Aluminum-lithium alloy and preparation method thereof

Abstract

The present invention relates to the technical field of aluminum alloy materials, and in particular to an aluminum-lithium alloy and a preparation method thereof. The aluminum-lithium alloy provided by the present invention has the following composition: Cu: 2.5% to 3.2%; Li: 1.7% to 2.2%; Sc: 0.2% to 0.3%; Al and unavoidable impurities: the balance; wherein the mass ratio of Cu / Li is 1.13 to 1.88. The present invention rationally designs the composition, using the rare earth element Sc to replace Zr and controlling its content, achieving lightweighting. Through homogenization treatment, hot rolling, solution treatment, and aging, the alloy precipitates a large amount of dispersed δ′ phase, T1 phase, and second-phase Al3Sc phase, resulting in an ultra-lightweight aluminum-lithium alloy material with excellent strength and plasticity. The preparation method of the present invention controls the morphology and size of the precipitated T1 (Al2CuLi) phase, while the heat treatment process regulates the grain structure morphology, thereby achieving excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of aluminum alloy materials, and in particular to an aluminum-lithium alloy and a preparation method thereof. Background Art

[0002] Aluminum-lithium alloy is a lightweight alloy with excellent comprehensive properties and huge development potential. Replacing ordinary aluminum alloy with it can reduce the weight of components and increase their stiffness. Therefore, it is considered to be a very ideal structural material for aerospace applications in the 21st century. It also has potential application space in the ship and weapons industry. At present, the aluminum-lithium alloy series successfully developed by various countries generally contain 2.3% to 3% lithium. Aluminum-lithium alloys (2090, 2195, 8090) are used as secondary structural components in fighter jets and civil aircraft, including wing leading edges and brackets within the fuselage. However, aluminum-lithium alloys (2090, 2195, 8090) contain 0.1wt.%-0.12 wt.% of the high-density element Zr (6.49 g / cm 3 ), there is a problem of poor comprehensive weight reduction effect. Specifically, its comprehensive weight reduction effect is generally only 5%-7%, which is half of that of composite materials.

[0003] Aluminum-lithium alloys are both deformable and heat-treatable aluminum alloys. The primary heat treatment method is solution-assisted aging. Through a series of heat treatments, strengthening phases are precipitated and the alloy's strength and toughness are controlled. For example, the common 2195 aluminum-lithium alloy can achieve a peak stress of 550-590 MPa through appropriate heat treatment. Numerous studies have shown that the primary strengthening phases in aluminum-lithium alloys include the T1 phase (Al2CuLi), the δ′ phase (Al3Li), and the θ′ phase (Al2Cu). The T1 phase, with its close-packed hexagonal structure, exhibits the strongest strengthening effect. Therefore, to achieve both good ductility and strength in the alloy, it is desirable to disperse and precipitate a large number of fine T1 phases (Al2CuLi) throughout the alloy through heat treatment.

[0004] One of the effective ways to improve the performance of aluminum-lithium alloys is to control the microstructure through alloying. Sc is the rare earth element with the lowest density and has the properties of a transition element, which makes it the most effective modifier for aluminum-lithium alloys. By adding Sc to aluminum-lithium alloys, through homogenization annealing and hot forging deformation processing, the alloy can precipitate small-sized, high-density, and dispersed Al3Sc / Al3Sc. xPhase particles can be firmly pinned to dislocations and subgrain boundaries, preventing the migration and merging of subgrains to stabilize the substructure. At the same time, they can increase the recrystallization temperature and have a significant inhibitory effect on the recrystallization behavior of the alloy. Theoretically, in Al-Li alloys, the addition of Sc can change the precipitation behavior of the alloy precipitates at the component level. However, in reality, the aging precipitation characteristics of Sc in Al-Cu-Li alloys and the mechanism of its microstructure regulation performance have not yet been fully understood, and the optimal aging treatment process is also different.

[0005] Xing Yuhan et al. proposed to use heat treatment method to improve the 2195 aluminum-lithium alloy (initial phase composition is θ′ phase, δ′ phase and β′ phase, density is 2.7 g / cm 3 ) room-temperature tensile properties of the plate (tensile strength of 597.9 MPa, elongation of 7.46%). Solution treatment of the 2195 aluminum-lithium alloy plate significantly reduced its tensile strength and increased its elongation. For example, after solution treatment at 510°C / 35 minutes, the alloy plate's elongation was 19.05%, a 155.36% increase compared to the original plate; the tensile strength was 302.43 MPa, a 49.42% decrease compared to the original plate. This indicates that solution treatment improves the alloy's plasticity, but at the expense of strength. After various aging treatments, the tensile strength of the 2195 aluminum-lithium alloy ranged from 500 to 600 MPa, but its elongation decreased significantly, with the decrease becoming more pronounced with increasing aging time. When the heat treatment process is solution treatment (510℃ / 35min) + aging treatment (180℃ / 18h), the alloy obtains a maximum elongation of 10.06%, which is 34.85% higher than that of the original plate; its tensile strength is 523.87MPa, which is 12.38% lower than that of the original plate.

[0006] In summary, the existing technology still has the following problems: 1. The composition and content composition of 2195 aluminum-lithium alloy are relatively complex, and the types and contents of high-density elements are relatively high, which cannot meet the needs of lightweighting well. 2. The plasticity of 2195 aluminum-lithium alloy has been improved to a certain extent through heat treatment, but at the expense of higher strength. 3. The main strengthening mechanism of 2195 aluminum-lithium alloy in the solid solution + aging process is precipitation strengthening and dispersion strengthening produced by the precipitation of θ′ phase and δ′ phase. There is no equilibrium phase T1 phase with a more obvious strengthening effect, which ultimately leads to poor strength-plasticity matching. 4. Due to the poor forming performance of aluminum-lithium alloy itself, the application direction is still in the simple low-density, high-strength lightweight material weight reduction. There is still a lack of research on the preparation and processing technology of large-size aluminum-lithium alloy plates with high requirements for comprehensive performance matching. Summary of the Invention

[0007] In view of this, the present invention provides an aluminum-lithium alloy and a preparation method thereof. The aluminum-lithium alloy provided by the present invention can achieve good lightweighting while also improving strength and obtaining good mechanical properties.

[0008] The present invention also provides an aluminum-lithium alloy comprising the following components, expressed in percentage by mass:

[0009] Cu: 2.5%~3.2%;

[0010] Li: 1.7%~2.2%;

[0011] Sc: 0.2%~0.3%;

[0012] Al and unavoidable impurities: balance;

[0013] Among them, the mass ratio of Cu / Li is 1.13~1.88.

[0014] The present invention also provides a method for preparing the aluminum-lithium alloy described in the above technical solution, comprising the following steps:

[0015] A) Prepare the materials according to the target alloy composition;

[0016] in,

[0017] In terms of mass percentage, the target alloy includes the following components:

[0018] Cu: 2.5%~3.2%;

[0019] Li: 1.7%~2.2%;

[0020] Sc: 0.2%~0.3%;

[0021] Al and unavoidable impurities: balance;

[0022] Among them, the mass ratio of Cu / Li is 1.13~1.88;

[0023] The raw materials used in the batching include: aluminum ingot, metal Cu, metal Li and master alloy Al-2Sc;

[0024] B) Furnace gas washing:

[0025] The smelting furnace is vacuumed and filled with inert gas after the vacuum level is lower than the target threshold. When the pressure in the furnace reaches the target pressure, the filling is stopped and the furnace is left to stand; then, the above-mentioned gas washing process is repeated;

[0026] C) Vacuum Melting:

[0027] The aluminum ingot is placed in a container and kept warm in a melting furnace preheated to 760°C until the aluminum ingot is completely melted. Then, the temperature is raised to 950°C, and metal Cu and master alloy Al-2Sc are added to the molten aluminum liquid. A covering agent is added for covering and protection, and the temperature is kept until the metal Cu is completely melted. Then, the temperature is lowered to 740°C, and a covering agent is applied to the surface of the melt. Under a protective atmosphere, metal Li is placed into the melt and allowed to stand. Afterwards, the melt is stirred to obtain a uniform melt.

[0028] D) Casting:

[0029] The casting mold is placed in a preheated melting furnace for degassing; the container containing the melt obtained in step C) is taken out of the melting furnace, the slag and surface oxides of the melt are skimmed off, and then the melt is poured into the casting mold. After the casting is completed, the melt is cooled and formed to obtain an ingot;

[0030] E) performing a homogenization treatment on the ingot;

[0031] F) hot rolling the alloy obtained in step E);

[0032] G) The alloy obtained in step F) is subjected to solution treatment and aging treatment in sequence to obtain an aluminum-lithium alloy.

[0033] Preferably, in step C):

[0034] The holding time until the aluminum ingot is completely melted is 30 minutes;

[0035] The holding time for holding until the metal Cu is completely melted is 2 hours;

[0036] The standing time is 20 min.

[0037] Preferably, in step D), the degassing is ammonia degassing.

[0038] Preferably, in step E), the conditions for the homogenization treatment are as follows:

[0039] The heating rate was 5°C / min, the homogenization temperature was 480°C, and the holding time was 16 h; then the furnace was cooled.

[0040] Preferably, in step F), the hot rolling process is three-pass rolling;

[0041] The rolling temperature is 480℃, and each pass is kept warm for 10 minutes during the rolling process.

[0042] Preferably, in step G), the conditions of the solution treatment are as follows: temperature of 500° C., holding time of 2 h; followed by water quenching.

[0043] Preferably, in step G), the aging treatment conditions are as follows: temperature is 190-210° C., and holding time is 22-40 h.

[0044] Preferably, in step F), the final total deformation of the hot rolling treatment is 60%.

[0045] Preferably, the purity of the aluminum ingot is ≥99.8%, the purity of the metal Cu is ≥99.9%, and the purity of the metal Li is ≥99.9%.

[0046] The present invention provides an aluminum-lithium alloy, which is an ultra-light aluminum-lithium alloy with added Sc. By rationally designing the composition, the rare earth element Sc is used to replace Zr and the Sc element content is controlled, thereby controlling the strengthening phase in the alloy, thereby achieving lightweighting. At the same time, through homogenization treatment → hot rolling → solid solution + aging, the alloy is precipitated with a large amount of dispersed δ' phase, T1 phase and second phase particles Al3Sc phase, thereby obtaining an ultra-light aluminum-lithium alloy material with good strength and plasticity. The preparation method of the present invention realizes the control of the morphology and size of the precipitated phase T1 (Al2CuLi), and the heat treatment process realizes the regulation of the grain structure morphology, thereby obtaining good mechanical properties.

[0047] The experimental results show that the density of the aluminum-lithium alloy obtained by the present invention is 2.47 g / cm 2 The room temperature tensile strength is above 528 MPa, achieving lightweight while having excellent mechanical properties. Among them, the density of the preferred alloy Al-3Cu-1.7Li-0.3Sc is 2.47 g / cm 2 The room temperature tensile strength reaches 554MPa, the elongation is 10.84%, and the comprehensive performance is the best. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0049] Figure 1 EBSD image of the Al-3Cu-1.7Li-0.3Sc ultra-light aluminum-lithium alloy obtained in Example 1;

[0050] Figure 2 This is the TEM image of the Al-3Cu-1.7Li-0.3Sc ultra-light aluminum-lithium alloy obtained in Example 1. DETAILED DESCRIPTION

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0052] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0053] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0054] As used herein, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0055] In this document, when referring to a range, if the unit is followed only by the right endpoint, it means that the units of the left and right endpoints are the same. For example, 190~210℃ means that the units of the left endpoint "190" and the right endpoint "210" are both °C.

[0056] Only certain numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0057] The present invention provides an aluminum-lithium alloy comprising the following components, expressed in percentage by mass:

[0058] Cu: 2.5%~3.2%;

[0059] Li: 1.7%~2.2%;

[0060] Sc: 0.2%~0.3%;

[0061] Al and unavoidable impurities: balance;

[0062] Among them, the mass ratio of Cu / Li is 1.13~1.88.

[0063] In the present invention, the content of Cu in the aluminum-lithium alloy is 2.5% to 3.2%, specifically 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, 3.1%, and 3.2%.

[0064] In the present invention, the content of Li in the aluminum-lithium alloy is 1.7% to 2.2%, specifically 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, and 2.2%.

[0065] In the present invention, the content of Sc in the aluminum-lithium alloy is 0.2% to 0.3%, specifically 0.20%, 0.21%, 0.22%, 0.23%, 0.24%, 0.25%, 0.26%, 0.27%, 0.28%, 0.29%, and 0.30%.

[0066] In the present invention, the mass ratio of Cu / Li is 1.13 to 1.88, specifically 1.13, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.47, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, and 1.88. The present invention controls w(Cu) / w(Li) within the above range, which is conducive to obtaining the optimal precipitate phase composition and strengthening the matrix. If the ratio is too low, it is easy to lead to a higher δ' phase ratio. If the ratio is too high, it is easy to lead to increased segregation of Cu atoms, there is obvious Cu element enrichment, and the number of Li-containing strengthening phase T1 phases is reduced, and both cannot effectively strengthen the matrix.

[0067] In one embodiment of the present invention, the composition of the aluminum-lithium alloy is as follows:

[0068] Cu: 3.0%;

[0069] Li: 1.7%;

[0070] Sc: 0.30%;

[0071] Al and unavoidable impurities: balance;

[0072] The mass ratio of Cu / Li is 1.88.

[0073] In another embodiment of the present invention, the composition of the aluminum-lithium alloy is as follows:

[0074] Cu: 2.5%;

[0075] Li: 1.7%;

[0076] Sc: 0.25%;

[0077] Al and unavoidable impurities: balance;

[0078] The mass ratio of Cu / Li is 1.47.

[0079] In another embodiment of the present invention, the composition of the aluminum-lithium alloy is as follows:

[0080] Cu: 2.9%;

[0081] Li: 2.0%;

[0082] Sc: 0.30%;

[0083] Al and unavoidable impurities: balance;

[0084] The mass ratio of Cu / Li is 1.45.

[0085] In another embodiment of the present invention, the composition of the aluminum-lithium alloy is as follows:

[0086] Cu: 2.5%;

[0087] Li: 2.2%;

[0088] Sc: 0.30%;

[0089] Al and unavoidable impurities: balance;

[0090] The mass ratio of Cu / Li is 1.13.

[0091] The present invention also provides a method for preparing the aluminum-lithium alloy described in the above technical solution, comprising the following steps:

[0092] A) Prepare the materials according to the target alloy composition;

[0093] in,

[0094] In terms of mass percentage, the target alloy includes the following components:

[0095] Cu: 2.5%~3.2%;

[0096] Li: 1.7%~2.2%;

[0097] Sc: 0.2%~0.3%;

[0098] Al and unavoidable impurities: balance;

[0099] Among them, the mass ratio of Cu / Li is 1.13~1.88;

[0100] The raw materials used in the batching include: aluminum ingot, metal Cu, metal Li and master alloy Al-2Sc;

[0101] B) Furnace gas washing:

[0102] The smelting furnace is vacuumed and filled with inert gas after the vacuum level is lower than the target threshold. When the pressure in the furnace reaches the target pressure, the filling is stopped and the furnace is left to stand; then, the above-mentioned gas washing process is repeated;

[0103] C) Vacuum Melting:

[0104] The aluminum ingot is placed in a container and kept warm in a melting furnace preheated to 760°C until the aluminum ingot is completely melted. Then, the temperature is raised to 950°C, and metal Cu and master alloy Al-2Sc are added to the molten aluminum liquid. A covering agent is added for covering and protection, and the temperature is kept until the metal Cu is completely melted. Then, the temperature is lowered to 740°C, and a covering agent is applied to the surface of the melt. Under a protective atmosphere, metal Li is placed into the melt and allowed to stand. Afterwards, the melt is stirred to obtain a uniform melt.

[0105] D) Casting:

[0106] The casting mold is placed in a preheated melting furnace for degassing; the container containing the melt obtained in step C) is taken out of the melting furnace, the slag and surface oxides of the melt are skimmed off, and then the melt is poured into the casting mold. After the casting is completed, the melt is cooled and formed to obtain an ingot;

[0107] E) performing a homogenization treatment on the ingot;

[0108] F) hot rolling the alloy obtained in step E);

[0109] G) The alloy obtained in step F) is subjected to solution treatment and aging treatment in sequence to obtain an aluminum-lithium alloy.

[0110] [About Step A]:

[0111] A) Prepare the materials according to the target alloy composition.

[0112] In the present invention, the composition of the target alloy is consistent with that described in the above technical solution, and will not be described in detail here.

[0113] In the present invention, the raw materials used in the formulation include: aluminum ingots, metallic Cu, metallic Li, and an Al-2Sc master alloy. The aluminum ingots are commercially pure Al with a purity of ≥99.8%. The metallic Cu is commercially pure Cu with a purity of ≥99.9%. The metallic Li is a high-purity Li block with a purity of ≥99.9%. The present invention does not specifically limit the sources of these raw materials; they can be commercially available products. Based on the composition of the target alloy, the required mass of these raw materials is calculated and cut and combined to form the matrix raw materials.

[0114] [About Step B]:

[0115] B) Furnace Purging: Evacuate the furnace and fill it with inert gas when the vacuum level is lower than the target threshold. When the pressure in the furnace reaches the target pressure, stop filling and let it stand; then repeat the above-mentioned purge process.

[0116] In the present invention, the melting furnace is not particularly limited and can be any conventional melting furnace in the art, such as a vacuum resistance furnace. First, the melting furnace is evacuated and filled with inert gas after the vacuum degree is less than the target threshold. When the pressure in the furnace reaches the target pressure, the filling is stopped and the furnace is left to stand. This is a gas washing process. The target threshold is preferably 9.9×10 -3 Pa. The inert gas is preferably argon. The purity of the argon is preferably 99.9%. The target pressure is preferably -0.07 MPa. The standing time is preferably 15 minutes.

[0117] After the first purge is complete, the purge is preferably repeated for a second vacuum purge, and then repeated again for a third vacuum purge; preferably, a total of three vacuum purges are performed. After the purge is complete, the furnace is vacuumed until the vacuum reaches the target threshold, and vacuum melting is then performed under this vacuum condition.

[0118] [About Step C]:

[0119] C) Vacuum Melting: Place an aluminum ingot in a container and hold it in a preheated furnace at 760°C until the ingot is completely melted. Then, raise the temperature to 950°C, add Cu and the master alloy Al-2Sc to the molten aluminum, add a covering agent for protection, and hold the temperature until the Cu is completely melted. Then, cool the container to 740°C, apply a covering agent to the surface of the melt, and place Li metal in the melt under a protective atmosphere. Allow the melt to stand for a while, then stir to obtain a uniform melt.

[0120] in:

[0121] The container is preferably a crucible. The melting furnace is preheated to 760°C in advance, and the aluminum ingot is placed in the furnace and kept warm until it is completely melted. The holding time is preferably 30 minutes, which allows the aluminum ingot to be fully melted.

[0122] After the aluminum ingot is melted to form molten aluminum, the temperature is raised to 950°C, and Cu metal and the Al-2Sc master alloy are added to the molten aluminum. In the present invention, the addition method is preferably to press aluminum foil balls wrapped with Cu metal and the Al-2Sc master alloy into the molten aluminum using a bell jar coated with BN. The aluminum foil balls wrapped with Cu metal and the Al-2Sc master alloy can be aluminum foil balls wrapped with both Cu metal and the Al-2Sc master alloy, or aluminum foil balls wrapped with both Cu metal and the Al-2Sc master alloy. After the Cu metal and Al-2Sc master alloy are added, a covering agent is added for protection. The covering agent, when sprinkled on the surface of the molten aluminum, quickly melts to form a covering layer, thereby providing a protective covering. Preferred covering agents include potassium chloride, sodium chloride, lithium chloride, lithium fluoride, sodium bisulfate, and sodium fluorosilicate. In the above-mentioned covering agent, the mass ratio of potassium chloride, sodium chloride, lithium chloride, lithium fluoride, sodium bisulfate and sodium fluorosilicate is preferably 1: (0.75-1): (0.175-0.3): (0.05-0.1): (0.025-0.0625): (0.0625-0.15), and in some embodiments it is 1: 1: 0.25: 0.075: 0.05: 0.125. The amount of the covering agent is not particularly limited and can be used according to the conventional amount in the art, which can be 0.6-1 kg / m 2 Melt, specifically 0.6 kg / m 2 Melt, 0.7 kg / m 2 Melt, 0.8 kg / m 2 Melt, 0.9 kg / m 2 Melt, 1.0 kg / m 2 After adding a covering agent for protection, the metal Cu is kept warm until it is completely melted. The holding time is preferably 2 hours, which allows the metal Cu to be fully melted.

[0123] After the metal Cu is melted, it is cooled to 740°C and a covering agent is applied to the surface of the melt. There is no special restriction on the manner of applying the covering agent, and it can be the conventional manner in this field, that is, a layer of covering agent is evenly sprinkled on the surface of the melt. Among them, the covering agent is preferably potassium chloride, sodium chloride, lithium chloride, lithium fluoride, sodium bisulfate and sodium fluorosilicate. In the above-mentioned covering agent, the mass ratio of potassium chloride, sodium chloride, lithium chloride, lithium fluoride, sodium bisulfate and sodium fluorosilicate is preferably 1: (0.75~1): (0.175~0.3): (0.05~0.1): (0.025~0.0625): (0.0625~0.15), and in some embodiments it is 1: 1: 0.25: 0.075: 0.05: 0.125. There is no special restriction on the amount of the covering agent, and it can be used according to the conventional amount in this field, which can be 0.6~1 kg / m 2 Melt, specifically 0.6 kg / m2 Melt, 0.7 kg / m 2 Melt, 0.8 kg / m 2 Melt, 0.9 kg / m 2 Melt, 1.0 kg / m 2 melt.

[0124] After the above treatment, metallic Li is placed into the melt under a protective atmosphere, preferably argon, and allowed to stand. The metallic Li is allowed to melt, preferably for 20 minutes. The aluminum is then stirred continuously to ensure uniform dissolution of all alloying elements, resulting in a homogeneous melt.

[0125] [About Step D]:

[0126] D) Casting: The mold is placed in a preheated melting furnace for degassing. The container containing the melt obtained in step C) is removed from the melting furnace, and the slag and surface oxides of the melt are skimmed off. The melt is then poured into the mold. After casting, the melt is cooled and formed into an ingot.

[0127] In the present invention, the casting mold is preferably one with a BN coating on its surface. The preheat temperature of the preheated melting furnace is preferably 650°C. The degassing is preferably performed with ammonia gas. The degassing time is preferably 5 minutes. The container containing the melt obtained in step C) is then removed from the melting furnace. The slag and surface oxides of the melt are skimmed off and slag removed to ensure the safety of the metal casting mold. The melt is then slowly and evenly poured into the casting mold. After casting is completed, the melt is allowed to cool naturally to form an ingot.

[0128] [Regarding Step E]:

[0129] E) performing a homogenization treatment on the ingot.

[0130] In the present invention, the homogenization treatment preferably has a heating rate of 5°C / min. The homogenization temperature is preferably 480°C. The homogenization treatment preferably has a holding time of 16 hours. After the homogenization heat treatment, furnace cooling is performed, specifically, cooling to room temperature.

[0131] [About Step F]:

[0132] F) The alloy obtained in step E) is subjected to hot rolling.

[0133] In the present invention, the hot rolling process is preferably performed in three passes. The rolling temperature is preferably 480°C. Each pass is held at this temperature for 10 minutes, i.e., after each pass, the temperature is held for 10 minutes before the next pass. After this hot rolling process, the final total deformation reaches 60%. After this process, a sheet with a thickness of 2.7 mm is obtained.

[0134] [Regarding Step G]:

[0135] G) The alloy obtained in step F) is subjected to solution treatment and aging treatment in sequence to obtain an aluminum-lithium alloy.

[0136] In the present invention, the temperature of the solution treatment is preferably 500° C. The holding time of the solution treatment is preferably 2 hours. After the solution treatment at the above temperature, water quenching is performed.

[0137] In the present invention, the temperature of the aging treatment is preferably 190-210° C., specifically 190° C., 195° C., 200° C., 205° C., or 210° C. The holding time of the aging treatment is preferably 22-40 h, specifically 22 h, 24 h, 26 h, 28 h, 30 h, 32 h, 34 h, 36 h, 38 h, or 40 h.

[0138] After the above-mentioned solution treatment + aging treatment, the main strengthening phase composition of the alloy of the present invention is δ'+T1 phase, and the proportion of T1 phase is greater than the proportion of δ' phase; the presence of dispersed Al3Sc phase plays the role of dispersion strengthening and fine grain strengthening on the matrix.

[0139] The present invention provides an aluminum-lithium alloy, which is an ultra-light aluminum-lithium alloy with added Sc. By rationally designing the composition, the rare earth element Sc is used to replace Zr and the Sc element content is controlled, thereby controlling the strengthening phase in the alloy, thereby achieving lightweighting. At the same time, through homogenization treatment → hot rolling → solid solution + aging, the alloy is precipitated with a large amount of dispersed δ' phase, T1 phase and second phase particles Al3Sc phase, thereby obtaining an ultra-light aluminum-lithium alloy material with good strength and plasticity. The preparation method of the present invention realizes the control of the morphology and size of the precipitated phase T1 (Al2CuLi), and the heat treatment process realizes the regulation of the grain structure morphology, thereby obtaining good mechanical properties.

[0140] The experimental results show that the density of the aluminum-lithium alloy obtained by the present invention is 2.47 g / cm 2 The room temperature tensile strength is above 528 MPa, achieving lightweight while having excellent mechanical properties. Among them, the density of the preferred alloy Al-3Cu-1.7Li-0.3Sc is 2.47 g / cm 2 The room temperature tensile strength reaches 554MPa, the elongation is 10.84%, and the comprehensive performance is the best.

[0141] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are intended only to further illustrate the features and advantages of the present invention and are not intended to limit the scope of the claims. In the following examples, the raw materials used are high-purity raw materials, with the purity of the aluminum ingot being ≥99.8%, the purity of the metal Cu being ≥99.9%, and the purity of the metal Li being ≥99.9%.

[0142] Example 1

[0143] 1. Preparation

[0144] A) Prepare the target alloy composition as follows: Cu 3.0%, Li 1.7%, Sc 0.3%, with the balance being Al and unavoidable impurities. Here, w(Cu) / w(Li) = 1.88.

[0145] The raw materials used include: aluminum ingot, metal Cu, metal Li and master alloy Al-2Sc.

[0146] B) Furnace gas washing:

[0147] The melting furnace (specifically a vacuum resistance furnace) is evacuated until the vacuum degree is less than 9.9×10 -3 Pa, then fill with argon (purity of 99.9%), and stop filling when the pressure in the furnace reaches -0.07MPa. Let it stand for 15 minutes; repeat the above purge process to perform the second vacuum purge operation, and then repeat the above purge process again to perform the third vacuum purge operation. After the purge is completed, the vacuum degree in the furnace is vacuumed to the above 9.9×10 -3 Pa, and subsequent vacuum melting is carried out under this vacuum condition.

[0148] C) Vacuum Melting:

[0149] Preheat the melting furnace to 760°C, place the aluminum ingot in the crucible inside the melting furnace, and keep it warm for 30 minutes until the aluminum ingot is completely melted. Then, raise the temperature to 950°C, use a bell jar coated with BN to press the aluminum foil ball wrapped with metal Cu and master alloy Al-2Sc into the molten aluminum liquid, and evenly sprinkle a layer of covering agent on the surface of the aluminum liquid for covering protection (the covering agent is potassium chloride + sodium chloride + lithium chloride + lithium fluoride + sodium bisulfate + sodium fluorosilicate, the mass ratio of each component is 1:1:0.25:0.075:0.05:0.125, and the covering agent dosage is 0.8 kg / m 2Melt), keep the temperature for 2 hours until the metal Cu is completely melted. Then, cool to 740℃ and evenly sprinkle a layer of covering agent on the surface of the melt again (the covering agent is potassium chloride + sodium chloride + lithium chloride + lithium fluoride + sodium hydrogen sulfate + sodium fluorosilicate, the mass ratio of each component is 1:1:0.25:0.075:0.05:0.125, and the amount of covering agent is 0.8 kg / m 2 Melt), under argon protection, place the Li block into the melt and let it stand for 20 minutes. After that, stir the aluminum liquid continuously to promote the uniform and sufficient dissolution of all alloying elements into the aluminum liquid to obtain a uniform melt.

[0150] D) Casting:

[0151] The BN-coated mold is placed in a preheated furnace (preheat temperature: 650°C) and degassed with ammonia for 5 minutes. The crucible containing the melt is removed from the furnace, and the slag and surface oxides are skimmed off to ensure the safety of the metal mold. The melt is then slowly and evenly poured into the mold. After casting, it is allowed to cool naturally to form an ingot.

[0152] E) Homogenize the ingot: heating rate 5°C / min, homogenization temperature 480°C, holding time 16 h, and then cool to room temperature in the furnace.

[0153] F) Hot rolling treatment:

[0154] The rolling process was repeated in three passes at a temperature of 480°C. Each pass was kept at this temperature for 10 minutes, and the final total deformation reached 60%, resulting in a sheet with a thickness of 2.7 mm.

[0155] G) Heat treatment: Solution treatment and aging treatment are carried out in sequence under the following conditions:

[0156] Solution treatment: solution temperature is 500℃, holding time is 2h, and water quenching is performed.

[0157] Aging treatment: aging temperature 210℃, holding time 22h.

[0158] After the above heat treatment, an Al-3Cu-1.7Li-0.3Sc ultra-light aluminum-lithium alloy is obtained.

[0159] 2. Test:

[0160] (1) EBSD and TEM characterization

[0161] The EBSD of the Al-3Cu-1.7Li-0.3Sc ultra-light aluminum-lithium alloy obtained in Example 1 is as follows: Figure 1 As shown, it can be seen that the grain orientation tends to <001> and <101> , and a large number of small-angle grain boundaries (2°-10°) are formed.

[0162] The TEM of the Al-3Cu-1.7Li-0.3Sc ultra-light aluminum-lithium alloy obtained in Example 1 is as follows: Figure 2 As shown in the figure, it can be seen that the aging precipitation phases are mainly dispersed θ′ phase and needle-shaped T1 phase. The content of T1 phase is higher than that of θ′ phase, and there are dispersed Al3Sc phase and a large number of dislocation entanglements.

[0163] (2) Mechanical properties test

[0164] The density test was carried out using the Archimedes drainage method. Each alloy sample was measured three times, and the average density was 2.47 g / cm 2 The room temperature mechanical properties test showed that the tensile strength was 554 MPa and the elongation was 10.84%.

[0165] Example 2

[0166] 1. Preparation

[0167] The method is implemented according to Example 1, except that the chemical composition and heat treatment process are different.

[0168] The chemical composition is: Cu 2.5%, Li 1.7%, Sc 0.25%, with the balance being Al and unavoidable impurities; where w(Cu) / w(Li) = 1.47. The resulting alloy is an Al-2.5Cu-1.7Li-0.25Sc ultra-light aluminum-lithium alloy.

[0169] The heat treatment process is: solution treatment (500℃ / 2h, water quenching) + aging treatment (190℃ / 40h).

[0170] 2. Testing

[0171] Through the analysis of the microstructure of the alloy after heat treatment, it was found that the precipitated phases were mainly dispersed θ′ phase and needle-shaped T1 phase, and the T1 phase content was almost equal to the θ′ phase content. At the same time, the precipitated phase contained Al3Sc phase and dislocation entanglement existed around it.

[0172] The density test was carried out using the Archimedes drainage method. Each alloy sample was measured 3 times, and the average density was 2.4 g / cm 2 The room temperature mechanical properties test showed that the tensile strength was 542 MPa and the elongation was 12.67%.

[0173] Example 3

[0174] 1. Preparation

[0175] The method is implemented according to Example 1, except that the chemical composition and heat treatment process are different.

[0176] The chemical composition is: Cu 2.9%, Li 2.0%, Sc 0.30%, with the balance being Al and unavoidable impurities; where w(Cu) / w(Li) = 1.45. The resulting alloy is an Al-2.9Cu-2Li-0.3Sc ultra-light aluminum-lithium alloy.

[0177] The heat treatment process is: solution treatment (500℃ / 2h, water quenching) + aging treatment (195℃ / 32h).

[0178] 2. Testing

[0179] Through the analysis of the microstructure of the alloy after heat treatment, it was found that the precipitated phase was mainly dispersed θ′ phase and needle-shaped T1 phase, and the content of T1 phase was slightly less than that of θ′ phase. At the same time, the precipitated phase contained Al3Sc phase and dislocation entanglement existed around it.

[0180] The density test was carried out using the Archimedes drainage method. Each alloy sample was measured three times, and the average density was 2.38 g / cm 2 The room temperature mechanical properties test showed that the tensile strength was 528 MPa and the elongation was 12.95%.

[0181] It can be seen from Examples 1-3 that the density of the aluminum-lithium alloy obtained in the present invention is 2.47 g / cm 2 The room temperature tensile strength is above 528 MPa, achieving lightweight while also possessing excellent mechanical properties. Compared to Examples 2-3, the Al-3Cu-1.7Li-0.3Sc alloy obtained in Example 1 exhibits the best tensile strength, the shortest experimental time, and the highest strength-to-ductility ratio. Therefore, considering the strength-to-ductility ratio, lightweighting, and cost savings in practical applications, Example 1 is optimal.

[0182] Comparative Example 1

[0183] 2195 aluminum-lithium alloy after heat treatment in the preparation process proposed by Xing Yuhan et al. (see the article "Effect of Heat Treatment on the Microstructure and Mechanical Properties of 2195 Al-Li Alloy").

[0184] Comparing the room temperature tensile test results of Example 1 of the present invention with those of Comparative Example 1, it was found that: the room temperature tensile strength of Comparative Example 1 was 523.87 MPa and the elongation was 10.06%; while the room temperature tensile strength of the Al-3Cu-1.7Li-0.3Sc alloy obtained by the present invention was 554 MPa and the elongation was 10.84%, which is superior to the existing alloy. In addition, the density of the present invention is reduced (Comparative Example 1 is 2.7 g / cm 2 , Example 1 is 2.47 g / cm 2 Moreover, the Al-3Cu-1.7Li-0.3Sc alloy obtained by the present invention has an excellent strength-to-plasticity ratio at room temperature and is suitable for industrial production.

[0185] The present invention provides an ultra-light aluminum-lithium alloy with added Sc. By rationally designing the component composition, controlling the preparation process and the solid solution + aging system, the mechanical properties and second phase precipitation behavior of the ultra-light aluminum-lithium alloy are regulated, which has positive guiding significance for the performance improvement and industrial application of new aluminum-lithium alloys.

[0186] Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core ideas, including the best mode, and also enable any technician in the field to practice the present invention, including making and using any device or system, and implementing any combined method. It should be pointed out that for ordinary technicians in this technical field, without departing from the principles of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. If these other embodiments have structural elements similar to the literal description of the claims, or if they include equivalent structural elements that are not substantially different from the literal description of the claims, then these other embodiments should also be included in the scope of the claims.

Claims

1. An aluminum-lithium alloy, characterized in that In terms of mass percentage, it is composed of the following ingredients composition: Cu: 2.5%~3.2%; Li: 1.7%~2.2%; Sc: 0.2%~0.3%; Al and unavoidable impurities: balance; Among them, the mass ratio of Cu / Li is 1.47~1.88; The density of the aluminum-lithium alloy is 2.47 g / cm 2 Below, the room temperature tensile strength is above 528MPa.

2. A method for preparing the aluminum-lithium alloy according to claim 1, characterized in that: The following steps are involved: A) Prepare the materials according to the target alloy composition; in, The target alloy consists of the following components in percentage by mass: Cu: 2.5%~3.2%; Li: 1.7%~2.2%; Sc: 0.2%~0.3%; Al and unavoidable impurities: balance; Among them, the mass ratio of Cu / Li is 1.47~1.88; The raw materials used in the batching include: aluminum ingot, metal Cu, metal Li and master alloy Al-2Sc; B) Furnace gas washing: The smelting furnace is vacuumed and filled with inert gas after the vacuum level is lower than the target threshold. When the pressure in the furnace reaches the target pressure, the filling is stopped and the furnace is left to stand; then, the above-mentioned gas washing process is repeated; C) Vacuum Melting: The aluminum ingot is placed in a container and kept warm in a melting furnace preheated to 760°C until the aluminum ingot is completely melted. Then, the temperature is raised to 950°C, and metal Cu and master alloy Al-2Sc are added to the molten aluminum liquid. A covering agent is added for covering and protection, and the temperature is kept until the metal Cu is completely melted. Then, the temperature is lowered to 740°C, and a covering agent is applied to the surface of the melt. Under a protective atmosphere, metal Li is placed into the melt and allowed to stand. Afterwards, the melt is stirred to obtain a uniform melt. D) Casting: The casting mold is placed in a preheated melting furnace for degassing; the container containing the melt obtained in step C) is taken out of the melting furnace, the slag and surface oxides of the melt are skimmed off, and then the melt is poured into the casting mold. After the casting is completed, the melt is cooled and formed to obtain an ingot; E) performing a homogenization treatment on the ingot; F) hot rolling the alloy obtained in step E); G) The alloy obtained in step F) is subjected to solution treatment and aging treatment in sequence to obtain an aluminum-lithium alloy.

3. The preparation method according to claim 2, characterized in that In step C): The holding time until the aluminum ingot is completely melted is 30 minutes; The holding time for holding until the metal Cu is completely melted is 2 hours; The standing time is 20 min.

4. The preparation method according to claim 2, characterized in that In step D), the degassing is ammonia degassing.

5. The preparation method according to claim 2, characterized in that In step E), the homogenization treatment conditions are as follows: The heating rate was 5°C / min, the homogenization temperature was 480°C, and the holding time was 16 h; then the furnace was cooled.

6. The preparation method according to claim 2, characterized in that In step F), the hot rolling process is performed in three passes; The rolling temperature is 480℃, and each pass is kept warm for 10 minutes during the rolling process.

7. The preparation method according to claim 2, characterized in that In step G), the solution treatment conditions are as follows: temperature of 500° C., holding time of 2 h, followed by water quenching.

8. The preparation method according to claim 2, characterized in that In step G), the aging treatment conditions are as follows: temperature is 190-210° C., and holding time is 22-40 hours.

9. The preparation method according to claim 2 or 6, characterized in that In step F), the final total deformation of the hot rolling process is 60%.

10. The preparation method according to claim 2, characterized in that The purity of the aluminum ingot is ≥99.8%, the purity of the metal Cu is ≥99.9%, and the purity of the metal Li is ≥99.9%.

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