7040 aluminum alloy thermal refining method

Abstract

The invention belongs to the technical field of metal material quenching and tempering, and particularly relates to a 7040 aluminum alloy quenching and tempering method which sequentially comprises the following steps: step 1, solution treatment: heating an aluminum alloy to enable a strengthening phase in the aluminum alloy to be fully dissolved in a matrix to form a uniform supersaturated solid solution; secondly, air mist cooling is conducted, rapid cooling is conducted after solution treatment, precipitation of a strengthening phase is restrained, meanwhile, it is guaranteed that a cooling medium evenly covers the surface of the workpiece in the cooling process, and the situation of uneven cooling is avoided; and thirdly, aging treatment is conducted, specifically, the alloy of a supersaturated solid solution is obtained through air mist cooling. The hardening and tempering process combining solution treatment, air mist cooling and aging treatment is provided, the process combination is matched with one another, the alloy performance is effectively regulated and controlled, and an existing single treatment mode is broken through.

Description

Technical Field

[0001] The invention belongs to the technical field of quenching and tempering treatment of metal materials, and in particular relates to a quenching and tempering treatment method for a 7040 aluminum alloy, in particular a quenching and tempering treatment method for a high-strength and low-quenching-sensitivity 7040 aluminum alloy. Background Art

[0002] The 7040 aluminum alloy primarily consists of aluminum (Al), zinc (Zn), magnesium (Mg), and copper (Cu). Zinc and magnesium form the strengthening phase MgZn2, resulting in an aging-hardening effect; copper improves the alloy's strength and heat resistance. Additionally, trace elements such as manganese (Mn), chromium (Cr), and zirconium (Zr) are added in small amounts. Mn and Cr inhibit recrystallization and refine grains, while Zr forms a dispersed Al3Zr phase, hindering dislocation motion and improving the alloy's strength and stability. These elements work together to give the 7040 aluminum alloy its high strength and excellent overall performance.

[0003] Compared to traditional high-strength aluminum alloys, 7040 aluminum alloy maintains excellent mechanical properties over a wider range of quenching cooling rates, reducing performance fluctuations caused by differences in quenching cooling rates. This reduces residual stress, improves product dimensional accuracy and stability, reduces subsequent correction steps, and improves production efficiency and product quality. Therefore, it can be simply called "low quenching sensitivity 7040 aluminum alloy."

[0004] One of the core goals of developing 7040 aluminum alloy is to reduce quenching sensitivity. However, in the actual quenching process, it is very difficult to control quenching sensitivity while ensuring high strength. If the quenching cooling rate is too slow, the alloy cannot be fully strengthened and it is difficult to achieve high strength requirements. If the cooling rate is too fast, it will produce large thermal stress and structural stress, increase the risk of quenching deformation and cracking, and increase quenching sensitivity. In addition, when the shape and size of the part are complex, the cooling rate of different parts varies greatly, making it difficult to ensure uniform performance of each part. How to determine the appropriate quenching cooling rate and process parameters, and achieve precise control of the cooling rate of each part of large and complex parts is a key problem.

[0005] To achieve high strength and low quenching sensitivity, 7040 aluminum alloy needs to be tempered to finely control its microstructure, including controlling grain size, morphology, and the type, size, and distribution of strengthening phases. Grain refinement can improve alloy strength and toughness and reduce quenching sensitivity, but in actual production, due to the influence of various factors, achieving a uniform and fine grain structure is not easy. The precipitation and distribution of strengthening phases are also difficult to control. If the strengthening phases are too large or unevenly distributed, the overall performance of the alloy will be reduced. Therefore, how to achieve precise control of the microstructure through composition adjustment and process optimization is a technical difficulty. Summary of the Invention

[0006] The present invention addresses the problems in the prior art and proposes a method for tempering 7040 aluminum alloy with high strength and low quenching sensitivity. The technical solution of the present invention is as follows:

[0007] The 7040 aluminum alloy quenching and tempering method comprises the following steps in sequence:

[0008] Step 1: Solution treatment: Heat the aluminum alloy and maintain the temperature between 470℃ and 485℃ to fully dissolve the strengthening phase in the aluminum alloy into the matrix, and promote the integration of strengthening phases such as MgZn2 and CuAl2 into the aluminum matrix. The solution treatment time is 30min to 60min to form a uniform supersaturated solid solution.

[0009] Step 2: Air-mist cooling: Rapid cooling after solution treatment to inhibit the precipitation of strengthening phase. During air-mist cooling, adjust the compressed air pressure to 0.4MPa~0.6MPa and the water mist flow rate to 5L / min~10L / min, so that the aluminum alloy workpiece is cooled to room temperature within 3min~10min. At the same time, during the cooling process, ensure that the cooling medium evenly covers the workpiece surface to avoid uneven cooling;

[0010] Step 3: Aging treatment: After air-mist cooling, the alloy is subjected to supersaturated solid solution. In the aging treatment stage, the aging temperature range is 120°C to 180°C, and the aging time is 10h to 24h. Single-stage aging or multi-stage aging can be used.

[0011] As an improvement of the above technical solution, in step one, the 7040 aluminum alloy is solution treated and rapidly cooled to form a supersaturated solid solution. The supersaturated solid solution is in an unstable state, and the solute atoms will gradually dissolve and precipitate to form a series of transition phases and stable phases.

[0012] As an improvement of the above technical solution, a GP zone enriched with solute atoms is first formed. As the aging time increases and the temperature rises, the GP zone gradually transforms into an η′ phase and finally forms a stable η phase.

[0013] As an improvement to the above technical solution, in step 2, the wind mist cooling time is 3 minutes to 10 minutes, and the compressed air flow rate is controlled at 10m 3 / h~30m 3 / h, and the water mist spray volume is controlled between 5L / h and 10L / h.

[0014] As an improvement to the above technical solution, in step three, a two-stage aging treatment is adopted. The first-stage aging temperature is 120°C to 140°C, and the holding time is 3h to 6h. The purpose of the first-stage aging is to form a large number of fine GP zones and η′ phases, laying the foundation for subsequent strengthening; the second-stage aging temperature is 160°C to 180°C, and the holding time is 2h to 4h, which promotes further growth and coarsening of the η′ phase, optimizes the distribution of the precipitated phase, and improves the comprehensive properties of the alloy.

[0015] The 7040 aluminum alloy quenching and tempering method described in the present invention finely controls its microstructure, ultimately obtaining a high-strength, low-quenching-sensitivity 7040 aluminum alloy. The 7040 aluminum alloy quenching and tempering method described in the present invention is significantly innovative in terms of process optimization, microstructure control, and performance improvement, effectively resolving existing technical difficulties and improving the overall performance of the 7040 aluminum alloy. Its beneficial effects are:

[0016] 1. Innovative Quenching and Tempering Process Combination: Existing technologies have difficulties controlling the quenching sensitivity of 7040 aluminum alloy while ensuring high strength. This invention proposes a quenching and tempering process that combines solution treatment, air mist cooling, and aging treatment. The solution treatment temperature is precisely set at 470°C to 485°C and the cooling time is 30 to 60 minutes to ensure full dissolution of the strengthening phase. During air mist cooling, the precipitation of the strengthening phase is suppressed by controlling the compressed air pressure, water mist flow rate, and cooling time to maintain a supersaturated solid solution state. The aging treatment adopts a temperature range of 120°C to 180°C and a duration of 10 to 24 hours, with single-stage or multi-stage aging options available. This process combination works together to effectively control the alloy's properties, breaking through the existing single treatment method.

[0017] 2. Fine-tuning the Microstructure: This invention addresses the challenges of microstructural control in 7040 aluminum alloy by providing a process for the transformation from a supersaturated solid solution to various precipitated phases. During aging, solute atoms sequentially form GP zones, η′ phases, and stable η phases. By controlling the aging temperature and time, the size, distribution, and number of these precipitated phases can be precisely controlled, achieving fine-tuned microstructural control and ultimately improving the alloy's overall performance.

[0018] 3. Significantly Improved 7040 Aluminum Alloy Performance: The quenching and tempering treatment method described in this invention significantly improves the mechanical properties of 7040 aluminum alloy. Comparing data before and after treatment, the tensile strength increases from 200MPa-300MPa to 450MPa-600MPa for single-stage aging and 600MPa-800MPa for double-stage aging. Yield strength, hardness, and fatigue strength also increase significantly, while elongation remains within a reasonable range. This comprehensive performance improvement, especially the reduction of quenching sensitivity while maintaining high strength, resolves a long-standing technical bottleneck and meets the stringent material requirements of high-end fields such as aerospace and automotive manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a flow chart of the 7040 aluminum alloy tempering treatment method described in the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0021] like Figure 1 In order to obtain a high-strength and low-quenching-sensitivity 7040 aluminum alloy, the 7040 aluminum alloy quenching and tempering treatment method of the present invention comprises the following steps in sequence:

[0022] Step 1: Solution treatment: Heat the aluminum alloy and maintain the temperature between 470℃ and 485℃ to fully dissolve the strengthening phase in the aluminum alloy into the matrix, and promote the integration of strengthening phases such as MgZn2 and CuAl2 into the aluminum matrix. The solution treatment time is 30min to 60min to form a uniform supersaturated solid solution.

[0023] Step 2: Air-mist cooling: Rapid cooling after solution treatment to inhibit the precipitation of strengthening phase. During air-mist cooling, adjust the compressed air pressure to 0.4MPa~0.6MPa and the water mist flow rate to 5L / min~10L / min, so that the aluminum alloy workpiece is cooled to room temperature within 3min~10min. At the same time, during the cooling process, ensure that the cooling medium evenly covers the workpiece surface to avoid uneven cooling;

[0024] Step 3: Aging treatment: After air-mist cooling, the alloy is subjected to supersaturated solid solution. In the aging treatment stage, the aging temperature range is 120°C to 180°C, and the aging time is 10h to 24h. Single-stage aging or multi-stage aging can be used.

[0025] The 7040 aluminum alloy quenching and tempering treatment method of the present invention, in step one, after solution treatment and rapid cooling, 7040 aluminum alloy forms a supersaturated solid solution. During the aging process, the supersaturated solid solution is in an unstable state, and solute atoms (such as zinc, magnesium, copper, etc.) are gradually precipitated and precipitated to form a series of transition phases and stable phases. First, a GP zone (i.e., GP zone, Guinier-Preston Zones) enriched with solute atoms is formed. As the aging time is extended and the temperature rises, the GP zone gradually transforms into η' phase (MgZn2), and finally forms a stable η phase (MgZn2). These precipitated phases are dispersed in the aluminum matrix, hindering dislocation movement, thereby realizing the strengthening of the alloy. Reasonable control of the aging temperature and time can make the alloy achieve a good balance in terms of strength, toughness and corrosion resistance.

[0026] The 7040 aluminum alloy quenching and tempering treatment method of the present invention, in step 2, the wind mist cooling time is 3min to 10min, and the compressed air flow rate is controlled at 10m 3 / h~30m 3 / h, and the water mist spray volume is controlled between 5L / h and 10L / h.

[0027] The cooling time for wind mist cooling depends primarily on the size and shape of the aluminum alloy workpiece, as well as the temperature after solution treatment. Generally speaking, for plates up to 10mm thick or workpieces with simple shapes, the cooling time is controlled within 3 to 5 minutes. For thicker workpieces (10mm to 30mm) or complex shapes, the cooling time can be extended to 5 to 10 minutes. In actual operation, the workpiece temperature is monitored in real time by a temperature sensor, and cooling is stopped when the workpiece temperature drops to room temperature (20°C to 25°C).

[0028] The compressed air flow rate of wind mist cooling directly affects the cooling effect and the distribution uniformity of the mist droplets. According to the size and shape of the workpiece, the compressed air flow rate is generally controlled at 10m 3 / h~30m 3 For large workpieces or workpieces with complex shapes, the compressed air flow rate should be appropriately increased to ensure that the cooling medium can fully cover the workpiece surface; for small workpieces, the compressed air flow rate can be appropriately reduced to avoid deformation of the workpiece caused by excessive cooling speed.

[0029] The water mist spray volume for air-mist cooling should match the compressed air flow rate to ensure uniform droplet distribution and cooling effectiveness. The water mist spray volume is generally controlled between 5L / h and 10L / h. In practice, the spray volume is controlled by adjusting the nozzle pressure and flow control valve of the water mist generation system. Furthermore, the water mist spray volume is adjusted appropriately based on the temperature changes and surface conditions of the workpiece during the cooling process to ensure stability and uniformity of the cooling process.

[0030] During the air mist cooling process, observe the cooling status of the workpiece at regular intervals (generally 0.5 to 1 minute) to check whether the cooling medium is evenly covering the workpiece surface and whether there is any local overheating or overcooling. At the same time, adjust the compressed air flow and water mist spray volume in a timely manner based on the temperature monitoring data to ensure the stability and uniformity of the cooling process. If any abnormal conditions are found during the cooling process, such as the temperature dropping too quickly or too slowly, or condensation on the workpiece surface, the cooling process should be stopped immediately, the cause analyzed, and appropriate measures taken to adjust it.

[0031] In the 7040 aluminum alloy tempering method described herein, air-mist cooling, a rapid cooling method in step 2, is employed after solution treatment of the 7040 aluminum alloy. This method maintains the supersaturated solid solution state formed at high temperatures. If the cooling rate is too slow, dissolved strengthening phases may reprecipitate, affecting the strengthening effect of subsequent aging treatment. Air-mist cooling, through the combination of high-speed airflow and fine water mist, provides a relatively uniform and rapid cooling rate, inhibiting the precipitation of strengthening phases and allowing the alloy to retain its supersaturated solid solution structure at room temperature.

[0032] The 7040 aluminum alloy quenching and tempering method of the present invention adopts a two-stage aging treatment in step three. The first-stage aging temperature is 120°C to 140°C, and the holding time is 3 hours to 6 hours. The purpose of the first-stage aging is to form a large number of fine GP zones and η' phases, laying the foundation for subsequent strengthening. The second-stage aging temperature is 160°C to 180°C, and the holding time is 2 hours to 4 hours, which promotes further growth and coarsening of the η' phase, optimizes the distribution of precipitated phases, and improves the comprehensive properties of the alloy.

[0033] During the aging treatment, a lower aging temperature (such as 120℃~140℃) is conducive to the formation of fine and dispersed precipitates, which can obtain higher strength and good toughness, but the aging time is relatively long; a higher aging temperature (such as 160℃~180℃) can accelerate the aging hardening rate and shorten the aging time, but may cause the precipitates to coarsen, reducing the strength and toughness of the alloy. The specific aging temperature can be determined comprehensively based on the performance requirements and production efficiency of the workpiece. For example, for structural parts in the aerospace field with extremely high requirements for strength and fatigue performance, an aging temperature of 130℃~140℃ can be selected; for fields such as automobile manufacturing that are more sensitive to cost and production efficiency, the aging temperature can be appropriately increased to 160℃~170℃.

[0034] The aging time is closely related to the aging temperature. At lower aging temperatures, the aging time is usually 10 to 24 hours; at higher aging temperatures, the aging time can be shortened to 4 to 8 hours. To determine the optimal aging time, an aging hardening curve can be drawn through preliminary experiments to observe how the alloy's strength, hardness, and other properties change over time, and find the aging time corresponding to when the properties reach their peak. At the same time, taking into account the size and shape of the workpiece, for workpieces with larger sizes or complex shapes, due to the relatively slow heat transfer and solute atomic diffusion, the aging time can be appropriately extended by 1 to 2 hours to ensure uniform and consistent overall performance of the workpiece.

[0035] Single-stage aging is simple to operate and suitable for general industrial applications with relatively low performance requirements, such as building doors and windows, and general mechanical parts. Multi-stage aging (such as double-stage aging and triple-stage aging) uses staged aging at different temperatures to better control the type, size, and distribution of precipitated phases. While increasing alloy strength, it also significantly improves its corrosion and fatigue resistance. It is suitable for applications with demanding performance requirements for aluminum alloys, such as aerospace and high-end automotive manufacturing.

[0036] During the aging treatment, the alloy is cooled by wind and mist to obtain a supersaturated solid solution. During the aging treatment stage, it is heated to a certain temperature and kept warm. This process promotes the solute atoms in the supersaturated solid solution to dissolve and precipitate, forming a dispersed and fine strengthening phase, thereby significantly improving the strength, hardness and other mechanical properties of the alloy. For 7040 aluminum alloy, the strengthening phase precipitated during the aging treatment hinders dislocation movement and achieves alloy strengthening. If the aging treatment is carried out before wind and mist cooling, since there is no supersaturated solid solution as a basis, the solute atoms cannot be effectively precipitated and evenly dispersed, and it is difficult to achieve the expected strengthening effect.

[0037] After solution treatment, air-mist cooling, and aging treatment, the mechanical properties of 7040 aluminum alloy are significantly improved. The specific changes are affected by many factors, and the treatment process needs to be optimized according to demand in actual application.

[0038]

[0039]

[0040] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. 7040 aluminum alloy quenching and tempering method, characterized in that: The following steps are included in sequence: Step 1: Solution treatment: Heat the aluminum alloy and maintain the temperature between 470℃ and 485℃ to fully dissolve the strengthening phase in the aluminum alloy into the matrix, and promote the integration of strengthening phases such as MgZn2 and CuAl2 into the aluminum matrix. The solution treatment time is 30min to 60min to form a uniform supersaturated solid solution. Step 2: Air-mist cooling: Rapid cooling after solution treatment to inhibit the precipitation of strengthening phase. During air-mist cooling, adjust the compressed air pressure to 0.4MPa~0.6MPa and the water mist flow rate to 5L / min~10L / min, so that the aluminum alloy workpiece is cooled to room temperature within 3min~10min. At the same time, during the cooling process, ensure that the cooling medium evenly covers the workpiece surface to avoid uneven cooling; Step 3: Aging treatment: After air-mist cooling, the alloy is subjected to supersaturated solid solution. In the aging treatment stage, the aging temperature range is 120°C to 180°C, and the aging time is 10h to 24h. Single-stage aging or multi-stage aging can be used.

2. The 7040 aluminum alloy quenching and tempering method according to claim 1, wherein: In the step 1, after the 7040 aluminum alloy is solution treated and rapidly cooled, a supersaturated solid solution is formed. The supersaturated solid solution is in an unstable state, and solute atoms gradually desolvate and precipitate to form a series of transition phases and stable phases.

3. The 7040 aluminum alloy quenching and tempering method according to claim 2, wherein: First, the GP zone enriched with solute atoms is formed. With the extension of aging time and the increase of temperature, the GP zone gradually transforms into the η′ phase and finally forms the stable η phase.

4. The 7040 aluminum alloy quenching and tempering method according to claim 1, wherein: In step 2, the wind and mist cooling time is 3 minutes to 10 minutes, and the compressed air flow rate is controlled at 10m 3 / h~30m 3 / h, and the water mist spray volume is controlled between 5L / h and 10L / h.

5. The 7040 aluminum alloy quenching and tempering method according to claim 1, wherein: In step three, a two-stage aging treatment is adopted. The first-stage aging temperature is 120℃~140℃, and the holding time is 3h~6h. The purpose of the first-stage aging is to form a large number of fine GP zones and η′ phases, laying the foundation for subsequent strengthening; the second-stage aging temperature is 160℃~180℃, and the holding time is 2h~4h, which promotes the further growth and coarsening of the η′ phase, optimizes the distribution of the precipitated phase, and improves the comprehensive performance of the alloy.

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