A rapid hot-pressing sintering-deformation heat treatment integrated method of high-performance 6061 aluminum alloy

Abstract

The application belongs to the technical field of metal material preparation, and discloses a rapid hot-pressing sintering-deformation heat treatment integrated method for high-performance 6061 aluminum alloy, which comprises the following steps: obtaining high-density sintered blanks by rapid hot-pressing sintering to provide a good organizational basis for subsequent deformation heat treatment; through a sequential combination deformation mode of cold rolling-low temperature rolling, the dislocation density presents a cumulative effect of cold rolling introduction to low temperature reservation and proliferation, effectively controls the size, distribution and number density of aging precipitation phase, realizes the superposition of precipitation strengthening and fine grain / subgrain strengthening; no intermediate annealing or pre-aging treatment is carried out between cold rolling and low temperature rolling, so as to reserve the deformation energy introduced by cold rolling and maximize the promoting effect of deformation on aging precipitation. Through the above method, the application can solve the technical problems of low strength of conventional sintered state of powder metallurgy 6061 aluminum alloy, imbalance of strength and plasticity after T6 heat treatment, and poor adaptability of existing deformation heat treatment and powder metallurgy materials.

Description

Technical Field

[0001] This invention relates to an integrated process of aluminum alloy powder metallurgy forming and deformation heat treatment, and particularly to an integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy. Background Technology

[0002] 6061 aluminum alloy (Al-Mg-Si system) possesses moderate strength, good corrosion resistance, weldability, and machinability, making it one of the most widely used wrought aluminum alloys. It is extensively applied in aerospace, automotive manufacturing, shipbuilding, and civil structural components. With the increasing demand for lightweight structures, higher requirements are being placed on the fabrication technology of high-performance, complex-shaped 6061 aluminum alloy parts. Currently, the industrial fabrication of 6061 aluminum alloy products is developing along two parallel technical routes. One is the casting-hot working route, which involves casting ingots followed by hot forming processes such as rolling, extrusion, or forging. The other is the powder metallurgy-hot working route, which involves powder forming followed by post-densification and forming processes such as hot extrusion or powder forging. Under typical T6 heat treatment, 6061 aluminum alloy prepared along the casting-hot working route has an ultimate tensile strength of 260–310 MPa, a yield strength of 240–276 MPa, and an elongation after fracture of 8–12%. In the powder metallurgy-hot working route, the tensile strength of sintered 6061 aluminum alloy can be increased from 112MPa to 245MPa after hot extrusion; after powder forging combined with T6 heat treatment, the yield strength can reach 245MPa, the tensile strength can reach 285MPa, and the elongation can reach 8%.

[0003] However, 6061 aluminum alloy still has significant performance deficiencies in industrial applications. Firstly, its overall strength is relatively low. The nominal yield strength of 6xxx series aluminum alloys after heat treatment is generally below 350 MPa, compared to 7xxx series high-strength aluminum alloys (yield strength > 450 MPa). This limits its application in structures requiring high load-bearing capacity, often resulting in oversized components and difficulty in meeting design targets. Secondly, there is an inverse relationship between strength and plasticity. While conventional T6 heat treatment improves strength, it usually sacrifices plasticity. After T6 heat treatment, the tensile strength of powder metallurgy 6061 aluminum alloy increases from 139 MPa to 271 MPa, but the elongation drops sharply from 11.9% to 2.2%. For complex structural components such as battery trays in new energy vehicles, when customers require comprehensive performance requirements of tensile strength ≥ 300 MPa, yield strength ≥ 260 MPa, and elongation ≥ 10%, conventional processes cannot simultaneously meet these requirements. Thirdly, there is a trade-off between extrudability and mechanical properties during extrusion molding. Increasing the extrusion speed improves production efficiency, but it can easily lead to cracking of the internal ribs of the profile and a decrease in formability; increasing the extrusion temperature improves formability, but it affects the aging strengthening effect.

[0004] The technical reasons for the aforementioned performance deficiencies are particularly prominent in powder metallurgy preparation routes, and are mainly manifested in the following aspects:

[0005] Firstly, there is the bottleneck in densification of powder-sintered bodies. Aluminum powder particles inherently possess a thermodynamically stable Al2O3 oxide film. This film is difficult to remove effectively if the sintering temperature is not properly controlled, severely hindering interparticle diffusion and metallurgical bonding. To promote densification, conventional sintering typically employs extended holding times. However, prolonged high-temperature holding leads to significant grain coarsening in the sintered body, with grain sizes increasing from a few micrometers initially to tens or even hundreds of micrometers. This coarse grain structure not only directly reduces the material's strength and plasticity but also severely weakens the potential for dislocation multiplication and grain refinement during subsequent deformation strengthening, limiting the ability of deformation heat treatment to deeply optimize the microstructure. Therefore, the relative density of sintered 6061 aluminum alloy is generally low (typically only 85%–95% of the theoretical density, with a typical value of approximately 94.34%), accompanied by microstructural degradation due to grain coarsening. Numerous residual pores not only constitute stress concentration sources, significantly reducing material strength and plasticity, but also, together with coarse grain structure and residual pores, restrict the microstructure basis for dislocation movement and uniform nucleation of precipitates during subsequent deformation heat treatment. This makes the powder metallurgy route less effective than the casting-hot working route in terms of strength-plasticity matching.

[0006] Secondly, the regulation of precipitated phases is constrained by porosity and oxide film. Residual pores and oxide film interfaces in powder metallurgy sintered bodies easily become heterogeneous nucleation sites for the Mg2Si equilibrium phase, promoting the preferential precipitation of coarse strengthening phases at pore edges and particle boundaries. This weakens the effective solute concentration in the matrix and reduces the uniform dispersion precipitation ability of the β″ metastable strengthening phase. Simultaneously, insufficient density of the sintered body leads to a decrease in thermal conductivity and cooling response. The cooling rate after extrusion or heat treatment is more sensitive to the control of the retention degree of supersaturated solid solution, making it difficult to achieve ideal quenching effects under industrial conditions, further restricting the full realization of the age-strengthening potential.

[0007] Third, there is insufficient synergy between post-densification processes and deformation strengthening. While post-densification methods such as powder forging, hot extrusion, or hot isostatic pressing can increase the relative density to over 98%–99%, significantly improving tensile strength, these processes often involve complex equipment, high costs, and significant limitations on product shape and size. More importantly, existing post-densification processes primarily address the density problem in the sintered state, failing to effectively connect with subsequent deformation heat treatment. There is a lack of deformation strengthening schemes designed specifically for the characteristics of powder metallurgy microstructures (such as residual oxide film distribution and pore closure behavior). Consequently, powder metallurgy 6061 aluminum alloy still struggles to meet the stringent requirements for strength and toughness in complex structural components such as battery trays for new energy vehicles in terms of strength, plasticity reserve, and overall mechanical properties.

[0008] Traditional casting-hot working methods suffer from limitations such as coarse casting structures, compositional segregation, and difficulty in achieving near-net-shape forming, especially for complex-shaped parts, resulting in long processing steps and low material utilization. Powder metallurgy technology provides another important pathway for the preparation of 6061 aluminum alloy, offering advantages such as near-net-shape forming, high material utilization, uniform structure, and avoidance of casting segregation, demonstrating unique potential for low-cost, high-efficiency, and large-scale production of aluminum alloy parts. However, the widespread application of powder metallurgy 6061 aluminum alloy faces a key bottleneck: difficulty in sintering densification. As mentioned earlier, the oxide film on the surface of aluminum powder is difficult to remove at conventional sintering temperatures, leading to generally low density in the sintered body, and residual porosity severely affects the mechanical properties and reliability of the product. To address this issue, research has been conducted on post-densification processes such as powder forging, hot extrusion, and hot isostatic pressing, but these processes typically involve complex equipment, high costs, and significant limitations on product shape. On the other hand, deformation heat treatment (combining plastic deformation with heat treatment) is an effective means to improve the mechanical properties of aluminum alloys. Studies have shown that by combining large plastic deformation (such as cumulative rolling) with aging treatment, the tensile strength of 6061 aluminum alloy can be increased to over 386 MPa, with an elongation of approximately 12.8%. By introducing dislocations and refining grains through deformation, and then controlling precipitates through aging treatment, a synergistic improvement in strength and toughness can be achieved. For example, existing techniques introduce pre-deformation before solution aging of aluminum alloys, utilizing the dislocations introduced by pre-deformation to provide more nucleation sites for precipitates, accelerating the desolvation process and improving mechanical properties. Some studies have also explored heat treatment processes that synergistically strengthen through deformation and phase transformation. However, these deformation heat treatment studies mainly target cast aluminum alloys, whose initial microstructure differs fundamentally from that of powder metallurgy materials. For powder metallurgy 6061 aluminum alloys, how to further optimize the microstructure through deformation heat treatment after solving the sintering densification problem remains a lack of systematic research.

[0009] In summary, current technologies lack an integrated process that effectively connects the rapid densification of powder metallurgy 6061 aluminum alloy with its subsequent deformation strengthening heat treatment. On the one hand, conventional powder metallurgy sintered bodies are difficult to directly undergo subsequent plastic deformation due to insufficient density; on the other hand, existing deformation heat treatment processes are not adapted to the microstructure characteristics of powder metallurgy materials, making it difficult to fully leverage the dual advantages of near-net-shape forming and deformation strengthening synergy in powder metallurgy.

[0010] The above background information is provided only to aid in understanding the inventive concept and technical solution of this invention. It does not necessarily belong to the prior art of this patent application. In the absence of clear evidence that the above information was disclosed on the filing date of this patent application, the above background information should not be used to evaluate the novelty and inventiveness of this invention. Summary of the Invention

[0011] In view of the technical defects of existing powder metallurgy 6061 aluminum alloy, which is difficult to effectively perform deformation strengthening due to insufficient density after sintering, and the technical defects of existing deformation heat treatment processes, which are not adapted to the microstructure characteristics of powder metallurgy materials and cannot give full play to the synergistic advantages of near-net-shape forming and deformation strengthening of powder metallurgy, this invention provides an integrated method for rapid hot pressing sintering and deformation heat treatment of 6061 aluminum alloy.

[0012] To achieve this objective, the present invention employs the following technical solution:

[0013] A rapid hot pressing sintering-deformation heat treatment integrated method for high-performance 6061 aluminum alloy includes the following steps:

[0014] (1) Rapid hot pressing sintering: 6061 aluminum alloy powder is placed in a vacuum-protected hot pressing sintering furnace, heated to 500-550°C at a heating rate of 100-150°C / min, and pressure of 30-50MPa is applied. The temperature and pressure are held for 10-20 minutes to obtain a sintered blank with a relative density ≥98%.

[0015] (2) Solution treatment: The sintered billet obtained in step (1) is heated to 500-580℃ and held for 0.5-4h, and then quenched to room temperature to obtain a supersaturated solid solution structure;

[0016] (3) Cold rolling deformation: The alloy after solution treatment in step (2) is subjected to room temperature cold rolling, with a reduction of 5% to 10% per pass and a total deformation of 30% to 60%;

[0017] (4) Low temperature rolling deformation: The alloy after cold rolling in step (3) is initially immersed in a low temperature environment of -196℃ to -50℃ for 1 to 3 hours to make the overall temperature of the alloy uniformly drop to the target temperature. Then, it is rolled at the same temperature. The reduction per pass is 8% to 12%, and the interval between rolling passes is immersing in liquid nitrogen for 5 to 10 minutes. The total deformation is 10% to 40%. No intermediate annealing or pre-aging treatment is performed between steps (3) and (4).

[0018] (5) Aging treatment: The alloy after low temperature rolling in step (4) is kept at 160-180℃ for 10-14h, and then water quenched to room temperature to obtain 6061 aluminum alloy with enhanced strength and plasticity.

[0019] Preferably, the aluminum alloy powder in step (1) has a particle size of 4 to 6 μm.

[0020] Preferably, the heating temperature in step (2) is 520 to 560°C.

[0021] Preferably, the heat preservation time in step (2) is 1 to 3 hours.

[0022] Preferably, the medium used for quenching in step (2) is water at room temperature.

[0023] Preferably, the total deformation in step (3) is 35% to 50%.

[0024] Preferably, the low-temperature environment described in step (4) is achieved by immersion in liquid nitrogen.

[0025] Preferably, the total deformation in step (4) is 20% to 30%.

[0026] Preferably, the alloy aging treatment temperature in step (5) is 170-180°C.

[0027] Preferably, the heat preservation time in step (5) is 12 to 14 hours.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) Simultaneous optimization of density and mechanical properties. This invention achieves densification within 10-20 minutes at a heating rate of 100-150℃ / min through rapid hot pressing sintering, obtaining a high-density sintered blank with a relative density ≥98%. This effectively solves the technical problem of low density (typically only 85%-93%) and high porosity in traditional powder metallurgy 6061 aluminum alloys due to the Al2O3 oxide film on the aluminum powder surface hindering sintering. The high-density sintered blank provides a good microstructure for subsequent deformation heat treatment, avoiding stress concentration and early failure caused by residual porosity. This invention can achieve a comparable or even higher density level through rapid hot pressing sintering, without the need for subsequent complex hot extrusion or powder forging processes, thus achieving a simultaneous improvement in density and preparation efficiency.

[0030] (2) The sequential combination of cold rolling and low-temperature rolling generates a dislocation density accumulation effect, achieving a synergistic improvement in strength and plasticity. This invention adopts a deformation mode combining cold rolling and low-temperature rolling, which produces a significant synergistic effect. The core mechanism is as follows: the cold rolling stage deforms the solid solution alloy at room temperature, introducing a large number of dislocations and deformation energy storage, forming high-density dislocation cells and subgrain structures; the low-temperature rolling stage deforms at -196℃ to -50℃, effectively suppressing dynamic recovery, allowing a large number of dislocations introduced in the cold rolling stage to be retained and further multiplied. The sequential combination of the two deformation modes generates a dislocation density accumulation effect from cold rolling to low-temperature retention and multiplication. Compared with single cold rolling or single low-temperature rolling, it can more effectively control the size, distribution, and number density of the aging precipitate phase (β″ phase). Dislocations and subgrain boundaries provide a large number of non-uniform nucleation sites for the β″ phase, promoting the uniform and dispersed distribution of the precipitate phase and avoiding the formation of coarse equilibrium phases caused by preferential precipitation at grain boundaries. Simultaneously, dislocations accumulated during low-temperature deformation under suppressed recovery conditions form finer subgrains through dynamic recovery, which, combined with the initial fine-grained structure formed by cold rolling, further refine the grain / subgrain structure. This multiple superposition of precipitation strengthening, dislocation strengthening, and fine-grain / subgrain strengthening enables the product of this invention to achieve high strength while maintaining good plasticity, breaking through the long-standing strength-plasticity contradiction in powder metallurgy 6061 aluminum alloys. Comparative results show that omitting the low-temperature rolling step significantly reduces tensile strength and elongation, fully demonstrating the irreplaceable role of low-temperature rolling.

[0031] (3) Short process advantage of avoiding intermediate annealing / pre-aging. The present invention does not perform intermediate annealing or pre-aging treatment between cold rolling and low temperature rolling, which has the following advantages: First, it simplifies the process flow, shortens the preparation cycle, and reduces energy consumption and production costs; Second, it avoids the elimination of cold rolling deformation energy by intermediate heat treatment. If intermediate annealing is performed, dislocations will recover and annihilate, and the deformation energy introduced by cold rolling will be released in large quantities, and the dislocation density will be greatly reduced, which directly weakens the dislocation accumulation effect and the promoting effect of aging precipitation in subsequent low temperature rolling; Third, it avoids the preferential precipitation of coarse Mg2Si phase formed by intermediate pre-aging at the grain boundary, preventing it from reducing the effective solute concentration in the matrix. At the same time, it avoids the coarse precipitated phase from re-dissolving and re-precipitating under the action of large deformation and frictional heat, ensuring the uniform and dispersed precipitation of β″ phase in subsequent aging treatment.

[0032] (4) It overcomes the technical prejudice of poor compatibility between powder metallurgy materials and deformation heat treatment. Existing deformation heat treatment research mainly targets cast aluminum alloy materials, whose initial microstructure is a coarse as-cast microstructure with uneven distribution of precipitates; while the initial microstructure of powder metallurgy materials consists of powder particle boundaries and residual pores, and is conventionally considered difficult to undergo effective plastic deformation due to insufficient density. This invention obtains a high-density sintered billet (relative density ≥98%) through rapid hot pressing sintering, which provides the microstructure basis for subsequent plastic deformation, and avoids the cracking risk caused by large deformation through a mild deformation combination of "cold rolling + low temperature rolling" (total deformation 55%~60%). It successfully extends the deformation heat treatment process to the field of powder metallurgy materials and provides a new technical path for deformation strengthening of powder metallurgy aluminum alloys.

[0033] (5) This invention solves the prominent problem of strength-plasticity imbalance in powder metallurgy 6061 aluminum alloy after conventional T6 heat treatment. After conventional T6 heat treatment (Comparative Example 4), the tensile strength of rapidly hot-pressed sintered 6061 aluminum alloy can be increased from 154 MPa to 362 MPa, but the elongation drops sharply from 15.1% to 5.4%, resulting in a severe strength-plasticity imbalance. This invention, through integrated process design, enables the alloy to maintain an elongation of ≥14.2% while achieving a tensile strength of 385 MPa (Example 1), with a strength-plasticity product reaching 5.47 GPa%, far superior to the 1.95 GPa% achieved by conventional T6 treatment. Compared with extruded 6061 aluminum alloy, this invention achieves a higher strength level while maintaining good plasticity matching.

[0034] (6) Fully leverage the dual advantages of near-net-shape forming and deformation strengthening synergistically in powder metallurgy. This invention organically integrates the near-net-shape forming advantages of powder metallurgy with the strengthening effect of deformation heat treatment. It avoids the shortcomings of long processes and low material utilization in the traditional casting-hot working route, and overcomes the limitation that conventional powder metallurgy products cannot be effectively deformed due to insufficient density. It realizes the integration of forming and strengthening of powder metallurgy 6061 aluminum alloy. This method is applicable to 6061 aluminum alloy products with different specifications and performance requirements. It has a wide process window (sintering temperature 500-550℃, cold rolling deformation 35%-50%, low-temperature rolling deformation 20%-30%, aging temperature 160-180℃), and the process parameters can be flexibly adjusted according to the target performance requirements. It has good prospects for industrial promotion. Attached Figure Description

[0035] Figure 1 Optical metallographic image (OM) of the sintered unrolled 6061 aluminum alloy sample from Example 1, wherein: Figure 1 (a) is a grayscale metallographic image; Figure 1 (b) is a polarized metallographic image; Figure 1 (c) is a diagram showing the distribution of false-color contrast;

[0036] Figure 2 Optical metallographic image (OM) of the 6061 aluminum alloy sample after rolling and aging treatment in Example 1, wherein: Figure 2 (a) is a grayscale metallographic image; Figure 2 (b) is a polarized metallographic image; Figure 2 (c) is a diagram showing the distribution of false-color contrast;

[0037] Figure 3 The image shows a transmission electron microscope (TEM) image of the precipitated phases in the 6061 aluminum alloy prepared in Example 1 after aging treatment.

[0038] Figure 4 The image shows the electron backscatter diffraction (EBSD) microstructure of the sintered 6061 aluminum alloy prepared in Example 2, wherein: Figure 4 (a) is a contrast (BC) diagram. Figure 4 (b) is a grain orientation distribution diagram of IPF. Figure 4 (c) is a grain boundary distribution diagram. Figure 4 (d) is the grain size distribution histogram;

[0039] Figure 5 The image shows the electron backscatter diffraction (EBSD) microstructure of the final state sample 6061 aluminum alloy from Example 2, where: Figure 5 (a) is a contrast (BC) diagram. Figure 5 (b) is a grain orientation distribution diagram of IPF. Figure 5 (c) is a grain boundary distribution diagram. Figure 5 (d) is the grain size distribution histogram;

[0040] Figure 6 The image shows the transmission electron microscope (TEM) morphology of the final state 6061 aluminum alloy sample prepared in Example 2, wherein: Figure 6 (a) The scale bar is 500 nm. Figure 6 (b) The scale bar is 200 nm;

[0041] Figure 7 The optical microstructure (OM) of the final state sample of 6061 aluminum alloy prepared in Example 3 is shown below: Figure 7 (a) is a grayscale metallographic image; Figure 7 (b) is a polarized metallographic image; Figure 7 (c) is a diagram showing the distribution of false-color contrast;

[0042] Figure 8 The image shows the precipitated phases of the 6061 aluminum alloy prepared in Example 3 after aging treatment, as captured by a transmission electron microscope (TEM). Detailed Implementation

[0043] To further illustrate the technical means and effects of this invention, the invention will be described in detail below with reference to the accompanying drawings and embodiments. However, the scope of protection of this invention is not limited to the following embodiments. Those skilled in the art can adjust the specific parameters of each step according to actual needs without departing from the principles and scope of this invention.

[0044] In this embodiment of the invention, the integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy includes the following steps:

[0045] (1) Rapid hot pressing sintering: 6061 aluminum alloy powder prepared by gas atomization was used as raw material, with a powder particle size of 4-6 μm. The aluminum alloy powder was loaded into a graphite mold and placed in a vacuum hot pressing sintering furnace, and the furnace vacuum degree was ≤1 Pa. The temperature was increased to 500-550℃ at a heating rate of 100-150℃ / min, while an axial pressure of 30-50 MPa was applied. The temperature and pressure were maintained at the target temperature for 10-20 min. After sintering, the furnace was cooled to room temperature to obtain the sintered billet.

[0046] (2) Solution treatment: The sintered billet obtained in step (1) is placed in a box-type resistance furnace and heated to 520-560°C. It is held for 1-3 hours and then quickly removed and quenched in room temperature water. The transfer time does not exceed 10 seconds to obtain a supersaturated solid solution structure.

[0047] (3) Cold rolling deformation: The alloy after solution treatment in step (2) is subjected to room temperature cold rolling. The sample surface is cleaned before rolling to remove oxide scale and oil. Multi-pass rolling is adopted, with the reduction in each pass controlled at 5% to 10%, and the total deformation at 35% to 50%. The sample thickness is measured after each pass to ensure the accuracy of the total deformation. No intermediate annealing is required between adjacent passes;

[0048] (4) Low-temperature rolling deformation: The alloy after cold rolling in step (3) is placed in a low-temperature environment of -196℃ to -50℃ for the first immersion time of 1 to 3 hours to allow the overall temperature of the alloy to drop uniformly to the target temperature. The low-temperature environment (-196℃ to -50℃) is provided by liquid nitrogen immersion. Rolling is carried out at the same temperature, with a reduction of 8% to 12% per pass and a total deformation of 20% to 30%. When liquid nitrogen immersion is used, the alloy is re-immersed in liquid nitrogen for 5 to 10 minutes before each rolling to ensure that the alloy temperature is restored to the liquid nitrogen temperature before rolling. During the entire low-temperature rolling process, it is necessary to ensure that the temperature of the rolls and the sample are maintained within the target low-temperature range. In particular, no intermediate annealing or pre-aging treatment is performed between steps (3) and (4) to retain the dislocations and deformation structures introduced by cold rolling;

[0049] (5) Aging treatment: The alloy after low temperature rolling in step (4) is kept at 160-180℃ for 10-14h, and then water quenched to room temperature to obtain 6061 aluminum alloy with synergistic improvement in strength and plasticity.

[0050] Technical principle of the invention:

[0051] 1. Rapid hot pressing sintering

[0052] The core advantage of rapid hot pressing sintering lies in the synergistic effect of hot pressing and speed. Hot pressing sintering is characterized by low sintering temperature, fast sintering speed, and high density. The applied pressure plays a crucial role: on the one hand, pressure promotes the plastic deformation and rearrangement of powder particles, eliminating voids between particles; on the other hand, under vacuum conditions, pressure can effectively break the thermodynamically stable Al2O3 oxide film on the surface of aluminum powder, forming a narrow metal / metal contact zone at the particle boundaries. Therefore, pressure is one of the keys to achieving metallurgical bonding in this step.

[0053] The selection of a heating rate of 100–150 °C / min is based on the concept of rapid sintering: a high heating rate can shorten the high-temperature dwell time, inhibit excessive grain growth, and at the same time preserve the fine substructure inside the powder particles, providing a fine-grained microstructure basis for subsequent deformation heat treatment. The selection of a sintering temperature of 500–550 °C needs to consider two aspects: if the temperature is too low, the diffusion coefficient will be insufficient, and the sintering neck will not grow sufficiently; if the temperature is too high, local liquid phases may appear (eutectic temperature is approximately 577 °C), causing microstructure loss of control. The selection of a pressure of 30–50 MPa needs to strike a balance between densification efficiency and mold life. The short holding time of 10–20 min is designed to minimize grain coarsening while achieving high density. Studies have confirmed that rapid hot pressing sintering can achieve densification with a relative density ≥98% in a short time.

[0054] 2. Solution treatment

[0055] The purpose of solution treatment is to obtain a supersaturated solid solution, which is a prerequisite for subsequent aging precipitation strengthening. The solution temperature of 520–560℃ is higher than the complete dissolution temperature of the Mg2Si phase (approximately 520℃) but lower than the eutectic temperature (approximately 577℃), ensuring that the strengthening phase is fully dissolved without causing local overheating. The holding time of 1–3 hours is necessary to ensure sufficient and uniform diffusion of solute atoms, but excessive time will lead to grain growth, weakening the fine-grain strengthening potential. Room temperature water is used as the quenching medium: water cooling (cooling rate approximately 7℃ / s) can achieve higher supersaturation and mechanical properties, while being both economical and convenient to operate.

[0056] 3. Cold rolling deformation

[0057] The physical essence of cold rolling is to introduce a large number of dislocations and deformation energy storage into the matrix through plastic deformation, forming dislocation cells and subgrain structures. These microscopic defects have a dual role: first, the high dislocation density directly generates dislocation strengthening; second, dislocations and subgrain boundaries, as non-uniform nucleation sites, can significantly promote the uniform and dispersed precipitation of the β″ phase during subsequent aging.

[0058] The selection of a total deformation amount of 35%–50% requires consideration of multiple factors: if the deformation amount is too small, the dislocation density will be insufficient, limiting its promoting effect on aging precipitation; if the deformation amount is too large (e.g., >50%), it may cause severe work hardening or even edge cracking, which is not conducive to subsequent low-temperature rolling. The control of the reduction per pass of 5%–10% is to avoid the risk of local temperature rise and cracking caused by excessive deformation in a single pass.

[0059] 4. Low-temperature rolling deformation

[0060] Low-temperature rolling is one of the core innovative aspects of this invention, and its core mechanism lies in the inhibitory effect of low temperature on dynamic recovery. During deformation at room temperature or high temperature, the aluminum matrix exhibits an extremely high dynamic recovery rate, with a large number of dislocations annihilating and rearranging during deformation, weakening the dislocation strengthening effect. However, in the cryogenic liquid nitrogen environment of -196℃ to -50℃, the atomic diffusion rate decreases sharply, effectively suppressing dislocation climb and cross-slip, significantly blocking the dynamic recovery process. This allows a large number of dislocations introduced during the cold rolling stage to be retained and multiply during continued deformation.

[0061] More importantly, the sequential combination of cold rolling and low-temperature rolling produces a dislocation density accumulation effect: dislocations introduced by cold rolling are retained during low-temperature rolling due to suppressed recovery, and superimposed with dislocations newly introduced by low-temperature deformation, forming a dislocation density much higher than that of a single deformation method. This high dislocation density state continues into the subsequent aging stage, providing a nucleation site density for the precipitation of the β″ phase that far exceeds that of conventional processes, thereby making the precipitated phase more uniformly dispersed, smaller in size, and significantly improving the aging strengthening effect.

[0062] Furthermore, low-temperature deformation itself can further refine the grain / subgrain structure: under the condition of suppressing dynamic recovery, the dislocations accumulated by deformation form finer subgrains through dynamic recovery, which superimpose with the initial fine-grained structure formed by cold rolling to produce a fine-grain strengthening effect. Among the selection of low-temperature rolling temperatures of -196℃ to -50℃, liquid nitrogen temperature (-196℃) is an ideal choice, which can suppress recovery to the greatest extent; the initial holding time of 1 to 3 hours ensures that the overall temperature of the sample is uniform and avoids uneven deformation caused by temperature difference.

[0063] Specifically, no intermediate annealing or pre-aging treatment is performed between steps (3) and (4). This design is the key guarantee for achieving the dislocation density accumulation effect in this invention. If intermediate annealing is performed after cold rolling, the high temperature will cause dislocations to recover and annihilate, and a large amount of the deformation energy introduced by cold rolling will be released, resulting in a significant reduction in dislocation density. This directly weakens the dislocation accumulation effect of subsequent low-temperature rolling and the promoting effect of aging precipitation. If pre-aging is performed, coarse Mg2Si phase may preferentially precipitate at grain boundaries, reducing the effective solute concentration in the matrix. Furthermore, under the action of large deformation and frictional heat, the coarse Mg2Si phase will undergo re-dissolution and re-precipitate, failing to generate particle-induced nucleation effect to further refine the grains. Therefore, not performing intermediate heat treatment is a necessary process condition for retaining deformation energy and maximizing the accumulation of dislocation density.

[0064] 5. Timeliness processing

[0065] The essence of aging treatment is to promote the precipitation of solute atoms in supersaturated solid solutions as strengthening phases. Within the temperature range of 160–180 °C, the precipitation kinetics of the GP zone and β″ phase are most suitable, forming uniformly dispersed nanoscale precipitates. The high dislocation density state after low-temperature rolling accelerates aging precipitation: dislocations act as short-circuit diffusion channels, significantly shortening the diffusion time of solute atoms and greatly accelerating the aging response. Simultaneously, the non-uniform nucleation sites provided by dislocations and subgrain boundaries result in a more uniform distribution of precipitates, avoiding localized coarsening caused by preferential grain boundary precipitation.

[0066] The selection of an aging temperature of 160–180℃ is based on the precipitation sequence characteristics of 6061 aluminum alloy: below 160℃, the GP region mainly precipitates, resulting in limited strengthening effect; above 180℃, the β″ phase may transform into the β′ or β equilibrium phase, leading to a decrease in strength due to over-aging. The selection of an aging time of 10–14 h, matched with different temperatures, allows for the precipitation of peak values: at 170–180℃ and 12–14 h, the peak aging state can be obtained, where the β″ phase is uniformly distributed in a fine, dispersed morphology, resulting in the best strengthening effect.

[0067] To make the present invention more fully disclosed, more specific embodiments are described below.

[0068] Example 1

[0069] A rapid hot pressing sintering-deformation heat treatment integrated method for high-performance 6061 aluminum alloy includes the following steps:

[0070] (1) Rapid hot pressing sintering: 6061 aluminum alloy powder prepared by gas atomization was used as raw material, with a powder particle size of 4.17 μm. The aluminum alloy powder was loaded into a graphite mold and placed in a vacuum hot pressing sintering furnace, and the vacuum degree inside the furnace was evacuated to ≤1 Pa. The temperature was increased to 550℃ at a heating rate of 100℃ / min, and an axial pressure of 30 MPa was applied simultaneously. The temperature and pressure were held at 550℃ for 15 min. After sintering, the furnace was cooled to room temperature to obtain the sintered billet;

[0071] (2) Solution treatment: The sintered billet obtained in step (1) is placed in a box-type resistance furnace, heated to 535°C, held for 1.5h, and then quickly taken out and quenched in room temperature water. The transfer time does not exceed 10s to obtain a supersaturated solid solution structure.

[0072] (3) Cold rolling deformation: The alloy after solution treatment in step (2) is subjected to room temperature cold rolling, using multi-pass rolling, with the reduction in each pass controlled at 10%, and the total deformation amount being 50%;

[0073] (4) Low-temperature rolling deformation: The alloy after cold rolling in step (3) is immersed in liquid nitrogen (-196℃) for 1 hour to uniformly reduce the overall temperature of the alloy to the liquid nitrogen temperature. Then, rolling is carried out under liquid nitrogen immersion conditions. Before each rolling pass, the alloy is re-immersed in liquid nitrogen for 8 minutes to ensure that the temperature is restored to the liquid nitrogen temperature before rolling. The reduction per low-temperature rolling pass is 8%, and the total deformation is 20%.

[0074] (5) Aging treatment: The alloy after low temperature rolling in step (4) is kept at 170℃ for 12 hours, and then quenched in water to room temperature to obtain the final product.

[0075] The microstructure of the sintered unrolled sample and the rolled and aged sample were observed using a metallographic microscope. The observation results are as follows: Figure 1 , Figure 2 As shown. The final-state sample was characterized using transmission electron microscopy, and the results are as follows. Figure 3 As shown, after aging treatment, the 6061 aluminum alloy prepared in Example 1 exhibited β″ metastable phases of the Mg2Si series, which were uniformly dispersed in the aluminum matrix in a nanoscale spherical morphology. The precipitates were small in size and high in number density, with no coarse equilibrium phases preferentially precipitating near the grain boundaries. This microstructure is direct microscopic evidence that the precipitation strengthening effect has been optimized.

[0076] Example 2

[0077] A rapid hot pressing sintering-deformation heat treatment integrated method for high-performance 6061 aluminum alloy includes the following steps:

[0078] (1) Rapid hot pressing sintering: 6061 aluminum alloy powder prepared by gas atomization was used as raw material, with a powder particle size of 4.17 μm. The aluminum alloy powder was loaded into a graphite mold and placed in a vacuum hot pressing sintering furnace. The furnace vacuum was evacuated to ≤1 Pa. The temperature was increased to 520 °C at a heating rate of 100 °C / min, while an axial pressure of 40 MPa was applied. The temperature and pressure were maintained at 520 °C for 10 min. After sintering, the furnace was cooled to room temperature to obtain the sintered billet.

[0079] (2) Solution treatment: The sintered billet obtained in step (1) is placed in a box-type resistance furnace, heated to 540°C, held for 2 hours, and then quickly removed and quenched in room temperature water. The transfer time does not exceed 10 seconds to obtain a supersaturated solid solution structure.

[0080] (3) Cold rolling deformation: The alloy after solution treatment in step (2) is subjected to room temperature cold rolling, using multi-pass rolling, with the reduction in each pass controlled at 10%, and the total deformation amount being 35%;

[0081] (4) Low-temperature rolling deformation: The alloy after cold rolling in step (3) is immersed in liquid nitrogen (-196℃) for 1 hour to uniformly reduce the overall temperature of the alloy to the liquid nitrogen temperature. Then, rolling is carried out under liquid nitrogen immersion conditions. Before each rolling pass, the alloy is re-immersed in liquid nitrogen for 8 minutes to ensure that the temperature is restored to the liquid nitrogen temperature before rolling. The reduction per low-temperature rolling pass is 10%, and the total deformation is 30%.

[0082] (5) Aging treatment: The alloy after low temperature rolling in step (4) is kept at 175°C for 10 hours, and then quenched in water to room temperature to obtain the final product.

[0083] Figure 4 The electron backscatter diffraction microstructure of the sintered sample in Example 2 shows that the sintered sample has equiaxed crystals, fine grains, few sintering voids, and high density. Figure 5 The electron backscatter diffraction (ESD) image of the final sample from Example 2 shows that the sample microstructure has clear grain / subgrain boundaries, finer grains, and a large number of dislocations. The 6061 aluminum alloy prepared in Example 2 has fine and uniformly distributed grain / subgrain sizes, clearly visible grain boundaries, and no obvious coarse grains or abnormal grain growth. No obvious residual porosity was observed in the microstructure, which is uniform and dense, indicating that the high density of rapid hot pressing sintering was maintained during subsequent deformation heat treatment. Figure 6 The image shown is a transmission electron microscope (TEM) image of the final state sample from Example 2. The sample structure contains a large number of dislocations, and the precipitated phase Mg2Si is uniformly dispersed in the aluminum matrix.

[0084] Example 3

[0085] A rapid hot pressing sintering-deformation heat treatment integrated method for high-performance 6061 aluminum alloy includes the following steps:

[0086] (1) Rapid hot pressing sintering: 6061 aluminum alloy powder prepared by gas atomization was used as raw material, with a powder particle size of 5.2 μm. The aluminum alloy powder was loaded into a graphite mold and placed in a vacuum hot pressing sintering furnace. The furnace pressure was evacuated to ≤1 Pa. The temperature was increased to 510 °C at a heating rate of 150 °C / min, while an axial pressure of 45 MPa was applied. The temperature and pressure were maintained at 510 °C for 20 min. After sintering, the furnace was cooled to room temperature to obtain the sintered billet.

[0087] (2) Solution treatment: The sintered blank obtained in step (1) is placed in a box-type resistance furnace, heated to 530°C, held for 2 hours, and then quickly removed and quenched in water at room temperature to cool to room temperature. The transfer time does not exceed 10 seconds to obtain a supersaturated solid solution structure.

[0088] (3) Cold rolling deformation: The alloy after solution treatment in step (2) is subjected to room temperature cold rolling, using multi-pass rolling, with the reduction in each pass controlled at 10%, and the total deformation amount being 40%;

[0089] (4) Low-temperature rolling deformation: The alloy after cold rolling in step (3) is immersed in liquid nitrogen (-196℃) for 1 hour to uniformly reduce the overall temperature of the alloy to the liquid nitrogen temperature. Then, rolling is carried out under liquid nitrogen immersion conditions. Before each rolling pass, the alloy is re-immersed in liquid nitrogen for 5 minutes to ensure that the temperature is restored to the liquid nitrogen temperature before rolling. The reduction per low-temperature rolling pass is 10%, and the total deformation is 25%.

[0090] (5) Aging treatment: The alloy after low temperature rolling in step (4) is kept at 165℃ for 14h, and then water quenched to room temperature to obtain the final product.

[0091] The 6061 aluminum alloy matrix prepared in Example 3 has a dense and uniform microstructure with clear grain / subgrain boundaries. The precipitates are dispersed granules and uniformly distributed in the matrix. No obvious casting microstructure residues (such as dendritic segregation, coarse eutectic phases) or particle boundary residual pores common in powder metallurgy processes were observed. Under high magnification, the uniform distribution of nanoscale precipitates within the grains can be further observed. Figure 7 These are metallographic micrographs of the final-state sample. The micrographs show that the alloy grains and subgrains are fine, with a relatively uniform overall grain distribution; no large coarse grains were observed. No obvious residual porosity was observed inside the sample, and the alloy structure is dense. Figure 8 The image shown is a transmission electron microscope (TEM) image of the final state sample of Example 3, which shows a large number of nanoprecipitates and a high dislocation density.

[0092] Comparative Example 1

[0093] To verify the synergistic effect of the combined deformation of "cold rolling + low-temperature rolling" in this invention, this comparative example was set up. The difference between this comparative example and Example 1 is that after the cold rolling deformation in step (3), the low-temperature rolling deformation in step (4) is not performed, but the aging treatment (170℃×12h) in step (5) is performed directly. The remaining process parameters are exactly the same as those in Example 1. Comparative example 1 is used to compare the difference in the effects of single cold rolling deformation and the combined deformation of "cold rolling + low-temperature rolling" on the final properties of 6061 aluminum alloy.

[0094] Comparative Example 2

[0095] To verify the effectiveness of the process route sequence of the present invention, this comparative example was set up. The difference between this comparative example and Example 2 is that step (3) cold rolling deformation and step (4) low-temperature rolling are advanced, followed by solution treatment and aging. The remaining process parameters are exactly the same as those in Example 2. Comparative example 2 is used to illustrate the negative impact of cold rolling / low-temperature rolling on the subsequent solution treatment and aging effects.

[0096] Comparative Example 3

[0097] To verify the advantages of subsequent deformation heat treatment, this comparative example was set up. The difference between this comparative example and Example 1 is that only step (1) rapid hot pressing sintering was used, that is, heating to 550°C at a heating rate of 100°C / min, applying a pressure of 30MPa, and holding at that temperature and pressure for 15min to obtain a sintered blank, without subsequent processing. Comparative example 3 was used to compare the effect of subsequent deformation heat treatment.

[0098] Comparative Example 4

[0099] To verify the advantages of the "cold rolling + low-temperature rolling" deformation treatment for sintered samples, this comparative example was set up. The difference between this comparative example and Example 1 is that step (3) cold rolling deformation and step (4) low-temperature rolling are skipped, and only the sintered sample (step 1) is subjected to solution treatment (step 2) and aging treatment (step 5). The remaining process parameters are exactly the same as those in Example 1. Comparative example 4 is used to compare the beneficial effects of the "cold rolling + low-temperature rolling" deformation treatment.

[0100] The products obtained from the above embodiments and comparative examples were subjected to the following tests:

[0101] (1) Density test: The actual density of the sintered billet and the final product was measured using the Archimedes displacement method, and compared with the theoretical density of 6061 aluminum alloy (2.70 g / cm³). 3 The relative density was calculated by comparison.

[0102] (2) Hardness test: Vickers hardness tester was used, with a load of 19.6N and a holding time of 15s. At least 8 points were tested for each sample and the average value was taken.

[0103] (3) Tensile property test: standard tensile specimens were processed according to GB / T228.1-2021 Metallic materials tensile test part 1: room temperature test method. The room temperature tensile test was carried out on a universal testing machine with a tensile rate of 0.2 mm / min. The tensile strength, yield strength and elongation after fracture were recorded.

[0104] (4) Microscopic tissue observation:

[0105] Grain / subgrain structure was observed using an optical microscope (OM);

[0106] Electron backscatter diffraction (EBSD) was used to observe grain orientation, grain boundary characteristics, and grain size distribution.

[0107] The morphology, size and distribution of dislocations and age-aged precipitates (β″ phase) were observed using transmission electron microscopy (TEM).

[0108] Table 1. Summary of mechanical properties of Examples 1-3 and Comparative Examples 1-4

[0109]

[0110] Table 1 above summarizes the product performance test results obtained from each embodiment and comparative example as follows:

[0111] (1) Density

[0112] The relative density of the sintered blanks in Examples 1 to 3 is ≥98%, and the relative density of Example 1 (sintering temperature 550℃, pressure 30MPa, holding time 15min) reaches 99.0%, indicating that high density of sintered blocks can be obtained by rapid hot pressing sintering through high heating rate and short holding time.

[0113] (2) Mechanical properties

[0114] The results showed that Example 1 exhibited the best overall mechanical properties, with a tensile strength of 385 MPa, a yield strength of 366 MPa, and an elongation of 14.2%, achieving a good balance between strength and plasticity. These values ​​were significantly higher than those of the four comparative examples, and the example also showed a longer, uniform elongation stage after reaching the tensile strength, indicating good plasticity at the same time.

[0115] (3) Comparative analysis of proportions

[0116] Comparative analysis based on Table 1 shows that, compared to Example 1, Comparative Example 1 (cold rolling only, without low-temperature rolling) exhibits a decrease in tensile strength, while its elongation decreases significantly from 14.2% to 7.6%, indicating that the additional dislocation accumulation and grain refinement introduced by low-temperature rolling significantly contribute to the strength improvement. Comparative Example 2 (cold rolling deformation followed by low-temperature rolling and then solution aging treatment) achieves a high elongation of 23.3%, but its tensile strength is only 268 MPa, indicating that the subsequent solution aging treatment weakens the strengthening and toughening effect of cold rolling / low-temperature rolling.

[0117] (4) Comprehensive analysis of micro-organisms

[0118] Combination Figures 1 to 8 Comprehensive comparison: Embodiment 1 of the present invention ( Figures 1-3 The precipitated phase is uniformly dispersed and small in size; Example 2 ( Figures 4-6 The grains are significantly refined, with a narrow grain size distribution range, resulting in a fine-grained structure; Example 3 ( Figures 7-8 The matrix structure remains uniform and dense; three sets of microstructure characterizations from different scales (nanometer to micrometer) and different dimensions (morphology, composition) jointly confirm the comprehensive advantages of the integrated process of the present invention in optimizing microstructure, providing a complete microscopic evidence chain for the improvement of macroscopic mechanical properties.

[0119] The applicant declares that this invention illustrates an integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy through the above embodiments. However, this invention is not limited to the above process steps, meaning that this invention does not necessarily rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials used in this invention, additions of auxiliary components, and selection of specific methods all fall within the protection and disclosure scope of this invention.

Claims

1. A rapid hot pressing sintering-deformation heat treatment integrated method for high-performance 6061 aluminum alloy, characterized in that, Includes the following steps: (1) Rapid hot pressing sintering: 6061 aluminum alloy powder is placed in a vacuum-protected hot pressing sintering furnace, heated to 500-550°C at a heating rate of 100-150°C / min, and pressure of 30-50MPa is applied. The temperature and pressure are held for 10-20 minutes to obtain a sintered blank with a relative density ≥98%. (2) Solution treatment: The sintered billet obtained in step (1) is heated to 500-580℃ and held for 0.5-4h, and then quenched to room temperature to obtain a supersaturated solid solution structure; (3) Cold rolling deformation: The alloy after solution treatment in step (2) is subjected to room temperature cold rolling, with a reduction of 5% to 10% per pass and a total deformation of 30% to 60%; (4) Low temperature rolling deformation: The alloy after cold rolling in step (3) is initially immersed in a low temperature environment of -196℃ to -50℃ for 1 to 3 hours. After the overall temperature of the alloy drops to the target temperature uniformly, it is rolled at the same temperature. The reduction per pass is 8% to 12%, and the interval between rolling passes is immersing in liquid nitrogen for 5 to 10 minutes. The total deformation is 10% to 40%. No intermediate annealing or pre-aging treatment is performed between step (3) and step (4). (5) Aging treatment: The alloy after low temperature rolling in step (4) is kept at 160-180℃ for 10-14h, and then water quenched to room temperature to obtain 6061 aluminum alloy with enhanced strength and plasticity.

2. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The aluminum alloy powder in step (1) has a particle size of 4 to 6 μm.

3. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The solution treatment heating temperature in step (2) is 520-560℃.

4. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The heat preservation time mentioned in step (2) is 1 to 3 hours.

5. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The medium used for quenching in step (2) is water at room temperature.

6. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The total deformation in step (3) is 35% to 50%.

7. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The low-temperature environment described in step (4) is achieved by immersion in liquid nitrogen.

8. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The total deformation in step (4) is 20% to 30%.

9. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The alloy aging treatment temperature in step (5) is 170-180℃.

10. The integrated method for rapid hot pressing sintering and deformation heat treatment of high-performance 6061 aluminum alloy according to claim 1, characterized in that: The heat preservation time mentioned in step (5) is 12 to 14 hours.

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