Hot isostatic pressing treatment method for aluminum alloy casting

Abstract

The invention provides a hot isostatic pressing treatment method for an aluminum alloy casting. The hot isostatic pressing treatment method has the characteristics of universality, small deformation and high comprehensive mechanical property. According to the method, an aluminum alloy casting is subjected to subzero treatment and heating treatment before hot isostatic pressing treatment, so that residual stress formed during casting of the aluminum alloy casting can be effectively eliminated, and meanwhile, the comprehensive mechanical property of the aluminum alloy casting can be improved; the method further comprises the steps that the aluminum alloy casting is loaded into a tool, gaps of the whole tool are filled with metal particles, the structure of the aluminum alloy casting can be effectively supported through filling of the metal particles, deformation of the aluminum alloy casting caused by high temperature during hot isostatic pressing treatment is reduced, and the size precision of the aluminum alloy casting is guaranteed. And after hot isostatic pressing, the mechanical property and the fatigue property are obviously improved.

Description

Technical Field

[0001] The invention belongs to the technical field of metal materials, and in particular relates to a hot isostatic pressing treatment method for an aluminum alloy casting. Background Art

[0002] Aluminum alloy castings have been widely used in various fields of people's livelihood and military industry in my country due to their light weight, high specific strength, good durability and good filling performance. In particular, some equipment industries generally use aluminum alloy castings to produce large and complex special-shaped components in order to achieve near-net-shape and rapid prototyping. With the further development of high-end equipment industry, some key parts, such as high-speed train parts, aircraft brackets, special vehicle load-bearing parts, etc., have put forward higher fatigue performance requirements for aluminum alloy castings, so that aluminum alloy castings can adapt to the design ideas and service requirements of long life and high reliability.

[0003] As an effective densification treatment method for metal materials, hot isostatic pressing has been widely used in the manufacture of titanium alloys and high-temperature alloys. In recent years, due to the improvement of equipment performance requirements, aluminum alloy castings have also begun to gradually introduce hot isostatic pressing technology to meet the requirements of high fatigue life and high comprehensive performance.

[0004] The hot isostatic pressing process usually places the aluminum alloy casting in a closed container, then applies equal pressure in all directions to the aluminum alloy casting, and applies high temperature at the same time. Under the action of high temperature and high pressure, the internal defects of the aluminum alloy casting can be effectively reduced, and the casting can be densified, thereby achieving the effect of effectively improving fatigue performance, which can generally achieve an improvement of 10 to 100 times. Summary of the invention

[0005] Research has found that during the casting process of aluminum alloy castings, due to the uneven cooling of the casting body, large internal stresses will be generated. These internal stresses will be gradually released during the subsequent heating of the aluminum alloy castings (such as hot isostatic pressing), and combined with the comprehensive effects of phase change volume fraction changes, the aluminum alloy castings will be deformed. Especially for large thin-walled aluminum alloy castings, after hot isostatic pressing, the weak rigidity parts are more obviously affected by heat, which can easily cause more serious deformation. In addition, in the subsequent solid solution quenching process of aluminum alloy castings, due to the large degree of correction required, this will further aggravate the occurrence of cracking problems in aluminum alloy castings. In severe cases, the aluminum alloy castings will be directly scrapped, which greatly affects the production and delivery of aluminum alloy castings.

[0006] In order to solve the problems of obvious deformation and cracking of aluminum alloy castings during hot isostatic pressing, the present invention provides a hot isostatic pressing method for aluminum alloy castings, which can effectively solve the problems of obvious deformation of aluminum alloy castings during hot isostatic pressing, and at the same time can significantly improve the comprehensive mechanical properties of aluminum alloy castings (mechanical properties and fatigue properties are significantly improved), better meet the use requirements of high-performance parts in certain equipment fields. The method can also avoid the problems of aluminum alloy castings cracking after solution quenching, greatly improving the production efficiency of aluminum alloy castings.

[0007] A hot isostatic pressing method for an aluminum alloy casting, the method comprising the following steps: 1) Place the aluminum alloy casting in a cryogenic treatment furnace for cryogenic treatment; 2) Heat the aluminum alloy casting after cryogenic treatment to 100~130℃, keep it warm for a period of time, and then cool it to room temperature with the furnace; 3) Repeat steps 1) and 2) 0 or more times; 4) placing the aluminum alloy casting cooled to room temperature in a hot isostatic pressing furnace for hot isostatic pressing treatment; Wherein, in step 1), the temperature of the cryogenic treatment is -150~-90°C; in step 4), the temperature of the hot isostatic pressing treatment is 490~530°C; and the pressure of the hot isostatic pressing treatment is 90~130MPa.

[0008] According to the embodiment of the present invention, the hot isostatic pressing method of the aluminum alloy casting of the present invention is to first perform deep cryogenic treatment on the aluminum alloy casting (the temperature of deep cryogenic treatment is -150~-90℃), then heat it to a certain temperature (100~130℃), keep it warm for a period of time, and then cool it to room temperature with the furnace, and finally place the aluminum alloy casting in a hot isostatic pressing furnace for hot isostatic pressing (the temperature of hot isostatic pressing treatment is 490~530℃; the pressure of hot isostatic pressing treatment is 90~130MPa). The method can realize hot isostatic pressing treatment of aluminum alloy castings with a small deformation amount, solve the problem of obvious deformation of aluminum alloy castings during hot isostatic pressing treatment, effectively improve the comprehensive mechanical properties of aluminum alloy castings, and better meet the use requirements of high-performance parts in certain equipment fields. The method can also avoid the problems of aluminum alloy castings cracking after solution quenching after hot isostatic pressing treatment, greatly improving the production efficiency of aluminum alloy castings.

[0009] According to an embodiment of the present invention, the aluminum alloy casting is made of Al-Si series, Al-Cu series or Al-Mg series aluminum alloy, such as aluminum alloy with grades ZL101A, ZL114A, ZL205A or ZL305A.

[0010] According to an embodiment of the present invention, the aluminum alloy casting is prepared by a method known in the art, for example, by gravity casting, low pressure casting or differential pressure casting.

[0011] According to an embodiment of the present invention, the size (length×width×height) of the aluminum alloy casting is (1000~2000) mm×(400~800) mm×(30~150) mm, for example, 1000 mm×600 mm×35 mm, 1200 mm×800 mm×100 mm or 1800 mm×500 mm×120 mm.

[0012] According to an embodiment of the present invention, the average thickness of the aluminum alloy casting is ≥1.5 mm, for example, 1.5 mm-20 mm, such as 1.5 mm, 3 mm, 5 mm, 8 mm or 20 mm.

[0013] According to an embodiment of the present invention, in step 1), the cryogenic treatment furnace is a device that is conventionally used in the art and can achieve cryogenic treatment. The cryogenic treatment temperature and time are controlled by introducing liquid nitrogen into the cryogenic treatment furnace (directly contacting the liquid nitrogen with the aluminum alloy casting).

[0014] According to an embodiment of the present invention, in step 1), the temperature of the deep freezing treatment is -150~-90°C, for example, -150°C, -145°C, -140°C, -135°C, -130°C, -125°C, -120°C, -115°C, -110°C, -105°C, -100°C, -95°C or -90°C.

[0015] According to an embodiment of the present invention, in step 1), the cryogenic treatment time is 1 to 2 hours, for example, 1 hour, 1.5 hours or 2 hours. The cryogenic treatment time refers to the insulation time after reaching the cryogenic treatment temperature.

[0016] According to an embodiment of the present invention, in step 1), the cooling process of the cryogenic treatment refers to the temperature from room temperature to the cryogenic treatment temperature (i.e., -150~-90°C). The cooling rate of the cryogenic treatment is 0.5~2°C / min, for example, 0.5°C / min, 1°C / min, 1.5°C / min or 2°C / min; research has found that by controlling the cooling rate of the cryogenic treatment, the rate of increase of the internal stress of the aluminum alloy casting can be effectively adjusted and controlled, and the internal stress of the aluminum alloy casting can be prevented from increasing sharply due to the rapid change of the external ambient temperature.

[0017] According to an embodiment of the present invention, step 1) specifically includes the following steps: placing the aluminum alloy casting in a cryogenic treatment furnace, controlling the furnace temperature to -150~-90°C, and keeping the temperature for 1~2 hours after reaching the temperature.

[0018] According to an embodiment of the present invention, in step 2), the heating process is carried out in a cryogenic treatment furnace.

[0019] According to an embodiment of the present invention, in step 2), the aluminum alloy casting after deep cryogenic treatment in step 1) is heated to 100-130°C (such as 100°C, 105°C, 110°C, 115°C, 120°C, 125°C or 130°C), kept at temperature for 1-2 hours (such as 1 hour, 1.5 hours or 2 hours) and then cooled to room temperature with the furnace.

[0020] According to an embodiment of the present invention, in step 2), the heating process refers to heating from the temperature of cryogenic treatment (i.e., -150 to -90°C) to 100 to 130°C. The heating rate is 0.5 to 2°C / min, for example, 0.5°C / min, 1°C / min, 1.5°C / min or 2°C / min. Studies have shown that by controlling the heating rate, the rate of increase of the internal stress of the aluminum alloy casting can be effectively adjusted and controlled, thereby avoiding a sharp increase in the internal stress of the aluminum alloy casting caused by a rapid change in the external ambient temperature.

[0021] According to the embodiment of the present invention, it is found that by subjecting the aluminum alloy casting to deep cryogenic treatment (temperature of -150~-90℃) and heating treatment (temperature of 100~130℃) before hot isostatic pressing, the residual stress formed during casting of the aluminum alloy casting can be effectively eliminated, and the comprehensive mechanical properties of the aluminum alloy casting can be improved. Specifically, the inventor of the present application found through research that when the aluminum liquid is poured into the mold cavity, due to the uneven cooling rate inside and outside the aluminum alloy casting and solidification shrinkage, a large stress is generated inside the aluminum alloy casting. However, the present application subjects the aluminum alloy casting to deep cryogenic treatment and heating treatment more than once before hot isostatic pressing. When the aluminum alloy casting is subjected to this cold and hot treatment (cold treatment refers to deep cryogenic treatment, and heat treatment refers to heating treatment at 100~130℃), due to the different stress states inside and outside the aluminum alloy casting, the internal and external stresses of the aluminum alloy casting will be partially offset, thereby effectively eliminating the residual stress inside the aluminum alloy casting. Furthermore, aluminum alloy castings will also shrink and expand during cold and hot treatments. When the cooling rate of cryogenic treatment and the heating rate of heating treatment are reasonably controlled, the tensile and compressive stresses generated by aluminum alloy castings can be effectively controlled, and the residual stress inside the aluminum alloy castings can be better eliminated. Furthermore, due to the subgraining and recovery recrystallization inside the aluminum alloy castings, controlling the cooling rate of cryogenic treatment and the heating rate of heating treatment can also adjust the grain refinement and grain preferential rotation effects, which has a positive effect on eliminating the internal stress of the aluminum alloy castings, and further reduces the influence of high temperature on the deformation of the aluminum alloy castings during the subsequent hot isostatic pressing process. In addition, when the aluminum alloy castings are subjected to cold and hot treatments, the aluminum alloy castings undergo repeated tensile and compressive deformations, and the internal defects existing in the aluminum alloy castings will be alleviated to varying degrees. A large number of vacancies and dislocations are prefabricated in the aluminum alloy casting matrix, which is conducive to the improvement of the mechanical properties of the aluminum alloy castings during the subsequent heat treatment process.

[0022] According to an embodiment of the present invention, in step 3), step 1) and step 2) are repeated 0-10 times; illustratively, step 1) and step 2) are repeated 0 times, 1 time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or 10 times. Studies have found that repeated cryogenic treatment and heating treatment are more conducive to reducing the internal residual stress of aluminum alloy castings after casting and pouring; especially for large-sized or thin-walled aluminum alloy castings with complex structures, repeated cryogenic treatment and heating treatment can significantly reduce the internal residual stress of aluminum alloy castings after casting and pouring, and improve the mechanical properties of aluminum alloy castings during subsequent heat treatment.

[0023] According to an embodiment of the present invention, in step 3), repeating step 1) and step 2) 0 times means that step 4) is directly performed after step 1) and step 2), that is, the aluminum alloy casting is treated in the manner of deep cryogenic treatment → heating treatment → hot isostatic pressing treatment. Repeating step 1) and step 2) once means that step 1) and step 2) are performed twice, and then step 4) is performed, that is, the aluminum alloy casting is treated in the manner of deep cryogenic treatment → heating treatment → deep cryogenic treatment → heating treatment → hot isostatic pressing treatment.

[0024] According to an embodiment of the present invention, in step 4), the hot isostatic pressing furnace is a device conventionally used in the art that can perform hot isostatic pressing treatment on aluminum alloy castings.

[0025] According to an embodiment of the present invention, in step 4), the hot isostatic pressing furnace is filled with high-purity argon gas, and the purity of the high-purity argon gas is not less than 99.99%.

[0026] According to an embodiment of the present invention, in step 4), the temperature of the hot isostatic pressing treatment is 490°C, 495°C, 500°C, 505°C, 510°C, 515°C, 520°C, 525°C or 530°C; the pressure of the hot isostatic pressing treatment is 90MPa, 95MPa, 100MPa, 105MPa, 110MPa, 115MPa, 120MPa, 125MPa or 130MPa.

[0027] According to an embodiment of the present invention, in step 4), the hot isostatic pressing treatment time is 3 to 4 hours, for example, 3 hours, 3.5 hours or 4 hours.

[0028] According to an embodiment of the present invention, in step 4), when the aluminum alloy casting after cryogenic treatment and heating treatment is then subjected to hot isostatic pressing, the high temperature and high pressure conditions are more conducive to pressing together the tiny holes, looseness and other internal defects inside the aluminum alloy casting, thereby improving the density of the aluminum alloy casting.

[0029] According to an embodiment of the present invention, in step 4), the aluminum alloy casting cooled to room temperature is placed in a tooling, and the gaps in the tooling are filled with metal particles until the metal particles fill the tooling and completely cover the aluminum alloy casting; the tooling containing the aluminum alloy casting and the filled metal particles is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment.

[0030] According to an embodiment of the present invention, in step 4), the workpiece containing the aluminum alloy casting and the filler metal particles is placed in a hot isostatic pressing furnace, heated to a furnace temperature of 490-530°C, and high-purity argon is simultaneously filled into the hot isostatic pressing furnace, and the pressure in the furnace is controlled to 90-130 MPa. After maintaining the pressure at high temperature and high pressure for 3-4 hours, the furnace is cooled to a furnace temperature of less than 150°C, and the furnace door is opened for air cooling.

[0031] According to an embodiment of the present invention, in step 4), considering the service life of the tooling and the deformation of the tooling during high-temperature use, the material of the tooling is selected to be heat-resistant material; illustratively, the material of the tooling is selected from heat-resistant steel or heat-resistant cast iron.

[0032] According to an embodiment of the present invention, in step 4), taking into account the differences in contour shapes and sizes of aluminum alloy castings and the placement and space utilization of the tooling in the hot isostatic pressing furnace, the shape of the tooling can be, for example, square, round or free-form (i.e., similar to the shape of the aluminum alloy casting).

[0033] According to an embodiment of the present invention, in step 4), the particle size of the metal particles is 3-10 mm, for example, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or 10 mm.

[0034] According to an embodiment of the present invention, in step 4), the shape of the metal particles is spherical or quasi-spherical; the material of the metal particles is cast steel or cast iron, that is, the metal particles are cast steel balls or cast iron balls.

[0035] According to an embodiment of the present invention, when the aluminum alloy casting is subjected to hot isostatic pressing, the aluminum alloy casting is preferably placed in a tooling and filled with metal particles, preferably filling the gaps in the tooling with metal particles until the metal particles fill the tooling and completely cover the aluminum alloy casting. The study found that when the aluminum alloy casting is heated, the aluminum alloy casting begins to soften due to the coarsening and softening of the grain boundaries and the coarsening and dissolution of the strengthening phase particles; when the combined force of the stress generated when the aluminum alloy casting is heated and the residual internal stress of the aluminum alloy casting is greater than the yield strength of the aluminum alloy casting, the aluminum alloy casting deforms; by filling the tooling for loading the aluminum alloy casting with metal particles (cast steel balls or cast iron balls) that have better heat resistance than aluminum alloy, and utilizing the supporting effect of the metal particles and the tooling on the aluminum alloy casting, the structure of the aluminum alloy casting in the tooling can be effectively supported, so that the aluminum alloy casting still maintains a good filling shape, avoiding the occurrence of deformation problems of the aluminum alloy casting when heated due to stress release, matrix softening and the self-weight of the aluminum alloy casting during high-temperature heating, further reducing the deformation of the aluminum alloy casting when heated, and ultimately achieving the effect of maintaining the dimensional accuracy and structural state of the original aluminum alloy casting as much as possible during the hot isostatic pressing process.

[0036] According to an embodiment of the present invention, in step 4), after the hot isostatic pressing treatment is completed, the aluminum alloy casting is cooled with the furnace to a furnace temperature of less than 150°C, and then the furnace door is opened for air cooling. The aluminum alloy casting is still under high pressure during the process of cooling with the furnace to a furnace temperature of less than 150°C, and the process of opening the furnace door for air cooling is under normal pressure.

[0037] According to the embodiment of the present invention, as described above, when the aluminum alloy casting is subjected to cold and hot treatment, the aluminum alloy casting undergoes repeated tensile and compressive deformation, which will form a large number of vacancies and dislocations in the aluminum alloy casting matrix. During the hot isostatic pressing process, these vacancies and dislocation defects are more conducive to atomic diffusion, and the large-sized primary phases (such as eutectic silicon, primary silicon, Al2Cu phase, Mg2Si phase, Mg2Al3 phase, etc.) originally existing in the matrix grain boundaries or grains are fully dissolved back under high temperature and high pressure; subsequently, during the furnace cooling process, the solute atoms (such as Cu, Si or Mg and other elements) dissolved in the matrix are precipitated again under high pressure, and the strengthening phases formed thereby are finer than the strengthening phases conventionally precipitated. Some fine precipitated phases (such as Al2Cu phase and Mg2Si phase) can be more fully dissolved back into the matrix during the subsequent solution treatment, and the solute atoms are more evenly and dispersedly precipitated during the aging process; some fine precipitated phases (such as eutectic Si phase and Mg2Al3 phase) directly strengthen the matrix, which can further improve the comprehensive mechanical properties of aluminum alloy castings.

[0038] According to an embodiment of the present invention, the method further comprises the following steps: 5) Perform solution treatment and aging treatment on the aluminum alloy castings after hot isostatic pressing.

[0039] According to an embodiment of the present invention, in step 5), the solution treatment is performed by a method known in the art. The aging treatment is performed by a method known in the art.

[0040] According to an embodiment of the present invention, the method comprises the following steps: S1) Place the aluminum alloy casting in a cryogenic treatment furnace, control the furnace temperature to -150~-90℃, and keep it warm for 1~2 hours; S2) Raise the furnace temperature to 100-130°C, keep it warm for 1-2 hours, and then cool the aluminum alloy casting to room temperature along with the furnace; S3) repeating step S1) and step S2) for more than 0 times, and taking the aluminum alloy casting cooled to room temperature out of the furnace; S4) placing the aluminum alloy casting cooled to room temperature in a tooling, and filling the gaps in the tooling with metal particles until the metal particles fill the tooling and completely cover the aluminum alloy casting; S5) placing the workpiece containing the aluminum alloy casting and metal particles in a hot isostatic pressing furnace, heating the furnace to a temperature of 490-530°C, and simultaneously filling the hot isostatic pressing furnace with argon gas, controlling the pressure in the furnace to 90-130MPa, and maintaining the temperature and pressure at high temperature and high pressure for 3-4 hours, cooling the furnace to a temperature less than 150°C, and then opening the furnace door for air cooling; S6) performing a solution treatment and an aging treatment on the aluminum alloy casting cooled to room temperature after the hot isostatic pressing treatment to obtain an aluminum alloy casting with improved performance.

[0041] Beneficial effects of the present invention: The present invention provides a hot isostatic pressing method for aluminum alloy castings, which has the characteristics of universal applicability, small deformation and high comprehensive mechanical properties. The method is to perform deep cryogenic treatment and heating treatment on the aluminum alloy castings before hot isostatic pressing, so that the residual stress formed during casting of the aluminum alloy castings can be effectively eliminated, and the comprehensive mechanical properties of the aluminum alloy castings can be improved; the method also includes loading the aluminum alloy castings into a tooling, and selecting metal particles to fill the entire tooling gap, and the filling of metal particles can effectively support the structure of the aluminum alloy castings, reduce the deformation of the aluminum alloy castings caused by high temperature during hot isostatic pressing, and ensure the dimensional accuracy of the aluminum alloy castings.

[0042] The treatment method of the present invention effectively bridges the internal defects of the aluminum alloy casting under the multiple effects of deep cryogenic treatment, heating treatment and hot isostatic pressing treatment; the aluminum alloy casting treated by the treatment method of the present invention is further subjected to conventional solid solution treatment and aging treatment, which can significantly improve the mechanical properties and fatigue properties of the aluminum alloy casting. The method of the present invention is applicable to Al-Si series, Al-Cu series and Al-Mg series cast aluminum alloys, and has good promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 : A process flow chart of hot isostatic pressing treatment of aluminum alloy castings according to a preferred embodiment of the present invention.

[0044] Figure 2 : A schematic structural diagram of a tooling for carrying aluminum alloy castings according to a preferred embodiment of the present invention (left: horizontal furnace loading method, right: vertical furnace loading method).

[0045] Figure 3 : Comparison of microstructures of the aluminum alloy casting of Example 1 before and after hot isostatic pressing (left: before treatment, right: after treatment). DETAILED DESCRIPTION

[0046] The method of the present invention will be described in further detail below in conjunction with specific examples. It should be understood that the following examples are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0047] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the reagents, materials, etc. used in the following examples, unless otherwise specified, can be obtained from commercial channels.

[0048] The aluminum alloy castings used in the following examples and comparative examples are prepared by low-pressure casting, and have dimensions of 1200 mm×800 mm×100 mm and an average wall thickness of 2.5 mm.

[0049] Example 1 S1. Place the ZL101A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1°C / min, and keep the furnace temperature at -143°C for 1h; S2, heating the cryogenic treatment furnace and setting the heating rate to 1.2°C / min. When the furnace temperature reaches 120°C, keep it warm for 1.2 hours and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 once; S4. Place the ZL101A aluminum alloy casting in a heat-resistant steel tooling, and fill the gaps in the tooling with cast steel balls with a particle size of 3 mm until the cast steel balls fill the tooling and completely cover the ZL101A aluminum alloy casting; S5. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 500°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 100MPa, and keep the temperature and pressure for 3 hours; slowly cool to 120°C with the furnace, open the furnace door and cool to room temperature; S6. The ZL101A aluminum alloy casting was kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a high-performance ZL101A-T6 state casting.

[0050] Example 2 S1. Place the ZL114A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1.8°C / min, and keep the furnace temperature at -96°C for 2h; S2, heating the cryogenic treatment furnace and setting the heating rate to 1.5°C / min. When the furnace temperature reaches 105°C, keep it warm for 1.9 hours and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 twice; S4, placing the ZL114A aluminum alloy casting in a heat-resistant cast iron tooling, and filling the tooling space with cast steel balls with a particle size of 8 mm, until the cast steel balls fill the tooling and completely cover the ZL114A aluminum alloy casting; S5. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 510°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 115MPa, and keep the temperature and pressure for 3 hours; slowly cool to 150°C with the furnace, open the furnace door and cool to room temperature; S6. The ZL114A aluminum alloy casting was kept at 535°C for 10 h, water quenched at 60°C, and then kept at 160°C for 6 h to obtain a high-performance ZL114A-T5 state casting.

[0051] Example 3 S1. Place the ZL205A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1.9°C / min, and keep the furnace temperature at -145°C for 1.8h; S2, heating the cryogenic treatment furnace and setting the heating rate to 1.5°C / min. When the furnace temperature reaches 105°C, keep it warm for 1.9 hours and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 once; S4, placing the ZL205A aluminum alloy casting in a heat-resistant steel tooling, and filling the tooling space with cast iron balls with a particle size of 6 mm, until the cast iron balls fill the tooling and completely cover the ZL205A aluminum alloy casting; S5. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 520°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 120 MPa, and keep the temperature and pressure for 2 hours; slowly cool to 110°C with the furnace, open the furnace door and cool to room temperature; S6. The ZL205A aluminum alloy casting was kept at 538°C for 18 hours, water quenched at 30°C, and then kept at 155°C for 8 hours to obtain a high-performance ZL205A-T5 state casting.

[0052] Example 4 S1. Place the ZL305 aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1.5°C / min, and keep the furnace temperature at -110°C for 1.8h; S2, heating the cryogenic treatment furnace and setting the heating rate to 2°C / min. When the furnace temperature reaches 110°C, keep it warm for 1.9 hours and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 once; S4, placing the ZL305 aluminum alloy casting on a heat-resistant steel tooling, and filling the tooling space with cast steel balls with a particle size of 10 mm, until the cast steel balls fill the tooling and completely cover the ZL305 aluminum alloy casting; S5. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 490°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 130MPa, and keep the temperature and pressure for 2.5h; slowly cool to 150°C with the furnace, open the furnace door and cool to room temperature; S6. The ZL305 aluminum alloy casting was kept at 490°C for 8 h, water quenched at 80°C, and then placed at room temperature for 24 h to obtain a high-performance ZL305-T4 casting.

[0053] Example 5 S1. Place the ZL101A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1°C / min, and keep the furnace temperature at -143°C for 1h; S2, heating the cryogenic treatment furnace, and setting the heating rate to 1.2°C / min. When the furnace temperature reaches 120°C, keep it warm for 1.2h, and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 once; S4. Place the ZL101A aluminum alloy casting directly in a hot isostatic pressing furnace, control the furnace temperature to 500°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the furnace pressure to 100MPa, and keep the temperature and pressure for 3 hours; slowly cool to 120°C with the furnace, open the furnace door and cool to room temperature; S5. The ZL101A aluminum alloy casting is kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a high-performance ZL101A-T6 state casting.

[0054] Example 6 S1. Place the ZL101A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 10°C / min, and keep the furnace temperature at -143°C for 1h; S2, set the heating rate to 12°C / min, when the furnace temperature reaches 120°C, keep it warm for 1.2 hours, and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 once; S4. Place the ZL101A aluminum alloy casting on a heat-resistant steel tooling, and fill the gaps in the tooling with carbon steel balls with a particle size of 3 mm until the carbon steel balls fill the tooling and completely cover the ZL101A aluminum alloy casting; S5. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 500°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 100MPa, and maintain the pressure for 3h; slowly cool to 120°C with the furnace, open the furnace door and cool to room temperature; S6. The ZL101A aluminum alloy casting was kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a high-performance ZL101A-T6 state casting.

[0055] Example 7 S1. Place the ZL101A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1°C / min, and keep the furnace temperature at -143°C for 1h; S2, heating the cryogenic treatment furnace and setting the heating rate to 1.2°C / min. When the furnace temperature reaches 120°C, keep it warm for 1.2 hours and then cool it to room temperature with the furnace; S3, placing the ZL101A aluminum alloy casting in a heat-resistant steel tooling, and filling the gaps in the tooling with cast steel balls with a particle size of 3 mm, until the cast steel balls fill the tooling and completely cover the ZL101A aluminum alloy casting; S4. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 500°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 100MPa, and keep the temperature and pressure for 3 hours; slowly cool to 120°C with the furnace, open the furnace door and cool to room temperature; S5. The ZL101A aluminum alloy casting is kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a high-performance ZL101A-T6 state casting.

[0056] Comparative Example 1 S1. Place the ZL101A aluminum alloy casting in a heat-resistant steel tooling, and fill the tooling space with cast steel balls with a particle size of 3 mm until the cast steel balls fill the tooling and completely cover the ZL101A aluminum alloy casting; S2. Place the device in a hot isostatic pressing furnace, control the furnace temperature to 500°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 100MPa, and keep the temperature and pressure for 3 hours; slowly cool to 120°C with the furnace, open the furnace door and cool to room temperature; S3. The ZL101A aluminum alloy casting was kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a ZL101A-T6 state casting.

[0057] Comparative Example 2 S1. Place the ZL101A aluminum alloy casting in a cryogenic treatment furnace, set the cooling rate to 1°C / min, and keep the furnace temperature at -143°C for 1h; S2, set the heating rate to 1.2℃ / min, when the furnace temperature reaches 120℃, keep it warm for 1.2h, and then cool it to room temperature with the furnace; S3, repeat steps S1 to S2 once; S4. The ZL101A aluminum alloy casting was kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a ZL101A-T6 state casting.

[0058] Comparative Example 3 S1. Place the ZL101A aluminum alloy casting in a heat-resistant steel tooling, and fill the gaps in the tooling with cast steel balls with a particle size of 3 mm until the cast steel balls fill the tooling and completely cover the ZL101A aluminum alloy casting; S2. Place the workpiece in a hot isostatic pressing furnace, control the furnace temperature to 500°C, simultaneously fill the furnace with high-purity (99.99%) argon gas, control the pressure in the furnace to 100MPa, and keep the temperature and pressure for 3 hours; slowly cool to 120°C with the furnace, open the furnace door and cool to room temperature; S3, placing the ZL101A aluminum alloy casting in a cryogenic treatment furnace, setting the cooling rate to 1°C / min, and when the furnace temperature reaches -143°C, keeping it warm for 1h; S4, heating the cryogenic treatment furnace and setting the heating rate to 1.2°C / min. When the furnace temperature reaches 120°C, keep it warm for 1.2 hours and then cool it to room temperature with the furnace; S5, repeat steps S1 to S2 once; S6. The ZL101A aluminum alloy casting was kept at 535°C for 10 h, water quenched at 60°C, and then kept at 180°C for 4 h to obtain a high-performance ZL101A-T6 state casting.

[0059] Figure 3 The figure below is a comparison of the microstructures of the ZL101A aluminum alloy casting of Example 1 before and after hot isostatic pressing. The left figure is a microstructure diagram of ZL101A without cryogenic treatment, heating treatment and hot isostatic pressing treatment, and the right figure is a microstructure diagram of ZL101A after cryogenic treatment, heating treatment and hot isostatic pressing treatment. Figure 3 It can be seen that there are many pinholes, looseness and other defects inside the untreated aluminum alloy castings. After the treated aluminum alloy castings are treated with high temperature and high pressure, the internal pinholes and looseness are closed, and the aluminum alloy casting structure is densified.

[0060] The room temperature mechanical properties, fatigue properties and dimensional accuracy of the aluminum alloy castings obtained in the above embodiments and comparative examples were tested. GB / T 228.1 "Tensile test of metallic materials Part 1: Room temperature test method" was used to test the cut test bars at the same position of the aluminum alloy castings at room temperature. GB / T 3075-2008 "Axial force control method for fatigue test of metallic materials" was used to test the fatigue properties of the cut test bars at the same position of the aluminum alloy castings. The dimensional accuracy of the aluminum alloy castings was tested by the scribing method. The dimensional accuracy level of the as-cast and hot isostatically pressed castings was determined according to GB / T 6414 "Dimensional tolerances and machining allowances of castings". The test results are shown in Table 1.

[0061] Table 1 Performance test results of aluminum alloy castings of embodiments and comparative examples

[0062] Remark: *Dimensional accuracy of deep-cooled aluminum alloy castings.

[0063] From the comparison of Examples 1-4, it can be seen that the deformation of the aluminum alloy casting obtained by the method of the present invention is significantly reduced. The aluminum alloy casting of Example 1 even maintains the dimensional accuracy of the cast aluminum alloy casting. At the same time, the aluminum alloy casting does not crack after heat treatment and correction. In addition, commonly used casting aluminum alloy castings such as Al-Si series, Al-Cu series and Al-Mg series can be processed by the hot isostatic pressing process of the present invention (see Figure 1) to optimize and improve performance. The mechanical properties of the treated aluminum alloy castings far exceed the standard value requirements and the fatigue life can reach 10 6 More than 10 times, especially Al-Si and Al-Mg cast aluminum alloys, the fatigue life reaches 10 7 The overall performance has been significantly improved after more than 10 times of cryogenic treatment + heating treatment + hot isostatic pressing treatment. This is mainly due to the fact that after deep cryogenic treatment + heating treatment + hot isostatic pressing treatment, the internal defects of aluminum alloy castings are treated by high temperature and high pressure, and the internal pinholes and looseness are closed (see Figure 3 ), the casting structure is densified, the failure sources are reduced during subsequent tensile or fatigue loading, and the overall performance is significantly improved.

[0064] From the comparison between Example 1 and Example 5, it can be seen that the dimensional accuracy of the aluminum alloy casting obtained is changed from CT6 level to CT9 level without using a tooling during the hot isostatic pressing process. It can be seen that by filling the tooling for loading the aluminum alloy casting with metal particles (cast steel balls or cast iron balls) with better heat resistance than the aluminum alloy, and using the supporting effect of the metal particles and the tooling on the aluminum alloy casting, the structure of the aluminum alloy casting in the tooling can be effectively supported, so that the aluminum alloy casting still maintains a good filling shape, avoiding the occurrence of deformation problems of the aluminum alloy casting when heated due to stress release, matrix softening and the self-weight of the aluminum alloy casting during the high-temperature heating process, further reducing the deformation of the aluminum alloy casting when heated, and finally achieving the effect of maintaining the dimensional accuracy and structural state of the original aluminum alloy casting as much as possible during the hot isostatic pressing process.

[0065] From the comparison between Example 1 and Example 6, it can be seen that the dimensional accuracy of the aluminum alloy casting obtained by slow cooling during cryogenic treatment and slow heating during heating treatment is changed from CT8 level to CT6 level. This shows that the cooling rate of cryogenic treatment and the heating rate of heating treatment can effectively adjust and reduce the increase of internal stress of aluminum alloy castings, and avoid a substantial increase in internal stress of aluminum alloy castings caused by rapid changes in external ambient temperature.

[0066] From the comparison between Example 1 and Example 7, it can be seen that repeated cryogenic treatment and heating treatment are more conducive to reducing the internal residual stress of the aluminum alloy casting after casting and pouring, while improving the mechanical properties of the aluminum alloy casting during subsequent heat treatment, and ultimately achieving the effect of maintaining the dimensional accuracy and structural state of the original aluminum alloy casting as much as possible during the hot isostatic pressing process.

[0067] From the comparison between Example 1 and Comparative Example 1, it can be seen that by subjecting the aluminum alloy casting to deep cryogenic treatment (temperature of -150~-90°C) and heating treatment (temperature of 100~130°C) before hot isostatic pressing, the residual stress formed during casting of the aluminum alloy casting can be effectively eliminated, and the comprehensive mechanical properties of the aluminum alloy casting can be improved. When the deep cryogenic treatment and heating treatment are cancelled, the aluminum alloy casting is severely deformed during the hot isostatic pressing process.

[0068] From the comparison between Example 1 and Comparative Example 2, it can be seen that the mechanical properties and fatigue properties of the aluminum alloy castings that have not been subjected to hot isostatic pressing are significantly lower than those of the aluminum alloy castings that have been subjected to hot isostatic pressing, indicating that hot isostatic pressing has a greater impact on the mechanical properties and fatigue properties of the aluminum alloy castings. At the same time, after the aluminum alloy castings are subjected to deep cryogenic treatment + heating treatment, the internal stress of the aluminum alloy castings is released to a certain extent, resulting in a smaller deformation amplitude of the aluminum alloy castings.

[0069] From the comparison between Example 1 and Comparative Example 3, it can be seen that although the mechanical properties of the aluminum alloy castings obtained by directly performing hot isostatic pressing without first undergoing cryogenic treatment and heating treatment to relieve stress only decrease slightly, the dimensional accuracy of the aluminum alloy castings is significantly deteriorated, indicating that the aluminum alloy castings are severely deformed; it can also be seen that the cryogenic treatment and heating treatment after the hot isostatic pressing treatment have little effect on the dimensional accuracy of the aluminum alloy castings after the hot isostatic pressing treatment, that is, the dimensional accuracy of the aluminum alloy castings obtained in Comparative Example 3 is basically the same as that in Comparative Example 1.

[0070] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for hot isostatic pressing of aluminum alloy castings, wherein: The method comprises the following steps: 1) Place the aluminum alloy casting in a cryogenic treatment furnace for cryogenic treatment; 2) Heat the aluminum alloy casting after cryogenic treatment to 100~130℃, keep it warm for a period of time, and then cool it to room temperature with the furnace; 3) Repeat steps 1) and 2) 0 or more times; 4) placing the aluminum alloy casting cooled to room temperature in a hot isostatic pressing furnace for hot isostatic pressing treatment; Wherein, in step 1), the temperature of the cryogenic treatment is -150~-90°C; in step 4), the temperature of the hot isostatic pressing treatment is 490~530°C; and the pressure of the hot isostatic pressing treatment is 90~130MPa.

2. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: The material of the aluminum alloy casting is Al-Si series, Al-Cu series or Al-Mg series aluminum alloy.

3. The hot isostatic pressing method for aluminum alloy castings according to claim 1 or 2, wherein: The size of the aluminum alloy casting is (1000-2000) mm×(400-800) mm×(30-150) mm; And / or, the average thickness of the aluminum alloy casting is ≥1.5 mm.

4. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: In step 1), the cryogenic treatment time is 1 to 2 hours; And / or, in step 1), the cooling rate of the cryogenic treatment is 0.5-2°C / min; And / or, in step 2), the heating rate is 0.5-2°C / min.

5. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: In step 3), repeat steps 1) and 2) 0-10 times.

6. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: In step 4), the hot isostatic pressing furnace is filled with high-purity argon gas, and the purity of the high-purity argon gas is not less than 99.99%; And / or, in step 4), the hot isostatic pressing treatment time is 3 to 4 hours.

7. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: In step 4), the aluminum alloy casting cooled to room temperature is placed in a tooling, and the gaps in the tooling are filled with metal particles until the metal particles fill the tooling and completely cover the aluminum alloy casting; the tooling containing the aluminum alloy casting and the filled metal particles is placed in a hot isostatic pressing furnace for hot isostatic pressing treatment; Wherein, the particle size of the metal particles is 3-10 mm; the material of the metal particles is cast steel or cast iron.

8. The hot isostatic pressing method for aluminum alloy castings according to claim 7, wherein: In step 4), the workpiece containing the aluminum alloy casting and the filler metal particles is placed in a hot isostatic pressing furnace and heated to a furnace temperature of 490-530°C. High-purity argon gas is simultaneously filled into the hot isostatic pressing furnace, and the pressure in the furnace is controlled to 90-130 MPa. After maintaining the pressure at high temperature and high pressure for 3-4 hours, the furnace is cooled to a furnace temperature of less than 150°C, and the furnace door is opened for air cooling.

9. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: The method further comprises the steps of: 5) Perform solution treatment and aging treatment on the aluminum alloy castings after hot isostatic pressing.

10. The hot isostatic pressing method for aluminum alloy castings according to claim 1, wherein: The method comprises the following steps: S1) placing the aluminum alloy casting in a cryogenic treatment furnace, controlling the furnace temperature to -150~-90℃, and keeping the temperature for 1~2 hours after reaching the temperature; S2) Raise the furnace temperature to 100-130°C, keep it warm for 1-2 hours, and then cool the aluminum alloy casting to room temperature along with the furnace; S3) repeating step S1) and step S2) for more than 0 times, and taking the aluminum alloy casting cooled to room temperature out of the furnace; S4) placing the aluminum alloy casting cooled to room temperature in a tooling, and filling the gaps in the tooling with metal particles until the metal particles fill the tooling and completely cover the aluminum alloy casting; S5) placing the workpiece containing the aluminum alloy casting and metal particles in a hot isostatic pressing furnace, heating the furnace to a temperature of 490-530°C, and simultaneously filling the hot isostatic pressing furnace with argon gas, controlling the pressure in the furnace to 90-130MPa, and maintaining the temperature and pressure at high temperature and high pressure for 3-4 hours, cooling the furnace to a temperature less than 150°C, and then opening the furnace door for air cooling; S6) performing a solution treatment and an aging treatment on the aluminum alloy casting cooled to room temperature after the hot isostatic pressing treatment to obtain an aluminum alloy casting with improved performance.

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