CN117949278A - Method for evaluating homogenization effect of 7xxx series aluminum alloy cast ingot - Google Patents
Method for evaluating homogenization effect of 7xxx series aluminum alloy cast ingot Download PDFInfo
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- 229910000838 Al alloy Inorganic materials 0.000 title claims abstract description 46
- 238000000034 method Methods 0.000 title claims abstract description 46
- 238000000265 homogenisation Methods 0.000 title claims abstract description 44
- 230000000694 effects Effects 0.000 title claims abstract description 30
- 238000010438 heat treatment Methods 0.000 claims abstract description 29
- 238000005498 polishing Methods 0.000 claims abstract description 29
- 238000002844 melting Methods 0.000 claims abstract description 18
- 238000005530 etching Methods 0.000 claims abstract description 12
- 238000010791 quenching Methods 0.000 claims abstract description 11
- 230000000171 quenching effect Effects 0.000 claims abstract description 11
- 238000000227 grinding Methods 0.000 claims abstract description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 7
- 238000001816 cooling Methods 0.000 claims abstract description 6
- 238000005520 cutting process Methods 0.000 claims abstract description 6
- 238000004321 preservation Methods 0.000 claims abstract description 5
- 238000004364 calculation method Methods 0.000 claims abstract description 4
- 238000002360 preparation method Methods 0.000 claims abstract description 4
- 230000008018 melting Effects 0.000 claims description 10
- 229910003460 diamond Inorganic materials 0.000 claims description 8
- 239000010432 diamond Substances 0.000 claims description 8
- 238000012546 transfer Methods 0.000 claims description 7
- 239000003795 chemical substances by application Substances 0.000 claims description 6
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 claims description 6
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 claims description 6
- 238000004090 dissolution Methods 0.000 claims description 5
- WGLPBDUCMAPZCE-UHFFFAOYSA-N Trioxochromium Chemical compound O=[Cr](=O)=O WGLPBDUCMAPZCE-UHFFFAOYSA-N 0.000 claims description 4
- 238000012545 processing Methods 0.000 claims description 3
- 230000000877 morphologic effect Effects 0.000 claims description 2
- 230000005496 eutectics Effects 0.000 abstract description 8
- 230000000052 comparative effect Effects 0.000 description 17
- 239000000956 alloy Substances 0.000 description 9
- 229910045601 alloy Inorganic materials 0.000 description 8
- 238000011156 evaluation Methods 0.000 description 7
- 238000004458 analytical method Methods 0.000 description 5
- 238000004519 manufacturing process Methods 0.000 description 4
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 239000000203 mixture Substances 0.000 description 3
- 238000005070 sampling Methods 0.000 description 3
- 238000010583 slow cooling Methods 0.000 description 3
- 239000003153 chemical reaction reagent Substances 0.000 description 2
- 239000003086 colorant Substances 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 238000010183 spectrum analysis Methods 0.000 description 2
- 241001085205 Prenanthella exigua Species 0.000 description 1
- 230000003044 adaptive effect Effects 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 210000001787 dendrite Anatomy 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000010191 image analysis Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000004901 spalling Methods 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G—PHYSICS
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Abstract
The invention discloses a method for evaluating homogenization effect of a 7xxx aluminum alloy cast ingot. The method comprises the following steps: (1) Cutting a cross section slice from the 7xxx series aluminum alloy cast ingot subjected to homogenization heat treatment, and cutting a sample at a characteristic position on the slice; (2) And (3) carrying out short-time redissolution treatment on the sample, wherein the treatment system is as follows: heat preservation treatment is carried out for 5-50 min at the temperature of 450-485 ℃, and water quenching and cooling are carried out at room temperature; (3) Preparing a metallographic sample from the sample subjected to short-time redissolution treatment, wherein the preparation steps comprise grinding, rough polishing, fine polishing and etching, and the etching time is 5-25 s; (4) taking a photograph under a metallographic microscope; (5) And evaluating the homogenization effect of the cast ingot according to the statistical calculation result of the residual low-melting-point second phase in the shot photo. The method can accurately distinguish the low-melting eutectic phase and the indissolvable phase in the 7xxx aluminum alloy, evaluates the homogenization effect of the cast ingot according to the area fraction of the low-melting eutectic phase, guides the homogenization heat treatment process of the cast ingot, and has the characteristics of simplicity in operation, economy and applicability.
Description
Technical Field
The invention relates to the field of nonferrous metal heat treatment processes, in particular to a method for evaluating homogenization effect of a 7xxx aluminum alloy cast ingot.
Background
The 7xxx series aluminum alloy has excellent comprehensive performance, is widely applied to the fields of aerospace and the like, and brings higher requirements to the performance of the 7xxx series aluminum alloy along with continuous progress of China in the fields of aerospace and the like.
The 7xxx aluminum alloy cast ingot is generally prepared by adopting a semi-continuous casting mode, has obvious segregation characteristics and tissue non-uniformity, can eliminate dendrite segregation and fully dissolve unbalanced phases by adopting good homogenization heat treatment, gradually homogenizes the concentration of solute, and obtains an ideal homogenization heat treatment tissue, thus preparing for subsequent deformation processing and heat treatment. If the homogenization heat treatment is imperfect, the second phase with coarse size of the residual part in the structure can obviously reduce the plasticity of the alloy and is easy to crack in the deformation process; in addition, the remaining second phase in the structure can also affect the properties of the finished aluminum alloy material, including spalling corrosion, fracture toughness, and the like.
At present, the method for evaluating the homogenization heat treatment structure of the 7xxx aluminum alloy ingot does not have uniform knowledge, and standard measurement standards are standardized for the quality and the lack of the homogenization heat treatment effect, so that a clear evaluation method for judging the homogenization heat treatment effect of the aluminum alloy ingot is very necessary.
Disclosure of Invention
The invention aims to provide a method for evaluating homogenization effect of a 7xxx aluminum alloy ingot, which is characterized in that a metallographic method is used for intuitively judging the number of low-melting eutectic phases in the ingot according to morphology and color differences of low-melting eutectic phases and indissolvable phases which are easy to remain in a homogenization heat treatment ingot, the homogenization heat treatment effect of the ingot is evaluated, and regulation and control of a homogenization heat treatment system of the 7xxx aluminum alloy ingot in actual production are guided.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a method for evaluating homogenization effect of 7xxx series aluminum alloy ingots comprises the following steps:
(1) Cutting a cross section slice from a 7xxx aluminum alloy round ingot or a flat ingot subjected to homogenization heat treatment, and selecting 1-5 characteristic positions from the center to the edge along the diameter (D) direction of the round ingot or the thickness (T) direction of the flat ingot on the slice to cut samples with the minimum size of more than 5 mm;
(2) And (3) carrying out short-time redissolution treatment on the sample, wherein the treatment system is as follows: heat preservation treatment is carried out for 5-50 min at the temperature of 450-485 ℃, and water quenching and cooling are carried out at room temperature;
(3) Preparing a metallographic sample from the sample subjected to short-time redissolution treatment, wherein the preparation steps comprise grinding, rough polishing, fine polishing and etching, and the etching time is 5-25 s;
(4) Observing the prepared metallographic sample by adopting a metallographic microscope, uniformly shooting by selecting proper magnification in a range of 50-1000 times, randomly selecting shooting fields, and shooting at least 10 photos with the same magnification;
(5) And (3) according to the morphological characteristics of the residual second phase, carrying out statistical calculation on the residual quantity of the low-melting-point AlZnMgCu quaternary phases in the metallographic obtained in the step (4) by utilizing image processing analysis software, and evaluating the homogenization effect of the cast ingot.
Further, in the step (1), the characteristic positions are selected from 3 equidistant positions (shown in fig. 1) of the center, the D/4 position and the edge of the cross section slice of the round ingot, or 3 equidistant positions (shown in fig. 2) of the center, the T/4 position and the edge of the cross section slice of the flat ingot along the thickness direction of the flat ingot, and 8-25 mm square samples are cut.
Further, in the step (1), the characteristic position is selected from the center and the D/4 position of the cross section slice of the round ingot, or the center and the T/4 position of the cross section slice of the flat ingot along the thickness direction of the flat ingot.
Further, in the step (2), the quenching and cooling transfer time of the short-time redissolution treatment is less than 60s.
In the short-time dissolution treatment process, when the temperature is too low, the dissolution and precipitation phases in the cast ingot are not completely dissolved back, and when the temperature is too high, the low-melting-point eutectic phases in the cast ingot are dissolved back and even are burnt excessively, so that the accuracy of judging the homogenization heat treatment effect of the cast ingot is affected. Further preferably, the short-time redissolution treatment temperature is 465-475 ℃, the heat preservation time is 25-35 min, and the transfer time of quenching and cooling is less than 15s.
Further, in step (3), the polishing paste or polishing agent used for polishing is a diamond polishing paste or polishing agent.
Further, in the step (3), chromic acid solution is selected as etching solution, the ratio of HF to HNO 3+83mL H2O+3g CrO3 is 1mL and 16mL, and the etching time is 5-15 s.
Further, in the step (4), the metallographic photograph is preferably 100-500 times as large as the observation magnification, wherein the 100-times magnification is selected to take not less than 10, the 200-times magnification is selected to take not less than 10, and the 500-times magnification is selected to take not less than 15.
Further, in the step (5), the low-melting eutectic phase is AlZnMgCu quaternary phase, black is shown, and other coarse second phases are light gray or reddish brown in appearance and are indissolvable phases. Thus, identification of the low melting AlZnMgCu quaternary phase is distinguished by its black, light gray or reddish brown morphology of the other coarse second phase.
The invention has the advantages that:
According to the invention, the second phase which is separated and separated out in the slow cooling process of the 7xxx aluminum alloy cast ingot after the homogenization heat treatment is eliminated by adopting the adaptive short-time redissolution treatment, so that the actual residual condition of the second phase of the cast ingot in the industrialized production process when the homogenization heat treatment is finished is accurately reduced, and the scientificity of the evaluation of the homogenization heat treatment effect of the cast ingot is ensured; according to the difference of the shapes of the low-melting eutectic phase and the indissolvable phase in the 7xxx aluminum alloy cast ingot and the characteristic that the two phases show different characteristic colors after specific grinding and polishing and etching (the second phase distinguishing schematic diagram in the 7xxx aluminum alloy homogenizing heat treatment cast ingot is shown in fig. 3), the second phase in the cast ingot is accurately distinguished, and therefore the homogenizing effect of the 7xxx aluminum alloy cast ingot can be accurately, efficiently and conveniently judged according to the statistical calculation result of the quantity of the low-melting eutectic phase in the cast ingot.
The invention innovatively provides a method for intuitively judging the homogenizing effect of a 7xxx series aluminum alloy cast ingot by a metallographic method, which can guide the homogenizing heat treatment process of the cast ingot and has the characteristics of simplicity in operation, economy and applicability.
Drawings
FIG. 1 is a schematic drawing of a round ingot sampling of aluminum alloy.
FIG. 2 is a schematic drawing of sampling an aluminum alloy flat ingot.
FIG. 3 is a schematic illustration of a second phase distinction in a 7xxx series aluminum alloy homogenized heat treated ingot.
Fig. 4 is a typical 200-fold metallographic photograph of a 7050 flat cast ingot sample in example 1.
FIG. 5 is a typical 500-fold scanning electron micrograph of a 7050 flat cast ingot sample of comparative example 1.
Fig. 6 is a typical 200-fold metallographic photograph of a 7050 flat cast ingot sample in comparative example 2.
Fig. 7 is a typical 200-fold metallographic photograph of a 7050 flat cast ingot sample in comparative example 3.
Fig. 8 is a typical 200-fold metallographic photograph of a 7055 round ingot sample in example 2.
Fig. 9 is a typical 200-fold metallographic photograph of a 7055 round ingot sample in comparative example 4.
Fig. 10 is a typical 200-fold metallographic photograph of a 7055 round ingot sample in comparative example 5.
Fig. 11 is a typical 200-fold metallographic photograph of a 7055 round ingot sample in example 3.
Detailed Description
The invention is further described below with reference to the drawings and examples. It should be emphasized that the following description is merely exemplary in nature and is in no way intended to limit the scope of the invention or its applications.
Fig. 1 and 2 show examples of sampling methods in the method of the invention, respectively. As shown in fig. 1, a cross-sectional slice with a certain thickness (thickness range D1 is 10-20 mm) is cut from an aluminum alloy round ingot, and samples are respectively cut from the cross-sectional slice at three characteristic positions of a center position 1, a position 2 away from the center D/4, a position 3 at the slicing edge along the diameter D direction.
As shown in fig. 2, a cross-sectional slice with a certain thickness (thickness range d2 is 10-20 mm) is cut from an aluminum alloy flat ingot, and samples are respectively cut from three characteristic positions, namely a center position 11, a distance center T/4 position 12, a slice edge position 13 and the like, along the thickness T direction of the flat ingot slice on the slice.
Example 1
The invention is applied to commercial 7050 aluminum alloy flat cast ingots subjected to homogenization heat treatment, and the nominal composition range (mass fraction,%): si:0.12, fe:0.15, cu:2.0 to 2.6, mn:0.10, mg:1.9 to 2.6, zn:5.7 to 6.7, cr:0.04, zr:0.08 to 0.15, ti:0.06, the balance Al and unavoidable other impurities, and the specification of the flat cast ingot is 400mm multiplied by 1320mm. A cross-section specimen having a thickness of 10mm was cut on the acceptable section of the flat ingot, and 3 specimens having a side length of 10mm were cut as shown in FIG. 2. The sample is kept at 470 ℃ for 30min, quenched with water at room temperature, and the quenching transfer time is 10s. Grinding the sample subjected to the short-time heat treatment on 240# to 7000# abrasive paper, and then carrying out rough polishing and fine polishing by using diamond polishing paste with the granularity of 0.5 mu m and diamond polishing agent with the granularity of 0.05 mu m. The polished sample was etched in chromic acid solution for 10 seconds and then dried by rinsing with alcohol. The prepared metallographic specimens were observed under a metallographic microscope, the field of view was randomly selected at 200 times magnification, and 10 metallographic photographs were taken for each specimen, and typical photographs are shown in fig. 4. The percentage of area of the black AlZnMgCu quaternary phase in the metallographic was counted using Image Pro Plus Image analysis processing software and the average value of the statistics for each sample is recorded in Table 1.
TABLE 1
Comparative example 1
The invention is applied to a 7050 aluminum alloy flat cast ingot subjected to homogenization heat treatment, and the nominal composition range (mass percent) of the aluminum alloy flat cast ingot is as follows: si:0.12, fe:0.15, cu:2.0 to 2.6, mn:0.10, mg:1.9 to 2.6, zn:5.7 to 6.7, cr:0.04, zr:0.08 to 0.15, ti:0.06, the balance Al and unavoidable other impurities, and the specification of the flat cast ingot is 400mm multiplied by 1320mm. A cross-section specimen having a thickness of 10mm was cut on the acceptable section of the flat ingot, and 3 specimens having a side length of 10mm were cut as shown in FIG. 2. The sample is kept at 470 ℃ for 30min, quenched with water at room temperature, and the quenching transfer time is 10s. Grinding the sample after the short-time redissolution treatment on 240# to 7000# abrasive paper, and then carrying out rough polishing and fine polishing by using diamond polishing paste with the granularity of 0.5 mu m and diamond polishing agent with the granularity of 0.05 mu m. And (5) washing the polished sample with alcohol and drying. And observing and photographing the polished samples by adopting a scanning electron microscope, distinguishing and marking the second phases in the field of view one by utilizing an energy spectrum analysis device carried by the electron microscope, and randomly taking 80 photos of each sample under the condition of selecting 500 times of magnification suitable for distinguishing the observation and the energy spectrum analysis (so as to ensure that the analysis statistical area of the electron microscope photos is basically consistent with that of the metallographic photos of the embodiment 1), wherein a typical photo is shown in fig. 5. The area percentage of AlZnMgCu quaternary phases with bright white color in the photographed scanning electron microscope photograph was counted, and the average value of the counted results of each sample is recorded in table 2.
TABLE 2
This comparative example is different from example 1 in that the polished sample was not etched while the sample was observed by a scanning electron microscope. As can be seen by comparing the data in tables 1 and 2, the statistical result is basically the same as the statistical result by using the scanning method, and the accuracy of the method for phase identification and the reliability of the statistical result are reflected. Moreover, the metallographic analysis method adopted in the embodiment 1 avoids the problems of inconvenient use, high cost, short time consumption, small field of view and the like of scanning electron microscope analysis, and can conveniently and rapidly realize the evaluation of the homogenization effect of the cast ingot.
Comparative example 2
This comparative example is different from example 1 in that after the sample was cut, a short-time dissolution treatment was not performed, and the other steps were the same as in example 1, and a typical metallographic photograph was taken as shown in fig. 6. The area percentage of black AlZnMgCu quaternary phase in the metallographic photograph was counted, and the average value of the counted results of each sample is recorded in table 3.
TABLE 3 Table 3
When the results of table 3 and table 1 are compared, the area percentage of the low-melting second phase counted in this comparative example is significantly higher than that counted in example 1, because the result of counting the number of the desolvated phases in the alloy which has not been subjected to the short-time re-dissolution treatment is shown in the counting process, as shown in fig. 6.
Comparative example 3
The 7050 aluminum alloy flat ingot slices (the sizes are 400mm multiplied by 1320mm multiplied by 80 mm) which are not subjected to homogenization heat treatment are adopted in the comparative example, and the 7050 aluminum alloy flat ingot slices are the same ingot as used in the example 1 and are positioned close to each other. And carrying out homogenization heat treatment with the same system on the ingot slice, and immediately carrying out water quenching treatment after completion, so that the generation of desolventized phase is avoided, and the actual residual condition of the second phase is maintained. The sample was cut without a short-time redissolution treatment, and the rest of the procedure was the same as in example 1. A typical metallographic photograph taken is shown in fig. 7. The area percentage of black AlZnMgCu quaternary phase in the metallographic photograph was counted, and the average value of the counted results of each sample is recorded in table 4.
TABLE 4 Table 4
The data of table 1, in contrast to the data of table 4, are consistent therewith, further demonstrating the reliability of the present method in terms of residual phase analysis and statistics after homogenization of the ingot. The data of the method are obviously lower than the data of the table 3, and further show that the short-time redissolution treatment adopted in the method can not influence the statistical result of the area percentage of the low-melting-point second phase in the alloy due to the increase of the heat treatment process, and avoid the deviation of the relative evaluation result caused by the desolventizing out generated in the slow cooling process of the production ingot, thereby further proving the accuracy of the method.
Example 2
The invention is applied to a 7055 aluminum alloy round ingot subjected to homogenization heat treatment, and the nominal composition range (mass percent) of the aluminum alloy round ingot is as follows: si:0.12, fe:0.15, cu:2.0 to 2.6, mn:0.10, mg:1.9 to 2.6, zn:5.7 to 6.7, cr:0.04, zr:0.08 to 0.15, ti:0.06 percent, the balance of Al and unavoidable other impurities, and the specification of the round ingot is phi 560mm. A cross-section specimen having a thickness of 20mm was cut on the round ingot passing section, and 3 specimens having a side length of 12mm were cut as shown in FIG. 1. The sample is incubated at 465 ℃ for 35min, quenched with water at room temperature, and the quenching transfer time is 12s. Grinding the sample subjected to the short-time redissolution treatment on 240# to 7000# abrasive paper, and then carrying out rough polishing and fine polishing by using diamond polishing paste with the granularity of 0.5 mu m and diamond polishing agent with the granularity of 0.05 mu m. The polished sample was etched in chromic acid solution for 8 seconds and then dried by rinsing with alcohol. The prepared metallographic specimens were observed under a metallographic microscope, the fields of view were randomly selected at 200 times magnification, 15 metallographic photographs were taken for each specimen, and typical photographs are shown in fig. 8. The area percentage of the black AlZnMgCu quaternary phase in the metallographic photograph was counted, and the average value of the counted results of each sample is recorded in table 5.
TABLE 5
Comparative example 4
The difference between this comparative example and example 2 is that the sample after polishing is etched in a Keller reagent in the following proportions: 1mLHF+1.5mL HCl+2.5mL HNO 3+95mL H2 O, the other steps are the same as in example 2, and a typical metallographic photograph taken is shown in FIG. 9. The area percentage of the black AlZnMgCu quaternary phase in the metallographic photograph was counted, and the average value of the counted results of each sample is recorded in table 6.
TABLE 6
Comparing the statistics of tables 5 and 6, it was found that the statistics of the area of the low melting second phase of the alloy etched with the Keller reagent was significantly higher than that of the present method, because the partially insoluble Al 2 CuMg phases in the alloy exhibited the same color as the low melting AlZnMgCu quaternary phase, and the statistics of these insoluble Al 2 CuMg phases were performed as the low melting AlZnMgCu quaternary phase during the statistics, thus increasing the percentage of area of the low melting second phase.
Comparative example 5
The difference between this comparative example and example 2 is that after polishing, the sample is etched in a chromic acid solution for 30 seconds, and the other steps are the same as in example 2, and a typical metallographic photograph taken is shown in fig. 10. The area percentage of the black AlZnMgCu quaternary phase in the metallographic photograph was counted, and the average value of the counted results of each sample is recorded in table 7.
TABLE 7
Comparing the statistics of tables 5 and 7, it was found that the statistics of the area of the low melting point second phase of the alloy when the sample was etched in chromic acid solution for 30 seconds was significantly higher than that of the present method because the etching time was prolonged and the partially insoluble Al 2 CuMg phase and the Fe-rich phase of the alloy exhibited the same color as the low melting point AlZnMgCu quaternary phase, and the statistics of these insoluble Al 2 CuMg phase and Fe-rich phase were performed as the low melting point AlZnMgCu quaternary phase during the statistics, thus increasing the area percentage of the low melting point second phase.
Example 3
A7055 aluminum alloy round ingot used in example 2 was selected, a sample with a side length of 12mm was cut from two characteristic positions at the center of the cross section of the ingot and at the position D/4, and a typical metallographic photograph taken in the same manner as in example 2 was shown in FIG. 11. The area percentage of the black AlZnMgCu quaternary phase in the metallographic photograph was counted, and the average value of the counted results of each sample is recorded in table 8.
TABLE 8
Comparing the statistical results of tables 8 and 5, the statistical results of cutting 2 samples at the center of the cross section of the ingot and at the D/4 position are basically the same as the statistical results of cutting 3 samples at the center of the cross section of the ingot, at the D/4 position and at the edge, and the statistical results of selecting 2 characteristic positions of the center and the D/4 position of the cross section of the ingot are shown to have good representativeness, so that accurate judgment on the homogenization effect of the ingot can be realized.
By comprehensively analyzing the above examples and comparative examples, the preparation of the metallographic specimen is carried out according to the method, and the low-melting-point AlZnMgCu quaternary phase and the indissolvable Al 2 CuMg phase and the Fe-rich phase in the 7xxx aluminum alloy can be accurately distinguished by observing the colors of the phases in the metallographic photograph; the short-time redissolution treatment is carried out by adopting the method, so that the influence of desolventizing out relative to the evaluation of the actual homogenization effect of the cast ingot in the slow cooling process after the homogenization heat treatment of the cast ingot is finished can be eliminated; by using the method, the homogenization effect of the 7xxx aluminum alloy cast ingot can be directly evaluated by adopting a metallographic microscope, observation by a scanning electron microscope is not needed, the result is accurate, the equipment conditions required by the evaluation of the homogenization effect of the cast ingot are reduced, the analysis and evaluation efficiency is remarkably improved, and the method is very helpful for directly guiding the adjustment of the actual production process and the regulation and control of the alloy structure.
Claims (9)
1. A method for evaluating homogenization effect of a 7xxx series aluminum alloy ingot, which is characterized by comprising the following steps:
(1) Cutting a cross section slice from a 7xxx aluminum alloy round ingot or a flat ingot subjected to homogenization heat treatment, and selecting 1-5 characteristic positions from the center to the edge along the diameter D direction of the round ingot or the thickness T direction of the flat ingot on the slice to cut a sample with the minimum size of more than 5 mm;
(2) And (3) carrying out short-time redissolution treatment on the sample, wherein the treatment system is as follows: heat preservation treatment is carried out for 5-50 min at the temperature of 450-485 ℃, and water quenching and cooling are carried out at room temperature;
(3) Preparing a metallographic sample from the sample subjected to short-time redissolution treatment, wherein the preparation steps comprise grinding, rough polishing, fine polishing and etching, and the etching time is 5-25 s;
(4) Observing the prepared metallographic sample by adopting a metallographic microscope, uniformly shooting by selecting proper magnification in a range of 50-1000 times, randomly selecting shooting fields, and shooting at least 10 photos with the same magnification;
(5) And (3) according to the morphological characteristics of the residual second phase, carrying out statistical calculation on the number of the low-melting-point AlZnMgCu quaternary phases in the metallographic obtained in the step (4) by utilizing image processing analysis software, and evaluating the homogenization effect of the cast ingot.
2. The method for evaluating homogenization effects of 7xxx aluminum alloy ingots according to claim 1, wherein in the step (1), the characteristic positions are selected from 3 equidistant positions of the center, the D/4 position and the edge of a cross section slice of a round ingot, or 3 equidistant positions of the center, the T/4 position and the edge of a cross section slice of a flat ingot in the thickness direction of the flat ingot, and 8-25 mm square samples are cut.
3. The method for evaluating homogenizing effect of a 7xxx series aluminum alloy ingot according to claim 1, wherein in the step (1), the characteristic position is selected from a center of a cross section slice of a round ingot and a D/4 position, or a center of a cross section slice of a flat ingot and a T/4 position in a thickness direction of the flat ingot.
4. The method for evaluating the homogenizing effect of a 7xxx series aluminum alloy ingot according to claim 1, wherein in the step (2), the transfer time of quenching is less than 60s.
5. The method for evaluating homogenization effects of 7xxx series aluminum alloy ingots according to claim 1, wherein in the step (2), the short-time dissolution treatment temperature is 465-475 ℃, the heat preservation time is 25-35 min, and the transfer time of quenching and cooling is less than 15s.
6. The method for evaluating homogenization effects of 7xxx aluminum alloy ingots according to claim 1, wherein in the step (3), diamond polishing paste or polishing agent is selected for polishing, chromic acid solution is selected as etching solution, the ratio of 1mL HF+16mL HNO 3+83mL H2O+3g CrO3 is adopted, and the etching time is 5-15 s.
7. The method for evaluating a homogenizing effect of a 7xxx series aluminum alloy ingot according to claim 1, wherein in the step (4), a magnification of 100 to 500 times is observed.
8. The method for evaluating homogenization efficacy of a 7xxx series aluminum alloy ingot according to claim 7, wherein 100-fold magnification shots are selected to be not less than 10, 200-fold magnification shots are selected to be not less than 10, and 500-fold magnification shots are selected to be not less than 15.
9. The method for evaluating the homogenizing effect of a 7xxx series aluminum alloy ingot according to claim 1, wherein in the step (5), the identification of the low melting point AlZnMgCu quaternary phase is distinguished by the morphology feature that it is black, and the other coarse second phase is light gray or reddish brown.
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