Stepped temperature-controllable annealing and deformation treatment process for improving damage resistance of aluminum-lithium alloy

Abstract

The invention discloses a stepped temperature-controllable annealing and deformation treatment process for improving the damage resistance of an aluminum-lithium alloy, which comprises the following steps: carrying out deformation treatment on an aluminum-lithium alloy ingot, and then carrying out two-stage temperature-controlled annealing treatment; the system of the two stages of annealing treatment is as follows: the first stage is 300-320 DEG C / 1-2h, and the second stage is 320-400 DEG C / 1-2h; and the heating rate of the second stage is 5-25 DEG C / min. The damage resistance of the aluminum-lithium alloy is greatly improved through grain structure regulation and control and the synergistic effect of second-phase particles. The alloy material treated by the method can meet the industrial engineering production application requirement of high damage resistance of the current aluminum-lithium alloy for aerospace.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation and processing of aerospace vehicle structural materials, and more specifically, relates to a step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys. Background Art

[0002] Aluminum-lithium alloys have excellent properties such as low density, high strength, high specific stiffness and high corrosion resistance. They are considered to be new damage-resistant lightweight structural alloy materials with huge development potential, and show broad prospects for future in-depth applications in the aerospace field. Among them, new ultra-high-strength aluminum-lithium alloys are expected to become structural materials for aircraft due to their excellent mechanical properties. Aluminum-lithium alloys that have undergone reasonable process treatment have excellent strength and fatigue properties and are expected to become the main materials for current aircraft cabin / pressure cabin skins, longitudinal beams and stringers. However, the aluminum-lithium alloy grades currently used still have a lot of gaps compared to the damage resistance requirements of high-strength aluminum alloys. It is crucial to further improve their damage resistance when serving in a stress environment with cyclic loading.

[0003] It is generally believed that the damage resistance of metals is closely related to the grain structure, and the main factors include grain size, grain orientation and grain boundaries. Therefore, regulating the grain structure characteristics of the alloy by adjusting the heat treatment system and then improving its damage resistance becomes the key to whether the alloy can be further applied in engineering. Chinese patent CN 105755409A discloses that the aluminum-lithium alloy sheet that has been cold-rolled to the final thickness is subjected to a short-time annealing treatment at a certain temperature, and then subjected to solid solution quenching and subsequent aging treatment to the required state; the temperature change treatment in the second stage of annealing eliminates part of the deformation energy storage caused by cold rolling, so that the structure after the solid solution treatment becomes a partially recrystallized structure, thereby improving the damage resistance of the alloy. However, the strength of the alloy is not high.

[0004] Chinese patent CN113215423 A reports that the raw materials are melted and cast into ingots, and then the ingots are annealed, hot-rolled, intermediate annealed, and cold-rolled into plates, and then subjected to solid solution quenching, pre-deformation, and aging treatment to obtain high-strength damage-resistant aluminum-lithium alloy. This method is complex, and multiple annealing and deformation treatments lead to an increase in the content of axial grains in the alloy, and the damage resistance of the resulting aluminum-lithium alloy is not greatly improved.

[0005] Therefore, there is an urgent need for a heat treatment process to regulate the alloy grain structure to achieve a stable and uniform state, and to optimize and regulate the structure to achieve the optimal grain structure morphological characteristics that are effective in inhibiting damage. Summary of the invention

[0006] Based on the above-mentioned technical problems existing in the prior art, one of the objects of the present invention is to provide a step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy. The heat treatment system 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 and can meet the current processing and serviceability requirements of aluminum-lithium alloy materials for aerospace.

[0007] In order to achieve the above object, the technical solution of the present invention is as follows:

[0008] A step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy comprises: subjecting the aluminum-lithium alloy ingot to deformation treatment and then subjecting it to two-stage temperature-controlled annealing treatment; the two-stage annealing treatment system is: 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 of the second stage is 5-25°C / min.

[0012] Furthermore, the deformation treatment is cold rolling or hot rolling.

[0013] Furthermore, it also includes: performing a temperature-controlled solid solution treatment or a solid solution treatment and an aging treatment after the annealing treatment; the system of the temperature-controlled solid solution treatment is:

[0014] The first stage is 320-340℃ / 2-4h + the second stage is 510-520℃ / 1-2h; or

[0015] The first stage is 360-400℃ / 10-20min+the second stage is 510-520℃ / 1-2h.

[0016] Furthermore, the heating rate from the first stage to the second stage in the temperature-controlled solution treatment is controlled to be 10-20°C / min.

[0017] Furthermore, the aging treatment system is: 6% rolling pre-deformation + 130-150°C / 12-35h.

[0018] Furthermore, it also includes: performing a homogenization heat treatment before the deformation treatment.

[0019] The principle of the present invention: First, on the basis of a certain deformation, the alloy obtains a predetermined range of energy storage. On this basis, the deformation mode can be changed. If a hot working method is used, the advantage of the texture formation in the deformed alloy and the annealing recrystallization texture and grain structure characteristics in the subsequent annealing process on the damage resistance of the alloy is utilized. In the subsequent two-stage annealing process, the temperature control treatment of the second stage of annealing can effectively regulate the grain structure morphology and grain boundary precipitation phase structure characteristics, and effectively regulate the grain boundary energy storage, providing a basis for forming an effective damage-resistant grain structure morphology of aluminum-lithium alloy.

[0020] In the aluminum-lithium alloy to which the current invention is applicable, the heat treatment used includes but is not limited to single-stage annealing, multi-stage annealing, solution heating rate, etc. It will mainly affect the recovery of the cold-deformed alloy and the precipitation of the second phase particles. In the recovery process of the aluminum-lithium alloy, the deformation energy storage is mainly consumed to accelerate the dislocation climb and polygonization, thereby forming subgrains and coarsening them. In addition, during the annealing process, the coarse second phase particles in the aluminum-lithium alloy will be rolled to precipitate in a band shape, hindering the migration of grain boundaries in the subsequent solution process, and forming a mixed crystal structure with alternating coarse and fine grains. These fine grain areas with high dislocation density will promote the precipitation of the unique semi-coherent strengthening phase (T1 and θ′ phase) in the alloy, and reduce the thickness and diameter of the precipitated phase. These fine precipitated phases are more easily cut back and forth by dislocations during crack propagation and release the energy at the crack tip, 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] The present invention uses a two-stage annealing treatment, especially a temperature-variable treatment in the second stage of annealing to regulate the storage amount of deformation energy brought by deformation, so that the characteristics of the recrystallization structure after the solution treatment change, forming a strip-shaped grain structure with a certain aspect ratio that is conducive to effectively improving the damage resistance of the alloy, thereby greatly improving the damage resistance of the medium-strength aluminum-lithium alloy. This is different from the goal of the traditional annealing process to form equiaxed grain characteristics to provide damage resistance, and provides a new idea for improving the damage resistance of the alloy from a fundamental scientific principle. It provides a solution to the specific requirements (high damage resistance) of aluminum-lithium alloys in special use environments such as aerospace and large aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention is a schematic diagram of a step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy.

[0024] Figure 2 OM images of the longitudinal sections 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 the fatigue crack growth curves of the alloy materials obtained in Examples 1-3 and Comparative Example 1 under the aging system;

[0026] Figure 4 EBSD images of the longitudinal sections of the aluminum-lithium alloys obtained in Examples 1-3 and Comparative Example 1;

[0027] Figure 5 The fatigue crack growth curves of the samples obtained in Examples 4-5 and Comparative Example 5 under the aging system. DETAILED DESCRIPTION

[0028] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0029] A step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloys, such as Figure 1 As shown, it includes: subjecting the aluminum-lithium alloy ingot to deformation treatment, and then subjecting it to at least two stages of annealing treatment, and then subjecting it to solution treatment and aging treatment; the two-stage annealing treatment system is: first stage 300-320℃ / 1-2h + second stage 320-400℃ / 1-2h.

[0030] The above-mentioned step-controlled temperature annealing and deformation treatment process comprises the following steps:

[0031] S1. Mixing materials according to the ratio of metal elements, smelting, refining and casting the prepared raw materials in sequence to obtain an ingot; homogenizing the ingot to obtain a homogenized alloy ingot; and subjecting the homogenized alloy ingot to a combined thermal processing system of a step-controlled temperature annealing process and a deformation treatment;

[0032] S2, performing a step-controlled temperature annealing treatment on the plate to obtain an annealed alloy plate;

[0033] S3, subjecting the annealed alloy plate to a controllable temperature solid solution treatment or a solid solution and quenching treatment to obtain a solid solution plate;

[0034] S4, immediately subjecting the solid solution alloy sheet to artificial aging treatment to obtain a formed sheet.

[0035] In aluminum-lithium alloys, the composition and formation of various particles are relatively complex. These particles will affect the grain structure morphology of the alloy after heat treatment under certain deformation conditions. In particular, the regional distribution of particles of different sizes containing Cu elements will have an important impact on the recrystallization growth in the alloy recrystallization behavior and the gradient distribution of the recrystallized grain structure. Therefore, the alloy composition targeted by the present 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 .

[0036] In some specific embodiments, in step S1, the deformation treatment is performed at room temperature after the 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 temperature of the aluminum-lithium alloy annealing process is 320-420°C, the holding time is 2-4h; when the double-stage annealing temperature is 300-320°C+320-420°C, the holding time of each stage in the double-stage annealing is 1-2h. After the first-stage annealing is completed, the plate is heated with the furnace to the second-stage aging annealing temperature, and the heating rate is 5-25°C / min; after the annealing and holding is completed, the plate is taken out for air cooling.

[0038] In some specific embodiments, the temperature increase of the aluminum-lithium alloy plate in the solution process in step S3 is divided into two stages, but specifically:

[0039] The first stage: quickly heat up to 320-420℃ and keep warm for 4h, or quickly heat up to 360-400℃ and keep warm for 20min;

[0040] The second stage: continue to heat up to 510℃ or 520℃, with a heating rate of 10-20℃ / min. After the furnace chamber temperature stabilizes at 510℃ or 520℃, keep it warm for 1h, then take out the plate for water cooling quenching.

[0041] In some specific embodiments, in step S4, rolling pre-deformation is performed before artificial aging, and the pressing amount is 6%. Then, the ultra-high strength aluminum-lithium alloy plate is immediately placed in a box furnace at 130-150° C. for insulation, and the aging time is 12-36 hours.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. It should be noted that the reagents used in the present embodiment are all common commercial products.

[0043] Example 1

[0044] The alloy plate used is an aluminum-lithium alloy, and its alloy composition is Cu 3.9wt.%, Li 1.3wt.%, Mg0.4wt.%, Ag 0.40wt.%, Mn 0.30wt.%, Zn 0.4wt.%, Zr0.12wt.%, inevitable impurities <0.05wt%, of which iron ≤0.02wt%, silicon ≤0.02wt%; the balance is Al.

[0045] The heat treatment system of the aluminum-lithium alloy material of this embodiment is:

[0046] The ingredients are prepared according to the ratio of metal elements, and the prepared raw materials are sequentially smelted, refined and cast to obtain an ingot; the ingot is homogenized to obtain a homogenized alloy ingot; the homogenized alloy ingot is sequentially hot-rolled or cold-rolled, and the plate is subjected to a two-stage annealing treatment of 320°C / 2h+340°C / 2h, with a second-stage heating rate of 20°C / min to obtain an annealed plate; the annealed plate is sequentially subjected to solution treatment (solution temperature is 510°C, and holding time is 1h), water-cooled quenching and aging treatment (rolling pre-deformation is 6%, aging temperature is 150°C, and holding time is 35h).

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is mainly the difference in the second stage annealing temperature. The second stage annealing temperature of Example 2 is 380° C., and the second stage heating rate is 20° C. / min.

[0049] Example 3

[0050] The difference between Example 3 and Example 2 is only the difference in 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 does not have a pre-solidification annealing system, and the solid solution system is: the furnace temperature is raised to 510°C, and the solid solution is kept warm for 1 hour. The grain structure of the aluminum-lithium alloy materials obtained in Example 1, Example 2, Example 3 and Comparative Example 1 is observed. Figure 2Subsequently, the alloys of Example 1, Example 2, Example 3 and Comparative Example 1 were subjected to fatigue crack growth tests, and the results are shown in Table 1 and Figure 3 and Figure 4 shown.

[0053] Comparative Example 2

[0054] The difference between Comparative Example 1 and Example 1 is that one annealing is performed, the annealing temperature is 400° C., and the holding time is 1 h.

[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 (blank control)

[0058] 2195 aluminum-lithium alloy was used, annealing was performed at 380°C / 2h and solution treatment was performed at 510°C / 1h, and the remaining steps were the same as those in Example 1.

[0059] The strength and elongation of the aluminum-lithium alloy material provided in the present application are slightly improved after annealing before solution treatment. When ΔK = 30 MPa·m 1 / 2 When the fatigue crack growth rate of Example 1, Example 2 and Example 3 is significantly reduced compared with Comparative Examples 1-4, and the KIC value is increased. Comparative Example 4 is an aluminum-lithium alloy prepared by conventional process, and its strength is greatly reduced compared with Example 1. Therefore, the new aluminum-lithium alloy sheet with reasonable pre-solution annealing treatment has excellent tensile properties and damage resistance at the same time.

[0060] Table 1 Mechanical properties of samples of Example 1, Example 2, Example 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 growth 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, and its alloy composition is Cu 3.87wt.%, Li 1.56wt.%, Mg 0.34wt.%, Mn 0.30wt.%, Zn 0.48wt.%, inevitable impurities <0.05wt%, of which iron ≤0.02wt%, silicon ≤0.02wt%; the balance is Al.

[0065] The preparation method of the aluminum-lithium alloy material of this embodiment is:

[0066] The aluminum-lithium alloy plate is cold rolled at room temperature with a deformation of 40%; temperature-controlled annealing (specifically, annealing temperature is 320°C, insulation for 2h, and the sample is taken out and air-cooled) to obtain an annealed plate; the annealed plate is sequentially solution treated (solution temperature is 400°C / 20min+520°C / 1h), when the furnace temperature reaches 400°C, it is kept for 20min, the annealed plate is put in, and then the temperature rate is controlled at 20°C / min, the temperature is raised to 520°C, and the insulation time is 1h), water-cooled quenching and aging treatment (rolling pre-deformation is 6%, aging temperature is 145°C, and insulation time is 36h) to obtain a damage-resistant aluminum-lithium alloy material.

[0067] Example 5

[0068] The difference between Example 6 and Example 5 is only the temperature of the temperature-controlled annealing. The temperature of the temperature-controlled annealing in Example 5 is 375°C.

[0069] Example 6

[0070] The difference between Example 6 and Example 5 is only the difference in the temperature-controlled annealing temperature. Example 6 is a two-stage annealing system with an annealing temperature of 320°C+360°C. The holding time of each stage in the two-stage annealing is 2h. After the first-stage annealing is completed, the plate is heated to the second-stage annealing temperature with the furnace, and the heating rate is 15°C / min.

[0071] Comparative Example 5

[0072] The difference between Comparative Example 5 and Example 5 is that there is no multi-stage solid solution system. Solid solution system: After the furnace temperature is raised to 500°C, the cold-rolled alloy plate is placed in it, and then the alloy plate is heated to 520°C with the furnace, the heating rate is 15°C / min, and the solid solution is kept for 3 hours.

[0073] Comparative Example 6 (blank control)

[0074] 2195 aluminum-lithium alloy was used, and one annealing at 380°C / 2h+solution treatment at 520°C / 1h was adopted. The remaining steps were the same as those in Example 5.

[0075] The fatigue crack growth characteristics of the aluminum-lithium alloy materials obtained in Examples 4-6 and Comparative Example 5 were characterized by different heat treatment samples. The results are shown in Table 2 and Figure 5 shown.

[0076] The damage-resistant aluminum-lithium alloy material provided in the present application has a strength of 35 MPa·m 1 / 2 When the pretreatment is carried out by a reasonable multi-stage annealing treatment, the fatigue crack growth rate is lower than that of the conventional direct solution treatment method, and the ΔKmax of Examples 4-6 is close to or even exceeds that of Comparative Examples 5-6. Therefore, the aluminum-lithium alloy sheet treated by a reasonable multi-stage annealing treatment has excellent damage resistance.

[0077] Table 2 shows the mechanical properties of Example 7 under different aging systems

[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 growth rate, and ΔK represents the stress intensity factor.

[0080] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy, characterized in that: include: The aluminum-lithium alloy ingot is subjected to a deformation treatment and then subjected to a two-stage temperature-controlled annealing treatment; The two-stage annealing treatment system is: first stage 300-320°C / 1-2h+second stage 320-400°C / 1-2h; the heating rate of the second stage is 5-25°C / min.

2. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 1 is characterized in that: 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.

3. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 1 is characterized in that: The deformation amount of the deformation treatment is 30-80%.

4. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 1 is characterized in that: The deformation treatment is cold rolling or hot rolling.

5. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 1 is characterized in that: Also includes: After the annealing treatment, a temperature-controlled solid solution treatment or a solution treatment and an aging treatment is performed; the system of the temperature-controlled solid solution treatment is: The first stage is 320-340℃ / 2-4h + the second stage is 510-520℃ / 1-2h; or The first stage is 360-400℃ / 10-20min+the second stage is 510-520℃ / 1-2h.

6. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 5 is characterized in that: The heating rate from the first stage to the second stage in the solution treatment is controlled at 10-20°C / min.

7. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 5 is characterized in that: The aging treatment system is: 6% rolling pre-deformation + 130-150°C / 12-35h.

8. The step-controlled temperature annealing and deformation treatment process for improving the damage resistance of aluminum-lithium alloy according to claim 1 is characterized in that: Also includes: Homogenization heat treatment is performed before deformation treatment.

Images