High-strength Al-Cu series aluminum alloy thin-wall angle profile and secondary extrusion process thereof

Abstract

The invention discloses a high-strength Al-Cu series aluminum alloy thin-wall angle profile and a secondary extrusion process thereof. The Al-Cu series aluminum alloy thin-wall angle profile comprises the following alloy components in percentage by weight: less than or equal to 0.05% of Si, less than or equal to 0.05% of Fe, 3.8-4.9% of Cu, 0.3-0.9% of Mn, 1.2-1.8% of Mg, 0.08-0.1% of Cr, 0.10-0.25% of Zn, 0.11-0.15% of Ti, 0.15-0.25% of Zr, 0.1-0.2% of V and the balance of Al and inevitable impurities. The extrusion process comprises the following steps: sequentially carrying out primary reverse extrusion, intermediate annealing and secondary reverse extrusion on a homogenized Al-Cu series aluminum alloy cast ingot to obtain a thin-wall angle profile; the intermediate annealing adopts a two-stage annealing process, the temperature of the first-stage intermediate annealing is 380-420 DEG C, and the heat preservation time is 2-4 hours; the second-stage intermediate annealing temperature is 460-480 DEG C, and the heat preservation time is 2-4 hours; the extrusion directions of the blanks of the secondary reverse extrusion and the primary reverse extrusion are opposite. According to the method, alloy components and a secondary extrusion process are optimized, the extrusion effect introduced by secondary extrusion and the influence of large deformation energy storage can be eliminated, and the thin-wall angle profile high in strength and uniform in head and tail performance is produced.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy preparation, in particular to a high-strength Al-Cu series aluminum alloy thin-wall angle profile and a secondary extrusion process thereof. Background Art

[0002] Al-Cu aluminum alloys are highly representative of the 2-series aluminum alloys. They are hard aluminum alloys characterized by high strength, low density, excellent heat resistance, and fatigue resistance. They are widely used in the aerospace and automotive sectors. With the growing demand for lightweight and high-mechanical performance materials in the automotive and aerospace industries, aluminum alloys' high strength-to-weight ratio and low cost have led to their increasing application in these sectors.

[0003] At present, thin-walled angle profiles are usually produced by a large-scale ingot single-extrusion large deformation process or a small-scale ingot single-extrusion small deformation process. However, the large-scale ingot single-extrusion molding process will lead to a significant difference in the mechanical properties of the head and tail of the thin-walled angle profile, and the thickness of the coarse grain layer is too large, and even the whole surface is coarse grained. On the other hand, the small-scale ingot single-extrusion molding process has a relatively small deformation amount, resulting in low mechanical properties. In order to further improve the mechanical property limit of Al-Cu aluminum alloys, secondary extrusion has gradually come into the sight of current scholars. Studies have shown that after a long period of homogenization of conventional 2xxx aluminum alloy round ingots to eliminate the eutectic network and after two consecutive extrusion plastic deformations, the internal grains of the 2xxx aluminum alloy are refined, the aluminum alloy deforms uniformly, and the stress concentration at the grain boundaries can be reduced to a certain extent, thereby reducing the tendency of grain boundary fracture. In other words, secondary extrusion plastic deformation is beneficial to improving the mechanical properties of 2xxx aluminum alloys. However, the current control of secondary extrusion and recrystallization behavior of thin-walled profiles with large deformation is still not ideal. The following problems mainly exist in the secondary extrusion production process of thin-walled profiles with large deformation: (1) Since 2xxx aluminum alloy itself is more prone to recrystallization, and the secondary extrusion causes the introduction of more deformation energy storage, it is more likely to cause recrystallization and grain growth in the subsequent solution heat treatment process; (2) Due to the greater difference in the microstructure of the head and tail of the extruded profile caused by secondary extrusion, the "extrusion effect" is more obvious, and abnormal grain growth may occur, which is specifically manifested as the sudden uneven growth of a few grains, and a few larger grains grow rapidly first, gradually swallowing up a large number of other small grains around them, and finally forming a coarse structure, which greatly reduces the mechanical properties, that is, secondary recrystallization occurs; (3) After the secondary extrusion, there is a difference in deformation energy storage between the head and tail of the profile, and the recrystallization threshold value is also different. In order to ensure the stability of the performance of the head, tail, core and edge of the profile, it is an urgent problem to control the recrystallization degree of the head and tail of the extruded profile in the same domain. Based on this, the present invention proposes a high-strength Al-Cu series aluminum alloy thin-wall angle profile and a secondary extrusion process thereof. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention provides a high-strength Al-Cu aluminum alloy thin-walled angle profile and its secondary extrusion process, which can eliminate the "extrusion effect" introduced by secondary extrusion and the influence of large deformation energy storage, and produce thin-walled angle profiles with high strength and uniform head and tail performance.

[0005] The technical solution adopted in the present invention is:

[0006] In a first aspect, the present invention provides a secondary extrusion process for a high-strength Al-Cu aluminum alloy thin-walled angle profile, comprising the steps of:

[0007] The Al-Cu aluminum alloy ingot after homogenization treatment is subjected to a first reverse extrusion, an intermediate annealing, and a second reverse extrusion in sequence to obtain a thin-walled angle profile;

[0008] The intermediate annealing adopts a two-stage annealing process, the first stage intermediate annealing temperature is 380-420°C, and the holding time is 2-4 hours; the second stage intermediate annealing temperature is 460-480°C, and the holding time is 2-4 hours;

[0009] The secondary reverse extrusion is in the opposite direction to the billet extrusion of the primary reverse extrusion.

[0010] Furthermore, the alloy composition range of the Al-Cu aluminum alloy thin-walled angle profile is: in mass percentage, Si≤0.05%, Fe≤0.05%, Cu 3.8-4.9%, Mn 0.3-0.9%, Mg 1.2-1.8%, Cr 0.08-0.1%, Zn 0.10-0.25%, Ti 0.11-0.15%, Zr 0.15-0.25%, V 0.1-0.2%, and the balance is Al and unavoidable impurities, and the content of a single impurity does not exceed 0.05%, and the total impurity content does not exceed 0.15%.

[0011] Furthermore, the homogenization treatment of the Al-Cu aluminum alloy ingot adopts a two-stage homogenization process, with the first-stage homogenization temperature being 480±5°C and the holding time being 20 to 25 hours; the second-stage homogenization temperature being 496±3°C and the holding time being 24 to 36 hours. After homogenization is completed, it is air-cooled to room temperature.

[0012] Furthermore, the parameters of the single reverse extrusion are: mold temperature of 390-410°C, extrusion barrel temperature of 390-430°C, ingot heating temperature of 360-380°C, extrusion ratio of 20-25, and extrusion speed of 0.3-0.7 mm / s.

[0013] Furthermore, after the intermediate annealing is completed, the steel sheet is first furnace-cooled to below 260° C. at a cooling rate of 20-25° C. / h, and then air-cooled to room temperature.

[0014] Furthermore, the secondary reverse extrusion parameters are: mold temperature of 390-410°C, extrusion barrel temperature of 390-430°C, primary extrusion billet heating temperature of 390-410°C, extrusion ratio of 25-30, and extrusion speed of 0.2-0.3 mm / s.

[0015] Furthermore, before the secondary reverse extrusion, the head and tail of the primary extruded billet obtained by the primary reverse extrusion are interchanged.

[0016] In a second aspect, the present invention provides a high-strength Al-Cu series aluminum alloy thin-wall angle profile, which is prepared by a secondary extrusion process.

[0017] Furthermore, the wall thickness of the thin-walled angle profile is 4 to 6 mm.

[0018] In the above technical solution, the present invention combines the following aspects to achieve the goal of improving the mechanical properties of thin-walled angle profiles by secondary extrusion while reducing the coarse grain problem caused by secondary extrusion deformation and reducing the mechanical properties and microstructure differences between the head and tail of the profile:

[0019] In the first aspect, the present invention optimizes the alloy composition of the Al-Cu aluminum alloy by adding Zr and V elements to form dispersed and fine precipitates in the matrix, thereby pinning the grain boundaries to regulate the recrystallization threshold and improve the overall grain boundary stability;

[0020] On the second aspect, the present invention performs two-stage intermediate annealing on the billet after the first extrusion to solve the recrystallization problem caused by the introduction of more deformation energy storage by the second extrusion, that is, to suppress the degree of recrystallization of the profile during the second extrusion. Among them, the first-stage intermediate annealing temperature adopts medium-temperature annealing, which is slightly lower. It is not only used to remove the internal stress generated by the first extrusion, but also to reduce the difference in deformation energy storage in different areas of the first-extrusion billet; then on this basis, a high-temperature and short-time second-stage recrystallization annealing is performed to make the grain structure of the first-extrusion billet completely recrystallize and return to a unified organizational state, and at the same time reduce the difference in grain structure at the head and tail. In addition, since the cross-sections of thin-walled angle profiles are different and "sensitive", if the recrystallization threshold is not regulated by optimizing the alloy composition or if a medium-temperature annealing is not performed before the recrystallization annealing, the degree of complete recrystallization in different areas will be different during the recrystallization annealing, which will cause "organizational chaos" during the second extrusion, that is, the grain sizes in different areas are different;

[0021] Thirdly, the present invention also interchanges the head and tail of the primary extruded billet during the secondary extrusion, thereby reducing the differences in tissue structure and mechanical properties between the head and tail.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a high-strength Al-Cu aluminum alloy thin-walled angle profile and a secondary extrusion process thereof. By optimizing the alloy composition and performing a two-stage intermediate annealing after the first extrusion, and by exchanging the head and tail of the first extruded billet during the second extrusion, not only the longitudinal mechanical properties of the Al-Cu aluminum alloy thin-walled thick angle profile product are improved, but also the extrusion effect and large deformation energy storage introduced by the second extrusion are eliminated, thereby producing a thin-walled angle profile with high strength and uniform performance at the head and tail. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a metallographic photograph of the thin-walled angle profile prepared in Example 1;

[0025] Figure 2 These are low-magnification inspection photos of the thin-walled angle profile prepared in Example 1, where (a) is a low-magnification photo of the head and (b) is a low-magnification photo of the tail;

[0026] Figure 3 This is a metallographic photograph of the thin-walled angle profile prepared in Comparative Example 1;

[0027] Figure 4 These are low-magnification inspection photos of the thin-walled angle profile prepared in Comparative Example 1, wherein (a) is a low-magnification photo of the head, and (b) is a low-magnification photo of the tail.

[0028] Figure 5 This is a metallographic photograph of the thin-walled angle profile prepared in Comparative Example 2;

[0029] Figure 6 This is a metallographic photograph of the thin-walled angle profile prepared in Comparative Example 5; DETAILED DESCRIPTION

[0030] The present invention provides a high-strength Al-Cu aluminum alloy thin-walled angle profile and a secondary extrusion process thereof. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is described in further detail below. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0031] Example 1

[0032] This embodiment prepares a high-strength Al-Cu aluminum alloy thin-walled angle profile in the following steps:

[0033] (1) Melting and casting: The ingredients are prepared according to the alloy composition ratio of Al-Cu aluminum alloy, wherein Si 0.03%, Fe 0.02%, Cu 4.5%, Mn 0.6%, Mg 1.6%, Cr 0.1%, Zn 0.25%, Ti 0.15%, Zr 0.2%, V 0.1%, and the balance is Al and unavoidable impurities, and the content of each unavoidable impurity does not exceed 0.05%, and the total does not exceed 0.15%; then, the Al-Cu aluminum alloy ingot is obtained by melting and casting;

[0034] (2) Homogenization treatment: The Al-Cu aluminum alloy ingot is placed in a homogenization furnace for homogenization treatment, wherein the first stage homogenization temperature is 480°C and the holding time is 24 hours; the second stage homogenization temperature is 497°C and the holding time is 36 hours. After the homogenization is completed, it is air-cooled to room temperature;

[0035] (3) Car skin: The ingot after homogenization treatment is cut into fixed lengths and car skins are made. The thickness of the single-side car skin is 10 mm to remove the segregation layer.

[0036] (4) Primary extrusion: The ingot of the car body is subjected to a reverse extrusion using a 150MN extruder. The parameters of the reverse extrusion are: die temperature of 400°C, extrusion barrel temperature of 390°C, ingot heating temperature of 380°C, extrusion ratio of 23.04, extrusion speed of 0.6 mm / s, and a primary extrusion bar with a diameter of 125 mm (i.e., primary extrusion billet) is obtained, and the head and tail are marked;

[0037] (5) Intermediate annealing: The extruded billet is subjected to two-stage intermediate annealing. The first stage intermediate annealing temperature is 390 °C and the holding time is 3 h; the second stage intermediate annealing temperature is 480 °C and the holding time is 4 h. After the intermediate annealing is completed, the billet is first furnace cooled to below 260 °C at a cooling rate of 23 °C / h, and then air cooled to room temperature.

[0038] (6) Secondary extrusion: The head and tail of the primary extrusion billet after intermediate annealing are interchanged, that is, the tail of the primary extrusion billet is used as the head of the secondary reverse extrusion, and the secondary reverse extrusion is performed using an 11MN extruder. The secondary reverse extrusion parameters are: die temperature of 400°C, extrusion barrel temperature of 410°C, primary extrusion billet heating temperature of 390°C, extrusion ratio of 28.21, and extrusion speed of 0.2 mm / s, to obtain a thin-walled angle profile with a wall thickness of 5.21 mm;

[0039] (7) Pre-stretching: Pre-stretch the thin-walled angle profile to produce a deformation of 0.8%;

[0040] (8) Head and tail sawing: The pre-stretched thin-walled angle profile is cut at the head and tail, with the head cut off 1000mm and the tail cut off 800mm;

[0041] (9) Solution treatment: The thin-walled angle profiles after head and tail sawing are subjected to solution treatment at a temperature of 496°C and a holding time of 60 min. The quenching method is water-cooled and the cooling rate is 112°C / min.

[0042] (10) Stretching and straightening: The thin-walled angle profile after solution treatment is subjected to two stretching and straightening treatments. The deformation rate of the first stretching and straightening is 0.3%, and the deformation rate of the second stretching and straightening is 1.0%. The stretching and straightening is completed within 1 hour after solution treatment to ensure the straightness and flatness of the angle profile.

[0043] (11) Aging treatment: The thin-walled angle profile after stretching and straightening treatment is placed in a room temperature environment for natural aging. The completion time of the solid solution heat treatment is recorded as the start time of natural aging. The natural aging time is 96 h, and finally the finished product of the Al-Cu aluminum alloy thin-walled angle profile in T3511 state is obtained.

[0044] Example 2

[0045] This embodiment prepares a high-strength Al-Cu aluminum alloy thin-walled angle profile in the following steps:

[0046] (1) Melting and casting: preparing the materials according to the alloy composition ratio of Al-Cu series aluminum alloy, wherein Si 0.04%, Fe 0.02%, Cu 4.9%, Mn 0.8%, Mg 1.7%, Cr 0.1%, Zn 0.25%, Ti 0.15%, Zr 0.25%, V 0.2%, and the balance being Al and unavoidable impurities, wherein the content of any single unavoidable impurity does not exceed 0.05%, and the total does not exceed 0.15%; then melting and casting to obtain Al-Cu series aluminum alloy ingot;

[0047] (2) Homogenization treatment: The Al-Cu aluminum alloy ingot is placed in a homogenization furnace for homogenization treatment, wherein the first stage homogenization temperature is 480°C and the holding time is 24 hours; the second stage homogenization temperature is 495°C and the holding time is 30 hours. After the homogenization is completed, it is air-cooled to room temperature;

[0048] (3) Car skin: The ingot after homogenization treatment is cut into fixed length and car skin. The thickness of the single-side car skin is 8mm to remove the segregation layer;

[0049] (4) Primary extrusion: The ingot of the car body is subjected to a reverse extrusion using a 150MN extruder. The parameters of the reverse extrusion are: die temperature of 410°C, extrusion barrel temperature of 430°C, ingot heating temperature of 370°C, extrusion ratio of 23.04, extrusion speed of 0.55 mm / s, and a primary extrusion bar with a diameter of 125 mm (i.e., primary extrusion billet) is obtained, and the head and tail are marked;

[0050] (5) Intermediate annealing: The extruded billet is subjected to two-stage intermediate annealing. The first stage intermediate annealing temperature is 420 °C and the holding time is 3 h. The second stage intermediate annealing temperature is 460 °C and the holding time is 2 h. After the intermediate annealing is completed, the billet is first furnace cooled to below 260 °C at a cooling rate of 22 °C / h, and then air cooled to room temperature.

[0051] (6) Secondary extrusion: The head and tail of the primary extrusion billet after intermediate annealing are interchanged, that is, the tail of the primary extrusion billet is used as the head of the secondary reverse extrusion, and the secondary reverse extrusion is performed using an 11MN extruder. The secondary reverse extrusion parameters are: die temperature of 410°C, extrusion barrel temperature of 430°C, primary extrusion billet heating temperature of 390°C, extrusion ratio of 28.21, and extrusion speed of 0.3 mm / s, to obtain a thin-walled angle profile with a wall thickness of 5.21 mm;

[0052] (7) Pre-stretching: Pre-stretch thin-walled angle profiles to produce a deformation of 1.0%;

[0053] (8) Head and tail sawing: The pre-stretched thin-walled angle profile is cut at the head and tail, with the head cut off 800mm and the tail cut off 500mm;

[0054] (9) Solution treatment: The thin-walled angle profiles after head and tail sawing are subjected to solution treatment at a temperature of 495°C and a holding time of 90 min. The quenching method is water-cooled and the cooling rate is 105°C / min.

[0055] (10) Stretching and straightening: The thin-walled angle profile after solution treatment is subjected to two stretching and straightening treatments. The deformation rate of the first stretching and straightening is 0.5%, and the deformation rate of the second stretching and straightening is 0.8%. The stretching and straightening is completed within 1.5 hours after the solution treatment to ensure the straightness and flatness of the angle profile.

[0056] (11) Aging treatment: The thin-walled angle profile after stretching and straightening treatment is placed in a room temperature environment for natural aging. The completion time of the solid solution heat treatment is recorded as the start time of natural aging. The natural aging time is 96 h, and finally the finished product of the Al-Cu aluminum alloy thin-walled angle profile in T3511 state is obtained.

[0057] Mechanical property testing and metallographic structure testing were performed on the finished Al-Cu aluminum alloy thin-wall angle profile prepared in this embodiment. The tensile strength was 462.0 MPa, the yield strength was 310.8 MPa, the elongation was 20.5%, and the depth of the coarse grain layer was less than 10%.

[0058] Example 3

[0059] This embodiment prepares a high-strength Al-Cu aluminum alloy thin-walled angle profile in the following steps:

[0060] (1) Melting and casting: preparing the materials according to the alloy composition ratio of Al-Cu series aluminum alloy, wherein Si 0.05%, Fe 0.05%, Cu 3.8%, Mn 0.7%, Mg 1.4%, Cr 0.1%, Zn 0.25%, Ti 0.15%, Zr 0.15%, V 0.15%, and the balance being Al and unavoidable impurities, wherein the content of any single unavoidable impurity does not exceed 0.05%, and the total does not exceed 0.15%; then melting and casting to obtain Al-Cu series aluminum alloy ingot;

[0061] (2) Homogenization treatment: The Al-Cu aluminum alloy ingot is placed in a homogenization furnace for homogenization treatment, wherein the first stage homogenization temperature is 480°C and the holding time is 24 hours; the second stage homogenization temperature is 499°C and the holding time is 24 hours. After the homogenization is completed, it is air-cooled to room temperature;

[0062] (3) Car skin: The ingot after homogenization treatment is cut into fixed length and car skin, with a single-side car skin thickness of 15 mm to remove the segregation layer;

[0063] (4) Primary extrusion: The ingot of the car body is subjected to a reverse extrusion using a 150MN extruder. The parameters of the reverse extrusion are: mold temperature of 390°C, extrusion barrel temperature of 400°C, ingot heating temperature of 360°C, extrusion ratio of 23.04, extrusion speed of 0.3 mm / s, and a primary extrusion bar with a diameter of 125 mm (i.e., primary extrusion billet) is obtained, and the head and tail are marked;

[0064] (5) Intermediate annealing: The extruded billet is subjected to two-stage intermediate annealing. The first stage intermediate annealing temperature is 480 °C and the holding time is 3 h; the second stage intermediate annealing temperature is 470 °C and the holding time is 4 h. After the intermediate annealing is completed, the billet is first furnace cooled to below 260 °C at a cooling rate of 20 °C / h, and then air cooled to room temperature.

[0065] (6) Secondary extrusion: The head and tail of the primary extrusion billet after intermediate annealing are interchanged, that is, the tail of the primary extrusion billet is used as the head of the secondary reverse extrusion, and the secondary reverse extrusion is performed using an 11MN extruder. The secondary reverse extrusion parameters are: die temperature of 390°C, extrusion barrel temperature of 390°C, primary extrusion billet heating temperature of 410°C, extrusion ratio of 28.21, and extrusion speed of 0.3 mm / s, to obtain a thin-walled angle profile with a wall thickness of 5.21 mm;

[0066] (7) Pre-stretching: Pre-stretch thin-walled angle profiles to produce a deformation of 0.5%;

[0067] (8) Head and tail sawing: The pre-stretched thin-walled angle profile is cut at the head and tail, with the head cut off 800mm and the tail cut off 500mm;

[0068] (9) Solution treatment: The thin-walled angle profiles after head and tail sawing are subjected to solution treatment at a temperature of 492°C and a holding time of 75 min. The quenching method is water-cooled and the cooling rate is 102°C / min.

[0069] (10) Stretching and straightening: The thin-walled angle profile after solution treatment is subjected to two stretching and straightening treatments. The deformation rate of the first stretching and straightening is 0.4%, and the deformation rate of the second stretching and straightening is 0.8%. The stretching and straightening is completed within 2 hours after solution treatment to ensure the straightness and flatness of the angle profile.

[0070] (11) Aging treatment: The thin-walled angle profile after stretching and straightening treatment is placed in a room temperature environment for natural aging. The completion time of the solid solution heat treatment is recorded as the start time of natural aging. The natural aging time is 96 h, and finally the finished product of the Al-Cu aluminum alloy thin-walled angle profile in T3511 state is obtained.

[0071] Mechanical property testing and metallographic structure testing were performed on the finished Al-Cu aluminum alloy thin-wall angle profile prepared in this embodiment. The tensile strength was 462.0 MPa, the yield strength was 310.8 MPa, the elongation was 20.5%, and the depth of the coarse grain layer was less than 10%.

[0072] Comparative Example 1

[0073] The difference between this comparative example and Example 1 is that this comparative example does not perform intermediate annealing after the first reverse extrusion. Instead, the first extruded billet is cooled to room temperature and then heated to the same second reverse extrusion parameters as Example 1 for second reverse extrusion.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that the intermediate annealing process in this comparative example is: 480° C.×7 h.

[0076] Comparative Example 3

[0077] The difference between this comparative example and Example 3 is that Zr and V are not added in this comparative example.

[0078] Comparative Example 4

[0079] The difference between this comparative example and Example 3 is that, in this comparative example, the head and tail of the primary extruded billet are not interchanged during the secondary reverse extrusion.

[0080] Comparative Example 5

[0081] The difference between this comparative example and Example 3 is that this comparative example uses a small-size ingot after homogenization treatment to prepare a thin-walled angle profile by one extrusion, that is, an 11MN extruder is used to perform a single reverse extrusion on a 125mm aluminum alloy ingot to prepare a thin-walled angle profile with a wall thickness of 5.21mm. The extrusion parameters are: mold temperature of 390°C, extrusion barrel temperature of 390°C, ingot heating temperature of 410°C, extrusion ratio of 28.21, and extrusion speed of 0.3mm / s.

[0082] The thin-walled angle profiles prepared in Examples 1-3 and Comparative Examples 1-5 were tested for mechanical properties and coarse-grained layer depth. The test results are shown in Table 1. A certain company's mechanical property standards for thin-walled angle profiles are: (tensile strength ≥ 450 MPa, yield strength ≥ 285 MPa); the coarse-grained layer depth requirement is less than 10%.

[0083] Table 1 Mechanical properties of thin-walled angle profiles and coarse-grained layer depth test results

[0084]

[0085]

[0086] Analysis of the test results in Table 1 above shows that Examples 1 to 3 have a tensile strength of 451.5-462.0 MPa, a yield strength of 296.8-310.8 MPa, and an elongation of 20.5-21.5%, demonstrating excellent comprehensive mechanical properties. Furthermore, the depth of the coarse-grained layer is controlled within 10%. In contrast, Comparative Example 1, due to the lack of intermediate annealing, has a higher strength but a lower plasticity, and the coarse-grained layer is unqualified. Comparative Example 2 has an excessively long annealing time, resulting in significant softening of the structure and a significant decrease in strength. Furthermore, the long recrystallization annealing process does not completely recrystallize all structures into fine, dispersed grains, leading to an unqualified coarse-grained layer depth. Comparative Example 3 does not add Zr and V, resulting in insufficient grain refinement and lower strength. Comparative Example 4 does not undergo head-to-tail exchange, resulting in severe coarse grains at the tail end. Comparative Example 5 uses direct extrusion of small ingots, resulting in small deformation and low overall performance. The above results show that Examples 1-3 of the present invention achieve a coordinated improvement in organizational uniformity and mechanical properties by optimizing the alloy composition, performing two-stage intermediate annealing after the first extrusion, and swapping the head and tail of the first extruded billet during the second extrusion, while effectively suppressing the formation of a coarse-grained layer.

[0087] In addition, the thin-walled angle profile prepared in Example 1 was subjected to metallographic examination (the sampling position is as follows: Figure 2 a), such as Figure 1 As shown. Figure 1 It can be seen that the grains of the thin-walled angle profile prepared in Example 1 are small and uniform. At the same time, the head and tail of the thin-walled angle profile prepared in Example 1 are also tested at low magnification, as shown in FIG. Figure 2 As shown. Figure 2 It can be seen that the macrostructure of the head and tail of the thin-walled angle profile prepared in Example 1 does not show an obvious coarse-grained layer.

[0088] The thin-walled angle profile prepared in the above comparative example 1 was subjected to metallographic examination (the sampling position is as follows Figure 2 a), such as Figure 3 As shown. Figure 3 It can be seen that the grains of the thin-walled angle profile prepared in Comparative Example 1 are coarse. At the same time, the head and tail of the thin-walled angle profile prepared in Comparative Example 1 are also tested at low magnification, such as Figure 4 As shown. Figure 4 It can be seen that the macrostructure of the head and tail of the thin-walled angle profile prepared in Comparative Example 1 shows an obvious coarse-grained layer, and the surface is basically covered with coarse grains.

[0089] The thin-walled angle profile prepared in the above comparative example 2 was subjected to metallographic examination (the sampling position was as follows Figure 2 a), such as Figure 5 As shown. Figure 5It can be seen from the figure that the metallographic structure of the thin-walled angle profile prepared in Comparative Example 2 has a layer of large grains and a layer of fine grains arranged alternately. This is because the extrusion deformation energy storage is different and the cross-sectional size of the profile is small, which makes the deformation energy storage sensitive to the influence of the grain structure. Even through long-term recrystallization annealing, the entire structure cannot be completely recrystallized to form fine and dispersed grains, that is, "organization chaos" occurs. At the same time, combined with the low-magnification and mechanical property test results of Comparative Example 2 in Table 1, this phenomenon will lead to unqualified coarse-grained layer depth, and long-term high-temperature recrystallization annealing will also lead to reduced profile performance.

[0090] The thin-walled angle profile prepared in the above comparative example 5 was subjected to metallographic examination (the sampling position is as follows Figure 2 a), such as Figure 6 As shown. Figure 6 It can be seen that the grains of the thin-walled angle profile prepared in Comparative Example 5 are uniform, but the grain size is larger than that of Example 1, which also reduces the strength of the profile to a certain extent.

[0091] It should be noted that the parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0092] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the scope of protection of the present invention.

Claims

1. A secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profiles, characterized in that: Including steps: The Al-Cu aluminum alloy ingot after homogenization treatment is subjected to a first reverse extrusion, an intermediate annealing, and a second reverse extrusion in sequence to obtain a thin-walled angle profile; The intermediate annealing adopts a two-stage annealing process, the first stage intermediate annealing temperature is 380-420°C, and the holding time is 2-4 hours; the second stage intermediate annealing temperature is 460-480°C, and the holding time is 2-4 hours; The secondary reverse extrusion is in the opposite direction to the billet extrusion of the primary reverse extrusion.

2. The secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 1, characterized in that: The alloy composition range of the Al-Cu series aluminum alloy thin-wall angle profile is as follows: in mass percentage, Si≤0.05%, Fe≤0.05%, Cu 3.8-4.9%, Mn 0.3-0.9%, Mg 1.2-1.8%, Cr 0.08-0.1%, Zn 0.10-0.25%, Ti0.11-0.15%, Zr 0.15-0.25%, V 0.1-0.2%, and the balance is Al and unavoidable impurities, and the content of each impurity does not exceed 0.05%, and the total impurity content does not exceed 0.15%.

3. The secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 1, characterized in that: The homogenization treatment of the Al-Cu aluminum alloy ingot adopts a two-stage homogenization process, wherein the first-stage homogenization temperature is 480±5° C. and the holding time is 20-25 hours; the second-stage homogenization temperature is 496±3° C. and the holding time is 24-36 hours. After the homogenization is completed, the ingot is air-cooled to room temperature.

4. The secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 1, characterized in that: The parameters of the single reverse extrusion are: mold temperature of 390-410° C., extrusion barrel temperature of 390-430° C., ingot heating temperature of 360-380° C., extrusion ratio of 20-25, and extrusion speed of 0.3-0.7 mm / s.

5. The secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 1, characterized in that: After the intermediate annealing is completed, the steel is firstly furnace-cooled to below 260° C. at a cooling rate of 20-25° C. / h, and then air-cooled to room temperature.

6. The secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 1, characterized in that: The secondary reverse extrusion parameters are: die temperature of 390-410°C, extrusion barrel temperature of 390-430°C, primary extrusion billet heating temperature of 390-410°C, extrusion ratio of 25-30, and extrusion speed of 0.2-0.3 mm / s.

7. The secondary extrusion process for high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 1, characterized in that: Before the secondary reverse extrusion, the head and tail of the primary extrusion billet obtained by the primary reverse extrusion are interchanged.

8. A high-strength Al-Cu aluminum alloy thin-wall angle profile produced by the secondary extrusion process according to any one of claims 1 to 7.

9. The high-strength Al-Cu aluminum alloy thin-wall angle profile according to claim 8, characterized in that: The wall thickness of thin-walled angle profiles is 4 to 6 mm.

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