A method of reducing residual stress in an aluminum alloy by cold treatment

Abstract

This invention relates to the field of aluminum alloy material processing technology, specifically to a cold treatment method for reducing residual stress in aluminum alloys; the method includes the following steps: aging the aluminum alloy material at a temperature of 140±5℃ using air as the cooling medium to cool the material to room temperature; placing the cooled aluminum alloy material into an ultra-low temperature device within 1 hour and cooling it to -125±5℃; maintaining this temperature for 6±0.5 hours after the temperature in the ultra-low temperature device stabilizes at -125±5℃; and after the heat preservation is completed, removing the aluminum alloy material and placing it in a room temperature environment to allow it to naturally warm up to room temperature. Through this method, the residual stress of the aluminum alloy is effectively reduced, thus minimizing workpiece deformation during processing.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy material processing technology, and in particular to a cold treatment method for reducing residual stress in aluminum alloys. Background Technology

[0002] With the rapid development of modern manufacturing towards lightweight, precision, and high performance, aluminum alloys, with their outstanding advantages such as low density, high specific strength, excellent thermal and electrical conductivity, and good processability, have become one of the core materials in key fields such as aerospace, automobile manufacturing, precision machinery, and turbomachinery.

[0003] In the field of turbomachinery, aluminum alloys are widely used as manufacturing materials for critical components such as bearings and oil seals, which have extremely high requirements for dimensional accuracy and operational stability. Their application has effectively promoted the upgrading of related equipment towards high efficiency, energy saving, and miniaturization. Meanwhile, industrial cryogenic treatment technology, as an important means of improving material performance, typically refers to the process of cooling materials to -70℃ to -196℃ after heat treatment quenching. The treatment at -100℃ to -196℃ is defined as deep cryogenic treatment. This technology plays a crucial role in improving the dimensional stability, hardness, wear resistance, and corrosion resistance of materials, reducing residual stress, and extending the service life of workpieces by controlling the internal microstructure of the material. It has already been maturely applied in many scientific research and industrial fields such as aviation, aerospace, weaponry, shipbuilding, and mold making.

[0004] The preparation of finished aluminum alloy products typically involves multiple processes, including pre-forging of aluminum alloy ingots, final forging, heat treatment strengthening, and machining. During the heat treatment process, due to factors such as the size differences and shape complexity of the aluminum alloy workpiece, uneven heating and cooling rates are formed between its surface and core, resulting in uneven temperature distribution and asynchronous microstructural transformation. Consequently, significant residual stress is generated inside the workpiece. Residual stress can seriously affect the fatigue strength, stress corrosion resistance, and dimensional stability of structural components, shorten the service life of the workpiece, and cause workpiece deformation during subsequent machining due to stress release, reducing the product machining accuracy.

[0005] In conclusion, it is essential to propose a cold treatment method that effectively reduces residual stress in aluminum alloys and minimizes workpiece deformation. Summary of the Invention

[0006] The purpose of this invention is to provide a cold treatment method for reducing residual stress in aluminum alloys, thereby achieving the goal of efficiently reducing residual stress in aluminum alloys and minimizing workpiece deformation during processing.

[0007] To achieve the above objectives, the present invention employs a cold treatment method for reducing residual stress in aluminum alloys, comprising the following steps: The aluminum alloy material is subjected to aging treatment at an aging temperature of 140±5℃, with air as the cooling medium, to cool the material to room temperature. Aluminum alloy material cooled to room temperature was placed in an ultra-low temperature device within 1 hour and cooled to -125±5℃; Once the temperature inside the cryogenic equipment stabilizes at -125±5℃, maintain this temperature for 6±0.5 hours. After the heat preservation is completed, remove the aluminum alloy material and place it in a room temperature environment to allow it to naturally warm up to room temperature.

[0008] In the step of placing aluminum alloy material cooled to room temperature into an ultra-low temperature device within 1 hour and cooling it to -125±5℃: The ultra-low temperature equipment is an ultra-low temperature freezer.

[0009] In the step of maintaining the temperature inside the cryogenic equipment at -125±5℃ for 6±0.5h: The constant temperature start time is calculated from when the temperature inside the ultra-low temperature equipment returns to the set -125±5℃.

[0010] One step involves removing the aluminum alloy material after the heat preservation process is complete and placing it in a room temperature environment to allow it to naturally warm up to room temperature. After the temperature recovery, the residual stress relief rate of the aluminum alloy material is not less than 45%, the ductility is increased by not less than 4.5%, the yield strength is increased by not less than 3MPa, and the tensile strength is increased by not less than 11MPa.

[0011] The aluminum alloy material includes bearings and oil seals used in the field of impeller machining.

[0012] The present invention discloses a cold treatment method for reducing residual stress in aluminum alloys, comprising the following steps: aging the aluminum alloy material at a temperature of 140±5℃ using air as the cooling medium to cool the material to room temperature; placing the cooled aluminum alloy material into an ultra-low temperature chamber within 1 hour and cooling it to -125±5℃; maintaining this temperature for 6±0.5 hours after the temperature in the ultra-low temperature chamber stabilizes at -125±5℃; and after the heat preservation is completed, removing the aluminum alloy material and placing it in a room temperature environment to allow it to naturally warm to room temperature. Through this method, the residual stress in the aluminum alloy is effectively reduced, thus minimizing workpiece deformation during processing. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a flowchart of the steps of the cold treatment method for reducing residual stress in aluminum alloys according to the present invention.

[0015] Figure 2 This is a flow chart of the material cold treatment process of the present invention.

[0016] Figure 3 This is the standard grading chart (level 5) for the grain size of aluminum and aluminum alloys of the present invention.

[0017] Figure 4 This is the standard grading chart (level 6) for the grain size of aluminum and aluminum alloys of the present invention.

[0018] Figure 5 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention before cold treatment.

[0019] Figure 6 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -75°C for 2 hours.

[0020] Figure 7 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -100℃ for 2 hours.

[0021] Figure 8 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -125°C for 2 hours.

[0022] Figure 9 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -125°C for 4 hours.

[0023] Figure 10 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -125°C for 6 hours.

[0024] Figure 11 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -125°C for 8 hours.

[0025] Figure 12 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -150°C for 4 hours.

[0026] Figure 13 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -125°C for 10 hours.

[0027] Figure 14 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -150℃ for 6 hours.

[0028] Figure 15 This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -150℃ for 8 hours.

[0029] Figure 16This is a schematic diagram of the grain structure of the aluminum alloy of the present invention after being kept at -150°C for 10 hours.

[0030] Figure 17 This is a hardness variation curve of the present invention.

[0031] Figure 18 This is a curve showing the change in yield strength of the present invention.

[0032] Figure 19 This is a graph showing the change in tensile strength of the present invention.

[0033] Figure 20 This is a graph showing the elongation variation of the present invention.

[0034] Figure 21 This is a schematic diagram of the oil seal structure of the present invention.

[0035] Figure 22 This is the stress detection location of the present invention.

[0036] Figure 23 This is a schematic diagram of the grain sample block of the present invention.

[0037] Figure 24 This is a schematic diagram of the mechanical performance test bar of the present invention.

[0038] Figure 25 This is a schematic diagram of the hardness testing block of the present invention. Detailed Implementation

[0039] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application.

[0040] The terminology used in this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The singular forms “a,” “the,” and “the” used in this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0041] It should be understood that although the terms first, second, third, etc., may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0042] Please see Figures 1-25 This invention provides a cold treatment method for reducing residual stress in aluminum alloys, comprising the following steps: S100: Aging treatment is performed on aluminum alloy materials at an aging temperature of 140±5℃, with air as the cooling medium, to cool the materials to room temperature. S200: Place aluminum alloy material cooled to room temperature into an ultra-low temperature device within 1 hour and cool it to -125±5℃; S300: After the temperature inside the cryogenic equipment stabilizes at -125±5℃, maintain this temperature for 6±0.5h; S400: After the heat preservation is completed, remove the aluminum alloy material and place it in a room temperature environment to allow it to naturally heat up to room temperature.

[0043] Furthermore, in the step of placing the aluminum alloy material cooled to room temperature into an ultra-low temperature device within 1 hour and cooling it to -125±5℃: The ultra-low temperature equipment is an ultra-low temperature freezer.

[0044] Furthermore, in the step of maintaining the temperature inside the cryogenic equipment at -125±5℃ for 6±0.5h: The constant temperature start time is calculated from when the temperature inside the ultra-low temperature equipment returns to the set -125±5℃.

[0045] Furthermore, after the heat preservation process is completed, the aluminum alloy material is removed and placed in a room temperature environment to allow it to naturally warm up to room temperature. After the temperature recovery, the residual stress relief rate of the aluminum alloy material is not less than 45%, the ductility is increased by not less than 4.5%, the yield strength is increased by not less than 3MPa, and the tensile strength is increased by not less than 11MPa.

[0046] Furthermore, the aluminum alloy material includes bearings and oil seals used in the field of impeller machining.

[0047] In this embodiment, the following steps are adopted: First, the aluminum alloy material is subjected to aging treatment at an aging temperature of 140±5℃ using air as the cooling medium to cool the material to room temperature; then, the aluminum alloy material cooled to room temperature is placed in an ultra-low temperature device within 1 hour and cooled to -125±5℃; after the temperature inside the ultra-low temperature device stabilizes at -125±5℃, this temperature is maintained for 6±0.5 hours; after the heat preservation is completed, the aluminum alloy material is taken out and placed in a room temperature environment to naturally warm up to room temperature; through the above method, the residual stress of the aluminum alloy is effectively reduced, and the deformation of the workpiece during processing is reduced.

[0048] In addition, the main functions of cold treatment are as follows: Reducing residual stress in materials, improving dimensional stability, and minimizing workpiece deformation during machining have been studied in related fields. For example, cold treatment of thin-walled aluminum alloy parts reduced the machining deformation rate from 50% to 32%, and lowered residual stress by 55%-83%. Improving material properties, enhancing wear resistance, and extending workpiece service life: Cold treatment significantly improves the wear resistance and fatigue resistance of materials.

[0049] To achieve the above objectives, this method employs industrial cryogenic treatment. Based on actual production conditions, the material is placed in a low-temperature environment of -70℃ to -150℃, and after holding at this temperature for a certain period, the changes in internal crystal structure and residual stress are observed. The specific scheme is as follows: The effect of different cold treatment temperatures on the microstructure of aluminum alloy materials was observed under the same holding time. Specifically, samples were placed in environments of -75℃, -100℃, and -125℃ for 2 hours respectively, and the grain changes were observed.

[0050] The effect of different holding times on the microstructure of aluminum alloy materials was observed by using the same cold treatment temperature. Specifically, different temperature gradients were set within the range of -70℃ to -150℃, and the grain changes of the samples were observed after holding them for 4h, 6h, 8h, and 12h, respectively.

[0051] The effects of heat treatment and cold treatment on the residual stress and mechanical properties of aluminum alloy materials under the same holding time and different cold treatment temperatures were observed. Samples that had been cooled to room temperature after heat treatment were further cooled to -100℃ to -150℃, and the changes in residual stress and mechanical properties before and after cold treatment were compared and analyzed. Beneficial effects

[0052] (1) Grain refinement helps improve the wear resistance and extend the service life of the material: After placing the samples in different temperature environments from -70℃ to -150℃, the aluminum alloy material showed no phase transformation after 2 hours of heat treatment. Based on the "Standard Rating of Grain Size of Aluminum and Aluminum Alloys" (GB / T3246.1-2000), no obvious grain refinement phenomenon was observed in the aluminum alloy material within the temperature range of -70℃ to -100℃ after 2 hours of heat treatment. The comparison results are shown in […]. Figures 6-7 The aluminum alloy sample exhibited grain refinement after being held at -125℃ for 2 hours, with the grain level index jumping to level 6. The grain change is shown in [reference needed]. Figure 8 After being kept at -125℃ and -150℃ for 4, 6, 8, and 10 hours respectively, the aluminum alloy samples showed significant grain changes, with grain refinement being observed. Figures 9-16 .

[0053] At the same temperature, the internal grain refinement of aluminum alloy grain samples becomes more pronounced with increasing cold treatment holding time. Under the same holding time, a lower treatment temperature accelerates the grain change process, allowing observation of grain changes in a shorter time compared to the sample before cold treatment (e.g., ...). Figure 5 At the same observation multiple, the tissue of the sample block after cold treatment will be more compact.

[0054] (2) Changes in mechanical properties: The aluminum alloy sample was kept at -100℃ to -150℃ for 6 hours, and the change in material hardness was relatively small (see Figure 17 The temperatures at which hardness changes most significantly are -125℃ and -150℃. In mechanical property testing, the material's mechanical properties decrease with decreasing temperature, but show an upward trend with further temperature reduction. Compared to materials treated at -70℃ to -100℃, the material treated at -125℃ to -150℃ exhibits a 4.5% increase in ductility, a 3MPa increase in yield strength, and an 11MPa increase in tensile strength (see...). Figures 18-20 ).

[0055] (3) Residual stress reduction: Residual stress is the main cause of part deformation. Three points are selected on the dissected oil seal body and marked as "Point 1, Point 2, Point 3" as stress detection locations, such as... Figure 22 The stress values ​​before and after cold treatment were measured. The residual stress test results (see Table 1) show that the residual stress of the workpiece was eliminated under three different temperature environments. The stress elimination rate was the highest at 69.73%, with a cold treatment temperature of -125℃ and a holding time of 6 hours.

[0056] Table 1 Residual Stress Testing Table

[0057] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein.

[0058] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope.

Claims

1. A method of reducing residual stress in an aluminum alloy by cold treatment, characterized by, Includes the following steps: The aluminum alloy material is subjected to aging treatment at an aging temperature of 140±5℃, with air as the cooling medium, to cool the material to room temperature. Aluminum alloy material cooled to room temperature was placed in an ultra-low temperature device within 1 hour and cooled to -125±5℃; Once the temperature inside the cryogenic equipment stabilizes at -125±5℃, maintain this temperature for 6±0.5 hours. After the heat preservation is completed, remove the aluminum alloy material and place it in a room temperature environment to allow it to naturally warm up to room temperature.

2. The method of stress relief by cold treatment of an aluminum alloy according to claim 1, characterized in that, In the step of placing aluminum alloy material cooled to room temperature into an ultra-low temperature device within 1 hour to cool it to -125±5℃: The ultra-low temperature equipment is an ultra-low temperature freezer.

3. The method of claim 1, wherein the cold treatment is performed at a temperature of 100 to 200°C. In the step of maintaining the temperature inside the cryogenic equipment at -125±5℃ for 6±0.5h: The constant temperature start time is calculated from when the temperature inside the ultra-low temperature equipment returns to the set -125±5℃.

4. The method of claim 1 wherein the cold treatment is performed at a temperature of about 100°C to about 200°C. After the heat preservation is completed, the aluminum alloy material is removed and placed in a room temperature environment to naturally warm up to room temperature. After the temperature recovery, the residual stress relief rate of the aluminum alloy material is not less than 45%, the ductility is increased by not less than 4.5%, the yield strength is increased by not less than 3MPa, and the tensile strength is increased by not less than 11MPa.

5. The cold treatment method for reducing residual stress in aluminum alloys as described in claim 1, characterized in that, The aluminum alloy material includes bearings and oil seals used in the field of impeller machining.

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