Precipitation hardening aluminum alloy and method for improving stress corrosion resistance

Abstract

The invention relates to a precipitation-hardening aluminum alloy and a method for improving stress corrosion performance. The method comprises the following steps: carrying out solution treatment on a precipitation-hardening aluminum alloy sample; polishing and cleaning the surface of the sample subjected to solution treatment to obtain a sample; applying pulse current to the sample for treatment; and carrying out stress corrosion test on the treated sample. According to the method disclosed by the invention, the dispersed and finely distributed intracrystalline precipitated phase and the discontinuously distributed grain boundary precipitated phase can be obtained at the same time by applying pulse current treatment to the sample subjected to solution treatment. According to the method, the problem that the strength and the stress corrosion performance of the aluminum alloy cannot be synergistically improved under traditional aging treatment is solved, the process is simple, the production efficiency is high, the traditional aging treatment can be replaced, the effect is excellent, complex additional procedures are avoided, and the cost is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of materials, and particularly relates to a precipitation-hardening aluminum alloy and a method for improving stress corrosion performance. Background Art

[0002] As a key structural material in the aerospace field, the performance optimization of aluminum alloy materials has always been the core topic in the field of materials engineering. 7xxx series (Al-Zn-Mg-Cu) aluminum alloys have become the preferred materials for key load-bearing components such as aircraft skins and wing beams due to their excellent specific strength and processing performance. However, this series of alloys generally face a serious threat of stress corrosion cracking (SCC) during service. According to statistics, more than 60% of the failure accidents of 7xxx series aluminum alloy components are directly related to SCC. The root cause of this problem lies in the anodic dissolution channels formed by the continuous distribution of its strengthening phase (η'-MgZn2) at grain boundaries.

[0003] Traditional solutions mainly regulate the microstructure through heat treatment processes: Although T6 aging can obtain high strength, it leads to the continuous distribution of precipitates at grain boundaries, deteriorating the SCC resistance; Although T73 over-aging can improve the grain boundary structure, it causes a strength loss of 15%-20%. Research shows that through double-stage aging (such as T76), the strength and corrosion resistance can be partially balanced, but it requires a treatment cycle of up to 24-48 hours, and there are still problems of coarsening of matrix precipitates. In recent years, the developed surface treatment technologies (such as micro-arc oxidation, laser shock) can improve the surface corrosion resistance, but there are defects such as poor bonding force between the treatment layer and the matrix, complex processes, and high costs.

[0004] Pulsed current treatment, as an emerging physical field regulation technology, shows the potential for microstructure regulation due to its unique non-thermal effects (such as electron wind force, vacancy migration). The prior art CN118756074A uses electromagnetic shock to treat the aged Al-Mg-Si alloy and obtains discontinuous precipitates at grain boundaries, improving the corrosion resistance of the material. The prior art CN116695034B performs short-time electromagnetic shock on finished aluminum alloy components, eliminates micro-damage, and improves the stress corrosion fatigue performance of aluminum alloys. However, these methods impose additional processing processes on aluminum alloys, and the temperature rises during the treatment process, which easily causes coarsening of precipitates. Therefore, how to efficiently break the continuous distribution of grain boundary precipitates through precise physical field regulation while maintaining the strength of the material has become a technical difficulty in improving the stress corrosion performance of precipitation-hardening aluminum alloys. Summary of the Invention

[0005] In order to overcome the above problems existing in the prior art, the present invention provides a precipitation-hardening aluminum alloy and a method for improving stress corrosion performance to solve the above problems existing in the prior art.

[0006] A method for improving the stress corrosion performance of precipitation hardening aluminum alloy, the method comprising the following steps:

[0007] S1. Solution-treat the precipitation hardening aluminum alloy specimen;

[0008] S2. Grind and clean the surface of the specimen after solution treatment to obtain a sample;

[0009] S3. Apply pulsed current treatment to the sample;

[0010] S4. Conduct stress corrosion test on the sample after pulsed current treatment.

[0011] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the precipitation hardening aluminum alloy includes 2xxx aluminum alloy, 6xxx aluminum alloy or 7xxx aluminum alloy.

[0012] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the solution treatment temperature in step S1 is 450 - 500 °C, and the treatment time is 30 - 120 min.

[0013] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the pulsed current density is 1 - 300 A / mm 2 , the frequency is 1 - 50 kHz, the duty cycle is 1 - 40%, and the treatment time is 5 - 24 h.

[0014] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the current density is 1 A / mm 2 , the frequency is 50 kHz, the duty cycle is 40%, and the treatment time is 24 h.

[0015] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the current density is 10 A / mm 2 , the frequency is 30 kHz, the duty cycle is 20%, and the treatment time is 22 h.

[0016] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the current density is 50 A / mm 2 , the frequency is 1 kHz, the duty cycle is 10%, and the treatment time is 20 h.

[0017] In the above-mentioned aspect and any possible implementation, a further implementation is provided, wherein the current density is 80 A / mm 2 , the frequency is 200 Hz, the duty cycle is 5%, and the treatment time is 16 h; or the current density is 100 A / mm 2, with a frequency of 100 Hz, a duty cycle of 4%, and a processing time of 12 h.

[0018] For the aspects and any possible implementation described above, a further implementation is provided, where the current density is 200 A / mm 2 , with a frequency of 50 Hz, a duty cycle of 2%, and a processing time of 8 h; or the current density is 300 A / mm 2 , with a frequency of 1 Hz, a duty cycle of 1%, and a processing time of 5 h.

[0019] The present invention also provides a precipitation hardening aluminum alloy, which is obtained by the method described above.

[0020] Advantages of the present invention

[0021] The method for improving the stress corrosion performance of the precipitation hardening aluminum alloy of the present invention includes the following steps: performing solution treatment on the precipitation hardening aluminum alloy specimen; grinding and cleaning the surface of the specimen after solution treatment to obtain a sample; applying pulsed current treatment to the sample; and performing stress corrosion testing on the treated sample. By applying pulsed current treatment to the solution-treated aluminum alloy, the present invention can simultaneously obtain dispersed and finely distributed intragranular precipitation phases and discontinuously distributed grain boundary precipitation phases. This method overcomes the problem that the strength and stress corrosion performance of aluminum alloy cannot be improved synergistically under traditional aging treatment, and has the advantages of simple process, high production efficiency, can replace traditional aging treatment, not only has excellent effects, but also avoids complex additional processes and greatly reduces costs. Description of the drawings

[0022] Figure 1 It is a diagram of the stress corrosion performance of aluminum alloy under heat treatment and pulsed current treatment;

[0023] Figure 2 It is a morphology diagram of grain boundary and intragranular precipitation phases after heat treatment and pulsed current treatment;

[0024] Figure 3 It is a flowchart of the method of the present invention. Detailed implementation manners

[0025] To better understand the technical solution of the present invention, the content of the present invention includes but is not limited to the following detailed implementation manners, and similar technologies and methods should be regarded as within the scope of protection of the present invention. To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0026] It should be clear that the embodiments described in this invention are only a part of the embodiments of this invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this invention without creative efforts belong to the scope of protection of this invention.

[0027] The terms used in the embodiments of this invention are only for the purpose of describing specific embodiments, and are not intended to limit this invention. The singular forms of "a", "the" and "said" used in the embodiments of this invention and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0028] This invention provides a method for improving the stress corrosion performance of precipitation hardening aluminum alloys, as Figure 3 shown, the method includes the following steps:

[0029] S1. Perform solution treatment on the precipitation hardening aluminum alloy specimen;

[0030] S2. Grind and clean the surface of the specimen after solution treatment to obtain a sample;

[0031] S3. Apply pulsed current treatment to the sample;

[0032] S4. Perform stress corrosion test on the sample after pulsed current treatment.

[0033] Further, the precipitation hardening aluminum alloy includes 2xxx aluminum alloy, 6xxx aluminum alloy or 7xxx aluminum alloy.

[0034] Further, the solution treatment temperature in step S1 is 450 - 500 °C, and the treatment time is 30 - 120 min.

[0035] Further, the pulsed current density is 10 - 300 A / mm 2 , the frequency is 1 - 50 kHz, the duty cycle is 1 - 40%, and the treatment time is 5 - 24 h.

[0036] Further, the current density is 1 A / mm 2 , the frequency is 50 kHz, the duty cycle is 40%, and the treatment time is 24 h.

[0037] Further, the current density is 10 A / mm 2 , the frequency is 30 kHz, the duty cycle is 20%, and the treatment time is 22 h.

[0038] Further, the current density is 50 A / mm 2 , the frequency is 1 kHz, the duty cycle is 10%, and the treatment time is 20 h.

[0039] Further, the current density is 80 A / mm 2 , the frequency is 200 Hz, the duty cycle is 5%, and the treatment time is 16 h; or the current density is 100 A / mm 2 , the frequency is 100 Hz, the duty cycle is 4%, and the treatment time is 12 h.

[0040] Further, the current density is 200 A / mm 2 , the frequency is 50 Hz, the duty cycle is 2%, and the treatment time is 8 h; or the current density is 300 A / mm 2 , the frequency is 1 Hz, the duty cycle is 1%, and the treatment time is 5 h.

[0041] Specifically, the specific process of the present invention is as follows: Step 1: Perform solution treatment on the precipitation hardening aluminum alloy sample. The solution treatment temperature is 450 - 500 °C, and the treatment time is 30 - 120 min, so that the alloying elements of the aluminum alloy are fully dissolved, so that a large number of strengthening phases can be precipitated during the pulsed current treatment.

[0042] Step 2: Grind and clean the surface of the sample after solution treatment to obtain a sample to ensure good contact between the sample and the pulsed electrode;

[0043] Step 3: Apply pulsed current treatment to the sample. Among them, the pulsed current density is 1 - 300 A / mm 2 , the frequency is 1 - 50 kHz, the duty cycle is 1 - 40%, and the treatment time is 5 - 24 h; select the density value, frequency, etc. of the pulsed current according to the sample and the treatment time. After the pulsed current treatment with the selected corresponding parameters and time, dispersed and fine intragranular precipitation phases and discontinuous grain boundary precipitation phases can be observed by transmission electron microscopy, as Figure 2 shown. At this time, the continuous corrosion channels (grain boundary precipitation phases) at the grain boundaries are interrupted, thereby improving the corrosion resistance of the aluminum alloy; and the dispersed and fine intragranular precipitation phases also ensure that the strength of the aluminum alloy does not decrease.

[0044] Step 4: Perform stress corrosion test on the aluminum alloy at room temperature, and the corrosion solution used is 3.5% NaCl solution.

[0045] Therefore, compared with the traditional peak aging treatment, after the aluminum alloy sample of the present invention is treated by the above method, the stress corrosion life of the obtained sample in 3.5% NaCl solution is increased by 3 times, and the tensile strength retention rate exceeds 95%. In addition, the elongation of the sample in air can be increased by 38%.

[0046] The present invention improves the stress corrosion resistance of aluminum alloy by using pulsed current. The aluminum alloy includes two regions: the grain boundary part and the intragranular part. However, the resistance at the grain boundary is much greater than that of the intragranular part. Therefore, based on the difference in the electrical conductivity between the intragranular and grain boundary regions of the aluminum alloy, when a pulsed current is applied to the aluminum alloy sample, the pulsed current preferentially accumulates at the grain boundary with a large resistance value. There is also pulsed current in the intragranular region due to the presence of resistance, but due to the smaller resistance, the current density is less than that at the grain boundary. The application of the pulsed current increases the migration rate of atoms in the aluminum alloy, accelerates the migration of elements in the aluminum alloy to the intragranular precipitation phase, enabling the intragranular precipitation phase to achieve peak aging of the aluminum alloy faster, thereby ensuring that the strength of the aluminum alloy remains unchanged or is not lost after pulsed current treatment.

[0047] In addition, due to the higher current density at the grain boundary, the elements at the grain boundary migrate to the grain boundary precipitation phase more rapidly. The grain boundary precipitation phase rapidly coarsens and shows a discontinuous distribution. After the treatment time ends, a dispersed and fine intragranular precipitation phase and a discontinuous grain boundary precipitation phase are obtained. At this time, the continuous corrosion channels (grain boundary precipitation phase) at the grain boundary are interrupted, thus improving the corrosion resistance of the aluminum alloy; and the dispersed and fine intragranular precipitation phase also ensures that the strength of the aluminum alloy is not lost. This enables the stress corrosion performance of the aluminum alloy to be significantly improved while not losing strength. Therefore, the present invention obtains a dispersed and fine intragranular precipitation phase and a discontinuous grain boundary precipitation phase by applying pulsed current, thereby improving the corrosion performance while ensuring the strength of the aluminum alloy.

[0048] Precipitation hardening aluminum alloys include 2xxx aluminum alloys, 6xxx aluminum alloys, or 7xxx aluminum alloys. The above precipitation hardening aluminum alloys need to be solutionized and age-hardened to obtain a dispersed intragranular precipitation phase to ensure the strength of the precipitation hardening aluminum alloy. However, continuous precipitation phases will form at the grain boundaries during the aging process. These grain boundary precipitation phases serve as continuous corrosion channels and have a serious tendency to stress corrosion cracking. By applying current during the aging stage, the continuous distribution of the grain boundary precipitation phase can be interrupted, improving the stress corrosion resistance.

[0049] Further, the solution-treated aluminum alloy is subjected to pulsed current treatment with different parameters. The specific parameters are a current density of 1 A / mm 2 , a frequency of 50 kHz, a duty cycle of 40%, and a treatment time of 24 h; or a current density of 10 A / mm 2 , a frequency of 30 kHz, a duty cycle of 20%, and a treatment time of 22 h; or a current density of 50 A / mm 2 , a frequency of 1 kHz, a duty cycle of 10%, and a treatment time of 20 h; or a current density of 80 A / mm 2 , a frequency of 200 Hz, a duty cycle of 5%, and a treatment time of 16 h; or a current density of 100 A / mm2 、 a frequency of 100 Hz, a duty cycle of 4%, and a processing time of 12 h; or, a current density of 200 A / mm 2 、 a frequency of 50 Hz, a duty cycle of 2%, and a processing time of 8 h; or, a current density of 300 A / mm 2 、 a frequency of 1 Hz, a duty cycle of 1%, and a processing time of 5 h. Compared with the traditional peak aging treatment, after the pulsed current treatment with the above parameters, the tested samples show that the stress corrosion life in 3.5% NaCl solution is increased by 2 - 3 times, and the tensile strength retention rate > 95%. In addition, the elongation of the samples in air can be increased by 20 - 38%.

[0050] Furthermore, the stress corrosion performance of the pulsed-treated samples was tested. As Figure 1 shown, compared with the traditional peak aging treatment, the stress corrosion life of the samples treated by pulsed current of the present invention in 3.5% NaCl solution is increased by 2 - 3 times, and the tensile strength retention rate exceeds 95%. In addition, the elongation of the samples in air can be increased by 38%.

[0051] The microstructural morphologies of the samples after pulsed current treatment and traditional peak aging treatment are as Figure 2 shown. It can be seen that the grain boundaries of the aluminum alloy treated by traditional peak aging show continuous distribution, while the grain boundaries of the aluminum alloy samples treated by the pulsed current of the present invention are intermittently distributed.

[0052] Hereinafter, 7xxx aluminum alloy is used as a specific example for illustration

[0053] Example 1

[0054] S1: Solution treatment of 7xxx aluminum alloy specimens at 475 °C;

[0055] S2: Grinding and cleaning the surface of the specimens;

[0056] S3: Applying a pulsed current treatment with a current density of 1 A / mm 2 、 a frequency of 50 kHz, a duty cycle of 40%, and a processing time of 24 h to obtain samples;

[0057] S4: Testing the stress corrosion performance of the samples after pulsed current treatment. Compared with the traditional peak aging treatment, the stress corrosion life of this sample in 3.5% NaCl solution is increased by 2 times, and the tensile strength retention rate is 95%. In addition, the elongation of the samples in air is also increased by 20%.

[0058] Example 2

[0059] S1: Solution treatment of 7xxx aluminum alloy at 475 °C;

[0060] S2: Polish and clean the surface of the specimen;

[0061] S3: Apply a pulsed current treatment with a current density of 10 A / mm 2 , a frequency of 30 kHz, a duty cycle of 20%, and a treatment time of 22 h to the cleaned specimen to obtain a sample;

[0062] S4: Conduct a stress corrosion performance test on the sample after pulsed current treatment. Compared with the traditional peak aging treatment, it can be seen from the test that the stress corrosion life of this sample in 3.5% NaCl solution is increased by 2 times, and the tensile strength retention rate is 95%. In addition, the elongation of the sample in air is also increased by 23%.

[0063] Example 3

[0064] S1: Perform a solution treatment on 7xxx aluminum alloy at 475 °C;

[0065] S2: Polish and clean the surface of the specimen;

[0066] S3: Apply a pulsed current treatment with a current density of 50 A / mm 2 , a frequency of 1 kHz, a duty cycle of 10%, and a treatment time of 20 h to the cleaned specimen to obtain a sample;

[0067] S4: Conduct a stress corrosion performance test on the sample after pulsed current treatment. Compared with the traditional peak aging treatment, it can be seen from the test that the stress corrosion life of this sample in 3.5% NaCl solution is increased by 2.3 times, and the tensile strength retention rate is 97%. In addition, the elongation of the sample in air is also increased by 25%.

[0068] Example 4

[0069] S1: Perform a solution treatment on 7xxx aluminum alloy at 475 °C;

[0070] S2: Polish and clean the surface of the specimen;

[0071] S3: Apply a pulsed current treatment with a current density of 80 A / mm 2 , a frequency of 200 Hz, a duty cycle of 5%, and a treatment time of 16 h to the cleaned specimen to obtain a sample;

[0072] S4: Conduct a stress corrosion performance test on the sample after pulsed current treatment. Compared with the traditional peak aging treatment, it can be seen from the test that the stress corrosion life of this sample in 3.5% NaCl solution is increased by 3 times, and the tensile strength retention rate is 99%. In addition, the elongation of the sample in air is also increased by 38%.

[0073] Example 5

[0074] S1: Solutionize the 7xxx aluminum alloy at 475 °C;

[0075] S2: Grind and clean the surface of the specimen;

[0076] S3: Apply pulsed current treatment with a current density of 100 A / mm 2 , a frequency of 100 Hz, a duty cycle of 4%, and a treatment time of 12 h to the cleaned specimen to obtain a sample;

[0077] S4: Test the stress corrosion performance of the sample after pulsed current treatment. Compared with the traditional peak aging treatment, it can be seen from the test that the stress corrosion life of this sample in 3.5% NaCl solution is increased by 3 times, and the tensile strength retention rate is 98%. In addition, the elongation of the sample in air is also increased by 33%.

[0078] Example 6

[0079] S1: Solutionize the 7xxx aluminum alloy at 475 °C;

[0080] S2: Grind and clean the surface of the specimen;

[0081] S3: Apply pulsed current treatment with a current density of 200 A / mm 2 , a frequency of 50 Hz, a duty cycle of 2%, and a treatment time of 8 h to the cleaned specimen to obtain a sample;

[0082] S4: Test the stress corrosion performance of the sample after pulsed current treatment. Compared with the traditional peak aging treatment, it can be seen from the test that the stress corrosion life of this sample in 3.5% NaCl solution is increased by 3 times, and the tensile strength retention rate is 98%. In addition, the elongation of the sample in air is also increased by 35%.

[0083] Example 7

[0084] S1: Solutionize the 7xxx aluminum alloy at 475 °C;

[0085] S2: Grind and clean the surface of the specimen;

[0086] S3: Apply pulsed current treatment with a current density of 300 A / mm 2 , a frequency of 1 Hz, a duty cycle of 1%, and a treatment time of 5 h to the cleaned specimen to obtain a sample;

[0087] S4: Test the stress corrosion performance of the sample after pulsed current treatment. Compared with the traditional peak aging treatment, it can be seen from the test that the stress corrosion life of this sample in 3.5% NaCl solution is increased by 3 times, and the tensile strength retention rate is 99%. In addition, the elongation of the sample in air is also increased by 35%.

[0088] In summary, the present method avoids improving the stress corrosion performance of aluminum alloy by sacrificing mechanical properties. After pulsed current treatment, the mechanical properties and stress corrosion resistance of the aluminum alloy are synergistically improved.

[0089] As an embodiment disclosed by the present invention, the present invention also provides a precipitation hardening aluminum alloy, which is prepared by the method described above. Compared with traditional peak aging treatment, it can be seen from tests that the tensile strength retention rate of the sample obtained by this method can reach 99% in 3.5% NaCl solution, and the stress corrosion life is increased by 3 times. In addition, the elongation of the sample in air can be increased by 38%.

[0090] The above description shows and describes several preferred embodiments of the present invention. However, as mentioned above, it should be understood that the present invention is not limited to the form disclosed herein, should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be within the scope of the application concept described herein, through the above teachings or the technology or knowledge in related fields. Any changes and modifications made by those skilled in the art without departing from the spirit and scope of the present invention shall fall within the protection scope of the appended claims of the present invention.

Claims

1. A method for improving the stress corrosion performance of a precipitation hardening aluminum alloy, characterized in that, The method includes the following steps: S1. Solution-treat the precipitation-hardening aluminum alloy sample; S2. Grind and clean the surface of the sample after solution treatment to obtain a sample; S3. Apply pulsed current treatment to the sample; S4. Conduct stress corrosion testing on the sample after pulsed current treatment.

2. The method according to claim 1, wherein The precipitation-hardening aluminum alloy includes 2xxx aluminum alloy, 6xxx aluminum alloy or 7xxx aluminum alloy.

3. The method according to claim 1 or 2, characterized in that, The solution treatment temperature in step S1 is 450-500 °C, and the treatment time is 30-120 min.

4. The method according to claim 1, wherein The pulsed current density is 1 - 300 A / mm 2 , the frequency is 1 - 50 kHz, the duty cycle is 1 - 40%, and the processing time is 5 - 24 h.

5. The method according to claim 4, characterized in that, The current density is 1 A / mm 2 , the frequency is 50 kHz, the duty cycle is 40%, and the processing time is 24 h.

6. The method according to claim 4, characterized in that, The current density is 10 A / mm 2 , the frequency is 30 kHz, the duty cycle is 20%, and the processing time is 22 h.

7. The method according to claim 4, wherein The current density is 50 A / mm 2 , the frequency is 1 kHz, the duty cycle is 10%, and the processing time is 20 h.

8. The method according to claim 1, characterized in that, The current density is 80 A / mm 2 , the frequency is 200 Hz, the duty cycle is 5%, and the treatment time is 16 h; or the current density is 100 A / mm 2 , the frequency is 100 Hz, the duty cycle is 4%, and the treatment time is 12 h.

9. The method according to claim 1, characterized in that The current density is 200 A / mm 2 , the frequency is 50 Hz, the duty cycle is 2%, and the treatment time is 8 h; or the current density is 300 A / mm 2 , the frequency is 1 Hz, the duty cycle is 1%, and the treatment time is 5 h.

10. A precipitation hardening aluminum alloy, characterized in that, The precipitation-hardening aluminum alloy is obtained by the method described in any one of claims 1-9.

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