Preparation method of 7-series aluminum alloy sheet with high strength, high toughness and hydrogen embrittlement resistance

Abstract

The present invention discloses a preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet, which is characterized in that the aluminum alloy raw materials are prepared according to the following alloy elements and mass percentages: Zn: 7.90 - 8.50%, Cu: 1.90 - 2.30%, Mg: 1.50 - 1.80%, Zr: 0.90% - 1.10%, Ti: 0.025 - 0.035%, Cr: 0 - 0.04%, and the balance is Al; then the aluminum alloy sheet is obtained through melting, casting, homogenization and hot rolling; and then the aluminum alloy sheet is subjected to double-stage solution quenching treatment and secondary or tertiary aging heat treatment to obtain a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet. The advantages are that this method obtains a high-quality alloy ingot by optimizing the content of alloy elements in the aluminum alloy raw materials and strictly controlling the content of impurity elements in the casting process, and at the same time increases the Zn / Mg ratio and decreases the Cu / Mg ratio in the alloy, so that the 7-series aluminum alloy sheet has excellent mechanical properties, and a relatively high content of Zr element is added to refine the grains, improve the hardenability of the product and enhance the hydrogen embrittlement resistance performance.

Description

Technical Field

[0001] The present invention relates to the technical field of manufacturing aluminum alloy plates, and particularly relates to a preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy plate. Background Art

[0002] Among the new high-strength Al-Zn-Mg-Cu aluminum alloys, 7-series aluminum alloys have the characteristics of low density, high strength, good toughness and corrosion resistance, and are one of the preferred materials for lightweight in the industry. Especially in the aviation field, 7-series aluminum alloys are excellent materials for manufacturing wing skins and fuselage panels. Potential hydrogen trapping sites in 7-series aluminum alloys include solute atoms, lattice interstices, dislocations, vacancies, precipitates, high-angle grain boundaries, second-phase particles and micropores, etc. After trapping atomic hydrogen, the tensile strength, yield strength and toughness of the aluminum alloy will decrease. At the same time, once hydrogen atoms invade the aluminum alloy, they will interact with microstructural defects, ultimately leading to a catastrophic deterioration of the mechanical properties of the aluminum alloy. For example, during the service of an aircraft, due to the presence of hydrogen atoms in the atmospheric environment, hydrogen atoms accumulate at the grain boundaries of the aluminum alloy plate, generating hydrogen pressure cracks, resulting in the embrittlement of the aluminum alloy of the wing, the fracture of the wing, and ultimately causing a catastrophic event. However, at present, the hydrogen embrittlement resistance of 7-series aluminum alloys is poor, and there is little relevant research, which seriously restricts the application of 7-series aluminum alloys in the aerospace field. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy plate. The prepared 7-series aluminum alloy plate not only has high strength and high toughness, but also has good hydrogen embrittlement resistance.

[0004] The technical solution adopted by the present invention to solve the above technical problem is as follows: A preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy plate includes the following specific steps:

[0005] A preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy plate includes the following specific steps:

[0006] (1), Prepare aluminum alloy raw materials according to the following alloy elements and mass percentages: Zn: 7.90 - 8.50%, Cu: 1.90 - 2.30%, Mg: 1.50 - 1.80%, Zr: 0.90% - 1.10%, Ti: 0.025 - 0.035%, Cr: 0 - 0.04%, and the balance is Al;

[0007] (2), Add the prepared aluminum alloy raw materials into a melting furnace, control the heating rate of the melting furnace to be 8 - 10 °C / min, keep it warm for 20 - 40 min after rising to 720 - 760 °C, and perform electromagnetic stirring after melting to obtain an aluminum alloy melt;

[0008] (3) Cast the aluminum alloy melt into an ingot, control the casting temperature at 670 - 690 °C, and the slag content of the ingot is less than 30 K / Kg;

[0009] (4) Conduct two-stage homogenization heat treatment on the ingot in a homogenization furnace, and immediately transfer it to a cooling chamber for air cooling after homogenization;

[0010] (5) Roll the ingot after homogenization heat treatment, control the starting rolling temperature at 360 - 430 °C, the final rolling temperature at 370 - 410 °C, and roll at least 7 passes. Among them: the average deformation of the 1st - 2nd passes is 9 - 12%, the average deformation of the 3rd - 5th passes is 17 - 20%, the average deformation of the remaining passes is 5 - 8%, the rolling speed is 1.5 ± 0.1 m / s, and control the total deformation at 80 - 90% to obtain an aluminum alloy sheet;

[0011] (6) Take a sample of the aluminum alloy sheet along the rolling direction and process it into a standard plate-shaped specimen;

[0012] (7) Conduct two-stage solution quenching treatment on the aluminum alloy sheet. After solution, quickly put the aluminum alloy sheet into water and cool it to room temperature;

[0013] (8) Then conduct secondary or tertiary aging heat treatment on the aluminum alloy sheet after the treatment in step (7) to obtain a high-strength, high-toughness, hydrogen embrittlement-resistant 7-series aluminum alloy sheet.

[0014] Further, in the step (1), the content of Zn is 4.40 - 4.70 times that of Mg, and the content of Cu is 1.20 - 1.50 times that of Mg.

[0015] Further, during the two-stage homogenization heat treatment in step (4), control the first-stage holding temperature at 465 - 468 °C, the heating rate at 35 - 40 °C / h, and the holding time at 10 - 18 h; the second-stage holding temperature at 475 - 480 °C, the heating rate at 3 - 5 °C / h, and the holding time at 20 - 25 h, and the air cooling time after homogenization is 3 - 6 h.

[0016] Further, in the two-stage solution quenching treatment in step (7), control the first-stage solution temperature at 470 - 475 °C for 30 min, and the second-stage solution temperature at 480 - 485 °C for 30 min.

[0017] Further, in step (7), the time interval from the end of solution of the aluminum alloy sheet to being put into water is less than 15 s to obtain a better supersaturated solid solution, which is beneficial to the more uniform distribution of the precipitated phases in the aluminum alloy sheet and reduces the activation energy of η' and η precipitated phases.

[0018] Further, in the step (8), during the secondary aging treatment, the holding temperature of the first-stage aging is controlled at 100 - 120°C and the holding time is 6 - 24 h, and the holding temperature of the second-stage aging is 140 - 160°C and the holding time is 12 - 20 h; during the tertiary aging treatment, the holding temperature of the first-stage aging is controlled at 100 - 120°C and the holding time is 6 - 24 h, the holding temperature of the second-stage aging is 140 - 170°C and the holding time is 1 - 2 h, and the holding temperature of the third-stage aging is 100 - 120°C and the holding time is 12 - 32 h.

[0019] Compared with the prior art, the advantages of the present invention are as follows:

[0020] (1) By optimizing the content of alloying elements in the aluminum alloy raw materials and strictly controlling the content of impurity elements during the casting process, high-quality alloy ingots are obtained. At the same time, the ratio of Zn / Mg in the alloy is increased and the ratio of Cu / Mg is reduced, so that the 7-series aluminum alloy sheet has excellent mechanical properties. In addition, a relatively high content of Zr element is added as a dispersoid, which can refine the grains, improve the hardenability of the product, and enhance the hydrogen embrittlement resistance.

[0021] (2) Through the double-stage solution treatment, the solute supersaturated solid solubility of the 7-series aluminum alloy sheet is increased. At the same time, the size and distribution of grain boundary precipitate phases are optimized, the coarse second-phase particles are reduced, and the sub-grains are refined, thereby improving the corrosion resistance of the 7-series aluminum alloy sheet.

[0022] (3) In the aging heat treatment, when the secondary aging heat treatment is adopted, the first-stage aging is controlled at a low temperature and the second-stage aging is at a medium temperature for a long time; when the tertiary aging heat treatment is adopted, the aging time of the second stage is reduced; this makes the grain boundary precipitate phases and the PFZ size of the 7-series aluminum alloy sheet moderate (about 5 - 10 nm), and there are more η phases in the grains, further improving the mechanical properties and hydrogen embrittlement resistance of the 7-series aluminum alloy sheet. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a comparison diagram of stress-strain curves of 7-series aluminum alloy sheets of Example 1, Example 2 and Comparative Example of the present invention;

[0024] Figure 2 It is a comparison diagram of stress-strain curves of 7-series aluminum alloy sheets of Example 1, Example 2 and Comparative Example of the present invention after the hydrogen charging test. DETAILED DESCRIPTION OF THE INVENTION

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and examples.

[0026] Example 1: A preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet, comprising the following specific steps:

[0027] (1). Prepare aluminum alloy raw materials according to the following alloying elements and mass percentages:

[0028]

[0029] In this aluminum alloy raw material, the content of Zn is 4.49 times that of Mg, and the content of Cu is 1.22 times that of Mg.

[0030] (2). Add the prepared aluminum alloy raw materials into a melting furnace, control the heating rate of the melting furnace at 8 °C / min, hold for 30 min after reaching 740 °C, and perform electromagnetic stirring after melting to obtain an aluminum alloy melt.

[0031] (3). Cast the aluminum alloy melt into an ingot, control the casting temperature at 680 °C, and the slag content of the ingot at 18 K / Kg.

[0032] (4). Perform two-stage homogenization heat treatment on the ingot in a homogenization furnace. Control the first-stage holding temperature at 465 °C, the heating rate at 35 °C / h, and the holding time at 12 h; the second-stage holding temperature at 475 °C, the heating rate at 5 °C / h, and the holding time at 20 h. Immediately transfer to a cooling chamber for air cooling after homogenization, and the air cooling time is 6 h.

[0033] (5). Roll the ingot after homogenization heat treatment. Control the starting rolling temperature at 386 °C, the final rolling temperature at 402 °C, and roll for 7 passes. Among them: the average deformation of the 1st - 2nd passes is 10%, the average deformation of the 3rd - 5th passes is 18%, the average deformation of the 6th - 7th passes is 6%, the rolling speed is 1.5 ± 0.1 m / s, control the total deformation at 86% to obtain an aluminum alloy sheet with a sheet thickness of 80.6 mm.

[0034] (6). Take samples of the aluminum alloy sheet along the rolling direction and process them into standard plate-shaped specimens.

[0035] (7). Perform two-stage solution quenching treatment on the aluminum alloy sheet. Control the first-stage solution temperature at 470 °C and the time at 30 min, the second-stage solution temperature at 482 °C and the time at 30 min; after solution treatment, remove the aluminum alloy sheet from the solution furnace and put it into water within 15 s (the shorter this time, the better), and then water-cool the aluminum alloy sheet to room temperature.

[0036] (8). Then perform secondary aging heat treatment on the aluminum alloy sheet after being treated in step (7). Control the first-stage aging holding temperature at 115 °C and the holding time at 6 h, the second-stage aging holding temperature at 150 °C and the holding time at 18 h to obtain a high-strength, high-toughness, hydrogen embrittlement-resistant 7-series aluminum alloy sheet.

[0037] Example 2 is different from Example 1 in step (8), and the other steps are the same. In this example, the aluminum alloy sheet is subjected to three-stage aging heat treatment, and the first-stage aging holding temperature is controlled at 115 °C and the holding time is 6 h, the second-stage aging holding temperature is 170 °C and the holding time is 1 h, and the third-stage aging holding temperature is 115 °C and the holding time is 22 h.

[0038] Comparative example: Taking 7075 aluminum alloy as the comparative example, its preparation method includes the following specific steps:

[0039] (1). Prepare the aluminum alloy raw materials according to the 7075 alloy elements and mass percentages:

[0040]

[0041] In this aluminum alloy raw material, the content of Zn is 2.23 times that of Mg, and the content of Cu is 1.0 times that of Mg;

[0042] (2). Add the prepared aluminum alloy raw materials into the melting furnace, control the heating rate of the melting furnace at 8 °C / min, hold for 30 min after reaching 740 °C, and perform electromagnetic stirring after melting to obtain the aluminum alloy melt;

[0043] (3). Cast the aluminum alloy melt into an ingot, control the casting temperature at 680 °C, and the slag content of the ingot is 18 K / Kg;

[0044] (4). Perform two-stage homogenization heat treatment on the ingot in the homogenization furnace, control the first-stage holding temperature at 465 °C, the heating rate at 35 °C / h, and the holding time at 12 h; the second-stage holding temperature is 475 °C, the heating rate is 5 °C / h, and the holding time is 20 h. After homogenization, immediately transfer it to the cooling chamber for air cooling, and the air cooling time is 6 h;

[0045] (5). Roll the ingot after homogenization heat treatment, control the starting rolling temperature at 386 °C, the final rolling temperature at 402 °C, and roll for 7 passes. Among them: the average deformation amount of the 1st - 2nd passes is 10%, the average deformation amount of the 3rd - 5th passes is 18%, the average deformation amount of the 6th - 7th passes is 6%, the rolling speed is 1.5 ± 0.1 m / s, control the total deformation amount at 86% to obtain the aluminum alloy sheet, and the sheet thickness is 80.1 mm;

[0046] (6). Take samples of the aluminum alloy sheet along the rolling direction and process them into standard plate-shaped specimens;

[0047] (7). Perform two-stage solution quenching treatment on the aluminum alloy sheet, control the first-stage solution temperature at 475 °C and the time at 30 min, and the second-stage solution temperature at 480 °C and the time at 30 min; after solution treatment, remove the aluminum alloy sheet from the solution furnace and quickly put it into water for water cooling to room temperature;

[0048] (8) Then, subject the aluminum alloy sheet processed in step (7) above to secondary aging heat treatment, controlling the first-stage aging holding temperature at 115 °C and the holding time at 6 h, and the second-stage aging holding temperature at 150 °C and the holding time at 18 h to obtain a 7075 aluminum alloy sheet.

[0049] Test the stress-strain curves of the 7xxx series aluminum alloy sheets prepared in Example 1, Example 2 and the comparative example. As Figure 1 shown, it can be seen from the figure that: the elongation of Example 1 is the highest, followed by the comparative example, and the lowest is Example 2; the tensile strength of Example 2 is the highest, but it is very close to that of Example 1, and the tensile strength of the comparative example is the lowest, about 50 MPa lower than that of Example 1. The overall comprehensive mechanical properties of Example 1 are the best. In summary, it can be concluded that Example 1 and the comparative example adopt secondary aging heat treatment, which improves the elongation of the 7xxx series aluminum alloy but slightly reduces the tensile strength; while Example 2 adopts tertiary aging heat treatment, which improves the tensile strength of the 7xxx series aluminum alloy but significantly reduces the elongation, indicating that different aging heat treatments have a great impact on the elongation of the 7xxx series aluminum alloy.

[0050] Conduct a hydrogen charging test on the 7xxx series aluminum alloy sheets prepared in Example 1, Example 2 and the comparative example. Specifically: Polish the gauge section of the 7xxx series aluminum alloy sheet specimen to mirror finish to reduce the influence of micro-damage on the specimen surface on the test. Then, use a hydrogen charging solution environment of 70% CH3OH, 24.4% deionized water, 5.6% H2SO4, and 0.35 ml / L CS2 aqueous solution, and introduce atomic hydrogen into the 7xxx series aluminum alloy sheet specimen under a constant current density (q = 10 mA / cm2, T = 120 h). It should be noted that the hydrogen charging surface of the specimen is exposed to the solution, and the rest of the specimen is covered with waterproof glue. Immediately after the hydrogen charging test, conduct a tensile test on the above 7xxx series aluminum alloy sheet specimens at a strain rate of 2 mm / s. The results are as Figure 2 shown. After hydrogen charging of the 7xxx series aluminum alloy, the tensile strengths of the 7xxx series aluminum alloys in Example 1 and Example 2 are basically the same, while the tensile strength of the 7xxx series aluminum alloy in the comparative example is significantly lower than that of Example 1 and Example 2, and the strength difference is about 80 MPa, which is 13% lower than the tensile strengths of Example 1 and Example 2.

[0051] Comparing the 7xxx series aluminum alloys in Example 1, Example 2 and the comparative example before and after hydrogen charging, the elongation of the 7xxx series aluminum alloy in Example 1 basically remains the same, and the tensile strength is slightly reduced by about 10 Mpa; the elongation of the 7xxx series aluminum alloy in Example 2 decreases significantly, with the elongation reduced by about 3%, and the tensile strength reduced by 40 MPa; the elongation of the 7xxx series aluminum alloy in the comparative example is reduced by about 2%, and the tensile strength is significantly reduced, by about 60 MPa; it can be seen that: the 7xxx series aluminum alloy in Example 1 has the best hydrogen embrittlement resistance effect.

[0052] In summary, the raw material ratio of aluminum alloy and the aging heat treatment in the preparation process have a great influence on the hydrogen embrittlement resistance of 7xxx series aluminum alloys.

[0053] The protection scope of the present invention includes but is not limited to the above embodiments. The protection scope is subject to the claims, and any substitutions, deformations, and improvements that are easily conceivable by those skilled in the art for this technology fall within the protection scope of the present invention.

Claims

1. A preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet, characterized in that It includes the following specific steps: (1) Prepare aluminum alloy raw materials according to the following alloy elements and mass percentages: Zn: 7.90 - 8.50%, Cu: 1.90 - 2.30%, Mg: 1.50 - 1.80%, Zr: 0.90% - 1.10%, Ti: 0.025 - 0.035%, Cr: 0 - 0.04%, and the balance is Al; and the content of Zn is 4.40 - 4.70 times that of Mg, and the content of Cu is 1.20 - 1.50 times that of Mg; (2) Add the prepared aluminum alloy raw materials into a melting furnace, control the heating rate of the melting furnace to be 8 - 10 °C / min, heat up to 720 - 760 °C and then hold for 20 - 40 min, and perform electromagnetic stirring after melting to obtain an aluminum alloy melt; (3) Cast the aluminum alloy melt into an ingot, control the casting temperature to be 670 - 690 °C, and the slag content of the ingot is less than 30 K / Kg; (4) Perform two-stage homogenization heat treatment on the ingot in a homogenization furnace, and immediately transfer it to a cooling chamber for air cooling after homogenization; (5) Roll the ingot after homogenization heat treatment, control the starting rolling temperature to be 360 - 430 °C, the final rolling temperature to be 370 - 410 °C, and roll at least 7 passes. Among them: the average deformation of the 1st - 2nd passes is 9 - 12%, the average deformation of the 3rd - 5th passes is 17 - 20%, the average deformation of the remaining passes is 5 - 8%, the rolling speed is 1.5 ± 0.1 m / s, and control the total deformation to be 80 - 90% to obtain an aluminum alloy sheet; (6) Take samples of the aluminum alloy sheet along the rolling direction and process them into standard plate-shaped specimens; (7) Perform two-stage solution quenching treatment on the aluminum alloy sheet, and quickly put the aluminum alloy sheet into water and cool it to room temperature after solution; (8) Then perform secondary or tertiary aging heat treatment on the aluminum alloy sheet processed in step (7) above to obtain a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet.

2. The preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet according to claim 1, characterized in that: During the two-stage homogenization heat treatment in step (4), control the first-stage holding temperature to be 465 - 468 °C, the heating rate to be 35 - 40 °C / h, and the holding time to be 10 - 18 h; the second-stage holding temperature to be 475 - 480 °C, the heating rate to be 3 - 5 °C / h, and the holding time to be 20 - 25 h, and the air cooling time after homogenization is 3 - 6 h.

3. The preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet according to claim 1, characterized in that: In the two-stage solution quenching treatment in step (7), control the first-stage solution temperature to be 470 - 475 °C and the time to be 30 min, and the second-stage solution temperature to be 480 - 485 °C and the time to be 30 min.

4. The preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet according to claim 1, wherein: In step (7), the time interval from when the aluminum alloy sheet is removed from the solution furnace to when it is put into water is less than 15 s.

5. The preparation method of a high-strength, high-toughness and hydrogen embrittlement-resistant 7-series aluminum alloy sheet according to claim 1, characterized in that: In the step (8), during the secondary aging treatment, the holding temperature of the first-stage aging is controlled to be 100 - 120 °C and the holding time is 6 - 24 h, and the holding temperature of the second-stage aging is 140 - 160 °C and the holding time is 12 - 20 h; during the tertiary aging treatment, the holding temperature of the first-stage aging is controlled to be 100 - 120 °C and the holding time is 6 - 24 h, the holding temperature of the second-stage aging is 140 - 170 °C and the holding time is 1 - 2 h, and the holding temperature of the third-stage aging is 100 - 120 °C and the holding time is 12 - 32 h.

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