A method for low-temperature heat treatment of age-strengthened aluminum alloys

Abstract

This invention relates to the field of metal material processing technology, and more particularly to a low-temperature heat treatment method for high-performance age-hardening aluminum alloys. Specifically, the method involves sequentially performing solution treatment, quenching, cryogenic treatment, and low-temperature aging treatment on the age-hardening aluminum alloy. The combination of cryogenic treatment and low-temperature aging treatment on the solution-quenched aluminum alloy induces dislocation multiplication and cold compressive stress, resulting in a microstructure with fine intragranular precipitation and discontinuous grain boundary precipitation, thereby improving the tensile strength, toughness, and corrosion resistance of the age-hardening aluminum alloy.

Description

Technical Field

[0001] This invention relates to the field of metal material processing technology, and in particular to a low-temperature heat treatment method for high-performance age-strengthened aluminum alloys. Background Technology

[0002] 2-series, 6-series, and 7-series age-hardened aluminum alloys are the preferred materials for lightweight applications in aerospace, transportation, and defense industries due to their excellent properties such as low density, high specific strength and stiffness, good impact resistance, corrosion resistance, easy surface coloring, and easy recyclability. To further improve the properties of aluminum alloys, aging treatment processes such as T6, T7X, T87, T6I4, and T6I6 are commonly used in this field. The T6I4 intermittent aging process disclosed in CN1507501A can produce aluminum alloys with higher strength and toughness than the T6 state, but this method has an excessively long low-temperature aging time, making it difficult to apply on a large scale in industry. CN115396916A discloses a pre-aging-deep cryogenic-re-aging process to improve the strength and toughness of aluminum alloys, but this process is relatively complex. Therefore, developing a simple heat treatment process for aluminum alloys that can improve their properties and is suitable for industrial applications is of great significance. Summary of the Invention

[0003] The purpose of this invention is to provide a high-performance low-temperature heat treatment method for age-strengthened aluminum alloys, which improves the tensile strength, elongation, and corrosion resistance of aluminum alloys, and simplifies the treatment method.

[0004] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0005] A method for low-temperature heat treatment of high-performance age-hardening aluminum alloys includes the following steps:

[0006] The aluminum alloy is subjected to solution treatment, quenching treatment, cryogenic treatment and sub-low temperature aging treatment in sequence.

[0007] The cryogenic treatment is performed at a temperature of -196 to -70°C for 0.5 to 5 hours; the aging treatment is performed at a temperature of 20 to 80°C for 120 to 480 hours.

[0008] Optionally, the aluminum alloy includes 2XXX series aluminum alloys, 6XXX series aluminum alloys, or 7XXX series aluminum alloys.

[0009] Optionally, the solution treatment is performed at a temperature of 450–570°C for a time of 0.5–5 hours.

[0010] Optionally, the solution treatment is performed at a temperature of 470–550°C for a time of 1–4 hours.

[0011] Optionally, the quenching treatment is water quenching, and the water temperature for water quenching is 5 to 30°C.

[0012] Optionally, the cryogenic treatment is performed at a temperature of -196 to -100°C for a duration of 1 to 4.5 hours.

[0013] Optionally, the temperature of the sub-low temperature aging treatment is 50-75°C, and the time is 150-300 hours.

[0014] This invention provides a high-performance low-temperature heat treatment method for age-hardened aluminum alloys. The method sequentially performs solution quenching, cryogenic treatment, and secondary low-temperature aging treatment on the aluminum alloy. Solution quenching yields a supersaturated solid solution, while cryogenic treatment induces dislocation multiplication. Compared to conventional aging temperatures, secondary low-temperature aging increases the matrix supersaturation and nucleation sites, resulting in fine intragranular precipitation, while reducing solute atom diffusion to grain boundaries and subgrain boundaries. Furthermore, the release of cold compressive stress generated by cryogenic treatment increases the spacing between the η phases at grain boundaries, resulting in a microstructure with discontinuous grain boundary precipitation, thus improving the tensile strength, elongation, and corrosion resistance of the age-hardened aluminum alloy.

[0015] The low-temperature heat treatment method for aluminum alloys provided by this invention is simple in process, easy to operate, and easy to industrialize. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of a low-temperature heat treatment method for high-performance age-strengthened aluminum alloys as described in Embodiments 1-3 of the present invention.

[0017] Figure 2 The image shows the age hardening curves of the treated 7A52 aluminum alloy in Example 3 and Comparative Example 3.

[0018] Figure 3 This is a microstructure diagram of the 7A52 aluminum alloy treated in Example 3;

[0019] Figure 4 The microstructure of the treated 7A52 aluminum alloy in Comparative Example 3 is shown.

[0020] Figure 5 The image shows the corrosion morphology of the 7A52 aluminum alloy treated in Example 3.

[0021] Figure 6 The image shows the corrosion morphology of the treated 7A52 aluminum alloy in Comparative Example 3. Detailed Implementation

[0022] like Figure 1 As shown, this invention provides a high-performance age-hardening aluminum alloy low-temperature heat treatment method, comprising the following steps:

[0023] The aluminum alloy is subjected to solution treatment, quenching treatment, cryogenic treatment and sub-low temperature aging treatment in sequence.

[0024] The cryogenic treatment is performed at a temperature of -196 to -70°C for 0.5 to 5 hours; the secondary cryogenic aging treatment is performed at a temperature of 20 to 80°C for 120 to 480 hours.

[0025] In this invention, the aluminum alloy preferably includes 2XXX series aluminum alloy, 6XXX series aluminum alloy or 7XXX series aluminum alloy; the aluminum alloys mentioned in this invention are all conventional aluminum alloys in the art, and their sources are not specifically limited.

[0026] In this invention, the solution treatment temperature is preferably 450–570°C, more preferably 470–530°C; the time is preferably 0.5–5 h, more preferably 1–4 h, and even more preferably 2–3 h.

[0027] In this invention, the quenching treatment is preferably water quenching, and the water temperature for water quenching is preferably 5-30°C, more preferably 20-25°C.

[0028] In this invention, the temperature of the cryogenic treatment is preferably -196 to -100°C, more preferably -180 to -120°C; the time is preferably 1 to 4.5 hours, more preferably 1.5 to 4 hours, and even more preferably 2 to 3 hours.

[0029] In this invention, the temperature of the sub-low temperature aging treatment is preferably 50-75°C, more preferably 60-65°C; the time is preferably 150-300h, more preferably 200-250h.

[0030] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0031] Example 1

[0032] The as-cast Al-6.82Si-0.34Mg alloy was solution treated at 530℃ for 3 hours, quenched with water at 25℃, and then subjected to cryogenic treatment at -196℃ for 2 hours; followed by a second cryogenic aging treatment at 50℃ for 200 hours.

[0033] Example 2

[0034] The 7A62 aluminum alloy was solution treated at 470℃ for 2 hours, quenched with water at 25℃, and then subjected to cryogenic treatment at -120℃ for 2 hours; followed by secondary low-temperature aging treatment at 60℃ for 200 hours.

[0035] Example 3

[0036] The 7A52 aluminum alloy was solution treated at 470℃ for 2 hours, quenched with water at 20℃, and then subjected to cryogenic treatment at -196℃ for 1.5 hours; followed by secondary low-temperature aging treatment at 65℃ for 250 hours.

[0037] Comparative Example 1

[0038] The as-cast Al-6.82Si-0.34Mg alloy described in Example 1 was subjected to T6I4 treatment, specifically: the as-cast Al-6.82Si-0.34Mg alloy was solution treated at 530℃ for 3 hours, quenched with water at 25℃, and then successively maintained at 160℃ for 1.5 hours and at 50℃ for 720 hours to complete the aging treatment.

[0039] Comparative Example 2

[0040] The 7A62 aluminum alloy described in Example 2 was subjected to T6 treatment, specifically: the 7A62 aluminum alloy was solution treated at 470℃ for 2 hours, quenched with water at 25℃, and then aged at 120℃ for 24 hours.

[0041] Comparative Example 3

[0042] The 7A52 aluminum alloy described in Example 3 was subjected to T6I4 treatment, specifically: the 7A52 aluminum alloy was solution treated at 470℃ for 2 hours, quenched with water at 20℃, and then aged sequentially by holding at 120℃ for 0.5 hours and at 65℃ for 512 hours.

[0043] Performance testing

[0044] The mechanical properties of the samples were tested after processing according to GB 6397-86.

[0045] 1) The tensile strength and elongation of the treated as-cast Al-6.82Si-0.34Mg alloys in Example 1 and Comparative Example 1 were tested; the results are shown in Table 1:

[0046] Table 1. Comparison of properties of the treated as-cast Al-6.82Si-0.34Mg alloys in Example 1 and Comparative Example 1.

[0047] Tensile strength (MPa) Elongation (%) Example 1 320.3 15.2 Comparative Example 1 311.2 13.6

[0048] As can be seen from Table 1, the mechanical properties of the as-cast Al-6.82Si-0.34Mg alloy sheet treated by the method described in this invention are superior to those of the as-cast Al-6.82Si-0.34Mg alloy sheet in the T6I4 state.

[0049] 2) Tensile strength and elongation tests were performed on the treated 7A62 aluminum alloys in Example 2 and Comparative Example 2; the results are shown in Table 2:

[0050] Table 2 Comparison of the properties of the treated 7A62 aluminum alloy in Example 2 and Comparative Example 2

[0051] Tensile strength (MPa) Elongation (%) Example 2 605.1 9.1 Comparative Example 2 587.2 7.2

[0052] As can be seen from Table 2, the mechanical properties of 7A62 aluminum alloy sheets treated by the method described in this invention are superior to those of 7A62 aluminum alloy sheets in the T6 state.

[0053] 3) Tensile strength and elongation tests were performed on the treated 7A52 aluminum alloys in Example 3 and Comparative Example 3; the results are shown in Table 3:

[0054] Table 3 Comparison of the properties of the treated 7A52 aluminum alloy in Example 3 and Comparative Example 3

[0055] Tensile strength (MPa) Elongation (%) Example 3 522.5 14.5 Comparative Example 3 517.0 12.6

[0056] As can be seen from Table 3, the mechanical properties of 7A52 aluminum alloy sheet treated by the method described in this invention are superior to those of 7A52 aluminum alloy sheet in the T6I4 state.

[0057] 4) The results of the hardness change over time during the aging treatment process described in Example 3 and Comparative Example 3 are as follows: Figure 2 As shown;

[0058] from Figure 2 As can be seen, the peak aging time of the 7A52 aluminum alloy treated in Example 3 was 250 hours, and the hardness was 151.8 HV; while the peak aging time of the T6I4 treatment in Comparative Example 3 was 512 hours, and the hardness was 149.1 HV. The 7A52 aluminum alloy treated using the aluminum alloy treatment method of the present invention reached its peak aging time earlier than the T6I4 process, and its hardness was higher than that of the T6I4 process.

[0059] 5) The microstructure of the treated 7A52 aluminum alloy in Example 3 and Comparative Example 3 was examined using transmission electron microscopy. The microstructure image of the treated 7A52 aluminum alloy in Example 3 is shown below. Figure 3 As shown; the microstructure of the treated 7A52 aluminum alloy in Comparative Example 3 is shown in Figure 3. Figure 4 As shown;

[0060] like Figure 3 and 4 As shown, cryogenic treatment causes the alloy to shrink in volume and decrease in lattice constant, increasing the supersaturation of solute atoms in the Al matrix and forming a supersaturated solid solution. This increases the precipitating force of solute atoms, while subsequent low-temperature aging is conducive to the nucleation of precipitated phases, thus obtaining fine, dispersed intragranular precipitates. Figure 3 As can be seen, the aging precipitates of 7A52 aluminum alloy treated using the method described in this invention are more dispersed and finer. Simultaneously, the cryogenic treatment generates cold compressive stress in the alloy; part of this compressive stress promotes precipitation behavior, while the other part releases stress through grain boundaries, resulting in increased spacing between the η phases at the grain boundaries, exhibiting a discontinuous distribution.

[0061] 6) The 7A52 aluminum alloys treated in Example 3 and Comparative Example 3 were immersed in a 3.5% NaCl solution for 72 hours for corrosion treatment. The corrosion morphology was then examined using a scanning electron microscope. The corrosion morphology of the 7A52 aluminum alloy treated in Example 3 is shown in the image below. Figure 5 As shown; the corrosion morphology of the treated 7A52 aluminum alloy in Comparative Example 3 is shown in the figure. Figure 6 As shown;

[0062] contrast Figure 5 and Figure 6 It can be observed that the surface of 7A52 aluminum alloy did not change significantly after treatment with the present invention, while many corrosion pits and corrosion products were generated in Comparative Example 3, indicating that the corrosion resistance of 7A52 aluminum alloy treated with the present invention is better than that of T6I4 process.

[0063] As can be seen from the above embodiments, the present invention provides a low-temperature heat treatment method for aluminum alloys. By first subjecting the solution-quenched age-strengthened aluminum alloy to a short-time low-temperature cryogenic treatment followed by a long-time secondary low-temperature aging treatment, the low-temperature cryogenic treatment induces dislocation multiplication and cold compressive stress, thereby obtaining a microstructure with fine intragranular precipitation and discontinuous grain boundary precipitation, which improves the tensile strength, elongation and corrosion resistance of the age-strengthened aluminum alloy.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for low-temperature heat treatment of age-strengthened aluminum alloys, characterized in that, Includes the following steps: The aluminum alloy is subjected to solution treatment, quenching treatment, cryogenic treatment and sub-low temperature aging treatment in sequence. The cryogenic treatment is performed at a temperature of -196 to -70°C for 0.5 to 5 hours; the aging treatment is performed at a temperature of 50 to 75°C for 120 to 480 hours.

2. The method for low-temperature heat treatment of age-strengthened aluminum alloys according to claim 1, characterized in that, The aluminum alloys include 2XXX series aluminum alloys, 6XXX series aluminum alloys, or 7XXX series aluminum alloys.

3. The method for low-temperature heat treatment of age-strengthened aluminum alloys according to claim 1, characterized in that, The solution treatment is performed at a temperature of 450–570°C for a time of 0.5–5 hours.

4. The method for low-temperature heat treatment of age-strengthened aluminum alloys according to claim 3, characterized in that, The solution treatment is performed at a temperature of 470–550°C for 1–4 hours.

5. The method for low-temperature heat treatment of age-strengthened aluminum alloys according to claim 1, characterized in that, The quenching process is water quenching, and the water temperature for water quenching is 5–30°C.

6. The low-temperature heat treatment method for age-strengthened aluminum alloys according to claim 1, characterized in that, The cryogenic treatment is performed at a temperature of -196 to -100°C for a duration of 1 to 4.5 hours.

7. The low-temperature heat treatment method for age-strengthened aluminum alloys according to claim 6, characterized in that, The duration of the secondary low-temperature aging treatment is 150–300 hours.

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