A method for reducing exfoliation corrosion susceptibility of aluminum-lithium alloy and aluminum-lithium alloy

Abstract

The present application relates to a kind of organization regulation method for reducing exfoliation corrosion sensitivity of aluminum lithium alloy and aluminum lithium alloy, belong to alloy heat treatment field.The method includes: aluminum lithium alloy ingot is treated, obtains homogenization state alloy;Again homogenization state alloy is sequentially deformed, solution treatment, grading quenching and aging treatment, namely obtains;The deformation of deformation treatment is 70~95%;Solution treatment temperature is 500~540 DEG C, time is 2~5h;Grading quenching system is scheme (a) or scheme (b):Scheme (a):alloy is cooled to 400~450 DEG C and keeps 1~5min then water quenching is cooled to 10~30 DEG C;Scheme (b):alloy is cooled to 250~300 DEG C and keeps 5~20min then water quenching is cooled to 10~30 DEG C.The method can effectively reduce the exfoliation corrosion sensitivity of aluminum lithium alloy by regulating alloy surface layer grain shape and blocking corrosion channel.

Description

Technical Field

[0001] This invention relates to a microstructure control method for reducing the susceptibility of aluminum-lithium alloys to exfoliation corrosion and to aluminum-lithium alloys, belonging to the field of alloy heat treatment. Background Technology

[0002] Aluminum-lithium alloys possess advantages such as high specific strength, high specific stiffness, and low density, making them widely used in aerospace and other fields. They are among the most competitive structural materials in the aerospace industry. However, the presence of the reactive element lithium increases the susceptibility of aluminum-lithium alloys to localized corrosion under complex service environments. Exfoliation corrosion, a special form of intergranular corrosion, mainly occurs through corrosion channels created by galvanic corrosion (precipitated phase / solute depletion region) at fine grains and grain boundaries. Exfoliation corrosion is one of the main forms of localized corrosion in aluminum alloys, causing significant damage to their strength, plasticity, and fatigue properties, thus shortening their service life.

[0003] Compared to traditional aluminum alloys, aluminum-lithium alloy sheets are generally not clad with aluminum and are used directly as "bare materials," which places higher demands on the aluminum-lithium alloy's resistance to exfoliation corrosion.

[0004] Therefore, developing a method to reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion is of great significance. Summary of the Invention

[0005] To address the problems existing in the prior art, one of the objectives of this invention is to provide a microstructure control method for reducing the susceptibility of aluminum-lithium alloys to exfoliation corrosion. This method can effectively reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion by controlling the grain shape of the alloy surface and blocking corrosion channels.

[0006] The second objective of this invention is to provide an aluminum-lithium alloy that has excellent mechanical properties and resistance to exfoliation corrosion.

[0007] To achieve the above objectives, a first aspect of the present invention provides a method for microstructure control to reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion, the method comprising:

[0008] (1) The aluminum-lithium alloy ingot is homogenized to obtain a homogenized alloy.

[0009] (2) The homogenized alloy is then subjected to deformation treatment, solution treatment, staged quenching and aging treatment in sequence to obtain the desired product;

[0010] The deformation amount in the deformation treatment is 70-95%;

[0011] The solution treatment is performed at a temperature of 500~540℃ for 2~5 hours.

[0012] The graded quenching system is either scheme (a) or scheme (b):

[0013] Option (a): The alloy after solution treatment is cooled to 400~450℃ in the first stage and held for 1~5 min, and then water-quenched to 10~30℃ in the second stage.

[0014] Option (b): The alloy after solution treatment is cooled to 250~300℃ in the first stage and held for 5~20min, and then water-quenched to 10~30℃ in the second stage.

[0015] This invention introduces greater deformation energy storage into the product surface through large deformation treatment (70-95% deformation). Subsequent high-temperature (500-540℃) long-term solution treatment achieves full solution and recrystallization, transforming the slender grains into coarse equiaxed grains dominated by large-angle grain boundaries. Through staged quenching, discontinuously distributed coarse, Cu-rich phases (Al-Cu phases) with relatively positive corrosion potentials are formed at these large-angle grain boundaries. The corrosion potential of these coarse Cu-rich phases is greater than that of the alloy matrix, blocking the path of corrosion crack propagation and thus reducing the alloy's susceptibility to exfoliation corrosion. The coarse equiaxed grains on the surface are beneficial in reducing exfoliation corrosion sensitivity. The large-angle grain boundaries and the coarse Cu-rich phases precipitated during staged quenching are unfavorable for the precipitation of the T1 phase (Al2CuLi phase) at the grain boundaries. After aging, the alloy grain boundaries are dominated by discontinuously distributed coarse Al-Cu phases. These coarse Al-Cu phases have a more positive corrosion potential than the Al matrix, making them more difficult to corrode and effectively blocking the path of corrosion crack propagation.

[0016] Furthermore, reducing the amount of deformation treatment, lowering the solution treatment temperature, or shortening the holding time will all lead to a decrease in the degree of recrystallization of the aluminum-lithium alloy surface, thereby increasing its susceptibility to exfoliation corrosion. Simultaneously, if the quenching temperature of the first stage is set outside the range of this invention, a large number of solute atoms will be consumed, significantly reducing the density of the fine strengthening phase T1 (Al2CuLi phase), resulting in a drastic decline in the performance of the aluminum-lithium alloy. At the same time, there will be more corrosion products from the coarse precipitates, leading to greater stress concentration at the corrosion crack tips and easier propagation, thus increasing the susceptibility of the aluminum-lithium alloy to exfoliation corrosion. If staged quenching is not performed, since the solute atoms at the grain boundaries are not consumed, a continuously distributed fine T1 phase appears at the grain boundaries after aging. This continuously distributed fine T1 phase (Al2CuLi phase) also promotes corrosion propagation, easily leading to exfoliation corrosion.

[0017] This invention effectively reduces the spalling corrosion susceptibility of aluminum-lithium alloys through the synergistic effect between recrystallized particles and the Al-Cu phase formed on the surface of the aluminum-lithium alloy.

[0018] As a preferred embodiment, the homogenization treatment conditions are: heat treatment at 380~470 °C for 12~18 h, followed by heat treatment at 480~520 °C for 18~36 h;

[0019] The deformation process is extrusion or rolling.

[0020] As a preferred embodiment, the graded quenching process is embodiment (a).

[0021] As a preferred embodiment, in embodiment (a), the cooling rate in the first stage is 100~300℃ / min;

[0022] In scheme (b), the cooling rate in the first stage is 200~400℃ / min.

[0023] As a more preferred embodiment, in embodiment (b), the cooling rate of the first stage is 300~400℃ / min.

[0024] As a preferred option, in staged quenching, the first stage of cooling is carried out in a salt bath furnace.

[0025] As a preferred embodiment, the deformation amount of the deformation treatment is 91-95%;

[0026] The solution treatment is performed at a temperature of 500-540℃ for 3-5 hours.

[0027] As a preferred embodiment, the aging treatment process is as follows: pre-deformation amount is 0~5%, temperature is 140~180℃, and time is 24~72h.

[0028] As a preferred embodiment, the raw material of the aluminum-lithium alloy ingot contains Al, Cu, Li and X, wherein X is selected from at least one of Mg, Ag, Zn, Mn and Zr;

[0029] The content of Cu is 3-4.5 wt% by mass, the content of Li is 0.6-2.0 wt%, and the mass ratio of Cu to Li is >2.5; the content of X is >0, wherein the content of Mg is 0-0.8 wt%, the content of Ag is 0-0.7 wt%, the content of Zn is 0-0.5 wt%, the content of Mn is 0-0.5 wt%, and the content of Zr is 0-0.2 wt%, with the balance being unavoidable impurities and Al. In aluminum-lithium alloys, the composition and the various second phases formed are relatively complex. Cu and Li are the main alloying elements. The limiting solid solubility of Cu in Al is about 5.65 wt%. Appropriate addition can reduce the width of the precipitation-free zone (PFZ), improve strength, and improve ductility and toughness. However, excessive Cu content will increase density, generate intermediate phases, and reduce toughness, while excessive Cu content will lead to a reduction in the main strengthening phases θ' and T1 phase, thus reducing the strengthening effect. The limiting solid solubility of Li in Al is approximately 4.2 wt.%. Appropriate addition can significantly reduce density and increase elastic modulus. However, excessive Li content leads to the early precipitation of a large amount of δ' phase, inhibiting the precipitation of S and Ti phases. A low Cu / Li mass ratio increases the tendency to form coarse Ti phases during staged quenching. Ti phases are more susceptible to corrosion than the matrix and cannot effectively prevent corrosion crack propagation. A Cu / Li mass ratio greater than 2.5 provides better corrosion resistance. Furthermore, the introduction of X element can further improve the overall performance of lithium alloys.

[0030] As a preferred embodiment, the raw materials for the aluminum-lithium alloy ingot, by mass, contain 3-4.5 wt% Cu, 0.6-2.0 wt% Li, with a Cu to Li mass ratio >2.5, 0.2-0.8 wt% Mg, 0.2-0.7 wt% Ag, 0.1-0.5 wt% Mn, and 0.1-0.2 wt% Zr, with the balance being unavoidable impurities and Al. Mg has high solid solubility and a strong solid solution strengthening effect. When Mg+Ag is added in combination, Mg-Ag atomic clusters are formed, promoting the nucleation and precipitation of the T1 phase, which is beneficial to improving the alloy strength. Appropriate amounts of Mn and Zr can form Al... 20 Dispersed Cu2Mn3 and Al3Zr particles inhibit alloy recrystallization, thereby controlling grain size and improving ductility and toughness.

[0031] As another preferred embodiment, the raw materials for the aluminum-lithium alloy ingot, by mass, contain 3-4.5 wt% Cu, 0.6-2.0 wt% Li, with a Cu to Li mass ratio >2.5, 0.2-0.8 wt% Mg, 0.2-0.5 wt% Zn, 0.3-0.5 wt% Mn, and 0.1-0.2 wt% Zr, with the balance being unavoidable impurities and Al. The combined addition of Mg and Zn promotes the nucleation and precipitation of the T1 phase, which is beneficial for improving alloy strength. Furthermore, Zn can increase the corrosion potential of the coarse-grained Cu-rich phase at grain boundaries, thus reducing susceptibility to exfoliation corrosion.

[0032] As a more preferred option, the mass ratio of Cu to Li is >3.

[0033] As a further preferred embodiment, the mass ratio of Cu to Li is 3 to 4. The inventors have found that, under this preferred condition, the lithium alloy exhibits superior corrosion resistance.

[0034] As a preferred embodiment, the raw materials for preparing the aluminum-lithium alloy ingot are sequentially smelted and cast to obtain the aluminum-lithium alloy ingot. This invention does not impose special requirements on the smelting and casting parameters; those known in the art can be used.

[0035] The second aspect of the present invention provides an aluminum-lithium alloy prepared by the tissue regulation method described in the first aspect above.

[0036] As a preferred embodiment, the surface of the aluminum-lithium alloy contains recrystallized grains, the grain boundaries contain discontinuously distributed Al-Cu phases, the interior of the grains is an Al2CuLi phase, and the area of ​​the recrystallized grains on the surface is greater than 90%.

[0037] Compared with the prior art, the present invention has at least the following advantages:

[0038] The microstructure control method provided by this invention can effectively reduce the exfoliation corrosion sensitivity of aluminum-lithium alloys while still maintaining their excellent mechanical properties. Attached Figure Description

[0039] Figure 1 This is a flowchart of the present invention;

[0040] Figure 2 These are the electron backscatter diffraction pattern and transmission electron microscope image of the aluminum-lithium alloy prepared in Example 1;

[0041] Figure 3 The electron backscatter diffraction pattern and transmission electron microscope image of the aluminum-lithium alloy prepared in Comparative Example 3 are shown.

[0042] Figure 4This is a transmission electron microscope image of the aluminum-lithium alloy prepared in Comparative Example 4.

[0043] Figure 5 This is a transmission electron microscope (TEM) image of the aluminum-lithium alloy prepared in Comparative Example 5. Detailed Implementation

[0044] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0045] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments. Obviously, the embodiments described below are only a part of the embodiments, and all other embodiments obtained by those skilled in the art without creative effort are still within the scope of protection of the present invention.

[0046] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0047] Example 1

[0048] The composition of the aluminum-lithium alloy raw material is: Cu 3.5wt.%, Li 0.9wt.%, Mg 0.4wt.%, Ag 0.45wt.%, Mn 0.35wt.%, Zr 0.10wt.%, unavoidable impurities <0.05wt%, and the balance is Al.

[0049] Based on the alloy composition, the experimental raw materials were pure Al, pure Cu, pure Li, pure Mg, pure Ag, Al-Mn master alloy, and Al-Zr master alloy, respectively. These were melted and cast at 720–750 °C and 710–720 °C to obtain ingots. The ingots were then homogenized (held at 470 °C for 16 h, followed by holding at 500 °C for 24 h). h), to obtain a homogenized alloy; the homogenized alloy is rolled sequentially with a total deformation of 90% to obtain a rolled plate, the rolled plate is solution treated (solution temperature of 530℃, holding time of 2.5h, with furnace heating), after the solution treatment is completed, a graded quenching treatment is performed, the graded quenching regime is as follows: the solution treated plate is cooled from 530℃ to 280℃ and held for 10min (in a salt bath furnace, cooling rate of 300℃ / min), and then water quenched to room temperature to obtain a quenched plate; the quenched plate is aged (rolling pre-deformation of 5%, aging temperature of 145℃, holding time of 24h) to obtain an aluminum-lithium alloy.

[0050] Example 2

[0051] This embodiment is carried out in a similar manner to that of Embodiment 1. The difference is that (1) the graded quenching process is as follows: the plate with solid solution treatment is cooled from 530°C to 430°C and held for 2 minutes (cooling rate is the same as in Embodiment 1), and then water quenched to room temperature to finally obtain aluminum-lithium alloy.

[0052] Example 3

[0053] This embodiment is carried out using a method similar to that of Embodiment 1, except that (1) the deformation treatment is performed by extrusion, with a total deformation of 95%; and (2) the solution treatment is performed at a solution temperature of 530°C for 4 hours, with the temperature increased in the furnace. The remaining process parameters are the same as those in Embodiment 1, and an aluminum-lithium alloy is finally obtained.

[0054] Example 4

[0055] This embodiment is carried out using a method similar to that of Example 1, except that the alloy composition is different. Specifically, the alloy composition in this embodiment is: Cu 3.8 wt.%, Li 1.2 wt.%, Mg 0.4 wt.%, Zn 0.4 wt.%, Mn 0.4 wt.%, Zr 0.12 wt.%, unavoidable impurities <0.05 wt%, and the balance is Al. The preparation steps are the same as in Example 1, and an aluminum-lithium alloy is finally obtained.

[0056] Example 5

[0057] This embodiment is carried out using a method similar to that of Example 1, except that the alloy composition is different. Specifically, the alloy composition in this embodiment is: Cu 2.5wt.%, Li 1.3wt.%, Mg 0.4wt.%, Ag 0.43wt.%, Mn 0.36wt.%, Zr 0.10wt.%, unavoidable impurities <0.05wt%, and the balance is Al. The preparation steps are the same as in Example 1, and an aluminum-lithium alloy is finally obtained.

[0058] Comparative Example 1

[0059] This comparative example was conducted using a method similar to that of Example 1, except that: (1) the total deformation during rolling was 60%; (2) the solution treatment was performed at a temperature of 480°C for 1 hour, with the temperature increased in the furnace; and (3) no graded quenching was used, and the solution was directly water-quenched to room temperature after the solution treatment was completed. The remaining process parameters were the same as in Example 1, and an aluminum-lithium alloy was finally obtained.

[0060] Comparative Example 2

[0061] This comparative example was carried out using a method similar to that of Example 1, except that the total deformation during rolling was 60%.

[0062] Comparative Example 3

[0063] This comparative example was carried out using a method similar to that of Example 1, except that the solution treatment process was performed at a solution temperature of 480°C for 1 hour, with the temperature increased during furnace heating.

[0064] Comparative Example 4

[0065] This comparative example was carried out using a method similar to that of Example 1, except that the graded quenching process involved cooling the solution-treated plate from 530°C to 430°C and holding it at that temperature for 1 hour (cooling rate was the same as in Example 1), followed by water quenching to room temperature.

[0066] Comparative Example 5

[0067] This comparative example was carried out using a method similar to that of Example 1, except that a graded quenching process was not used; instead, the sample was directly water-quenched to room temperature after solution treatment.

[0068] Test case

[0069] The mechanical properties and exfoliation corrosion resistance of the aluminum-lithium alloy prepared above were tested, and the specific results are shown in Table 1. The test standard for mechanical properties is GB / T 16865-2013, and the test standard for exfoliation corrosion resistance is GB / T22639-2022.

[0070]

[0071] The microstructure of the aluminum-lithium alloys prepared in the above examples was characterized, specifically, Figure 2 This is a microstructure diagram of the aluminum-lithium alloy prepared in Example 1. Figure 2 The left image in the middle is the EBSD graph. Figure 2 The image on the right is a TEM image; from Figure 2 As can be seen, the surface layer of the aluminum-lithium alloy is basically fully recrystallized (the recrystallized grains account for 93.2% of the surface layer), and the grains are coarse equiaxed grains, dominated by large-angle grain boundaries, with discontinuously distributed coarse Al-Cu phases at the grain boundaries. The coarse equiaxed grains on the surface layer help reduce the susceptibility to exfoliation corrosion. The large-angle grain boundaries and the coarse Al-Cu phase precipitated during the staged quenching process are not conducive to the precipitation of the T1 phase (Al2CuLi) at the grain boundaries. After aging, the alloy grain boundaries are dominated by discontinuously distributed coarse Al-Cu phases. The corrosion potential of the coarse Al-Cu phase is more positive than that of the Al matrix, making it more difficult to corrode. It can effectively block the path of corrosion crack propagation and reduce the susceptibility of the alloy to exfoliation corrosion.

[0072] Figure 3 This is a microstructure diagram of the aluminum-lithium alloy prepared in Comparative Example 3. Figure 3 The left image in the middle is the EBSD graph. Figure 3 The rightmost one in the middle is TEM; from Figure 3 As can be seen, Comparative Example 3 still contains a large number of fibrous deformed grains and numerous subgrain boundaries. Subgrain boundaries are conducive to the precipitation of the T1 phase, resulting in a continuous distribution of coarse T1 phase at the grain boundaries. The corrosion potential of the T1 phase is more negative than that of the Al matrix, so it will preferentially corrode. The continuous distribution of the T1 phase at grain boundaries is an excellent path for corrosion propagation, which will greatly increase the alloy's susceptibility to exfoliation corrosion.

[0073] Figure 4 The image shows a TEM image of the aluminum-lithium alloy prepared in Comparative Example 4; from Figure 4 As can be seen, the presence of extremely coarse (greater than 1 μm) precipitates in the alloy consumes a large number of solute atoms, and the density of the fine strengthening phase T1 is greatly reduced, resulting in a sharp decline in the performance of the aluminum-lithium alloy. At the same time, the coarse precipitates produce more corrosion products, leading to greater stress concentration at the corrosion crack tip, which is more likely to propagate and also increases the spalling corrosion sensitivity of the aluminum-lithium alloy.

[0074] Figure 5 The image shows a TEM image of the aluminum-lithium alloy prepared in Comparative Example 5; from Figure 5 As can be seen, without graded quenching, the solute atoms at the grain boundaries are not consumed. After aging, a continuous distribution of fine T1 phase appears at the grain boundaries. The continuous distribution of fine T1 phase is also conducive to the spread of corrosion and makes it easy for exfoliation corrosion to occur.

[0075] The experimental results above show that the aluminum-lithium alloy products treated by the method of the present invention exhibit significantly reduced exfoliation corrosion sensitivity. Examples 1-3 show increased strength and reduced exfoliation corrosion sensitivity compared to Comparative Examples 1-4. Comparative Example 5, an aluminum-lithium alloy product prepared by a conventional solution-water quenching method, has strength essentially equivalent to Examples 1-3, but its exfoliation corrosion sensitivity is significantly higher. Therefore, the microstructure control method provided by the present invention can effectively reduce the exfoliation corrosion sensitivity of the alloy.

[0076] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for controlling the microstructure to reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion, characterized in that: (1) The aluminum-lithium alloy ingot is homogenized to obtain a homogenized alloy. (2) The homogenized alloy is then subjected to deformation treatment, solution treatment, staged quenching and aging treatment in sequence to obtain the desired product; The deformation amount in the deformation treatment is 70-95%; The solution treatment is performed at a temperature of 500~540℃ for 2~5 hours. The graded quenching system is either scheme (a) or scheme (b): Option (a): The alloy after solution treatment is cooled to 400~450℃ in the first stage and held for 1~5 min, and then water-quenched to 10~30℃ in the second stage. Option (b): The alloy after solution treatment is first cooled to 250~300℃ and held for 5~20min, and then water quenched to 10~30℃ in the second stage; The raw materials of the aluminum-lithium alloy ingot contain Al, Cu, Li and X, wherein X is selected from at least one of Mg, Ag, Zn, Mn and Zr; The content of Cu is 3-4.5 wt% by mass, the content of Li is 0.6-2.0 wt%, and the mass ratio of Cu to Li is >2.5; the content of X is >0, wherein the content of Mg is 0-0.8 wt%, the content of Ag is 0-0.7 wt%, the content of Zn is 0-0.5 wt%, the content of Mn is 0-0.5 wt%, and the content of Zr is 0-0.2 wt%, with the balance being unavoidable impurities and Al.

2. The microstructure control method for reducing the susceptibility of aluminum-lithium alloys to exfoliation corrosion according to claim 1, characterized in that: The homogenization treatment conditions are: heat treatment at 380~470 °C for 12~18 h, and then heat treatment at 480~520 °C for 18~36 h; The deformation process is extrusion or rolling.

3. A method for controlling the microstructure to reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion according to claim 1 or 2, characterized in that: In scheme (a), the cooling rate in the first stage is 100~300℃ / min; In scheme (b), the cooling rate in the first stage is 200~400℃ / min.

4. A method for controlling the microstructure to reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion according to claim 1 or 2, characterized in that: The deformation amount of the deformation treatment is 91%~95%; The solution treatment is performed at a temperature of 500-540℃ for 3-5 hours.

5. A method for controlling the microstructure to reduce the susceptibility of aluminum-lithium alloys to exfoliation corrosion according to claim 1 or 2, characterized in that: The aging process is as follows: the pre-deformation amount is 0~5%, the temperature is 140~180℃, and the time is 24~72h.

6. The microstructure control method for reducing the susceptibility of aluminum-lithium alloys to exfoliation corrosion according to claim 1, characterized in that: The raw materials for the aluminum-lithium alloy ingot contain, by mass, 3-4.5 wt% Cu, 0.6-2.0 wt% Li, with a Cu to Li mass ratio >2.5, 0.2-0.8 wt% Mg, 0.2-0.7 wt% Ag, 0.1-0.5 wt% Mn, and 0.1-0.2 wt% Zr, with the balance being unavoidable impurities and Al.

7. An aluminum-lithium alloy prepared by the tissue regulation method according to any one of claims 1 to 6.

8. The aluminum-lithium alloy according to claim 7, characterized in that: The surface of the aluminum-lithium alloy contains recrystallized grains, the grain boundaries contain discontinuously distributed Al-Cu phases, the interior of the grains is an Al2CuLi phase, and the area of ​​the recrystallized grains on the surface is greater than 90%.

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