Method for efficiently aging aluminum-lithium alloy on basis of dynamic strain precipitation

Abstract

A method for efficiently aging an aluminum-lithium alloy on the basis of dynamic strain precipitation. The method comprises aluminum-lithium alloy ingot casting, homogenization treatment, hot rolling, solid solution quenching treatment and aging treatment, wherein temperature-controlled and speed-controlled deformation treatment is further comprised between the solid solution quenching treatment and the aging treatment, and specifically comprises sequentially subjecting an aluminum-lithium alloy plate, which has been subjected to the solid solution quenching treatment, to preheating and temperature-controlled and speed-controlled hot rolling, and then subjecting same to cooling treatment after the hot rolling is finished, the rolling temperature of the temperature-controlled and speed-controlled hot rolling being 250-330°C, the rolling reduction being 10-30%, and the strain rate being 0.001 s-1 to 0.5 s-1. One-step temperature-controlled and speed-controlled hot rolling is used to replace cold deformation processing, thereby forming a dual distribution form in which an Al2CuLi phase (a strengthening phase) is intensively distributed on dislocation cell walls as well as uniformly distributed in dislocation cells, and the distribution form is conducive to improving the comprehensive mechanical properties of the alloy.

Description

An efficient aluminum-lithium alloy aging method based on dynamic strain precipitation Technical Field

[0001] The invention relates to the technical field of heat treatment of aluminum-lithium alloys. Background Art

[0002] New aluminum-lithium alloys (Al-Cu-Li system) are age-hardened, deformed aluminum alloys with excellent specific strength, specific stiffness, and fracture toughness, making them ideal structural materials for aerospace applications. The excellent comprehensive mechanical properties of these new aluminum-lithium alloys are inseparable from the precipitation of the primary strengthening phase, the T1 phase, during the aging process. The precipitation process in these new aluminum-lithium alloys is complex. Influenced by alloying elements, the precipitated phases include δ' (Al3Li), θ' (Al2Cu), S' (Al2CuMg), and T1 (Al2CuLi). These different precipitates exhibit distinct structural and precipitation characteristics, thus impacting alloy properties. During plastic deformation, the δ' phase causes stress concentration, degrading the alloy's plasticity. Under corrosive conditions, the θ' phase can cause pitting corrosion in the matrix. In aluminum-lithium alloys with medium and low Cu / Li ratios, the T1 phase exhibits the greatest age-hardening effect, growing at the expense of both δ' and θ' during aging.

[0003] However, during the heat treatment process, atomic (Cu) segregation zones (GP zones) are also generated in the matrix. Their strengthening effect on the matrix is ​​far less than that of the T1 phase. However, there is a competitive precipitation relationship between the T1 phase and the GP zone. The increase of the GP zone will lead to a decrease in the strength, hardness and other properties of the alloy. In order to improve the strengthening effect on the matrix, it is necessary to increase the content of the T1 phase and reduce the formation of the GP zone. In the prior art, cold deformation treatment is performed before aging treatment to introduce dislocations in the matrix to promote the precipitation of the T1 phase. In the processing of aluminum-lithium alloys, there are many heat treatment processes to improve the mechanical properties of the matrix, among which the T6 process (cold deformation + solution treatment + aging) and the T8 process (solution treatment + cold deformation + aging) are both used. It has been reported that after the 2195 aluminum-lithium alloy is solution treated, it is pre-deformed by 3-6%, and then aged. As the aging time increases, the amount of T1 phase is effectively increased. However, pre-deformation + aging treatment (T8 treatment) requires a long aging time and cannot completely inhibit the formation of GP zone, which reduces the number density of T1 phase precipitation.

[0004] Summary of the Invention

[0005] The purpose of the present invention is to provide an efficient aluminum-lithium alloy aging method based on dynamic strain precipitation, which can significantly shorten the aging treatment time of aluminum-lithium alloy and reduce the energy consumption of the process. At the same time, it promotes the precipitation of T1 phase and inhibits the formation of GP, thereby achieving the purpose of optimizing the mechanical properties of the alloy.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A high-efficiency aluminum-lithium alloy aging method based on dynamic strain precipitation includes aluminum-lithium alloy ingot casting, homogenization treatment, hot rolling, solution quenching treatment and aging treatment, characterized in that: the solution quenching treatment and aging treatment also include a temperature-controlled and speed-controlled deformation treatment, specifically, the aluminum-lithium alloy plate after the solution quenching treatment is sequentially preheated, temperature-controlled and speed-controlled hot rolling, and cooling treatment after the hot rolling is completed. The temperature-controlled and speed-controlled hot rolling is performed at a rolling temperature of 250-330°C, a rolling reduction of 10-30%, and a strain rate of 0.001s. -1 ~0.5s -1 .

[0008] The traditional aging process of aluminum-lithium alloy is usually solution treatment + cold stretching + aging (T8 process), especially two-stage aging, in which cold deformation is combined with two-stage aging to improve the formation of T1 phase in the matrix and reduce the formation of GP zone. However, a large number of GP zones still exist in the aluminum-lithium alloy treated in this way, and the aging time used in the T8 process is long, which is time-consuming and energy-intensive.

[0009] In the present invention, a temperature-controlled and speed-controlled hot rolling process is used after solution treatment to replace cold deformation. During the temperature-controlled and speed-controlled hot rolling process, a large number of dispersed and fine Al2CuLi phases (T1 phases) formed in the matrix are precipitated through dynamic strain and are simultaneously distributed in the dislocation cell walls and dislocation cells generated during the temperature-controlled and speed-controlled hot rolling deformation. The Al2CuLi phase is evenly distributed in the dislocation cells in parallel and concentrated in a stepped manner on the dislocation cell walls. This special dual distribution of precipitated phases is further strengthened during the subsequent aging process, effectively improving the comprehensive mechanical properties of the aluminum-lithium alloy. At the same time, the addition of such a specific temperature-controlled and speed-controlled hot rolling process eliminates the cold stretching step and the primary aging step, while greatly shortening the secondary aging time, effectively saving time and energy consumption.

[0010] Further preferably, the rolling temperature of the temperature-controlled and speed-controlled hot rolling is 280-320°C.

[0011] More preferably, the rolling reduction of the temperature-controlled and speed-controlled hot rolling is 15-25%.

[0012] Further preferably, the strain rate of the temperature-controlled and speed-controlled hot rolling is 0.025s -1 ~0.1s -1 .

[0013] Furthermore, the preheating is to raise the temperature of the plate after solution quenching treatment to the temperature for temperature-controlled and speed-controlled hot rolling within 2 to 8 minutes.

[0014] Preferably, the preheating time in the temperature-controlled and speed-controlled deformation treatment is 3 to 5 minutes.

[0015] Furthermore, the cooling treatment is specifically cooling by air cooling.

[0016] Furthermore, the temperature of the solution quenching treatment is 535-545° C., the solution time is 0.9-1.2 h, and after the solution is completed, quenching is performed using 25° C. cold water as the medium.

[0017] Furthermore, the aging treatment is performed at 160° C. for 8 to 15 hours, and then air-cooled to room temperature.

[0018] Most specifically, a high-efficiency aluminum-lithium alloy aging method based on dynamic strain precipitation is characterized by the following steps:

[0019] (1) A vacuum melting casting method is used to prepare an aluminum-lithium alloy ingot, wherein the alloy chemical composition of the aluminum-lithium alloy is Cu: 2.7-2.8 wt%; Li: 1.7-1.9 wt%; Mg: 0.3-0.5 wt%; Mn: 0.3-0.5 wt%; Zn: 0.5-0.7 wt%; Zr: 0.08-0.12 wt%; Si: ≤0.05 wt%; Fe ≤0.07 wt%; the balance is aluminum;

[0020] (2) homogenizing the ingot at 510°C to 530°C for 70 to 80 hours;

[0021] (3) preheating the homogenized ingot at 420°C to 460°C, keeping the temperature for 20 to 40 minutes, and then performing multiple hot rolling to form a plate;

[0022] (4) subjecting the aluminum-lithium alloy plate to a solution treatment at 535°C to 545°C for 0.5 to 1.5 h, and then quenching with cold water at 25°C;

[0023] (5) The quenched aluminum-lithium alloy plate is subjected to temperature-controlled hot rolling at 250°C to 330°C. The plate is preheated before rolling, specifically, the temperature is raised to the hot rolling temperature within 2 to 8 minutes, the rolling reduction is 10% to 30%, and the strain rate is 0.001s -1 ~0.1s -1 After rolling, the plate is cooled to room temperature by air cooling;

[0024] (6) The hot-rolled aluminum-lithium alloy plate is subjected to aging treatment at 160°C for 8 to 12 hours, and then cooled to room temperature by air cooling.

[0025] The present invention has the following technical effects:

[0026] The present invention is an efficient and environmentally friendly aluminum-lithium alloy aging method based on dynamic strain precipitation. It uses one-step temperature-controlled and speed-controlled hot rolling instead of cold stretching, eliminating the need for primary aging treatment. This creates a unique T1 precipitate distribution pattern, in which the strengthening Al2CuLi phase is simultaneously concentrated on the dislocation cell walls and evenly distributed within the dislocation cells. This distribution pattern helps improve the alloy's overall mechanical properties. At the same time, compared to the cold deformation + aging process, temperature-controlled and speed-controlled hot rolling significantly shortens the aging time, improving production efficiency and reducing energy consumption during the production process. The peak aging time is shortened from the original 36h to 48h to less than 12h. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1: Scanning electron microscope image of the aluminum-lithium alloy prepared in Example 1. DETAILED DESCRIPTION

[0028] The following examples are only used to further illustrate the present invention and are not to be construed as limiting the scope of protection of the present invention.

[0029] Example 1

[0030] An efficient aluminum-lithium alloy aging method based on dynamic strain precipitation is carried out in the following steps:

[0031] (1) A vacuum melting casting method is used to prepare an aluminum-lithium alloy ingot, wherein the alloy chemical composition of the aluminum-lithium alloy is Cu: 2.7wt%; Li: 1.8wt%; Mg: 0.4wt%; Mn: 0.4wt%; Zn: 0.6wt%; Zr: 0.1wt%; Si: 0.05wt%; Fe: 0.07wt%; the balance is aluminum;

[0032] (2) homogenizing the ingot at 520°C for 75h;

[0033] (3) preheating the homogenized ingot at 450°C, holding the ingot at that temperature for 30 minutes, and then performing multiple hot rolling to produce a plate;

[0034] (4) The aluminum-lithium alloy plate was solution treated at 540°C for 1 h and then quenched in cold water at 25°C;

[0035] (5) The quenched aluminum-lithium alloy plate was subjected to temperature-controlled hot rolling at 270°C. The plate was preheated before rolling, specifically, the temperature was raised to the hot rolling temperature within 4 minutes, the rolling reduction was 20%, and the strain rate was 0.05s -1 After rolling, the plate is cooled to room temperature by air cooling;

[0036] (6) The hot-rolled aluminum-lithium alloy sheet was aged at 160°C for 10 h and then cooled to room temperature by air cooling.

[0037] The corresponding scanning electron microscope image of the aluminum-lithium alloy prepared in Example 1 is shown in Figure 1. It can be seen from (b) that the T1 phase is uniformly distributed in the dislocation cells in the matrix. It can be clearly seen from (a) that the T1 phase is also concentrated on the dislocation cell walls, specifically in a parallel stepped distribution.

[0038] On the basis of Example 1, by adjusting the aging time, the changes in the mechanical properties of the aluminum-lithium alloy processed at different aging times were tested. The results are shown in Table 1.

[0039] Table 1: Mechanical properties of aluminum-lithium alloy samples after temperature and speed controlled hot rolling with a reduction of 20%

[0040] It can be seen that when the hot rolling reduction is 20%, the yield strength and tensile strength of the aluminum-lithium alloy increase with the increase of aging time. When the aging time is as long as 24h, although the yield strength is significantly improved, the tensile strength is not significantly improved, and the elongation of the alloy decreases seriously.

[0041] Comparative Example 1

[0042] The traditional cold deformation + long aging processing is used for processing. The specific steps are as follows:

[0043] (1) A vacuum melting casting method is used to prepare an aluminum-lithium alloy ingot, wherein the alloy chemical composition of the aluminum-lithium alloy is Cu: 2.7wt%; Li: 1.8wt%; Mg: 0.4wt%; Mn: 0.4wt%; Zn: 0.6wt%; Zr: 0.1wt%; Si: 0.05wt%; Fe: 0.07wt%; the balance is aluminum;

[0044] (2) homogenizing the ingot at 520°C for 75h;

[0045] (3) preheating the homogenized ingot at 450°C, holding the ingot at that temperature for 30 minutes, and then performing multiple hot rolling to produce a plate;

[0046] (4) The aluminum-lithium alloy plate was solution treated at 540°C for 1 h and then quenched in cold water at 25°C;

[0047] (5) pre-deform the quenched aluminum-lithium alloy plate to a deformation amount of 3 to 6%;

[0048] (6) The aluminum-lithium alloy plate after pre-deformation treatment is subjected to aging treatment at a temperature of 160°C for 16 to 36 hours, and then cooled to room temperature by air cooling.

[0049] In Comparative Example 1, the effects of deformation amount and aging time on the mechanical properties of the aluminum-lithium alloy under different conditions are shown in Table 2, where T83 and T86 represent the T8 heat treatment processes with pre-stretching amounts of 3% and 6%, respectively.

[0050] Table 2: Mechanical properties of typical aluminum-lithium alloys prepared by T8 treatment

[0051] It can be seen that under the same conditions, the increase in deformation improves the yield strength and tensile strength to a certain extent. Under the same deformation, the mechanical properties of the alloy also gradually increase with the increase in aging time. In the early stage, the elongation does not change much with the extension of aging time. When the aging time is extended to more than 36 hours, the elongation of the alloy increases significantly.

[0052] Example 2

[0053] On the basis of Example 1, the reduction during the temperature-controlled and speed-controlled hot rolling process was adjusted, and the mechanical properties of each alloy were tested. The results are shown in Table 3.

[0054] Table 3: Mechanical properties of aluminum-lithium alloy samples prepared with different reductions

[0055] As can be seen from the above table, with the increase of the reduction, the yield strength and tensile strength of the alloy gradually increase. When the reduction is 15-20%, the yield strength and tensile strength of the alloy remain at a high level, and the elongation also remains good. However, as the reduction continues to increase, although the yield strength and tensile strength also increase further, the elongation shows a significant decrease.

[0056] Example 3

[0057] An efficient aluminum-lithium alloy aging method based on dynamic strain precipitation is carried out in the following steps:

[0058] (1) A vacuum melting casting method is used to prepare an aluminum-lithium alloy ingot, wherein the alloy chemical composition of the aluminum-lithium alloy is Cu: 2.8wt%; Li: 1.9wt%; Mg: 0.5wt%; Mn: 0.5wt%; Zn: 0.7wt%; Zr: 0.12wt%; Si: ≤0.05wt%; Fe ≤0.07wt%; the balance is aluminum;

[0059] (2) homogenizing the ingot at 510°C for 80 h;

[0060] (3) preheating the homogenized ingot at 420°C, holding the ingot at that temperature for 40 minutes, and then performing multiple hot rolling to produce a plate;

[0061] (4) The aluminum-lithium alloy plate was solution treated at 535°C for 1.5 h and then quenched in cold water at 25°C;

[0062] (5) The quenched aluminum-lithium alloy plate was subjected to temperature-controlled hot rolling at 330°C. The plate was preheated before rolling, specifically, the temperature was raised to the hot rolling temperature within 2 minutes, the rolling reduction was 20%, and the strain rate was 0.001s -1 After rolling, the plate is cooled to room temperature by air cooling;

[0063] (6) The hot-rolled aluminum-lithium alloy sheet was aged at 160°C for 10 h and then cooled to room temperature by air cooling.

[0064] The mechanical properties of the aluminum-lithium alloy sample prepared in Example 3 are shown in Table 4.

[0065] Table 4: Mechanical properties of aluminum-lithium alloy samples prepared in Example 3

[0066] It can be seen from the above table that the aluminum-lithium alloy prepared in Example 3 has excellent mechanical properties.

[0067] Example 4

[0068] An efficient aluminum-lithium alloy aging method based on dynamic strain precipitation is carried out in the following steps:

[0069] (1) A vacuum melting casting method is used to prepare an aluminum-lithium alloy ingot, wherein the alloy chemical composition of the aluminum-lithium alloy is Cu: 2.8wt%; Li: 1.7wt%; Mg: 0.3wt%; Mn: 0.3wt%; Zn: 0.5wt%; Zr: 0.08wt%; Si: ≤0.05wt%; Fe ≤0.07wt%; the balance is aluminum;

[0070] (2) homogenizing the ingot at 530°C for 70 h;

[0071] (3) preheating the homogenized ingot at 460°C, holding the ingot at that temperature for 20 minutes, and then hot rolling it to form a plate;

[0072] (4) The aluminum-lithium alloy plate was solution treated at 545°C for 0.5 h and then quenched in cold water at 25°C;

[0073] (5) The quenched aluminum-lithium alloy plate was subjected to temperature-controlled hot rolling at 250°C. The plate was preheated before rolling, specifically, the temperature was raised to the hot rolling temperature within 8 minutes, the rolling reduction was 20%, and the strain rate was 0.1s -1 After rolling, the plate is cooled to room temperature by air cooling;

[0074] (6) The hot-rolled aluminum-lithium alloy sheet was aged at 160°C for 10 h and then cooled to room temperature by air cooling.

[0075] The mechanical properties of the aluminum-lithium alloy sample prepared in Example 4 are shown in Table 5.

[0076] Table 5: Mechanical properties of aluminum-lithium alloy samples prepared in Example 4

[0077] It can be seen from the above table that the aluminum-lithium alloy prepared in Example 4 has excellent mechanical properties.

Claims

1. An efficient aluminum-lithium alloy aging method based on dynamic strain precipitation, comprising aluminum-lithium alloy ingot casting, homogenization treatment, hot rolling, solution quenching treatment and aging treatment, characterized in that: The solution quenching treatment and the aging treatment also include a temperature-controlled speed deformation treatment, specifically, the aluminum-lithium alloy plate after the solution quenching treatment is preheated, temperature-controlled speed hot rolled, and cooled after the hot rolling. The rolling temperature of the temperature-controlled speed hot rolling is 250-330°C, the rolling reduction is 10-30%, and the strain rate is 0.001s -1 ~0.5s -1 .

2. The high-efficiency aluminum-lithium alloy aging method based on dynamic strain precipitation as claimed in claim 1, characterized in that: The preheating is to raise the temperature of the plate after solution quenching treatment to the temperature of temperature-controlled and speed-controlled hot rolling within 2 to 8 minutes.

3. The high-efficiency aluminum-lithium alloy aging method based on dynamic strain precipitation as claimed in claim 1 or 2, characterized in that: The temperature of the solution quenching treatment is 535-545° C., the solution time is 0.9-1.2 h, and after the solution is completed, quenching is performed using 25° C. cold water as the medium.

4. The high-efficiency aluminum-lithium alloy aging method based on dynamic strain precipitation as claimed in claim 3, characterized in that: The aging treatment is performed at 160° C. for 8 to 15 hours, followed by air cooling to room temperature.

5. An efficient aluminum-lithium alloy aging method based on dynamic strain precipitation, characterized in that: Proceed as follows: (1) A vacuum melting method is used to prepare an aluminum-lithium alloy ingot, wherein the alloy chemical composition of the aluminum-lithium alloy is Cu: 2.7-2.8wt%; Li: 1.7-1.9wt%; Mg: 0.3-0.5wt%; Mn: 0.3-0.5wt%; Zn: 0.5-0.7wt%; Zr: 0.08-0.12wt%; Si: ≤0.05wt%; Fe ≤0.07wt%; the balance is aluminum; (2) homogenizing the ingot at 510°C to 530°C for 70 to 80 hours; (3) preheating the homogenized ingot at 420°C to 460°C, keeping the temperature for 20 to 40 minutes after the ingot reaches the temperature, and then hot rolling to form a plate; (4) subjecting the aluminum-lithium alloy plate to a solution treatment at 535°C to 545°C for 0.5 to 1.5 h, and then quenching with cold water at 25°C; (5) The quenched aluminum-lithium alloy plate is subjected to temperature-controlled hot rolling at 250°C to 330°C. The plate is preheated, specifically, it is heated to the hot rolling temperature within 2 to 8 minutes, the rolling reduction is 10% to 30%, and the strain rate is 0.001s -1 ~0.1s -1 After rolling, the plate is cooled to room temperature by air cooling; (6) The hot-rolled aluminum-lithium alloy sheet is subjected to aging treatment at 160° C. for 8 to 15 h, and then cooled to room temperature by air cooling.

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