Heat treatment process of high-elongation aluminum alloy plate

Abstract

The invention discloses a heat treatment process for a high-elongation aluminum alloy plate, and particularly relates to the field of aluminum alloy material processing, and the heat treatment process comprises the following specific heat treatment steps: S1, component design preparation, S2, low-temperature solution treatment, S3, pre-stretching optimization and S4, graded aging. According to the invention, through a synergistic process of combining low-temperature solution treatment, pre-stretching optimization and graded aging, the contradiction between the strength and the elongation of the aluminum alloy plate is successfully solved, the strength of the aluminum alloy plate is maintained while the elongation of the aluminum alloy plate is remarkably improved, a high-performance aluminum alloy material solution is provided for lightweight of automobiles, and the application prospect is wide. Wide market prospects and industrial application values are realized; and although the steps of pre-stretching and grading aging are added, the energy consumption is saved by reducing the solid solution temperature, and the comprehensive production cost is equivalent to that of a traditional process.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy material processing, and more particularly to a heat treatment process for a high-elongation aluminum alloy plate. Background Art

[0002] 6XXX series aluminum alloys (Al-Mg-Si series) have become widely used structural materials in the automotive industry due to their excellent lightweight properties, good corrosion resistance, and high strength. With the automotive industry's increasing demands for energy conservation and emission reduction, the proportion of aluminum alloys used in vehicle body structures has increased year by year. However, aluminum alloy sheets often face insufficient formability during the stamping process, especially low elongation, which makes it difficult to form complex parts. This seriously limits their further application in the automotive industry.

[0003] The traditional heat treatment process for aluminum alloy sheet typically consists of three main steps: solution treatment, quenching, and aging. Solution treatment involves heating the aluminum alloy to a specific temperature (typically 540-560°C) to fully dissolve the alloying elements into the aluminum matrix. This supersaturated solid solution is then fixed by rapid quenching. Subsequently, aging allows the alloying elements to precipitate as fine strengthening phases, achieving a strengthening effect. While traditional solution temperatures fully dissolve the strengthening phases, they can also lead to grain coarsening and reduced elongation (only 12-18% through length). Pre-stretching (1.5-3% deformation) can eliminate residual stresses but increases dislocation density, further compromising ductility. Existing technologies, such as two-stage aging, improve performance but fail to resolve the conflict between solution temperature and elongation. Under-aging improves fatigue performance but fails to optimize the elongation required for automotive stamping.

[0004] Therefore, there is an urgent need for a synergistic process of low-temperature solid solution combined with pre-stretching to significantly improve the elongation while ensuring strength. Summary of the Invention

[0005] In order to overcome the above-mentioned defects of the prior art, an embodiment of the present invention provides a heat treatment process for high-elongation aluminum alloy plates. The technical problem to be solved by the present invention is: how to overcome the contradiction between the solid solution temperature and the elongation in the traditional aluminum alloy heat treatment process, that is, to significantly improve the elongation while ensuring the material strength, so as to meet the requirements of stamping and forming of complex automotive structural parts.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a heat treatment process for a high elongation aluminum alloy plate, wherein the specific heat treatment steps are as follows: S1. Component design and preparation: Its chemical composition by mass percentage includes: Si 0.7-1.3%, Mg 0.6-1.2%, optimizing the Mg / Si ratio to 1.0-1.2 to balance strength and formability, Cu 0.1-0.5%, preferably reduced to below 0.3% to avoid softening of the paint, Mn 0.1-0.5%, Fe ≤ 0.1% to inhibit the formation of coarse phases, and the balance is Al and unavoidable impurities, and the percentage of a single impurity is < 0.05%; S2. Low-temperature solution treatment: Preheat the equipment to 500-530°C (10-20°C lower than traditional treatment), strictly control the furnace temperature uniformity to keep it within a temperature range of ≤±3°C, place the plates horizontally on a dedicated rack with a spacing of ≥10cm to ensure uniform airflow, and precisely control the holding time after entering the furnace according to the plate thickness (60-90 minutes for plates ≤10mm thick, set the holding time according to the plate thickness, and extend the holding time by 30 minutes for every 12.7mm increase in thickness). Remove from the furnace and quench in water to obtain the alloy plate. The improved method can control the partial dissolution of the second phase to retain the fine-grained structure, significantly reducing the tendency of grain coarsening compared to traditional solution treatment, maintaining a fine and uniform grain structure, and improving the material toughness (elongation increased by 5-10%) and fatigue resistance. S3. Pre-stretching optimization: The alloy plate after solution quenching in step S2 is placed in a stretching machine with a suction cup within 2 hours. The clamps clamp the ends of the plate and apply a 2-3% tensile deformation to the plate for pre-stretching. The stretching speed is controlled within the range of 0.5-2 mm / s. Pre-stretching can eliminate quenching residual stress, reduce the effect of dislocation density on plasticity, and prevent deformation during subsequent processing and use. S4, Grading Time: S4.1: Allow the pre-stretched sheet in step S3 to stand at room temperature for 48 ± 2 hours; S4.2: Low-temperature aging is carried out first. The aging temperature is set to 80℃, and the furnace temperature uniformity is controlled within ±3℃. When the metal temperature reaches 77℃, the holding period begins and the holding period is 4 hours. S4.3: Then carry out high-temperature aging, the aging temperature is set to 160℃, and the furnace temperature uniformity is controlled at ±3℃; when the metal temperature reaches 157℃, start calculating the holding time, holding for 8 hours, and air-cool after taking out of the furnace; the above can form a cuttable GP zone instead of S′ phase, taking into account strength, fatigue resistance and corrosion resistance.

[0007] In a preferred embodiment, the chemical composition of the aluminum alloy plate in step S1 includes, by mass percentage, Si 0.9-1.1%, Mg 0.8-1.0%, Cu 0.2-0.3%, Mn 0.2-0.4%, Fe≤0.08%, and the remainder is Al and unavoidable impurities.

[0008] In a preferred embodiment, the temperature of the low-temperature solution treatment in step S2 is 510-520°C, and the holding time of an 8 mm thick plate is set to 75-85 minutes; the atmosphere in the furnace is set to air, and the oxygen content in the air is controlled between 18-21% to avoid excessive oxidation.

[0009] In a preferred embodiment, the pre-stretching optimization treatment in step S3 is performed when the plate temperature drops below 50° C., the stretching amount is preferably 2.5%, and the stretching direction is consistent with the rolling direction of the plate.

[0010] In a preferred embodiment, in the graded aging treatment in step S4: Low-temperature aging is preferably carried out in the range of 78-82°C, with a holding time of 4 hours; High temperature aging is preferably carried out in the range of 158-162°C, with a holding time of 8 hours; The heating rate between the two stages is 0.5-1°C / min.

[0011] Technical effects and advantages of the present invention: The present invention successfully resolves the conflict between strength and elongation of aluminum alloy sheet through a synergistic process combining low-temperature solution treatment, pre-stretching optimization, and graded aging. This process significantly improves the elongation of aluminum alloy sheet while maintaining its strength. This process is particularly suitable for components with high requirements for material formability and strength, such as automotive body panels, door inner panels, anti-collision beams, and battery trays for new energy vehicles. It can significantly improve elongation while maintaining material strength, meeting the automotive industry's demand for highly formable aluminum alloy sheet. Although the present invention adds the pre-stretching and graded aging steps, it saves energy consumption by lowering the solid solution temperature, and the comprehensive production cost is comparable to that of the traditional process. DETAILED DESCRIPTION

[0012] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example

[0013] The present invention provides a heat treatment process for a high-elongation aluminum alloy plate. The specific heat treatment steps are as follows: S1. Component design and preparation: Its chemical composition by mass percentage includes: Si 0.7-1.3%, Mg 0.6-1.2%, optimizing the Mg / Si ratio to 1.0-1.2 to balance strength and formability, Cu 0.1-0.5%, preferably reduced to below 0.3% to avoid softening of the paint, Mn 0.1-0.5%, Fe ≤ 0.1% to inhibit the formation of coarse phases, and the balance is Al and unavoidable impurities, and the percentage of a single impurity is < 0.05%; S2. Low-temperature solution treatment: Preheat the equipment to 500-530°C (10-20°C lower than traditional treatment), strictly control the furnace temperature uniformity to keep it within a temperature range of ≤±3°C, place the plates horizontally on a dedicated rack with a spacing of ≥10cm to ensure uniform airflow, and precisely control the holding time after entering the furnace according to the plate thickness (60-90 minutes for plates ≤10mm thick, set the holding time according to the plate thickness, and extend the holding time by 30 minutes for every 12.7mm increase in thickness). Remove from the furnace and quench in water to obtain the alloy plate. The improved method can control the partial dissolution of the second phase to retain the fine-grained structure, significantly reducing the tendency of grain coarsening compared to traditional solution treatment, maintaining a fine and uniform grain structure, and improving the material toughness (elongation increased by 5-10%) and fatigue resistance. S3. Pre-stretching optimization: The alloy plate after solution quenching in step S2 is placed in a stretching machine with a suction cup within 2 hours. The clamps clamp the ends of the plate and apply a 2-3% tensile deformation to the plate for pre-stretching. The stretching speed is controlled within the range of 0.5-2 mm / s. Pre-stretching can eliminate quenching residual stress, reduce the effect of dislocation density on plasticity, and prevent deformation during subsequent processing and use. S4, Grading Time: S4.1: Allow the pre-stretched sheet in step S3 to stand at room temperature for 48 ± 2 hours; S4.2: Low-temperature aging is carried out first. The aging temperature is set to 80℃, and the furnace temperature uniformity is controlled within ±3℃. When the metal temperature reaches 77℃, the holding period begins and the holding period is 4 hours. S4.3: Then, high-temperature aging is performed. The aging temperature is set at 160°C, and the furnace temperature uniformity is controlled within ±3°C. When the metal temperature reaches 157°C, the holding time is calculated and it is kept at this temperature for 8 hours. After being taken out of the furnace, it is air-cooled. This can form a cuttable GP zone instead of an S′ phase, which takes into account strength, fatigue resistance, and corrosion resistance. Specifically in this embodiment, a 6XXX series aluminum alloy plate with a thickness of 2 mm was selected. Its chemical composition, as determined by spectral analysis, was as follows: Si 1.0%, Mg 0.9%, Cu 0.25%, Mn 0.3%, Fe 0.07%, and the remainder being Al and unavoidable impurities (each impurity content was less than 0.05%). Heat treatment process: Low-temperature solution treatment: Preheat the box-type resistance furnace to 515°C, and control the furnace temperature uniformity within ±2°C; Place the plates horizontally on a dedicated rack with a spacing of 12 cm between plates; Start timing after loading into the furnace and keep warm for 75 minutes; After the end of the heat preservation, quickly remove from the furnace and quench in 20°C water, with the transfer time less than 15 seconds; Pre-stretching treatment: After quenching, pre-stretch the plate when the temperature drops to 40°C; use a hydraulic stretching machine with a clamping length of 200mm; apply 2.5% tensile deformation at a speed of 1mm / s; maintain tension for 10 seconds and then unload; Staged aging treatment: The pre-stretched plate is placed at room temperature (25±2℃) for 48 hours; first stage aging: the plate is placed in an aging furnace at 80℃, and the timing starts when the metal temperature reaches 77℃, and the temperature is kept at this temperature for 4 hours; second stage aging: the temperature is increased to 160℃ at a rate of 0.8℃ / min, and the timing starts when the metal temperature reaches 157℃, and the temperature is kept at this temperature for 8 hours; after aging, the plate is taken out of the furnace and air-cooled to room temperature; Performance test results: Tensile strength: 275MPa Yield strength: 245MPa Elongation: 31% Fatigue life (2×10 6 Cycles): 185MPa Grain size: ASTM grade 12. Example

[0014] Specifically in this embodiment, a 6XXX series aluminum alloy plate with a thickness of 5 mm was selected. Its chemical composition, as determined by spectral analysis, was as follows: Si 0.8%, Mg 0.7%, Cu 0.2%, Mn 0.4%, Fe 0.05%, with the remainder being Al and unavoidable impurities (each impurity content being less than 0.05%). Heat treatment process: Low-temperature solution treatment: Preheat the box-type resistance furnace to 505°C, and control the furnace temperature uniformity within ±2°C; Place the plates horizontally on a dedicated rack with a spacing of 12 cm between plates; Start timing after loading into the furnace and keep warm for 90 minutes; After the end of the heat preservation, quickly remove from the furnace and quench in 20°C water, with the transfer time less than 15 seconds; Pre-stretching treatment: After quenching, pre-stretch the plate when the temperature drops to 40°C; use a hydraulic stretching machine with a clamping length of 200mm; apply 3% tensile deformation at a speed of 1mm / s; maintain tension for 10 seconds and then unload; Staged aging treatment: The pre-stretched plate is placed at room temperature (25±2℃) for 48 hours; first stage aging: the plate is placed in an aging furnace at 80℃, and the timing starts when the metal temperature reaches 77℃, and the temperature is kept at this temperature for 4 hours; second stage aging: the temperature is increased to 160℃ at a rate of 0.8℃ / min, and the timing starts when the metal temperature reaches 157℃, and the temperature is kept at this temperature for 8 hours; after aging, the plate is taken out of the furnace and air-cooled to room temperature; Performance test results: Tensile strength: 265MPa Yield strength: 230MPa Elongation: 29% Fatigue life (2×10 6 Cycles): 175MPa Grain size: ASTM grade 11. Example

[0015] Specifically in this embodiment, a 6XXX series aluminum alloy plate with a thickness of 10 mm is selected, and its chemical composition is as follows: Si 1.2%, Mg 1.1%, Cu 0.3%, Mn 0.2%, Fe 0.09%, and the rest is Al and unavoidable impurities (the content of each impurity is less than 0.05%); Heat treatment process: Low-temperature solution treatment: Preheat the box-type resistance furnace to 525°C, and control the furnace temperature uniformity within ±2°C; Place the plates horizontally on a dedicated rack with a spacing of 12 cm between plates; Start timing after loading into the furnace and keep warm for 120 minutes; Remove from the furnace quickly after the end of the holding period and quench in 20°C water, with the transfer time less than 15 seconds; Pre-stretching treatment: After quenching, pre-stretch the plate when the temperature drops to 40°C; use a hydraulic stretching machine with a clamping length of 200mm; apply 2% tensile deformation at a speed of 1mm / s; maintain tension for 10 seconds and then unload; Staged aging treatment: The pre-stretched plate is placed at room temperature (25±2℃) for 48 hours; first stage aging: the plate is placed in an aging furnace at 80℃, and the timing starts when the metal temperature reaches 77℃, and the temperature is kept at this temperature for 4 hours; second stage aging: the temperature is increased to 160℃ at a rate of 0.8℃ / min, and the timing starts when the metal temperature reaches 157℃, and the temperature is kept at this temperature for 8 hours; after aging, the plate is taken out of the furnace and air-cooled to room temperature; Performance test results: Tensile strength: 285MPa Yield strength: 255MPa Elongation: 27% Fatigue life (2×10 6 Cycles): 195MPa Grain size: ASTM grade 10.

[0016] Comparative Example 1 (Traditional Solution Temperature) The same aluminum alloy plate as in Example 1 was used, but the solution temperature was changed to 550° C., and the other process parameters were the same as in Example 1; Performance test results: Tensile strength: 290MPa Yield strength: 260MPa Elongation: 18% Grain size: ASTM grade 8 Comparative Example 2 (without pre-stretching) The same aluminum alloy plate as in Example 1 was used, the pre-stretching step was omitted, and other process parameters were the same as in Example 1; Performance test results: Tensile strength: 270MPa Yield strength: 240MPa Elongation: 23% Dimensional stability: poor (warpage reached 1.2 mm / m after one week) Comparative Example 3 (single-stage aging) The same aluminum alloy plate as in Example 1 was used, and the aging process was changed to single-stage aging: 175° C. for 8 hours, and other process parameters were the same as in Example 1; Performance test results: Tensile strength: 295MPa Yield strength: 270MPa Elongation: 20% Fatigue life: 150MPa; From the comparison between the above embodiment and the comparative example, it can be seen that: Although the low-temperature solution treatment (Examples 1-3) slightly reduced the strength (about 5-10 MPa) compared to the traditional high-temperature solution treatment (Comparative Example 1), the elongation was increased by more than 50%, which was due to the fine grain structure (ASTM 10-12 grade vs. 8 grade); the introduction of the pre-stretching process (Example 1 vs. Comparative Example 2) not only increased the elongation (31% vs. 23%), but also significantly improved the dimensional stability, which is crucial for the assembly accuracy of automotive panels; the graded aging process (Example 1) improved the elongation (31% vs. 20%) and fatigue performance (185 MPa vs. 150 MPa) while maintaining similar strength compared to the single-stage aging process (Comparative Example 3), showing better comprehensive performance; the plates of different thicknesses (Examples 1-3) can all achieve excellent performance of more than 27% elongation using the process of the present invention, indicating that the process has good adaptability; In summary, the performance of the alloy plates in Examples 1-3 and Comparative Examples 1-3 was tested, and the following data analysis was obtained: Table 1 Comparison of process parameters for plates of different thicknesses Thickness (mm) Solution temperature (℃) Holding time (min) Pre-stretching amount (%) Elongation (%) 2 515±3 75±2 2.5±0.1 31.2 5 505±3 90±2 3.0±0.1 29.5 10 525±3 120±3 2.0±0.1 27.8 15 520±3 150±3 2.2±0.1 26.3 Table 2 Performance data of the process of the present invention and the comparative process Process Type Tensile strength (MPa) Yield strength (MPa) Elongation (%) Grain size (ASTM) Fatigue limit (MPa) The present invention (Example 1) 275±5 245±4 31±0.8 12 185 Traditional solid solution (Comparative Example 1) 290±6 260±5 18±1.2 8 160 No pre-stretching (Comparative Example 2) 270±4 240±3 23±1.0 11 170 Single-stage aging (Comparative Example 3) 295±7 270±6 20±0.9 10 150 Table 3 Graded aging parameter optimization experimental data Time limit plan Tensile strength (MPa) Elongation (%) Precipitation phase type (TEM) 80℃ / 4h→160℃ / 8h 275 31 β″ mainly (nano-needle-shaped) 80℃ / 2h→160℃ / 8h 270 29 β″+a small amount of β′ 80℃ / 6h→160℃ / 8h 273 30 β″+GP region Direct 160℃ / 8h 295 20 β′+ coarse β phase Table 4 Industrial mass production statistics (1000 batches) Performance indicators average value Standard deviation Pass rate (%) Elongation (%) 30.5 ±0.8 99.2 Tensile strength (MPa) 273 ±5 98.7 Stamping cracking rate - - 0.8% Dimensional warpage (mm / m) 0.15 ±0.05 100 As can be seen from the table above, the present invention proposes a synergistic process of "low-temperature solution treatment + precise pre-stretching + graded aging". This organic combination of the three rather than a simple superposition produces unexpected technical effects. The low-temperature solution treatment controls the partial dissolution of the second phase, retaining the fine-grained structure, and enables the material elongation to reach over 28%, a 50-100% increase over traditional processes. This makes it particularly suitable for parts with high formability requirements, such as door inner panels (elongation ≥ 30%). They discovered that there is a maximum elongation point within the solution temperature range of 500-530°C; an optimal elongation value exists within the pre-stretching range of 2-3%, with either too little or too much pre-stretching reducing plasticity; a two-stage aging system (low temperature first, then high temperature) prioritizes the formation of the GP zone over the direct precipitation of the S′ phase, achieving an optimal balance between strength and plasticity; an optimized graded aging process forms the GP zone rather than the S′ phase, maintaining a tensile strength above 260 MPa, meeting the strength requirements of structural components such as anti-collision beams; By strictly controlling the connection time between each process (for example, the time from quenching to pre-stretching should not exceed 2 hours, and the time from pre-stretching to aging must be 48 hours), the controllable evolution of the microstructure is achieved. Low-temperature solid solution reduces the tendency of grain coarsening, pre-stretching optimization eliminates residual stress, and graded aging balances strength and plasticity, so that the material has both good fatigue resistance (fatigue life increased by more than 20%) and collision energy absorption performance (the collision energy absorption of the battery tray of new energy vehicles is increased by 15%).

[0017] Finally: 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 in the scope of protection of the present invention.

Claims

1. A heat treatment process for high elongation aluminum alloy sheet, characterized in that: The specific heat treatment steps are as follows: S1. Component design and preparation: Its chemical composition by mass percentage includes: Si 0.7-1.3%, Mg 0.6-1.2%, Cu0.1-0.5%, Mn 0.1-0.5%, Fe≤0.1%, the balance is Al and unavoidable impurities, and the percentage of a single impurity is less than 0.05%; S2. Low-temperature solution treatment: Preheat the equipment to 500-530℃, strictly control the furnace temperature uniformity to keep the temperature range ≤±3℃, place the plates horizontally on a special rack with a spacing of ≥10cm, and accurately control the holding time according to the thickness of the plates after entering the furnace. After leaving the furnace, water quench and obtain the alloy plates; S3, pre-stretching optimization: the alloy plate after solution quenching in step S2 is placed in a stretching machine with a suction cup within 2 hours, the clamps are clamped at both ends of the plate, and a tensile deformation of 2-3% is applied to the plate for pre-stretching treatment, and the stretching speed is controlled within the range of 0.5-2 mm / s; S4, Grading Time: S4.1: Allow the pre-stretched sheet in step S3 to stand at room temperature for 48 ± 2 hours; S4.2: Low-temperature aging is carried out first. The aging temperature is set to 80℃, and the furnace temperature uniformity is controlled within ±3℃. When the metal temperature reaches 77℃, the holding period begins and the holding period is 4 hours. S4.3: Then carry out high temperature aging, the aging temperature is set to 160℃, and the furnace temperature uniformity is controlled at ±3℃; when the metal temperature reaches 157℃, start calculating the holding time, hold it for 8 hours, and air cool after taking it out of the furnace.

2. The heat treatment process for a high elongation aluminum alloy sheet according to claim 1, characterized in that: The chemical composition of the aluminum alloy plate in step S1 includes, by mass percentage, Si 0.9-1.1%, Mg 0.8-1.0%, Cu 0.2-0.3%, Mn 0.2-0.4%, Fe≤0.08%, and the remainder is Al and unavoidable impurities.

3. The heat treatment process for a high elongation aluminum alloy sheet according to claim 1, characterized in that: The temperature of the low-temperature solution treatment in step S2 is 510-520° C., and the holding time of an 8 mm thick plate is set to 75-85 minutes; the atmosphere in the furnace is set to air, and the oxygen content in the air is controlled between 18-21%.

4. The heat treatment process for a high elongation aluminum alloy sheet according to claim 1, characterized in that: The pre-stretching optimization treatment in step S3 is performed when the plate temperature drops below 50° C., the stretching amount is preferably 2.5%, and the stretching direction is consistent with the rolling direction of the plate.

5. The heat treatment process for a high elongation aluminum alloy plate according to claim 1, characterized in that: In the grading and aging treatment in step S4: Low-temperature aging is preferably carried out in the range of 78-82°C, with a holding time of 4 hours; High temperature aging is preferably carried out in the range of 158-162°C, with a holding time of 8 hours; The heating rate between the two stages is 0.5-1°C / min.