A step controlled temperature annealing and deformation treatment process for improving damage resistance of aluminum-lithium alloy
By using stepped temperature-controlled annealing and deformation treatment processes, the grain structure of aluminum-lithium alloys is controlled to form strip-shaped grains that are beneficial to damage resistance. This solves the problem of insufficient damage resistance of aluminum-lithium alloys under cyclic loading stress environment and achieves improved high damage resistance and strength.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2025-01-23
- Publication Date
- 2026-05-12
AI Technical Summary
Existing aluminum-lithium alloys have insufficient damage resistance under cyclic loading stress environments, and traditional heat treatment processes are complex and have limited improvement effects.
A stepped temperature-controlled annealing and deformation treatment process is adopted, including two-stage annealing and solution treatment, to regulate the grain structure characteristics and form a strip-shaped grain structure that is beneficial to damage resistance.
It significantly improves the damage resistance of aluminum-lithium alloys, meets the service requirements of aerospace materials, and enhances fatigue performance and strength.
Smart Images
Figure CN119932450B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aerospace vehicle structural material preparation and processing technology, and more specifically, relates to a stepped controlled temperature annealing and deformation treatment process to improve the damage resistance of aluminum-lithium alloys. Background Technology
[0002] Aluminum-lithium alloys possess excellent properties such as low density, high strength, high specific stiffness, and high corrosion resistance, and are considered to be novel damage-resistant lightweight structural alloy materials with enormous development potential, showing broad prospects for future in-depth applications in the aerospace field. Among them, novel ultra-high-strength aluminum-lithium alloys, with their outstanding mechanical properties, are expected to become structural materials for aircraft. After proper processing, aluminum-lithium alloys exhibit excellent strength and fatigue properties, and are expected to become the main materials for current aircraft cabin / pressure chamber skins, longitudinal beams, and stringers. However, currently used aluminum-lithium alloy grades still fall short of the damage resistance requirements of high-strength aluminum alloys. Further improving their damage resistance is crucial for service in cyclically loaded stress environments.
[0003] It is generally believed that the damage resistance of metals is closely related to their grain structure, with key factors including grain size, grain orientation, and grain boundaries. Therefore, adjusting the heat treatment process to control the grain structure characteristics of an alloy and thereby improve its damage resistance is crucial for its further engineering applications. Chinese patent CN 105755409A discloses a method of short-time annealing of cold-rolled aluminum-lithium alloy sheets to their final thickness at a certain temperature, followed by solution quenching and subsequent aging to the desired state. The variable-temperature treatment in the second stage of annealing eliminates some of the deformation energy stored from cold rolling, transforming the solution-treated structure into a partially recrystallized structure, thus improving the alloy's damage resistance. However, the strength of this alloy is not high.
[0004] Chinese patent CN113215423 A reports a method of melting and casting raw materials into ingots, then annealing, hot-rolling, intermediate-annealing, and cold-rolling the ingots into plates, followed by solution quenching, pre-deformation, and aging treatments to obtain a high-strength, damage-resistant aluminum-lithium alloy. This method is complex, and the multiple annealing and deformation treatments increase the content of axial grains in the alloy, resulting in only a limited improvement in the damage resistance of the aluminum-lithium alloy.
[0005] Therefore, there is an urgent need for a heat treatment process to control the alloy grain structure to achieve a stable and uniform state, and to optimize the grain structure morphology to effectively suppress damage. Summary of the Invention
[0006] Based on the aforementioned technical problems in the existing technology, one of the objectives of this invention is to provide a stepped temperature-controlled annealing and deformation treatment process to improve the damage resistance of aluminum-lithium alloys. This heat treatment process includes a specific annealing temperature based on a certain deformation and a fixed holding time, so that the target ultra-high strength aluminum-lithium alloy has high damage resistance, which can meet the processing and service requirements of current aerospace aluminum-lithium alloy materials.
[0007] To achieve the above objectives, the technical solution of the present invention is as follows:
[0008] A stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys includes: deforming an aluminum-lithium alloy ingot, followed by two-stage temperature-controlled annealing; the two-stage annealing process is as follows: first stage 300-320℃ / 1-2h + second stage 320-400℃ / 1-2h; the heating rate of the second stage is 5-25℃ / min.
[0009] Furthermore, the composition of the aluminum-lithium alloy is AlCu. 3.6-4.5 Li 1.0-2.0 X, wherein X includes any one or more of Mg, Ag, Zn, Mn, and Zr.
[0010] Furthermore, the deformation amount of the deformation treatment is 30-80%.
[0011] Furthermore, the heating rate in the second stage is 5-25℃ / min.
[0012] Furthermore, the deformation treatment is cold rolling or hot rolling.
[0013] Furthermore, it also includes: performing a controlled-temperature solution treatment or a solution treatment and aging treatment after annealing; the controlled-temperature solution treatment process is as follows:
[0014] First stage: 320-340℃ / 2-4h + Second stage: 510-520℃ / 1-2h; or
[0015] First stage: 360-400℃ / 10-20 min + Second stage: 510-520℃ / 1-2 h.
[0016] Furthermore, the heating rate in the first to second stages of the temperature-controlled solution treatment is controlled at 10-20℃ / min.
[0017] Furthermore, the aging treatment regime is: 6% rolling pre-deformation + 130-150℃ / 12-35 h.
[0018] Furthermore, it also includes: homogenization heat treatment before deformation treatment.
[0019] The principle of this invention is as follows: First, based on a certain deformation, the alloy acquires energy storage within a predetermined range. Based on this, the deformation method can be varied. If hot working is used, the advantages of the texture structure formed in the deformed alloy, and the subsequent annealing process's recrystallization texture and grain structure characteristics, are utilized to improve the alloy's damage resistance. In the subsequent two-stage annealing process, the temperature control treatment in the second stage of annealing effectively regulates the grain structure morphology and grain boundary precipitate characteristics, and effectively controls grain boundary energy storage, providing a foundation for forming an effective damage-resistant grain structure morphology for the aluminum-lithium alloy.
[0020] In the aluminum-lithium alloys to which this invention is applicable, the heat treatment methods used include, but are not limited to, single-stage annealing, multi-stage annealing, and solution heating rates. These primarily affect the recovery of cold-deformed alloys and the precipitation of second-phase particles. During the recovery process of aluminum-lithium alloys, dislocation climb and polygonization are accelerated mainly by consuming deformation energy, thereby forming subgrains and coarsening them. In addition, during annealing, coarse second-phase particles in the aluminum-lithium alloy precipitate in a banded manner along the rolling direction, hindering grain boundary migration during subsequent solution treatment and forming a mixed-grain structure with alternating coarse and fine grains. These fine-grained regions with high dislocation density promote the precipitation of unique semi-coherent strengthening phases (T1 and θ´ phases) in the alloy and reduce the thickness and diameter of the precipitated phases. These fine precipitates are more easily cut back and forth by dislocations during crack propagation, releasing crack tip energy, thereby improving the damage resistance of the aluminum-lithium alloy.
[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:
[0022] This invention employs a two-stage annealing process, particularly the variable-temperature treatment in the second stage, to regulate the storage of deformation energy caused by deformation. This alters the recrystallization microstructure after solution treatment, forming a strip-shaped grain structure with a specific aspect ratio that effectively enhances the damage resistance of the alloy, thereby significantly improving the damage resistance of medium-strength aluminum-lithium alloys. This differs from traditional annealing processes that aim to create equiaxed grains to provide damage resistance, offering a fundamentally new approach to improving the damage resistance of this alloy. It provides a solution for the specific requirements (high damage resistance) of aluminum-lithium alloys in special operating environments such as aerospace and large aircraft. Attached Figure Description
[0023] Figure 1 This is a schematic diagram of a stepped controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to the present invention.
[0024] Figure 2 The images show the longitudinal section OM images of the ultra-high strength aluminum-lithium alloys obtained in Examples 1-3 and Comparative Example 1;
[0025] Figure 3 The engineering stress-strain curves and fatigue crack propagation curves of the alloy materials obtained in Examples 1-3 and Comparative Example 1 under the aging regime are shown.
[0026] Figure 4 The images shown are EBSD images of the longitudinal sections of the aluminum-lithium alloy obtained in Examples 1-3 and Comparative Example 1.
[0027] Figure 5 The fatigue crack propagation curves of the alloy materials obtained in Examples 4-5 and Comparative Example 5 under the aging regime are shown. Detailed Implementation
[0028] Numerous specific details are set forth in the following description to provide a full understanding of the invention. However, the invention can be practiced in many other ways than those described herein, and similar modifications can be made by those skilled in the art without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.
[0029] A stepped, temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys, such as Figure 1 As shown, it includes: deforming an aluminum-lithium alloy ingot, then performing at least two stages of annealing, followed by solution treatment and aging treatment; the two-stage annealing process is as follows: first stage 300-320℃ / 1-2h + second stage 320-400℃ / 1-2h.
[0030] The above-mentioned stepped temperature-controlled annealing and deformation treatment process includes the following steps:
[0031] S1. Prepare the raw materials according to the metal element ratio, and then melt, refine and cast the prepared raw materials in sequence to obtain an ingot; homogenize the ingot to obtain a homogenized alloy ingot; and subject the homogenized alloy ingot to a combined heat treatment process of stepped controlled temperature annealing and deformation treatment.
[0032] S2. Perform step-controlled temperature annealing on the plate to obtain an annealed alloy plate.
[0033] S3. The annealed alloy sheet is subjected to controlled-temperature solution treatment or solution and quenching treatment to obtain a solution-treated sheet.
[0034] S4. Immediately subject the solid solution alloy sheet to artificial aging treatment to obtain a shaped sheet.
[0035] In aluminum-lithium alloys, the composition and formation of various particles are complex. These particles influence the grain morphology controlled after heat treatment under certain deformation conditions. In particular, the regional distribution of Cu-containing particles of different sizes significantly affects recrystallization growth and the gradient distribution of recrystallized grains. Therefore, the alloy composition targeted in this invention is: AlCu 3.6-4.5 Li 1.0-2.0 X, where X = Mg 0.2-1.2 Ag 0.05-0.25 Zn 0.2-0.8 Mn 0.05-0.45 Zr 0.05-0.35 Any one or more of the following.
[0036] In some specific embodiments, step S1, the deformation treatment is carried out at room temperature after homogenization heat treatment, the total pressing amount is 30-80% of the initial thickness of the alloy plate, and the thickness of a single pressing amount does not exceed 2 mm.
[0037] In some specific embodiments, in step S2, when the annealing temperature of the aluminum-lithium alloy is 320~420℃, the holding time is 2-4 h; when the two-stage annealing temperature is 300-320℃ + 320-420℃, the holding time for each stage of the two-stage annealing is 1-2 h. After the first-stage annealing, the plate is heated in the furnace to the second-stage aging annealing temperature at a heating rate of 5-25℃ / min; after the annealing holding is completed, the plate is removed and air-cooled.
[0038] In some specific embodiments, the heating process of the aluminum-lithium alloy plate in step S3 is divided into two stages, but specifically:
[0039] First stage: rapidly heat to 320~420℃ and hold for 4 hours, or rapidly heat to 360-400℃ and hold for 20 minutes;
[0040] Second stage: Continue heating to 510℃ or 520℃, with a heating rate of 10-20℃ / min. After the furnace temperature stabilizes at 510℃ or 520℃, hold it at that temperature for 1 hour, then remove the plate for water quenching.
[0041] In some specific embodiments, in step S4, before artificial aging, the sheet is pre-deformed by rolling with a reduction of 6%, and then the ultra-high strength aluminum-lithium alloy sheet is immediately placed in a box furnace at 130-150°C for heat preservation, and the aging time is 12-36 hours.
[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. It should be noted that the reagents and other materials used in these embodiments are all commercially available products.
[0043] Example 1
[0044] The alloy plate used is an aluminum-lithium alloy with the following composition: Cu 3.9 wt.%, Li 1.3 wt.%, Mg 0.4 wt.%, Ag 0.40 wt.%, Mn 0.30 wt.%, Zn 0.4 wt.%, Zr 0.12 wt.%, unavoidable impurities <0.05 wt%, of which iron ≤0.02 wt% and silicon ≤0.02 wt%; the balance is Al.
[0045] The heat treatment process for the aluminum-lithium alloy material in this embodiment is as follows:
[0046] The raw materials are batched according to the metal element ratio, and then melted, refined and cast sequentially to obtain an ingot. The ingot is homogenized to obtain a homogenized alloy ingot. The homogenized alloy ingot is then hot-rolled or cold-rolled sequentially. The plate is then subjected to a two-stage annealing treatment at 320℃ / 2 h + 340℃ / 2 h, with a heating rate of 20℃ / min in the second stage, to obtain an annealed plate. The annealed plate is then subjected to solution treatment (solution temperature of 510℃, holding time of 1 h), water quenching and aging treatment (rolling pre-deformation of 6%, aging temperature of 150℃, holding time of 35 h).
[0047] Example 2
[0048] The main difference between Example 2 and Example 1 is the difference in the second-stage annealing temperature. The second-stage annealing temperature in Example 2 is 380℃, and the second-stage heating rate is 20℃ / min.
[0049] Example 3
[0050] The only difference between Example 3 and Example 2 is the second-stage annealing temperature. The second-stage annealing temperature of Example 3 is 420°C, and the second-stage heating rate is 20°C / min.
[0051] Comparative Example 1
[0052] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 did not have a pre-solution annealing process. The solution treatment process involved raising the furnace temperature to 510°C and holding the solution at that temperature for 1 hour. The grain structure of the aluminum-lithium alloy materials obtained from Examples 1, 2, 3, and Comparative Example 1 was observed, as follows... Figure 2 As shown in Table 1. Subsequently, fatigue crack propagation tests were conducted on the alloys of Example 1, Example 2, Example 3, and Comparative Example 1, and the results are shown in Table 1 and... Figure 3 and Figure 4 As shown.
[0053] Comparative Example 2
[0054] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 is subjected to one annealing process at a temperature of 400°C and a holding time of 1 hour.
[0055] Comparative Example 3
[0056] The difference between Comparative Example 3 and Example 1 is that the heating rate is 45°C / min.
[0057] Comparative Example 4
[0058] The 2195 aluminum-lithium alloy was used, and the process involved annealing at 380℃ for 2 hours and solution treatment at 510℃ for 1 hour. The remaining steps were the same as in Example 1.
[0059] The aluminum-lithium alloy material provided in this application exhibits slightly improved strength and elongation after pre-solution annealing treatment, when ΔK = 30 MPa·m. 1 / 2 In comparison, Examples 1, 2, and 3 showed significantly lower fatigue crack propagation rates and increased KIC values compared to Comparative Examples 1-4. Comparative Example 4, an aluminum-lithium alloy prepared using conventional processes, exhibited a significant decrease in strength compared to Example 1. Therefore, the novel aluminum-lithium alloy sheet obtained through appropriate solution treatment and pre-annealing treatment simultaneously possesses excellent tensile properties and damage resistance.
[0060] Table 1 Mechanical properties of specimens from Examples 1, 2, 3 and Comparative Example 1
[0061]
[0062] In Table 1, YS represents the yield strength of the material, UTS represents the tensile strength of the material, EL represents the elongation of the material, da / dn represents the crack propagation rate, ΔK represents the stress intensity factor, and KIC represents the maximum ΔK.
[0063] Example 4
[0064] The alloy plate used is an aluminum-lithium alloy with the following composition: Cu 3.87 wt.%, Li 1.56 wt.%, Mg 0.34 wt.%, Mn 0.30 wt.%, Zn 0.48 wt.%, unavoidable impurities <0.05 wt%, of which iron ≤0.02 wt% and silicon ≤0.02 wt%; the balance is Al.
[0065] The preparation method of the aluminum-lithium alloy material in this embodiment is as follows:
[0066] Aluminum-lithium alloy sheets were cold-rolled at room temperature with a deformation of 40%; then annealed at a controlled temperature (specifically, annealing temperature 320℃, holding temperature for 2 hours, and air-cooling the sample) to obtain annealed sheets; the annealed sheets were then subjected to solution treatment (solution temperature 400℃ / 20min + 520℃ / 1h), with the furnace temperature reaching 400℃ and holding for 20 min, the annealed sheets were placed in, and then the temperature was increased to 520℃ at a controlled rate of 20℃ / min and held for 1 hour), water quenching, and aging treatment (rolling pre-deformation of 6%, aging temperature 145℃, holding time 36 hours) to obtain damage-resistant aluminum-lithium alloy materials.
[0067] Example 5
[0068] The only difference between Example 6 and Example 5 is the temperature of the controlled annealing process. The controlled annealing temperature of Example 5 is 375°C.
[0069] Example 6
[0070] The only difference between Example 6 and Example 5 is the temperature of the controlled annealing. Example 6 is a two-stage annealing system with an annealing temperature of 320℃ + 360℃. The holding time for each stage of the two-stage annealing is 2 hours. After the first-stage annealing is completed, the plate is heated to the second-stage annealing temperature in the furnace at a heating rate of 15℃ / min.
[0071] Comparative Example 5
[0072] The difference between Comparative Example 5 and Example 5 is that there is no multi-stage solution treatment process. Solution treatment process: After the furnace temperature is raised to 500°C, the cold-rolled alloy sheet is placed in the furnace, and then the alloy sheet is heated to 520°C with the furnace at a heating rate of 15°C / min, and the solution treatment is held for 3 hours.
[0073] Comparative Example 6
[0074] The 2195 aluminum-lithium alloy was used, and the process involved a single annealing at 380℃ for 2 hours followed by a solution treatment at 520℃ for 1 hour. The remaining steps were the same as in Example 5.
[0075] The aluminum-lithium alloy materials obtained in Examples 4-6 and Comparative Example 5 were subjected to fatigue crack propagation characterization using specimens with different heat treatments. The results are shown in Table 2 and... Figure 5 As shown.
[0076] The damage-resistant aluminum-lithium alloy material provided in this application, when ΔK=35 MPa·m 1 / 2In practice, through reasonable pre-treatment with multi-stage annealing, the fatigue crack propagation rate was lower than that of the traditional direct solution treatment method, and the ΔKmax of Examples 4-6 was close to or even exceeded that of Comparative Examples 5-6. Therefore, aluminum-lithium alloy plates treated with reasonable pre-treatment with multi-stage annealing exhibit excellent damage resistance.
[0077] Table 2 Mechanical properties under different aging regimes
[0078]
[0079] In Table 2, YS represents the yield strength of the material, UTS represents the tensile strength of the material, Elongation represents the elongation of the material, da / dn represents the crack propagation rate, and ΔK represents the stress intensity factor.
[0080] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.
Claims
1. A stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys, characterized in that, include: The aluminum-lithium alloy ingot is deformed and then subjected to two-stage temperature-controlled annealing. The two-stage annealing process is as follows: first stage 300-320℃ / 1-2h + second stage 320-400℃ / 1-2h; the heating rate of the second stage is 5-25℃ / min; The alloy composition of the aluminum-lithium alloy is Cu 3.9 wt.%, Li 1.3 wt.%, Mg 0.4 wt.%, Ag 0.40 wt.%, Mn 0.30 wt.%, Zn 0.4 wt.%, Zr 0.12 wt.%, with unavoidable impurities <0.05 wt%, of which iron ≤0.02 wt% and silicon ≤0.02 wt%; the balance is Al.
2. The stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to claim 1, characterized in that, The deformation amount of the deformation treatment is 30-80%.
3. The stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to claim 1, characterized in that, The deformation treatment is either cold rolling or hot rolling.
4. The stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to claim 1, characterized in that, Also includes: After annealing, a controlled-temperature solution treatment or a combination of solution treatment and aging treatment is performed; the controlled-temperature solution treatment process is as follows: First stage: 320-340℃ / 2-4h + Second stage: 510-520℃ / 1-2h; or First stage: 360-400℃ / 10-20 min + Second stage: 510-520℃ / 1-2 h.
5. The stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to claim 4, characterized in that, The heating rate from the first to the second stage of the solution treatment is controlled at 10-20℃ / min.
6. The stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to claim 4, characterized in that, The aging treatment regime is: 6% pre-deformation by rolling + 130-150℃ / 12-35 h.
7. The stepped temperature-controlled annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys according to claim 1, characterized in that, Also includes: Homogenization heat treatment is performed before deformation treatment.