A heat treatment method of a spray-formed Sc-containing high lithium content Al-Li alloy

Abstract

This invention discloses a heat treatment method for spray-formed aluminum-lithium alloys containing high lithium (Sc), comprising the following steps: Step 1: placing the spray-formed high-lithium (Sc) aluminum-lithium alloy ingot in a vacuum heat treatment furnace; Step 2: raising the furnace temperature from room temperature to 470-485℃ at a first heating rate, maintaining a core-to-surface temperature difference of less than or equal to 15℃ during the heating process; Step 3: holding the ingot at 470-485℃; Step 4: raising the furnace temperature to 495-500℃ at a second heating rate; Step 5: performing a two-stage holding treatment at 495-508℃; Step 6: progressively cooling the high-lithium (Sc) aluminum-lithium alloy ingot after the holding period. This invention solves the problems of poor alloy toughness and easy cracking during processing caused by low-melting-point phases, avoids abnormal phase coarsening caused by excessive diffusion of Sc, and significantly improves the overall rationality and stability of the phase structure.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy heat treatment technology, and in particular to a highly efficient homogenization heat treatment method for spray-formed aluminum-lithium alloys with high Sc content. Background Technology

[0002] Compared to traditional high-strength aerospace aluminum alloys, lithium (Li) has a density of only 0.534 g / cm³. 3 Lithium is the lightest metal in nature. Adding 1 wt.% lithium to aluminum alloys can result in a 3% reduction in density and an approximately 6% increase in elastic modulus. Due to its advantages such as low density, high elastic modulus, high specific strength and specific stiffness, fatigue resistance, and corrosion resistance, aluminum-lithium alloys are widely used in lightweighting aerospace equipment. Aluminum-lithium alloys can reduce the overall weight of aircraft by 10%-20%.

[0003] The lithium content of aluminum-lithium alloys prepared by traditional casting methods generally does not exceed 2.8%. Exceeding this level results in the formation of a large amount of lithium-containing intergranular compounds at grain boundaries, leading to poor plasticity and toughness, and decreased performance. Lower lithium content results in higher alloy density, leading to less effective weight reduction in applications. However, spray forming technology can break the lithium content limit of traditional casting and allows for the simultaneous addition of multiple alloying elements such as Mg, Cu, Mn, Zn, and Sc. For multi-component high-alloy aluminum-lithium alloys containing Li, Cu, Mg, and Sc, while spray forming can refine the solidification structure and reduce macroscopic segregation, the deposited structure may still contain low-melting-point eutectic phases at grain boundaries, localized solute segregation, and non-equilibrium second phases. If subsequent homogenization heat treatment is not appropriate, these defects will lead to reduced hot working plasticity, increased tendency for grain boundary cracking, and uneven precipitation of strengthening phases. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a heat treatment method for spray-formed aluminum-lithium alloys with high lithium content containing Sc, thereby solving the technical problems of insufficient re-dissolution of low-melting-point eutectic phases, segregation of element diffusion, difficulty in precisely controlling the precipitation density and particle size of Al3(Sc,Zr) strengthening phases, and damage to alloy properties due to easy volatilization and oxidation of lithium elements at high temperatures in traditional aluminum-lithium alloy homogenization heat treatment.

[0005] This invention provides a heat treatment method for spray-formed aluminum-lithium alloys with high lithium content (Sc), comprising the following steps:

[0006] Step 1: Place the spray-formed high-lithium aluminum-lithium alloy ingot containing scandium in a vacuum heat treatment furnace;

[0007] Step 2: Raise the furnace temperature from room temperature to 470-485℃ at the first heating rate, and keep the core-to-surface temperature difference of the scandium-containing high-lithium aluminum-lithium alloy ingot less than or equal to 15℃ during the heating process;

[0008] Step 3: Perform heat treatment at 470-485℃ to promote the re-dissolution of the low-melting-point eutectic phase;

[0009] Step 4: Raise the furnace temperature to 495-500℃ at the second heating rate;

[0010] Step 5: Perform a two-stage heat preservation treatment at 495-508℃. The first stage is heat preservation treatment within the temperature range of 495-508℃, with periodic temperature oscillation applied to the heat preservation temperature. The second stage is two-stage temperature control and regulation within the temperature range of 495-508℃.

[0011] Step 6: After the heat preservation is completed, the scandium-containing high-lithium aluminum-lithium alloy ingot is gradually cooled to obtain a homogenized spray-formed scandium-containing high-lithium aluminum-lithium alloy.

[0012] Furthermore, in step 1, before placing the scandium-containing high-lithium aluminum-lithium alloy ingot into the vacuum heat treatment furnace, the furnace cavity is purged three times with argon gas to ensure that the oxygen content inside the furnace is less than 50 ppm and the ambient humidity is less than 30%; the vacuum degree in the vacuum heat treatment furnace is less than or equal to 10. -2 Pa; The distance between the scandium-containing high-lithium aluminum-lithium alloy ingot and the furnace wall of the vacuum heat treatment furnace is greater than or equal to 50 mm.

[0013] Furthermore, in step 2, the first heating rate ranges from 80 to 100 °C / h, achieving a balance between heat conduction and phase change kinetics at the first heating rate.

[0014] Furthermore, in step 3, the heat treatment time range is 8-12 hours, while the furnace pressure inside the vacuum heat treatment furnace is maintained at 0.5-0.8 times the atmospheric pressure to eliminate the low-melting-point eutectic phase.

[0015] Furthermore, in step 4, the second heating rate range is 50-60℃ / h; when the temperature range is in the transition zone of 480-490℃, the gradient temperature control mode is activated: hold for 3 minutes every 5℃ increase, and circulated argon gas is introduced.

[0016] Furthermore, in step 5, during the first 4 hours of the heat preservation treatment, periodic temperature oscillations are applied to the scandium-containing high-lithium aluminum-lithium alloy ingot, wherein the oscillation amplitude and frequency are dynamically adjusted according to the real-time diffusion process feedback.

[0017] Furthermore, the formula for calculating the oscillation amplitude is as follows:

[0018] ;

[0019] in, ;

[0020] In the formula, A maxD represents the maximum oscillation amplitude. max denoted as the maximum value of the diffusion rate; D(T) is the diffusion rate; D0 is the diffusion constant; Q is the activation energy; R is the gas constant; and T is the temperature.

[0021] Furthermore, the formula for calculating the oscillation frequency is:

[0022] ;

[0023] In the formula, Let t be the initial oscillation frequency. max The point in time when maximum diffusion is achieved; t is the current time.

[0024] Furthermore, in step 5, during the last 8 hours of the heat preservation treatment, a two-stage temperature control is adopted. The first stage involves controlling the temperature within the range of 495-498℃ to promote high-density nucleation of the Al3(Sc,Zr) strengthening phase, with a nucleation density greater than or equal to 10. 15 pcs / m 3 The second stage involves controlling the temperature within the range of 502-508℃ to suppress excessive growth of the strengthening phase nuclei, ultimately controlling the particle size of the Al3(Sc,Zr) strengthening phase to below 20nm.

[0025] Furthermore, in step 6, the progressive cooling includes: a high-temperature slow cooling stage, a medium-temperature transitional cooling stage, a low-temperature accelerated cooling stage, and a final cooling stage performed sequentially.

[0026] The high-temperature slow cooling stage involves cooling the scandium-containing high-lithium aluminum-lithium alloy ingot from an initial temperature of 495-508℃ to 450-460℃ at a cooling rate of 5-15℃ / h.

[0027] The intermediate temperature transition cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is cooled from an initial temperature of 450-460℃ to 380-400℃ at a cooling rate of 15-30℃ / h.

[0028] The low-temperature accelerated cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is cooled from an initial temperature of 380-400℃ to 200-250℃ at a cooling rate of 30-80℃ / h.

[0029] The final cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is removed from the furnace and air-cooled or cooled to room temperature in the furnace.

[0030] The beneficial effects of this invention are:

[0031] The targeted temperature oscillation process of this invention successfully breaks the diffusion boundary layer formed during the diffusion of Li and Cu elements, completely eliminating the hindering effect of the boundary layer on atomic migration, significantly improving the efficiency and uniformity of element lattice diffusion inside the alloy, effectively solving the inherent microsegregation problem of scandium-containing high-lithium aluminum-lithium alloy ingots in spray forming, and allowing key alloying elements such as Li and Cu to achieve uniform distribution throughout the matrix without local enrichment or deficiency, laying a homogenized compositional foundation for the uniform precipitation of subsequent strengthening phases and the stable performance of the alloy. At the same time, the oscillation process is controlled throughout the core range of 495-500℃, without causing abnormal alloy phase structure, thus balancing diffusion efficiency and matrix stability.

[0032] This invention employs a two-stage temperature control strategy to achieve precise and controllable precipitation of the Al3(Sc,Zr) strengthening phase. First, a temperature of 495-498℃ is used to promote the nucleation of the strengthening phase, achieving a nucleation density of 10. 15 pcs / m 3 The high density achieved above, combined with precise temperature control at 502-508℃ to suppress excessive growth of the strengthening phase nuclei and strictly control their particle size to the nanoscale range below 20nm, ultimately forms a high-density, fine-grained Al3(Sc,Zr) dispersed strengthening phase within the alloy matrix. This strengthening phase maintains a good coherent relationship with the matrix, providing core structural support for pinning grain boundaries and suppressing recrystallization during subsequent hot deformation. This fundamentally solves the problems of uneven precipitation and uncontrolled particle size of the strengthening phase in traditional processes.

[0033] This invention achieves an orderly connection and coordinated advancement of element diffusion and strengthening phase precipitation. The first 4 hours focus on element diffusion to eliminate segregation, while the next 8 hours focus on strengthening phase precipitation to achieve structural regulation. The two stages have clear process objectives and well-matched rhythms, which avoids the problem of uneven strengthening phase precipitation sites caused by insufficient element diffusion, and also prevents the situation where strengthening phase precipitation hinders element diffusion. This allows the alloy to achieve the dual process objectives of compositional homogenization and structural strengthening within a single heat treatment stage, significantly improving the efficiency of homogenization heat treatment. Compared with the traditional step-by-step heat treatment process, it effectively shortens the overall processing cycle and reduces the process implementation cost.

[0034] This invention achieves comprehensive optimization of the alloy phase structure through dynamic control. Building upon previous processes, it further ensures the complete dissolution of low-melting-point eutectic phases such as Al6CuLi3 and Al2CuLi, completely eliminating the continuous network eutectic phase at grain boundaries and achieving deep purification of the alloy matrix. This solves the problems of poor alloy toughness and easy cracking during processing caused by low-melting-point phases. Furthermore, through precise phase transformation control, it avoids the abnormal coarsening of the Al3Sc phase caused by excessive diffusion of Sc elements, retaining the strengthening effect of Sc elements. This results in an alloy matrix that is both clean and free of harmful phases, and has a uniform distribution of strengthening phases, significantly improving the overall rationality and stability of the phase structure. Attached Figure Description

[0035] The features and advantages of the invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the invention in any way. In the drawings:

[0036] Figure 1 This is a flowchart illustrating a specific embodiment of the present invention. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] The present invention will be further illustrated below with reference to specific embodiments. Those skilled in the art should understand that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Modifications to the present invention in various equivalent forms all fall within the scope defined by the appended claims.

[0039] This invention provides a heat treatment method for spray-formed aluminum-lithium alloys containing high lithium (Sc). To achieve efficient homogenization of spray-formed aluminum-lithium alloys containing high lithium (Sc), this method addresses issues such as microscopic segregation, insoluble low-melting-point phases, and uneven precipitation of strengthening phases. It fully leverages the alloy's performance advantages due to the combination of scandium and high lithium content. Through a comprehensive process design including clean thermal field construction, precise step-by-step temperature control, staged heat preservation, dynamic phase transformation regulation, and gradual cooling, the method achieves complete dissolution of the low-melting-point eutectic phase and uniform, controllable precipitation of the nanoscale strengthening phase.

[0040] like Figure 1 As shown, it includes the following steps:

[0041] Step S1: The spray-formed high-lithium aluminum-lithium alloy ingot containing scandium is placed in a vacuum heat treatment furnace. During solidification, the high-lithium aluminum-lithium alloy ingot containing scandium prepared by spray forming exhibits micro-segregation; therefore, the initial treatment environment is crucial for subsequent phase transformation. The alloy ingot is placed in a vacuum furnace with a vacuum degree ≤10. -2 Inside the sealed heat treatment furnace, the vacuum environment effectively prevents lithium volatilization and oxidation at high temperatures, as well as surface contamination. Before loading, the furnace cavity must be flushed three times with argon gas to ensure an oxygen content <50ppm. The scandium-containing high-lithium aluminum-lithium alloy ingot maintains a distance of ≥50mm from the furnace wall, and thermocouples are directly welded to the geometric center and one-quarter edge of the ingot to achieve real-time temperature gradient monitoring. This process must be carried out under ambient humidity <30% to avoid the risk of hydrogen embrittlement due to moisture absorption, establishing a clean thermal field foundation for subsequent stepped heating.

[0042] Step S2: The temperature is increased to the initial melting temperature of the ingot at a first rate of 80-100℃ / h, reaching 470-485℃. This rate has been verified by thermal simulation experiments to achieve a balance between heat conduction and phase transformation kinetics: when the heating rate is <80℃ / h, the Al3Sc strengthening phase coarsens prematurely; when the heating rate is >100℃ / h, surface overheating occurs. During the heating process, the heating power is dynamically adjusted using a PID algorithm to ensure that the temperature difference between the core and surface of the ingot is ≤15℃. The key control point is the isothermal buffer at 465℃, which allows the Al-Li-Cu ternary eutectic phase to partially dissolve, preparing for subsequent complete dissolution.

[0043] Step S3: After the low-melting-point eutectic phase dissolution is completed, precise temperature control is implemented at a temperature platform of 470-485℃ for 8-12 hours of heat treatment. The core objective of this stage is to eliminate low-melting-point phases such as Al6CuLi3 and Al2CuLi, while simultaneously inhibiting the abnormal growth of the Al3Sc phase caused by Sc element diffusion. In-situ X-ray monitoring confirmed that the T2 phase dissolution rate was >85% after 4 hours of heat treatment, reaching over 98% by the 8th hour. The furnace pressure was controlled at 0.5-0.8 times atmospheric pressure, and a slight positive pressure was applied to suppress lithium volatilization. After the heat treatment, the rapid cooling rate was verified: samples were quenched in water, and metallographic analysis showed that the continuous network eutectic phase at the grain boundaries completely disappeared, proving the sufficiency of dissolution.

[0044] Step S4: The temperature is increased to the diffusion homogenization temperature of 495-500℃ at a second rate of 50-60℃ / h. This rate design is based on diffusion kinetic calculations: when the heating rate is >60℃ / h, the probability of remelting of the residual eutectic phase in the core increases by 37%; when the heating rate is <50℃ / h, excessive precipitation of the Al3Sc phase occurs. In the 480-490℃ transition zone, a gradient temperature control mode needs to be activated, holding the temperature for 3 minutes every 5℃ increase to compensate for thermal hysteresis, while simultaneously starting the circulating argon system to enhance temperature uniformity. At the end of this stage, in-situ resistivity testing confirms that the alloy has reached a completely dissolved state, establishing single-phase matrix conditions for element diffusion.

[0045] Step S5: Heat preservation to achieve element diffusion and strengthening phase precipitation. The alloy is subjected to heat preservation treatment for 12±0.5 hours within the temperature range of 495-508℃ to complete the synergistic phase transformation. The entire heat preservation stage is divided into two core stages:

[0046] During the first 4 hours of heat preservation, the focus of the process is on the lattice diffusion of Li and Cu elements. By applying periodic temperature oscillations to the alloy matrix, the diffusion boundary layer formed during the element diffusion process is directly broken, eliminating the obstacle of the boundary layer to element diffusion. This allows Li and Cu elements to diffuse rapidly and uniformly in the alloy lattice, fully eliminating the microsegregation problem that originally existed in the spray-formed alloy ingot.

[0047] Centered on a reference temperature range of 495-508℃, small-amplitude heating and cooling cycles were performed, maintaining a stable rate for each heating and cooling cycle. A brief holding period of 1-3 minutes was incorporated at the extreme oscillation point to ensure that all parts of the alloy matrix responded to temperature changes. This created periodic thermal stress and atomic thermal motion variations within the alloy. The alternating intensity of atomic thermal motion impacted the structural stability of the diffusion boundary layer, gradually breaking down the boundary layer's obstruction of Li and Cu atoms' diffusion. This allowed Li and Cu atoms, previously blocked by the boundary layer, to overcome the barrier and migrate rapidly and uniformly within the alloy lattice, effectively improving… To improve the efficiency and uniformity of Li and Cu diffusion, diffusion process data within the alloy was obtained simultaneously through in-situ resistivity detection and real-time diffusion kinetic monitoring. Based on the detection results, the amplitude and frequency of temperature oscillations were dynamically adjusted. When the boundary layer significantly hindered the diffusion process in its early stages, the oscillation frequency and amplitude were appropriately increased to enhance the breaking effect on the diffusion boundary layer. As the diffusion process progressed and the boundary layer gradually disintegrated, the oscillation frequency and amplitude were slowly reduced to avoid excessive oscillation causing unnecessary thermal effects on the alloy matrix. This continued until the diffusion boundary layer was completely eliminated and uniform lattice diffusion of Li and Cu was achieved, at which point the temperature oscillations were stopped.

[0048] The purpose of temperature oscillation mode is to promote lattice diffusion of elements in the alloy by disrupting the diffusion boundary layer, thereby improving diffusion efficiency and controlling the uniformity of precipitates. By combining heat transfer simulation and diffusion kinetic calculations, a multi-order oscillation mode is adopted. In actual processes, the oscillation frequency and amplitude are dynamically adjusted according to the diffusion process of the alloy. The key to the design of this multi-order oscillation mode is to adjust the temperature oscillation amplitude in real time to optimize the diffusion rate of elements, and to further control the nucleation and particle size of precipitates through reverse feedback control.

[0049] A temperature oscillation model is defined to describe the temperature change process. The initial temperature is set to T0, and the amplitude and frequency of the temperature oscillations change dynamically according to the diffusion process at different stages. Within each oscillation cycle, the temperature is described by the following formula:

[0050] ;

[0051] In the formula, T(t) is the temperature at time t; T0 is the initial temperature; and A(t) is the oscillation amplitude that varies with time. Let A(t) be the oscillation frequency that varies with time. It is dynamically adjusted based on real-time feedback results from diffusion dynamics; For phase.

[0052] The relationship between the oscillation amplitude A(t) and the diffusion process can be established using the Arrhenius equation for diffusion rate and temperature. Specifically, the relationship between the diffusion rate D and temperature T is expressed as:

[0053] ;

[0054] In the formula, D0 is the diffusion constant; Q is the activation energy; R is the gas constant; and T is the temperature.

[0055] The diffusion rate D directly affects the efficiency of element diffusion. To optimize the diffusion process, the relationship between the temperature oscillation amplitude A(t) and the diffusion rate D(T) is set as follows:

[0056] ;

[0057] In the formula, A max D represents the maximum oscillation amplitude. max As the diffusion rate reaches its maximum value, the increase in D(T) leads to a gradual decrease in A(t) as the element diffuses, and the oscillation amplitude tends to stabilize, preventing excessive oscillation from affecting the alloy phase structure.

[0058] Oscillation frequency The relationship with temperature is to ensure a rapid temperature rise in the initial stage to promote nucleation, while the temperature oscillation slows down in the later stage to ensure a uniform distribution of precipitates. Frequency Controlled by the following formula:

[0059] ;

[0060] In the formula, Let t be the initial oscillation frequency. maxTo achieve the maximum diffusion time point; t is the current time, by gradually reducing the oscillation frequency, the temperature fluctuation can gradually stabilize, thereby preventing the influence of excessive oscillation on the precipitates and ensuring that the strengthening phase precipitates in the final alloy have ideal morphology and particle size distribution.

[0061] During the temperature rise process, the diffusion process of elements is precisely controlled by adjusting the oscillation amplitude and frequency. In the initial stage, a larger oscillation amplitude and higher frequency help to increase the diffusion rate and promote rapid diffusion of elements. As time progresses, the oscillation amplitude and frequency gradually decrease, which helps to homogenize the precipitates and avoid excessive precipitation and coarsening. At the end of the oscillation, the nucleation density of the strengthening phase in the alloy is effectively controlled, and the particle size is maintained in the nanometer range, ultimately achieving optimized mechanical properties.

[0062] First, the basic formula framework for the temperature oscillation mode is determined through heat transfer simulation and diffusion kinetic calculation. Then, the alloy diffusion process data monitored in real time during the process is used as input to dynamically adjust the oscillation amplitude A(t) and oscillation frequency in the formula. Key parameters such as nucleation and particle size of precipitates are controlled by a reverse feedback control mechanism. The actual detection results of nucleation and particle size of precipitates in the process are substituted into the formula to correct the parameters. The calculation results of the formula are continuously matched with the actual needs of the process on site. The theoretical formula provides precise guidance for temperature oscillation operation in the actual process. Finally, the element diffusion rate is optimized through the process operation under calculation and control, and the nucleation and particle size of precipitates are precisely controlled.

[0063] After 8 hours of heat preservation, the focus shifted to the controllable precipitation of nanoscale Al3(Sc,Zr) reinforced phases. A two-stage temperature control method was employed for precise regulation. First, the temperature was maintained at 495-498℃ to create suitable conditions for the nucleation of the Al3(Sc,Zr) reinforced phases, promoting the formation of high-density crystal nuclei and achieving a nucleation density of 10. 15 pcs / m 3 The temperature is then adjusted to 502-508℃. By precisely controlling the temperature, the excessive growth of the strengthening phase nuclei is suppressed, and the growth process of the nuclei is precisely controlled. Finally, the particle size of the Al3(Sc,Zr) strengthening phase is controlled to below 20nm, achieving high-density, fine-particle-size controllable precipitation of the nanoscale strengthening phase.

[0064] By combining thermodynamics and diffusion kinetics, temperature is monitored in real time and temperature gradient and holding time are dynamically adjusted to precisely control the particle size and distribution of precipitates, ensuring that the phase transformation process of the alloy achieves the best results at each stage. By customizing the precipitation characteristics of different alloy compositions, excessive growth or uneven distribution of precipitates can be effectively avoided, especially in the precipitation process of strengthening phases.

[0065] At different temperatures, different elements in an alloy diffuse at different rates, thus affecting the nucleation and growth of precipitates. Therefore, dynamic adjustment of the temperature gradient is crucial for precisely controlling the grain size and morphology of precipitates. Based on the diffusion process, the adjustment of the temperature gradient is described by the following formula:

[0066] ;

[0067] In the formula, For temperature gradient; D is the coefficient of the temperature gradient; D(T) is the diffusion rate at temperature T; D max The maximum diffusion rate; It is an index of the sensitivity of temperature to the diffusion rate.

[0068] By dynamically adjusting the temperature gradient and responding in real time to changes in the diffusion rate, more precise control of strengthening phase precipitation can be achieved in the alloy. In the early stages of diffusion, a larger temperature gradient can accelerate element diffusion, thereby promoting nucleation; while when the precipitates tend to stabilize, reducing the temperature gradient helps to avoid excessive growth.

[0069] As diffusion progresses, optimizing the holding time is equally important. Based on thermodynamic and diffusion kinetic calculations, the holding time is adjusted using the following formula:

[0070] ;

[0071] In the formula, Let t be the holding time; t is the initial holding time; Q is the activation energy; R is the gas constant; T(t) is the temperature at time t.

[0072] As temperature increases, the diffusion rate accelerates, leading to a shorter required holding time. By monitoring the temperature in real time and dynamically adjusting the holding time based on the current temperature T(t), it is ensured that the strengthening phase can reach a stable precipitation state within an appropriate time when the temperature rises. This ensures that, under the control of the temperature gradient, elements in the alloy can diffuse and precipitate in the shortest possible time, while avoiding excessively large or uneven precipitates.

[0073] At different stages of the alloying process, by adjusting the temperature gradient To promote the diffusion of elements, and by adjusting the retention time This ensures the precise growth of precipitates. Such a strategy not only improves the alloy's performance but also guarantees that the particle size and morphology of the precipitates meet expectations under different alloy compositions.

[0074] Step S6: In the initial stage of the cooling process, a slower cooling rate is used to avoid excessive precipitation of precipitates. In the later stage, the cooling rate is gradually increased (accelerated cooling) to ensure the uniform distribution and stability of the precipitates.

[0075] The progressive cooling process includes: a high-temperature slow cooling stage, a medium-temperature transitional cooling stage, a low-temperature accelerated cooling stage, and a final cooling stage, performed sequentially.

[0076] The high-temperature slow cooling stage involves cooling the scandium-containing high-lithium aluminum-lithium alloy ingot from an initial temperature of 495-508℃ to 450-460℃ at a cooling rate of 5-15℃ / h.

[0077] The intermediate temperature transition cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is cooled from an initial temperature of 450-460℃ to 380-400℃ at a cooling rate of 15-30℃ / h.

[0078] The low-temperature accelerated cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is cooled from an initial temperature of 380-400℃ to 200-250℃ at a cooling rate of 30-80℃ / h.

[0079] The final cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is removed from the furnace and air-cooled or cooled to room temperature in the furnace.

[0080] The design of a progressive cooling mode is crucial for the uniform distribution and stability of precipitates. Controlling the cooling rate directly affects the nucleation density, grain size, and distribution of the precipitates, thus influencing the final mechanical properties of the alloy. Based on metallographic analysis and electron microscopy observations, a progressive cooling mode combining slow and accelerated cooling can effectively control the precipitate growth process, preventing excessive precipitation or aggregation, thereby improving the alloy's uniformity and mechanical properties.

[0081] In the initial cooling stage, slow cooling is employed to reduce excessively rapid precipitation. Slow cooling helps elements diffuse more evenly in the matrix and avoids inhomogeneous precipitation of strengthening phases caused by excessively rapid cooling. If the cooling rate is too fast, the strengthening phase may precipitate excessively in a short time, forming large particles. Uneven distribution of these particles in the alloy can affect its strength and toughness. Therefore, in the initial cooling stage, the cooling rate is controlled using the following formula:

[0082] ;

[0083] Let be the cooling rate at time t; t represents the initial cooling rate; max t represents the maximum time of the cooling process; t represents the current time.

[0084] In the initial stage of cooling, the cooling rate gradually slows down over time, with a low initial rate, thereby reducing the premature precipitation of precipitates.

[0085] In the later stages of cooling, to ensure uniform distribution of the precipitates and improve their stability, the cooling rate should be gradually accelerated. Accelerated cooling helps to quickly terminate the precipitation of the strengthening phase and stabilize the final morphology of the precipitates. Based on thermodynamic and kinetic analysis, rapidly reducing the temperature in the later stages of cooling helps to reduce further growth of the precipitates, maintain their nanoscale particle size, and avoid uneven growth of the precipitates. The cooling rate in this stage is controlled by the following formula:

[0086] ;

[0087] In the formula, This refers to the cooling rate during the later cooling phase. For the final accelerated cooling rate; t max t represents the point in time during the cooling process where slow cooling transitions to accelerated cooling; final t represents the total time until cooling ends; t represents the current time. In the later stages of cooling, the cooling rate gradually increases with time to ensure the uniform distribution and stability of the precipitates by accelerating cooling.

[0088] To achieve the synergistic phase transition goal of element diffusion and precise precipitation of enhanced phases, and to ensure the accuracy of process effects at each stage, we carried out refined operations from three dimensions: temperature oscillation mode design, dynamic control of temperature gradient and holding time, and progressive planning of cooling process. These operations respectively achieved the destruction of diffusion boundary layer and efficient element diffusion, precise control of precipitate particle size and distribution, and the final guarantee of precipitate morphology and stability.

[0089] The following is a comparative example of this embodiment:

[0090] Comparative Example: To verify the core advantage of the heat treatment method described in this invention in eliminating microsegregation in spray-formed high-lithium aluminum-lithium alloys containing scandium, a control experiment was set up.

[0091] The comparative example uses the same batch and composition of spray-formed high-scandium aluminum-lithium alloy ingots as the embodiments of the present invention, and the furnace loading, environmental conditions and cooling process are completely consistent. Only the core steps such as intermediate heating rate, heat preservation method and temperature control strategy are changed. By detecting the segregation degree of key elements such as Li, Cu and Sc, the segregation elimination effect of the two processes is compared to ensure that the experiment is a single variable.

[0092] Only the intermediate heating and heat preservation steps are adjusted, and the industry-standard aluminum-lithium alloy homogenization treatment method is adopted, without stepped heating, isothermal buffering, temperature oscillation, or dynamic gradient control. Specific operation:

[0093] Heating stage: The temperature is directly increased from room temperature to 490℃ at a single rate of 120℃ / h, without PID algorithm temperature control, without setting a 465℃ isothermal buffer step, and the temperature difference between the core and surface of the spindle is not controlled during the heating process.

[0094] The heat preservation stage: The temperature was kept at 490℃ for 24 hours without a staged heat preservation design. No positive pressure of 0.5-0.8 times the atmospheric pressure was applied (normal pressure heat preservation). There was no temperature oscillation mode and the circulating argon system was not turned on. Element diffusion was achieved solely by maintaining a single constant temperature.

[0095] Temperature control without transition zone: After heating to the target temperature, the temperature is directly held without a 480-490℃ transition zone temperature control, without thermal hysteresis compensation of holding for 3 minutes every 5℃, and without confirming the solid solution state through in-situ resistivity detection.

[0096] Alloy samples from the comparative and example examples were selected, and elemental distribution was detected by electron probe microanalysis (EPMA), grain boundary / intragranular elemental content was detected by energy dispersive spectroscopy (EDS), and grain boundary segregation bands were observed by metallographic microscopy. The core indicators are compared in Table 1 below:

[0097] Table 1 Comparison of Core Indicators

[0098]

[0099] Segregation: The ratio of the mass content of key elements at grain boundaries to that within grains. The closer the ratio is to 1, the more uniform the element distribution and the lower the degree of segregation.

[0100] Uniformity coefficient: calculated based on EPMA surface distribution data, with a value of 0~1, and ≥0.9 is considered to indicate no significant elemental segregation;

[0101] Microsegregation elimination rate: Based on the original segregation in the solidified alloy, the proportion of segregation eliminated after heat treatment is calculated, reflecting the core improvement effect of the process on segregation.

[0102] Therefore, a single rapid heating method, such as 120℃ / h, without isothermal buffering, fails to partially dissolve the low-melting-point eutectic phase beforehand. Direct heating leads to local melting and reaggregation of the grain boundary segregated phase, exacerbating element enrichment. Furthermore, the lack of PID temperature control results in a large temperature difference between the core and surface, leading to uneven element diffusion rates. The absence of staged holding for dissolution followed by diffusion means that the low-melting-point segregated phase is not eliminated before direct isothermal diffusion. Undissolved phases hinder element diffusion within the crystal lattice. Even with a holding time of 24 hours, only a small amount of intracrystalline micro-segregation can be eliminated, with no improvement in grain boundary segregation. Without temperature oscillation to disrupt the diffusion boundary layer and without circulating argon to enhance temperature uniformity, elements diffuse slowly relying solely on molecular thermal motion, failing to achieve effective migration of grain boundary-enriched elements into the grain, resulting in extremely low segregation elimination efficiency.

[0103] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A heat treatment method for spray-formed aluminum-lithium alloy with high lithium content (Sc), comprising the following steps: Step 1: Place the spray-formed high-lithium aluminum-lithium alloy ingot containing scandium in a vacuum heat treatment furnace; Step 2: Raise the furnace temperature from room temperature to 470-485℃ at the first heating rate, and keep the core-to-surface temperature difference of the scandium-containing high-lithium aluminum-lithium alloy ingot less than or equal to 15℃ during the heating process; Step 3: Perform heat treatment at 470-485℃ to promote the re-dissolution of the low-melting-point eutectic phase; Step 4: Raise the furnace temperature to 495-500℃ at the second heating rate; Step 5: Perform a two-stage heat preservation treatment at 495-508℃, during which... The first stage involves heat preservation treatment within a temperature range of 495-508℃, with periodic temperature oscillations applied to the heat preservation temperature. The second stage involves two-stage temperature control and regulation within a temperature range of 495-508℃. Step 6: After the heat preservation is completed, the scandium-containing high-lithium aluminum-lithium alloy ingot is gradually cooled to obtain a homogenized spray-formed scandium-containing high-lithium aluminum-lithium alloy.

2. The heat treatment method for spray-formed aluminum-lithium alloy with high lithium content (Sc) as described in claim 1, characterized in that, In step 1, before placing the scandium-containing high-lithium aluminum-lithium alloy ingot into the vacuum heat treatment furnace, the furnace cavity is purged three times with argon gas to ensure that the oxygen content inside the furnace is less than 50 ppm and the ambient humidity is less than 30%; the vacuum degree in the vacuum heat treatment furnace is less than or equal to 10. -2 Pa; The distance between the scandium-containing high-lithium aluminum-lithium alloy ingot and the furnace wall of the vacuum heat treatment furnace is greater than or equal to 50 mm.

3. The heat treatment method for spray-formed aluminum-lithium alloy with high lithium content (Sc) as described in claim 1, characterized in that, In step 2, the first heating rate ranges from 80 to 100 °C / h, and the balance between heat conduction and phase change kinetics is achieved at the first heating rate.

4. The heat treatment method of spray-formed Sc-containing high lithium content Al-Li alloy of claim 1, wherein In step 3, the heat treatment time range is 8-12 hours. At the same time, the furnace pressure inside the vacuum heat treatment furnace is maintained at 0.5-0.8 times the atmospheric pressure to eliminate the low-melting-point eutectic phase.

5. The heat treatment method for spray-formed aluminum-lithium alloy with high lithium content (Sc) as described in claim 1, characterized in that, In step 4, the second heating rate range is 50-60℃ / h; when the temperature range is in the transition zone of 480-490℃, the gradient temperature control mode is activated: hold for 3 minutes every 5℃ increase, and circulated argon gas is introduced.

6. The heat treatment method for spray-formed aluminum-lithium alloy with high lithium content (Sc) as described in claim 1, characterized in that, In step 5, during the first 4 hours of the heat preservation treatment, periodic temperature oscillations are applied to the scandium-containing high-lithium aluminum-lithium alloy ingot, wherein the oscillation amplitude and frequency are dynamically adjusted according to the real-time diffusion process feedback.

7. The heat treatment method of spray-formed Sc-containing high lithium content Al-Li alloy of claim 6, wherein The formula for calculating the oscillation amplitude is: A(t) = A max (1 - DT(T) / DT max ); Where D(T) = D0·exp(-Q / (R·T)); In the formula, A max D represents the maximum oscillation amplitude. max denoted as the maximum value of the diffusion rate; D(T) is the diffusion rate; D0 is the diffusion constant; Q is the activation energy; R is the gas constant; and T is the temperature.

8. The heat treatment method for spray-formed aluminum-lithium alloy with high lithium content containing Sc as described in claim 6 or 7, characterized in that, The formula for calculating the oscillation frequency is: ω(t) = ω0(1 - t / t max ); In the formula, ω0 is the initial oscillation frequency, and t max The point in time when maximum diffusion is achieved; t is the current time.

9. The heat treatment method of spray forming Sc-containing high lithium content Al-Li alloy according to claim 1 or 6, characterized in that, In step 5, during the last 8 hours of the heat preservation treatment, a two-stage temperature control is adopted. The first stage involves controlling the temperature within the range of 495-498℃ to promote high-density nucleation of the Al3(Sc,Zr) strengthening phase, with a nucleation density greater than or equal to 10. 15 pcs / m 3 The second stage involves controlling the temperature within the range of 502-508℃ to suppress excessive growth of the strengthening phase nuclei, ultimately controlling the particle size of the Al3(Sc,Zr) strengthening phase to below 20nm.

10. The heat treatment method of spray-formed Sc-containing high lithium content Al-Li alloy of claim 1, wherein, In step 6, the progressive cooling includes: a high-temperature slow cooling stage, a medium-temperature transitional cooling stage, a low-temperature accelerated cooling stage, and a final cooling stage performed sequentially. The high-temperature slow cooling stage involves cooling the scandium-containing high-lithium aluminum-lithium alloy ingot from an initial temperature of 495-508℃ to 450-460℃ at a cooling rate of 5-15℃ / h. The intermediate temperature transition cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is cooled from an initial temperature of 450-460℃ to 380-400℃ at a cooling rate of 15-30℃ / h. The low-temperature accelerated cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is cooled from an initial temperature of 380-400℃ to 200-250℃ at a cooling rate of 30-80℃ / h. The final cooling stage is as follows: the scandium-containing high-lithium aluminum-lithium alloy ingot is removed from the furnace and air-cooled or cooled to room temperature in the furnace.

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