A method for preparing and evaluating center-layer segregation samples of 8011 aluminum alloy cast-rolled strip.

Abstract

This invention discloses a method for preparing and evaluating center layer segregation samples of 8011 aluminum alloy cast-rolled strip, including on-site sampling, sample preparation, metallographic analysis, and center layer segregation evaluation. This invention standardizes the technical steps of sampling, sample preparation, metallographic analysis, and center layer segregation evaluation. Through standardized operating procedures and testing methods, it comprehensively analyzes the influence of the proportion of precipitated phase area in the crystallization centerline region of the cast-rolled strip, the influence of segregation layer particle size, and the influence of the segregation layer's limiting length on the strip quality. The center layer segregation value is calculated using a formula, and the severity of center layer segregation is evaluated by comparing it with a standard range. Compared with conventional methods that use low-magnification microstructure analysis or rely on experience to roughly judge the severity of center layer segregation in the strip, this method improves the accuracy and reliability of the analysis and evaluation results for center layer segregation samples.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aluminum alloy cast-rolled strip blank structure detection and analysis, and particularly relates to a 8011 aluminum alloy cast-rolled strip blank center layer segregation sample preparation and evaluation method. BACKGROUND

[0002] The center layer position of the aluminum alloy cast-rolled strip blank is farthest from the roll surface, has a small cooling speed and a slow solidification speed, and due to the "channel effect", liquid aluminum rich in alloying elements is "squeezed into" the center hot area from the surface layer area under the action of the roll pressure, the alloying elements and impurity elements are gathered in the center area, eutectic is formed in the middle after complete solidification, and peritectic can also appear locally, thereby forming center layer segregation, which reduces the mechanical properties of the cast-rolled strip blank and affects the subsequent processing process, and is a common defect of the cast-rolled strip blank.

[0003] The center layer segregation exists in different degrees in each system product due to different alloy characteristics and cast-rolling processes, on-site technical personnel generally focus on the stability of production, and the center layer segregation defect is more analyzed by using macrostructure or roughly judged by experience, a systematic research on the center layer segregation problem of each system product is not carried out, and a standardized test method is not used to accurately quantify the center layer segregation defect. Different products have different processing processes and purposes, and the sensitivity to the center layer segregation is also different, and it is generally considered that the aluminum foil product with a thickness less than 0.1 mm of the final product is more affected. In order to accurately evaluate the influence of the center layer segregation on the quality of the strip blank, a standardized and standardized quantitative analysis method is urgently needed in the industry. SUMMARY

[0004] The purpose of the application is to provide a 8011 aluminum alloy cast-rolled strip blank center layer segregation sample preparation and evaluation method to quantitatively analyze the severity of the center layer segregation defect of the cast-rolled strip blank.

[0005] In order to achieve the above purpose, the technical scheme adopted by the application is:

[0006] A 8011 aluminum alloy cast-rolled strip blank center layer segregation sample preparation and evaluation method, comprising the following steps:

[0007] S1, on-site sampling:

[0008] According to the on-site production condition, after the stability of each cast-rolling production parameter, the 8011 aluminum alloy cast-rolled strip blank sample plate capable of representing the current production state is cut on line;

[0009] S2, sample preparation:

[0010] The cast-rolled strip sample obtained in step S1 is cut into sample blocks for sample preparation, and the sample blocks include 5 blocks, which are respectively taken from 100 mm away from both ends of the cast-rolled strip sample, 1 / 2 of the length of the cast-rolled strip sample and 1 / 4 of the length of the cast-rolled strip sample away from both ends of the cast-rolled strip sample. The specific sampling positions are shown in Figure 1 The size of the sample block is 15 mm x 15 mm, the sample block is completed by the sample mounting machine, and the sample mounting sample is polished by metallographic water sandpaper and mechanically polished, and finally prepared by electrolytic polishing;

[0011] S3, metallographic analysis:

[0012] The sample prepared in step S2 is observed and analyzed by an optical microscope, the most serious composition segregation area near the crystallization center line of the cast-rolled strip sample is selected for metallographic photography, and the center segregation organization length L of the largest size in the field of view is measured by using a metallographic analysis software;

[0013] S4, center layer segregation evaluation:

[0014] The metallographic picture obtained in step S3 is processed by using the ImageJ metallographic analysis software, the Threshold value in the ImageJ metallographic analysis software is set to 150-160, the average size S of the precipitated phase in the field of view and the area ratio A of the precipitated phase are calculated, and the L obtained in step S3 is combined to obtain the quantitative center layer segregation value η according to the calculation formula as follows:

[0015] η=ε·A+θ·S+ω·L

[0016] Wherein, η is the center layer segregation value;

[0017] ε is the area ratio of the precipitated phase, and the value is 42;

[0018] A is the area ratio of the center layer segregation, %;

[0019] θ is the segregation layer particle size influence factor, and the value is 99;

[0020] S is the average particle size of the segregation layer, μm;

[0021] ω is the segregation layer limit length influence factor, and the value is 0.3;

[0022] L is the limit length of the segregation layer, μm;

[0023] The center layer segregation values η of the obtained sample blocks are averaged to obtain the center layer segregation value of the analyzed cast-rolled strip sample:

[0024] When the center layer segregation value η is 0-30, it is a slight defect; when the center layer segregation value η is 31-60, it is a general defect; when the center layer segregation value η is 61-80, it is a heavier defect; and when the center layer segregation value η is above 81, it is a serious defect.

[0025] In order to further realize the present application, the sample block in S2 is left with a longitudinal section observation surface after being individually mounted, sample information is marked on the side of the sample, and the mounting material at the tail of the sample is cut off by a cutting machine, so that the sample has sample block metal surfaces exposed at both ends, and a sample to be ground is obtained.

[0026] In order to further realize the present application, the metallographic water sand paper polishing in S2 uses 400#, 800# and 1200# water sand paper in sequence to polish the sample to be ground, and after the mechanical polishing, a polishing cloth is used in combination with 0.25um diamond polishing agent to obtain a metallographic sample with bright and no obvious scratches, and after the polishing is completed, the sample observation surface is washed with clean water and dried.

[0027] In order to further realize the present application, the electrolytic polishing electrolytic solution in S2 uses an ethanol perchlorate solution, and a recommended electrolytic polishing device in the national standard GB / T3246.1-2012 is used, the exposed metal at the tail of the sample is connected to the loop of the electrolytic polishing device through a copper foil tape, the polishing voltage is 20-25V, the polishing time is 5-10S, the polishing current is 0.3A-0.8A, and after the electrolytic polishing, the sample observation surface is cleaned using a nitric acid solution.

[0028] In order to further realize the present application, the volume ratio of perchloric acid and ethanol in the ethanol perchlorate solution is 1:9, and the volume ratio of concentrated nitric acid and water in the nitric acid solution is 1:1.

[0029] In order to further realize the present application, the observation and analysis in S3 uses a 50 times field of view to browse the distribution of the center layer segregation layer near the center line of the sample crystal center, selects a region with the most concentrated segregation structure as a photographing region, takes a metallographic picture required for analysis under a 200 times field of view, selects one most representative picture for each sample, the picture size is 2560*1920 pixels, and the largest size of the precipitated phase length in the field of view region is measured by using a metallographic measurement software carried by a microscope, and L is obtained.

[0030] The present application has the following beneficial effects compared with the prior art:

[0031] The application standardizes the technical links of sampling, sample preparation, metallographic analysis and center layer segregation evaluation, comprehensively analyzes the influence of the area ratio of precipitated phase in the crystallization center line area of the cast-rolled strip blank, the influence of the segregation layer granularity and the influence of the limit length of the segregation layer on the quality of the strip blank through standardized operation processes and detection methods, calculates the center layer segregation value through a formula, and compares the center layer segregation value with a standard range to evaluate the severity of the center layer segregation. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 It is a schematic diagram of sampling position in the application. DETAILED DESCRIPTION

[0033] The application will be further described in combination with the drawings and specific embodiments.

[0034] A center layer segregation sample preparation and evaluation method for 8011 aluminum alloy cast-rolled strip blank, characterized in that it comprises the following steps:

[0035] S1, on-site sampling:

[0036] According to the on-site production condition, after the stability of various cast-rolling production parameters, the 8011 aluminum alloy cast-rolled strip blank sample board representing the current production state is cut on line;

[0037] S2, sample preparation:

[0038] The cast-rolled strip sample obtained in step S1 is cut into sample blocks after sample preparation, the sample blocks include 5 blocks, which are respectively taken from 100 mm away from both ends of the cast-rolled strip sample (wherein one end close to the operation side is marked as WS, and one end close to the transmission side is marked as DS), 1 / 2 of the length of the cast-rolled strip sample (marked as Mid), and 1 / 4 of the length of the cast-rolled strip sample away from both ends (wherein one end close to the operation side is marked as 1 / 4 WS, and one end close to the transmission side is marked as 1 / 4 DS), the size of the sample block is 15 mm x 15 mm, the sample block is individually inlaid after leaving a longitudinal section observation surface, the sample information is marked on the side of the sample, and the inlaid material at the tail of the sample is cut off by a cutting machine, so that the sample has sample block surfaces exposed at both ends, obtaining a sample to be ground. The sample to be ground is polished with 400#, 800# and 1200# metallographic sandpaper in turn, and then polished mechanically, and then polished with a cloth and 0.25um diamond polishing agent to obtain a bright metallographic sample without obvious scratches. After polishing, the sample observation surface is washed with water and dried, and finally the sample preparation is completed by electrolytic polishing, the electrolytic solution for electrolytic polishing is hydrochloric acid ethanol solution (1+9), the polishing voltage is 20-25V, the polishing time is 5-10S, the polishing current is 0.3A-0.8A, and the sample observation surface is cleaned with nitric acid solution (1+1) after electrolytic polishing;

[0039] S3, metallographic analysis:

[0040] The sample prepared in step S2 is observed and analyzed by an optical microscope, the observation and analysis uses 50 times field of view to browse the distribution of the center layer segregation layer near the center line of the sample crystal, selects the area where the segregation structure is most concentrated as the photographing area, takes the metallographic picture required for analysis under 200 times field of view, selects 1 most representative picture for each sample, the picture size is 2560x1920 pixels, and the largest size of the precipitated phase length in the field of view is measured by using the metallographic measurement software carried by the microscope to obtain L, and the most serious composition segregation area near the center line of the cast-rolled strip sample is selected for metallographic photography, and the largest size of the center segregation structure phase length L in the field of view is measured by using the metallographic analysis software;

[0041] S4, center layer segregation evaluation:

[0042] The metallographic picture obtained in step S3 is processed by using ImageJ metallographic analysis software, the Threshold value in the ImageJ metallographic analysis software is set to 150-160, the average precipitated phase size S and the precipitated phase area ratio A in the field of view are calculated, and the L obtained in step S3 is combined to obtain the quantitative center layer segregation value η according to the calculation formula as follows:

[0043] η=ε·A+θ·S+ω·L

[0044] η is the center layer segregation value;

[0045] ε is the area ratio of precipitated phase, and the value is 42;

[0046] A is the area ratio of the center layer segregation, %;

[0047] θ is the particle size influence factor of the segregation layer, and the value is 99;

[0048] S is the average particle size of the secondary phase of the segregation layer, μm;

[0049] ω is the limiting length influence factor of the segregation layer, and the value is 0.3;

[0050] L is the limiting length of the segregation layer, μm;

[0051] The center layer segregation value η of each sample block is averaged to obtain the center layer segregation value of the analyzed cast rolling strip, and the calculation formula is as follows:

[0052] η Av =(η WS +η 1 / 4WS +η Mid +η 1 / 4DS +η DS ) / 5

[0053] When the center layer segregation value is 0-30, it is a slight defect, when the center layer segregation value is 31-60, it is a general defect, when the center layer segregation value is 61-80, it is a heavier defect, and when the center layer segregation value is above 81, it is a serious defect.

[0054] Example 1:

[0055] S1. On-site sampling: according to the on-site production situation, after the stability of various cast rolling production parameters, the 8011 aluminum alloy cast rolling strip sample plate representing the current production state is cut on-line, the width is 100mm along the rolling direction, and the position information of the operation side (WS) and the driving side (DS) is accurately marked on the upper plate. The cutting tool is a hydraulic shear on-line of the casting and rolling machine;

[0056] S2. Sample preparation: the sample plate obtained in step S1 is cut, and the specific sampling position of the cast rolling strip sample plate is as follows Figure 1As shown, the sample width and length are 15 mm x 15 mm, and the sample surface is marked with WS, 1 / 4WS, Mid, 1 / 4DS, DS position information, respectively, and the cutting tool is a cutting machine. The cut sample is separately inlaid to leave a longitudinal section observation surface, the sample information is marked on the side of the sample, and the inlaid material at the tail of the sample is cut off by the cutting machine, so that the both ends of the sample have sample metal surface exposed, and the sample to be ground is obtained. The sample is polished with 400#, 800#, and 1200# water sandpaper in turn, and then mechanically polished with a polishing cloth and 0.25um diamond polishing agent, to obtain a bright metallographic sample without obvious scratches. After polishing, the sample observation surface is washed with water and dried to prevent the sample from corroding. The scratch-free metallographic sample obtained by mechanical polishing is electrolytically polished by the electrolytic polishing device recommended in the national standard GB / T3246.1-2012, the solution is high-chloric acid ethanol solution (1+9), the polishing voltage is 20V, the polishing time is 10S, and the peak value of the polishing current is 0.37A. After electrolytic polishing, the sample preparation is finally completed by cleaning with nitric acid solution (1+1);

[0057] S3. Metallographic analysis: the prepared sample of S1 is observed and analyzed by an optical microscope. The distribution of the center layer segregation layer near the center line of the sample crystal center is first browsed under 50x field of view, the area with the most concentrated segregation structure is selected as the photographing area, and the metallographic picture required for analysis is taken under 200x field of view. One representative picture is selected for each sample, the picture size is 2560x1920 pixels, and the metallographic measurement software carried by the microscope is used to measure the length of the largest size precipitated phase in the field of view, and L is obtained.

[0058] S4. Center layer segregation evaluation: the metallographic pictures obtained in step S3 are processed one by one using the ImageJ metallographic analysis software, the Threshold value is set to 160, and then the average precipitated phase size S and the precipitated phase area ratio A are calculated through the Analyze Particle function of the ImageJ software. Then the center layer segregation value calculation formula is: η = ε·A + θ·S + ω·L, where ε is 42, θ is 99, and ω is 0.3. The center layer segregation values of WS, 1 / 4WS, Mid, 1 / 4DS, and DS samples are calculated by the center layer segregation value calculation formula, and then the formula η Av =(η WS +η 1 / 4WS +η Mid +η 1 / 4DS +η DS ) / 5 is used to obtain the average center layer segregation value of the sample plate, which is 28.2, i.e. the center layer segregation value of the analyzed 8011 aluminum alloy cast strip. Since η Av =28.2 is in the range of "0-30", the center layer segregation degree of the strip is evaluated as a slight defect.

[0059] Example 2:

[0060] S1. On-site sampling: Based on the on-site production conditions, after the various casting and rolling production parameters have stabilized, an 8011 aluminum alloy casting and rolling strip sample that can represent the current production status is cut online. The sample is 200mm wide along the rolling direction, and the position information of the operating side (WS) and the transmission side (DS) is accurately marked on the upper plate. The cutting tool is the online hydraulic shear of the casting and rolling mill.

[0061] S2. Sample Preparation: Cut the sample obtained in step S1. The specific sampling locations of the cast-rolled strip sample are as follows: Figure 1 As shown, the sample block has a width and length of 15mm × 15mm, and the positions of WS, 1 / 4WS, Mid, 1 / 4DS, and DS are marked on the surface of the sample block in sequence. The cutting tool is a cutting machine. After the cut sample block is individually mounted, a longitudinal section observation surface is left. The sample information is marked on the side of the sample, and the mounting material at the tail of the sample is cut off with a cutting machine, so that the metal surface of the sample block is exposed at both ends of the sample, thus obtaining the sample to be ground. The sample is successively polished with 400#, 800#, and 1200# wet sandpaper, followed by mechanical polishing with a soft cloth and 0.25um diamond polishing agent to obtain a bright metallographic sample without obvious scratches. After polishing, the sample is rinsed with clean water and dried to prevent corrosion. The scratch-free metallographic sample obtained by mechanical polishing was subjected to electrolytic polishing using the electrolytic polishing apparatus recommended in GB / T3246.1-2012. The solution used was perchloric acid ethanol solution (1+9), the polishing voltage was 22V, the polishing time was 8s, and the peak polishing current was 0.49A. After electrolytic polishing, the sample was cleaned with nitric acid solution (1+1) to complete the sample preparation.

[0062] S3. Metallographic Analysis: The samples prepared in S1 were observed and analyzed using an optical microscope. First, the distribution of the segregated layer in the central layer near the crystallization center line of the entire sample was viewed at 50x magnification. The area with the most concentrated segregated structure was selected as the photographing area. Metallographic images of the required analysis were taken at 200x magnification. One most representative image was selected for each sample, with a photo size of 2560×1920 pixels. The metallographic measurement software carried by the microscope was used to measure the length of the largest precipitate in the field of view, and L was obtained.

[0063] S4. Evaluation of Central Segregation: The metallographic images obtained in step S3 were processed one by one using ImageJ metallographic analysis software. The Threshold value was set to 150. Then, the average precipitate size S and the precipitate area ratio A were calculated using the Analyze Particle function of ImageJ software. The central segregation value η was then calculated using the formula: η = ε·A + θ·S + ω·L, where ε is 42, θ is 99, and ω is 0.3. The central segregation values ​​η for the WS, 1 / 4WS, Mid, 1 / 4DS, and DS samples were calculated using this formula. Then, the results were analyzed using the formula η... Av =(η WS +η 1 / 4WS +η Mid +η 1 / 4DS +η DS The average center-layer segregation value of the sample, calculated as 73.4, is obtained by dividing the result by 5. This value is the center-layer segregation value of the 8011 aluminum alloy cast-rolled strip analyzed. Because η Av =73.4 falls within the "61-80" range, and the degree of segregation in the center layer of the billet is evaluated as a relatively serious defect.

[0064] Example 3:

[0065] S1. On-site sampling: Based on the on-site production conditions, after the various casting and rolling production parameters have stabilized, an 8011 aluminum alloy casting and rolling strip sample that can represent the current production status is cut online. The sample is 180mm wide along the rolling direction, and the position information of the operating side (WS) and the transmission side (DS) is accurately marked on the upper plate surface. The cutting tool is the online hydraulic shear of the casting and rolling mill.

[0066] S2. Sample Preparation: Cut the sample obtained in step S1. The specific sampling locations of the cast-rolled strip sample are as follows: Figure 1As shown, the sample block has a width and length of 15mm × 15mm, and the positions of WS, 1 / 4WS, Mid, 1 / 4DS, and DS are marked on the surface of the sample block in sequence. The cutting tool is a cutting machine. After the cut sample block is individually mounted, a longitudinal section observation surface is left. The sample information is marked on the side of the sample, and the mounting material at the tail of the sample is cut off with a cutting machine, so that the metal surface of the sample block is exposed at both ends of the sample, thus obtaining the sample to be ground. The sample is successively polished with 400#, 800#, and 1200# wet sandpaper, followed by mechanical polishing with a soft cloth and 0.25um diamond polishing agent to obtain a bright metallographic sample without obvious scratches. After polishing, the sample is rinsed with clean water and dried to prevent corrosion. The scratch-free metallographic sample obtained by mechanical polishing was prepared by electrolytic polishing device recommended by national standard GB / T3246.1-2012. The solution used was perchloric acid ethanol solution (1+9), the polishing voltage was 25V, the polishing time was 6s, and the peak polishing current was 0.8A. After electrolytic polishing, the sample was cleaned with nitric acid solution (1+1) to complete the sample preparation.

[0067] S3. Metallographic Analysis: The samples prepared in S1 were observed and analyzed using an optical microscope. First, the distribution of the segregated layer in the central layer near the crystallization center line of the entire sample was viewed at 50x magnification. The area with the most concentrated segregated structure was selected as the photographing area. Metallographic images of the required analysis were taken at 200x magnification. One most representative image was selected for each sample, with a photo size of 2560×1920 pixels. The metallographic measurement software carried by the microscope was used to measure the length of the largest precipitate in the field of view, and L was obtained.

[0068] S4. Evaluation of Central Layer Segregation: The metallographic images obtained in step S3 were processed one by one using ImageJ metallographic analysis software. The Threshold value was set to 157. Then, the average precipitate size S and the precipitate area ratio A were calculated using the Analyze Particle function of ImageJ software. The central layer segregation value η was then calculated using the formula: η = ε·A + θ·S + ω·L, where ε is 42, θ is 99, and ω is 0.3. The central layer segregation values ​​η for the WS, 1 / 4WS, Mid, 1 / 4DS, and DS samples were calculated using this formula. Then, the formula η... Av =(η WS +η 1 / 4WS +η Mid +η 1 / 4DS +η DS The average center-layer segregation value of the sample, 55.6, is obtained by dividing the result by η. This is the center-layer segregation value of the 8011 aluminum alloy cast-rolled strip analyzed. Av =55.6 falls within the "31-60" range, and the degree of segregation in the center layer of the billet is evaluated as a general defect.

[0069] Example 4:

[0070] S1. On-site sampling: Based on the on-site production conditions, after the various casting and rolling production parameters have stabilized, an 8011 aluminum alloy casting and rolling strip sample that can represent the current production status is cut online. The sample is 140mm wide along the rolling direction, and the position information of the operating side (WS) and the transmission side (DS) is accurately marked on the upper plate surface. The cutting tool is the online hydraulic shear of the casting and rolling mill.

[0071] S2. Sample Preparation: Cut the sample obtained in step S1. The specific sampling locations of the cast-rolled strip sample are as follows: Figure 1 As shown, the sample block has a width and length of 15mm × 15mm, and the positions of WS, 1 / 4WS, Mid, 1 / 4DS, and DS are marked on the surface of the sample block in sequence. The cutting tool is a cutting machine. After the cut sample block is individually mounted, a longitudinal section observation surface is left. The sample information is marked on the side of the sample, and the mounting material at the tail of the sample is cut off with a cutting machine, so that the metal surface of the sample block is exposed at both ends of the sample, thus obtaining the sample to be ground. The sample is successively polished with 400#, 800#, and 1200# wet sandpaper, followed by mechanical polishing with a soft cloth and 0.25um diamond polishing agent to obtain a bright metallographic sample without obvious scratches. After polishing, the sample is rinsed with clean water and dried to prevent corrosion. The scratch-free metallographic sample obtained by mechanical polishing was subjected to electrolytic polishing using the electrolytic polishing apparatus recommended in GB / T3246.1-2012. The solution used was perchloric acid ethanol solution (1+9), the polishing voltage was 22V, the polishing time was 10s, and the peak polishing current was 0.73A. After electrolytic polishing, the sample was cleaned with nitric acid solution (1+1) to complete the sample preparation.

[0072] S3. Metallographic Analysis: The samples prepared in S1 were observed and analyzed using an optical microscope. First, the distribution of the segregated layer in the central layer near the crystallization center line of the entire sample was viewed at 50x magnification. The area with the most concentrated segregated structure was selected as the photographing area. Metallographic images of the required analysis were taken at 200x magnification. One most representative image was selected for each sample, with a photo size of 2560×1920 pixels. The metallographic measurement software carried by the microscope was used to measure the length of the largest precipitate in the field of view, and L was obtained.

[0073] S4. Evaluation of Central Segregation: The metallographic images obtained in step S3 were processed one by one using ImageJ metallographic analysis software. The Threshold value was set to 154. Then, the average precipitate size S and the precipitate area ratio A were calculated using the Analyze Particle function of ImageJ software. The central segregation value η was then calculated using the formula: η = ε·A + θ·S + ω·L, where ε is 42, θ is 99, and ω is 0.3. The central segregation values ​​η for the WS, 1 / 4WS, Mid, 1 / 4DS, and DS samples were calculated using this formula. Then, the results were analyzed using the formula η... Av =(η WS +η 1 / 4WS +η Mid +η 1 / 4DS +η DS The average center-layer segregation value of the sample, calculated as 93.1, is obtained by dividing the result by 5. This value is the center-layer segregation value of the analyzed 8011 aluminum alloy cast-rolled strip. Because η Av =93.1 is in the range of "above 81", and the degree of segregation in the center layer of the billet is evaluated as a serious defect.

Claims

1. A method for evaluating center segregation of a 8011 aluminum alloy cast-rolled strip, characterized by Comprising the following steps: S1, on-site sampling: According to the on-site production situation, after the stability of various casting and rolling production parameters, the 8011 aluminum alloy cast strip sample plate representing the current production state is cut on line; S2, sample preparation: After the cast strip sample plate obtained in step S1 is cut into sample blocks, sample preparation is carried out, the sample blocks include 5 blocks, which are respectively taken from 100mm away from both ends of the cast strip sample plate, 1 / 2 of the length of the cast strip sample plate and 1 / 4 of the length of the sample plate away from both ends of the cast strip sample plate, the size of the sample block is 15mm*15mm, the sample block is completed by the sample mounting machine, the mounted sample is polished by metallographic water sandpaper and mechanically polished, and finally the sample preparation is completed by electrolytic polishing; S3, metallographic analysis: The sample prepared in step S2 is observed and analyzed by using an optical microscope, the most serious composition segregation area near the crystallization center line of the cast strip sample is selected for metallographic photography, and the center layer segregation organization length L with the maximum size in the field of view is measured by using a metallographic analysis software, wherein the observation and analysis adopts 50 times field of view to browse the distribution of the center layer segregation layer near the crystallization center line of the whole sample, selects the area with the most concentrated segregation organization as the photographing area, takes the required metallographic picture under 200 times field of view, selects 1 most representative picture for each sample, the picture size is 2560*1920 pixels, and the length of the precipitated phase with the maximum size in the field of view is measured by using the metallographic measurement software carried by the microscope, and L is obtained; S4, center layer segregation evaluation: The metallographic picture obtained in step S3 is processed by using the ImageJ metallographic analysis software, the Threshold value in the ImageJ metallographic analysis software is set to 150-160, the average grain size S of the center layer segregation layer and the area ratio A of the precipitated phase in the field of view are calculated, and L obtained in step S3 is combined to obtain the quantitative center layer segregation value η according to the calculation formula as follows: η=ε·A+θ·S+ω·L Wherein, η is the center layer segregation value; ε is the precipitated phase area ratio influence factor, which is 42; A is the area ratio of the precipitated phase, %; θ is the center layer segregation layer grain size influence factor, which is 99; S is the average grain size of the center layer segregation layer, μm; ω is the center layer segregation layer limit length influence factor, which is 0.3; L is the limit length of the center layer segregation layer, μm; The center layer segregation values η of each sample block are averaged to obtain the center layer segregation value of the analyzed cast strip sample: When the center layer segregation value η is 0-30, it is a slight defect, when the center layer segregation value η is 31-60, it is a general defect, when the center layer segregation value η is 61-80, it is a heavier defect, and when the center layer segregation value η is more than 81, it is a serious defect.

2. The method of claim 1, wherein the cast-rolled 8011 aluminum alloy strip billet centerline segregation evaluation method is characterized by: The sample blocks in S2 are individually mounted to leave a longitudinal section observation surface, the sample information is marked on the side of the sample, and the sample tail is cut off by a cutting machine, so that the metal surface of the sample block is exposed at both ends of the sample to obtain a sample to be polished.

3. The method of claim 2, wherein the cast-rolled 8011 aluminum alloy strip slab centerline segregation evaluation method is characterized by: The metallographic sand paper polishing in S2 uses 400#, 800# and 1200# sand paper in sequence to polish the sample to be polished, and after mechanical polishing, a polishing agent of 0.25um diamond is used with a cloth to obtain a bright metallographic sample without obvious scratches, and after polishing, the sample is washed with water and dried to observe the surface.

4. The method of claim 3, wherein the cast-rolled 8011 aluminum alloy strip slab centerline segregation evaluation method is characterized by: The electrolytic solution for the electrolytic polishing in S2 is an ethanol solution of perchloric acid, the tail of the sample is connected to the loop of the electrolytic polishing device through a copper foil tape, the polishing voltage is 20-25V, the polishing time is 5-10S, the polishing current is 0.3A-0.8A, and after electrolytic polishing, the sample is cleaned with a nitric acid solution to observe the surface.

5. The method of claim 4, wherein the cast-rolled 8011 aluminum alloy strip slab centerline segregation evaluation method is characterized by: The volume ratio of perchloric acid to ethanol in the ethanol solution of perchloric acid is 1:9, and the volume ratio of concentrated nitric acid to water in the nitric acid solution is 1:1.

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