Residual stress distribution uniformity treatment method for aluminum alloy skin plate

Abstract

The invention discloses a residual stress distribution uniformity treatment method for an aluminum alloy skin plate. The residual stress distribution uniformity treatment method comprises the following steps that 1, the aluminum alloy skin plate is subjected to solid solution quenching; 2, residual stress values of different areas of the plate are obtained through measurement; step 3, establishing a function relationship among the quenching water temperature, the surface heat exchange coefficient temperature and the surface heat exchange coefficient; 4, a finite element model for regional quenching is constructed and obtained, and meanwhile, a corresponding regional quenching experiment is set; 5, selecting a model path to obtain residual stress values at different areas; and step 6, obtaining a corrected residual stress distribution uniformity prediction model. According to the method, by establishing the quantitative relation between the plate cooling rate and the area and residual stress distribution uniformity, the experiment trial and error cost is predicted and reduced in advance, and the process stability and the product consistency are improved on the premise that the good mechanical performance is guaranteed (the tensile strength is larger than or equal to 435 MPa, the yield strength is larger than or equal to 270 MPa, and the ductility is larger than or equal to 13%).

Description

A method for treating the uniformity of residual stress distribution in aluminum alloy skin panels Technical Field

[0001] This invention relates to the field of aluminum alloy processing technology, specifically a method for treating the uniformity of residual stress distribution in aluminum alloy skin panels. Background Technology

[0002] Modeling research based on the prediction of the uniformity of residual stress distribution during the heat treatment of aluminum alloy skin plates for aerospace applications can effectively reduce trial and error costs and significantly reduce scrap rates, offering substantial economic advantages compared to traditional control methods.

[0003] Traditional methods for improving the uniformity of residual stress distribution include: heat treatment (thermal aging elimination, cryogenic treatment), mechanical loading (pre-stretching / pre-compression, mechanical vibration aging), and surface impact (laser shock peening (LSP), high-energy acoustic beam modulation).

[0004] Key heat treatment methods studied in improving the uniformity of residual stress distribution in aluminum alloy thin sheets include thermal aging, quenching process optimization, solution treatment combined with graded aging, cyclic heat treatment, cryogenic treatment, and thermal gradient control. However, due to the varying sizes and shapes of aluminum alloy thin sheets, especially in larger sheets, differences in temperature gradients can lead to uneven thermal expansion. Furthermore, when the sheet has a complex shape or local thickness variations, controlling the uniformity of heat treatment is difficult, potentially resulting in larger residual stress in localized areas and affecting the overall flatness of the sheet. To avoid excessive temperature gradient differences, many researchers have adjusted process parameters, altering heating rates and cooling strategies during heat treatment (such as gradient heating and segmented cooling) to reduce internal temperature gradient differences. They have also introduced thermal field compensation techniques (such as infrared heating zone control and electromagnetic induction heating optimization) to reduce localized overheating or undercooling areas, thereby suppressing thermal stress concentration caused by temperature gradient differences.

[0005] Disadvantages of existing technology:

[0006] 1. Mechanical loading is suitable for simple flat plates or profiles, but it is difficult to implement on curved parts or thin-walled structures.

[0007] 2. The surface impact method is prone to generating "residual stress holes" when the power density is not appropriate, resulting in limited improvement, and the probe may damage the surface of the thin plate.

[0008] 3. Parameters such as heating / cooling rate and thermal field zoning scheme are highly sensitive to the influence of material properties and residual stress distribution.

[0009] 4. Even minor parameter deviations (such as fluctuations in heating rate) can cause the residual stress distribution to deviate significantly from the target range. The heat treatment process window for aluminum alloy thin sheets is narrow; excessively high temperature gradient differences may cause localized overheating or grain coarsening, further affecting the uniformity of residual stress.

[0010] Therefore, there is an urgent need to find a simple and effective method to improve the uniformity of residual stress distribution in aluminum alloy thin plates. Summary of the Invention

[0011] To address the problems existing in the prior art, this invention provides a method for treating the uniformity of residual stress distribution in aluminum alloy skin panels. By establishing a quantitative relationship between the cooling rate, region, and uniformity of residual stress distribution in the panel, it can predict in advance, reduce experimental trial and error costs, and improve process stability and product consistency while ensuring good mechanical properties (tensile strength ≥ 435 MPa, yield strength ≥ 270 MPa, elongation ≥ 13%).

[0012] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0013] A method for treating the uniformity of residual stress distribution in aluminum alloy skin panels includes the following steps:

[0014] Step 1: Solution harden the aluminum alloy skin sheet by placing it in a box-type resistance furnace and heating it to 500°C at a rate of 5°C / min. Hold it at that temperature for 3 minutes and then open the furnace door. Next, place the aluminum alloy skin sheet flat into the water for quenching. The water temperature for quenching should be between 30°C and 90°C, and the transfer time in the air should not exceed 5 seconds.

[0015] Step 2: Measure the residual stress values ​​in different areas of the plate. Obtain the residual stress values ​​in different areas of the plate through X-ray diffraction and micro-indentation test. Take 3 points from the edge to the middle area along the rolling direction of the plate and 3 points from the edge to the middle area perpendicular to the rolling direction as the residual stress test positions.

[0016] Step 3: Establish the functional relationship between quenching water temperature, surface heat transfer coefficient temperature, and surface heat transfer coefficient:

[0017] The residual stress obtained in step 2 is input into the finite element model, along with material parameters and boundary conditions. Temperature data and residual stress in the S11 and S22 directions at the same residual stress test locations as the actual plate are extracted from the temperature and residual stress cloud maps obtained during the operation. When the simulated data matches the experimental data, the quenching water temperature and the corresponding surface heat transfer coefficient temperature and surface heat transfer coefficient data are obtained from the model. Based on multiple linear regression analysis, the functional relationship between the quenching water temperature (t1), surface heat transfer coefficient temperature (t2), and surface heat transfer coefficient (h) is obtained, specifically:

[0018] h(t1,t2)=127912.5-758.33t1-60.46t2

[0019] Where h is the surface heat transfer coefficient, t1 is the quenching water temperature, and t2 is the surface heat transfer coefficient temperature;

[0020] Step 4: Construct a finite element model for obtaining zoned quenching;

[0021] Combining the surface heat transfer coefficient function obtained in step 3, quenching water temperatures of 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃ are substituted into the function in step 2 to obtain the surface heat transfer coefficient corresponding to each quenching water temperature. A partitioned quenching finite element model considering zoned quenching is established; the quenching water temperature for the middle region is set to 30℃, and the quenching water temperature for the edge region is set to 30-90℃. Simultaneously, the material property parameters and the calculated corresponding heat transfer coefficients are input, and the model is set to be similar to that of a conventional quenching finite element model. The same boundary conditions were simulated; the water tank temperature was kept constant throughout the finite element simulation process; the alloy skin sheet was placed in a box-type resistance furnace and heated to 500℃ at a heating rate of 5℃ / min, held for 3 minutes, and then the furnace door was opened; the aluminum alloy skin sheet was then laid flat, and the nozzles were controlled to spray water at the same flow rate and different quenching temperatures in the middle and edge areas of the sheet to conduct a zoned quenching experiment; the quenching water temperature in the middle area was 30℃, and the quenching water temperature in the edge area was between 30℃ and 90℃, with the transfer time in the air not exceeding 5 seconds;

[0022] The temperature of the water tank was kept constant throughout the finite element simulation process, and the influence of the time interval between the furnace exit and complete contact with water was ignored.

[0023] Step 5: Select the model path to obtain the residual stress values ​​in different regions;

[0024] In the finite element models of (intermediate quenching water temperature - edge quenching water temperature) 30-30℃, 30-40℃, 30-50℃, 30-60℃, 30-70℃, 30-80℃, and 30-90℃ in step 4, display the residual stress cloud map in the S11 and S22 directions of the working parts in each group of sectional quenching finite element models. Extract the residual stress in the S11 and S22 directions at the same residual stress test location points as the actual plate from the cloud map and perform post-processing to obtain the residual stress value at the same test location points as the actual plate.

[0025] Step 6: Obtain the modified prediction model for the uniformity of residual stress distribution;

[0026] Substitute the residual stress values ​​obtained in step 5 into the multiple linear regression equation to construct a prediction model for the uniformity of residual stress distribution in s(x1,x2).

[0027] The prediction model for the uniformity of residual stress distribution based on differentiated cooling rate control is: S 11 (x1,x2)=0.3777 x1-0.00701 x2+ 27.2491, S 22 (x1,x2)=0.25156 x1+0.06753 x2+ 25.06176;

[0028] Among them, S 11 S represents the standard deviation of residual stress in the horizontal rolling direction. 22 x1 represents the standard deviation of residual stress perpendicular to the rolling direction, and x2 represents the quenching water temperature corresponding to the middle and edge regions, respectively.

[0029] Step 7: Based on the standard deviation of residual stress in the horizontal and vertical rolling directions of the actual aluminum alloy skin sheet, calculate the corresponding quenching water temperature for the middle and edge regions.

[0030] Furthermore, the quenching water temperature applied to the middle region is 30℃, and the quenching water temperature applied to the edge region is 50℃, resulting in the minimum residual stress standard deviation.

[0031] Furthermore, the aluminum plate has a thickness of 0.4 mm, a length of 34 cm, and a width of 17 cm.

[0032] The beneficial effects of this invention are:

[0033] This invention utilizes zoned control of the quenching water temperature in different areas of the sheet metal, applying low and high quenching water temperatures to the central and edge areas respectively. Simultaneously, this differentiated quenching water temperature control suppresses uneven distribution of residual stress on the thin sheet surface, reducing residual stress and thus improving the dimensional stability of the sheet metal while maintaining good mechanical properties. Attached Figure Description

[0034] Figure 1 is a diagram showing the location of residual stress testing in an embodiment of the present invention.

[0035] Figure 2 is a schematic diagram of the partitioned quenching simulation in an embodiment of the present invention.

[0036] Figure 3 is a schematic diagram of the partitioned quenching experiment in an embodiment of the present invention.

[0037] Figure 4 is a graph showing the simulated and experimental values ​​of the standard deviation of residual stress distribution during partitioned quenching in the embodiment of the present invention.

[0038] Figure 5 is a bar chart of the mechanical properties of ordinary and partitioned quenching in the embodiments of the present invention;

[0039] Figure 6 is a cloud map of the finite element simulation of partitioned quenching in an embodiment of the present invention.

[0040] Figure 7 is a finite element simulation cloud map of ordinary quenching in an embodiment of the present invention. Detailed Implementation

[0041] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments and accompanying drawings.

[0042] As shown in Figures 1-3, a method for treating the uniformity of residual stress distribution in aluminum alloy skin panels includes the following steps:

[0043] Step 1: Solution harden the aluminum alloy skin sheet by placing it in a box-type resistance furnace and heating it to 500°C at a rate of 5°C / min. Hold it at that temperature for 3 minutes and then open the furnace door. Next, place the aluminum alloy skin sheet flat into the water for quenching. The water temperature for quenching should be between 30°C and 90°C, and the transfer time in the air should not exceed 5 seconds.

[0044] Step 2: Measure the residual stress values ​​in different areas of the sheet metal. Obtain the residual stress values ​​in different areas of the sheet metal through X-ray diffraction and microindentation testing. Take three points along the horizontal rolling direction from the edge to the middle area (points 5, 4, and 3 in Figure 1); and three points along the vertical rolling direction from the edge to the middle area (points 1, 2, and 3 in Figure 1). These are used as the residual stress test locations, as shown in Figure 1.

[0045] Step 3: Establish the functional relationship between quenching water temperature, surface heat transfer coefficient temperature, and surface heat transfer coefficient:

[0046] The residual stress obtained in step 2 is input into the finite element model, along with material parameters and boundary conditions. Temperature data and residual stress in the S11 and S22 directions at the same residual stress test locations as the actual plate are extracted from the temperature and residual stress cloud maps obtained during the operation. When the simulated data matches the experimental data, the quenching water temperature and the corresponding surface heat transfer coefficient temperature and surface heat transfer coefficient data are obtained from the model. Based on multiple linear regression analysis, the functional relationship between the quenching water temperature (t1), surface heat transfer coefficient temperature (t2), and surface heat transfer coefficient (h) is obtained, specifically:

[0047] h(t1,t2)=127912.5-758.33t1-60.46t2

[0048] Where h is the surface heat transfer coefficient, t1 is the quenching water temperature, and t2 is the surface heat transfer coefficient temperature;

[0049] Step 4: Construct the finite element model for the sectional quenching; as shown in Figure 2, the red area is the middle area and the blue area is the edge area;

[0050] Combining the surface heat transfer coefficient function obtained in step 3, quenching water temperatures of 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, and 90℃ are substituted into the function in step 2 to obtain the surface heat transfer coefficient corresponding to each quenching water temperature. A partitioned quenching finite element model considering zoned quenching is established; the quenching water temperature for the middle region is set to 30℃, and the quenching water temperature for the edge regions is set to 30-90℃. Simultaneously, the material property parameters and the calculated corresponding heat transfer coefficients are input, and the model is set to be similar to that of ordinary quenching finite element simulation. The same boundary conditions were applied; the water tank temperature was kept constant throughout the finite element simulation process; the alloy skin sheet was placed in a box-type resistance furnace and heated to 500℃ at a rate of 5℃ / min, held for 3 minutes, and then the furnace door was opened; as shown in Figure 3, the aluminum alloy skin sheet was then laid flat, and the nozzles were controlled to spray water at the same flow rate in the middle and edge areas of the sheet, with different quenching water temperatures, to conduct a zoned quenching experiment; the quenching water temperature in the middle area was 30℃, and the quenching water temperature in the edge area was between 30℃ and 90℃, with the transfer time in the air not exceeding 5s;

[0051] The temperature of the water tank was kept constant throughout the finite element simulation process, and the influence of the time interval between the furnace exit and complete contact with water was ignored.

[0052] Step 5: Select the model path to obtain the residual stress values ​​in different regions;

[0053] Substitute the intermediate quenching water temperature and the edge quenching water temperature from step 4, which are 30-30℃, 30-40℃, 30-50℃, 30-60℃, 30-70℃, 30-80℃, and 30-90℃ respectively, into the finite element model. Display the residual stress cloud map in the S11 horizontal direction and S22 vertical direction of the working part in the finite element model of each group of quenching zones. Extract the residual stress in the S11 horizontal direction and S22 vertical direction at the same residual stress test position point as the actual plate from the cloud map and perform post-processing to obtain the residual stress value at the same test position point as the actual plate.

[0054] Step 6: Obtain the modified prediction model for the uniformity of residual stress distribution;

[0055] Substitute the residual stress values ​​obtained in step 5 into the multiple linear regression equation to construct a prediction model for the uniformity of residual stress distribution in s(x1,x2).

[0056] The prediction model for the uniformity of residual stress distribution based on differentiated cooling rate control is: S 11 (x1,x2)=0.3777 x1-0.00701 x2+ 27.2491, S 22 (x1,x2)=0.25156 x1+0.06753 x2+ 25.06176;

[0057] Among them, S 11 S represents the standard deviation of residual stress in the horizontal rolling direction. 22 x1 represents the standard deviation of residual stress perpendicular to the rolling direction, and x2 represents the quenching water temperature corresponding to the middle and edge regions, respectively.

[0058] In this embodiment, the aluminum plate has a thickness of 0.4 mm, a length of 34 cm, and a width of 17 cm.

[0059] In this embodiment, the simulated and experimental values ​​of the standard deviation of residual stress distribution in the partitioned quenching are shown in Table 1, and the specific curve changes are shown in the curve in Figure 4. It can be clearly seen that when the quenching water temperature applied to the middle region is 30℃ and the quenching water temperature applied to the edge region is 50℃, the residual stress distribution on the surface of the thin plate is the most uniform and the residual stress is the smallest. It also has good mechanical properties and meets the mechanical property requirements of the product, namely, tensile strength ≥435MPa, yield strength ≥270MPa, and elongation ≥13%.

[0060] Table 1. Standard deviation of residual stress distribution in different regions after partitioned quenching

[0061] Figure 6 shows the residual stress distribution cloud diagram in the S11 and S22 directions of the plate material with a central temperature of 30℃ and an edge temperature of 30-90℃.

[0062] Multiple linear regression analysis data:

[0063] S 11 (x1,x2)=0.3777 x1-0.00701 x2+ 27.2491, S 22 (x1,x2)=0.25156 x1+0.06753 x2+ 25.06176;

[0064]

[0065] The comparative experiment used ordinary quenching, and the residual stress test location map was the same as in the above implementation method. The test results are shown in the table below:

[0066] Table of Residual Stress Data from X-ray Diffraction Measurement in Ordinary Quenching

[0067] Standard deviation data of residual stress distribution in different regions after ordinary quenching

[0068] The finite element simulation cloud diagram of ordinary quenching is shown in Figure 7. Although the residual stress on the surface of the thin plate is smaller at 50℃, 70℃ and 90℃, its mechanical properties do not meet the product requirements, namely tensile strength ≥435MPa, yield strength ≥270MPa and elongation ≥13%.

[0069] As can be seen from the comparison of the experimental data above, this invention, by controlling the quenching water temperature in different areas of the plate in zones, applies low and high quenching water temperatures to the central and edge areas respectively. While ensuring good mechanical properties of the plate, this differentiated control of quenching water temperature also suppresses uneven distribution of residual stress on the thin plate surface and reduces residual stress.

[0070] Although the present invention has been described in detail above with specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A method for treating the uniformity of residual stress distribution in aluminum alloy skin panels, characterized in that: The process includes the following steps: Step 1: Solution hardening of the aluminum alloy skin sheet. The aluminum alloy skin sheet is placed in a box-type resistance furnace and heated to 500℃ at a heating rate of 5℃ / min. After holding at this temperature for 3 minutes, the furnace door is opened. Then, the aluminum alloy skin sheet is placed flat and quenched in water. The quenching water temperature is between 30℃ and 90℃, and the transfer time in air does not exceed 5 seconds. Step 2: Residual stress values ​​in different areas of the sheet are measured. The residual stress values ​​in different areas of the sheet are obtained through X-ray diffraction and micro-indentation tests. Three points are taken along the rolling direction from the edge to the middle of the sheet, perpendicular to the rolling direction. Three points from the edge to the middle area are selected as residual stress test locations; Step 3: Establish the functional relationship between quenching water temperature, surface heat transfer coefficient temperature and surface heat transfer coefficient: Substitute the residual stress obtained in Step 2 into the finite element model, input the material parameters, set the boundary conditions, and extract the temperature data and residual stress in the S11 and S22 directions at the same residual stress test locations as the actual plate from the temperature cloud map and residual stress cloud map in the operation. When the above simulation data is consistent with the experimental data, obtain the quenching water temperature and the corresponding surface heat transfer coefficient temperature and surface heat transfer coefficient data from the model.Based on multiple linear regression analysis, the functional relationship between quenching water temperature (t1), surface heat transfer coefficient temperature (t2), and surface heat transfer coefficient (h) is obtained, specifically: h(t1,t2) = 127912.5 - 758.33t1 - 60.46t2, where h is the surface heat transfer coefficient, t1 is the quenching water temperature, and t2 is the surface heat transfer coefficient temperature. Step 4: Construct a finite element model for zoned quenching and set up corresponding zoned quenching experiments. Combining the surface heat transfer coefficient functional relationship obtained in Step 3, quenching water temperatures of 30℃, 40℃, 50℃, 60℃, and 70℃ are used. Substituting 80℃ and 90℃ into the functional relationship in step 2, the surface heat transfer coefficient corresponding to each quenching water temperature is obtained; a partitioned quenching finite element model considering zoned quenching is established; the quenching water temperature in the middle region is set to 30℃, and the quenching water temperature in the edge region is set to 30-90℃; at the same time, the material property parameters and the calculated corresponding heat transfer coefficients are input, and the same boundary conditions as in ordinary quenching finite element simulation are set; the water bath temperature is kept constant throughout the finite element simulation process; the aluminum alloy skin sheet is placed in a box-type resistance furnace and heated to 500℃ at a heating rate of 5℃ / min, held for 3 minutes, and then opened. Furnace door; then lay the aluminum alloy skin sheet flat, control the nozzles to spray the same flow rate of water at different quenching temperatures in the middle and edge areas of the sheet to conduct a zoned quenching experiment; the quenching water temperature in the middle area is 30℃, and the quenching water temperature in the edge area is between 30℃ and 90℃, with the transfer time in the air not exceeding 5s; Step 5: Select the model path to obtain the residual stress values ​​in different areas; from the finite element models of the middle quenching water temperature-edge quenching water temperature combination in Step 4 (30-30℃, 30-40℃, 30-50℃, 30-60℃, 30-70℃, 30-80℃, 30-90℃), from each group The residual stress cloud map in the working part of the partitioned quenching finite element model is displayed in the S11 and S22 directions. The residual stress in the S11 and S22 directions at the same residual stress test location as the actual plate is extracted from the cloud map and post-processed to obtain the residual stress value at the same test location as the actual plate residual stress; Step 6: Obtain the modified residual stress distribution uniformity prediction model; Substitute the residual stress value obtained in step 5 into the multiple linear regression equation to construct the residual stress distribution uniformity prediction model of s(x1,x2); The residual stress distribution uniformity prediction model of differentially controlled cooling rate is: S. 11 (x1,x2)=0.3777 x1-0.00701 x2+ 27.2491, S 22 (x1,x2)=0.25156x1+0.06753x2+25.06176; where, S 11 S represents the standard deviation of residual stress in the rolling direction. 22 x1 represents the standard deviation of residual stress perpendicular to the rolling direction; x2 represents the quenching water temperature corresponding to the middle and edge regions, respectively.

2. The method for treating the uniformity of residual stress distribution in aluminum alloy skin panels according to claim 1, characterized in that: The residual stress standard deviation is minimized when the quenching water temperature applied to the middle region is 30℃ and the quenching water temperature applied to the edge region is 50℃.

3. The method for treating the uniformity of residual stress distribution in aluminum alloy skin panels according to claim 1, characterized in that: The aluminum alloy skin sheet has a thickness of 0.4 mm, a length of 34 cm, and a width of 17 cm.

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