A process for reducing residual stress inside aluminum alloy sheets

Abstract

This invention discloses a process for reducing residual stress inside aluminum alloy sheets, specifically relating to the field of non-ferrous metal processing. The process includes the following steps: Step S1 solution quenching, Step S2 stretching, Step S3 incomplete annealing, and Step S4 artificial aging. This invention creatively introduces an incomplete annealing process, located after stretching and before aging, into the traditional solution quenching-stretching-aging process. This process is not a simple low-temperature tempering, but rather a precisely controlled low-temperature recovery process specifically designed to effectively eliminate the micro-stress remaining inside the sheet after stretching. This achieves a dual reduction of macro- and micro-stress, lowering the overall residual stress level of the sheet. Due to the extremely low internal residual stress, the stress release during subsequent large-mass milling, turning, drilling, and other machining operations is minimal, avoiding deformation problems such as warping, bending, and twisting caused by stress release.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal processing technology, and more specifically, to a process method for reducing residual stress inside aluminum alloy sheets. Background Technology

[0002] 6061 aluminum alloy is an Al-Mg-Si heat-treatable aluminum alloy with moderate strength, good weldability, excellent corrosion resistance, and good machinability. It is widely used in shipbuilding, rail transportation, automotive industry, aerospace, construction formwork, precision instruments, and various molds. The T651 temper refers to a specific state after solution treatment, stress relief through stretching, and artificial aging. Aluminum alloy sheets in this temper exhibit the best overall performance, retaining high strength and hardness while possessing good machinability. Therefore, 6061T651 aluminum alloy sheets have become one of the preferred raw materials for many precision machining companies.

[0003] Currently, the standard production process for 6061T651 aluminum alloy sheets in the industry typically includes: casting → homogenization treatment → hot rolling → solution quenching → tensile straightening → artificial aging → sawing → inspection → packaging. The solution quenching process involves heating the hot-rolled sheet to its solution temperature (usually 515-530℃) and holding it at that temperature to allow the alloying elements to fully dissolve into the aluminum matrix. Then, it is rapidly cooled (water quenching) to obtain a supersaturated solid solution, laying the foundation for subsequent aging precipitation of strengthening phases. However, the quenching process is accompanied by drastic temperature changes, and the cooling rates of the sheet surface and core are inconsistent, generating significant thermal and structural stresses, leading to a complex residual stress field within the sheet. To eliminate quenching stress, a subsequent tensile straightening process is introduced. By applying a tensile force exceeding the material's yield strength, the sheet undergoes plastic deformation, releasing most (approximately 80%-90%) of the macroscopic residual stress and simultaneously improving the sheet's flatness.

[0004] However, existing technologies have the following obvious defects and shortcomings: 1. Incomplete stress relief during the stretching process: The stretching process itself is a non-uniform plastic deformation process. Due to the inhomogeneity of the material's microstructure (such as grain orientation, second-phase distribution, etc.) and the differences in stress distribution across the cross-section of the sheet, some stress will remain inside the sheet after stretching. Although this stress is relatively small, it is still a major cause of workpiece deformation and dimensional deviations for subsequent precision machining processes that require significant material removal, such as deep milling and turning. For example, when a layer of material is removed from the sheet by milling, the original stress balance is broken, and the residual stress will redistribute, causing the workpiece to warp, bend, or even twist, seriously affecting machining accuracy and product yield.

[0005] 2. Wide range of process parameters, lacking targeted optimization: In the traditional 6061T651 production process, the solution quenching temperature, tensile amount, and aging parameters often use a wide range. For example, the solution temperature is often 515-530℃, the tensile amount is generally 1%-3%, the aging temperature is 170-180℃, and the time is 6-12 hours. While this wide range of parameter control can meet general needs, it cannot meet the requirements of high-end applications that require extreme dimensional stability (such as precision molds, optical instrument structural components, etc.). Under different parameter combinations, the microstructure, precipitate characteristics, and residual stress level of the sheet metal vary significantly, but existing technologies lack systematic parameter optimization for minimizing residual stress.

[0006] 3. Lack of specific methods for eliminating microscopic residual stress after stretching: Current technologies mainly rely on the stretching process to eliminate macroscopic residual stress generated by quenching, but there is a lack of effective post-treatment methods for newly generated microscopic residual stresses after stretching (such as dislocation entanglement, lattice distortion, etc.). Although some researchers have tried to perform additional annealing after aging, the material has already obtained stable precipitates after aging, and further annealing can easily lead to over-aging, resulting in a significant decrease in strength, which is not worthwhile.

[0007] 4. The problem of machining deformation has not been fundamentally solved for a long time: Although the 6061T651 plates produced by the existing process may meet the standard flatness requirements when they leave the factory, users still frequently encounter deformation problems in the actual machining process. They have to use multiple processing, allowance, and repeated straightening and leveling methods, which not only reduces production efficiency and increases costs, but sometimes even fails to meet design requirements, resulting in product scrap.

[0008] Therefore, how to develop a new process to minimize the internal residual stress (especially the micro-stress remaining after stretching) of 6061T651 aluminum alloy sheet while ensuring its excellent comprehensive mechanical properties, thereby completely solving the problem of deformation during subsequent machining, has become a technical bottleneck that needs to be overcome by those skilled in the art. Summary of the Invention

[0009] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a process method for reducing the internal residual stress of aluminum alloy plates. The technical problem to be solved by the present invention is: how to overcome the defect that 6061T651 aluminum alloy plates still have residual stress after solution quenching and stretching, which leads to deformation and out-of-tolerance dimensional accuracy due to stress release during subsequent machining.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a process for reducing residual stress inside aluminum alloy sheets, specifically comprising the following steps: Step S1, Solution Quenching: The hot-rolled 6061 aluminum alloy sheet is placed in a roller hearth furnace for heating. The furnace temperature is precisely controlled within the range of 517-523℃, and the temperature uniformity is controlled within ±3℃. The heating and holding time is adjusted according to the specific thickness of the sheet to ensure that the core of the sheet reaches the set temperature and is fully solution-treated (e.g., 1-2 minutes per millimeter of thickness). The quenching transfer speed is controlled to ensure that the time from furnace exit to water immersion does not exceed 15 seconds to reduce temperature drop and pre-precipitation. The quenching medium is room temperature water. The cooling rate is ensured by adjusting the water pressure and flow rate to obtain a highly saturated solid solution. The purpose of this step is to control the final mechanical properties of the sheet within an optimized range that is conducive to subsequent stress relief, laying the foundation for subsequent processes.

[0011] Step S2, Tensile Treatment: The solution-quenched sheet metal is subjected to tensile straightening treatment, with the stretching amount strictly controlled between 2.5% and 2.8%. This stretching amount is slightly higher than the conventional process (usually 1.5%-2.0%), aiming to maximize the release of macroscopic residual stress generated during quenching through greater plastic deformation, while ensuring that the flatness of the sheet metal meets product standards (e.g., warpage less than 2mm per meter) and the requirements of subsequent processes. The higher stretching amount helps to activate more slip systems, resulting in a more uniform stress distribution and providing more sufficient driving force for recovery during the subsequent incomplete annealing process.

[0012] Step S3, Incomplete Annealing: After stretching and before artificial aging, the sheet material undergoes incomplete annealing. The sheet is placed in an annealing furnace, with the furnace gas temperature controlled at 220-250℃ and the furnace temperature uniformity controlled within ±3℃. The heating and holding time is controlled at 1-2 hours. Cooling after annealing is done in the furnace; the sheet is removed from the furnace and air-cooled after the temperature drops below 60℃. The core of this process is to utilize the recovery process at low temperatures to promote the redistribution and partial elimination of micro-stresses (dislocation entanglements, lattice distortion, etc.) within the stretched material, while maintaining the fibrous structure and preventing recrystallization and significant strength loss. By precisely controlling the temperature and time, internal stress can be relaxed to the maximum extent without significantly reducing strength.

[0013] Step S4, Artificial Aging Treatment: The incompletely annealed sheet is subjected to artificial aging treatment to precipitate strengthening phases and obtain the target mechanical properties. The furnace temperature is controlled between 167-173℃, with a uniformity requirement of ±3℃, and the holding time is controlled between 12-14 hours. After aging, the sheet is cooled to below 100℃ in the furnace and then air-cooled to avoid generating new thermal stress.

[0014] In a preferred embodiment, the determination of the incomplete annealing process parameters in step S3 is obtained through the following systematic experimental process: First, set multiple different furnace gas temperatures, including but not limited to 413℃, 365℃, 260℃, 250℃, 240℃, 230℃, 220℃, 210℃, and 200℃; Secondly, different heating and holding times are set for each temperature group, including but not limited to 3 hours, 2 hours, 1 hour, 0.5 hours, and 0 hours (i.e., cooling immediately after heating to the desired temperature). Then, the mechanical properties (tensile strength, yield strength, elongation) of the samples after treatment at different temperatures and holding times were tested, and the process parameter group that still meets the requirements of the 6061T651 standard was selected. Finally, residual stress was evaluated on the sample groups that met the mechanical property requirements. The evaluation method was as follows: a 2mm thick layer of surface material was milled away perpendicular to the rolling direction of the sheet metal, and the changes in flatness (warpage) of the samples before and after milling were accurately measured and compared. The smaller the change in flatness, the lower the residual stress inside the sheet metal. By comparing the experimental data, the combination of process parameters that resulted in the lowest residual stress and qualified mechanical properties was finally selected.

[0015] In a preferred embodiment, the final selected process parameters for the incomplete annealing treatment are as follows: the furnace gas temperature is controlled at 220°C; heating is stopped and a holding time is started when the metal temperature of the sheet reaches 217°C; the holding time is 2 hours. Immediately after the holding time, furnace cooling is performed until the temperature drops below 60°C before removal from the furnace, followed by air cooling to room temperature. Under these process conditions, internal residual stress is minimized and machining deformation is reduced to a minimum while ensuring that the material's mechanical properties meet the T651 standard.

[0016] The technical effects and advantages of this invention are as follows: This invention creatively introduces an incomplete annealing process, located after stretching and before aging, into the traditional solution quenching-stretching-aging process. This process is not a simple low-temperature tempering, but rather a precisely controlled low-temperature recovery process specifically designed to effectively eliminate the micro-stress remaining inside the sheet metal after stretching. This achieves dual reduction of macro-stress and micro-stress, lowering the overall residual stress level of the sheet metal. Due to the extremely low internal residual stress, the stress release is minimal during subsequent machining operations such as large-margin milling, turning, and drilling. The workpiece can maintain extremely high dimensional stability and positional accuracy, avoiding deformation problems such as warping, bending, and twisting caused by stress release. This is crucial for manufacturing high-precision products such as precision molds, optical instrument structural components, and aerospace thin-walled parts, improving yield, reducing straightening processes, and lowering manufacturing costs. This invention not only adds a new process but also refines the control of the two pre-processes, solution quenching and stretching. The solution quenching temperature is controlled within a narrow window of 517-523℃, creating a favorable initial microstructure for subsequent stress relief. The stretching amount is increased to 2.5%-2.8%, which, combined with subsequent incomplete annealing, allows for more complete stress release and ultimately achieves the target properties through aging. The optimal parameter point for the incomplete annealing process is determined: treatment at a mild temperature of 220℃ / 2h. This effectively drives dislocation movement and stress relaxation while avoiding over-aging or significant strength reduction due to excessively high temperatures or long processing times. This achieves an ideal balance between maintaining the excellent comprehensive mechanical properties of 6061T651 alloy and minimizing residual stress. It can be easily integrated into existing production lines without adding expensive new equipment; only adjustments to furnace temperature control and process sequence are needed, demonstrating promising prospects for industrial application. The present invention adopts a method of cooling in the furnace to below 60°C after incomplete annealing and then air cooling after removal from the furnace, which can reduce the thermal stress caused by uneven cooling. If the plate is directly removed from the furnace and air cooled, the difference in cooling rate between the surface and the core will still introduce new residual stress, weakening the annealing effect. The slow cooling method ensures the maximization of stress relief effect. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. The 6061 aluminum alloy sheet raw material used in the embodiments of the present invention is a hot-rolled intermediate billet, and its chemical composition conforms to the requirements of grade 6061 in GB / T3190 standard. Mechanical property testing is performed in accordance with GB / T228.1-2021 "Metallic materials, tensile testing—Part 1: Test method at room temperature", and flatness is measured using a precision straightedge and feeler gauge. Example

[0018] This embodiment provides a process method for reducing the internal residual stress of 6061T651 aluminum alloy sheet, and the specific steps are as follows: Solution quenching: A 6061 hot-rolled plate with a thickness of 50mm, a width of 1500mm, and a length of 6000mm was selected and fed into a roller hearth furnace. The furnace temperature was raised to and controlled at 520±2℃ (target value 520℃, fluctuation range ±2℃). Furnace temperature uniformity was monitored by multiple thermocouples within the furnace to ensure the temperature difference within the entire heating zone did not exceed ±3℃. The holding time was calculated based on the plate thickness, set at 1.5 minutes per millimeter of thickness, for a total of 75 minutes, ensuring the core of the plate reached the set temperature and was fully solution-treated. Subsequently, the plate was quenched in room temperature water at the fastest speed (transfer time <10 seconds), using high-pressure spraying of the quenching water to ensure a high cooling rate.

[0019] Stretching treatment: The quenched sheet metal is stretched and straightened, with the stretching amount controlled at 2.6%. The stretching machine is precisely controlled, and the stretching speed is uniform. After stretching, the flatness of the sheet metal is tested, and the warping per meter is less than 1.5mm.

[0020] Incomplete annealing: The stretched sheet is placed in an annealing furnace, with the furnace gas temperature set to 220℃ and the furnace temperature uniformity controlled within ±2℃. The sheet is heated along with the furnace after entering the furnace. Timing begins when the sheet metal temperature reaches 217℃, and the sheet is held at this temperature for 2 hours. After holding, the heat source is cut off, the furnace door is closed, and the sheet is allowed to cool slowly with the furnace. When the furnace temperature drops to 50℃ (approximately 4-6 hours), the sheet is removed and air-cooled to room temperature.

[0021] Artificial aging treatment: The incompletely annealed sheet material is transferred to an aging furnace, with the furnace temperature set and controlled at 170±2℃. It is held at this temperature for 13 hours. During the aging process, the furnace temperature uniformity is also controlled within ±3℃. After aging, the sheet material is cooled in the furnace to below 100℃ and then air-cooled.

[0022] Subsequent processing: The aged boards are then subjected to routine sawing and brushing to obtain the final product. Example

[0023] This embodiment is basically the same as Embodiment 1, except that the process parameters for the incomplete annealing treatment in step three are different. In this embodiment, the furnace gas temperature for the incomplete annealing treatment is set to 250°C, and timing begins when the metal temperature of the sheet reaches 247°C. The holding time is 1 hour. After the holding time, the sheet is cooled in the furnace to below 60°C and then air-cooled. The remaining parameters for solution treatment, tensile testing, and aging are consistent with those in Embodiment 1. Example

[0024] This embodiment is basically the same as Embodiment 1, except that the process parameters for the incomplete annealing treatment in step three are different. In this embodiment, the furnace gas temperature for the incomplete annealing treatment is set to 240℃, and timing begins when the metal temperature of the sheet reaches 237℃, with a holding time of 2 hours. After the holding time, the sheet is cooled in the furnace to below 60℃ and then air-cooled. The remaining parameters for solution treatment, tensile testing, and aging are consistent with those in Embodiment 1. Example

[0025] This embodiment is basically the same as Embodiment 1, except that the process parameters for the incomplete annealing treatment in step three are different. In this embodiment, the furnace gas temperature for the incomplete annealing treatment is set to 230°C, and timing begins when the metal temperature of the sheet reaches 227°C. The holding time is 2 hours. After the holding time, the sheet is cooled in the furnace to below 60°C and then air-cooled. The remaining parameters for solution treatment, tensile testing, and aging are consistent with those in Embodiment 1.

[0026] Example 5 (Comparative Example 1, conventional process) This embodiment is a comparative example using a traditional process method, used to illustrate the beneficial effects of the present invention. The steps are as follows: Solution quenching treatment: Same as in Example 1.

[0027] Stretching treatment: The stretching amount is controlled at 1.8%, which is common in the industry.

[0028] Artificial aging treatment: Same as in Example 1 (170℃ / 13h).

[0029] Subsequent processing: Same as in Example 1.

[0030] That is, the incomplete annealing process is omitted in this comparative example.

[0031] Example 6 (Comparative Example 2, High Temperature Short-Time Annealing) This example is a comparative example using annealing at a higher temperature. The steps are as follows: Solution quenching treatment: Same as in Example 1.

[0032] Stretch treatment: The stretching amount is controlled at 2.6%.

[0033] Incomplete annealing: The furnace gas temperature is set to 300℃, held for 0.5 hours, and then cooled with the furnace.

[0034] Artificial aging treatment: Same as in Example 1.

[0035] Subsequent processing: Same as in Example 1.

[0036] Example 7 (Comparative Example 3, Low-Temperature Long-Time Annealing) This example is a comparative example using a lower temperature and longer annealing time. The steps are as follows: Solution quenching treatment: Same as in Example 1.

[0037] Stretch treatment: The stretching amount is controlled at 2.6%.

[0038] Incomplete annealing: The furnace gas temperature is set to 200℃, held for 4 hours, and then cooled with the furnace.

[0039] Artificial aging treatment: Same as in Example 1.

[0040] Subsequent processing: Same as in Example 1.

[0041] Performance Testing and Evaluation The finished boards obtained in Examples 1-7 above were subjected to performance tests and evaluations. Samples were cut from the same location on each board (avoiding edge defect areas).

[0042] 1. Mechanical property testing: Standard circular tensile specimens were processed according to GB / T228.1-2021 standard, and their tensile strength (Rm), yield strength (Rp0.2), and elongation after fracture (A) were tested. Three specimens were tested for each example, and the average value was taken. The results are shown in Table 1. Referring to GB / T3880.2-2012 "General Industrial Aluminum and Aluminum Alloy Plates and Strips - Part 2: Mechanical Properties", the typical mechanical property requirements for 6061T651 plate are: Rm≥290MPa, Rp0.2≥240MPa, A≥8%.

[0043] 2. Residual Stress Evaluation (Machining Deformation Test): A 500mm × 500mm template was selected. First, its original flatness was measured using a high-precision straightedge and feeler gauge, and the maximum warpage (i.e., the maximum gap between the template surface and the straightedge) was recorded. Then, on a CNC milling machine, using the same cutting parameters (tool diameter, spindle speed, feed rate, depth of cut), a 2mm thick layer of surface material was uniformly milled away perpendicular to the rolling direction of the sheet metal (single cutting depth 0.5mm, completed in 4 passes). The flatness of the template after machining was measured again, and the maximum warpage was recorded. The maximum change in flatness before and after machining (i.e., warpage after machining minus warpage before machining) was used to characterize the degree of residual stress release. The smaller the change, the lower the residual stress. The results are shown in Table 2.

[0044] Table 1: Comparison of mechanical properties of boards prepared by different processes Example Tensile strength Rm (MPa) Yield strength Rp0.2 (MPa) Elongation after fracture A (%) Does it conform to the T651 standard? Example 1 312 281 11.5 yes Example 2 306 274 12.0 yes Example 3 308 276 11.8 yes Example 4 310 278 11.2 yes Example 5 321 292 10.5 yes Example 6 270 235 14.5 no Example 7 315 285 11.0 yes Table 2: Comparison of flatness changes before and after machining of sheets prepared by different processes Example Maximum warpage before processing (mm) Maximum warpage after processing (mm) Change in warping (mm) Example 1 0.8 1.2 0.4 Example 2 0.9 1.6 0.7 Example 3 0.8 1.5 0.7 Example 4 0.9 1.4 0.5 Example 5 0.9 3.8 2.9 Example 6 1.0 1.3 0.3 Example 7 0.8 2.1 1.3 It can be seen from Table 1 above: The mechanical properties of Examples 1-4 and Comparative Examples 1 and 3 all meet the standard requirements of 6061T651 (Rm≥290MPa, Rp0.2≥240MPa, A≥8%).

[0045] The strength of Example 1 was slightly lower than that of Comparative Example 1 (without annealing) (approximately 9 MPa), but it was still within the acceptable range. This is consistent with the recovery phenomenon during stress relief, where partial dislocation rearrangement leads to a slight decrease in strength but a slight increase in toughness.

[0046] The strength of Examples 2, 3, and 4 is slightly higher than that of Example 1, but the stress relief effect (see Table 2) is slightly inferior to that of Example 1.

[0047] The strength of Example 6 decreased significantly and no longer met the T651 standard, indicating that the temperature of 300℃ was too high, resulting in partial recrystallization or over-recovery, which led to excessive strength loss and was unacceptable.

[0048] Example 7 showed good strength retention, but the stress relief effect (see Table 2) was not ideal.

[0049] It can be seen from Table 2 above: Comparative Example 5: After milling 2mm, the sheet metal exhibited significant warping deformation (change of up to 2.9mm), indicating the presence of substantial residual stress within it. The stress release after material removal led to severe deformation. This is a typical problem faced by most users today.

[0050] Example 6: Although the deformation is very small (0.3mm), it has no practical value because its strength is unqualified.

[0051] Example 7: The deformation was 1.3 mm, which is an improvement over the traditional process, but still relatively large. This indicates that the temperature of 200℃ was too low, the recovery was insufficient, and the stress relief was limited.

[0052] Examples 2, 3, and 4: The warpage changes after processing were 0.7 mm, 0.7 mm, and 0.5 mm, respectively, all significantly smaller than Comparative Example 1, indicating that incomplete annealing within the 220-250℃ range effectively eliminated most of the residual stress. Example 4 showed even better results (0.5 mm).

[0053] Example 1: The warpage after processing was only 0.4 mm, the smallest among all qualified samples. This indicates that incomplete annealing at 220℃ / 2h can reduce the residual stress inside the sheet to an extremely low level, resulting in the best dimensional stability after machining.

[0054] Combining Tables 1 and 2, we can conclude that: If the incomplete annealing temperature is too low (e.g., 200℃), the stress relief effect is not significant (the deformation still reaches 1.3mm).

[0055] If the incomplete annealing temperature is too high (such as 300℃), although the stress relief effect is good, the mechanical properties will be severely reduced and will not meet the application requirements.

[0056] Within the temperature range of 220-250℃, stress can be effectively reduced while maintaining acceptable mechanical properties. Among them, the 220℃ / 2h process (Example 1) achieves the lowest residual stress level (deformation of 0.4mm) while ensuring the required strength, making it the optimal implementation scheme in terms of overall performance. The 230℃ / 2h process (Example 4) also performs well (0.5mm) and can be considered as an alternative.

[0057] This invention finds the optimal balance between performance and stress by precisely controlling the temperature and time of incomplete annealing. That is, the recovery treatment is carried out at around 220°C, which can effectively relax the stress without causing a significant decrease in strength.

[0058] Therefore, the process parameters represented by Example 1 (solution treatment 517-523℃, stretching 2.5%-2.8%, incomplete annealing 220℃ / 2h / furnace cooling, aging 170℃ / 13h) are the preferred embodiments of the present invention.

[0059] Example 8: Industrial Production Verification The process described in Example 1 was applied to an industrial production line in an aluminum alloy processing plant, continuously producing three batches of 50mm thick 6061T651 sheet metal (10 sheets per batch). Random sampling inspection of the finished sheets showed that all mechanical properties met the requirements. Five sheets were randomly selected for machining deformation testing (milling 2mm as described above). The results showed that the warpage of all samples was between 0.3-0.6mm, with an average of 0.45mm, significantly better than traditional processes (typically >2.5mm). Customer feedback indicated that the sheet metal produced using this invention exhibits minimal deformation when machining precision mold cavities, requiring no additional straightening, reducing the processing cycle by 30%, and increasing the yield from 75% to over 98%.

[0060] In summary, this invention optimizes solution quenching and tensile parameters, and creatively introduces a low-temperature incomplete annealing process after tensile testing and before aging, thereby achieving the ultimate elimination of residual stress inside 6061T651 aluminum alloy sheets. While ensuring the excellent mechanical properties of the material, it significantly improves its dimensional stability during machining, solves a long-standing technical problem that has plagued the industry, and has extremely high industrial application value and promotion prospects.

[0061] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for reducing residual stress inside aluminum alloy sheets, characterized in that: Specifically, the following steps are included: Step S1, Solution quenching treatment: Heat the aluminum alloy sheet to the solution temperature and hold it at that temperature, then quench it rapidly; Step S2, stretching treatment: The sheet metal quenched in step S1 is stretched by 2.5%-2.8%; Step S3, Incomplete Annealing Treatment: The sheet material stretched in Step S2 is heated and held at a temperature of 220℃-250℃ for 1-2 hours, and then cooled in the furnace. Step S4, Artificial Aging Treatment: Heat the incompletely annealed board to the aging temperature and hold it at that temperature for aging treatment.

2. The process for reducing residual stress inside aluminum alloy sheets according to claim 1, characterized in that: The solution temperature in step S1 is 517-523℃, and the furnace temperature uniformity is controlled within ±3℃; the aluminum alloy sheet is 6061 aluminum alloy sheet.

3. The process for reducing residual stress inside aluminum alloy sheets according to claim 1, characterized in that: In step S3, the heating temperature for the incomplete annealing treatment is preferably 220°C. When the metal temperature of the plate reaches 217°C, heating is stopped and the holding time is started for 2 hours. The end point of furnace cooling is when the plate temperature drops below 60°C, and then the plate is removed from the furnace and air-cooled.

4. The process for reducing residual stress inside aluminum alloy sheets according to claim 1, characterized in that: In step S4, the temperature for artificial aging treatment is 167-173℃, the holding time is 12-14 hours, and the furnace temperature uniformity is controlled within ±3℃.

5. The process for reducing residual stress inside aluminum alloy sheets according to claim 1, characterized in that: In step S2, the flatness of the sheet material after stretching is controlled to have a warping of less than 2 mm per meter.

6. The process for reducing residual stress inside aluminum alloy sheets according to claim 1, characterized in that: In step S1, the quenching transfer time of the solution quenching treatment shall not exceed 15 seconds.

7. The process for reducing residual stress inside aluminum alloy sheets according to claim 1, characterized in that: After step S4, sawing and brushing processes are also included.