Method of manufacturing high-strength thin-walled aluminum alloy extrusion cast parts

Abstract

The application relates to the field of aluminum alloy materials, and provides a manufacturing method of a high-strength thin-wall aluminum alloy extrusion casting part, and aims to solve the problems of insufficient strength and large heat treatment deformation of the existing aluminum alloy extrusion casting part. The method adopts an Al-Si-Mg-Cu-Zn series casting alloy with a specific component proportion, and through steps of an optimized extrusion casting process, solid solution treatment, precooling treatment and isothermal quenching, an organizational structure containing 1.0-3.5 vol% Al5Mg8Si6Cu2 strengthening phase is formed, the strengthening phase forms a semi-coherent interface with a matrix during precipitation, and the mechanical properties of the casting are effectively improved. The casting prepared by the application has a tensile strength of greater than or equal to 368 MPa, a yield strength of greater than or equal to 316 MPa, and a flatness deviation of 0.1-0.25 mm / 100 mm, is suitable for manufacturing thin-wall structural parts with high requirements for high strength and high dimensional accuracy, and has a wide engineering application prospect.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy castings, and more specifically to a method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts. Background Technology

[0002] In the context of the simultaneous advancement of lightweighting and high performance in modern transportation equipment, especially in fields such as new energy vehicles, electric aircraft, and rail transit equipment, thin-walled metal structural components are widely used as key load-bearing elements. Their manufacturing quality directly affects the safety, energy efficiency, and service life of the entire system. Taking new energy vehicles as an example, thin-walled aluminum alloy components are extensively used in body structural parts, battery casings, and thermal management modules to reduce curb weight and improve driving range and dynamic response performance. However, during the manufacturing process, heat treatment, a crucial process for improving the mechanical properties of materials, often leads to significant deformation problems. Due to the complex temperature field distribution and material microstructure transformation during heat treatment, thin-walled aluminum alloy parts are prone to warping, torsion, and other deformation exceeding tolerances, resulting in a high scrap rate and severely impacting manufacturing costs and production efficiency. Excessive deformation exceeding tolerances during heat treatment has become a key technical bottleneck restricting the mass production of thin-walled aluminum alloy parts. Excessive deformation not only directly causes material waste and increased processing costs but also extends production cycles, reduces delivery efficiency, and affects enterprise competitiveness. Furthermore, high dimensional accuracy and low defect rate are crucial for improving system integration, shortening assembly cycles, and reducing manufacturing costs. Therefore, developing a manufacturing method for thin-walled aluminum alloy extrusion casting parts that simultaneously possesses high mechanical properties and low heat treatment deformation is of great value in promoting the intelligent, lightweight, and highly reliable development of high-end equipment manufacturing, and also provides key technical support for the engineering application of next-generation high-performance structural materials.

[0003] Although aluminum alloy extrusion casting technology has made some progress in material design and process control in recent years, existing research still has significant shortcomings in simultaneously meeting the performance requirements of high strength and low heat treatment deformation. These shortcomings are mainly reflected in the limited ability to regulate the microstructure of strengthening phases and the lack of precise control over the heat treatment process. For example, Chinese patent CN101758194B discloses an indirect extrusion casting method for deformed aluminum alloy castings. While it has some effect on improving material strength, its heat treatment process uses uniform fixed parameters and fails to differentiate the heat transfer characteristics of different wall thickness regions. This leads to thin-walled areas being prone to deformation and collapse under gravity during prolonged high-temperature holding. The root cause of these problems lies in the single strengthening mechanism of traditional alloy systems, the lack of multi-scale collaborative design, and the use of fixed parameters in heat treatment processes, which fail to combine the casting's structural characteristics and thermal conduction behavior for personalized control. This results in irreversible thermal deformation of thin-walled parts during prolonged high-temperature exposure. This invention employs different solution heating times for parts with varying wall thicknesses, minimizing the holding time at high temperatures while ensuring sufficient dissolution of alloying elements. This minimizes deformation caused by gravity during furnace heating, effectively balancing the conflict between strengthening and deformation control. Therefore, there is an urgent need to develop a novel manufacturing method based on the synergistic design of compositional system optimization and precise heat treatment control. This method aims to achieve a harmonious balance between high strength and low deformation characteristics in thin-walled aluminum alloy castings, thereby meeting the pressing demand in high-end manufacturing for continuous performance upgrades of advanced lightweight alloy materials. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The purpose of this invention is to provide a manufacturing method for high-strength thin-walled aluminum alloy extrusion casting parts, thereby solving the problem of large deformation during heat treatment of high-strength aluminum alloy extrusion casting parts.

[0006] (2) Technical solution

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for manufacturing high-strength, thin-walled aluminum alloy extrusion casting parts includes the following steps:

[0009] S1. Thin-walled aluminum alloy castings are prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with the following chemical composition by mass percentage: Si: 5.0-9.0%, Mg: 0.8-1.2%, Cu: 0.3-0.9%, Zn: 1.5-3.5%, Cr+Mn≤0.2%, Fe≤0.2%, Ti+Zr: 0.05-0.2%, Sr: 0.01-0.1%, with the balance being Al and unavoidable impurities.

[0010] S2. Place the casting obtained in step S1 in an air resistance furnace and perform solution treatment and heat preservation at 510~520℃. The heat preservation time t1(h) satisfies the functional relationship: t1=3+0.015×|D-6|2, where D is the maximum wall thickness of the casting in mm, and it is applicable to D of 6~14mm.

[0011] S3. After the solution treatment and heat preservation are completed, the furnace is cooled to 460±5℃ at a controlled cooling rate V1, and the temperature is maintained within this range for 5 to 10 minutes. The cooling rate V1 is constantly controlled at 2.0 to 3.5℃ / min.

[0012] S4. Immediately after the heat preservation in step S3, transfer the casting to a molten salt containing water at a temperature of 175-220℃ for isothermal quenching, wherein the moisture content W (%) in the molten salt satisfies the following functional relationship:

[0013] W = 3.5 - 0.077 × (Tq - 175);

[0014] Where Tq is the salt bath temperature (°C), and Tq ranges from 175 to 220°C.

[0015] The technical solution of this invention aims to systematically improve the comprehensive performance of thin-walled aluminum alloy extrusion casting parts, especially in terms of mechanical strength and casting dimensional stability, through the synergistic design of composition optimization and heat treatment processes. Firstly, at the material design level, an Al-Si-Mg-Cu-Zn casting alloy system with Al as the matrix is ​​selected, combining multiple alloying elements such as Si, Mg, Cu, and Zn. Through the scientific synergistic configuration of the component ratios, both the strengthening mechanism and casting fluidity of the alloy system are considered. Si helps improve casting performance and promotes the formation of eutectic structures, while Mg and Cu participate in the formation of precipitation strengthening phases. Zn regulates the morphology and precipitation behavior of strengthening phases, while trace amounts of Cr, Mn, Ti, Zr, and Sr play an auxiliary role in controlling grain size, inhibiting the precipitation of harmful phases, and improving microstructure stability. Simultaneously, the total amount of Cr and Mn in the alloy is limited to reduce the sensitivity of the alloy solution to cooling rate, allowing the solution effect to be achieved using a molten salt cooling system. This compositional system design not only achieves synergistic strengthening among multiple elements but also provides a good microstructure foundation for subsequent heat treatment processes. In terms of heat treatment, the solution treatment temperature is controlled between 510 and 520℃, and the holding time t1 is determined as a function of the maximum wall thickness D of the casting. This ensures that structures of different thicknesses achieve sufficient and uniform element diffusion and solution effect during the solution treatment process, avoiding uneven microstructure or performance fluctuations due to over- or under-treatment. Furthermore, using an air resistance furnace for solution treatment helps improve the temperature control accuracy and environmental stability of the heat treatment process, thereby effectively reducing the risk of thermal stress accumulation and initial deformation. Overall, this technical solution, through the coupled control of diversified composition and functional heat treatment parameters, fully leverages the combined effects of various alloying elements in microstructure regulation and performance enhancement. This allows aluminum alloy castings to achieve a dual improvement in strength and dimensional stability while maintaining a thin-walled structure, meeting the growing engineering demand for high-performance lightweight structural materials.

[0016] Furthermore, the aqueous molten salt is composed of water and a molten salt matrix, wherein the molten salt matrix is ​​a eutectic mixture of sodium nitrate, sodium nitrite and potassium nitrate in a mass ratio of 45.0-46:26-28:26-28.

[0017] Furthermore, the isothermal quenching time in step S4 is 30-300s, after which the casting is removed and cleaned in hot water at 50-60℃ to obtain high-strength thin-walled aluminum alloy extrusion casting parts.

[0018] Furthermore, the thin-walled aluminum alloy casting contains Al5Mg8Si6Cu2 reinforcing phase with a volume fraction of 1.0 to 3.5 vol%.

[0019] Furthermore, the functional relationship between the average size Y and W of the Al5Mg8Si6Cu2 strengthening phase is as follows:

[0020] Y(nm)=80-4.5×W+0.4×(Tq-175);

[0021] Where W is the molten salt content (%), ranging from 0 to 3.5%; Tq is the salt bath temperature (°C), ranging from 175 to 220°C.

[0022] Furthermore, when the Al5Mg8Si6Cu2 reinforcing phase precipitates from the supersaturated solid solution, it forms a semi-coherent interface transition structure with the Al matrix.

[0023] Furthermore, in step S1, the melting temperature during casting is 670–680°C, the casting pressure is 110 MPa, and the holding time is 15–22 seconds.

[0024] Furthermore, the tensile strength of the casting treated by this method is ≥368MPa, and the yield strength is ≥316MPa; the flatness deviation of the casting is 0.1~0.25mm / 100mm.

[0025] This invention, in the cooling and quenching process after solution treatment, aims to achieve stable microstructure regulation and controllable precipitation of strengthening phases by precisely controlling the cooling rate and constructing an aqueous molten salt system matched to the salt bath temperature, thereby improving the mechanical properties and dimensional stability of thin-walled aluminum alloy extruded castings. After solution treatment and holding, the temperature is gradually reduced to 460±5℃ using a furnace cooling method, and held for a short time within this temperature range. This process, by stably controlling the cooling rate V1 at 2.0~3.5℃ / min, not only effectively avoids aggravated deformation of the parts due to rapid cooling, but also lays the thermodynamic and kinetic foundation for the precipitation of strengthening phases in the subsequent isothermal quenching stage. Immediately afterwards, the casting is rapidly transferred to an aqueous molten salt at a temperature of 175~220℃ for isothermal quenching. Furthermore, by utilizing the functional relationship between the water content W in the molten salt and the salt bath temperature Tq, the reactivity and heat transfer efficiency in the isothermal environment are precisely controlled, thereby promoting the stable precipitation of specific strengthening phases and the refinement and homogenization of the microstructure. This aqueous molten salt system, through dynamic adjustment of moisture content, achieves high cooling efficiency during the quenching process while avoiding deformation problems caused by excessively rapid cooling in traditional quenching methods, thus improving the microstructure integrity and interfacial bonding quality after quenching. Particularly during the precipitation of the strengthening phase Al5Mg8Si6Cu2, the synergistic effect of temperature and moisture content in the isothermal quenching environment promotes the stable existence of this phase with favorable size and distribution, enhancing its interfacial bonding with the matrix and further improving the overall mechanical properties and deformation resistance of the material. Overall, this technical solution, through close linkage between temperature gradient control and molten salt system formulation, not only achieves refined management of the heat treatment process but also fully leverages the microstructure optimization effect brought about by multi-factor coupling, demonstrating the material preparation advantages of combining high strength and low deformation performance.

[0026] This invention aims to synergistically improve the strength and dimensional stability of thin-walled aluminum alloy extrusion casting parts by constructing a heat treatment strategy centered on strengthening phase control and combining it with systematic optimization of composition design and process parameters. In the isothermal quenching stage, the quenching time is set to 30 to 300 seconds to ensure that the strengthening phase is fully precipitated in a controlled environment and achieves the ideal morphology and distribution. Subsequently, cleaning in hot water at 50–60°C effectively removes residual molten salt from the surface and stabilizes the material microstructure. This design not only improves the controllability of the process but also provides a clean environment for the formation of the strengthening phase. In particular, the Al5Mg8Si6Cu2 strengthening phase formed in the casting, with its volume fraction controlled within a specific range, becomes one of the key factors in improving the material strength. Its average size has a clear functional relationship with the molten salt content W and the salt bath temperature Tq during quenching. By precisely controlling this relationship, the size of the strengthening phase can be predictably adjusted, thereby further optimizing its strengthening effect. The setting of the solution treatment holding time range ensures the full dissolution of alloying elements and the homogenization of the microstructure, laying the microstructural conditions for the high-quality precipitation of the strengthening phase. Therefore, the parameter settings and organizational control objectives at each stage of the entire manufacturing process are closely linked. By strengthening the systematic control of phase composition, size, distribution and interface structure, the comprehensive performance of aluminum alloy castings is significantly improved, enabling them to have excellent mechanical properties and dimensional stability while maintaining complex thin-walled structures, thus meeting the multiple requirements of high-performance structural components for material properties.

[0027] (3) Beneficial technical effects

[0028] 1. This invention achieves a synergistic improvement in the strength and dimensional stability of thin-walled aluminum alloy extrusion casting parts by organically combining an Al-Si-Mg-Cu-Zn multi-element alloy system with a gradient heat treatment process. Unlike traditional techniques where high-strength alloys are typically highly sensitive to quenching and require water quenching to suppress the decomposition of supersaturated solid solutions (which results in significant stress and deformation), this invention employs an innovative process combining isothermal quenching with molten salt. This process ensures that the Al5Mg8Si6Cu2 strengthening phase exhibits optimal size and distribution, forming a semi-coherent interface and significantly reducing the risk of heat treatment deformation. Functionalized process parameter design enables components of varying wall thicknesses to achieve stable performance, effectively solving key challenges in automotive lightweighting and aerospace component manufacturing. Compared to traditional methods, castings prepared using this invention maintain high strength while significantly reducing flatness deviations caused by heat treatment deformation, providing reliable technical support for high-end equipment manufacturing.

[0029] 2. This invention overcomes the technical bottleneck of traditional aluminum alloy heat treatment, which struggles to balance strength and dimensional stability, through a synergistic design of temperature control and isothermal quenching with molten salt containing water. By controlling the cooling rate and establishing a thermal stress relief mechanism at an intermediate holding temperature of 460±5℃, combined with a quenching medium whose moisture content dynamically adjusts with the salt bath temperature, a balance is achieved between quenching cooling intensity and deformation control. This innovative process results in the Al5Mg8Si6Cu2 strengthening phase exhibiting optimal size and a semi-coherent interface structure, maintaining high strength while keeping deformation low. This method is particularly suitable for high-precision applications such as lightweight components in automotive transmission systems and aerospace structural parts, effectively solving the problem of excessive deformation caused by traditional water quenching, reducing the manufacturing cycle of parts, lowering subsequent machining costs, and providing a novel heat treatment solution with both high performance and high stability for the field of aluminum alloy precision casting.

[0030] 3. This invention achieves a comprehensive improvement in the performance of thin-walled aluminum alloy castings through precise control of the strengthening phase. Isothermal quenching creates the optimal growth environment for the Al5Mg8Si6Cu2 strengthening phase, and the quantitative relationship established between its size and molten salt parameters (Y=80-4.5×W+0.4×(Tq-175)) significantly improves the precision of microstructure control. Compared with traditional processes, this invention maintains high strength (tensile strength ≥368MPa, yield strength ≥316MPa) while controlling the flatness deviation of the casting within the range of 0.1~0.25mm / 100mm, which is significantly better than conventional processing methods. This technology has broad application prospects in fields such as new energy vehicle transmission components and aerospace precision structural parts. By reducing subsequent straightening processes, it lowers production costs and provides a high-performance and high-stability aluminum alloy parts manufacturing method for high-end manufacturing industries. Attached Figure Description

[0031] Figure 1 The microstructure of the thin-walled aluminum alloy casting prepared in Example 1 of this invention is shown.

[0032] Figure 2 This is a physical image of the thin-walled aluminum alloy casting prepared in Example 1 of the present invention.

[0033] Figure 3 This is a comparison diagram of tensile strength and yield strength of embodiments and comparative examples of the present invention.

[0034] Figure 4 This is a comparison chart of elongation and flatness deviation in the embodiments and comparative examples of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments and comparative examples.

[0036] Example 1

[0037] S1. Thin-walled aluminum alloy castings were prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with the following chemical composition by mass percentage: Si: 5.0%, Mg: 0.8%, Cu: 0.3%, Zn: 1.5%, Cr+Mn: 0.1%, Fe: 0.2%, Ti+Zr: 0.05%, Sr: 0.01%, with the balance being Al and unavoidable impurities. The melting temperature during casting was 670℃, the casting pressure was 110MPa, and the holding time was 15s.

[0038] S2. Place the casting obtained in step S1 in an air resistance furnace and perform solution treatment and heat preservation at 510℃. The heat preservation time t1 (h) satisfies the functional relationship: t1=3+0.015×|D-6|2, where D is the maximum wall thickness of the casting in mm. In this embodiment, D is 6mm. The solution treatment and heat preservation time is 180min.

[0039] S3. After the solution treatment and heat preservation are completed, the furnace is cooled to 460±5℃ at a controlled cooling rate V1, and the temperature is maintained within this range for 5 minutes. The cooling rate V1 is constantly controlled at 2.0℃ / min.

[0040] S4. Immediately after the heat preservation in step S3, the casting is transferred to a molten salt bath at 175°C for isothermal quenching. The moisture content W (%) in the molten salt bath satisfies the functional relationship: W = 3.5 - 0.077 × (Tq - 175); where Tq is the salt bath temperature (°C), and in this embodiment, Tq is 175°C. The molten salt bath consists of moisture and a molten salt matrix, which is a eutectic mixture of sodium nitrate, sodium nitrite, and potassium nitrate in a mass ratio of 45:26:26. The isothermal quenching time is 30 seconds. The casting is then removed and cleaned in hot water at 50°C to obtain a high-strength, thin-walled aluminum alloy extrusion-cast part.

[0041] The thin-walled aluminum alloy casting of this embodiment contains a 1 vol% Al5Mg8Si6Cu2 strengthening phase. The average size Y and W of the Al5Mg8Si6Cu2 strengthening phase have the following functional relationship: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175); where W is the molten salt content (%) and Tq is the salt bath temperature (°C), which is 175°C in this embodiment. When the Al5Mg8Si6Cu2 strengthening phase precipitates from the supersaturated solid solution, it forms a semi-coherent interface transition structure with the Al matrix. The tensile strength of the aluminum alloy casting is 368 MPa, and the yield strength is 316 MPa. The flatness deviation of the casting is 0.25 mm / 100 mm.

[0042] Depend on Figure 1 and Figure 2The microstructure and physical characteristics of the thin-walled aluminum alloy casting prepared in Example 1 of this invention can be directly observed, wherein... Figure 1 The microstructure of the casting shows a uniformly distributed Al5Mg8Si6Cu2 reinforcing phase. These nanoscale reinforcing phases exhibit a regular needle-like and spherical distribution, forming a good semi-coherent interface with the aluminum matrix. This avoids the coarse eutectic phases and irregular precipitates commonly found in conventional casting alloys. The refined and uniformly distributed microstructure provides a foundation for the material's excellent mechanical properties. Figure 2 The physical castings demonstrate that the thin-walled aluminum alloy products prepared by the process of this invention have the characteristics of smooth surface, sharp edges and corners and no obvious deformation. In particular, they maintain good forming accuracy even in complex shapes and thin-walled areas. This directly proves that the heat treatment process of this invention, which combines controlled cooling rate and isothermal quenching with molten salt containing water, has indeed effectively solved the technical problems of insufficient strength and large casting deformation in traditional aluminum alloy extrusion casting parts.

[0043] Example 2

[0044] A method for manufacturing high-strength, thin-walled aluminum alloy extrusion casting parts includes the following steps:

[0045] S1. Thin-walled aluminum alloy castings were prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with the following chemical composition by mass percentage: Si: 6.2%, Mg: 0.9%, Cu: 0.6%, Zn: 2.1%, Cr+Mn: 0.2%, Fe: 0.2%, Ti+Zr: 0.1%, Sr: 0.04%, with the balance being Al and unavoidable impurities. The melting temperature during casting was 673℃, the casting pressure was 110MPa, and the holding time was 17 seconds.

[0046] S2. Place the casting obtained in step S1 in an air resistance furnace and perform solution treatment and heat preservation at 512℃. The heat preservation time t1 (h) satisfies the functional relationship: t1=3+0.015×|D-6|2, where D is the maximum wall thickness of the casting in mm. In this embodiment, D is 8mm. The solution treatment and heat preservation time is 183.6min.

[0047] S3. After the solution treatment and heat preservation are completed, the furnace is cooled to 460±5℃ at a controlled cooling rate V1, and the furnace is kept at this temperature range for 6 minutes. The cooling rate V1 is constantly controlled at 2.2℃ / min.

[0048] S4. Immediately after the heat preservation in step S3, the casting is transferred to a molten salt bath at 189℃ for isothermal quenching. The moisture content W (%) in the molten salt bath satisfies the functional relationship: W = 3.5 - 0.077 × (Tq - 175); where Tq is the salt bath temperature (℃), and Tq is taken as 189℃. The molten salt bath consists of moisture and a molten salt matrix, which is sodium nitrate, sodium nitrite, and potassium nitrate in a mass ratio of 45.5:27:27. The isothermal quenching time is 111s. The casting is then removed and cleaned in hot water at 53℃ to obtain a high-strength, thin-walled aluminum alloy extrusion-cast part.

[0049] The thin-walled aluminum alloy casting of this embodiment contains a 1.5 vol% Al5Mg8Si6Cu2 strengthening phase. The average size Y and W of the Al5Mg8Si6Cu2 strengthening phase are related as follows: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175); where W is the molten salt content (%) and Tq is the salt bath temperature (°C), ranging from 189°C. When the Al5Mg8Si6Cu2 strengthening phase precipitates from the supersaturated solid solution, it forms a semi-coherent interface transition structure with the Al matrix. The tensile strength of the aluminum alloy casting is 378 MPa, and the yield strength is 325 MPa. The flatness deviation of the casting is 0.18 mm / 100 mm.

[0050] Example 3

[0051] A method for manufacturing high-strength, thin-walled aluminum alloy extrusion casting parts includes the following steps:

[0052] S1. Thin-walled aluminum alloy castings were prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with the following chemical composition by mass percentage: Si: 7.4%, Mg: 1.0%, Cu: 0.5%, Zn: 2.7%, Cr+Mn: 0.2%, Fe: 0.2%, Ti+Zr: 0.1%, Sr: 0.06%, with the balance being Al and unavoidable impurities. The melting temperature during casting was 676℃, the casting pressure was 110MPa, and the holding time was 19 seconds.

[0053] S2. Place the casting obtained in step S1 in an air resistance furnace and perform solution treatment and heat preservation at 518℃. The heat preservation time t1 (h) satisfies the functional relationship: t1=3+0.015×|D-6|2, where D is the maximum wall thickness of the casting in mm, and it is applicable to D=12mm; the solution treatment and heat preservation time is 212.4min.

[0054] S3. After the solution treatment and heat preservation are completed, the furnace is cooled to 460±5℃ at a controlled cooling rate V1, and the furnace is kept at this temperature range for 8 minutes. The cooling rate V1 is constantly controlled at 3.1℃ / min.

[0055] S4. Immediately after the heat preservation in step S3, the casting is transferred to a molten salt bath at 202℃ for isothermal quenching. The moisture content W (%) in the molten salt bath satisfies the functional relationship: W = 3.5 - 0.077 × (Tq - 175); where Tq is the salt bath temperature (℃), and Tq is taken as 202℃. The molten salt bath consists of moisture and a molten salt matrix, which is a eutectic mixture of sodium nitrate, sodium nitrite, and potassium nitrate in a mass ratio of 46:28:28. The isothermal quenching time is 192s. The casting is then removed and cleaned in hot water at 56℃ to obtain a high-strength, thin-walled aluminum alloy extrusion-cast part.

[0056] The thin-walled aluminum alloy casting of this embodiment contains a 3.0 vol% Al5Mg8Si6Cu2 strengthening phase. The average size Y and W of the Al5Mg8Si6Cu2 strengthening phase are related as follows: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175); where W is the molten salt content (%) and Tq is the salt bath temperature (°C), ranging from 202°C. The interface between the Al5Mg8Si6Cu2 strengthening phase and the Al matrix in this embodiment contains a semi-coherent interface. The tensile strength of the aluminum alloy casting is 382 MPa, and the yield strength is 336 MPa. The flatness deviation of the casting is 0.15 mm / 100 mm.

[0057] Example 4

[0058] A method for manufacturing high-strength, thin-walled aluminum alloy extrusion casting parts includes the following steps:

[0059] S1. Thin-walled aluminum alloy castings were prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with the following chemical composition by mass percentage: Si: 9.0%, Mg: 1.2%, Cu: 0.9%, Zn: 3.5%, Cr+Mn: 0.2%, Fe: 0.2%, Ti+Zr: 0.2%, Sr: 0.1%, with the balance being Al and unavoidable impurities. The melting temperature during casting was 680℃, the casting pressure was 110MPa, and the holding time was 22 seconds.

[0060] S2. Place the casting obtained in step S1 in an air resistance furnace and perform solution treatment and heat preservation at 520℃. The heat preservation time t1 (h) satisfies the functional relationship: t1=3+0.015×|D-6|2, where D is the maximum wall thickness of the casting in mm, and it is applicable to D=10mm; the solution treatment and heat preservation time is 194.4min.

[0061] S3. After the solution treatment and heat preservation are completed, the furnace is cooled to 460±5℃ at a controlled cooling rate V1, and the furnace is kept at this temperature range for 10 minutes. The cooling rate V1 is constantly controlled at 3.5℃ / min.

[0062] S4. Immediately after the heat preservation in step S3, the casting is transferred to a molten salt bath at 220℃ for isothermal quenching. The moisture content W (%) in the molten salt bath satisfies the functional relationship: W = 3.5 - 0.077 × (Tq - 175); where Tq is the salt bath temperature (℃), and Tq is taken as 220℃. The molten salt bath consists of moisture and a molten salt matrix, which is a eutectic mixture of sodium nitrate and potassium nitrate with a mass ratio of 52:48. The isothermal quenching time is 100s. The casting is then removed and cleaned in hot water at 60℃ to obtain a high-strength, thin-walled aluminum alloy extrusion-cast part.

[0063] The thin-walled aluminum alloy casting of this embodiment contains a 3.5 vol% Al5Mg8Si6Cu2 strengthening phase. The average size Y and W of the Al5Mg8Si6Cu2 strengthening phase are related as follows: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175); where W is the molten salt content (%) and Tq is the salt bath temperature (°C), ranging from 220°C. The interface between the Al5Mg8Si6Cu2 strengthening phase and the Al matrix in this embodiment contains a semi-coherent interface. The tensile strength of the aluminum alloy casting is 378 MPa, and the yield strength is 326 MPa. The flatness deviation of the casting is 0.25 mm / 100 mm.

[0064] Comparative Example 1

[0065] The process is basically the same as in Example 1, except that in step S3, the cooling rate is not controlled. Instead, the casting is taken directly out of the solution furnace and air-cooled, without going through the intermediate holding stage of 460±5℃, and directly enters the isothermal quenching step.

[0066] Comparative Example 2

[0067] The process is basically the same as in Example 1, except that in step S4, anhydrous pure molten salt (0% moisture content) is used for isothermal quenching, while the molten salt matrix remains unchanged.

[0068] Comparative Example 3

[0069] It is basically the same as Example 1, except that in step S4, isothermal quenching with molten salt containing water is not used, but direct quenching with 70°C warm water is used instead.

[0070] Comparative Example 4

[0071] The process is basically the same as in Example 1, except that the moisture content W (%) of the molten salt in step S4 is fixed at 5.0% and does not change with the salt bath temperature Tq.

[0072] Comparative Example 5

[0073] The method is basically the same as in Example 1, except that the moisture content W (%) of the hydrated molten salt in step S4 is fixed at 2.0%, instead of using the function relationship W = 3.5 - 0.077 × (Tq - 175) in Example 1 for calculation.

[0074] Comparative Example 6

[0075] It is basically the same as Example 1, except that the Cu content in the alloy composition of S1 is 1.2%.

[0076] Comparative Example 7

[0077] It is basically the same as Example 1, except that the solution temperature in step S2 is 550°C.

[0078] Comparative Example 8

[0079] The process is basically the same as in Example 1, except that the solution treatment and heat preservation time t1 in step S2 does not satisfy the functional relationship t1=3+0.015×|D-6|2, but instead uses a fixed time of 180min.

[0080] Comparative Example 9

[0081] It is basically the same as Example 1, except that the isothermal quenching temperature in step S4 is 250°C.

[0082] Comparative Example 10

[0083] It is basically the same as Example 1, except that the salt bath temperature Tq in step S4 is set to 170°C.

[0084] Performance testing:

[0085] Room temperature tensile properties test: Dumbbell-shaped specimens were prepared according to ASTM E8 / E8M-24 standard and tested using an electronic universal testing machine at a strain rate of 0.5 mm / s. The tensile strength, yield strength (Rp0.2) and elongation were recorded.

[0086] Deformation: The dimensional changes of the casting before and after heat treatment were accurately measured using a coordinate measuring machine (CMM), with particular attention paid to the flatness deviation. Measurements were performed in a constant temperature environment of 20±1℃ and relative humidity of 50±10%. At least 20 feature points were selected on the casting surface for measurement to construct the flatness deviation of the casting before and after heat treatment.

[0087] The properties of the aluminum alloy castings from Examples 1-4 and Comparative Examples 1-10 are summarized in Table 1. Figure 3-4The experimental results show that Examples 1-4 prepared using the technical solution of this invention are significantly superior to Comparative Examples 1-10 in all performance indicators. Among them, Example 3 exhibits the best comprehensive performance, fully demonstrating that the heat treatment process of controlling the cooling rate combined with isothermal quenching with molten salt using the present invention effectively controls casting deformation while improving the mechanical properties of thin-walled aluminum alloy castings. This solves the technical problems of insufficient strength and excessive deformation in traditional extrusion casting processes, achieving a balance between high strength and high precision, and providing important technical support for the industrial production of thin-walled aluminum alloy castings. The table shows that in the comparative experiments, different process deviations had multiple effects on the mechanical properties and dimensional stability of aluminum alloy castings. Uncontrolled cooling rate leads to microstructure coarsening and internal stress accumulation, significantly affecting the flatness and yield strength of the castings. If anhydrous molten salt is used during isothermal quenching, insufficient precipitation of the strengthening phase results in an overall decrease in strength indicators. If water quenching is used instead of isothermal quenching, the microstructure transformation process becomes uncontrolled, the strengthening mechanism fails, and the overall performance is the worst. When the molten salt content is fixed at 5% and not adjusted with temperature, the size of the strengthening phase deviates from the optimal value. Precipitation conditions slightly reduce performance; while a higher Cu content in the alloy can improve strength to some extent, it easily introduces brittle phases, leading to a decrease in elongation; excessively high solution treatment temperatures may cause grain coarsening and overheating, resulting in uneven microstructure and a significant decrease in strength; insufficient solution holding time leads to incomplete dissolution of the strengthening phase, which, although reducing performance, has a manageable impact; when the quenching temperature is set too high, the strengthening phase is prone to rapid coarsening, leading to a significant decrease in strength; conversely, if the quenching temperature is too low, the strengthening phase precipitation is insufficient, and although the strength decreases, the overall performance is still better than that of direct water quenching. Overall, these comparative results fully demonstrate the importance of synergistic control of various process parameters in this invention.

[0088] Table 1. Performance summary of aluminum alloy castings from Examples 1-4 and Comparative Examples 1-10

[0089]

[0090]

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any equivalent structural transformations made under the concept of the present invention and using the contents of the specification and drawings of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts, characterized in that, Includes the following steps: S1. Thin-walled aluminum alloy castings are prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with the following chemical composition by mass percentage: Si: 5.0-9.0%, Mg: 0.8-1.2%, Cu: 0.3-0.9%, Zn: 1.5-3.5%, Cr+Mn≤0.2%, Fe≤0.2%, Ti+Zr: 0.05-0.2%, Sr: 0.01-0.1%, with the balance being Al and unavoidable impurities. S2. Place the casting obtained in step S1 in an air resistance furnace and perform solution treatment and heat preservation at 510~520℃. The heat preservation time t1 (h) satisfies the functional relationship: t1=3+0.015×|D-6|2, where D is the maximum wall thickness of the casting in mm, and it is applicable to D of 6.0~14.0mm. S3. After the solution treatment and heat preservation are completed, the furnace is cooled to 460±5℃ at a controlled cooling rate V1, and the temperature is maintained within this range for 5 to 10 minutes. The cooling rate V1 is constantly controlled at 2.0 to 3.5℃ / min. S4. Immediately after the heat preservation in step S3, transfer the casting to a molten salt containing water at a temperature of 175-220℃ for isothermal quenching, wherein the moisture content W (%) in the molten salt satisfies the following functional relationship: W = 3.5 - 0.077 × (Tq - 175); Where Tq is the salt bath temperature (°C), and Tq ranges from 175 to 220°C.

2. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 1, characterized in that, The aqueous molten salt is composed of water and a molten salt matrix, wherein the molten salt matrix is ​​a eutectic mixture of sodium nitrate, sodium nitrite and potassium nitrate in a mass ratio of 45.0-46:26-28:26-28.

3. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 1, characterized in that, The isothermal quenching time in step S4 is 30-300s. Then the casting is taken out and cleaned in hot water at 50-60℃ to obtain high-strength thin-walled aluminum alloy extrusion casting parts.

4. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 1, characterized in that, The thin-walled aluminum alloy casting contains Al5Mg8Si6Cu2 strengthening phase with a volume fraction of 1.0 to 3.5 vol%.

5. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 4, characterized in that, The functional relationship between the average size Y and W of the Al5Mg8Si6Cu2 strengthening phase is as follows: Y(nm)=80-4.5×W+0.4×(Tq-175); Where W is the molten salt content (%), ranging from 0 to 3.5%; Tq is the salt bath temperature (°C), ranging from 175 to 220°C.

6. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 4, characterized in that, When the Al5Mg8Si6Cu2 reinforcing phase precipitates from the supersaturated solid solution, it forms a semi-coherent interface transition structure with the Al matrix.

7. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 1, characterized in that, In step S1, the melting temperature during casting is 670–680℃, the casting pressure is 110MPa, and the holding time is 15–22s.

8. The method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts as described in claim 1, characterized in that, The casting treated by this method has a tensile strength ≥368MPa and a yield strength ≥316MPa; the flatness deviation of the casting is 0.1~0.25mm / 100mm.

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