Manufacturing method of high-strength thin-wall aluminum alloy extrusion casting part

Abstract

The invention relates to the field of aluminum alloy materials, provides a manufacturing method of a high-strength thin-wall aluminum alloy extrusion casting part, and aims at solving the problems that an existing aluminum alloy extrusion casting part is insufficient in strength and large in heat treatment deformation. According to the method, an Al-Si-Mg-Cu-Zn series casting alloy with a specific component proportion is adopted, an organization structure containing 1.0-3.5 vol% of Al5Mg8Si6Cu2 strengthening phase is formed through the steps of an optimized extrusion casting process, solution treatment, pre-cooling treatment, isothermal quenching and the like, the strengthening phase forms a semi-coherent interface with a matrix in the precipitation process, and the mechanical property of a casting is effectively improved. According to the casting manufactured through the method, the tensile strength is larger than or equal to 368 MPa, the yield strength is larger than or equal to 316 MPa, the flatness deviation is 0.1-0.25 mm / 100 mm, and the method is suitable for manufacturing thin-wall structural parts with the high requirements for high strength and high dimensional precision and has wide engineering application prospects.

Description

Technical Field

[0001] The invention relates to the field of aluminum alloy castings, and in particular to a method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts. Background Art

[0002] As modern transportation equipment advances toward lightweighting and higher performance, thin-walled metal structural components are widely used as key load-bearing components, particularly in new energy vehicles, electric aircraft, and rail transit equipment. Their manufacturing quality is directly impacted by the safety, energy efficiency, and service life of the entire vehicle. For example, new energy vehicles utilize a large number of thin-walled aluminum alloy components in body structures, battery housings, and thermal management modules to reduce curb weight, improve range, and enhance dynamic response. However, heat treatment, a key process for improving material mechanical properties, often leads to significant deformation during component manufacturing. Due to the complex temperature distribution and material microstructure transformations during heat treatment, thin-walled aluminum alloy parts are prone to warping, torsion, and other deformation-prone conditions. This leads to high part scrap rates and severely impacts manufacturing costs and efficiency. Excessive deformation during heat treatment has become a key technical bottleneck hindering the mass production of thin-walled aluminum alloy parts. This deformation-prone condition not only directly results in material waste and increased processing costs, but also extends production cycles, reduces delivery efficiency, and impacts company competitiveness. Furthermore, high dimensional accuracy and low defect rates 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 combine high mechanical properties with minimal heat treatment distortion is crucial for promoting intelligent, lightweight, and highly reliable high-end equipment manufacturing. It also provides key technical support for the engineering application of a new generation of high-performance structural materials.

[0003] Although aluminum alloy extrusion casting technology has made certain progress in material design and process control in recent years, existing research still has obvious shortcomings in meeting the performance requirements of high strength and low heat treatment deformation at the same time, mainly reflected in the limited ability to control the structure of the strengthening phase and the lack of precise control of the heat treatment process. For example, the Chinese patent with publication number CN101758194B discloses an indirect extrusion casting method for deformed aluminum alloy castings. Although it has a certain effect in improving the strength of the material, its heat treatment process adopts a unified fixed parameter and fails to differentiate the heat transfer characteristics of different wall thickness areas. As a result, the thin-walled area is prone to deformation and collapse under the action of gravity during long-term high-temperature insulation. The fundamental reason for the above problems is that the traditional alloy system has a single strengthening mechanism and lacks multi-scale collaborative design. At the same time, the heat treatment process mostly adopts fixed parameters and fails to combine the structural characteristics of the casting with the heat conduction behavior for personalized control, which causes irreversible thermal deformation of thin-walled parts during excessively long high-temperature exposure. This invention uses different solution heating times for parts of varying wall thicknesses, minimizing the high-temperature holding time while ensuring sufficient dissolution of alloying elements. This minimizes the deformation of the parts caused by gravity during furnace heating, effectively balancing the conflict between strengthening and deformation control. Therefore, there is an urgent need to develop a new manufacturing method based on the coordinated design of component system optimization and precise heat treatment control to achieve the organic combination of high strength and low deformation characteristics of thin-walled aluminum alloy castings during heat treatment, thereby meeting the urgent demand for continuous performance upgrades of advanced light alloy materials in the high-end manufacturing field. Summary of the Invention

[0004] (1) Technical problems solved

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

[0006] (2) Technical solution

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

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

[0009] S1. Using an Al-Si-Mg-Cu-Zn casting alloy having a chemical composition by mass percentage of 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%, and the balance being Al and unavoidable impurities, to produce thin-walled aluminum alloy castings by squeeze casting;

[0010] S2. The casting obtained in step S1 is solution-treated in an air resistance furnace at 510-520°C for a holding time t1 (h) satisfying the functional relationship: t1 = 3 + 0.015 × |D-6|2, where D is the maximum wall thickness of the casting in mm and is applicable to D of 6-14 mm;

[0011] S3. After the solution heat preservation is completed, the temperature is cooled to 460 ± 5 ℃ with the controlled cooling rate V1 and kept in this temperature range for 5 to 10 min. The cooling rate V1 is constantly controlled at 2.0 to 3.5 ℃ / min;

[0012] S4. Immediately after the end of step S3, the casting is transferred to a molten salt at a temperature of 175 to 220°C for austempering, wherein the moisture content W (%) in the molten salt satisfies the functional relationship:

[0013] W = 3.5 - 0.077 × (Tq - 175);

[0014] Wherein Tq is the salt bath temperature (°C), and the Tq value is 175~220°C.

[0015] The technical solution of the present 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 coordinated design of composition optimization and heat treatment process. First, at the material design level, an Al-Si-Mg-Cu-Zn casting alloy based on Al is selected, which contains a variety of alloying elements such as Si, Mg, Cu, and Zn. Through the scientific and coordinated configuration of the composition ratio, the strengthening mechanism and casting fluidity in the alloy system are taken into account. The Si element helps to improve the casting performance and promote the formation of eutectic structure, Mg and Cu participate in the formation of precipitation strengthening phase, Zn regulates the morphology and precipitation behavior of the strengthening phase, and trace amounts of Cr, Mn, Ti, Zr and Sr elements play an auxiliary role in controlling grain size, inhibiting the precipitation of harmful phases and improving structural stability. At the same time, the total amount of Cr and Mn elements in the alloy is limited to reduce the sensitivity of low alloy solid solution to cooling rate, so that the solid solution effect can be achieved by cooling using a molten salt system. The design of this composition system not only achieves synergistic strengthening between multiple elements, but also provides a good organizational foundation for subsequent heat treatment processes. In terms of heat treatment, the solution treatment temperature is controlled at 510-520°C, and the functional relationship of the holding time t1 is determined in combination with the maximum wall thickness D of the casting to ensure that structures of different thicknesses obtain sufficient and uniform element diffusion and solution effects during the solution process, avoiding uneven organization or performance fluctuations due to excessive or insufficient treatment. In addition, the use of an air resistance furnace for solution treatment helps to improve the temperature control accuracy and environmental stability of the heat treatment process, thereby effectively reducing the accumulation of thermal stress and the risk of initial deformation. Overall, this technical solution fully utilizes the composite role of various alloying elements in organizational regulation and performance enhancement through the functional coupling regulation of component diversification and heat treatment parameters, so that aluminum alloy castings can 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 consists of water and a molten salt matrix, and 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 austempering time in step S4 is 30 to 300 seconds, and then the casting is taken out and cleaned in hot water at 50 to 60° C., thereby obtaining a high-strength thin-walled aluminum alloy extrusion casting part.

[0018] Furthermore, the thin-walled aluminum alloy casting contains an Al5Mg8Si6Cu2 strengthening 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:

[0020] Y(nm)=80-4.5×W+0.4×(Tq-175);

[0021] Wherein, W is the molten salt water 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 strengthening 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 after being treated by the method is ≥368 MPa, and the yield strength is ≥316 MPa; the flatness deviation of the casting is 0.1-0.25 mm / 100 mm.

[0025] The present invention aims to achieve stable regulation of the microstructure and controlled precipitation of strengthening phases in the cooling and quenching process after solution treatment by precisely controlling the cooling rate and constructing a water-containing molten salt system that matches the salt bath temperature, thereby improving the mechanical properties and dimensional stability of thin-walled aluminum alloy extrusion casting parts. After the solution heat preservation is completed, the temperature is gradually reduced to 460±5℃ by furnace cooling, and a short period of heat preservation is carried out within this temperature range. This process not only effectively avoids the aggravation of part deformation caused by rapid cooling by stably controlling the cooling rate V1 at 2.0~3.5℃ / min, but also lays a thermodynamic and kinetic foundation for the precipitation of strengthening phases in the subsequent isothermal quenching stage. Subsequently, the casting is quickly transferred to a water-containing molten salt at a temperature of 175~220℃ for isothermal quenching. The functional relationship between the water content W in the molten salt and the salt bath temperature Tq is further utilized to precisely regulate the reaction activity and heat transfer efficiency in the isothermal environment, thereby promoting the stable precipitation of specific strengthening phases and the refinement and homogenization of the microstructure. This aqueous molten salt system dynamically adjusts the water content, making the quenching process have a high cooling efficiency while avoiding the deformation problem caused by excessive cooling rate in traditional quenching methods, thereby improving the integrity of the structure and the quality of interface bonding after quenching. In particular, during the precipitation of the strengthening phase Al5Mg8Si6Cu2, the temperature and water content in the isothermal quenching environment work together to promote the stable existence of this phase in a favorable size and distribution form, thereby strengthening the interface bonding between it and the matrix, and further improving the mechanical properties and deformation resistance of the overall material. Overall, the technical solution at this stage, through the close linkage of temperature gradient control and molten salt system allocation, not only achieves the refined management of the heat treatment process, but also gives full play to the organizational optimization effect brought about by the coupling of multiple factors, showing the advantages of material preparation with both high strength and low deformation properties.

[0026] The present invention aims to achieve a synergistic improvement in the strength and dimensional stability of thin-walled aluminum alloy extrusion casting parts by constructing a heat treatment strategy centered on strengthening phase regulation, combining composition design with systematic optimization of process parameters. During the austempering 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 state. Subsequently, by washing in 50-60°C hot water, the residual molten salt on the surface is effectively removed and the material structure is stabilized. This design not only improves the controllability of the process, but also provides a clean environment for the formation of strengthening phases. In particular, the Al5Mg8Si6Cu2 strengthening phase formed in the casting is controlled within a specific volume fraction range, becoming one of the key factors in improving material strength. There is a clear functional relationship between its average size and the molten salt content W and the salt bath temperature Tq in the quenching conditions. By precisely controlling this relationship, the size of the strengthening phase can be predictably adjusted, thereby further optimizing its strengthening performance. The setting of the solution holding time range ensures the full dissolution of alloying elements and the homogenization of the structure, laying the microstructural conditions for the high-quality precipitation of the strengthening phase. As a result, the parameter settings at each stage of the entire manufacturing process are closely linked to the organizational control objectives. 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 a complex thin-walled structure, meeting the multiple requirements of high-performance structural parts for material properties.

[0027] (3) Beneficial technical effects

[0028] 1. The present invention achieves a synergistic improvement in the strength and dimensional stability of thin-walled aluminum alloy extrusion casting parts through the organic combination of the Al-Si-Mg-Cu-Zn multi-element alloy system and the gradient heat treatment process. Different from the traditional technology, high-strength alloys are usually highly sensitive to quenching and require water quenching to suppress the decomposition of the supersaturated solid solution, but the water quenching stress is significant, causing the parts to deform. The innovative process of combining aqueous molten salt isothermal quenching is adopted to make the Al5Mg8Si6Cu2 strengthening phase present the optimal size and distribution state, forming a semi-coherent interface, which significantly reduces the risk of heat treatment deformation. The functionalized process parameter design enables components with different wall thicknesses to obtain stable performance, effectively solving the key problems in automobile lightweighting and aviation component manufacturing. Compared with traditional treatment methods, the castings prepared by the present invention maintain high strength while significantly reducing the flatness deviation caused by heat treatment deformation, providing reliable technical support for high-end equipment manufacturing.

[0029] 2. The present invention breaks through the technical bottleneck of traditional aluminum alloy heat treatment in which it is difficult to strike a balance between strength and dimensional stability through the coordinated design of temperature reduction control and aqueous molten salt austempering. A thermal stress release mechanism is formed by controlling the cooling rate and the intermediate holding stage of 460±5°C, and a balance is achieved between quenching cooling intensity and deformation control by coordinating the quenching medium whose moisture content is dynamically adjusted with the salt bath temperature. This process innovation enables the Al5Mg8Si6Cu2 strengthening phase to present an optimal size and semi-coherent interface structure, maintaining a high strength level while maintaining low deformation. This method is particularly suitable for high-precision scenarios such as lightweight components of automotive transmission systems and aviation structural parts. It effectively solves the problem of excessive deformation caused by traditional water quenching, reduces the manufacturing cycle of parts, and reduces the cost of subsequent machining. It provides a new heat treatment solution with both high performance and high stability for the field of aluminum alloy precision casting.

[0030] 3. The present invention achieves a comprehensive improvement in the performance of thin-walled aluminum alloy castings through precise control of the strengthening phase. Austempering creates the optimal growth environment for the Al5Mg8Si6Cu2 strengthening phase, and the quantitative relationship established between its size and the molten salt parameters (Y = 80-4.5 × W + 0.4 × (Tq-175)) greatly improves the accuracy of organizational control. Compared with traditional processes, the present invention controls the flatness deviation of the casting within the range of 0.1 to 0.25 mm / 100 mm while maintaining higher strength (tensile strength ≥ 368 MPa, yield strength ≥ 316 MPa), which is significantly better than conventional processing methods. This technology has broad application prospects in the fields of new energy vehicle transmission components, aerospace precision structural parts, etc. By reducing subsequent correction processes, it reduces production costs and provides a method for manufacturing aluminum alloy parts with both high performance and high stability for the high-end manufacturing industry. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0033] Figure 3 The figure is a comparison chart of tensile strength and yield strength of the embodiment of the present invention and the comparative example.

[0034] Figure 4 1 is a comparison chart of elongation and flatness deviation of the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0035] In order to make the purpose, 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 drawings in the embodiments of the present invention and the 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 a chemical composition of 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%, and the balance being Al and unavoidable impurities. The casting temperature was 670°C, the casting pressure was 110 MPa, and the holding time was 15 s.

[0038] S2. The casting obtained in step S1 is placed in an air resistance furnace and subjected to solution heat preservation at 510°C. The holding 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 6 mm; the solution heat preservation time is 180 min.

[0039] S3. After the solution heat preservation is completed, the furnace is cooled to 460 ± 5 ℃ with the controlled cooling rate V1, and the temperature is kept in this temperature range for 5min. The cooling rate V1 is constantly controlled at 2.0 ℃ / min;

[0040] S4. Immediately after the completion of step S3, the casting is austempered in a molten salt bath at 175°C. The moisture content (W%) of the molten salt satisfies the following function: W = 3.5 - 0.077 × (Tq - 175°C), where Tq is the bath temperature (°C). In this embodiment, Tq is 175°C. The molten salt bath consists of water 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 warm quenching time is 30 seconds. The casting is then removed and rinsed in hot water at 50°C to produce a high-strength, thin-walled aluminum alloy extrusion casting part.

[0041] The thin-walled aluminum alloy casting of this embodiment contains a strengthening phase of Al5Mg8Si6Cu2 at a volume fraction of 1 vol%. The average size Y of the strengthening phase of Al5Mg8Si6Cu2, as a function of W, is: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175), where W is the molten salt water content (%) and Tq is the salt bath temperature (°C), which in this embodiment is 175°C. When the strengthening phase of Al5Mg8Si6Cu2 precipitates from the supersaturated solid solution, it forms a semi-coherent interfacial transition structure with the Al matrix. The aluminum alloy casting has a tensile strength of 368 MPa and a yield strength of 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 features of the thin-walled aluminum alloy casting prepared in Example 1 of the present invention can be visually observed, wherein Figure 1 The results show that the Al5Mg8Si6Cu2 strengthening phase is evenly distributed in the casting structure. These nano-scale strengthening phases are regularly distributed in needle and spherical shapes, forming a good semi-coherent interface with the aluminum matrix, avoiding the coarse eutectic phase and irregular precipitation phase commonly seen in conventional casting alloys. The characteristics of refined and evenly distributed microstructure provide a foundation for the material's excellent mechanical properties. Figure 2 The actual castings show that the thin-walled aluminum alloy products prepared by the process of the present invention have the characteristics of smooth surface, sharp edges and corners and no obvious deformation, especially in complex shapes and thin-walled areas. Good forming accuracy is also maintained. This directly proves that the heat treatment process combined with controlled cooling rate and aqueous molten salt isothermal quenching adopted by the present invention has indeed effectively solved the technical problems of traditional aluminum alloy extrusion casting parts in insufficient strength and large casting deformation.

[0043] Example 2

[0044] A method for manufacturing high-strength thin-walled aluminum alloy extrusion casting parts comprises 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 a chemical composition of 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%, and the balance being Al and unavoidable impurities; the casting temperature during casting was 673°C, the casting pressure was 110 MPa, and the holding time was 17 seconds.

[0046] S2. The casting obtained in step S1 is placed in an air resistance furnace and subjected to solution holding at 512°C. The holding 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 8 mm; the solution holding time is 183.6 min.

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

[0048] S4. Immediately after the completion of step S3, the casting is austempered in a molten salt bath at 189°C. The water content (W%) of the molten salt bath satisfies the following function: W = 3.5 - 0.077 × (Tq - 175°C), where Tq is the bath temperature (°C) and is 189°C. The molten salt bath consists of water and a molten salt matrix composed of sodium nitrate, sodium nitrite, and potassium nitrate in a mass ratio of 45.5:27:27. The warm quenching time is 111 seconds. The casting is then removed and rinsed in hot water at 53°C to produce a high-strength, thin-walled aluminum alloy extrusion casting part.

[0049] The thin-walled aluminum alloy casting of this embodiment contains a strengthening phase of Al5Mg8Si6Cu2 at a volume fraction of 1.5 vol%. The average size Y of the strengthening phase of Al5Mg8Si6Cu2 is a function of W as follows: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175), where W is the molten salt water content (%) and Tq is the salt bath temperature (°C), which ranges from 189°C. When the strengthening phase of Al5Mg8Si6Cu2 precipitates from the supersaturated solid solution, it forms a semi-coherent interfacial transition structure with the Al matrix. The aluminum alloy casting has a tensile strength of 378 MPa and a yield strength of 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 comprises 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 chemical composition in mass percentages of 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%, and the balance being Al and unavoidable impurities; the casting temperature during casting was 676°C, the casting pressure was 110 MPa, and the holding time was 19 seconds.

[0053] S2. The casting obtained in step S1 is placed in an air resistance furnace and subjected to solution holding at 518°C. The holding 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 is applicable to D of 12 mm; the solution holding time is 212.4 min.

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

[0055] S4. Immediately after the completion of step S3, the casting is austempered in a molten salt bath at 202°C. The water content (W%) of the molten salt satisfies the following function: W = 3.5 - 0.077 × (Tq - 175°C), where Tq is the bath temperature (°C) and is 202°C. The molten salt bath consists of water 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 warm quenching time is 192 seconds. The casting is then removed and rinsed in hot water at 56°C to produce a high-strength, thin-walled aluminum alloy extrusion casting part.

[0056] The thin-walled aluminum alloy casting of this embodiment contains an Al5Mg8Si6Cu2 strengthening phase with a volume fraction of 3.0 vol%. The average size Y of the Al5Mg8Si6Cu2 strengthening phase is a function of W: Y (nm) = 80 - 4.5 × W + 0.4 × (Tq - 175), where W is the molten salt water content (%) and Tq is the salt bath temperature (°C), ranging from 202°C. The interface between the Al5Mg8Si6Cu2 strengthening phase and the Al matrix of this embodiment is semi-coherent. The aluminum alloy casting has a tensile strength of 382 MPa and a yield strength of 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 comprises the following steps:

[0059] S1. Thin-walled aluminum alloy castings are prepared by extrusion casting using an Al-Si-Mg-Cu-Zn casting alloy with a chemical composition in percentage by mass of 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%, and the balance being Al and unavoidable impurities; the casting temperature during casting is 680°C, the casting pressure is 110 MPa, and the holding time is 22 seconds.

[0060] S2. The casting obtained in step S1 is placed in an air resistance furnace and subjected to solution holding at 520°C. The holding 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 is applicable to D of 10 mm; the solution holding time is 194.4 min.

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

[0062] S4. Immediately after the completion of the insulation in step S3, the casting is austempered in a molten salt bath at 220°C. The moisture content (W%) of the molten salt satisfies the following function: W = 3.5 - 0.077 × (Tq - 175°C), where Tq is the bath temperature (°C) and is 220°C. The molten salt bath consists of water and a molten salt matrix, which is a eutectic mixture of sodium nitrate and potassium nitrate in a mass ratio of 52:48. The warm quenching time is 100 seconds. The casting is then removed and rinsed in hot water at 60°C to produce a high-strength, thin-walled aluminum alloy extrusion casting part.

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

[0064] Comparative Example 1

[0065] It is basically the same as Example 1, except that in step S3, the cooling rate is not controlled. Instead, the casting is directly taken out of the solution furnace for air cooling without going through the intermediate holding stage of 460±5°C and directly enters the austempering step.

[0066] Comparative Example 2

[0067] The method is basically the same as Example 1, except that pure molten salt (with a water content of 0%) without water is used for isothermal quenching in step S4, and the molten salt matrix remains unchanged.

[0068] Comparative Example 3

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

[0070] Comparative Example 4

[0071] The method is basically the same as Example 1, except that the moisture content W (%) of the aqueous 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 Example 1, except that the moisture content W (%) of the aqueous molten salt in step S4 is fixed at 2.0%, and the functional relationship W=3.5-0.077×(Tq-175) in Example 1 is not used for calculation.

[0074] Comparative Example 6

[0075] The method 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] It is basically the same as Example 1, except that the solution holding time t1 in step S2 does not satisfy the functional relationship t1=3+0.015×|D-6|2, but adopts a fixed time of 180 minutes.

[0080] Comparative Example 9

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

[0082] Comparative Example 10

[0083] The process 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 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: Use a coordinate measuring machine (CMM) to accurately measure the dimensional changes of castings before and after heat treatment, paying particular attention to flatness deviation. Measurements are performed in a constant temperature environment of 20±1°C and 50±10% relative humidity. At least 20 characteristic points on the casting surface are measured to construct the flatness deviation of the casting before and after heat treatment.

[0087] The properties of the aluminum alloy castings of Examples 1 to 4 and Comparative Examples 1 to 10 are summarized in Table 1. Figure 3-4The experimental results show that Examples 1-4 prepared by the technical solution of the present invention are significantly better than Comparative Examples 1-10 in all performance indicators, among which Example 3 shows the best comprehensive performance, which fully proves that the heat treatment process of controlling the cooling rate combined with austempering of molten salt containing water adopted by the present invention effectively controls the casting deformation while improving the mechanical properties of thin-walled aluminum alloy castings, solves the technical problems of insufficient strength and excessive deformation in the traditional extrusion casting process, realizes the unity of high strength and high precision, and provides important technical support for the industrial production of thin-walled aluminum alloy castings. It can be seen from the table that in the comparative test, different process deviations have a variety of effects on the mechanical properties and dimensional stability of aluminum alloy castings. Among them, failure to control the cooling rate will lead to microstructure coarsening and internal stress accumulation, which significantly affects the flatness and yield strength of the castings; if anhydrous molten salt is used in the austempering process, the precipitation of the strengthening phase is insufficient, resulting in an overall decrease in strength indicators; if water quenching is used instead of austempering, the microstructure transformation process is out of control, the strengthening mechanism fails, and the overall performance is the worst; when the molten salt water content is fixed at 5% and is not adjusted with temperature, the size of the strengthening phase deviates from the optimal Precipitation conditions, resulting in a slight decrease in performance; although a high Cu content in the alloy can improve strength to a certain extent, it is easy to introduce brittle phases, resulting in a decrease in elongation; too high a solution treatment temperature may lead to grain coarsening and overburning, resulting in uneven structure and a significant decrease in strength; insufficient solution holding time will cause incomplete dissolution of the strengthening phase, and although the performance is reduced, the impact is still controllable; when the quenching temperature is set too high, the strengthening phase tends to coarsen rapidly, resulting in a significant decrease in strength; on the contrary, if the quenching temperature is too low, the strengthening phase is insufficiently precipitated, and although the strength is reduced, the overall performance is still better than that of direct water quenching. Overall, the results of these comparative examples fully illustrate the importance of coordinated regulation of various process parameters in the present invention.

[0088] Table 1 Performance summary of aluminum alloy castings of Examples 1 to 4 and Comparative Examples 1 to 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 are not intended to limit the present invention. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that any equivalent structural transformations made within the scope of the present invention using the contents of the present invention's description and drawings should be included 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: The following steps are involved: S1. Using an Al-Si-Mg-Cu-Zn casting alloy having a chemical composition by mass percentage of 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%, and the balance being Al and unavoidable impurities, to produce thin-walled aluminum alloy castings by squeeze casting; S2. The casting obtained in step S1 is solution-treated in an air resistance furnace at 510-520°C for a holding time t1 (h) satisfying the functional relationship: t1 = 3 + 0.015 × |D-6|2, where D is the maximum wall thickness of the casting in mm and is applicable to D of 6.0-14.0 mm; S3. After the solution heat preservation is completed, the temperature is cooled to 460 ± 5 ℃ with the controlled cooling rate V1 and kept in this temperature range for 5 to 10 min. The cooling rate V1 is constantly controlled at 2.0 to 3.5 ℃ / min; S4. Immediately after the end of step S3, the casting is transferred to a molten salt at a temperature of 175 to 220°C for austempering, wherein the moisture content W (%) in the molten salt satisfies the functional relationship: W = 3.5 - 0.077 × (Tq - 175); Wherein Tq is the salt bath temperature (°C), and the Tq value is 175~220°C.

2. The method for manufacturing a high-strength thin-walled aluminum alloy extrusion casting part according to claim 1, wherein: The aqueous molten salt consists of water and a molten salt matrix, and 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 a high-strength thin-walled aluminum alloy extrusion casting part according to claim 1, wherein: The austempering time in step S4 is 30 to 300 seconds, and then the casting is taken out and cleaned in hot water at 50 to 60° C., thereby obtaining a high-strength thin-walled aluminum alloy extrusion casting part.

4. The method for manufacturing a high-strength thin-walled aluminum alloy extrusion casting part according to claim 1, wherein: The thin-walled aluminum alloy casting contains an Al5Mg8Si6Cu2 strengthening phase with a volume fraction of 1.0-3.5 vol%.

5. The method for manufacturing a high-strength thin-walled aluminum alloy extrusion casting part according to claim 4, wherein: The functional relationship between the average size Y and W of the Al5Mg8Si6Cu2 strengthening phase is: Y(nm)=80-4.5×W+0.4×(Tq-175); Wherein, W is the molten salt water 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 a high-strength thin-walled aluminum alloy extrusion casting part according to claim 4, wherein: When the Al5Mg8Si6Cu2 strengthening phase precipitates from the supersaturated solid solution, it forms a semi-coherent interface transition structure with the Al matrix.

7. The method for manufacturing a high-strength thin-walled aluminum alloy extrusion casting part according to claim 1, wherein: During casting in step S1, the melting temperature is 670-680° C., the casting pressure is 110 MPa, and the holding time is 15-22 seconds.

8. The method for manufacturing a high-strength thin-walled aluminum alloy extrusion casting part according to claim 1, wherein: The tensile strength of the casting after being treated by the method is ≥368MPa, and the yield strength is ≥316MPa; the flatness deviation of the casting is 0.1-0.25mm / 100mm.

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