A method for preparing Al-Zn-Mg-Cu series aluminum alloy free forging

Abstract

The invention discloses a method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging, which comprises sequentially subjecting an Al-Zn-Mg-Cu aluminum alloy ingot after homogenization to variable temperature forging, solution treatment, cryogenic treatment, cold compression treatment and aging treatment. The method can improve the differences in the transverse, longitudinal and high-direction properties of high-strength aluminum alloy free forgings by introducing variable temperature forging technology and combining cryogenic treatment during the forging process, and has the advantages of simple operation and wide applicability.

Description

Technical Field

[0001] The invention relates to a method for preparing an Al-Zn-Mg-Cu series aluminum alloy free forging, belonging to the technical field of aluminum alloy forging. Background Art

[0002] The Al-Zn-Mg-Cu aluminum alloys among aluminum alloys have the characteristics of low density, high specific strength and good processing performance. They are widely used as key structural materials in aviation, aerospace, weapons, electronics, ships and other fields.

[0003] With the increasing demand for large structural parts in my country, the application of Al-Zn-Mg-Cu series aluminum alloy thick materials has become more prominent, and higher requirements have been put forward for the uniformity of the performance of thick materials. At present, the organization and performance of Al-Zn-Mg-Cu series aluminum alloy thick forgings have obvious non-uniformity along the thickness direction, which seriously affects the overall performance of the material. In engineering design, the direction with lower performance is often used as the basis for design, which brings difficulties to the design. In the existing technology, the comprehensive performance of aluminum alloys is mainly improved through multi-directional forging, isothermal forging, adding rare earth elements, heat treatment and other processes. Although these methods can achieve initial results for some aluminum alloy free forgings, they have not been widely promoted in production due to the complicated process and low production efficiency. At the same time, for materials with thicker thickness, these processes have little improvement on the anisotropy of the material. For example, Chinese patent CN 115747592 A discloses an isotropic high-strength deformed aluminum alloy and a preparation method thereof. This method promotes the activation of non-basal surface slip during plastic deformation by adding rare earth elements Sc, and greatly weakens the strong texture of the plastic deformation basal surface through isothermal reciprocating extrusion combining elongation strain and compression strain, thereby eliminating the anisotropy of mechanical properties caused by the texture. This method can improve the anisotropy of aluminum alloy materials to a certain extent, but requires the addition of rare earth elements, which is costly and has poor applicability. Summary of the invention

[0004] In view of the defect in the prior art that the transverse (LT), longitudinal (L) and height (ST) properties of Al-Zn-Mg-Cu series aluminum alloy free forgings are greatly different, the purpose of the present invention is to provide a preparation method of Al-Zn-Mg-Cu series aluminum alloy free forgings, the method has the advantages of simple process and easy implementation, and the anisotropy of the Al-Zn-Mg-Cu series aluminum alloy forgings can be reduced while maintaining the high strength and high elongation of the aluminum alloy.

[0005] In order to achieve the above technical objectives, the present invention provides a method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging, which comprises subjecting the Al-Zn-Mg-Cu aluminum alloy ingot after homogenization treatment to variable temperature forging, solid solution treatment, deep cryogenic treatment, cold compression treatment and aging treatment in sequence to obtain the obtained Al-Zn-Mg-Cu aluminum alloy free forging.

[0006] As a preferred solution, the conditions for the cryogenic treatment are: using liquid nitrogen as the medium, the temperature is -150°C to -190°C, and the time is 10 to 24 hours.

[0007] The key to the present invention is to achieve the goal of significantly reducing the anisotropy of Al-Zn-Mg-Cu aluminum alloy forgings while ensuring that the prepared aluminum alloy forgings have high strength and high elongation without adding rare earth elements through the mutual synergy between variable temperature forging and deep cryogenic treatment processes.

[0008] First, the inventor optimized the forging process of Al-Zn-Mg-Cu aluminum alloy ingots. The forging adopts variable temperature forging technology. On the one hand, the original grain structure of the ingot can be fully fragmented by high temperature forging, which changes the degree of recrystallization of the aluminum alloy forging and increases the deformation of the core; on the other hand, medium temperature forging can introduce sufficient deformation energy storage into the aluminum alloy. The fully fragmented grain structure can be combined with solution treatment to improve the strength of the prepared aluminum alloy. At the same time, the introduction of deep cold treatment on the basis of conventional solution treatment makes the Al-Zn-Mg-Cu aluminum alloy have a greater degree of supercooling than ordinary solution treatment, increases the nucleation rate during subsequent artificial aging, and is conducive to the precipitation of the second phase in the matrix. At an appropriate aging temperature, the precipitates are dispersed, improving the uniformity of the organization, and can further improve the strength, hardness, elongation and other properties of the Al-Zn-Mg-Cu aluminum alloy, and significantly reduce the anisotropy in the Al-Zn-Mg-Cu aluminum alloy. At the same time, the Al-Zn-Mg-Cu aluminum alloy shrinks in volume during the deep cooling process, which fills the vacancies and micropores inside the material and increases the density of the material. Deep cooling treatment can also reduce or eliminate residual stress or internal stress during processing, improve dimensional stability, and has the characteristics of simple operation, no pollution and low cost.

[0009] Further preferably, the temperature of the cryogenic treatment is -170°C to -190°C, and the holding time is 15 to 24 hours. In the present invention, by controlling the temperature and holding time of the cryogenic treatment, the precipitation of the second phase in the Al-Zn-Mg-Cu aluminum alloy during the aging process can be regulated, thereby controlling the comprehensive properties of the Al-Zn-Mg-Cu aluminum alloy. If the temperature or time of the cryogenic treatment is not within the scope of the present invention, the effect of improving the anisotropy in the Al-Zn-Mg-Cu aluminum alloy cannot be achieved.

[0010] As a preferred solution, the Al-Zn-Mg-Cu aluminum alloy is first heated to a temperature of 350-500°C. After the material reaches the set temperature, it is kept warm for 2-10 hours, and taken out of the furnace at 350-500°C for the first forging, with a deformation of 10-35% reserved in the thickness direction; the material is cooled to 230-310°C or the material is cooled to room temperature and then heated to 230-310°C, and kept warm for 2-10 hours, and the second forging is performed, and the deformation in the thickness direction during the second forging is controlled to be 10-35%. In the technical solution of the present invention, the degree of recrystallization of the aluminum alloy forging is changed by the deformation, and the coarse second phase of the grain boundary is broken. When the deformation is small, the deformation energy storage is small, the degree of recrystallization of the alloy is low, and the deformation structure obtained by the high-temperature forging part is retained; when the deformation is large, the deformation energy storage becomes larger, the uniformity of deformation is better, which is conducive to the recrystallization and improves the degree of recrystallization. It is further preferably 15-25%.

[0011] As a preferred solution, the solution treatment conditions are: temperature of 400-500°C, holding time of 2-10 hours. Further preferred temperature is 450-500°C, holding time of 2-10 hours. Solution treatment within the temperature range of the present invention is beneficial to improve the strength of the aluminum alloy in combination with variable temperature forging.

[0012] As a preferred solution, the conditions of the cold compression treatment are: a compression amount of 1.5-3.0% and a temperature less than 35°C.

[0013] As a preferred solution, the aging treatment is a single-stage aging treatment or a double-stage aging treatment.

[0014] As a preferred solution, the temperature of the single-stage aging treatment is 110-160°C.

[0015] As a preferred solution, the conditions of the double-stage aging treatment are: the primary aging temperature is 110-130°C, and the secondary aging temperature is 140-170°C.

[0016] As a preferred solution, the time interval between the solution treatment and the cryogenic treatment is less than or equal to 30 seconds. The transfer time has a great influence on the performance of the material, because the material is in contact with cold air as soon as it comes out of the furnace, and the temperature drops rapidly. In order to prevent the local decomposition and precipitation of the supersaturated solid solution, which reduces the effect of the cryogenic treatment, the transfer time should be as short as possible.

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0018] 1) The present invention proposes a method for preparing aluminum alloy free forgings with near-isotropy, which can significantly reduce the anisotropy of Al-Zn-Mg-Cu aluminum alloy forgings while ensuring that the prepared aluminum alloy forgings have high strength and high elongation without adding rare earth elements by introducing the synergistic effect between the variable temperature forging technology and the deep cold treatment process during the forging process.

[0019] 2) The present invention can change the degree of recrystallization of the aluminum alloy forging through variable temperature forging, and fully fragment the coarse second phase at the grain boundary.

[0020] 3) The present invention uses cryogenic treatment after variable temperature forging to make the Al-Zn-Mg-Cu aluminum alloy have a greater degree of supercooling than ordinary solution treatment, increase the nucleation rate during subsequent artificial aging, and at an appropriate aging temperature, the precipitates are dispersedly distributed, improve the uniformity of the organization, and further improve the strength, hardness, elongation and other properties of the Al-Zn-Mg-Cu aluminum alloy, and significantly reduce the anisotropy in the Al-Zn-Mg-Cu aluminum alloy. Eliminate the internal stress in the aluminum alloy, significantly reduce the anisotropy in the aluminum alloy, and further improve the strength of the aluminum alloy.

[0021] 4) The method described in the present invention is simple and easy to implement, has low requirements on personnel and equipment, is of great use value in engineering applications, and has broad application prospects. DETAILED DESCRIPTION

[0022] The following examples are only specific descriptions of the preferred embodiments of the present invention, and are not intended to limit the scope of implementation of the present invention. For ordinary technicians in the technical field, any improvements made without departing from the present invention should be deemed to be within the scope of protection of the present invention.

[0023] Example 1

[0024] A method for preparing an aluminum alloy free forging comprises the following steps:

[0025] (1) The 7A85 aluminum alloy raw material ingot conforming to GB3190 is homogenized and processed to obtain a 7A85 aluminum alloy forging blank of φ390×160 mm;

[0026] (2) The processed 7A85 forging blank is placed in a heating furnace for the first stage heating to 420°C, the holding time is 7 hours, and then taken out of the furnace for the first forging. A 25% deformation amount is reserved in the thickness direction of the first forging. After the forging is completed, when the material temperature is cooled to 270°C, the blank is heated in the second stage, the heating temperature is 270°C, the holding time is 5 hours, and the blank is taken out of the furnace for the second forging. The deformation amount in the thickness direction is 25%, and a forging blank with a size of 225×215×125 mm is obtained;

[0027] (3) subjecting the forging blank to a solution treatment at a temperature of 475°C for 6 hours;

[0028] (4) The forgings after the solid solution treatment are cryogenically treated. The treatment method is to put the solid solution forgings into liquid nitrogen at a temperature of -170°C for cryogenic treatment. The treatment time is 20 hours and the transfer time is 20 seconds.

[0029] (5) cold compression of the cryogenically treated forgings with a compression amount of 2.0% and a temperature of room temperature;

[0030] (6) The forgings were subjected to a double-stage aging treatment, with the primary aging treatment temperature being 120°C for 8 h and the secondary aging treatment temperature being 157°C for 11 h, thereby obtaining a nearly isotropic Al-Zn-Mg-Cu aluminum alloy final forging.

[0031] Example 2

[0032] (1) The raw material is 7A09-O1 aluminum alloy extruded bar conforming to GJB3539, the bar diameter is φ300 mm, and the bar is processed into 7A09 aluminum alloy forging blank of φ300 mm×235 mm;

[0033] (2) The processed 7A09 forging blank is placed in a heating furnace for the first stage heating to 380°C, the holding time is 6 hours, and then taken out of the furnace for conventional forging, and a 23% deformation in the thickness direction is reserved. After the forging is completed, when the material temperature is cooled to 285°C, the blank is heated in the second stage, the heating temperature is 285°C, the holding time is 5 hours, and the blank is taken out of the furnace for the second forging. The deformation in the thickness direction during forging is 23%, and a forging blank with a size of 532 mm × 215 mm × 118 mm is obtained.

[0034] (3) subjecting the forging blank to a solution treatment at a temperature of 470°C for 6 hours;

[0035] (4) The forgings after the solid solution treatment are cryogenically treated. The treatment method is to put the solid solution forgings into liquid nitrogen at a temperature of -190°C for cryogenic treatment. The cryogenic treatment lasts for 18 hours, and the time interval between the solid solution treatment and the cryogenic treatment is 25 seconds;

[0036] (5) cold compression of the quenched forgings with a compression amount of 3.0% and a temperature of room temperature;

[0037] (6) The forgings were subjected to aging treatment at an aging temperature of 120°C for a treatment time of 16 h to obtain a nearly isotropic 7A09 aluminum alloy final forging.

[0038] Comparative Example 1

[0039] The difference between this comparative example and Example 1 is that the variable temperature forging process is replaced by an isothermal forging process at 420° C. and kept at this temperature for 12 hours, and the other conditions are the same.

[0040] It can be seen from the data in Table 1 that when only high-temperature forging is performed, the tensile strength and yield strength in the L and LT directions do not decrease significantly, the tensile strength, yield strength and elongation in the ST direction decrease significantly, and the anisotropy of the prepared aluminum alloy is obvious.

[0041] Comparative Example 2

[0042] The difference between this comparative example and Example 1 is that no cryogenic treatment is performed, and the other conditions are the same.

[0043] It can be seen from Table 1 that when cryogenic treatment is not performed, the grains are coarser, which is less conducive to the precipitation of the second phase than cryogenic treatment. Therefore, the yield strength and tensile strength in the LT and ST directions of the aluminum alloy prepared in this comparative example are reduced, and the elongation in the three directions is reduced, especially in the ST direction, resulting in obvious anisotropy.

[0044] Comparative Example 3

[0045] The difference between this comparative example and Example 2 is that the variable temperature forging process is replaced with 285° C. and kept warm for 11 hours, and the other conditions are the same.

[0046] It can be seen from Table 1 that when only medium-temperature forging is performed, the original grain structure of the ingot cannot be fully fragmented and the degree of recrystallization in the aluminum alloy forging cannot be changed, so the strength and elongation of the prepared aluminum alloy will be greatly reduced.

[0047] Comparative Example 4

[0048] The difference between this comparative example and Example 2 is that the cryogenic treatment is not added, and the other conditions are the same.

[0049] Comparative Example 5

[0050] The only difference between this comparative example and Example 1 is that the deformation amount in the thickness direction during the second forging of the variable temperature forging process is 8%, and the other conditions are the same.

[0051] It can be seen from Table 1 that when the deformation in the thickness direction during the second forging of the variable temperature forging treatment is too small, the strength and elongation of the prepared aluminum alloy will decrease, especially in the ST direction, resulting in obvious anisotropy.

[0052] Comparative Example 6

[0053] The only difference between this comparative example and Example 1 is that the first forging temperature of the variable temperature forging process is 600° C., and the other conditions are the same.

[0054] Since the first forging temperature was too high, the aluminum alloy was overburned and multiple cracks appeared on the surface of the aluminum alloy due to the high heating temperature during the process, and the material was scrapped.

[0055] The performance of the aluminum alloy final forgings prepared in the above embodiments and comparative examples was tested according to the test method in accordance with the standard: GB / T 228.1, and the results are summarized in Table 1.

[0056] Table 1 Test results of tensile properties of aluminum alloys prepared in Examples 1 to 2 and Comparative Examples 1 to 5

[0057]

[0058]

Claims

1. A method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging, characterized in that: The Al-Zn-Mg-Cu aluminum alloy ingot after homogenization treatment is subjected to variable temperature forging, solution treatment, deep cryogenic treatment, cold compression treatment and aging treatment in sequence to obtain; The cryogenic treatment conditions are: using liquid nitrogen as the medium, the temperature is -150°C to -190°C, and the time is 10 to 24 hours; The conditions of the variable temperature forging are as follows: the Al-Zn-Mg-Cu aluminum alloy ingot is first heated to a temperature of 350-500°C, and after the material reaches the set temperature, it is kept warm for 2-10 hours, and the first forging is performed at 350-500°C, and a deformation of 10-35% is reserved in the thickness direction; the material is cooled to 230-310°C or the material is cooled to room temperature and then heated to 230-310°C, and kept warm for 2-10 hours, and the second forging is performed, and the deformation in the thickness direction during the second forging is controlled to be 10-35%; The conditions of the cold compression treatment are: a compression amount of 1.5-3.0% and a temperature less than 35°C.

2. The method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging according to claim 1, characterized in that: The conditions of the solution treatment are: temperature of 400-500° C. and holding time of 2-10 hours.

3. The method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging according to claim 1 or 2, characterized in that: The aging treatment is a single-stage aging treatment or a double-stage aging treatment.

4. The method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging according to claim 3, characterized in that: The temperature of the single-stage aging treatment is 110-160°C.

5. The method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging according to claim 3, characterized in that: The conditions of the double-stage aging treatment are: the primary aging temperature is 110-130°C, and the secondary aging temperature is 140-170°C.

6. The method for preparing an Al-Zn-Mg-Cu aluminum alloy free forging according to claim 1, characterized in that: The time interval between the solution treatment and the cryogenic treatment is less than or equal to 30 seconds.

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