Cooling treatment method for 6061 aluminum alloy

Abstract

The invention belongs to the technical field of metal material quenching and tempering treatment, and particularly relates to a 6061 aluminum alloy cooling treatment method which comprises the steps of high-temperature quenching, low-temperature slow cooling and tail-section deep cooling. According to the cooling treatment method, the cooling process combining high-temperature quenching, low-temperature slow cooling and tail-section deep cooling is adopted, and the traditional single cooling mode is broken through. Grain growth is inhibited through high-temperature quenching, grains are refined, impurity phase distribution is improved, and a supersaturated solid solution is formed; low-temperature slow cooling promotes decomposition of a supersaturated solid solution, and impurity phase distribution and microstructure uniformity are optimized; and the microstructure is further optimized through tail section deep cooling, lattice defects are reduced, the grain boundary structure is stabilized, the existing problems are cooperatively solved from multiple aspects, and the electric conductivity of the 6061 aluminum alloy is comprehensively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal material quenching and tempering treatment, and in particular relates to a cooling treatment method for 6061 aluminum alloy. Background Art

[0002] 6061 aluminum alloy is a heat-strengthenable aluminum alloy with excellent comprehensive properties and is widely used in various fields. The electrical conductivity of 6061 aluminum alloy is crucial, directly affecting the fast and accurate transmission of signals. In electronic circuits, the high conductivity of 6061 aluminum alloy facilitates the rapid transmission of high-speed signals, reducing signal delay and distortion. For example, in electronic devices such as computer motherboards and mobile phone circuit boards, the use of high-conductivity aluminum alloys as connecting wires or shielding layers ensures stable transmission of electronic signals, improving device speed and stability. The high conductivity of 6061 aluminum alloy ensures efficient transmission of electrical energy. In power transmission applications such as wires and cables, high conductivity means low resistance to current flow. According to Joule's law, low resistance generates less heat, thereby reducing power loss during transmission and improving power transmission efficiency. For example, in long-distance power transmission lines, the use of high-conductivity 6061 aluminum alloy cables can effectively reduce line losses and save energy.

[0003] To improve the electrical conductivity of 6061 aluminum alloy, measures such as improving and optimizing the alloy composition and heat treatment can be taken. However, the existing 6061 aluminum alloy heat treatment process, due to limited heat treatment process means and a single control process, is prone to defects such as large internal stress, uneven structure, and difficulty in eliminating residual stress, which directly affect the electrical conductivity of 6061 aluminum alloy. Summary of the Invention

[0004] The present invention addresses the problems in the prior art and proposes a cooling treatment method for 6061 aluminum alloy. The technical solution of the present invention is as follows:

[0005] The cooling treatment method of 6061 aluminum alloy comprises the following steps in sequence:

[0006] Step1, rapid cooling at high temperature

[0007] Step 1.1 Select a quenching tank with rapid cooling capabilities and equip it with an efficient circulating cooling system. Ensure that the volume of the quenching tank can accommodate the 6061 aluminum alloy workpiece to be processed, and that the circulating cooling system can operate normally to quickly remove heat.

[0008] Step 1.2 Prepare the cooling medium, using water or quenching oil. If water is selected as the cooling medium, ensure that the water is clean and free of impurities. Filter the water in advance. If quenching oil is used, select the appropriate quenching oil type based on the characteristics of the aluminum alloy, such as fast bright quenching oil, which has the characteristics of fast cooling speed and can make the workpiece surface bright.

[0009] Step 1.3 High temperature rapid cooling control process

[0010] The 6061 aluminum alloy workpiece after melting and casting is quickly placed in the quenching tank. At this time, the workpiece temperature is 600-700℃. Water or quenching oil is used as the cooling medium to continuously cool the workpiece until the temperature drops to 450-500℃.

[0011] Step 2: Slow cooling at low temperature

[0012] Step 2.1 Switch the cooling device to a cooling box with a controllable air cooling system;

[0013] Step 2.1 Low temperature slow cooling control process

[0014] Transfer the aluminum alloy workpiece that has been rapidly cooled at high temperature to a cooling box. At this time, gradually reduce the cooling rate and control the cooling rate at 3-5°C / s by adjusting the air cooling system. During the cooling process, allow the workpiece to cool evenly to avoid uneven structure caused by local excessive cooling or excessive slowness. Continue cooling until the workpiece temperature drops to 150-200°C.

[0015] Step 3: Deep cooling at the end

[0016] Step 3.1 Select a liquid nitrogen cryogenic box and ensure that the temperature of the cryogenic box can be stably maintained at -196℃±5℃ and has good thermal insulation performance to reduce the volatilization loss of liquid nitrogen;

[0017] Step 3.2 End-stage cryogenic control process

[0018] The aluminum alloy workpiece that has been slowly cooled at low temperature is quickly placed in a liquid nitrogen cryogenic box and kept at -196°C for 1 to 2 hours. After the cryogenic cooling is completed, the workpiece is taken out of the cryogenic box and allowed to slowly return to room temperature.

[0019] As an improvement of the above technical solution, in step 1.3, water is used as the cooling medium, the initial temperature of the water is controlled at 15-25°C, and the water is made to flow rapidly through a circulating cooling system to ensure that the cooling rate reaches 20-30°C / s.

[0020] As an improvement of the above technical solution, in step 1.3, quenching oil is used as the cooling medium, the oil temperature is controlled at 40-60°C, and the characteristics of quenching oil are utilized to achieve rapid cooling, with the cooling rate maintained at 15-20°C / s.

[0021] As an improvement to the above technical solution, the final cryogenic treatment adopts a graded cooling method, first cooling the aluminum alloy to -80°C at a cooling rate of 5 to 10°C / min, and then cooling it to -196°C at a cooling rate of 1 to 2°C / min.

[0022] As an improvement of the above technical solution, after the final cryogenic treatment, the aluminum alloy is restored from the cryogenic temperature to room temperature by slowly heating, with the heating rate controlled at 1 to 5°C / min, and a pressure of 5 to 10 MPa can be applied during the heating process.

[0023] The 6061 aluminum alloy cooling treatment method of the present invention effectively solves the cooling problem of 6061 aluminum alloy heat treatment and improves the electrical conductivity of 6061 aluminum alloy. Its beneficial effects are:

[0024] 1. To address the existing 6061 aluminum alloy heat treatment processes, which suffer from high internal stress, uneven microstructure, and difficulty eliminating residual stress, which affect electrical conductivity, the cooling method proposed in this invention utilizes a cooling process that combines high-temperature rapid cooling, low-temperature slow cooling, and a final deep cooling stage, breaking away from the traditional single cooling mode. High-temperature rapid cooling inhibits grain growth, refines grains, improves impurity phase distribution, and forms a supersaturated solid solution; low-temperature slow cooling promotes the decomposition of the supersaturated solid solution, optimizing impurity phase distribution and microstructural uniformity; and the final deep cooling stage further optimizes the microstructure, reduces lattice defects, and stabilizes grain boundary structure. This multi-faceted approach synergistically addresses existing issues and comprehensively improves the electrical conductivity of 6061 aluminum alloy.

[0025] 2. The cooling treatment method proposed in the present invention is adapted to the needs of internal structural transformation. The three steps of the cooling treatment have a strict sequence, which is in line with the characteristics of aluminum alloy structural transformation and the need to improve conductivity. High-temperature rapid cooling forms a supersaturated solid solution, which lays the foundation for subsequent treatment; low-temperature slow cooling optimizes the structure based on the decomposition of the supersaturated solid solution; and the final deep cooling further improves the microstructure based on the previous treatment. This combined cooling method is carefully optimized and verified by actual experiments based on the characteristics of aluminum alloy materials. Compared with traditional random or single cooling methods, it has clear targeting and can accurately control the structural transformation of aluminum alloys to achieve improved conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a flow chart of the cooling treatment method for 6061 aluminum alloy described in the present invention. DETAILED DESCRIPTION

[0027] 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.

[0028] like Figure 1 The cooling treatment method of 6061 aluminum alloy of the present invention comprises the following steps in sequence:

[0029] Step1, rapid cooling at high temperature

[0030] Step 1.1 Select a quenching tank with rapid cooling capabilities and equip it with an efficient circulating cooling system. Ensure that the volume of the quenching tank can accommodate the 6061 aluminum alloy workpiece to be processed, and that the circulating cooling system can operate normally to quickly remove heat.

[0031] Step 1.2 Prepare the cooling medium, using water or quenching oil. If water is selected as the cooling medium, ensure that the water is clean and free of impurities. Filter the water in advance. If quenching oil is used, select the appropriate quenching oil type based on the characteristics of the aluminum alloy, such as fast bright quenching oil, which has the characteristics of fast cooling speed and can make the workpiece surface bright.

[0032] Install high-precision temperature sensors in the cooling equipment to monitor the temperature changes of the aluminum alloy workpiece in real time with an accuracy of ±1°C to accurately grasp the cooling process;

[0033] Step 1.3 High temperature rapid cooling control process

[0034] The 6061 aluminum alloy workpiece after melting and casting is quickly placed in the quenching tank. At this time, the workpiece temperature is generally between 600 and 700°C. When water is used as the cooling medium, the initial temperature of the water is controlled at 15 to 25°C. The water is made to flow rapidly through the circulating cooling system to ensure that the cooling rate reaches 20 to 30°C / s. If quenching oil is used, the oil temperature is controlled at 40 to 60°C. The characteristics of the quenching oil are used to achieve rapid cooling, and the cooling rate is maintained at 15 to 20°C / s.

[0035] Continue cooling until the workpiece temperature drops to 450-500°C. During the cooling process, pay close attention to the data from the temperature sensor to ensure a stable cooling rate to avoid affecting the structure and conductivity of the aluminum alloy due to excessively fast or slow cooling.

[0036] Step 2: Slow cooling at low temperature

[0037] Step 2.1 Switch the cooling equipment to a cooling box with a controllable air cooling system. Adjust the wind speed and air volume of the cooling system to achieve slow cooling. Install a temperature control device in the cooling box to precisely control the temperature inside the box with an accuracy of ±2°C, providing a stable environment for low-temperature slow cooling.

[0038] Step 2.1 Low temperature slow cooling control process

[0039] Transfer the aluminum alloy workpiece that has been rapidly cooled at high temperature to the cooling box. At this time, gradually reduce the cooling rate and control the cooling rate at 3-5°C / s by adjusting the air cooling system. During the cooling process, allow the workpiece to cool evenly to avoid uneven structure caused by local cooling that is too fast or too slow.

[0040] Continue cooling until the workpiece temperature drops to 150-200°C. At this stage, due to the slow cooling rate, the supersaturated solid solution inside the alloy has enough time to decompose, reducing lattice distortion and improving conductivity.

[0041] Step 3: Deep cooling at the end

[0042] Step 3.1 Select a liquid nitrogen cryogenic box to ensure that the temperature of the cryogenic box can be stably maintained at around -196°C and has good thermal insulation performance to reduce the volatilization loss of liquid nitrogen;

[0043] A temperature monitoring device is installed in the cryogenic box to monitor the temperature change of the workpiece in real time during the cryogenic process with an accuracy of ±5°C. At the same time, a safety protection device is installed to prevent operators from being harmed by low temperatures during operation.

[0044] Step 3.2 End-stage cryogenic control process

[0045] The aluminum alloy workpiece that has been slowly cooled at low temperatures is quickly placed in a liquid nitrogen cryogenic box and kept at -196°C for 1 to 2 hours. During the cryogenic process, the microstructure inside the aluminum alloy is further optimized, and the solute atoms are more evenly distributed, thereby improving the conductivity.

[0046] After deep cooling, take the workpiece out of the cryogenic box and allow it to slowly return to room temperature. During the recovery process, be careful to avoid frost or other contamination on the workpiece surface, which may affect the final conductivity improvement effect.

[0047] The cooling treatment method for 6061 aluminum alloy described in the present invention utilizes high-temperature rapid cooling to achieve grain refinement and improve electrical conductivity. 6061 aluminum alloy is at a high temperature of 600-700°C, resulting in high atomic mobility. When rapidly placed in a quenching tank for high-temperature rapid cooling, with cooling rates reaching 20-30°C / s (water cooling) or 15-20°C / s (oil cooling), atoms do not have enough time to fully diffuse, resulting in the rapid formation of a large number of crystal nuclei. Due to the rapid cooling rate, the nuclei growth time is shortened, thus inhibiting grain growth and forming a large number of fine and uniform grains. From a microscopic perspective, fine grains increase the number of grain boundaries. Grain boundaries are a type of planar defect in a crystal, with irregular atomic arrangement. During electrical conduction, free electrons traveling within a uniform crystal are scattered upon encountering grain boundaries. However, compared to coarse grains, fine grains have denser and more evenly distributed grain boundaries, which reduces the probability of electron scattering and makes it easier for electrons to conduct between grains. This reduces obstacles to electron conduction and, in turn, improves the electrical conductivity of the aluminum alloy.

[0048] The 6061 aluminum alloy cooling treatment method described in the present invention adopts high-temperature rapid cooling treatment to improve the precipitation and distribution of impurity phases and improve electrical conductivity. Impurity elements such as Fe and Cr are present in the 6061 aluminum alloy. During the high-temperature rapid cooling process, the diffusion of these impurity elements is suppressed. Some impurity elements do not have time to form coarse metal compounds, but are precipitated in the form of small dispersions. For example, the Fe element may form a coarse AlFeSi phase when slowly cooled, which seriously hinders the movement of electrons and reduces electrical conductivity. However, under high-temperature rapid cooling conditions, the AlFeSi phase formed by the Fe element is small in size and evenly distributed in the matrix, reducing the obstruction to the electron conduction path and reducing the negative impact on electrical conductivity. Moreover, rapid cooling makes the distribution of impurity phases more uniform within the crystal and at the grain boundary, avoiding the large-scale aggregation of impurity phases at the grain boundary, further reducing the interference with the movement of electrons, and improving electrical conductivity.

[0049] The 6061 aluminum alloy cooling treatment method of the present invention adopts high-temperature rapid cooling treatment, which helps supersaturated solid solution to form and improve electrical conductivity. During high-temperature rapid cooling, the alloying elements (such as Mg, Si, etc.) in the 6061 aluminum alloy do not have enough time to fully diffuse and precipitate during the rapid cooling process, and are retained in the aluminum matrix in large quantities, forming a supersaturated solid solution. Although the supersaturated solid solution can cause lattice distortion to a certain extent, which has a certain hindering effect on electrical conduction, in the subsequent cooling and processing process, this supersaturated state provides a basis for the optimization of alloy properties. In the subsequent low-temperature slow cooling stage, the supersaturated solid solution can be more evenly decomposed to precipitate fine and dispersed strengthening phases, which have a smaller negative impact on electrical conductivity while improving alloy strength. The presence of the supersaturated solid solution makes the distribution of alloying elements in the matrix more uniform, provides a more uniform microenvironment for electronic conduction, and is conducive to improving electrical conductivity.

[0050] The 6061 aluminum alloy cooling treatment method described in the present invention adopts low-temperature slow cooling treatment to promote the decomposition of the supersaturated solid solution and improve the electrical conductivity. After high-temperature rapid cooling, the 6061 aluminum alloy forms a supersaturated solid solution, in which a large amount of alloying elements (such as Mg, Si, etc.) are supersaturatedly dissolved in the aluminum matrix. Although this supersaturated state provides a basis for subsequent strengthening treatment, it also causes lattice distortion, increases electron scattering, and thus reduces electrical conductivity. In the low-temperature slow cooling stage, the cooling rate is controlled at 3 to 5°C / s, the atoms inside the alloy acquire a certain degree of mobility, and the supersaturated solid solution begins to decompose. Elements such as Mg and Si gradually precipitate from the aluminum matrix to form a dispersed Mg2Si strengthening phase. The precipitation of these strengthening phases reduces the content of alloying elements dissolved in the matrix, reduces the degree of lattice distortion, and makes the movement of electrons in the crystal smoother, thereby improving electrical conductivity.

[0051] The 6061 aluminum alloy cooling treatment method described in the present invention adopts low-temperature slow cooling treatment to optimize the distribution of impurity phases and improve electrical conductivity. 6061 aluminum alloy inevitably contains some impurity elements, such as Fe, Cr, etc. During the high-temperature rapid cooling process, although some impurity elements are precipitated in the form of fine dispersions, some may still be in a supersaturated state and solid-dissolved in the matrix. During the low-temperature slow cooling stage, these impurity elements have more time to diffuse and aggregate, forming a more stable impurity phase. At the same time, the slow cooling rate enables the impurity phase to be more evenly distributed in the matrix, avoiding local aggregation of the impurity phase. For example, the size and distribution of the AlFeSi phase formed by the Fe element are further optimized during the low-temperature slow cooling process, reducing the obstruction to electron conduction and helping to improve electrical conductivity.

[0052] The 6061 aluminum alloy cooling treatment method described in the present invention adopts low-temperature slow cooling treatment to improve the uniformity of microstructure and enhance electrical conductivity. During the low-temperature slow cooling process, the temperature gradient inside the alloy is small and the structural transformation is more uniform. Due to the slow cooling rate, the alloy structure in each part has enough time to adjust and balance, reducing structural stress and composition segregation. From a microscopic point of view, a uniform microstructure means that the obstacles encountered by electrons during conduction are more consistent, reducing electron scattering and conductivity differences caused by structural unevenness. In the case of uneven cooling, inconsistent grain sizes in local areas or uneven concentrations of alloying elements may occur, which will affect the conduction of electrons. Low-temperature slow cooling can effectively improve this situation, making the microstructure of the alloy more uniform, thereby improving the overall electrical conductivity.

[0053] The cooling treatment method for 6061 aluminum alloy described in the present invention adopts a tail-stage cryogenic treatment to promote microstructure optimization and improve electrical conductivity. In a cryogenic environment of -196°C, the atomic activity inside the aluminum alloy is sharply reduced, and the diffusion rate of solute atoms in the supersaturated solid solution is also significantly reduced. This allows the solute atoms to be redistributed in a more stable state and dispersed more evenly in the aluminum matrix. For example, solute atoms such as Mg and Si will form smaller and more dispersed precipitates. These precipitates are evenly distributed in the lattice, reducing obstacles to electron scattering, thereby increasing the electron mobility and further improving the electrical conductivity.

[0054] The 6061 aluminum alloy cooling treatment method described in the present invention adopts a tail-stage cryogenic treatment to reduce lattice defects and improve electrical conductivity. During the cryogenic treatment process, defects such as vacancies and dislocations in the aluminum alloy lattice will aggregate or rearrange. Vacancies are positions where atoms are missing in the crystal, which will scatter electrons and hinder electron conduction. Dislocations are linear defects in the crystal, which will cause lattice distortion and also affect electron movement. Under cryogenic conditions, vacancies may aggregate to form stable clusters, and dislocations may also undergo a certain degree of climb and cross-slip, making the distribution of lattice defects more reasonable, reducing the degree of lattice distortion, and reducing the obstacles encountered by electrons when conducting in the lattice, which is conducive to improving electrical conductivity.

[0055] The 6061 aluminum alloy cooling treatment method of the present invention utilizes a tail-stage cryogenic treatment to stabilize the grain boundary structure and improve electrical conductivity. Grain boundaries are interfaces between crystal grains and typically contain high energy and numerous defects, which scatter electrons. Cryogenic treatment can further order the atomic arrangement at the grain boundaries, reduce grain boundary energy, and stabilize the grain boundary structure. Simultaneously, impurity atoms and precipitated phases at the grain boundaries are redistributed during the cryogenic process, reducing impurity aggregation and coarsening of precipitated phases at the grain boundaries. This reduces the scattering effect of the grain boundaries on electrons and improves the electrical conductivity of the aluminum alloy.

[0056] The cooling treatment method for 6061 aluminum alloy described in the present invention adopts high-temperature rapid cooling, low-temperature slow cooling, and final deep cooling in a strict order, which is determined by the structural transformation characteristics of the aluminum alloy and the need to improve electrical conductivity.

[0057] The goal is to rapidly cool the 6061 aluminum alloy from a high temperature to 450-500°C in a short period of time, allowing the alloying elements to form a supersaturated solid solution in the aluminum matrix. This preserves some of the structural characteristics of the high-temperature phase, laying the foundation for subsequent processing. Without this initial high-temperature rapid cooling, the alloying elements will fully diffuse and precipitate during the slow cooling process, preventing the formation of a supersaturated solid solution and making it impossible to effectively improve the conductivity through subsequent processing.

[0058] Secondly, low-temperature slow cooling is used. On the basis of forming a supersaturated solid solution through high-temperature rapid cooling, the supersaturated solid solution is gradually decomposed through slow cooling, allowing the alloy elements to precipitate in the form of fine, dispersed strengthening phases, such as Mg2Si phase. At the same time, low-temperature slow cooling can also make the impurity phase distribution more uniform, reduce lattice distortion and structural stress, and further optimize the microstructure. If low-temperature slow cooling is performed first, since a supersaturated solid solution is not formed through high-temperature rapid cooling, the precipitation behavior of the alloy elements and the changes in the microstructure during the low-temperature slow cooling process will not meet the requirements for improving conductivity. Moreover, if low-temperature slow cooling is performed directly at high temperature, the cooling rate difference is too large, which may cause large internal stress in the workpiece and even deformation and cracking.

[0059] The final cryogenic treatment is to further treat the aluminum alloy after high-temperature rapid cooling and low-temperature slow cooling. Under cryogenic conditions, the internal microstructure of the aluminum alloy is further optimized, solute atoms are more evenly distributed, lattice defects are reduced, and the grain boundary structure is stabilized, thereby further improving conductivity. If the final cryogenic treatment is performed first, without the first two steps, the aluminum alloy's microstructure will not reach a state suitable for cryogenic treatment to improve conductivity, and the cryogenic treatment effect will not be fully realized. Direct cryogenic treatment may even lead to increased structural defects, thereby reducing performance.

[0060] In the cooling treatment method for 6061 aluminum alloy described in the present invention, the faster the cooling is, the better the final cryogenic treatment. Too fast a cooling is likely to cause new defects. A graded cooling method can be adopted, first cooling the aluminum alloy to -80°C at a relatively fast rate, and then slowly cooling it to -196°C. In the stage before -80°C, the cooling rate can be controlled at 5-10°C / min, and in the subsequent stage, it can be controlled at 1-2°C / min. This allows the internal structure of the aluminum alloy sufficient time to adjust, reducing the internal stress and micro defects caused by excessive cooling.

[0061] The cooling treatment method for 6061 aluminum alloy described herein involves slowly heating the aluminum alloy from the cryogenic temperature to room temperature after the final cryogenic treatment, with the heating rate controlled at 1 to 5°C / min. This prevents rapid heating that could redistribute stress within the structure or create new defects. Furthermore, a certain pressure, such as 5 to 10 MPa, can be applied during the heating process to further stabilize the microstructure and improve the material's density, thereby further enhancing electrical conductivity.

[0062] After the high-temperature rapid cooling, low-temperature slow cooling, and final cryogenic treatment described in the present invention, the electrical conductivity of 6061 aluminum alloy is improved as shown in the following table:

[0063]

[0064] 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. 6061 aluminum alloy cooling treatment method, characterized in that, The following steps are included in sequence: Step1. Rapid cooling at high temperature Step 1.1 Select a quenching tank with rapid cooling capabilities and equip it with an efficient circulating cooling system. Ensure that the volume of the quenching tank can accommodate the 6061 aluminum alloy workpiece to be processed, and that the circulating cooling system can operate normally to quickly remove heat. Step 1.2 Prepare the cooling medium, using water or quenching oil. If water is selected as the cooling medium, ensure that the water is clean and free of impurities. Filter the water in advance. If quenching oil is used, select the appropriate quenching oil type based on the characteristics of the aluminum alloy, such as fast bright quenching oil, which has the characteristics of fast cooling speed and can make the workpiece surface bright. Step 1.3 High temperature rapid cooling control process The 6061 aluminum alloy workpiece after melting and casting is quickly placed in the quenching tank. At this time, the workpiece temperature is 600-700℃. Water or quenching oil is used as the cooling medium to continuously cool the workpiece until the temperature drops to 450-500℃. Step 2: Slow cooling at low temperature Step 2.1 Switch the cooling device to a cooling box with a controllable air cooling system; Step 2.1 Low temperature slow cooling control process Transfer the aluminum alloy workpiece that has been rapidly cooled at high temperature to a cooling box. At this time, gradually reduce the cooling rate and control the cooling rate at 3-5°C / s by adjusting the air cooling system. During the cooling process, allow the workpiece to cool evenly to avoid uneven structure caused by local excessive cooling or excessive slowness. Continue cooling until the workpiece temperature drops to 150-200°C. Step 3: Deep cooling at the end Step 3.1 Select a liquid nitrogen cryogenic box and ensure that the temperature of the cryogenic box can be stably maintained at -196℃±5℃ and has good thermal insulation performance to reduce the volatilization loss of liquid nitrogen; Step 3.2 End-stage cryogenic control process The aluminum alloy workpiece that has been slowly cooled at low temperature is quickly placed in a liquid nitrogen cryogenic box and kept at -196°C for 1 to 2 hours. After the cryogenic cooling is completed, the workpiece is taken out of the cryogenic box and allowed to slowly return to room temperature.

2. The cooling treatment method for 6061 aluminum alloy according to claim 1, characterized in that: In Step 1.3, water is used as the cooling medium, and the initial temperature of the water is controlled at 15-25°C. The water is made to flow rapidly through the circulating cooling system to ensure that the cooling rate reaches 20-30°C / s.

3. The cooling treatment method for 6061 aluminum alloy according to claim 1, wherein: In step 1.3, quenching oil is used as the cooling medium, the oil temperature is controlled at 40-60°C, and the characteristics of quenching oil are used to achieve rapid cooling, and the cooling rate is maintained at 15-20°C / s.

4. The cooling treatment method for 6061 aluminum alloy according to claim 1, wherein: The final cryogenic treatment adopts a graded cooling method, first cooling the aluminum alloy to -80°C at a cooling rate of 5-10°C / min, and then cooling it to -196°C at a cooling rate of 1-2°C / min.

5. The cooling treatment method for 6061 aluminum alloy according to claim 1, wherein: After the final cryogenic treatment, the aluminum alloy is restored from the cryogenic temperature to room temperature by slowly heating, with the heating rate controlled at 1-5°C / min, and a pressure of 5-10 MPa can be applied during the heating process.

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