working Zones This test case uses the industry-standard dye penetrant testing method to conduct a large-scale blind test and statistical analysis of the macroscopic continuity and microcrack frequency of the surface of the thin-walled working zone of the profile after extrusion and cooling.

[0089] From the finished product batches treated with the quenching processes of Examples 1 to 4 and Comparative Examples 1 to 5, continuous profiles with a total cumulative length of 100 meters were randomly cut. The thin-walled areas of the profiles were degreased and cleaned with an organic solvent cleaner to remove residual dielectric film and oil stains, and then allowed to air dry at room temperature.

[0090] Apply a special coloring penetrant containing red dye evenly to the surface of the thin-walled working zone of the profile, keep the surface continuously wet, and let it stand for 20 minutes to allow the penetrant to fully penetrate into the micro-defects of the surface opening under capillary action.

[0091] After the penetration stage, wipe the profile surface with a lint-free cloth dampened with a special cleaning agent to completely remove any excess red penetrant that has not penetrated the substrate, ensuring the surface regains its metallic color without any base color residue. Then, evenly spray a thin layer of white developer onto the cleaned area and let it stand at room temperature for 10 minutes.

[0092] Under a standard white light source with an illumination of 1200 lux, the thin-walled surface after imaging was fully inspected using the naked eye and a 5x industrial magnifying glass. Spot-like and linear traces formed by the red dye seeping from the interior were recorded. The cumulative number of microcracks and surface tears was counted, and the frequency of defect occurrence per 100 meters of test length was calculated and output.

[0093] Test results: Table 5. Statistical results of color penetrant testing for surface defects in thin-walled areas of aluminum alloy profiles.

[0094] Results analysis: According to the data in Table 5, the detection frequency of defects in the thin-walled regions of Examples 1 to 4 ranged from 0 to 2 times per 100 meters. The data indicates that, under this formulation system and the set temperature and hydrodynamic boundary conditions, the polyether polyol and inorganic silicate composite microporous membrane generated in situ on the thin-walled surface provides thermal insulation and slow cooling while also acting as an extreme pressure lubricating layer between the high-temperature solid and liquid interfaces. The precipitated high-viscosity polyether polyol droplets penetrate and encapsulate the porous silicate framework, maintaining continuous and stable physical adhesion under a low-pressure flow field of 0.15 to 0.25 MPa. This composite membrane layer blocks the high-frequency thermal shock of the cooling fluid to the thin-walled metal, reduces the amplitude of cold contraction tensile stress on the metal surface, and cuts off the initiation and propagation path of thermal stress microcracks at the microscopic level.

[0095] In Comparative Example 2, without the addition of temperature-sensitive polyether polyol, the defect detection frequency surged to 134 times / 100 meters. The inorganic foam skeleton formed by single liquid sodium silicate on the surface at 530°C exhibited high brittleness and completely lacked lubrication and coating. Under continuous cold fluid thermal shock and kinetic energy scouring, the brittle porous layer underwent pulverization and peeling, resulting in the re-exposing of fresh metal on the thin-walled substrate surface. The locally exposed areas instantly entered a nucleation boiling state, and the violent fluctuations in heat transfer flux induced dense alternating thermal stress on the thin-walled surface, leading to a large number of micro-mechanical tears. In Comparative Example 1, without the addition of liquid sodium silicate, the defect frequency was 47 times / 100 meters. After losing the underlying support of the rigid inorganic skeleton, the pure polyether polyol polymer liquid film could not resist the surface shearing physical action of the fluid, resulting in large-area turbulent detachment. The rupture of the local film layer led to uneven cold shrinkage cracking of the thin-walled metal.

[0096] Comparative Example 3 employed a high injection pressure of 1.0 MPa, resulting in a defect frequency of 89 times per 100 meters. The high fluid kinetic energy directly penetrated and destroyed the mechanical compressive strength of the composite interface film, causing the thin-walled metal to completely lose its dual physical barriers of insulation and lubrication. The high-pressure water flow directly contacted the high-temperature metal substrate, generating destructive cold contraction stress. Comparative Example 4 controlled the thin-walled material discharge temperature at 475℃. Because the dehydration phase change foaming triggering conditions of silicates were not met, an insulation and lubrication composite film could not be constructed on the thin-walled surface. Rapid cooling occurred under conventional fluid convection heat transfer, causing the surface metal to undergo internal yielding and tearing under its own large-scale volume contraction, resulting in a defect frequency of 112 times per 100 meters. Comparative Example 5 raised the temperature of the entire cross-section to 530℃. Both the thick and thin walls were simultaneously covered by the composite foam film, significantly reducing the cooling rate and alleviating localized alternating thermal shock. However, because the fundamental thermal stress under high-temperature extrusion could not be released through rapid and uniform synchronous cooling, the defect frequency still reached 56 times per 100 meters. Test data confirms the physicochemical mechanism of the synergistic temperature control and stress tear resistance at the high-temperature solid-liquid interface between the rigid porous framework and the high-viscosity flexible polymer.

Claims

1. A dynamic extrusion forming process for large-section thin-walled aluminum alloy profiles, characterized in that, Includes the following steps: Prepare a composite quenching medium consisting of 770-825g deionized water, 120-150g thermosensitive polyether polyol, 40-60g liquid sodium silicate, and 15-20g diethylene glycol butyl ether. The preheated aluminum alloy ingot is fed into a preheated extrusion die for hot extrusion. The extrusion speed is adjusted to create an asymmetric frictional heat gradient in the cross section, so that the surface temperature of the thin-walled area at the moment of extrusion die is 520-540℃ and the surface temperature of the thick-walled area is 470-480℃. A composite quenching medium with a system spray pressure of 0.15-0.25 MPa is used to spray quench the surface of the profile. By utilizing the difference in heat flux between thin and thick walls, the composite quenching medium causes the inorganic salt dehydration and expansion and the polymer phase segregation in situ in the thin-walled area to form a composite insulating microporous film for slow cooling. In the thick-walled area, a brittle shell is formed and peeled off by the fluid to achieve rapid cooling. After cooling, a large-section thin-walled aluminum alloy profile is obtained.

2. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, The thermosensitive polyether polyol is a random copolymer generated by copolymerizing ethylene oxide and propylene oxide with n-butanol as the initiator, and the polymerization mass ratio of ethylene oxide to propylene oxide is 1:1.0-1.

4.

3. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 2, characterized in that, The method for preparing the thermosensitive polyether polyol includes: n-Butanol and potassium hydroxide are mixed and dehydrated under vacuum at 105-115℃. Then, a mixture of ethylene oxide and propylene oxide monomers with a mass ratio of 1:1.0-1.4 is added dropwise. The mixture is then subjected to a constant-temperature aging reaction at a reaction temperature of 115-125℃ and a reaction pressure of 0.2-0.4MPa. The mixture is then cooled and neutralized to obtain the final product.

4. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 3, characterized in that, In the vacuum dehydration step of preparing the thermosensitive polyether polyol, the absolute pressure of vacuum dehydration is controlled at 0.05-0.09 MPa, and the water mass fraction of the system after dehydration is controlled at 0.01-0.05%.

5. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, In the process of preparing the composite quenching medium, each component is added sequentially at a temperature of 25-35℃ and continuously stirred at a mechanical stirring speed of 300-500 rpm for 50-70 minutes until a homogeneous transparent solution is formed.

6. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, Before the hot extrusion step, the aluminum alloy ingot is preheated to 450-480℃ and the extrusion die is preheated to 445-455℃.

7. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, The cross-sectional dimensions of the aluminum alloy profile are as follows: The thickness of the thin-walled region ranges from 1.5 to 2.0 mm, and the thickness of the thick-walled region ranges from 20 to 25 mm.

8. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, In the spray quenching step, an annular spray water tank is set up within a distance range of 450-550mm from the extrusion die outlet to deliver the composite quenching medium to the nozzle for uniform spraying.

9. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, Following the spray quenching step, a media recycling step is included: The quenching reflux liquid is introduced into a gravity settling tank and left to stand for 40-60 minutes. Then it is pumped into a centrifuge with a speed of 3000-4000 rpm for slag removal. The purified liquid is cooled to 28-32℃ and then recycled.

10. The dynamic extrusion forming process for large cross-section thin-walled aluminum alloy profiles according to claim 1, characterized in that, The aluminum alloy ingot is selected from an alloy system with an aluminum content of 95.0-99.0% by mass, specifically 6000 series aluminum alloy or 7000 series aluminum alloy.

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