A method of strengthening an aluminum alloy

Abstract

The present application relates to a kind of aluminum alloy strengthening method, including solid solution treatment, sine wave cyclic tension and compression treatment and artificial aging etc., by specific setting to raw material and each step and the specific setting of parameter etc. Conditions in step and the specific setting for specific processing object, the size and distribution of specific aluminum alloy precipitated phase are optimized, yield strength and tensile strength are greatly improved under not too much loss of elongation, so that it can be effectively applied in the process of aluminum alloy strengthening.

Description

TECHNICAL FIELD

[0001] The application relates to an aluminum alloy strengthening method. BACKGROUND

[0002] Aluminum alloys are widely used in transportation, construction, aviation and other fields due to their low density, good plasticity and toughness; aluminum alloys containing lithium have a certain content (about 1-2 wt%) of lithium added on the basis of aluminum alloys, and the density is further reduced, and the aluminum alloys containing lithium have high specific strength and specific stiffness, good damage resistance, corrosion resistance, fatigue resistance, thermal stability and forming property and other advantages, and are widely used in the field of aerospace. However, the strength of the aluminum alloy containing lithium is relatively low compared with steel and other metal materials, so the strengthening of the aluminum alloy containing lithium is an important research direction, and the development of the aluminum alloy containing lithium with low density and high strength has important strategic significance for promoting the high-level development of the manufacturing industry in China.

[0003] Heat treatment strengthening is the main strengthening method for aluminum alloys, especially aluminum alloys containing lithium. Heat treatment can cause fine second phases to precipitate, which can hinder the movement of dislocations, thereby achieving the purpose of strengthening. The main heat treatment methods at present are solid solution + artificial aging (T6) and solid solution + pre-deformation + artificial aging (T8). The T6 process is to heat the solid-solution-treated aluminum alloy containing lithium to the aging temperature (generally 100-200 DEG C) and keep it for a long time. The second phase is precipitated by heating, but the time for reaching the peak aging is relatively long, and the effect of improving the strength of the aluminum alloy containing lithium is not significant enough. In order to further improve the strength of the aluminum alloy containing lithium, the T8 process with pre-deformation is gradually applied in industry. Pre-deformation can generate a large number of dislocations in the matrix, providing heterogeneous nucleation sites for the precipitation of the second phase and promoting the precipitation of the second phase during artificial aging. Pre-deformation can also accelerate the precipitation of the second phase in the matrix, reduce the artificial aging period, and greatly reduce the time and process cost. The commonly used pre-deformation method is tensile pre-deformation, that is, using a stretching device to stretch the solid-solution-treated aluminum alloy containing lithium by a certain deformation amount, and the commonly used strain is 3%-7%. The T8 process shows more excellent mechanical properties compared with the T6 process, can greatly improve the strength of the aluminum alloy containing lithium, and shorten the artificial aging time. However, the pre-stretching affects the deformation of the grains due to the orientation of the grains in the material, and the number and size of the dislocations generated are quite different, and the size of the precipitated phase also has a large difference, so it cannot meet the application requirements of higher strength, and also has a relatively obvious effect on the size of the material. In order to further expand the application scenarios of the aluminum alloy containing lithium and further improve the strength of the aluminum alloy containing lithium, it is urgent to develop a new heat treatment process for the aluminum alloy containing lithium with higher strength.

[0004] The Chinese invention patent publication CN112226707A discloses a processing method of room temperature strengthened aluminum alloy, which is cyclically strengthened by linear broken line type reciprocating plastic deformation, and obtains a strengthened aluminum alloy. However, the research does not study the type of aluminum alloy targeted by the processing method, and the broken line processing method is not optimized for strengthening effect. SUMMARY

[0005] To solve the above technical problems, the present application provides a method for strengthening aluminum alloy containing lithium, namely solid solution + cyclic tension and compression treatment + artificial aging. This method has a very obvious effect on improving the strength of aluminum alloy containing lithium, and also greatly reduces the final strain of the material.

[0006] The technical scheme is specifically as follows:

[0007] A method for strengthening aluminum alloy, the aluminum alloy is an aluminum alloy containing 0.5-2.5wt.% lithium, comprising the following steps:

[0008] (1) Heat the aluminum alloy to the supersaturated solid solution temperature single-phase region, and keep warm for 1-3 hours, and then quench with water or oil as medium to room temperature.

[0009] (2) After quenching of step (1), the aluminum alloy is placed in a cyclic tension and compression treatment device at room temperature, and the aluminum alloy is clamped and subjected to cyclic tension and compression treatment. The tension and compression treatment adopts a sinusoidal waveform cyclic tension and compression treatment method, the tension and compression treatment time of each sinusoidal waveform is the same, both are 1-5s, and the deformation of each cycle of tension and compression is based on the size obtained in the previous cycle, and the strain amplitude of the tension deformation is set to (2-6) x 10 -3(0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, and 0.6%), the frequency of the cyclic tensile-compressive treatment is set to 0.2-1 Hz (0.2 Hz, 0.25 Hz, 0.3 Hz, 0.35 Hz, 0.4 Hz, 0.45 Hz, 0.5 Hz, 0.55 Hz, 0.6 Hz, 0.65 Hz, 0.7 Hz, 0.75 Hz, 0.8 Hz, 0.85 Hz, 0.9 Hz, 0.95 Hz, 1 Hz, etc.), and the stress intensity of the tensile treatment and the stress intensity of the compressive treatment of the sinusoidal waveform are rapidly increased before the 100th cycle of the cyclic tensile-compressive treatment, the stress intensity of the tensile treatment and the stress intensity of the compressive treatment at the 100th cycle are 1.15-2.12 times (1.15 times, 1.18 times, 1.20 times, 1.21 times, 1.22 times, 1.23 times, 1.24 times, 1.25 times, 1.26 times, 1.27 times, 1.28 times, 1.29 times, 1.30 times, 1.4 times, 1.5 times, 1.6 times, 1.7 times, 1.8 times, 1.9 times, 2.0 times, 2.05 times, 2.10 times, 2.12 times, etc.) of the stress intensity of the tensile treatment and the stress intensity of the compressive treatment at the 1st cycle, the stress intensity of the tensile treatment and the stress intensity of the compressive treatment of the sinusoidal waveform are slowly increased from the 100th cycle to the 200th cycle, the stress intensity of the tensile treatment and the stress intensity of the compressive treatment at the 200th cycle are 1.01-1.15 times (1.01 times, 1.02 times, 1.03 times, 1.04 times, 1.05 times, 1.06 times, 1.07 times, 1.08 times, 1.09 times, 1.10 times, 1.11 times, 1.12 times, 1.13 times, 1.14 times, 1.15 times, etc.) of the stress intensity of the tensile treatment and the stress intensity of the compressive treatment at the 100th cycle, the stress intensity of the tensile treatment and the stress intensity of the compressive treatment after the 200th cycle are more slowly increased, and the stress intensity of the tensile treatment and the stress intensity of the compressive treatment every 100 cycles are 1-1.05 (preferably 1-1.01) times (1.000001 times, 1.00001 times, 1.0001 times, 1.001 times, 1.01 times, 1.02 times, 1.03 times, 1.04 times, 1.05 times, etc.) of the stress intensity of the tensile treatment and the stress intensity of the compressive treatment at the end of the previous 100 cycles, the number of cycles of the cyclic tensile-compressive treatment is 480-600 (490, 495, 498, 500, 510, 520, 530, 540, 550, 555, 560, 570, 580, 590, 600, etc.), and then the cyclic tensile-compressive treatment is stopped.

[0010] (3) placing the aluminum alloy obtained after the cyclic tension-compression treatment in step (2) into an aging furnace, heating to 140-185°C (which can be 140°C, 145°C, 149°C, 150°C, 155°C, 158°C, 160°C, 168°C, 170°C, 175°C, 180°C, 185°C), aging for 5-48 hours (which can be 5 hours, 6 hours, 8 hours, 10 hours, 11 hours, 15 hours, 18 hours, 20 hours, 22 hours, 25 hours, 30 hours, 33 hours, 35 hours, 38 hours, 40 hours, 45 hours, 48 hours), and then cooling to room temperature to obtain the strengthened aluminum alloy.

[0011] Preferably, in step (2), the cyclic tension-compression treatment device is an electronic universal mechanical testing machine or other device capable of cyclic tension-compression treatment in a sinusoidal waveform.

[0012] Preferably, in step (2), the strain ratio of the cyclic tension-compression treatment in a sinusoidal waveform is R = -1.

[0013] Preferably, the chemical composition of the aluminum alloy is: Cu: 3.6-4.3 wt.%, Li: 0.8-1.2 wt.%, Mg: 0.25-0.8 wt.%, Ag: 0.25-0.6 wt.%, Zr: 0.08-0.16 wt.%, Si: <0.12 wt.%, Fe: <0.15 wt.%, and the balance being Al and unavoidable impurities.

[0014] Preferably, in step (2), the aluminum alloy is clamped, the upper part is clamped first, then the pressure is zeroed, then the lower part is clamped, and the zero pressure operation is not performed when clamping the lower part; the upper limit of displacement is set to 1.8-2.5 (which can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5), and the lower limit of displacement is set to -0.8 to -1.2 (which can be -0.8, -0.9, -1.0, -1.1, -1.2).

[0015] Preferably, in step (1), the supersaturated solid solution temperature single-phase region is preferably 485-550°C (which can be 485°C, 490°C, 492°C, 496°C, 505°C, 512°C, 525°C, 532°C, 538°C, 541°C, 545°C, 550°C).

[0016] Preferably, in step (3), heating is preferably to 145-182°C, and the peak aging time is 14-17 hours.

[0017] Preferably, the aging treatment in step (3) is artificial aging treatment.

[0018] As preferred, the aluminum alloy is an aluminum alloy of a grade of 2020, 2090, 2091, 8090, 1430, 1440, 1441, 1450, 1460, 2195, 2196, 2297, 2397, 2098, 2198, 2099, 2199, 2076, 2296, Weldlite-210, 2050, 2055 or 2060.

[0019] As preferred, the tensile stress intensity and the compressive stress intensity of the sine wave-shaped tensile-compressive treatment in step (2) increase more rapidly before 50 times of the cycle of the tensile-compressive treatment, and the tensile stress intensity and the compressive stress intensity at the 50th time are 1.18-2.01 times (may be 1.18 times, 1.19 times, 1.20 times, 1.25 times, 1.35 times, 1.5 times, 1.58 times, 1.65 times, 1.85 times, 1.88 times, 1.96 times, 2.01 times) of the tensile stress intensity and the compressive stress intensity at the 1st time.

[0020] The technical effect of the present application is that:

[0021] (1) The present application aims at the strengthening problem of aluminum-lithium alloy, and invents a solid solution + sine wave-shaped cycle tensile-compressive treatment + aging process. The specific sine wave-shaped cycle tensile-compressive treatment makes the solid solution alloy produce uniformly distributed dislocation loops and dislocation lines, which can better promote the uniform precipitation of the second phase, reduce the size of the second phase, and increase the number density of the second phase, so that the strength of the aluminum-lithium alloy is obviously improved compared with the existing process, and the aging time is reduced. Moreover, the sine wave-shaped cycle tensile-compressive treatment has little effect on the size of the aluminum-lithium alloy, and the overall strain is about 0.2-0.6%.

[0022] (2) the present application adopts specific sinusoidal waveform cyclic tension and compression treatment on aluminum alloy corresponding to specific lithium content, since the aluminum-lithium alloy contains a certain content of lithium element, the T1 (Al2CuLi) phase is the main strengthening phase, which is a hexagonal structure and disc-shaped. The strength of aluminum-lithium alloy is directly related to the diameter, thickness, volume fraction and distribution state of T1 phase, the greater the diameter, the smaller the thickness, the higher the volume fraction, and the more uniform the distribution of precipitated phase, which is more conducive to improving the strength of aluminum-lithium alloy. The specific sinusoidal waveform cyclic tension and compression treatment of the present application can produce uniform dislocations in the alloy after solid solution, including dislocation loops and dislocation lines, which provide more uniform nucleation sites for the nucleation of T1 phase, and can accelerate the precipitation of T1 phase and inhibit the precipitation of θ' (Al2Cu) and other weak strengthening phases, thereby creating favorable conditions for improving the volume fraction of T1 phase. The alloy after solid solution and cyclic tension and compression treatment has a strength comparable to that of T6 process alloy, but still has a large room for improvement. At the same time, the present application can precipitate uniform and high volume fraction T1 phase after sinusoidal waveform cyclic tension and compression treatment and specific temperature and time artificial aging, which can maximize the role of T1 phase and significantly improve the strength of the alloy, far exceeding the conventional T8 process. That is, the sinusoidal waveform cyclic tension and compression treatment and the lithium element in the aluminum alloy are closely coordinated, and both are closely coordinated with the subsequent artificial aging and the previous solid solution treatment, so that the process steps and parameters as a whole are coordinated to realize the present application. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic diagram of the sinusoidal waveform cyclic tension and compression treatment curve of the present application.

[0024] Figure 2 is a micro-morphology schematic diagram of one embodiment of the present application.

[0025] Figure 3 is a micro-morphology schematic diagram of one embodiment of the present application.

[0026] Figure 4 is a load trend schematic diagram of one embodiment of the present application.

[0027] Figure 5 is a micro-morphology schematic diagram of Comparative Example 3.

[0028] Figure 6 is a micro-morphology schematic diagram of Comparative Example 3. DETAILED DESCRIPTION

[0029] The technical solutions of the present application will be further illustrated below by combining with the embodiments and the drawings. The specific embodiments are only one example of a series of equivalent or similar features unless specifically described. Only to help understand the present application, the skilled in the art should understand that the embodiments are only to help understand the present application, and should not be regarded as a specific limitation on the protection scope of the present application.

[0030] The technical solutions of the present application will be further illustrated below by combining with the embodiments and the drawings. The specific embodiments are only one example of a series of equivalent or similar features unless specifically described. Only to help understand the present application, the skilled in the art should understand that the embodiments are only to help understand the present application, and should not be regarded as a specific limitation on the protection scope of the present application.

[0031] Example 1

[0032] This embodiment uses 2195 aluminum alloy containing lithium rolling plate, the composition is 3.6-4.3wt.% of Cu, 0.8-1.2wt.% of Li, 0.25-0.8wt.% of Mg, 0.25-0.6wt.% of Ag, 0.08-0.16wt.% of Zr, less than 0.12wt.% of Si, less than 0.15wt.% of Fe, and the balance of Al. The thickness of the plate is 12mm, the solid solution temperature is 515℃, the solid solution time is 2h, and immediately after solid solution, water quenching is used, and the quenched sample is subjected to cyclic tension and compression treatment, the strain amplitude is (3-6) x 10 -3 (the example of this embodiment is set to 0.5%, i.e. 5 x 10 -3 ), the frequency is 0.2-1HZ (the example of this embodiment is set to 0.2HZ), and the cycle period is 500 times, and the load trend is shown in Figure 4 After the cyclic tension and compression treatment, artificial aging is carried out, the aging temperature is 155℃, and the peak aging time is 16 hours, which is 2h lower than the conventional T84 aging time. The main strengthening phase of 2195 aluminum alloy containing lithium is T1 (Al2CuLi), as shown in Figure 2 and Figure 3 Through microstructure analysis, the precipitated phase of 2195 aluminum alloy containing lithium after cyclic tension and compression treatment is more fine and uniform than that of T8 process, the average diameter of T1 phase is 40nm, which is 20nm lower than that of T1 phase of T84 process, and the precipitated phase density is higher; through mechanical property detection, the yield strength and tensile strength are 562±4MPa and 585±2MPa respectively, which are increased by more than 30MPa and 40MPa respectively compared with the conventional T84 process, and the elongation is 12.4%, which is reduced by about 1.7% compared with the T84 process, but the plasticity is still at a good level, that is, in the case of a large increase in strength, the plasticity is not lost too much.

[0033] Comparative Example 1

[0034] The present comparative example adopts the existing linear broken line shape cyclic reciprocating loading of Instron hydraulic blank, and other setting modes are the same as those of Example 1. The present comparative example is tested for 5 times, among which, the aluminum alloy is fractured in 4 times in the process of linear broken line shape cyclic reciprocating loading, and only 1 time is not fractured. The yield strength and tensile strength of the aluminum alloy obtained in the 1 time are about 480 MPa and about 535 MPa respectively. The Example 1 of the present application does not appear the fracture in the process, thereby indicating that the stability is relatively poor by using the linear broken line shape cyclic reciprocating loading mode of the present comparative example (this is mainly because the stress is increased at a certain ratio, which may exceed the limit that can be borne in the process, so the fracture will occur, and the present application is controlled by sinusoidal strain, not by stress, so the stability is good), and the yield strength and tensile strength of the successfully loaded aluminum alloy also decrease compared with those of the Example 1 of the present application, which indicates that the improvement of the present application on the reciprocating cyclic loading mode and specific details has very obvious advantages.

[0035] Comparative Example 2

[0036] The present comparative example adopts 2524 aluminum alloy rolling plate without lithium, and the composition thereof is 4-4.5 wt.% of Cu, 1.2-1.6 wt.% of Mg, 0.45-0.7 wt.% of Mn, less than 0.12 wt.% of Fe, less than 0.06 wt.% of Si, less than 0.05 wt.% of Cr, less than 0.1 wt.% of Ti, less than 0.15 wt.% of Zn, and the balance of Al. Other setting modes are the same as those of Example 1. Through the mechanical property detection, the yield strength and tensile strength are 505±3 MPa and 530±5 MPa respectively, which are increased by 25 MPa and 30 MPa respectively compared with the conventional T84 process, and the elongation is 10±0.2%. Although the aluminum alloys are different, the strength thereof is different, but through the comparison, it can be seen that the strength thereof is much lower than that of Example 1, and the strength increasing range of the present comparative example is not very obvious compared with the T8 treatment process of the same alloy. From this aspect, it can be compared that the aluminum alloy containing lithium uses the specific sinusoidal waveform cyclic tension and compression treatment process of the present application, and the strength increasing range is larger and more optimized.

[0037] Comparative Example 3

[0038] The present comparative example adopts the existing T8 treatment process to obtain the results shown in Figure 4 and Figure 5 Through the comparison of Figure 2 , Figure 3 and Figure 5 , Figure 6The microstructure of the 2195 lithium-containing aluminum alloy after the cyclic tensile-compressive treatment of Example 1 can be seen to have finer and more uniform precipitates than the T8 process of the comparative example. The average diameter of the T1 phase in Example 1 is 40 nm, while the average diameter of the T1 phase in the comparative example is 60 nm, which is 20 nm larger than the average diameter of the T1 phase in Example 1. The density of the precipitates is also lower. The yield strength of the comparative example is about 530 MPa, the tensile strength is about 545 MPa, and the elongation is 14.1%. Although the elongation of the comparative example is higher than that of Example 1, the yield strength and the tensile strength are both lower than those of Example 1, which proves that the method of the present application can greatly improve the strength without losing much elongation.

[0039] The above examples and comparative examples of the present application are examples and do not limit the scope of protection of the technical solutions. The technical features that are not compared do not mean that there are no outstanding substantial features, but only the setting method is described in the form of a description.

Claims

1. A method of strengthening an aluminum alloy characterized by, The aluminum alloy is an aluminum alloy containing 0.5-2.5 wt.% lithium and having a brand of 2020, 2090, 2091, 8090, 1430, 1440, 1441, 1450, 1460, 2195, 2196, 2297, 2397, 2098, 2198, 2099, 2199, 2076, 2296, 2050, 2055 or 2060, comprising the following steps: (1) heating the aluminum alloy to a supersaturated solid solution temperature single-phase zone, holding for 1-3 hours, and then quenching to room temperature using water or oil as a medium; (2) after quenching the aluminum alloy of step (1), the aluminum alloy is placed into a cyclic tensile-compressive treatment device at room temperature, and after clamping, the cyclic tensile-compressive treatment is performed, the tensile-compressive treatment is performed in a sinusoidal waveform, the tensile and compressive treatment time of each sinusoidal waveform is the same, and is 1-5s, the deformation of each cycle of tensile and compression is based on the size obtained in the previous cycle, the strain amplitude of tensile deformation is set to (2-6) x 10 -3 , the frequency of the cyclic tensile-compressive treatment is set to 0.2-1HZ, and the stress intensity of the sinusoidal waveform tensile-compressive treatment is rapidly increased before 100 times of the cyclic tensile-compressive treatment, the tensile stress intensity and the compressive stress intensity at the 100th time are 1.15-2.12 times of the tensile stress intensity and the compressive stress intensity at the first time, the stress intensity of the sinusoidal waveform tensile-compressive treatment is slowly increased from the 100th cycle to the 200th cycle, the tensile stress intensity and the compressive stress intensity at the 200th time are 1.01-1.15 times of the tensile stress intensity and the compressive stress intensity at the 100th time, the tensile stress intensity and the compressive stress intensity after the 200th time are more slowly increased, the tensile stress intensity and the compressive stress intensity every 100 times are 1-1.05 times of the tensile stress intensity and the compressive stress intensity at the end of the previous 100 times and do not contain 1 times; the number of cyclic tensile-compressive treatment is 480-600 times, and then the cyclic tensile-compressive treatment is stopped; wherein the strain ratio of the sinusoidal waveform cyclic tensile-compressive treatment is R=-1; (3) placing the aluminum alloy obtained after the cyclic tension-compression treatment in step (2) into an aging furnace, heating to 140-185℃, aging for 5-48 hours, and then cooling to room temperature to obtain the strengthened aluminum alloy.

2. The aluminum alloy strengthening method of claim 1, wherein In step (2), the cyclic tension-compression treatment device is an electronic universal mechanical testing machine or other device capable of cyclic tension-compression treatment of a sinusoidal waveform.

3. The aluminum alloy strengthening method of claim 1, wherein In step (2), the aluminum alloy is clamped, the upper part is clamped first, then the pressure is zeroed, and then the lower part is clamped, and the pressure is not zeroed when the lower part is clamped.

4. The aluminum alloy strengthening method of claim 1 wherein, In step (1), the supersaturated solid solution temperature single-phase zone is 480-550℃.

5. The aluminum alloy strengthening method of claim 1 wherein, In step (3), heating to 145-182℃, and the peak aging time is 14-30 hours.

6. The aluminum alloy strengthening method of claim 1 wherein, In step (2), the stress intensity of the tensile treatment and the stress intensity of the compression treatment of the sinusoidal waveform increase more rapidly before 50 cycles of the cyclic tension-compression treatment, and the tensile stress intensity and the compression stress intensity at the 50th cycle are 1.18-2.01 times the tensile stress intensity and the compression stress intensity at the 1st cycle.

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