Mechanical heat treatment method for improving chemical milling roughness of aluminum alloy skin sheet

Abstract

The invention provides a mechanical heat treatment method for improving chemical milling roughness of an aluminum alloy skin thin plate, which comprises the following steps: step 1, soaking the aluminum alloy thin plate in liquid nitrogen for preset soaking time after solid solution quenching; 2, under the liquid nitrogen temperature, deep cooling rolling deformation treatment is conducted according to preset rolling deformation; and 3, the aluminum alloy obtained after deep cold rolling is subjected to peak aging treatment and then subjected to chemical milling treatment, and the chemical milling plate with the low chemical milling surface roughness is obtained.

Description

Technical Field

[0001] The invention patent relates to the field of aluminum alloy heat treatment, specifically to a mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plates. Background Art

[0002] 2024 aluminum alloy sheet is widely used in aircraft skins and other structural components due to its superior strength-to-weight ratio, high heat resistance, and excellent processing and fatigue properties. Traditional mechanical milling of 2024 aluminum alloy sheet is prone to generating cutting stresses. However, chemical milling, which operates through a chemical reaction, prevents material deformation and generates no cutting stresses during processing. This process has therefore become a crucial technology in advanced manufacturing, particularly in high-precision applications such as aerospace. Chemical milling is a common technique for skin milling.

[0003] 2024 aluminum alloy has high contents of Cu, Mg and Mn. Alkaline (NaOH) chemical milling fluid is often used in the chemical milling process. Al is an amphoteric metal and can react chemically with NaOH, while Mg and Mn do not react with NaOH. Therefore, in the chemical milling fluid, the activity of Mg and Mn is lower than that of Al, and thus the electrode potential of Mg and Mn is higher than that of the Al matrix. In addition, the second phase particles such as S (Al2CuMg), θ (Al2Cu) and T (Al20Cu2Mn3) in the alloy all contain the inactive element Cu, so their electrode potential is higher than that of the Al matrix. When a chemical reaction occurs, the Al matrix reacts first, while the second phase particles θ, S and T phases in the 2024 aluminum alloy do not participate in the reaction, and remain to form protrusions, fall off to form corrosion pits, resulting in a high surface roughness of the chemically milled parts, affecting the fatigue life of the aircraft skin, thereby limiting its industrial application. Summary of the Invention

[0004] The present invention provides a mechanical heat treatment method for improving the roughness of aluminum alloy skin thin plates after milling, which can solve the problem of large roughness of 2024 aluminum alloy skin thin plates after milling.

[0005] Technical solution: A mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plates, the method comprising: Step 1: After solution quenching, the aluminum alloy sheet is immersed in liquid nitrogen for a preset immersion time; Step 2: Under liquid nitrogen temperature, perform deep cold rolling deformation treatment according to a preset rolling deformation amount; Step 3: After deep cold rolling, the aluminum alloy is subjected to peak aging treatment and then chemical milling treatment to obtain a chemical milling plate with low surface roughness.

[0006] Specifically, the aluminum alloy sheet undergoes solution treatment including: The solution temperature range is 465℃~530℃; the holding time is 30min~2.5h; the atmosphere in the solution furnace is an air circulation electric furnace.

[0007] Specifically, the quenching process of the aluminum alloy sheet after solution treatment includes: The time interval between the workpiece being transferred from the furnace to the quenching medium is ≤ 20s; The cooling medium is water, and the water temperature is controlled at ≤40℃.

[0008] Specifically, the deep cold rolling deformation treatment in step 2 includes: Step 21: Take out the aluminum alloy cryogenically treated with liquid nitrogen and place it on the rolling mill. The transfer time is ≤10s. Step 22: Start deep cold rolling, and the reduction in a single rolling should not exceed 10%; Step 23: After each rolling, the workpiece must be quickly transferred from the rolling mill to be immersed in liquid nitrogen to ensure that the deformation temperature of the alloy is at the liquid nitrogen temperature; Step 24: Add up the deformation of each rolling process to get the total deformation of the aluminum alloy.

[0009] Specifically, the liquid nitrogen temperature is -196°C; and the preset range of the total rolling deformation is 15% to 70%.

[0010] Specifically, the pressure force during each rolling deformation cannot exceed 0.4 mm; before each rolling process, the sample needs to be immersed in liquid nitrogen for 20 minutes to ensure that the deformation temperature of the alloy is the liquid nitrogen temperature.

[0011] Specifically, the peak aging treatment is artificial aging, the aging temperature range is: 120℃~190℃, and the aging time is: 6h~24h.

[0012] Specifically, the chemical milling process is carried out according to the HB / Z 5125-2008 industry standard; the chemical milling samples are mechanically polished with 180#, 400#, 600#, and 800# water-abrasive sandpaper in sequence, and then polished with 400#, 600#, 800#, and 1000# metallographic sandpaper in sequence, and finally ultrasonically cleaned and dried for use.

[0013] Specifically, the specific chemical milling process of the aluminum alloy in step 3 is as follows: Step 31: alkaline washing with 40% NaOH solution; Step 32: The pre-treated workpiece is subjected to light treatment using a 30% HNO3 solution; Step 33: Apply HH968-2 peelable coating protective glue to the workpiece after polishing and leave it at room temperature for 24 hours to fully cure; Step 34: Remove the protective adhesive from the area to be processed; Step 35: chemical milling, processing the workpiece processed in step 34 using a chemical milling fluid; Step 36: After chemical milling, rinse the workpiece in 40°C hot water for 2 minutes; Step 37: Rinse the workpiece processed in step 36 with cold water for 1 minute; Step 38: The workpiece processed in step 37 is treated with 30% HNO3 solution for 2 minutes; Step 39: Use hot air to dry the workpiece processed in step 38 and remove the glue layer for subsequent roughness testing.

[0014] Specifically, the milling liquid formula for the milling treatment is 170 g / L NaOH + 19 g / L Na2S + 45 g / L TEA + 19 g / L Al3+, the milling temperature is 80 ° C, and the milling time is 5 minutes.

[0015] In summary, the present invention provides a mechanical heat treatment method for improving the roughness of chemical milling of aluminum alloy skin sheets by adding a cryogenic deformation step between solution quenching and aging. Experimental results show that the surface roughness of chemical milling of 2024 sheet metal after cryogenic rolling decreases with increasing deformation, significantly reducing the roughness of chemical milling of 2-series aluminum alloy skin sheets, providing practical theoretical guidance for its industrial application. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 Processing flow of 2024 aluminum alloy: (a) conventional heat treatment process; (b) mechanical heat treatment process; Figure 2 3D microstructure scanning diagram of 2024 aluminum alloy with different cryogenic deformation amounts; Figure 3 Average milling roughness of 2024 aluminum alloy with different cryogenic deformation amounts. Specific embodiments The invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the contents described above.

[0017] like Figure 1 As shown, the present invention discloses a mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plates, comprising: Step 1: After solution quenching, the aluminum alloy sheet is immersed in liquid nitrogen for a preset immersion time; Specifically, the solution treatment of aluminum alloy thin plates includes: the solution temperature is selected according to the type of aluminum alloy, usually 465℃~530℃ (for example, 2024 aluminum alloy: 480~505℃; 7075 aluminum alloy: 465~480℃); the holding time is 30min~2.5h; the atmosphere in the solution furnace is an air circulation electric furnace, and the temperature control accuracy must be within ±5℃.

[0018] Specifically, the quenching process of aluminum alloy thin plates after solid solution treatment includes: the time interval for transferring the workpiece from the furnace to the quenching medium is ≤20s (to prevent the alloy precipitation phase from reducing the material properties due to too long a time); water is selected as the cooling medium, and the water temperature is controlled at ≤40°C. The lower the water temperature, the better the aluminum alloy quenching effect.

[0019] The preset immersion time range is 15-30 min to ensure that the workpiece is completely cooled within the liquid nitrogen temperature range.

[0020] Among them, aluminum alloys include 2xxx aluminum alloys, 5xxx aluminum alloys and 7xxx aluminum alloys.

[0021] Among them, there must be sufficient liquid nitrogen in the cryogenic container to fully immerse the workpiece.

[0022] The specific composition of the 2024 aluminum alloy for the skin used in the present invention is shown in Table 1.

[0023] Table 1 Composition of AA2024 aluminum alloy used in the present invention

[0024] Step 2: Under liquid nitrogen temperature, perform deep cold rolling deformation treatment according to a preset rolling deformation amount; Specifically, the deep cold rolling deformation treatment in step 2 includes: Step 21: Take out the aluminum alloy cryogenically treated with liquid nitrogen and place it on the rolling mill (transfer time ≤ 10s to prevent the workpiece temperature from rising); Step 22: Start deep cold rolling, and the reduction in a single rolling should not exceed 10%; Step 23: After each rolling, the workpiece must be quickly transferred from the rolling mill to be immersed in liquid nitrogen to ensure that the deformation temperature of the alloy is at the liquid nitrogen temperature; Step 24: Add up the deformation of each rolling process to get the total deformation of the aluminum alloy.

[0025] Among them, the temperature of liquid nitrogen is -196℃.

[0026] Among them, the preset range of total rolling deformation is 15%~70%.

[0027] Specifically, the pressure force during each rolling deformation cannot exceed 0.4 mm.

[0028] Specifically, before each rolling process, the sample needs to be immersed in liquid nitrogen for 20 minutes to ensure that the deformation temperature of the alloy is the liquid nitrogen temperature.

[0029] Step 3: After deep cold rolling, the aluminum alloy is subjected to peak aging treatment and then chemical milling treatment to obtain a chemical milling plate with low surface roughness.

[0030] Specifically, the peak aging treatment is artificial aging, the aging temperature range is: 120℃~190℃, and the aging time is: 6h~24h.

[0031] Specifically, the chemical milling process for aluminum alloys in this patent is conducted in accordance with the industry standard HB / Z 5125-2008. The chemically milled samples are mechanically polished with 180#, 400#, 600#, and 800# water-abrasive sandpaper, followed by polishing with 400#, 600#, 800#, and 1000# metallographic sandpaper. Finally, the samples are ultrasonically cleaned and dried for later use.

[0032] Specifically, the specific chemical milling process of aluminum alloy in step 3 is as follows: Step 31: pretreatment, alkaline washing with 40% NaOH solution; Step 32: The pre-treated workpiece is subjected to light treatment using a 30% HNO3 solution; Step 33: Apply HH968-2 peelable coating protective glue to the workpiece after polishing and leave it at room temperature for 24 hours to fully cure; Step 34: Remove the protective adhesive from the area to be processed; Step 35: chemical milling, processing the workpiece processed in step 34 using a chemical milling fluid; Step 36: After chemical milling, rinse the workpiece in 40°C hot water for 2 minutes; Step 37: Rinse the workpiece processed in step 36 with cold water for 1 minute; Step 38: The workpiece processed in step 37 is treated with 30% HNO3 solution for 2 minutes; Step 39: Use hot air to dry the workpiece processed in step 38 and remove the glue layer for subsequent roughness testing.

[0033] The specific milling fluid formula for the patented milling process is 170 g / L NaOH + 19 g / L Na2S + 45 g / LTEA + 19 g / L Al3+, the milling temperature is 80°C, and the milling time is 5 minutes.

[0034] The main principles of the technical solution of the present invention are: Due to the presence of significant amounts of alloying elements such as Cu, Mg, and Mn in 2024 aluminum alloy sheets, numerous Cu-containing non-equilibrium phases (S, θ, T, and AlCuFeMn) are formed during the alloy's smelting process. After homogenization and solution heat treatment, most of these non-equilibrium phases dissolve into the aluminum matrix, but a small amount of second-phase particles remain in the matrix. Due to the presence of inactive Cu in the NaOH milling solution, these residual phases have a higher electrode potential than the Al matrix. During chemical reactions, the Al matrix reacts first, while the second-phase particles θ, S, and T in 2024 aluminum alloy remain, resulting in protrusions and detachment. Corrosion pits are the primary cause of excessive roughness during milling. After deep cold rolling, the alloy's grain structure shifts from equiaxed grains to flat, fibrous structures. Furthermore, coarse particles in the matrix are crushed and evenly distributed. The residual second-phase particles in alloys with extensive deep cold rolling exhibit finer particle size. Therefore, after the deep cold deformation of the aluminum alloy milling reaction, the residual second phase inside the matrix falls off, and the pits or protrusions left behind are small and uniform in size. This results in low surface roughness and high surface quality of the aluminum alloy milling plate under this mechanical heat treatment method.

[0035] The surface roughness of the chemically milled plate obtained in this application is greatly improved compared with the traditional T6 state chemically milled plate, which can effectively solve the problem of high roughness of chemical milling of aluminum alloy thin plates and meet the requirements of aircraft skin for aluminum alloy performance.

[0036] Example 1 The present invention discloses a mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plates. Taking a deformation amount of 15% as an example, the method comprises: Step 1: Select 3mm thick 2024 aluminum alloy and subject it to solution treatment at 498±5℃ / 1h; Step 2: Transfer the workpiece after solution treatment into water for quenching; Step 3: Transfer the quenched workpiece to liquid nitrogen and soak it for about 20 minutes for cryogenic treatment; Step 4: The workpiece, which is also immersed in liquid nitrogen, is quickly transferred to the rolling mill for deep cold rolling deformation treatment, with a total rolling deformation of 15%; Specifically, step 4 deep cold rolling includes: Step 41: rolling the 3 mm deep cold plate to 2.8 mm, with a rolling pressure of 0.2 mm; Step 42: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 41 is eliminated; Step 43: rolling the 2.8 mm deep cold plate to 2.6 mm, with a rolling pressure of 0.2 mm; Step 34: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 43 is eliminated; Step 45: rolling the 2.6 mm deep cold rolled plate to 2.4 mm with a rolling pressure of 0.2 mm; Step 46: quickly transferring the deformed cold rolled plate to liquid nitrogen and soaking it for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 45 is eliminated; Step 47: Roll the 2.4 mm deep cold plate to 2.2 mm, with a rolling pressure of 0.2 mm; Step 48: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 47 is eliminated; Step 49: The 2.2 mm deep cold plate is rolled and deformed to 2.13 mm, with a rolling pressure of 0.07 mm.

[0037] Step 5: The deep cold rolled aluminum alloy sheet is subjected to peak aging treatment at 185±5°C; Step 6: Use wire cutting to cut into 25mm × 25mm × 2.13mm chemical milling specimens along the rolling direction. Prepare 3 pieces.

[0038] Step 7: Perform chemical milling according to the chemical milling standard HB / Z 5125-2008. The test results are as follows: Figure 3 shown.

[0039] Example 2 The present invention discloses a mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plates. Taking a deformation amount of 30% as an example, the method comprises: Step 1: Select 3mm thick 2024 aluminum alloy and subject it to solution treatment at 498±5℃ / 1h; Step 2: Transfer the workpiece after solution treatment into water for quenching; Step 3: Transfer the quenched workpiece to liquid nitrogen and soak it for about 20 minutes for cryogenic treatment; Step 4: The workpiece soaked in liquid nitrogen is quickly transferred to the rolling mill for deep cold rolling deformation treatment, with a total rolling deformation of 30%; Specifically, step 4 deep cold rolling includes: Step 41: rolling the 3 mm deep cold plate to 2.8 mm, with a rolling pressure of 0.2 mm; Step 42: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 41 is eliminated; Step 43: rolling the 2.8 mm deep cold plate to 2.6 mm, with a rolling pressure of 0.2 mm; Step 34: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 43 is eliminated; Step 45: rolling the 2.6 mm deep cold rolled plate to 2.4 mm with a rolling pressure of 0.2 mm; Step 46: quickly transferring the deformed cold rolled plate to liquid nitrogen and soaking it for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 45 is eliminated; Step 47: Roll the 2.4 mm deep cold plate to 2.2 mm, with a rolling pressure of 0.2 mm; Step 48: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 47 is eliminated; Step 49: Roll the 2.2 mm deep cold plate to 2.0 mm, with a rolling pressure of 0.2 mm; Step 410: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 49 is eliminated; Step 411: rolling and deforming the 2.0 mm deep cold plate to 1.8 mm, with a rolling pressure of 0.2 mm; Step 412: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 411 is eliminated; Step 413: rolling the 1.8 mm deep cold plate to 1.75 mm, with a rolling pressure of 0.05 mm; Step 5: The deep cold rolled aluminum alloy sheet is subjected to peak aging treatment at 185±5°C; Step 6: Use wire cutting to cut into 25mm × 25mm × 2.13mm chemical milling specimens along the rolling direction. Prepare 3 pieces.

[0040] Step 7: Perform chemical milling according to the chemical milling standard HB / Z 5125-2008. The test results are as follows: Figure 3 shown.

[0041] Example 3 The present invention discloses a mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plates. Taking a deformation amount of 70% as an example, the method comprises: Step 1: Select 3mm thick 2024 aluminum alloy and subject it to solution treatment at 498±5℃ / 1h; Step 2: Transfer the workpiece after solution treatment into water for quenching; Step 3: Transfer the quenched workpiece to liquid nitrogen and soak it for about 20 minutes for cryogenic treatment; Step 4: The workpiece, which is also immersed in liquid nitrogen, is quickly transferred to the rolling mill for deep cold rolling deformation treatment, with a total rolling deformation of 70%; Specifically, step 4 deep cold rolling includes: Step 41: rolling the 3 mm deep cold plate to 2.8 mm, with a rolling pressure of 0.2 mm; Step 42: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 41 is eliminated; Step 43: rolling the 2.8 mm deep cold plate to 2.6 mm, with a rolling pressure of 0.2 mm; Step 34: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 43 is eliminated; Step 45: rolling the 2.6 mm deep cold rolled plate to 2.4 mm with a rolling pressure of 0.2 mm; Step 46: quickly transferring the deformed cold rolled plate to liquid nitrogen and soaking it for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 45 is eliminated; Step 47: Roll the 2.4 mm deep cold plate to 2.2 mm, with a rolling pressure of 0.2 mm; Step 48: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 47 is eliminated; Step 49: Roll the 2.2 mm deep cold plate to 2.0 mm, with a rolling pressure of 0.2 mm; Step 410: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 49 is eliminated; Step 411: rolling and deforming the 2.0 mm deep cold plate to 1.8 mm, with a rolling pressure of 0.2 mm; Step 412: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 411 is eliminated; Step 413: rolling the 1.8 mm deep cold plate to 1.6 mm, with a rolling pressure of 0.2 mm; Step 414: quickly transfer the deformed cold-rolled sheet to liquid nitrogen and soak it for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 413 is eliminated; Step 415: rolling the 1.6 mm deep cold plate to 1.4 mm, with a rolling pressure of 0.2 mm; Step 416: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 415 is eliminated; Step 417: rolling the 1.4 mm deep cold plate to 1.2 mm, with a rolling pressure of 0.2 mm; Step 418: The cold-rolled sheet that has been deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 417 is eliminated; Step 419: rolling the 1.2 mm deep cold plate to 1.0 mm, with a rolling pressure of 0.2 mm; Step 420: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 419 is eliminated; Step 421: rolling the 1.0 mm deep cold plate to 0.8 mm, with a rolling pressure of 0.2 mm; Step 422: The cold-rolled sheet deformed by rolling is quickly transferred to liquid nitrogen and immersed for 20 minutes to ensure that the temperature increase caused by the deep cold deformation in step 421 is eliminated; Step 423: rolling the 0.8 mm deep cold plate to 0.75 mm, with a rolling pressure of 0.05 mm; Step 5: The deep cold rolled aluminum alloy sheet is subjected to peak aging treatment at 185±5°C; Step 6: Use wire cutting to cut into 25mm × 25mm × 0.75mm chemical milling specimens along the rolling direction. Prepare 3 pieces.

[0042] Step 7: Perform chemical milling according to the chemical milling standard HB / Z 5125-2008. The test results are as follows: Figure 3 shown.

[0043] Comparative Example 3mm thick 2024 aluminum alloy was selected and solutionized at 498±5℃ / 1h, followed by cold water quenching. It was then subjected to peak aging treatment at 185±5℃. Three chemical milling specimens of 25mm × 25mm × 3mm were prepared using wire cutting along the rolling direction. Chemical milling was performed according to the chemical milling standard HB / Z 5125-2008. The test results are shown in the figure. Figure 3 shown.

[0044] Table 2 Surface roughness of alloyed milling plates after treatment with different process methods

[0045] like Figure 2 The following are 3D microstructure scanning images (SEM) of 2024 aluminum alloy with different cryogenic deformation amounts. Figure 2 a is the structure of the traditional 2024-T6 aluminum alloy in the comparative example, Figure 2 b is the structure of the peak-aged state of the 2024 aluminum alloy with a cryogenic deformation of 15% in Example 1, Figure 2 c is the microstructure of the 2024 aluminum alloy in peak aging state with a cryogenic deformation of 30% in Example 2, Figure 2 Figure d shows the microstructure of the peak-aged 2024 aluminum alloy in Example 3, cryogenically deformed to 70%. The figure clearly shows that the distribution of second-phase particles in the T6 alloy is clustered along the rolling direction. With increasing cryogenic deformation, the second-phase particles are evenly distributed within the alloy at 15% deformation, and the agglomeration of precipitated phases near grain boundaries is reduced. In the alloy at 30% deformation, the number density of second-phase particles decreases, and agglomeration disappears. At 70% deformation, the second-phase particles are essentially gone.

[0046] like Figure 3 The figure below shows the average roughness of 2024 aluminum alloy at different cryogenic deformation levels. It can be seen that solutionizing followed by cryogenic rolling significantly improves the roughness of the alloy. The average roughness of the alloy decreases with increasing cryogenic deformation. The alloy achieves the optimal average roughness when the cryogenic deformation reaches 70%.

[0047] This application adds a cryogenic deformation process between traditional solution quenching and aging. Experimental results show that the surface roughness of the chemical milling of 2024 thin plate after cryogenic rolling decreases with increasing deformation, indicating that this process can improve the chemical milling roughness of 2024 aluminum alloy thin plate.

[0048] The above-mentioned specific implementation can be partially adjusted in different ways by those skilled in the art without departing from the principles and purpose of the present invention. The scope of protection of the present invention shall be based on the claims and shall not be limited by the above-mentioned specific implementation. All implementation schemes within its scope shall be subject to the constraints of the present invention.

Claims

1. A mechanical heat treatment method for improving the milling roughness of aluminum alloy skin thin plate, characterized in that: Methods include: Step 1: After solution quenching, the aluminum alloy sheet is immersed in liquid nitrogen for a preset immersion time; Step 2: Under liquid nitrogen temperature, perform deep cold rolling deformation treatment according to a preset rolling deformation amount; Step 3: After deep cold rolling, the aluminum alloy is subjected to peak aging treatment and then chemical milling treatment to obtain a chemical milling plate with low surface roughness.

2. The mechanical heat treatment method according to claim 1, characterized in that Aluminum alloy sheet undergoes solution treatment including: The solution temperature range is 465℃~530℃; the holding time is 30min~2.5h; the atmosphere in the solution furnace is an air circulation electric furnace.

3. The mechanical heat treatment method according to claim 1, characterized in that The quenching process of aluminum alloy sheet after solid solution includes: The time interval between the workpiece being transferred from the furnace to the quenching medium is ≤ 20s; The cooling medium is water, and the water temperature is controlled at ≤40℃.

4. The mechanical heat treatment method according to claim 1, characterized in that The deep cold rolling deformation treatment in step 2 includes: Step 21: Take out the aluminum alloy cryogenically treated with liquid nitrogen and place it on the rolling mill. The transfer time is ≤10s. Step 22: Start deep cold rolling, and the reduction in a single rolling should not exceed 10%; Step 23: After each rolling, the workpiece must be quickly transferred from the rolling mill to be immersed in liquid nitrogen to ensure that the deformation temperature of the alloy is at the liquid nitrogen temperature; Step 24: Add up the deformation of each rolling process to get the total deformation of the aluminum alloy.

5. The mechanical heat treatment method according to claim 1, characterized in that The liquid nitrogen temperature is -196°C; the preset total rolling deformation range is 15%~70%.

6. The mechanical heat treatment method according to claim 1, characterized in that The pressure force during each rolling deformation cannot exceed 0.4 mm; before each rolling process, the sample needs to be immersed in liquid nitrogen for 20 minutes to ensure that the deformation temperature of the alloy is the liquid nitrogen temperature.

7. The mechanical heat treatment method according to claim 1, characterized in that Peak aging treatment is artificial aging, aging temperature range: 120℃~190℃, aging time: 6h~24h.

8. The mechanical heat treatment method according to claim 1, characterized in that Chemical milling was carried out according to the industry standard HB / Z 5125-2008. The chemical milling samples were mechanically polished with 180#, 400#, 600#, and 800# water-abrasive sandpapers in sequence, and then polished with 400#, 600#, 800#, and 1000# metallographic sandpapers in sequence. Finally, they were ultrasonically cleaned and dried for use.

9. The mechanical heat treatment method according to claim 1, characterized in that The specific chemical milling process of aluminum alloy in step 3 is as follows: Step 31: Alkaline washing with 40% NaOH solution; Step 32: The pre-treated workpiece is subjected to light treatment using a 30% HNO3 solution; Step 33: Apply HH968-2 peelable coating protective glue to the workpiece after polishing and leave it at room temperature for 24 hours to fully cure; Step 34: Remove the protective adhesive from the area to be processed; Step 35: chemical milling, processing the workpiece processed in step 34 using a chemical milling fluid; Step 36: After chemical milling, rinse the workpiece in 40°C hot water for 2 minutes; Step 37: Rinse the workpiece processed in step 36 with cold water for 1 minute; Step 38: The workpiece processed in step 37 is treated with 30% HNO3 solution for 2 minutes; Step 39: Use hot air to dry the workpiece processed in step 38 and remove the glue layer for subsequent roughness testing.

10. The mechanical heat treatment method according to claim 1, characterized in that: The milling fluid formula for chemical milling treatment is 170g / L NaOH + 19 g / L Na2S + 45 g / L TEA + 19 g / L Al3+, the milling temperature is 80 ℃, and the milling time is 5min.

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