A method for controlling weld defects in stir and friction welding of 2195 aluminum-lithium alloy plates

Abstract

This invention relates to a method for controlling defects in 2195 aluminum-lithium alloy plates and friction stir welds, belonging to the field of manufacturing technology for ultra-large storage tank bottoms. Specifically, addressing the challenge of controlling weld defects in 2195 aluminum-lithium alloy plates using friction stir welding, the method comprehensively plans and designs the process path for controlling defects in the 2195 aluminum-lithium alloy plate friction stir welding process. A two-stage aging process is adopted to maintain the small size and abundant dispersed distribution of the strengthening phases T1, δ′, and β′. Through stepped heat treatment, residual stress is reduced / eliminated while the strengthening phases in the weld and base metal tend to be synergistic and consistent, ensuring the thermal stability of the strengthening phases δ′ and β′, effectively pinning grain boundaries and inhibiting grain growth. The abundant T1 phase ensures the strength level of the weld and improves the continuity of the microstructure at the base metal-weld interface.

Description

Technical Field

[0001] This application belongs to the field of manufacturing technology of ultra-large storage tank bottoms, and relates to a method for controlling weld defects in friction stir welding (FSW) of aluminum-lithium alloy plates, and particularly to a method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates. Background Technology

[0002] Employing more efficient rocket body structures and lighter, higher-strength rocket body structural materials is an effective way to achieve lightweight and high reliability in launch vehicles. To meet the requirements for lightweighting and high reliability of ultra-large launch vehicles, a demand has been placed on the integral manufacturing technology of the Φ5000mm diameter 2195 aluminum-lithium alloy propellant tank hemispherical shell.

[0003] For the hemispherical shell of an ultra-large, lightweight, high-strength 2195 aluminum-lithium alloy storage tank with an inner diameter ≥ Ф5000mm, a height ≥ 1200mm, and a wall thickness ≤ 2mm, the width of the sheet metal used for its integral forming must be greater than 5000mm. However, the maximum width of the sheet metal currently available in China is 4300mm, and after trimming, the effective width of the sheet metal is ≤ 4100mm, which cannot meet the integral forming requirements of the Ф5000mm-class ultra-large, lightweight, high-strength 2195 aluminum-lithium alloy storage tank hemispherical shell. However, by employing welding technology, assembling and welding smaller sheet metal into ultra-wide sheet metal with a width greater than 5000mm, the raw material requirement for the integral forming of the ultra-large 2195 aluminum-lithium alloy storage tank hemispherical shell can be solved.

[0004] The following are some of the processes for welding small-width plates into large-width plates: argon arc welding, laser welding, electron beam welding, friction stir welding, etc. Among them, friction stir welding has a high welding coefficient (≥0.8) and is particularly suitable for the assembly and connection of aluminum alloy materials such as 2219 and 2195. Therefore, it is widely used in the preparation of large-width / ultra-large-width aluminum alloy plates in the aerospace field.

[0005] The main challenge of assembling and connecting small-width 2195 aluminum-lithium alloy plates into large-width 2195 aluminum plates using friction stir welding is that incomplete fusion often occurs at the weld seams after friction stir welding. Additionally, the microstructure at the weld seams is uneven, with significant differences between the microstructure of the base material and the weld seams. Furthermore, abnormal grain growth is highly likely to occur in the weld microstructure after friction stir welding, severely affecting the mechanical properties of the 2195 aluminum plate weld seams and leading to instability and cracking at the weld seams during subsequent overall forming. Summary of the Invention

[0006] The technical problem solved by this application is to overcome the shortcomings of the prior art and provide a method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates. The method uses a two-stage aging process to ensure the uniform and dispersed precipitation of the strengthening phase at the weld, pinning grain boundaries and inhibiting abnormal grain growth at the weld. The method uses a stepped heat treatment process to regulate the uniformity of the weld microstructure, so that the second phase of the weld and the base metal are consistent and coordinated. This reduces / eliminates residual stress while improving the continuity of the microstructure at the base metal-weld interface.

[0007] The technical solution provided in this application is as follows:

[0008] A method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates includes the following steps:

[0009] S1. Prepare small-width 2195 aluminum-lithium alloy plates;

[0010] S2. The small-width 2195 aluminum-lithium alloy sheet is subjected to solution treatment and two-stage aging treatment in sequence.

[0011] S3. Carry out milling and polishing of small-width 2195 aluminum-lithium alloy plates;

[0012] S4. At least two small-width 2195 aluminum-lithium alloy plates are welded together by friction stir welding to prepare a large-width 2195 aluminum-lithium alloy plate. The width of the small-width 2195 aluminum-lithium alloy plate is smaller than the width of the large-width 2195 aluminum-lithium alloy plate, so it is a small-width 2195 aluminum-lithium alloy plate.

[0013] S5. Step heat treatment of wide 2195 aluminum-lithium alloy plates.

[0014] The solution treatment process involves holding at 520–540℃ for 90–150 minutes followed by quenching, with a quenching transfer time ≤40 seconds.

[0015] The two-stage aging process includes sequential low-temperature pre-aging and high-temperature aging. The low-temperature pre-aging involves holding at 100–120°C for 4–8 hours followed by air cooling, while the high-temperature aging involves holding at 170–180°C for 32–36 hours followed by air cooling.

[0016] After the two-stage aging treatment, the second phase δ′ and β′ phases in the small-width 2195 aluminum-lithium alloy sheet are diffusely distributed and have sizes ranging from 20 to 50 nm and 20 to 70 nm, respectively; at the same time, a large amount of T1 phase is precipitated in the alloy. The T1 phase is uniformly distributed in a needle-like parallel arrangement and has a size ranging from 100 to 150 nm.

[0017] The milled and polished surface is the subsequent welding surface of the narrow-width 2195 aluminum-lithium alloy sheet, with a surface roughness of 6.3 and a flatness of ≤0.1.

[0018] Wide 2195 aluminum-lithium alloy plates were obtained by friction stir welding and then subjected to step heat treatment to reduce / eliminate internal residual stress, while achieving synergistic consistency of strengthening phases in the weld and the base material, thereby inhibiting abnormal grain growth at the weld location.

[0019] The stepped heat treatment includes:

[0020] The wide 2195 aluminum-lithium alloy sheet is placed in a heat treatment furnace and heated to 260-330℃ with a heating rate of 5-8℃ / s and a holding time of 16-18h.

[0021] Continue heating the furnace to 360–460℃ at a rate of 3–5℃ / h, and hold for 12–14 hours.

[0022] The furnace temperature is lowered to 260–330℃ at a rate of 3–5℃ / h, and the holding time is 4–6h.

[0023] The large-width 2195 aluminum-lithium alloy sheet is taken out of the furnace and air-cooled until it reaches room temperature.

[0024] During the stepped heat treatment process, the δ′ and β′ phases located at the grain boundaries have strong thermal stability, which can pin the grain boundaries and effectively inhibit abnormal grain growth in the weld. At the same time, a large amount of T1 phase ensures the strength level of the weld and improves the continuity of the microstructure at the base material-weld interface.

[0025] A 2195 aluminum-lithium alloy sheet is prepared using any of the above-described methods for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy sheets.

[0026] In summary, this application includes at least the following beneficial technical effects:

[0027] (1) This invention addresses the problem of difficult weld defect control in friction stir welding of 2195 aluminum-lithium alloy plates. It comprehensively plans and designs a process path for friction stir welding and weld defect control of 2195 aluminum-lithium alloy plates. Through a two-stage aging process, the strengthening phases T1 phase, δ′ phase, and β′ phase are kept small in size and widely dispersed. Through stepped heat treatment, the strengthening phases in the weld and the base material tend to be synergistic and consistent while reducing / eliminating residual stress. This ensures the thermal stability of the strengthening phases δ′ phase and β′ phase, effectively pinning grain boundaries and inhibiting grain growth. The large amount of T1 phase ensures the strength level of the weld and improves the continuity of the microstructure at the base material-weld interface.

[0028] (2) The present invention performs a solution treatment on 2195 aluminum-lithium alloy plates before friction stir welding. The solution temperature is 520-540℃ and the holding time is 90-150min. After the holding time is completed, the plates are quenched. The quenching transfer time is ≤40s, which ensures the supersaturation of the alloy after solution treatment and lays the foundation for subsequent aging precipitation.

[0029] (3) In this invention, a two-stage aging treatment is performed on 2195 aluminum-lithium alloy plates before friction stir welding. The pre-aging temperature is 100-120℃, the holding time is 4-8h, and the plates are air-cooled after the holding time is completed. The high-temperature aging temperature is 170-180℃, the holding time is 32-36h, and the plates are air-cooled after the holding time is completed. The two-stage aging ensures that the second phases δ′ and β′ in the alloy are dispersed and have a size of 50-80nm. At the same time, a large amount of T1 phase is precipitated in the alloy. The T1 phase is uniformly distributed and has a size of 100-150nm.

[0030] (4) The step heat treatment process of the present invention on the 2195 aluminum-lithium alloy plate after friction stir welding reduces / eliminates the residual stress of the assembly D while achieving synergistic consistency between the strengthening phases in the weld and the base material.

[0031] (5) In the step heat treatment process of 2195 aluminum-lithium alloy plate after friction stir welding, the δ′ phase and β′ phase located at the grain boundary can pin the grain boundary and effectively inhibit abnormal grain growth in the weld. At the same time, a large amount of T1 phase ensures the strength level of the weld and improves the continuity of the structure of the base material-weld interface.

[0032] (6) This invention relates to a method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates. It comprehensively plans and designs the process path for friction stir welding and weld defect control of 2195 aluminum-lithium alloy plates, and adopts a two-stage aging process to keep the strengthening phases T1 phase, δ′ phase, and β′ phase small in size and widely dispersed. Through step heat treatment, while reducing / eliminating residual stress, the strengthening phases in the weld and the base material tend to be consistent, ensuring the thermal stability of the strengthening phases δ′ phase and β′ phase, effectively pinning grain boundaries and inhibiting grain growth. The large amount of T1 phase ensures the strength level of the weld and improves the continuity of the microstructure of the base material-weld interface. Attached Figure Description

[0033] Figure 1 A schematic diagram of a 1000mm×1000mm×30mm square plate;

[0034] Figure 2a This is a schematic diagram of the δ′ phase in a dark-field image obtained by transmission electron microscopy.

[0035] Figure 2b This is a schematic diagram of the β′ phase in a bright-field image obtained by transmission electron microscopy.

[0036] Figure 2c This is a schematic diagram of the T1 phase in a dark-field image obtained by a transmission electron microscope.

[0037] Figure 3 This is a schematic diagram of the friction stir welding process;

[0038] Figure 4a This is a schematic diagram showing the location of the δ′ phase at the grain boundary in a bright-field image from a transmission electron microscope.

[0039] Figure 4b This is a schematic diagram showing the location of the β′ phase and T1 phase at the grain boundary in a dark-field image obtained by transmission electron microscopy. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments disclosed in the present invention will be described in further detail below with reference to the accompanying drawings.

[0041] This application discloses a method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates. The method includes the following steps:

[0042] (1) Preparation of small-width 2195 aluminum-lithium alloy plates

[0043] Four 1000mm×1000mm×30mm 2195 aluminum-lithium alloy square plates were successively cut from four annealed (O-state) 2195 aluminum-lithium alloy square plates with dimensions of 1050mm×1050mm×30mm. Figure 1 As shown.

[0044] (2) Solution treatment and two-stage aging treatment

[0045] The 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm obtained in step (1) was subjected to solution treatment at a temperature of 520~540℃ and a holding time of 90~150min. After the holding time, the plate was subjected to quenching treatment with a quenching transfer time of ≤40s, so that the alloying elements could be dissolved into the Al matrix of the 2195 aluminum-lithium alloy as much as possible, creating conditions for subsequent aging precipitation of strengthening phases.

[0046] The strengthening phases in 2195 aluminum-lithium alloy include elongated T1 phase (Al2CuLi), δ′ phase (Al3Li), and dot / spherical β′ phase (Al3Zr). The small-sized strengthening phases and their abundant dispersion can effectively pin grain boundaries and inhibit grain growth, especially the δ′ and β′ phases.

[0047] Step (1) involves the aging treatment of a 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm, which is divided into two stages: pre-aging at a lower temperature and high-temperature aging at a higher temperature. The pre-aging temperature is 100~120℃, the holding time is 4~8h, and the plate is then air-cooled after being removed from the furnace. The high-temperature aging temperature is 170~180℃, the holding time is 32~36h, and the plate is then air-cooled after being removed from the furnace.

[0048] The 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm obtained in step (1) undergoes a two-stage aging treatment. The second phases δ′ and β′ in the alloy are diffusely distributed with sizes ranging from 20 to 50 nm and 20 to 70 nm, respectively. Figure 2a and 2b As shown; simultaneously, a large amount of T1 phase precipitates in the alloy, the T1 phase is uniformly distributed and has a size on the order of 100-150 nm, such as Figure 2c As shown.

[0049] (3) Milling and polishing treatment

[0050] The 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm, which has undergone step (2), is milled and polished so that the surface of the plane containing 1000mm×30mm is smooth, with a surface roughness of 6.3 and a flatness of ≤0.1.

[0051] (4) Preparation of wide-width 2195 aluminum-lithium alloy plates

[0052] Two 2195 aluminum-lithium alloy square plates with dimensions of 1000mm×1000mm×30mm, which have undergone step (3), are installed and fixed on the welding platform. A 1000mm×30mm plane is randomly selected from one of the plates and defined as A1. A 1000mm×30mm plane is randomly selected from the other plate and defined as A2. A1 and A2 are connected by friction stir welding along the length direction of A1 and A2. The resulting assembly is defined as A, and the weld is defined as A0.

[0053] Continue to select two 2195 aluminum-lithium alloy square plates with dimensions of 1000mm×1000mm×30mm that have undergone step (3) and repeat the above process. The 1000mm×30mm planes that are in contact are defined as B1 and B2 respectively. B1 and B2 are connected by friction stir welding along the length direction of B1 and B2. The resulting assembly is defined as B, and the weld is defined as B0.

[0054] Assemble A and B and fix them on the welding platform. Select any 2000mm × 30mm plane from A and define it as A. 11 Choose any 2000mm × 30mm plane from B and define it as B. 11 Using friction stir welding, along A 11 and B 11 The length direction connects A and B, the resulting assembly is defined as C, and the weld is defined as C0.

[0055] A new weld seam is formed along the A0B0 direction using friction stir welding and defined as D0. The resulting assembly is defined as D.

[0056] In step (4), D0 starts at end A0 and ends at end B0, and the distance between the starting position of D0 and C0 is A0 / 2, and the distance between the ending position of D0 and C0 is B0 / 2, as shown. Figure 3 As shown.

[0057] In step (4), the friction stir welding method used is double-sided welding. That is, after a certain weld is formed, the assembly is flipped 180° and welding continues on the back side of the weld along the direction of the weld.

[0058] (5) Stepped heat treatment

[0059] The composite body D obtained after step (4) is subjected to step heat treatment to reduce / eliminate the residual stress of the composite body D, while achieving synergistic consistency between the strengthening phases in the weld and the base material, thereby inhibiting abnormal grain growth at the weld location.

[0060] In step (5), the stepped heat treatment of the assembly D is as follows:

[0061] 1) Place assembly D into a heat treatment furnace and heat it to 260-330℃ with the furnace. The heating rate is 5-8℃ / s, and the holding time is 16-18h.

[0062] 2) Continue to heat assembly D in the heat treatment furnace to 360-460℃, with a heating rate of 3-5℃ / h and a holding time of 12-14h;

[0063] 3) Cool the assembly D in the heat treatment furnace to 260-330℃ along with the furnace, at a cooling rate of 3-5℃ / h, and hold for 4-6h.

[0064] 4) Remove assembly D from the heat treatment furnace and air cool it until it reaches room temperature.

[0065] In step (5), during the stepped heat treatment of the composite D, the δ′ and β′ phases located at the grain boundaries have strong thermal stability and can pin the grain boundaries, such as... Figure 4a and Figure 4b As shown, it effectively inhibits abnormal grain growth in the weld and base metal, especially at the weld location; at the same time, the strengthening phases in the weld and base metal tend to be synergistic and consistent, and a large amount of T1 phase ensures the strength level of the weld and base metal, especially at the weld location, and improves the continuity of the microstructure at the base metal-weld interface.

[0066] Example 1

[0067] In this embodiment, the raw material is an annealed (O-state) 2195 aluminum-lithium alloy square plate with dimensions of 1050mm × 1050mm × 30mm. The following is a detailed process of a method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates:

[0068] A method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates includes the following steps:

[0069] Step (1) Preparation of small-width 2195 aluminum-lithium alloy sheet

[0070] Four 1000mm×1000mm×30mm 2195 aluminum-lithium alloy square plates were successively cut from four annealed (O-state) 2195 aluminum-lithium alloy square plates with dimensions of 1050mm×1050mm×30mm. Figure 1 As shown.

[0071] Step (2) Solution treatment and two-stage aging treatment

[0072] The 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm obtained in step (1) was subjected to solution treatment at a temperature of 530℃ and a holding time of 120min. After the holding time, the plate was subjected to quenching treatment with a quenching transfer time of ≤40s, so that the alloying elements could be dissolved into the Al matrix of the 2195 aluminum-lithium alloy as much as possible, creating conditions for subsequent aging precipitation of strengthening phases.

[0073] The strengthening phases in 2195 aluminum-lithium alloy include elongated T1 phase (Al2CuLi), δ′ phase (Al3Li), and dot / spherical β′ phase (Al3Zr). The small-sized strengthening phases and their abundant dispersion can effectively pin grain boundaries and inhibit grain growth, especially the δ′ and β′ phases.

[0074] Step (1) involves the aging treatment of a 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm, which is divided into two stages: pre-aging at a lower temperature and high-temperature aging at a higher temperature. The pre-aging temperature is 120℃, the holding time is 6h, and the plate is then air-cooled after the holding time is completed. The high-temperature aging temperature is 175℃, the holding time is 32h, and the plate is then air-cooled after the holding time is completed.

[0075] The 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm obtained in step (1) undergoes a two-stage aging treatment. The second phases δ′ and β′ in the alloy are diffusely distributed with sizes ranging from 20 to 50 nm and 20 to 70 nm, respectively. Figure 2a and 2b As shown; simultaneously, a large amount of T1 phase precipitates in the alloy, the T1 phase is uniformly distributed and has a size on the order of 100-150 nm, such as Figure 2c As shown.

[0076] Step (3) Milling and polishing

[0077] The 2195 aluminum-lithium alloy square plate with dimensions of 1000mm×1000mm×30mm, which has undergone step (2), is milled and polished so that the surface of the plane containing 1000mm×30mm is smooth, with a surface roughness of 6.3 and a flatness of ≤0.1.

[0078] Step (4) Preparation of wide-width 2195 aluminum-lithium alloy sheet

[0079] Two 1000mm×1000mm×30mm 2195 aluminum-lithium alloy square plates, processed in step (3), are installed and fixed on a welding platform. A 1000mm×30mm plane is randomly selected from one plate and defined as A1, and a 1000mm×30mm plane is randomly selected from the other plate and defined as A2. Friction stir welding is used to connect A1 and A2 along their lengths. The resulting assembly is defined as A, and the weld is defined as A0. Figure 3 As shown.

[0080] Continue by selecting two 1000mm×1000mm×30mm 2195 aluminum-lithium alloy square plates that have undergone step (3) and repeating the above process. The 1000mm×30mm planes that are in contact with each other are defined as B1 and B2, respectively. Using friction stir welding, B1 and B2 are connected along their length directions. The resulting assembly is defined as B, and the weld is defined as B0. Figure 3 As shown.

[0081] Assemble A and B and fix them on the welding platform. Select any 2000mm × 30mm plane from A and define it as A. 11 Choose any 2000mm × 30mm plane from B and define it as B. 11 Using friction stir welding, along A 11 and B 11 The length direction connects A and B, the resulting assembly is defined as C, and the weld is defined as C0, such as... Figure 3 As shown.

[0082] A new weld seam is formed along the A0B0 direction using friction stir welding and defined as D0. The resulting assembly is defined as D. Figure 3 As shown.

[0083] In step (4), D0 starts at end A0 and ends at end B0, and the distance between the starting position of D0 and C0 is A0 / 2, and the distance between the ending position of D0 and C0 is B0 / 2, as shown. Figure 3 As shown.

[0084] In step (4), the friction stir welding method used is double-sided welding. That is, after a certain weld is formed, the assembly is flipped 180° and welding continues on the back side of the weld along the direction of the weld.

[0085] Step (5) Step heat treatment

[0086] The composite body D obtained after step (4) is subjected to step heat treatment to reduce / eliminate the residual stress of the composite body D, while achieving synergistic consistency between the strengthening phases in the weld and the base material, thereby inhibiting abnormal grain growth at the weld location.

[0087] In step (5), the stepped heat treatment of the assembly D is as follows:

[0088] 1) Place assembly D into a heat treatment furnace and heat it to 300℃ with the furnace. The heating rate is 5℃ / s and the holding time is 16h.

[0089] 2) Continue to heat assembly D in the heat treatment furnace to 420℃, with a heating rate of 3℃ / h and a holding time of 12h;

[0090] 3) The assembly D in the heat treatment furnace is cooled to 300℃ along with the furnace, the cooling rate is 3℃ / h, and the holding time is 6h;

[0091] 4) Remove assembly D from the heat treatment furnace and air cool it until it reaches room temperature.

[0092] In step (5), during the stepped heat treatment of the composite D, the δ′ and β′ phases located at the grain boundaries have strong thermal stability and can pin the grain boundaries, as shown in Figure 4. This effectively inhibits abnormal grain growth in the weld and the base material, especially at the weld location. At the same time, the strengthening phases in the weld and the base material tend to be synergistic and consistent. A large amount of T1 phase ensures the strength level of the weld and the base material, especially at the weld location, and improves the continuity of the base material-weld interface structure.

[0093] In this embodiment, addressing the challenge of controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates, a comprehensive planning and design of the process path for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates was undertaken. A two-stage aging process was adopted to ensure that the strengthening phases T1, δ′, and β′ are kept small in size and widely dispersed. Through stepped heat treatment, residual stress was reduced / eliminated while the strengthening phases in the weld and the base metal became more synergistic and consistent, ensuring the thermal stability of the strengthening phases δ′ and β′, effectively pinning grain boundaries and inhibiting grain growth. The abundant T1 phase ensured the strength level of the weld and improved the continuity of the microstructure at the base metal-weld interface.

[0094] The contents not described in detail in this application specification are common knowledge to those skilled in the art.

[0095] The present application has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present application. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and implementation methods of the present application without departing from the spirit and scope of the present application, and all such modifications and improvements fall within the scope of the present application. The scope of protection of the present application is determined by the appended claims.

Claims

1. A method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates, characterized in that, Includes the following steps: S1. Prepare small-width 2195 aluminum-lithium alloy plates; S2. The small-width 2195 aluminum-lithium alloy sheet is subjected to solution treatment and two-stage aging treatment in sequence. The two-stage aging process includes sequential low-temperature pre-aging and high-temperature aging. The low-temperature pre-aging involves holding at 100~120 ℃ for 4~8 h followed by air cooling, and the high-temperature aging involves holding at 170~180 ℃ for 32~36 h followed by air cooling. After the two-stage aging treatment, the second phase δ′ phase and β′ phase in the small-width 2195 aluminum-lithium alloy plate are dispersed and have size scales of 20~50 nm and 20~70 nm, respectively; at the same time, a large amount of T1 phase is precipitated in the alloy, and the T1 phase is uniformly distributed in needle-like parallel arrangement with a size scale of 100~150 nm. S3. Carry out milling and polishing of small-width 2195 aluminum-lithium alloy plates; S4. At least two small-width 2195 aluminum-lithium alloy plates are welded together by friction stir welding to prepare a large-width 2195 aluminum-lithium alloy plate. S5. Step heat treatment of wide 2195 aluminum-lithium alloy plates. The stepped heat treatment includes: The wide 2195 aluminum-lithium alloy sheet is placed in a heat treatment furnace and heated to 260~330 ℃ with a heating rate of 5~8℃ / s and a holding time of 16~18 h. Continue heating the furnace to 360~460 ℃, with a heating rate of 3~5 ℃ / h and a holding time of 12~14 h; The furnace temperature is lowered to 260~330 ℃ at a rate of 3~5 ℃ / h, and the holding time is 4~6 h. The large-width 2195 aluminum-lithium alloy sheet is taken out of the furnace and air-cooled until it reaches room temperature.

2. The method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates according to claim 1, characterized in that: The solution treatment process involves holding at 520~540 ℃ for 90~150 min followed by quenching, with a quenching transfer time ≤40s.

3. The method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates according to claim 1, characterized in that: The milled and polished surface is the subsequent welding surface of the narrow-width 2195 aluminum-lithium alloy sheet, with a surface roughness of 6.3 and a flatness of ≤0.

1.

4. The method for controlling weld defects in friction stir welding of 2195 aluminum-lithium alloy plates according to claim 1, characterized in that: During the stepped heat treatment process, the δ′ and β′ phases located at the grain boundaries have strong thermal stability, which can pin the grain boundaries and effectively inhibit abnormal grain growth in the weld. At the same time, a large amount of T1 phase ensures the strength level of the weld and improves the continuity of the microstructure at the base material-weld interface.

5. A 2195 aluminum-lithium alloy sheet, characterized in that: The 2195 aluminum-lithium alloy plate was prepared using the method for controlling weld defects in friction stir welding as described in any one of claims 1-4.

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