Preparation method of large-size high-strength Al-Cu alloy plate

Abstract

The invention discloses a preparation method of a large-size high-strength Al-Cu alloy plate, and relates to the technical field of aluminum alloy processing. The specific preparation technological process comprises the steps of burdening, smelting, melt purification, casting, homogenization heat treatment, machining, hot rolling, straightening, solid solution quenching, deformation heat treatment and saw cutting, and an alloy comprises the following element components of smaller than or equal to 0.02% of Si, smaller than or equal to 0.05% of Fe, 3.7%-6.4% of Cu, smaller than or equal to 0.5% of Mg, smaller than or equal to 1.2% of Li, smaller than or equal to 0.4% of Ag, 0.001%-0.4% of Mn, smaller than or equal to 0.25% of Zn, 0.015%-0.035% of Ti, 0.09%-0.15% of Zr and the balance Al and inevitable impurity elements. The hot rolling is multi-directional composite deformation hot rolling; the thermomechanical treatment comprises the steps of pre-aging, pre-stretching, rolling and re-aging. According to the alloy prepared through the method, the density of an Al-Cu alloy plate can be effectively reduced, the strength performance is improved, the alloy has higher elasticity modulus, and the alloy is a structural material with very good application prospects in the aerospace field.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy processing, and in particular to a method for preparing a large-size high-strength Al-Cu alloy plate. Background Art

[0002] For aerospace vehicles, every additional 1kg of payload can bring benefits of 20,000 to 600,000 yuan. Payload is a key point in the field of aerospace vehicles. From the perspective of the development system of aerospace fuel tank materials in my country, the materials commonly used in my country are 2A14 and 2219, which have a strength of 400MPa and belong to the second generation of fuel tank structural materials. Foreign 500MPa-level high-strength Al-Cu aluminum alloy tank materials have been widely used. The current largest fuel tank diameter abroad is 10m, far exceeding the largest 5m level in my country. Summary of the invention

[0003] In view of the above shortcomings, the present invention provides a method for preparing a large-size high-strength Al-Cu alloy plate. The alloy prepared by the method of the present invention can not only effectively reduce the density of the Al-Cu alloy plate and improve the strength performance, but also has a higher elastic modulus, and is a structural material with great application prospects in the aerospace field. The specific technical scheme is as follows:

[0004] A method for preparing a large-size high-strength Al-Cu alloy plate comprises the following steps:

[0005] (1) Ingredients: The Al-Cu alloy includes the following elements in percentage by weight: Si≤0.02%, Fe≤0.05%, Cu: 3.7-6.4%, Mg≤0.5%, Li≤1.2%, Ag≤0.4%, Mn: 0.001-0.4%, Zn≤0.25%, Ti: 0.015-0.035%, Zr: 0.09-0.15%, and the remainder is Al and unavoidable impurity elements.

[0006] (2) Melting: Melting the ingredients.

[0007] (3) Melt purification: A multi-stage composite melt purification method is used for melt purification.

[0008] (4) Casting: Casting the alloy to obtain an ingot, specifically: using a semi-continuous casting device with argon inert atmosphere protection to cast the alloy to obtain a square ingot with a thickness of 350 to 450 mm, a width of 1300 to 1850 mm, and a length of 2300 to 3900 mm;

[0009] The purpose of filling with argon inert protective gas is to prevent the melt from coming into contact with air during the casting process and reacting with oxygen and water vapor in the air to produce impurities such as oxides, thereby improving the quality of the melt.

[0010] (5) Homogenizing heat treatment: the ingot is subjected to homogenizing heat treatment.

[0011] (6) Machining: The ingot after homogenization heat treatment is machined, specifically: after cutting off the bottom (starting casting) and top (gate at the end of casting) from the ingot, the large surface is milled to remove 15 mm, and the side is milled to remove 10 mm. The specifications of the ingot after machining are 370 mm (thickness) × 1440 mm (width) × 2300 mm (length).

[0012] (7) Hot rolling: the machined ingot is heated to 450-470°C for 3-18 hours, and the ingot after the insulation is subjected to multi-directional composite deformation hot rolling using a hot rolling mill, wherein the deformation rate of the first rolling deformation direction is 16.5%-30%, and then the ingot is subjected to reversing rolling, the rolling deformation is suspended, the plate is subjected to temperature-controlled cooling, and then 1-3 passes of temperature-controlled rolling are performed to the target thickness;

[0013] The conveyor roller end of the hot rolling mill is equipped with an ingot steering device to assist the ingot in rotating 90 degrees according to process requirements;

[0014] During hot rolling, a better microstructure is obtained through reversing rolling deformation. The texture formed after longitudinal rolling may be partially retained in the subsequent transverse rolling process, and new texture components are generated. The evolution of texture depends on the deformation rate of longitudinal rolling and transverse rolling. The technology described in the present invention "the deformation rate of the first rolling deformation direction is 16.5% to 30%, and then reversing rolling is performed", on the one hand, it can obtain a texture combination with excellent performance, reduce the strength of a single texture type, reduce the anisotropy of microstructure and performance, and improve the service performance of the material; on the other hand, the cross-rolling deformation with appropriate proportions described in the present invention increases the dislocation density of the grains, rearranges the dislocations by means of slip and climb, and finally forms an ideal subgrain structure, improves the fracture toughness and corrosion resistance of the material, and reduces the fatigue crack growth rate.

[0015] (8) Straightening: The hot-rolled plate is deformed by a pre-stretching machine to a permanent plastic deformation of 0.5 to 1.0%;

[0016] The straightening process before the deformation heat treatment can effectively improve the straightness of the plate before entering the roller-bottom quenching furnace. If the straightening process described in the present invention is missing, the hot-rolled plate is directly placed in the roller-bottom quenching furnace for solution quenching treatment. The unevenness of the hot-rolled plate will be further amplified after quenching (the fundamental reason is that the unevenness of the plate before quenching is poor, resulting in uneven cooling and increased quenching residual stress). Even if a pre-stretching machine is used to reduce the residual stress after solution quenching, the residual stress of the ultra-wide Al-Cu aluminum alloy plate in the embodiment of the present invention cannot be fully reduced to the quality level that meets the high-end application field.

[0017] (9) Solution quenching: Use a roller bottom quenching furnace to perform solution quenching on the hot rolled and straightened plates. The solution temperature is 490-510°C. For plates with a thickness of ≤50 mm, the holding time is 10-150 min and the quenching speed is 12-35 m / min. For plates with a thickness of >50-100 mm, the holding time is 120-270 min and the quenching speed is 4-10 m / min.

[0018] (10) Deformation heat treatment: Use an aging furnace and a pre-stretching machine / rolling mill to perform deformation heat treatment to obtain the final heat treatment state. The specific steps include: (a) pre-aging: After the solid solution quenching heat treatment, the plate is artificially aged at 150-160°C in an aging heat treatment furnace for 1-4 hours, and then quenched and cooled after being taken out of the furnace; (b) deformation processing: use a pre-stretching machine to perform 2-7% plastic deformation, and then use a rolling mill to perform 8-15% plastic deformation, and the accumulated total plastic deformation is 10-18%; (c) re-aging: artificial aging is performed in an aging heat treatment furnace, the first stage aging temperature is 65-85°C, the insulation time is 48-168h; the second stage aging temperature is 150-160°C, and the insulation time is 12-48h;

[0019] Among them, the role of the pre-aging process is: heating the plate to 155℃ for insulation at a very high heating rate (150℃ / h) to inhibit the precipitation of excessive δ' phase in the matrix during the slow heating process (resulting in increased anisotropy of the plate) and increase the probability of subsequent precipitation of T1 phase. Through a shorter pre-aging insulation time (e.g. 1h), fine and dispersed GP zones are precipitated in the aluminum alloy matrix as the basis for the subsequent precipitation of high-quality strengthening phases. After the insulation is completed, rapid cooling can form a certain number of vacancies in the aluminum matrix as a carrier for the diffusion of supersaturated solid solution precipitation elements (some elements must diffuse through vacancies, otherwise the diffusion rate is about one order of magnitude lower than that of other elements);

[0020] Effect of deformation processing (pre-stretching + rolling): The pre-stretching machine generates about 2% plastic deformation on the sheet. On the one hand, it can reduce the heat treatment residual stress brought by quenching. On the other hand, it can introduce a certain number of dislocations into the matrix of the alloy through plastic deformation; about 10% rolling plastic deformation. The rolling deformation compresses the metal on the plane perpendicular to the rolling direction. This compression helps to eliminate or weaken the texture and anisotropy of the metal in this direction.

[0021] Effect of re-aging: The effect of the first-stage low-temperature long-holding-time aging treatment is to use the high-density dislocations obtained by the "pre-stretching + rolling" deformation processing as nucleation sites, and use the vacancies formed by pre-aging quenching as carriers for alloy element diffusion. Keep warm for a long time under low-temperature conditions to precipitate very fine GP zones from the supersaturated solid solution, which are very beneficial to improving the strength and fatigue resistance of the sheet; then enter the second-stage high-temperature short-holding-time aging treatment, whose effect is to obtain ideal number density and size of T1 phase and δ' phase on the basis of very fine and dispersed GP zones.

[0022] (11) Sawing: Sawing to obtain finished sheets.

[0023] Preferably, in step (1), in the elemental composition of the Al-Cu alloy, the Cu / Li ratio is 4-4.5, the addition amount of Ag element is 0.35%, the addition amount of Mn element is 0.02%, and the addition amount of Mg element is 0.4%;

[0024] Through a reasonable Cu / Li ratio, a high volume fraction of T1 strengthening phase can be obtained. By controlling the total content of Cu + Li, both the density reduction and strength improvement of the alloy are taken into account; through the compound microalloying of Zn + Mg + Ag elements in the above ratio, it further promotes the formation of fine and dispersed T1 phase, thereby obtaining higher tensile strength, yield strength and elongation, and effectively reducing the fatigue crack propagation rate of the alloy; through the compound microalloying of Mn + Zr + Ti elements in the above ratio, on the one hand, by adding sufficient amounts of these 3 elements, fine grain size can be obtained during casting solidification, and subgrain structure can be induced during the solution process. On the other hand, by controlling the amount of these 3 elements not to exceed the upper limit, the formation of coarse metal compounds during the casting solidification process can be avoided; the chemical composition of the present invention enables the prepared alloy to maintain high strength while significantly reducing the density of the alloy.

[0025] Preferably, in step (2), the melting is carried out in a vacuum induction furnace with high sealing performance, high corrosion resistance and precise temperature control ability. The furnace body material in contact with the melt is a composite material of alumina and silicon nitride, and the atmosphere in contact with the melt is argon inert protective gas to prevent the melt from being oxidized during the melting process, thereby effectively reducing metallurgical defects such as oxides. An electromagnetic stirring device is used to stir the melt during the melting process to make the temperature in the melt pool uniform.

[0026] The high-sealing and high-corrosion-resistant melting furnace can avoid chemical reactions between the melt and the materials in contact with the furnace body. The materials in contact with the melt can be one or more of the following materials: stainless steel, high-purity iron, molybdenum, graphite, ceramic materials (alumina series, silicon carbide series, silicon carbide + silicon oxynitride series); high sealing and argon inert protective gas filling are to avoid the melt from contacting the air and reacting with oxygen and water vapor in the air to produce impurities such as oxides, thereby improving the quality of the melt.

[0027] Preferably, in step (3), the multi-stage composite melt purification method is: firstly, melt refining is performed with a melt covering agent to achieve the first-stage melt purification, then 1 to 4 argon mixed gas rotation purge refining devices are used for the second-stage melt purification, and finally vacuum degassing is used as the third-stage melt purification, preferably through multi-stage combined melt purification, the hydrogen content and slag content in the melt are effectively reduced;

[0028] The use of a multi-stage composite melt purification method comprehensively utilizes the advantages of various methods and makes up for the shortcomings of other methods: the first-stage melt purification - melt covering agent, has the advantages of isolating the melt from oxygen and water vapor in the air, thereby reducing the oxidation and air absorption of the melt, reducing the evaporation loss of volatile elements, and improving the control accuracy of the alloy composition, but the effect of removing inclusions and gases inside the melt is limited, so other purification methods are needed to supplement it; the second-stage melt purification - argon mixed gas rotary purge is the most important device for removing hydrogen and slag inside the melt in the technology described in the present invention. The rotary purge method can make the bubbles evenly dispersed in the melt. , increase the contact area between bubbles and melt, and react with hydrogen in the melt to improve the efficiency of degassing and slag removal. However, this method of melt purification is difficult to break through the purification limit due to the existence of atmospheric pressure, and requires vacuum degassing for assistance; the third level of melt purification - vacuum degassing, can effectively remove gases in the melt, especially volatile elements such as hydrogen, and at the same time, inclusions are also removed as bubbles float up, so as to achieve the purpose of impurity removal. A large amount of energy is consumed in the vacuum degassing process to maintain the vacuum state, so the cost is relatively high. It is only used in the final stage of melt purification. On the one hand, it can effectively improve product quality, and on the other hand, it can effectively save costs.

[0029] Preferably, in step (5), the homogenization heat treatment is performed by placing the ingot into a homogenization heat treatment furnace at room temperature, specifically: firstly heating the ingot from room temperature to a first-stage insulation temperature of 415-425°C at a heating rate of 40-60°C / h, and keeping the temperature for 8-16h, then heating the ingot to a second-stage insulation temperature of 500-530°C at a heating rate of 25-35°C / h, and keeping the temperature for 24-30h, and finally cooling the ingot to room temperature by water mist cooling;

[0030] Homogenization heat treatment principle:

[0031] (a) By controlling the heating rate as described above, Al 3 The Zr particles are densely packed in the nucleus and energy is avoided. The heating rate from room temperature to the first stage homogenization heat treatment holding temperature is similar to that of Al 3 The nucleation rate of Zr particles is closely related. 3 The nucleation rate of Zr particles can fully exert the effect of the Zr element added to the alloy, and obtain finely dispersed Al 3 Zr particles, thereby controlling the recovery and recrystallization behavior of the grains in the subsequent processing process, and obtaining excellent performance. When the heating rate is greater than the upper limit of the heating rate control of the present invention, Al 3 The nucleation rate of Zr particles is low, resulting in only a small amount of Al 3 Zr particles grow and the ability to inhibit grain recrystallization is insufficient. When the heating rate is less than the lower limit of the heating rate control described in the present invention, Al 3 The nucleation rate of Zr particles no longer increases, but the production efficiency of homogenization heat treatment is sacrificed, wasting energy;

[0032] (b) The first stage target holding temperature of the present invention is 415-425°C, and the holding time is 8-16 hours, which can effectively allow the supersaturated Zr element in the ingot to be fully precipitated, and the Al3Zr particles to grow to a relatively stable size. If the first stage holding temperature is too low or the holding time is too short, the supersaturated Zr element in the ingot has not been fully precipitated, and the ingot directly enters the second stage of high temperature homogenization, then a part of the Al3Zr particles will quickly grow to a size that cannot play a role in pinning the grain boundary movement, causing these Al3Zr particles to lose the function of inhibiting recrystallization;

[0033] (c) The second-stage target insulation temperature of the present invention is 500-530°C, and the insulation time is 24-30 hours, which can fully dissolve the primary phase formed in the casting process into the matrix as much as possible, thereby avoiding the coarse primary phase from remaining and destroying the continuity of the matrix. If the temperature of the second-stage homogenization heat treatment is too low or too short, the coarse primary phase inevitably generated during the casting solidification process will remain, reducing the elongation and fatigue resistance of the alloy and the fatigue crack growth rate. If the temperature of the second-stage homogenization heat treatment is too high or too long, it will lead to energy waste and cause the Al3Zr particles to merge with each other and grow to the point where they can no longer inhibit recrystallization;

[0034] (d) After the second stage homogenization heat treatment described in the present invention, the ingot is cooled to room temperature by water mist cooling, in order to prevent the alloying elements that have dissolved back into the matrix from gradually precipitating to form coarse intermetallic compounds during the process of slowly cooling the ingot to room temperature, thereby improving the plastic deformation properties of the alloy during rolling.

[0035] Preferably, in step (7), during the multi-directional composite deformation hot rolling process, when the plate thickness is reduced to 100-120 mm, a heavy hydraulic shear is used to perform the first plate head and tail cutting, and when the plate thickness is reduced to 30-60 mm, a heavy hydraulic shear is used to perform the second plate head and tail cutting.

[0036] Using heavy hydraulic shears to cut off the head and tail of the plate can effectively prevent the head and tail of the rolling deformation and the depression of the edges from evolving into cracks, affecting the final effective size of the plate, thereby ensuring that the edge delamination / cracking of the large-size plate is well controlled when rolling. Because when the temperature is controlled and cooled to about 300℃, the aluminum alloy plate has a strong rolling cracking sensitivity. Therefore, the measure of cutting off the head and tail of the plate creates the necessary conditions for rolling with temperature controlled cooling to about 300℃.

[0037] Preferably, in step (7), the temperature-controlled cooling is: using a spray cooling device of the hot rolling unit to control the temperature of the plate to cool to 250-350° C.;

[0038] Temperature-controlled cooling can effectively avoid dynamic recrystallization of the microstructure of aluminum alloy plates, synergistically improve the strength and corrosion resistance of the material, and reduce the fatigue crack growth rate.

[0039] Preferably, in step (7), the method of multi-directional composite deformation hot rolling is: firstly, transverse rolling is performed in a direction perpendicular to the direction of movement of the casting ingot starter, and then longitudinal rolling is performed in a direction parallel to the casting direction.

[0040] Preferably, in step (7), the method of multi-directional composite deformation hot rolling is: firstly, longitudinal rolling is performed in a direction parallel to the movement direction of the casting starter head, and then transverse rolling is performed in a direction perpendicular to the movement direction of the casting starter head.

[0041] Preferably, in step (7), the method of multi-directional composite deformation hot rolling is: firstly, longitudinal rolling is performed in a direction parallel to the movement direction of the casting ingot head, then transverse rolling is performed in a direction perpendicular to the movement direction of the casting ingot head, and then longitudinal rolling is performed in a direction parallel to the movement direction of the casting ingot head.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. The present invention optimizes the raw material composition and the preparation method to obtain an aluminum alloy with low density, high strength and high elastic modulus. The density of the aluminum alloy prepared by the present invention is about 2.70g / cm 3 The aluminum alloy has a yield strength of more than 530MPa, a tensile strength of more than 580MPa, an elongation of more than 9MPa, and an elastic modulus of 77-79GPa. It has higher strength properties and elastic modulus than aluminum alloys such as 2A14, 2219 and 5A06 that are widely used in spacecraft, and has lower residual stress, lower crack growth rate, and lower mechanical anisotropy of the material. It is a structural material with great application prospects in the aerospace field.

[0044] 2. The present invention can obtain a high volume fraction of T1 strengthening phase, fine grains, and sub-grain structure by optimizing the raw material composition, and avoid the formation of coarse metal compounds during the casting solidification process.

[0045] 3. The present invention obtains Al2O3 dispersed in the microstructure and in a coherent state with the matrix through a reasonably designed homogenization heat treatment process. 3 Zr particles improve the alloy's ability to inhibit recrystallization, allowing the Al-Cu alloy sheet to obtain an ideal sub-grain structure. In addition, this process also has the advantages of saving time and avoiding energy waste.

[0046] 4. The hot rolling process of the present invention can reduce the strength of a single texture type, reduce the anisotropy of microstructure and performance, improve the service performance of the material, avoid dynamic recrystallization of the microstructure of the aluminum alloy plate (obtaining a sub-grain structure), improve the fracture toughness and corrosion resistance of the material, and reduce the fatigue crack growth rate. Use heavy hydraulic shears to cut the head and tail of the plate to improve the hot rolling forming ability and avoid rolling cracking.

[0047] 5. The reasonable heating rate of "pre-aging" in the thermomechanical treatment of the present invention inhibits the precipitation of excessive δ' phase in the matrix; the shorter pre-aging holding time causes fine and dispersed GP zones to precipitate in the aluminum alloy matrix; and the rapid cooling can form a certain number of vacancies in the aluminum matrix, which serve as carriers for the diffusion of the precipitated elements of the supersaturated solid solution.

[0048] The "pre-stretching + rolling" deformation processing in the thermomechanical treatment of the present invention introduces dislocations in a composite manner, allowing numerous dislocations to create more precipitation nucleation sites for strengthening phases, so that a large number of T1 strengthening phases that are beneficial to reducing the anisotropy of the plate are precipitated in the microstructure (the T1 phase undergoes bypassing / alternating slip during deformation), and the number density of the δ' phase is reduced (the δ' phase undergoes coplanar slip during deformation). Even if the δ' phase still exists in the microstructure, its size is mostly ≤50nm, which is beneficial to improving the mechanical properties.

[0049] The "re-aging" in the thermomechanical treatment of the present invention, the role of the first stage low-temperature long-holding time aging treatment is to use the high-density dislocations obtained by the "pre-stretching + rolling" deformation processing as nucleation sites, and the vacancies formed by the pre-aging quenching as carriers for the diffusion of alloy elements, and to keep the heat for a long time under low temperature conditions to precipitate very fine GP zones that are very beneficial to improving the strength and fatigue resistance of the plate from the supersaturated solid solution; and then enter the second stage high-temperature short-holding time aging treatment, which is used to obtain T1 phase and δ' phase with ideal number density and size on the basis of very fine dispersed GP zones. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for describing the embodiments are briefly introduced below.

[0051] Figure 1 It is the principle diagram of the present invention;

[0052] Figure 2 The following is a comparison of the transmission electron microscope microstructure photos of the plates prepared in Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0053] The specific embodiments of the present invention are described in detail below, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

[0054] Example 1

[0055] The principle diagram of this embodiment is as follows Figure 1 As shown, the goal is to prepare large-size high-strength Al-Cu alloy plates with a thickness of 15 mm and a width of 2800 mm. The detailed steps are as follows:

[0056] (1) Ingredients: High-purity metals or intermediate alloys of corresponding purity are used for ingredient preparation according to weight percentage. The actual measured composition of the melt is: Si = 0.01%, Fe = 0.02%, Cu = 3.9%, Mg = 0.4%, Li = 0.9%, Ag = 0.35%, Mn = 0.02%, Zn = 0.02%, Ti = 0.03%, Zr = 0.12%, and the balance is Al and unavoidable impurity elements.

[0057] (2) Melting: Use a melting furnace with high sealing, high corrosion resistance and precise temperature control capabilities for melting. During the melting process, use an electromagnetic stirring device to properly stir the melt to ensure that the temperature in the molten pool is uniform. The atmosphere in contact with the melt is an argon inert protective gas to prevent the melt from being oxidized during the melting process.

[0058] (3) Melt purification: First, melt refining is performed with a melt covering agent to achieve the first stage of melt purification, and then 1 to 4 argon mixed gases are used to rotate and purge the refining device for the second stage of melt purification, and finally vacuum degassing is used as the third stage of melt purification.

[0059] (4) Casting: Casting was performed using an argon inert atmosphere to obtain a square ingot with a thickness of 400 mm and a width of 1460 mm.

[0060] (5) Homogenization heat treatment: The ingot is placed in a homogenization heat treatment furnace at room temperature for homogenization heat treatment. The ingot is heated from room temperature to a first-stage insulation temperature of 420°C at a heating rate of 50°C / h and kept at that temperature for 10 h. The ingot is heated to a second-stage insulation temperature of 510°C at a heating rate of 30°C / h and kept at that temperature for 26 h. The ingot is then cooled to room temperature by water mist cooling.

[0061] (6) Machining: After cutting off the bottom (starting casting) and top (gate at the end of casting) from the ingot, 15 mm is removed by large surface milling and 10 mm is removed by side milling. The specifications of the ingot after machining are 370 mm (thickness) × 1440 mm (width) × 2300 mm (length).

[0062] (7) Hot rolling: The ingot is heated to 460°C in a heating furnace and kept at this temperature for 6 hours. First, longitudinal rolling is performed in a direction parallel to the direction of motion of the casting ingot starter. The ingot is extended from 2300 mm in the longitudinal direction to 3000 mm by rolling. The deformation rate in the rolling deformation direction is 23%. Then, the ingot is rotated 90° by the ingot turning device at the end of the conveyor roller table of the hot rolling mill. Then, transverse rolling is performed in a direction perpendicular to the direction of motion of the casting ingot starter. The ingot is extended from 1440 mm in the width direction by rolling. When the thickness is 110 mm, the first plate head and tail are cut off by heavy hydraulic shears. When the thickness is 40 mm, the second plate head and tail are cut off. The rolling deformation is suspended. The plate is cooled to 300°C by the spray cooling device of the hot rolling unit. Then, two passes of temperature-controlled rolling are performed until the plate thickness is 16.3 mm.

[0063] (8) Straightening: Use a pre-stretching machine to perform deformation with a permanent plastic deformation of 0.5%.

[0064] (9) Solution quenching treatment: The hot rolled plate was solution quenched in a roller hearth quenching furnace at a solution temperature of 500°C, a holding time of 60 min, and a quenching speed of 25 m / min.

[0065] (10) Deformation heat treatment: (a) Pre-aging: Artificial aging is carried out in an aging heat treatment furnace, using a heating rate of 150℃ / h, heating from room temperature to 155℃ and keeping warm for 1h, then taking it out of the furnace and letting the plate quench and cool rapidly. (b) Deformation processing: Use a pre-stretching machine to perform about 2% pre-stretching plastic deformation, and then use a rolling mill to perform about 10% rolling plastic deformation to make the plate thickness reach 15mm. (c) Re-aging: Artificial aging is carried out in an aging heat treatment furnace, the first stage aging temperature is 85℃, the holding time is 48h; the second stage aging temperature is 155℃, the holding time is 28h.

[0066] (11) Sawing: Sawing the edges and head and tail areas will produce a finished plate with a width of 2800 mm.

[0067] Example 2

[0068] The goal of this example is to prepare a large-sized high-strength Al-Cu alloy plate with a thickness of 15 mm and a width of 2800 mm. The detailed steps are as follows:

[0069] (1) Ingredients: High-purity metals or intermediate alloys of corresponding purity are used for ingredient preparation according to weight percentage. The actual measured composition of the melt is: Si = 0.02%, Fe = 0.05%, Cu = 5.4%, Mg = 0.5%, Li = 1.2%, Ag = 0.4%, Mn = 0.4%, Zn = 0.25%, Ti = 0.035%, Zr = 0.15%, and the balance is Al and unavoidable impurity elements.

[0070] (2) Melting: Use a melting furnace with high sealing, high corrosion resistance and precise temperature control capabilities for melting. During the melting process, use an electromagnetic stirring device to properly stir the melt to ensure that the temperature in the molten pool is uniform. The atmosphere in contact with the melt is an argon inert protective gas to prevent the melt from being oxidized during the melting process.

[0071] (3) Melt purification: First, melt refining is performed with a melt covering agent to achieve the first stage of melt purification, and then 1 to 4 argon mixed gases are used to rotate and purge the refining device for the second stage of melt purification, and finally vacuum degassing is used as the third stage of melt purification.

[0072] (4) Casting: Casting was performed using an argon inert atmosphere to obtain a square ingot with a thickness of 400 mm and a width of 1460 mm.

[0073] (5) Homogenization heat treatment: The ingot is placed in a homogenization heat treatment furnace for homogenization heat treatment at room temperature, specifically: the ingot is first heated from room temperature to a first-stage insulation temperature of 425°C at a heating rate of 60°C / h, and kept warm for 8 hours; then the ingot is heated to a second-stage insulation temperature of 530°C at a heating rate of 35°C / h, and kept warm for 28 hours; finally, the ingot is cooled to room temperature by water mist cooling.

[0074] (6) Machining: After cutting off the bottom (starting casting) and top (gate at the end of casting) from the ingot, 15 mm is removed by large surface milling and 10 mm is removed by side milling. The specifications of the ingot after machining are 370 mm (thickness) × 1440 mm (width) × 2300 mm (length).

[0075] (7) Hot rolling: The ingot is heated to 470°C in a heating furnace and kept at this temperature for 3 hours. First, the ingot is rolled transversely in a direction perpendicular to the direction of motion of the casting ingot starter. The ingot is extended from 2300 mm in the longitudinal direction to 3000 mm by rolling. The deformation rate in the rolling deformation direction is 30%. Then, the ingot turning device at the end of the conveyor roller table of the hot rolling mill is used to rotate the ingot 90°. Then, the ingot is rolled longitudinally in a direction parallel to the casting direction. The ingot is extended from 1440 mm in the width direction by rolling. When the thickness is 120 mm, the plate head and tail are cut off for the first time using heavy hydraulic shears. When the thickness is 60 mm, the plate head and tail are cut off for the second time. The rolling deformation is suspended. The plate is cooled to 350°C by the spray cooling device of the hot rolling unit. Then, three passes of temperature-controlled rolling are performed until the plate thickness is 16.3 mm.

[0076] (8) Straightening: Use a pre-stretching machine to perform deformation with a permanent plastic deformation of 1.0%.

[0077] (9) Solution quenching treatment: The hot rolled plate was solution quenched in a roller hearth quenching furnace at a solution temperature of 500°C, a holding time of 60 min, and a quenching speed of 25 m / min.

[0078] (10) Deformation heat treatment: (a) Pre-aging: Artificial aging is carried out in an aging heat treatment furnace, using a heating rate of 150℃ / h, heating from room temperature to 155℃ and keeping warm for 4h, then taking it out of the furnace and letting the plate quench and cool rapidly. (b) Deformation processing: Use a pre-stretching machine to perform 7% pre-stretching plastic deformation, and then use a rolling mill to perform about 15% rolling plastic deformation to make the plate thickness reach 18mm. (c) Re-aging: Artificial aging is carried out in an aging heat treatment furnace, the first stage aging temperature is 65℃, the holding time is 68h; the second stage aging temperature is 155℃, the holding time is 28h.

[0079] (11) Sawing: Sawing the edges and head and tail areas will produce a finished plate with a width of 2800 mm.

[0080] Example 3

[0081] The goal of this implementation is to prepare large-size high-strength Al-Cu alloy plates with a thickness of 15mm and a width of 2800mm. The detailed steps are as follows:

[0082] (1) Ingredients: High-purity metals or master alloys of corresponding purity are used for ingredient preparation according to weight percentage. The actual measured composition of the melt is: Si = 0.015%, Fe = 0.04%, Cu = 4.0%, Mg = 0.3%, Li = 1.0%, Ag = 0.4%, Mn = 0.09%, Zn = 0.10%, Ti = 0.02%, Zr = 0.10%, and the balance is Al and unavoidable impurity elements.

[0083] (2) Melting: Use a melting furnace with high sealing, high corrosion resistance and precise temperature control capabilities for melting. During the melting process, use an electromagnetic stirring device to properly stir the melt to ensure that the temperature in the molten pool is uniform. The atmosphere in contact with the melt is an argon inert protective gas to prevent the melt from being oxidized during the melting process.

[0084] (3) Melt purification: First, melt refining is performed with a melt covering agent to achieve the first stage of melt purification, and then 1 to 4 argon mixed gases are used to rotate and purge the refining device for the second stage of melt purification, and finally vacuum degassing is used as the third stage of melt purification.

[0085] (4) Casting: Casting was performed using an argon inert atmosphere to obtain a square ingot with a thickness of 400 mm and a width of 1460 mm.

[0086] (5) Homogenization heat treatment: The ingot is placed in a homogenization heat treatment furnace for homogenization heat treatment at room temperature. The ingot is first heated from room temperature to a first-stage insulation temperature of 415°C at a heating rate of 40°C / h and kept at that temperature for 16 hours. The ingot is then heated to a second-stage insulation temperature of 500°C at a heating rate of 25°C / h and kept at that temperature for 30 hours. Finally, the ingot is cooled to room temperature by water mist cooling.

[0087] (6) Machining: After cutting off the bottom (starting casting) and top (gate at the end of casting) from the ingot, 15 mm is removed by large surface milling and 10 mm is removed by side milling. The specifications of the ingot after machining are 370 mm (thickness) × 1440 mm (width) × 2300 mm (length).

[0088] (7) Hot rolling: Use a heating furnace to heat the ingot to 450℃, keep it warm for 18h, first perform longitudinal rolling, the rolling direction is parallel to the direction of movement of the casting ingot head, then perform transverse rolling, the rolling direction is perpendicular to the direction of movement of the casting ingot head, and then perform longitudinal rolling, the rolling direction is parallel to the direction of movement of the casting ingot head, so that the width of the ingot 1440mm is continuously extended under the action of rolling, and when the thickness is rolled to 100mm, use heavy hydraulic shears to perform the first plate head and tail cutting, and when the thickness is rolled to 30mm, perform the second plate head and tail cutting. Pause rolling deformation, use the spray cooling device of the hot rolling unit to control the temperature of the plate to 250℃, and then perform three passes of temperature-controlled rolling until the plate thickness is 16.3mm.

[0089] (8) Straightening: Use a pre-stretching machine to perform deformation with a permanent plastic deformation of 0.8%.

[0090] (9) Solution quenching treatment: The hot rolled plate was solution quenched in a roller hearth quenching furnace at a solution temperature of 500°C, a holding time of 60 min, and a quenching speed of 25 m / min.

[0091] (10) Deformation heat treatment: (a) Pre-aging: Artificial aging is carried out in an aging heat treatment furnace, using a heating rate of 150℃ / h, heating from room temperature to 155℃ and keeping warm for 1h, then taking it out of the furnace and letting the plate quench and cool rapidly. (b) Deformation processing: Use a pre-stretching machine to perform pre-stretching plastic deformation of about 4%, and then use a rolling mill to perform rolling plastic deformation of about 8% to make the plate thickness reach 15mm. (c) Re-aging: Artificial aging is carried out in an aging heat treatment furnace, the first stage aging temperature is 70℃, the holding time is 68h; the second stage aging temperature is 155℃, the holding time is 28h.

[0092] (11) Sawing: Sawing the edges and head and tail areas will produce a finished plate with a width of 2800 mm.

[0093] Comparative Example 1

[0094] The target of this comparative example is to prepare a large-size high-strength Al-Cu alloy plate with a thickness of 15 mm and a width of 2800 mm, which is the same as Example 1. The difference between Comparative Example 1 and Example 1 mainly lies in the chemical composition, and the other process is the same as the embodiment. The specific composition of Comparative Example 1 is: Si=0.03%, Fe=0.10%, Cu=6.2%, Mg=0.002%, Mn=0.28%, Zn=0.01%, Ti=0.04%, V=0.08%, Zr=0.13%, and the rest is Al and unavoidable impurity elements.

[0095] Comparative Example 2

[0096] The target of Comparative Example 2 is to prepare a large-size high-strength Al-Cu alloy plate with a thickness of 15 mm and a width of 2800 mm, which is the same as Example 1. The difference between Comparative Example 2 and Example 1 mainly lies in the (10) deformation heat treatment after solution quenching, while the composition, all other rolling and homogenization heat treatments are the same as the embodiment. The process path of step (10) of Comparative Example 2 is "pre-stretching-aging (single stage)", which is different from the process path of step (10) of Example 1 "pre-aging-deformation processing (pre-stretching + rolling)-re-aging (double stage)". The specific implementation of step (10) of Comparative Example 2 is as follows:

[0097] Pre-stretching: Within 4 hours after solution quenching, use a pre-stretching machine to stretch the plate with a permanent plastic deformation rate of 4%.

[0098] Aging: After pre-stretching, enter the aging heat treatment furnace within 24 hours at room temperature, heat up to 155℃ and keep warm for 28 hours.

[0099] Comparative Example 3

[0100] The target of comparative example 3 is to prepare a large-sized high-strength Al-Cu alloy plate with a thickness of 15 mm and a width of 2800 mm, which is the same as that of example 1. Comparative example 3 is a conventional technology, and the detailed steps are as follows:

[0101] (1) Ingredients: The ingredients are prepared according to weight percentage. The actual measured composition of the melt is: Si = 0.03%, Fe = 0.11%, Cu = 6.1%, Mg = 0.003%, Mn = 0.27%, Zn = 0.01%, Ti = 0.038%, V = 0.09%, Zr = 0.12%, and the remainder is Al and unavoidable impurity elements.

[0102] (2) Melting: Use ordinary melting furnace for melting.

[0103] (3) Melt purification: Use single-stage argon gas rotary purge to purify the melt.

[0104] (4) Casting: A common semi-continuous casting system is used for casting to obtain a square ingot with a thickness of 520 mm and a width of 2600 mm.

[0105] (5) Homogenization heat treatment: The ingot is placed in a homogenization heat treatment furnace at room temperature for homogenization heat treatment. The ingot is heated from room temperature to a holding temperature of 520°C at a heating rate of 100°C / h for 20 hours. After homogenization heat treatment, the ingot is taken out of the furnace and cooled in air.

[0106] (6) Machining: After cutting off the bottom (starting casting) and top (gate at the end of casting) from the ingot, the large surface is milled to remove 15 mm, and the side is milled to remove 10 mm. The specifications of the ingot after machining are 480 mm (thickness) × 2570 mm (width).

[0107] (7) Hot rolling: The ingot is heated to 460°C in a heating furnace and kept at this temperature for 6 hours. Longitudinal rolling is performed in a direction parallel to the direction of motion of the casting starter head. The plate with a thickness of 15.4 mm and a width of about 2570 mm is rolled using a unidirectional deformation method (0.4 mm is retained for subsequent pre-stretching and thinning).

[0108] (8) Solution quenching: The hot rolled plate is solution quenched in a roller hearth quenching furnace at a solution temperature of 500°C, a holding time of 60 min, and a quenching speed of 25 m / min.

[0109] (9) Pre-stretching: A pre-stretching machine is used to perform deformation to a permanent plastic deformation of 4.0%.

[0110] (10) Aging: Artificial aging is carried out in an aging heat treatment furnace at a temperature of 163°C and a holding time of 12 h.

[0111] (11) Sawing: Sawing is performed to obtain finished panels.

[0112] Comparative Example 4

[0113] The target of this comparative example is to prepare a large-size high-strength Al-Cu alloy plate with a thickness of 15 mm and a width of 2800 mm, which is the same as Example 1. The difference between Comparative Example 1 and Example 1 mainly lies in the chemical composition, and the other process is the same as the embodiment. The specific composition of Comparative Example 1 is: Si=0.01%, Fe=0.02%, Cu=4.1%, Mg=0.4%, Li=0.7%, Ag=0.35%, Mn=0.02%, Zn=0.02%, Ti=0.03%, Zr=0.12%, and the rest is Al and unavoidable impurity elements.

[0114] The properties of the alloys obtained in the embodiments and comparative examples were tested, and the results are shown in Table 1:

[0115] Table 1 Performance comparison of the examples and comparative alloys

[0116]

[0117]

[0118] Table 1 shows that the yield strength and tensile strength of the embodiment are higher than those of comparative examples 1, 3 and 4, and the density is only about 2.70 g / cm 3, which is significantly lower than 2.83 g / cm2 of Comparative Examples 1 and 3. 3 This indicates that the chemical composition of the present invention enables the alloy to maintain high strength while significantly reducing the density of the alloy, which is of great significance for the lightweighting of aerospace vehicles.

[0119] From the data of Example 1 and Comparative Example 2, it can be seen that: the anisotropy of the tensile properties of the plate prepared in Example 1 is lower, the tensile strength in the L direction and the LT direction of Example 1 are equivalent (almost no anisotropy), but the difference in tensile strength in the L direction and the LT direction of Comparative Example 2 (the deformation heat treatment of step 10 of the present invention is not used) reaches 29 MPa (obvious anisotropy); the residual stress of Example 1 is lower; the fatigue crack growth rate of Example 1 is lower.

[0120] The transmission electron microscope microstructure photo of the plate obtained in Example 1 is as follows: Figure 2 As shown in (a), Figure 2 (a) shows that the deformation processing of "pre-stretching + rolling" can introduce dislocations in a composite manner, allowing numerous dislocations to create more precipitation nucleation sites for strengthening phases, so that a large number of T1 strengthening phases that are beneficial to reducing the anisotropy of the plate are precipitated in the microstructure (the T1 phase undergoes bypassing / alternating slip during deformation), and the number density of the δ' phase is reduced (the δ' phase undergoes coplanar slip during deformation). Even if the δ' phase still exists in the microstructure, most of its size is ≤50nm, which is beneficial to improving the mechanical properties.

[0121] The transmission electron microscope microstructure photo of the plate obtained in Comparative Example 2 is as follows: Figure 2 (b) Figure 2 (b) shows that the number density of T1 phase is low, the number density of δ' phase is larger, and the sizes of both T1 and δ' phases are larger, which is not conducive to the performance of the sheet.

[0122] From the data of Example 1 and Comparative Example 4, it can be seen that the Cu / Li ratio in the composition has a certain influence on the strength of the finished product. When the Cu / Li ratio is 4 to 4.5, a high volume fraction of T1 strengthening phase can be obtained, which effectively improves the strength.

[0123] In summary, the present invention obtains an aluminum alloy having low density, high strength and high elastic modulus properties by optimizing the raw materials and the preparation method thereof. The density of the aluminum alloy obtained by the present invention is about 2.70 g / cm 3 The aluminum alloy has a yield strength of more than 530MPa, a tensile strength of more than 580MPa, an elongation of more than 9MPa, and an elastic modulus of 77-79GPa. It has higher strength properties and elastic modulus than aluminum alloys such as 2A14, 2219 and 5A06 that are widely used in spacecraft, and has lower residual stress, lower crack growth rate, and lower mechanical anisotropy of the material. It is a structural material with great application prospects in the aerospace field.

[0124] The foregoing description of specific exemplary embodiments of the present invention is for the purpose of illustration and demonstration. These descriptions are not intended to limit the present invention to the precise form disclosed, and it is clear that many changes and variations can be made based on the above teachings. The purpose of selecting and describing the exemplary embodiments is to explain the specific principles of the present invention and its practical application, so that those skilled in the art can realize and utilize various different exemplary embodiments of the present invention and various different selections and changes. The scope of the present invention is intended to be limited by the claims and their equivalents.

Claims

1. A method for preparing a large-size high-strength Al-Cu alloy plate, characterized in that: The following steps are involved: (1) Ingredients: The Al-Cu alloy includes the following elements by weight percentage: Si≤0.02%, Fe≤0.05%, Cu: 3.7-6.4%, Mg≤0.5%, Li≤1.2%, Ag≤0.4%, Mn: 0.001-0.4%, Zn≤0.25%, Ti: 0.015-0.035%, Zr: 0.09-0.15%, and the balance is Al and unavoidable impurity elements; (2) smelting: smelting the ingredients; (3) Melt purification: melt purification is carried out by adopting a multi-stage composite melt purification method; (4) Casting: Casting the alloy to obtain an ingot; (5) homogenization heat treatment: subjecting the ingot to homogenization heat treatment; (6) Machining: machining the ingot after homogenization heat treatment; (7) Hot rolling: the machined ingot is heated to 450-470°C for 3-18 hours, and the ingot after the insulation is subjected to multi-directional composite deformation hot rolling using a hot rolling mill, wherein the deformation rate of the first rolling deformation direction is 16.5%-30%, and then the ingot is subjected to reversing rolling, the rolling deformation is suspended, the plate is subjected to temperature-controlled cooling, and then 1-3 passes of temperature-controlled rolling are performed to the target thickness; (8) Straightening: The hot-rolled plate is deformed to a permanent plastic deformation of 0.5 to 1.0%; (9) Solution quenching: The hot-rolled and straightened plate is subjected to solution quenching treatment; (10) Deformation heat treatment: the plate in step (9) is subjected to deformation heat treatment to obtain a final heat treatment state, and the specific steps include: (a) pre-aging: the plate after solution quenching heat treatment is subjected to artificial aging at 150-160°C in an aging heat treatment furnace for 1-4 hours, and then quenched and cooled after being taken out of the furnace; (b) deformation processing: a pre-stretching machine is used to perform 2-7% plastic deformation, and then a rolling mill is used to perform 8-15% plastic deformation, and the accumulated total plastic deformation is 10-18%; (c) re-aging: artificial aging is performed in an aging heat treatment furnace, the first stage aging temperature is 65-85°C, the holding time is 48-168 hours; the second stage aging temperature is 150-160°C, and the holding time is 12-48 hours; (11) Sawing: Sawing is performed to obtain finished boards.

2. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (1), in the element composition of the Al-Cu alloy, the Cu / Li ratio is 4 to 4.5, the addition amount of the Ag element is 0.35%, the addition amount of the Mn element is 0.02%, and the addition amount of the Mg element is 0.4%.

3. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (2), the smelting is carried out in a vacuum induction furnace with high sealing, high corrosion resistance and precise temperature control capability. The furnace body material in contact with the melt is a composite material of aluminum oxide and silicon nitride, the atmosphere in contact with the melt is an argon inert protective gas, and an electromagnetic stirring device is used to stir the melt during the smelting process.

4. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (3), the multi-stage composite melt purification method is: firstly, melt refining is performed with a melt covering agent to achieve the first stage melt purification, then 1 to 4 argon mixed gases are used to rotate and purge the refining device to perform the second stage melt purification, and finally vacuum degassing is used as the third stage melt purification.

5. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (5), the homogenization heat treatment is performed by placing the ingot into a homogenization heat treatment furnace at room temperature, specifically: firstly heating the ingot from room temperature to a first-stage insulation temperature of 415-425°C at a heating rate of 40-60°C / h, and keeping it warm for 8-16h, then heating the ingot to a second-stage insulation temperature of 500-530°C at a heating rate of 25-35°C / h, and keeping it warm for 24-30h, and finally cooling the ingot to room temperature by water mist cooling.

6. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (7), during the multi-directional composite deformation hot rolling process, when the thickness is reduced to 100-120 mm, a heavy hydraulic shear is used to perform the first plate head and tail cutting, and when the thickness is reduced to 30-60 mm, a heavy hydraulic shear is used to perform the second plate head and tail cutting.

7. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (7), the temperature-controlled cooling is: using a spray cooling device of the hot rolling unit to temperature-controlled cool the plate to 250-350°C.

8. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (7), the method of multi-directional composite deformation hot rolling is: firstly, transverse rolling is performed in a direction perpendicular to the direction of movement of the casting ingot starter, and then longitudinal rolling is performed in a direction parallel to the casting direction.

9. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (7), the method of multi-directional composite deformation hot rolling is: firstly, longitudinal rolling is performed in a direction parallel to the movement direction of the casting starter head, and then transverse rolling is performed in a direction perpendicular to the movement direction of the casting starter head.

10. The method for preparing a large-size high-strength Al-Cu alloy sheet according to claim 1, characterized in that: In step (7), the method of multi-directional composite deformation hot rolling is: firstly, longitudinal rolling is performed in a direction parallel to the direction of movement of the casting ingot starter, then transverse rolling is performed in a direction perpendicular to the direction of movement of the casting ingot starter, and then longitudinal rolling is performed in a direction parallel to the direction of movement of the casting ingot starter.

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