Heat treatment process capable of synergistically improving strength and plasticity of 6061 aluminum alloy rolled plate

Abstract

The invention discloses a heat treatment process capable of synergistically improving the strength and plasticity of a 6061 aluminum alloy rolled plate. The heat treatment process comprises the following steps: 1) heating a 6061 cast ingot to 545-555 DEG C, preserving heat for 4-10 hours, cooling to room temperature, heating to 450-490 DEG C, preserving heat for 20-40 minutes, carrying out primary hot rolling, then preserving heat for 5-15 minutes at 450-490 DEG C, and carrying out secondary hot rolling; cooling the sample to below 80 DEG C, and carrying out two-pass cold rolling; (2) the temperature of the final rolled plate is increased to 200-270 DEG C, heat preservation is conducted for 6-18 h, low-temperature pre-recovery is conducted, then the temperature is increased to 530-545 DEG C, heat preservation is conducted for 0.5-2 h, and solution treatment is conducted; and 3) performing water-cooling quenching on the sample subjected to solution treatment, and then performing aging treatment. Through a series of heat treatment modes of combining homogenizing annealing with two-stage solution treatment coupling, the problem that the mechanical property of the 6061 aluminum alloy plate is not high after solution treatment at present can be solved, meanwhile, the homogenizing annealing process does not need to be specially regulated and controlled, and the homogenizing annealing process is simplified.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy rolling, and in particular to a heat treatment process capable of synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plates. Background Art

[0002] Aluminum alloys have been widely used in modern transportation vehicles, mechanical equipment and structural parts due to their excellent specific strength, corrosion resistance, welding performance and other properties. Among them, Al-Mg-Si aluminum alloys (such as 6061 and other grades) with medium and high strength and good welding performance are widely used in the manufacture of rail transit bodies, automobiles, ships and low-temperature pressure vessels and other structural parts. This type of aluminum alloy material needs to be produced through a series of complex processing steps such as smelting, casting, deformation, and heat treatment to ensure that its various performance requirements are met. Rolling processing, as a deformation processing technology used in large-scale industrial applications, can effectively eliminate defects in cast aluminum alloys and improve the performance of aluminum alloys. Therefore, an economical and effective method is needed to simultaneously improve the performance of the material.

[0003] For age-hardened aluminum alloys, methods for simultaneously improving both strength and plasticity have been disclosed in the prior art. Chinese patent application CN119980093 A discloses a method for preparing a high-strength and high-plasticity 7075 alloy. The process includes two-stage homogenization annealing, rolling, two-stage solution treatment, and two-stage or three-stage aging. The resulting 7075 aluminum alloy sheet exhibits both high strength and plasticity.

[0004] Chinese patent application CN103334069 A discloses a heat treatment method for improving the performance of 7085 aluminum alloy, which includes pretreatment, pre-recovery annealing, solution treatment, and aging. The pre-recovery annealing is a step-by-step annealing process with rising temperatures. After pre-recovery annealing, the alloy's strength increases by 50 to 100 MPa, the grain size decreases from 100 microns to micron-level, the proportion of low-angle grain boundaries increases by 2 to 3 times, and resistance to intergranular and exfoliation corrosion is significantly improved.

[0005] Chinese patent CN 105603340 B discloses a processing technology that can improve the tensile and fatigue properties of 2xxx series alloy plates. The technology includes homogenization treatment, rolling, recovery pre-annealing, and solution quenching. Among them, the recovery pre-annealing can effectively control the average equivalent diameter and grain aspect ratio of the plate, so that the tensile mechanical properties and fatigue crack growth rate of the plate meet the requirements of the AMS 4296 aviation standard.

[0006] The aforementioned methods for improving the strength and ductility of aluminum alloys, as disclosed in patent application CN119980093A, are relatively complex, increasing the difficulty of heat treatment and reducing production efficiency. While the recovery pre-annealing treatments disclosed in patent applications CN103334069 A and CN 105603340B can improve strength, their effects on ductility are unclear or insignificant.

[0007] In summary, two-stage solution treatment (pre-recovery annealing) can improve the strength of 7xxx series aluminum alloys by inhibiting recrystallization or grain growth, but it often fails to simultaneously improve plasticity. However, this has not been reported in 6061 alloy.

[0008] The existing production process for 6061 aluminum alloy rolled plate typically involves casting, homogenization annealing, rolling, solutionizing, and aging. To increase the number density of the dispersed phase, thereby suppressing grain growth during the solutionizing process and improving overall mechanical properties, a slow heating rate or multi-stage homogenization process is often employed during the homogenization annealing process. For example, Chinese patent application CN 118207488 A discloses a graded homogenization heat treatment method for improving the mechanical properties of 6XXX series aluminum alloys containing Mn and Cr. This method divides the homogenization annealing process into three heating stages, making it relatively cumbersome and impacting production efficiency.

[0009] For solution treatment, a single-stage heating process is currently widely used. However, this often results in low mechanical properties after aging, failing to fully tap the hardening potential of 6061 aluminum alloy. Chinese patent application CN101549454A discloses a production process for aluminum alloy sheet, which involves solution treatment at 520-530°C for 3 hours, followed by stretching and aging at 165°C for 10 hours. However, this method does not guarantee optimal mechanical properties.

[0010] Therefore, there are still two technical problems that need to be solved in the current 6061 aluminum alloy plate rolling production process: (1) Solving the problem of insufficient comprehensive mechanical properties of 6061 aluminum alloy rolled plates. (2) Solving the problem of complex heat treatment process caused by achieving synergistic improvement of strength and plasticity. Summary of the Invention

[0011] The present invention aims to provide a heat treatment process that can synergistically enhance the strength and ductility of 6061 aluminum alloy rolled sheet. This process, a coupled series of heat treatments combining homogenization annealing and two-stage solution treatment, addresses the current issue of low mechanical properties of 6061 aluminum alloy sheet after solution treatment. Furthermore, this process eliminates the need for specialized homogenization annealing control, simplifying the homogenization annealing process.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0013] A heat treatment process for synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plate comprises the following steps:

[0014] 1) Homogenization heat treatment:

[0015] 1-1) Heating the 6061 ingot after semi-continuous casting to 545-555°C at a heating rate of 2-10°C / min, holding for 4-10 hours, and then cooling to room temperature;

[0016] 1-2) heating the sample to 450-490°C, holding the temperature for 20-40 minutes, and performing the first hot rolling, with a reduction of 30%-50% compared to the initial sample; then holding the temperature at 450-490°C for 5-15 minutes, and performing the second hot rolling, with a reduction of 30%-50% compared to the first hot rolling;

[0017] 1-3) The sample is cooled to below 80°C and cold rolled twice, with the first cold rolling reducing the plate by 25%-40% compared to the second hot rolling, and the second cold rolling reducing the plate by 40%-60% compared to the first cold rolling, to obtain a final rolled plate. The final rolled plate has a reduction of 80%-90% compared to the original sample.

[0018] 2) Solution treatment

[0019] In order to achieve a synergistic improvement in the strength and plasticity of the rolled plate, a low-temperature pre-recovery is required before the temperature reaches the solution temperature. The temperature of the final rolled plate is raised to 200-270°C and kept at this temperature for 6-18 hours for low-temperature pre-recovery. The temperature is then raised to 530-545°C at a rate of 2-10°C / min and kept at this temperature for 0.5-2 hours for solution treatment.

[0020] 3) Aging treatment

[0021] The sample after solution treatment is water-quenched and then transferred to an aging furnace for aging treatment within 5 to 6 minutes. The aging treatment temperature is 170°C-185°C and the holding time is 4 to 12 hours.

[0022] Furthermore, the composition of the 6061 ingot after semi-continuous casting is: Mg: 0.8-1.2%, Si: 0.4%-0.8%, Cu: 0.1%-0.4%, Zn: 0%-0.25, Mn: 0.08%-0.15, Ti: 0-0.15, Cr: 0.08-0.35, Fe: 0%-0.7%.

[0023] The present invention achieves a synergistic improvement in the strength and ductility of 6061 aluminum alloy by coupling homogenization annealing with a recovery pre-annealing process in a relatively simple process. Compared with the existing technology, the present invention has the following advantages:

[0024] 1. In order to ensure the required matching content of Mn and Cr in the dispersed phase, the present invention limits the content of Mn and Cr in the 6061 aluminum alloy composition to no less than 0.08wt%.

[0025] 2. The heat treatment process route of the present invention has low requirements for the previous homogenization annealing, and no special adjustment of the homogenization annealing is required. The heating rate can be higher to improve the efficiency of the homogenization annealing. The material is then deformed and rolled, and the rolled plate is subjected to a solution treatment including low-temperature pre-recovery, which is coupled with the previous homogenization heat treatment to achieve a simultaneous improvement in the strength and plasticity of the material.

[0026] 3. The present invention does not require multi-stage homogenization, has low uniformity requirements, and is simple to operate. Traditional multi-stage homogenization not only does not produce good results, but can even have negative effects. Furthermore, the present invention does not require a multi-stage aging process, which simplifies the aging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 1 is a schematic diagram of the process flow of Example 1 of the present invention.

[0028] Figure 2 Characterization of dispersed phases during homogenization annealing at 550℃ for 8h at 3℃ / min. (a) Low-rate dispersed phase distribution; (b) High-rate dispersed phase distribution near grain boundaries; (c) High-rate dispersed phase distribution near grain interiors.

[0029] Figure 3 Schematic diagram of the process flow of Comparative Example 1.

[0030] Figure 4 Schematic diagram of the process flow of Comparative Example 2.

[0031] Figure 5 Characterization of dispersed phases during a homogenization annealing process at 3°C / min (250°C / 4h + 400°C / 4h + 550°C / 8h). (a) Low-rate dispersed phase distribution; (b) High-rate dispersed phase distribution near grain boundaries; (c) High-rate dispersed phase distribution near grain interiors.

[0032] Figure 6 Schematic diagram of the process flow of Comparative Example 3.

[0033] Figure 7 Figure 1 shows the grain morphology, recrystallization, and precipitation phase characterization of Example 1 of the present invention. (a) Grain morphology diagram; (b) Grain size statistics diagram; (c) Grain recrystallization diagram; (d) Characterization of aging-hardened precipitation phases.

[0034] Figure 8Grain morphology, recrystallization, and precipitation characterization of Comparative Example 1. (a) Grain morphology diagram; (b) Grain size statistics diagram; (c) Grain recrystallization diagram; (d) Characterization of aging-hardened precipitation phases.

[0035] Figure 9 Grain morphology, recrystallization, and precipitation characterization of Comparative Example 2. (a) Grain morphology diagram; (b) Grain size statistics diagram; (c) Grain recrystallization diagram; (d) Characterization of aging-hardened precipitation phases.

[0036] Figure 10 Grain morphology, recrystallization, and precipitation characterization of Comparative Example 3. (a) Grain morphology diagram; (b) Grain size statistics diagram; (c) Grain recrystallization diagram; (d) Characterization of aging-hardened precipitation phases. DETAILED DESCRIPTION

[0037] Example 1

[0038] This example uses 6061 aluminum alloy as the research object. The alloy is prepared according to the following mass percentages: Al-0.88Mg-0.71Si-0.28Cu-0.31Fe-0.1Mn-0.16Cr. The alloy is produced by semi-continuous casting. The process flow is as follows: Figure 1 shown.

[0039] 1) Homogenization heat treatment:

[0040] 1-1) A sample of 100×20×8 mm was taken from the ingot and subjected to homogenization heat treatment. The temperature was raised to 550°C at a heating rate of 3°C / min, kept at this temperature for 8 h, and then water quenched. The process parameters are shown in Table 1 (H1). The dispersed phase characteristics are as follows: Figure 2 As shown;

[0041] 1-2) The sample was heated to 480°C in a muffle furnace and kept at this temperature for 30 minutes, and then hot rolled for the first time, with the thickness of the press being 3 mm. The sample was then placed in the furnace and kept at 480°C for 5 minutes, and then hot rolled for the second time, with the thickness of the press being 2 mm.

[0042] 1-3) After cooling the sample to room temperature, cold rolling was performed twice, with each cold rolling having a thickness of 1 mm, and the final thickness of the sample was 1 mm.

[0043] 2) Solution treatment

[0044] In order to achieve a synergistic improvement in the strength and plasticity of the rolled plate, a low-temperature pre-recovery is required before the temperature reaches the solution temperature. The sample temperature is raised to 200-270°C and kept at this temperature for 6-18 hours for low-temperature pre-recovery. The sample is then heated to 530-545°C at a rate of 2-10°C / min and kept at this temperature for 0.5-2 hours for solution treatment.

[0045] The rolled plate was subjected to solution treatment. The solution heat treatment process is shown in Table 2. The temperature of the sample was raised to 250 ° C and kept at this temperature for 12 hours for low temperature pre-recovery. Then the temperature was raised to 535 ° C at a rate of 10 ° C / min and kept at this temperature for 1 hour for solution treatment. Then water quenching was performed. The recrystallization and grain morphology after solution treatment are shown in Table 2. Figure 7 shown.

[0046] 3) The sample after solid solution was subjected to aging treatment at 175℃ / 8h. The precipitated phase was as follows: Figure 7 (d) The final mechanical properties of the plate are shown in Table 3.

[0047] Comparative Example 1

[0048] The 6061 aluminum alloy was used as the research object. The alloy was prepared according to the following mass percentage: Al-0.88Mg-0.71Si-0.28Cu-0.31Fe-0.1Mn-0.16Cr. The alloy was produced by semi-continuous casting. The process flow is as follows: Figure 3 As shown. A sample of 100×20×8mm was taken from the ingot and subjected to homogenization heat treatment. The temperature was raised to 550℃ at a heating rate of 3℃ / min, kept at this temperature for 8h and then water quenched. The process parameters are shown in Table 1 (H1). Dispersed phase characterization is shown in Figure 2 As shown. The sample was then heated to 480°C in a muffle furnace and kept warm for 30 minutes before the first hot rolling was carried out, with a pressing thickness of 3mm. The sample was then placed in a furnace and kept warm at 480°C for 5 minutes, with a pressing thickness of 2mm. Finally, it was cooled to room temperature and cold rolled twice, with each pressing thickness being 1mm. The final thickness of the sample was 1mm. Subsequently, the rolled plate was solution treated. The solution heat treatment process is shown in Table 2 (Comparative Example 1). The temperature was raised to 535°C at a rate of 3°C / min and kept warm for 1h, and then water quenched. The recrystallization and grain morphology after solution treatment are shown in Table 2 (Comparative Example 1). Figure 8 The sample after solution treatment was aged at 175℃ / 8h. The precipitation phase is shown in Figure 8 (d) The final mechanical properties of the plate are shown in Table 3.

[0049] Comparative Example 2

[0050] The 6061 aluminum alloy was used as the research object. The alloy was prepared according to the following mass percentage: Al-0.88Mg-0.71Si-0.28Cu-0.31Fe-0.1Mn-0.16Cr. The alloy was produced by semi-continuous casting. The process flow is as follows: Figure 4As shown. A sample of 100×20×8mm was taken from the ingot and subjected to homogenization heat treatment. The temperature was raised to 250℃ at a rate of 3℃ / min and kept for 4h, then raised to 400℃ and kept for 4h, and then continued to rise to 550℃ and kept for 8h. The process parameters are shown in Table 1 (H3). Dispersed phase characterization is shown in Figure 5 As shown. The sample was then heated to 480°C in a muffle furnace and kept warm for 30 minutes before the first hot rolling was carried out, with a pressing thickness of 3mm. The sample was then placed in a furnace and kept warm at 480°C for 5 minutes, with a pressing thickness of 2mm. Finally, it was cooled to room temperature and cold rolled twice, with each pressing thickness being 1mm, and the final thickness of the sample was 1mm. Subsequently, the rolled plate was solution treated. The solution heat treatment process is shown in Table 2 (Comparative Example 2). The temperature of the sample was raised to 250°C and kept warm for 12 hours for low-temperature pre-recovery. The sample was then heated to 535°C at a rate of 10°C / min and kept warm for 1 hour for solution treatment. The recrystallization and grain morphology after solution treatment are shown in Table 2 (Comparative Example 2). Figure 9 The sample after solution treatment was aged at 175℃ / 8h. The precipitation phase is shown in Figure 9 (d) The final mechanical properties of the plate are shown in Table 3.

[0051] Comparative Example 3

[0052] The 6061 aluminum alloy was used as the research object. The alloy was prepared according to the following mass percentage: Al-0.88Mg-0.71Si-0.28Cu-0.31Fe-0.1Mn-0.16Cr. The alloy was produced by semi-continuous casting. The process flow is as follows: Figure 6 As shown. A sample of 100×20×8mm was taken from the ingot and subjected to homogenization heat treatment. The temperature was raised to 250℃ at a rate of 3℃ / min and kept for 4h, then raised to 400℃ and kept for 4h, and then continued to rise to 550℃ and kept for 8h. The process parameters are shown in Table 1 (H3). Dispersed phase characterization is shown in Figure 5 As shown. The sample was then heated to 480°C in a muffle furnace and kept warm for 30 minutes before the first hot rolling was carried out, with a pressing thickness of 3mm. The sample was then placed in a furnace and kept warm at 480°C for 5 minutes, with a pressing thickness of 2mm. Finally, it was cooled to room temperature and cold rolled twice, with each pressing thickness being 1mm. The final thickness of the sample was 1mm. Subsequently, the rolled plate was solution treated. The solution heat treatment process is shown in Table 2 (Comparative Example 3). The temperature was raised to 535°C at a rate of 3°C / min and kept warm for 1h, and then water quenched. The recrystallization and grain morphology after solution treatment are shown in Table 2 (Comparative Example 3). Figure 10 The sample after solution treatment was aged at 175℃ / 8h. The precipitation phase is shown in Figure 10 (d) The final mechanical properties of the plate are shown in Table 3.

[0053] Table 1 Homogenization heat treatment process scheme

[0054]

[0055] Table 2 Solution heat treatment process plan

[0056]

[0057] Table 3 Mechanical properties performance test

[0058]

[0059] Compared with the comparative example, the product strength of the embodiment of the present invention is significantly improved, as shown in Table 3. The reason for the improvement of its mechanical properties is significantly different from that of the pre-recovery process of 7xxx aluminum alloy. The pre-recovery of 7xxx aluminum alloy mainly improves the mechanical properties by inhibiting recrystallization and grain growth. In the present invention, the grain size after pre-recovery is significantly coarsened, as shown in Table 3. Figure 7 As shown. Compared with the comparative example, Example 1 has the highest degree of recrystallization and the largest grain size, but its comprehensive mechanical properties are the highest. This is because less dispersed phases are precipitated in the single-stage homogenization heat treatment stage, and after the subsequent two-stage solid solution at a low temperature of 250 ° C / 12h for pre-recovery, a large number of dislocation structures are eliminated, thereby inhibiting the precipitation of dispersed phases during the solid solution treatment, resulting in a weakening of the ability to inhibit grain growth and recrystallization. At the same time, after single-stage homogenization annealing + two-stage solid solution treatment, although less dispersed phases are precipitated, which is conducive to recrystallization, a large amount of Si elements required for aging are retained in the matrix, thereby precipitating a high number density and relatively fine precipitates in the aging stage, which becomes a key factor in improving strength and plasticity. Although multi-stage homogenization and two-stage solid solution can refine the grains, as shown in FIG. Figure 7-10 As shown in the figure, the contribution of grain refinement strengthening is not enough to offset the negative impact of coarsening of precipitate phase and reduction of number density, which is not conducive to the improvement of comprehensive mechanical properties.

Claims

1. A heat treatment process that can synergistically improve the strength and plasticity of 6061 aluminum alloy rolled plate, characterized in that: The following steps are involved: 1) Homogenization heat treatment: 1-1) Heat the 6061 ingot after semi-continuous casting to 545-555°C, keep it at this temperature for 4-10 hours and then cool it to room temperature; 1-2) heating the sample to 450-490°C, holding the temperature for 20-40 minutes, and performing the first hot rolling, with a reduction of 30%-50% compared to the initial sample; then holding the temperature at 450-490°C for 5-15 minutes, and performing the second hot rolling, with a reduction of 30%-50% compared to the first hot rolling; 1-3) Cool the sample to below 80° C. and perform two cold rolling operations, wherein the first cold rolling operation reduces the plate by 25%-40% compared to the second hot rolling operation, and the second cold rolling operation reduces the plate by 40%-60% compared to the first cold rolling operation, to obtain a final rolled plate. 2) Solution treatment The temperature of the final rolled plate is raised to 200-270°C and kept at this temperature for 6-18 hours for low temperature pre-recovery, and then raised to 530-545°C and kept at this temperature for 0.5-2 hours for solution treatment; 3) Aging treatment The sample after solution treatment is water-cooled and quenched and then transferred to an aging furnace for aging treatment. The aging treatment temperature is 170℃-185℃ and the holding time is 4-12h.

2. The heat treatment process for synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plate according to claim 1, characterized in that: The composition of the 6061 ingot after the semi-continuous casting is: Mg: 0.8-%1.2%, Si: 0.4%-0.8%, Cu: 0.1%-0.4%, Zn: 0%-0.25, Mn: 0.08%-0.15, Ti: 0-0.15, Cr: 0.08-0.35, Fe: 0%-0.7%.

3. The heat treatment process for synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plate according to claim 1, characterized in that: The heating rate of step 1-1) is 2°C / min-10°C / min.

4. The heat treatment process for synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plate according to claim 1, characterized in that: The final rolled plate obtained in step 1) has a downward pressure of 80%-90% compared to the initial sample.

5. The heat treatment process for synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plate according to claim 1, characterized in that: The heating rate of step 2) is 2°C / min-10°C / min.

6. The heat treatment process for synergistically improving the strength and plasticity of 6061 aluminum alloy rolled plate according to claim 1, characterized in that: Step 2) After solution treatment, the sample is water-quenched and then transferred to an aging furnace for aging treatment within 5 to 6 minutes.

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