CN114717495A - Homogenization heat treatment method for low-Cu-content 7xxx series aluminum alloy - Google Patents
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- 229910000838 Al alloy Inorganic materials 0.000 title claims abstract description 26
- 238000000265 homogenisation Methods 0.000 title abstract description 59
- 239000000956 alloy Substances 0.000 claims abstract description 73
- 229910045601 alloy Inorganic materials 0.000 claims abstract description 72
- 238000004321 preservation Methods 0.000 claims abstract description 19
- 238000002844 melting Methods 0.000 claims abstract description 9
- 230000008018 melting Effects 0.000 claims abstract description 8
- 230000000630 rising effect Effects 0.000 claims abstract description 7
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- 230000005496 eutectics Effects 0.000 description 4
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Abstract
The invention relates to a homogenization heat treatment method of a low-Cu-content 7xxx series aluminum alloy, belonging to the technical field of metal heat treatment. The method comprises the following steps: (1) a temperature rising stage: the alloy adopts a temperature rise process with the temperature rise rate gradually reduced, so that dispersed phases are uniformly separated out, and the initial melting temperature of an AlZnMgCu phase is increased; (2) and (3) a heat preservation stage: homogenizing and preserving the temperature of the alloy to dissolve the AlZnMgCu phase back. The homogenization heat treatment method can effectively improve the initial melting temperature of the quaternary phase, realize the rapid redissolution of the quaternary phase, save the heat treatment time and ensure that the size and the number density of the precipitated disperse phase meet the requirements. More importantly, the method has the advantages of simple process control, strong operability and high heat treatment efficiency, can achieve the effect of conventional two-stage homogenization treatment, and is particularly suitable for homogenization treatment of industrial large-scale cast ingots.
Description
Technical Field
The invention relates to a homogenization heat treatment method of a low-Cu-content 7xxx series aluminum alloy, belonging to the technical field of metal heat treatment.
Background
The 7xxx series aluminum alloy has the properties of high strength, high toughness, good corrosion resistance, easy processing and the like, and has wide application in the fields of aerospace, oil drilling, transportation and the like. Generally, the cast structure of the 7xxx series alloy has more obvious dendritic segregation, and a large amount of coarse eutectic structures exist in a network structure at grain boundaries in a matrix, so that the structure and the components of the alloy are not uniform. In the subsequent deformation process, stress concentration is easy to occur at the intersection of the eutectic structure and the matrix, further cracks are generated, and the performance of the alloy is seriously influenced, so that the elimination of the coarse eutectic structure in the as-cast structure through the homogenization heat treatment is very necessary.
The homogenization treatment can fully dissolve the re-soluble non-equilibrium eutectic phase in the as-cast structure, eliminate dendrite segregation, obtain a solid solution with more uniform distribution of alloy elements, and ensure the effect of subsequent solution treatment to the greatest extent. In addition, trace elements such as Zr and Cr in the alloy can form Al in the homogenization process3Zr、Al3The dispersed phase of Er, etc. has size of several tens of nm and is coherent with the matrix. In the subsequent thermal deformation process, the grain boundary can be effectively pinned, recrystallization is inhibited, and the performance of the final finished product state is improved.
The solidification precipitated phase type in the 7xxx series aluminum alloy cast structure mainly comprises an AlZnMgCu phase,Al2CuMg phase, Al2Cu phase, MgZn2Phase, Fe-rich phase, etc. Wherein, AlZnMgCu phase and MgZn2Phases, Fe-rich phases, MgZn, are present in all types of 7xxx alloys2The phase can be redissolved at 200-300 ℃, the redissolution temperature of the AlZnMgCu phase is 460-475 ℃, and the Fe-rich phase belongs to the non-redissolution phase. Al is liable to be present in 7 xxx-series alloys having a high Cu content2CuMg phase and Al2Cu phase, and Al phase of AlZnMgCu easily occurs during homogenization2Transformation of CuMg phase. Generally, homogenization treatment of a 7 xxx-series aluminum alloy is classified into single-stage, two-stage, and three-stage homogenization. The single-stage homogenization process is generally to select the temperature to keep the temperature for 24-48 h at the initial melting temperature of the AlZnMgCu phase, so that the redissolution of the AlZnMgCu phase can be realized through the process, but the number of dispersed phases is small, the size is large, and the subsequent recrystallization inhibition effect is poor. The two-stage homogenization process generally comprises the steps of heating to 400-440 ℃, preserving heat for 10-20 hours, and then preserving heat for 24-72 hours at 460-475 ℃. The process can realize the redissolution of the AlZnMgCu phase and the uniform precipitation of the dispersed phase. In addition, if the alloy has AlZnMgCu phase Al in the homogenization process2The transformation of CuMg phase needs to be carried out by adding heat preservation for 15-30 h at 480-490 ℃ to ensure Al2And (4) re-dissolving the CuMg phase, wherein the homogenization process is a three-stage homogenization heat treatment process. For the 7xxx series alloy with low Cu content, a Cu-rich phase hardly exists in an as-cast structure, the phase transformation basically does not occur in the subsequent homogenization heat treatment process, and the AlZnMgCu phase is directly dissolved back, so that a three-stage homogenization process is not needed. A two-stage homogenization heat treatment process may be employed in view of uniform precipitation of the dispersed phase. However, the upper limit of the second-stage temperature of the conventional two-stage homogenization process is 460 to 475 ℃, and a longer heat preservation time is required, so that a simpler treatment method needs to be provided, and the homogenization effect can be achieved in a shorter time.
Disclosure of Invention
The invention aims to provide a homogenization heat treatment method of a low-Cu-content 7 xxx-series alloy, which can remarkably save heat treatment time and achieve the effect of conventional two-stage homogenization treatment while realizing rapid redissolution of a quaternary phase and precipitation of a fine and uniform dispersed phase through simple process control.
The purpose of the invention is realized by adopting the following technical scheme.
A homogenization heat treatment method of a low-Cu-content 7xxx series aluminum alloy adopts a homogenization treatment process for controlling the temperature rise rate in the homogenization treatment process, and mainly comprises the following steps: (1) a temperature rising stage: the alloy adopts a uniform heating process with gradually reduced heating rate, so that the uniform precipitation of a dispersed phase is ensured, and the initial melting temperature of an AlZnMgCu phase is increased; (2) and (3) a heat preservation stage: the alloy is subjected to a homogenization heat preservation process to ensure the redissolution of the AlZnMgCu phase.
In the method of the invention, the Cu content in the 7xxx series alloy is not more than 0.8 wt%, and the Cu/Mg ratio is not more than 0.6; wherein the Cu content is preferably not more than 0.7 wt%, and the Cu/Mg ratio is preferably 0.20 to 0.45.
In the method, the heating of the 7xxx series alloy refers to that the temperature of the 7xxx series aluminum alloy cast ingot is increased to 475-485 ℃ from room temperature (25 ℃; preferably, the temperature of the 7xxx series aluminum alloy ingot is increased to 475-480 ℃ from room temperature.
In the method, the temperature rise rate is controlled to be gradually reduced from large to small in the temperature rise process of the 7xxx series alloy; preferably, the process in which the temperature increase rate decreases gradually from large to small is an acceleration decrease process.
In the method, the initial heating rate in the heating process is 300-400 ℃/h, and the final heating rate is 2-20 ℃/h; preferably, the initial heating rate is 350-400 ℃/h, and the final heating rate is 2-15 ℃/h.
In the method, the temperature rise rate is 5-50 ℃/h when the temperature is 400-440 ℃ in the temperature rise process; preferably, the temperature rise rate is 5-15 ℃/h when the temperature is 400-430 ℃ in the temperature rise process.
In the method, in the temperature rise process, the temperature rise time is 2-5 h when the temperature rise rate is 2-20 ℃/h; preferably, the temperature rise time is 2-4 h when the temperature rise rate is 2-5 ℃/h.
In the method, the total temperature rise time is 13-20 h; preferably, the total temperature rise time is 13-18 h.
In the method, the heat preservation time is 12-18 h; preferably, the heat preservation time is 14-17 h.
The homogenization heat treatment method of the low-Cu-content 7xxx series aluminum alloy comprises the following steps:
(1) a temperature rising stage: the alloy starts to be heated from room temperature at a heating rate of 300-400 ℃/h, and the heating rate is gradually reduced along with the temperature rise; when the alloy temperature is 400-440 ℃, the heating rate is reduced to 5-50 ℃/h; the temperature rising rate is gradually reduced, when the alloy temperature is 465-475 ℃, the temperature rising rate is 2-20 ℃/h, the temperature rising rate is gradually reduced or kept unchanged until the alloy temperature is 475-485 ℃, and the time is 2-5 h; the total time of the heating stage is 13-20 h.
(2) And (3) a heat preservation stage: and (3) preserving the heat of the alloy at 475-485 ℃ for 12-18 h, and performing air cooling or water quenching treatment on the alloy after the heat preservation is finished.
The homogenizing heat treatment method of the low-Cu-content 7xxx series aluminum alloy has the following advantages:
a) the dispersed phase can be uniformly separated out by controlling the temperature rise rate in the temperature rise process;
b) the slow temperature rise rate is adopted in the final temperature rise stage, so that the initial melting temperature of the AlZnMgCu phase is effectively increased, and the re-dissolution speed is remarkably accelerated at a relatively high heat preservation temperature;
c) the treatment mode of variable rate temperature rise and heat preservation obviously saves the heat treatment time and has higher efficiency while achieving the effect of conventional two-stage homogenization treatment.
Drawings
FIG. 1 is a schematic process diagram of a homogenization heat treatment method for a low Cu content 7xxx series aluminum alloy.
FIG. 2 shows the metallographic structure after the temperature rise process of the present invention is completed.
FIG. 3 is a scanned tissue after the warming procedure of the present invention is completed.
FIG. 4 is the metallographic structure of water quenching after the heat preservation process of the present invention is finished.
FIG. 5 is a scanned structure of water quenching after the incubation process of the present invention is completed.
FIG. 6 shows the metallographic structure of air-cooled steel after the heat-insulating process of the present invention is completed.
FIG. 7 shows the scanning structure of air cooling after the incubation process of the present invention is completed.
FIG. 8 is a transmission profile of dispersed phase particles after the incubation process of the present invention is completed.
Detailed Description
The homogenization treatment process adopts a homogenization treatment process for controlling the heating rate, and the process flow is shown as figure 1 and mainly comprises the following steps: (1) in the temperature rise stage, the temperature rise rate is gradually reduced in a homogenization temperature rise process, the temperature rise rate is a process of accelerating reduction, and the initial melting temperature of the AlZnMgCu phase is increased while the precipitation of dispersed phases is ensured; (2) and in the heat preservation stage, homogenizing and preserving heat to ensure the redissolution of the AlZnMgCu phase.
The invention discloses a homogenizing heat treatment method of a low-Cu-content 7xxx series aluminum alloy, which comprises the following steps of:
(1) a temperature rise stage: the alloy starts to be heated from room temperature at the heating rate of 350-400 ℃/h, and the heating rate is gradually reduced along with the temperature rise; when the alloy temperature is 400-430 ℃, the heating rate is reduced to 5-15 ℃/h; the heating rate is gradually reduced, and when the alloy temperature is 465-475 ℃, the heating rate is 2-5 ℃/h; the heating rate is gradually reduced or kept unchanged until the alloy temperature is 475-480 ℃, and the time is 2-4 hours; the total time of the heating stage is 13-18 h.
(2) And (3) a heat preservation stage: and (3) preserving the heat of the alloy for 14-17 h at 475-480 ℃, and performing air cooling or water quenching treatment after the heat preservation is finished.
The invention is further illustrated with reference to the following figures and specific examples, which are not meant to limit the scope of the invention.
Example 1
The aluminum alloy comprises Al-4.5Zn-1.0Mg-0.2Cu-0.25Mn-0.25Cr-0.20Fe-0.20Si (wt.%), and the specification of the ingot is phi 220 mm.
The alloy is homogenized by adopting the method of the invention, and the specific process comprises the following steps: the temperature is raised from room temperature at the temperature raising rate of 400 ℃/h, and the temperature raising rate is gradually reduced; when the alloy temperature reaches 400 ℃, the heating rate is reduced to 15 ℃/h; when the alloy temperature reaches 430 ℃, the heating rate is reduced to 10 ℃/h; when the alloy temperature reaches 465 ℃, the heating rate is reduced to 5 ℃/h; when the alloy temperature reaches 475 ℃, the heating rate is reduced to 2 ℃/h, and the time is 2 h; the total temperature rise time was 14 h. Then incubated at 475 ℃ for 15 h.
As shown in FIG. 2, the metallographic structure of the alloy of example 1 after the completion of the temperature-raising process showed that the second phase had been redissolved to some extent.
As shown in FIG. 3, which is a scanned structure after the temperature raising process of the alloy of example 1 is completed, it can be seen that the second phase is in a certain discontinuous state, and the edges are relatively rounded due to partial re-melting.
As shown in FIG. 4, the metallographic structure of the water quenched alloy after the completion of the heat retaining process of example 1 was confirmed to be good in the re-dissolution of the second phase.
As shown in FIG. 5, which is a scanned structure of water quenching after the completion of the heat-retaining process of the alloy of example 1, it can be seen that the re-dissolution of the second phase is good and only a very small amount of residual phase is sporadically distributed.
As shown in FIG. 6, which is the metallographic structure of the alloy of example 1 after the heat-insulating process was completed and air-cooled, it can be seen that the matrix had fine-sized and densely distributed precipitates, and the grain boundary precipitates had small-sized and intermittently distributed phases.
As shown in FIG. 7, which is a scanned structure of air cooling after the completion of the heat-retaining process of the alloy of example 1, it can be seen that the matrix and the intergranular precipitated phase have small sizes, are uniformly distributed, and have no coarse second phase.
As shown in FIG. 8, the transmission morphology of the dispersed phase particles after the heat preservation process of the alloy of example 1 is completed, and it can be seen from the figure that the dispersed phase is precipitated in a large amount and uniformly distributed in the matrix.
Example 2
The ingot casting used in the embodiment 1 is adopted for homogenization treatment, and the specific process is as follows: the temperature was raised as in example 1 and then incubated at 475 ℃ for 18 h.
Example 3
The ingot casting used in the embodiment 1 is adopted for homogenization treatment, and the specific process is as follows: heating is started from room temperature at a heating rate of 350 ℃/h, and the heating rate is gradually reduced; when the alloy temperature reaches 400 ℃, the heating rate is reduced to 10 ℃/h; when the alloy temperature reaches 430 ℃, the heating rate is reduced to 5 ℃/h; when the alloy temperature reaches 465 ℃, reducing the heating rate to 2 ℃/h, keeping the heating rate, heating to 475 ℃, and using for 4 h; the whole temperature rise time was 18 hours. Then incubated at 475 ℃ for 15 h.
Example 4
The ingot used in the embodiment 1 is adopted for homogenization treatment, and the specific process is as follows: the temperature was raised as in example 3 and then incubated at 475 ℃ for 18 h.
Example 5
The aluminum alloy comprises Al-5.9Zn-2.5Mg-0.7Cu-0.20Mn-0.22Cr-0.15Fe-0.15Si (wt.%), and the specification of the ingot is phi 220 mm.
The alloy is homogenized by adopting the method of the invention, and the specific process comprises the following steps: the temperature is raised from room temperature at the temperature raising rate of 400 ℃/h, and the temperature raising rate is gradually reduced; when the alloy temperature reaches 400 ℃, the heating rate is reduced to 15 ℃/h; when the alloy temperature reaches 430 ℃, the heating rate is reduced to 10 ℃/h; when the alloy temperature reaches 465 ℃, the heating rate is reduced to 5 ℃/h; when the alloy temperature reaches 475 ℃, the heating rate is reduced to 2 ℃/h, and the time is 2 h; the total temperature rise time was 14 hours. Then incubated at 475 ℃ for 15 h.
Example 6
The ingot casting used in the embodiment 5 is adopted for homogenization treatment, and the specific process is as follows: the temperature was raised as in example 5 and then incubated at 475 ℃ for 18 h.
Example 7
The ingot casting used in the embodiment 5 is adopted for homogenization treatment, and the specific process is as follows: the temperature is raised from room temperature at the temperature raising rate of 350 ℃/h, and the temperature raising rate is gradually reduced; when the alloy temperature reaches 400 ℃, the heating rate is reduced to 10 ℃/h; when the alloy temperature reaches 430 ℃, the heating rate is reduced to 5 ℃/h; when the alloy temperature reaches 465 ℃, reducing the heating rate to 2 ℃/h, keeping the heating rate, heating to 475 ℃, and consuming for 3 h; the whole temperature rise time was 18 hours. Then incubated at 475 ℃ for 15 h.
Example 8
The ingot casting used in the embodiment 5 is adopted for homogenization treatment, and the specific process is as follows: the temperature was raised in the same manner as in example 7, and then incubated at 475 ℃ for 18 hours.
Comparative example 1
The ingot casting used in the embodiment 1 is adopted to carry out single-stage homogenization treatment, and the specific process is as follows: the temperature is raised from room temperature at a heating rate of 400 ℃/h, and the temperature is kept for 18h, 36h and 42h when the temperature reaches 470 ℃.
Comparative example 2
The ingot casting used in the embodiment 1 is adopted to carry out single-stage homogenization treatment, and the specific process is as follows: the temperature is raised from the room temperature at the heating rate of 400 ℃/h, and the temperature is kept for 15h when the alloy temperature reaches 475 ℃.
Comparative example 3
The ingot casting used in the embodiment 1 is adopted for two-stage homogenization treatment, and the specific process is as follows: the temperature is raised from room temperature at the heating rate of 400 ℃/h, the temperature is kept for 12h when the alloy temperature reaches 430 ℃, then the temperature is raised at the heating rate of 100 ℃, and the temperature is kept for 18h, 36h and 42h when the alloy temperature reaches 470 ℃.
Comparative example 4
The ingot casting used in the embodiment 1 is adopted for two-stage homogenization treatment, and the specific process is as follows: the temperature is raised from room temperature at the heating rate of 400 ℃/h, the temperature is kept for 12h when the alloy temperature reaches 430 ℃, then the temperature is raised at the heating rate of 100 ℃, and the temperature is kept for 15h when the alloy temperature reaches 475 ℃.
Comparative example 5
The ingot casting used in the embodiment 5 is adopted to carry out single-stage homogenization treatment, and the specific process is as follows: the temperature is raised from the room temperature at the heating rate of 400 ℃/h, and the temperature is kept for 18h, 36h and 48h when the alloy temperature reaches 470 ℃.
Comparative example 6
The ingot casting used in the embodiment 5 is adopted to carry out single-stage homogenization treatment, and the specific process is as follows: the temperature is raised from room temperature at the heating rate of 400 ℃/h, and the temperature is kept for 15h when the alloy temperature reaches 475 ℃.
Comparative example 7
The ingot casting used in the embodiment 5 is adopted for double-stage homogenization treatment, and the specific process is as follows: the temperature is increased from room temperature at the heating rate of 400 ℃/h, the temperature is kept for 12h when the alloy temperature reaches 430 ℃, then the temperature is increased at the heating rate of 100 ℃, and the temperature is kept for 18h, 36h and 48h when the alloy temperature reaches 470 ℃.
Comparative example 8
The ingot casting used in the embodiment 5 is adopted for double-stage homogenization treatment, and the specific process is as follows: the temperature is raised from room temperature at the heating rate of 400 ℃/h, the temperature is kept for 12h when the alloy temperature reaches 430 ℃, then the temperature is raised at the heating rate of 100 ℃, and the temperature is kept for 15h when the alloy temperature reaches 475 ℃.
The alloys after heat treatment of examples 1 to 8 and comparative examples 1 to 8 were subjected to the performance test, and the results are shown in tables 1 and 2.
TABLE 1 effect of redissolution of the second phase in the different homogenization heat treatment processes in the examples and comparative examples
TABLE 2 precipitation results of dispersed phases under different homogenization heat treatment processes in examples and comparative examples
As can be seen from Table 1, the time taken for the homogenization heat treatment method of the present invention is shorter than that of the conventional single-stage or two-stage homogenization heat treatment while ensuring good re-dissolution of the second phase (i.e., 0 endothermic peak area) without overburning.
As can be seen from Table 2, the number density of the dispersed phase obtained by the homogenization heat treatment method of the invention is basically consistent with the result of the two-stage homogenization heat treatment, and is obviously superior to the one-stage homogenization heat treatment.
The homogenization heat treatment method can effectively improve the initial melting temperature of the quaternary phase, realize the rapid redissolution of the quaternary phase, save the heat treatment time and ensure that the size and the number density of the precipitated disperse phase meet the requirements. More importantly, the method has the advantages of simple process control, strong operability and high heat treatment efficiency, can achieve the effect of conventional two-stage homogenization treatment, and is particularly suitable for homogenization treatment of industrial large-scale cast ingots.
Claims (10)
1. A homogenizing heat treatment method for a low-Cu-content 7xxx series aluminum alloy comprises the following steps: (1) a temperature rising stage: the alloy adopts a temperature rise process with the temperature rise rate gradually reduced, so that dispersed phases are uniformly separated out, and the initial melting temperature of an AlZnMgCu phase is increased; (2) and (3) a heat preservation stage: homogenizing and preserving the temperature of the alloy to dissolve the AlZnMgCu phase back.
2. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 1, wherein: the temperature of the 7xxx series alloy is raised from room temperature to 475-485 ℃.
3. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 2, wherein: in the heating process of the 7xxx series alloy, the process that the heating rate is gradually reduced from large to small is an accelerated reduction process.
4. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 3, wherein: the initial heating rate in the heating process is 300-400 ℃/h, and the final heating rate is 2-20 ℃/h.
5. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 4, wherein: in the temperature rise process, the temperature rise rate is 5-50 ℃/h when the temperature is 400-440 ℃.
6. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 5, wherein: in the temperature rise process, the temperature rise time is 2-5 h when the temperature rise rate is 2-20 ℃/h.
7. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 6, wherein: the total heating time is 13-20 h.
8. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 1, wherein: the heat preservation time is 12-18 h.
9. The method of homogenizing heat treatment of a low Cu content 7 xxx-series aluminum alloy according to claim 7, wherein: the method comprises the following specific steps:
(1) a temperature rise stage: the alloy starts to be heated from room temperature at a heating rate of 300-400 ℃/h, and the heating rate is gradually reduced along with the temperature rise; when the alloy temperature is 400-440 ℃, the heating rate is reduced to 5-50 ℃/h; the temperature rise rate is gradually reduced, when the alloy temperature is 465-475 ℃, the temperature rise rate is 2-20 ℃/h, the temperature rise rate is gradually reduced or kept unchanged until the alloy temperature is 475-485 ℃, and the time is 2-5 h; the total time of the heating stage is 13-20 h.
(2) And (3) a heat preservation stage: the alloy is kept warm for 12-18 h at 475-485 ℃.
10. The method of homogenizing heat treatment of a low Cu content 7xxx series aluminum alloy of claim 1, wherein: the Cu content in the 7xxx series alloy is not more than 0.8 wt%, and the Cu/Mg ratio is not more than 0.6.
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| CN117107172A (en) * | 2023-10-24 | 2023-11-24 | 中铝材料应用研究院有限公司 | Method for homogenizing aluminum alloy |
| CN117949450A (en) * | 2024-03-26 | 2024-04-30 | 有研工程技术研究院有限公司 | Method for evaluating homogenization effect of 6xxx series aluminum alloy cast ingot |
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| CN110964993A (en) * | 2019-12-17 | 2020-04-07 | 中铝材料应用研究院有限公司 | Grading homogenization treatment process for high-copper-magnesium-ratio Al-Zn-Mg-Cu-Zr ultrahigh-strength aluminum alloy cast ingot |
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