Method for evaluating rolling residual stress of copper alloy based on dislocation density and hardness

Abstract

This application discloses a method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness, comprising: pre-treatment of the sample to be tested; XRD testing of the sample to be tested, and acquisition of the XRD diffraction pattern; statistical analysis of the XRD diffraction pattern, and further calculation of the dislocation density of the sample using the obtained results; testing the surface microhardness of the processed sample; testing the internal residual stress of the sample; and using normalized data processing to determine the relationship between the synergistic effect of dislocation density and hardness and residual stress through data fitting. An indirect testing method is used to transform residual stress testing into dislocation density and hardness testing, and the residual stress is evaluated using a functional relationship based on the test results of dislocation density and hardness. This method combines the advantages of non-destructive testing and low cost and high accuracy of traditional testing methods, while simplifying the testing process and improving experimental testing efficiency.

Description

Technical Field

[0001] This application relates to the field of residual stress measurement technology in copper alloy rolling, and specifically to a method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness. Background Technology

[0002] Copper and copper alloys inevitably experience external forces and undergo transformations in their internal metallographic structure during processing and heat treatment, resulting in residual stress within the product. This stress affects the material's fatigue strength, resistance to stress corrosion, dimensional stability, and service life. Therefore, the study and control of stress during processing are receiving increasing attention.

[0003] With advancements in technology, residual stress detection has become increasingly simpler. For example, the method has evolved from position-sensitive detectors to linear array detectors, and combined with robots, it allows for flexible measurement at different test locations, reducing measurement time from tens of minutes to tens of seconds, thus significantly improving efficiency. However, different residual stress measurement methods have varying applicability, requiring selection based on relevant technical requirements such as accuracy, range, sample destructiveness, and field conditions.

[0004] Based on current techniques for residual stress measurement, methods can be broadly categorized into two types: destructive and non-destructive. Destructive methods involve separating or cutting away the portion with residual stress from the product to release the stress, then measuring the strain change to determine the residual stress. These methods are characterized by high accuracy but cause significant damage to the product. Non-destructive methods, including X-ray methods, magnetic methods, and ultrasonic methods, are characterized by non-destructive testing but are costly. Summary of the Invention

[0005] In order to solve the above-mentioned technical problems, this application proposes the following technical solution: In a first aspect, embodiments of this application provide a method for evaluating residual stress during the rolling of copper alloys based on dislocation density and hardness, including: Pre-treatment of the samples to be tested; The pretreated sample to be tested was subjected to XRD test, and the XRD diffraction pattern of the sample was collected. The XRD diffraction pattern was statistically analyzed, and the dislocation density of the sample was further derived and calculated using the results. The surface microhardness of the processed sample was tested. Test the residual stress inside the sample to be tested; By using normalized data processing, the relationship between the synergistic effect of dislocation density and hardness and residual stress was determined through data fitting.

[0006] In one possible implementation, the pre-testing of the sample to be tested includes: The rolled sample was polished with SiC sandpaper, from 180# to 1500# in sequence; The surface was cleaned with deionized water and anhydrous ethanol, and the sample surface was polished with a metallographic polishing machine. Place the sample to be tested in the diffraction analysis sample cell, and ensure that the surface to be tested is flush with the upper surface of the diffraction analysis sample cell by adding modeling clay or a pad on the back of the sample.

[0007] In one possible implementation, the pre-processed sample to be tested is subjected to XRD testing, and the XRD diffraction pattern of the sample is acquired. This includes: using CuKα rays as the X-ray source, with specific parameters as follows: scanning range: 10°~90°, scanning speed: 0.12s / step, step size: 0.02°, accelerating voltage: 40kV, current: 40mA, scanning axis set to 2Theta, scanning multiple sets of samples and obtaining XRD scanning data.

[0008] In one possible implementation, the step of performing statistical analysis on the XRD diffraction pattern and using the results to further derive and calculate the sample dislocation density includes: The obtained XRD test data were imported into Jade for analysis. The experimental data were processed and calculated using Jade.6.5 software. Before calculating the dislocation density, the background of the diffraction peaks was subtracted and the Kα2 diffraction lines were stripped. After determining the sample diffraction peaks and corresponding diffraction planes, Jade is used to perform peak finding operations so that all diffraction peaks are included in the statistics. If diffraction peaks are not automatically recognized by the software, they need to be added manually. After peak finding is completed, the data report is processed to obtain the FHWM values ​​of different diffraction peaks. This value is the full width at half maximum (FWHM) of the diffraction peak. After obtaining the accurate full width at half maximum (FWHM) value, the dislocation density corresponding to different diffraction planes and the total dislocation density inside the sample can be calculated using the following formula: In the formula: D is the full width at half maximum (FWHM) of the diffraction peak, b is the Burgers vector (the Burgers vector varies for different materials), and ρ is the dislocation density. Substituting the FWHM value and the Burgers vector into the above formula will give the dislocation density corresponding to a specific diffraction peak.

[0009] In one possible implementation, the step of testing the surface microhardness of the processed sample to be tested includes: After the dislocation density test, the opposite side of the sample test surface is polished to remove surface scratches to ensure accurate hardness results. The Vickers hardness tester was selected as the testing instrument, and the specific conditions and parameters were set as follows: test force: 100gf, holding time: 15s, objective lens magnification: 40X. During the testing process, seven different locations were selected as test areas to obtain bright and clear indentation areas. After obtaining the test report, the maximum and minimum hardness values ​​are removed, and the average of the remaining five test values ​​is taken as the final hardness result of the current sample.

[0010] In one possible implementation, the test includes measuring the residual stress inside the sample to be tested, which includes: The side-tilt method was chosen as the residual stress testing method. The testing principle is that when there is residual stress in the sample, the interplanar spacing will change, and when Bragg diffraction occurs, the diffraction peaks will also shift accordingly. Moreover, the magnitude of the shift distance is related to the magnitude of the stress. The sample was irradiated several times with X-rays of wavelength λ at different incident angles, and the corresponding diffraction angles were measured. Find right The stress can be calculated from the slope M. , It is the azimuth angle in any direction in space, that is, the angle between the incident ray and the perpendicular line of the test surface; After grinding and polishing, the sample is placed in a direction perpendicular to the stress test. First, a large-scale scan of the sample is performed to observe the diffraction peaks. In accordance with the requirements for residual stress measurement, different sample tilt angles were set to select four different ψ angles for measurement. After the test, the peak position was read using the half-width at half-maximum method with the Leptos software, and the sample's elastic modulus and Poisson's ratio were substituted into the data to process the data and calculate the fit. A straight line is used to obtain the residual stress in a specific direction of the specimen.

[0011] In one possible implementation, the step of utilizing normalized data processing to determine the relationship between the synergistic effect of dislocation density and hardness and residual stress through data fitting includes: Define dislocation density as X, hardness as Y, and residual stress as Z. Import the three sets of data into Origin and convert them into matrices. After plotting the transformed matrix as a surface, nonlinear surface fitting was performed. Lorentz2D was selected as the model, and a reasonable range of fitting parameters was chosen. Automatic fitting was selected as the fitting method, resulting in the following nonlinear surface fitting formula: This function expression is a nonlinear surface fitting relationship between the combined effect of dislocation density and hardness and the residual stress in copper alloy rolling.

[0012] In this embodiment, an indirect testing method is used to transform residual stress testing into dislocation density and hardness testing. The residual stress is then evaluated using a functional relationship based on the test results of dislocation density and hardness. This method combines the advantages of non-destructive testing and low cost and high accuracy found in traditional testing methods, while simplifying the testing process and improving experimental testing efficiency. Attached Figure Description

[0013] Figure 1 This application provides a schematic flowchart of a method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness, as an embodiment of the present application. Figure 2 This is a schematic diagram of the XRD diffraction results of the rolled sample provided in the embodiments of this application; Figure 3 This is a schematic diagram of dislocation density results for a specific diffraction plane provided in an embodiment of this application; Figure 4 This is a schematic diagram of the hardness values ​​of different regions of the sample provided in the embodiments of this application; Figure 5 The three-dimensional co-fitting diagram of hardness, dislocation density, and residual stress provided in the embodiments of this application; Figure 6 A schematic diagram of the function fitting results provided in the embodiments of this application. Detailed Implementation

[0014] The present solution will now be described in conjunction with the accompanying drawings and specific embodiments.

[0015] See Figure 1 The method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness provided in this application includes: S101, Pre-treatment of the sample to be tested.

[0016] The specific sample pretreatment method is as follows: the rolled sample is polished with SiC sandpaper, successively from 180# to 1500#. The surface is cleaned with deionized water and anhydrous ethanol, and the sample surface is polished with a metallographic polishing machine. First, coarse polishing is performed with 2.5# diamond polishing paste, followed by fine polishing with 0.5# polishing paste. After ensuring that the surface is as bright as possible, the sample is placed in the diffraction analysis sample cell. The test surface of the sample is ensured to be flush with the upper surface of the diffraction analysis sample cell by adding modeling clay or a pad on the back of the sample.

[0017] S102, perform XRD testing on the pretreated sample to be tested and collect the XRD diffraction pattern of the sample.

[0018] XRD testing was conducted using CuKα rays as the X-ray source. Specific parameters were: scanning range: 10°~90°, scanning speed: 0.12 s / step, step size: 0.02°, accelerating voltage: 40 kV, current: 40 mA, and scanning axis set to 2 Theta. Multiple samples were scanned, and XRD data were obtained. The results are as follows: Figure 2 As shown.

[0019] S103, perform statistical analysis on the XRD diffraction pattern, and use the results to further derive and calculate the dislocation density of the sample.

[0020] XRD test data obtained from S102 were imported into Jade for analysis. Jade.6.5 software was used for data processing and calculations. Before calculating dislocation density, the background of the diffraction peaks was subtracted, and Kα2 diffraction lines were removed. After determining the sample diffraction peaks and their corresponding diffraction planes, Jade was used for peak finding to ensure all diffraction peaks were included. If a diffraction peak was not automatically identified by the software, it needed to be added manually to ensure all samples had the same diffraction planes and the same number of diffraction peaks. After peak finding, the data report was processed to obtain the FHWM values ​​of different diffraction peaks, which are the half-widths (FWMs) of the diffraction peaks. Since the diffraction peak data obtained from the report is in angular form, while the FWM values ​​required for calculating dislocation density are in radians, the angular values ​​in the report need to be converted to radians. After obtaining the accurate FWM values, the dislocation densities corresponding to different diffraction planes (as shown in Table 1) and the total dislocation density inside the sample can be calculated using the following formula: In the formula: D is the full width at half maximum (FWHM) of the diffraction peak, b is the Burgers vector (the Burgers vector varies for different materials), and ρ is the dislocation density. Substituting the FWHM value and the Burgers vector into the above formula yields the dislocation density corresponding to a specific diffraction peak. The sum of the dislocation densities of each diffraction plane is the total dislocation density inside the sample.

[0021] Table 1 Dislocation density corresponding to different diffraction planes S104 is used to test the surface microhardness of the treated sample.

[0022] After testing with S103, the opposite surface of the sample was polished to remove surface scratches as much as possible to ensure accurate hardness results. A Vickers hardness tester was selected, with specific parameters set as follows: test force: 100gf, holding time: 15s, objective lens magnification: 40X. Seven different locations were selected as test areas during the test, with the goal of obtaining a bright and clear indentation area. After obtaining the test report, the maximum and minimum hardness values ​​were removed, and the average of the remaining five test values ​​was taken as the final hardness result of the current sample. Table 2 shows the test values ​​of the five points after removing the maximum and minimum hardness values.

[0023] Table 2 shows the test values ​​at 5 points after removing the maximum and minimum hardness values. S105, testing the residual stress inside the sample to be tested.

[0024] In this embodiment, the residual stress testing method selected is the tilt method. The testing principle is that when residual stress exists in the sample, the interplanar spacing will change, and when Bragg diffraction occurs, the resulting diffraction peaks will also shift accordingly. Moreover, the magnitude of the shift distance is related to the magnitude of the stress. X-rays of wavelength λ are used to irradiate the sample several times at different incident angles, and the corresponding diffraction angles are measured. Find right The slope M can be used to calculate the stress. , It is the azimuth angle in any direction in space, that is, the angle between the incident ray and the perpendicular line of the test surface.

[0025] After grinding and polishing, the sample was placed perpendicular to the stress test direction. A large-scale scan was performed using the coupled TwoTheta / Theta mode to observe the diffraction peaks. To improve the sensitivity of the stress measurement, strong diffraction peaks in the high-angle region were selected as the research targets (2θ above 90°, with peak intensity greater than 1000 cps). According to the requirements for residual stress measurement, different sample tilt angles were set to select four different... Angle measurement After the test, the peak position was read using the half-width at half-maximum method with the Leptos software, and the sample's elastic modulus, Poisson's ratio, and other parameters were input to process the data and calculate the fit. A straight line is used to obtain the residual stress in a specific direction of the specimen.

[0026] S106, using normalized data processing, determined the relationship between the synergistic effect of dislocation density and hardness and residual stress through data fitting.

[0027] The dislocation density obtained in step three is defined as X, the hardness obtained in step four as Y, and the residual stress obtained in step five as Z. These three sets of data are imported into Origin and converted into matrices. Specifically, an XYZ mesh matrix is ​​selected for the conversion, with 10 rows and 10 columns. The converted matrix is ​​then plotted as a surface and subjected to nonlinear surface fitting. The Lorentz2D model is selected, and a reasonable range of fitting parameters is chosen. Automatic fitting is selected as the fitting method. The resulting nonlinear surface fitting formula is as follows: This function expression is a nonlinear surface fitting relationship between the combined effect of dislocation density and hardness and the residual stress in copper alloy rolling. The fitted results are verified, and R is adjusted. 2 The value reached 0.98338, which showed excellent fitting effect, verifying the applicability and accuracy of the function expression.

[0028] In this application embodiment, "at least one" refers to one or more, and "more than one" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent the existence of A alone, the simultaneous existence of A and B, or the existence of B alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, and c can represent: a, b, c, ab, ac, bc, or abc, where a, b, and c can be single or multiple.

[0029] The above description is merely a specific embodiment of this application. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the protection scope of this application. The protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness, characterized in that, include: Pre-treatment of the samples to be tested; The pretreated sample to be tested was subjected to XRD test, and the XRD diffraction pattern of the sample was collected. The XRD diffraction pattern was statistically analyzed, and the dislocation density of the sample was further derived and calculated using the results. The surface microhardness of the processed sample was tested. Test the residual stress inside the sample to be tested; Using normalized data processing, the relationship between the synergistic effect of dislocation density and hardness and residual stress was determined through data fitting, including: Define dislocation density as X, hardness as Y, and residual stress as Z. Import the three sets of data into Origin and convert them into matrices. After plotting the transformed matrix as a surface, nonlinear surface fitting was performed. Lorentz2D was selected as the model, and a reasonable range of fitting parameters was chosen. Automatic fitting was selected as the fitting method, resulting in the following nonlinear surface fitting formula: This function expression is a nonlinear surface fitting relationship between the combined effect of dislocation density and hardness and the residual stress in copper alloy rolling.

2. The method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness according to claim 1, characterized in that, The pretreatment of the sample to be tested includes: The rolled sample was polished with SiC sandpaper, from 180# to 1500# in sequence; The surface was cleaned with deionized water and anhydrous ethanol, and the sample surface was polished with a metallographic polishing machine. Place the sample to be tested in the diffraction analysis sample cell, and ensure that the surface to be tested is flush with the upper surface of the diffraction analysis sample cell by adding modeling clay or a pad on the back of the sample.

3. The method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness according to claim 1, characterized in that, The pretreated sample to be tested is subjected to XRD testing, and the XRD diffraction pattern of the sample is acquired. The XRD diffraction pattern is acquired by using CuKα rays as the X-ray source, with the following parameters: scanning range: 10°~90°, scanning speed: 0.12s / step, step size: 0.02°, accelerating voltage: 40kV, current: 40mA, scanning axis set to 2Theta, scanning multiple sets of samples and obtaining XRD scanning data.

4. The method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness according to claim 1 or 3, characterized in that, The statistical analysis of the XRD diffraction pattern, and the subsequent derivation and calculation of the sample dislocation density using the results, includes: The obtained XRD test data were imported into Jade for analysis. The experimental data were processed and calculated using Jade.6.5 software. Before calculating the dislocation density, the background of the diffraction peaks was subtracted and the Kα2 diffraction lines were stripped. After determining the sample diffraction peaks and corresponding diffraction planes, Jade is used to perform peak finding operations so that all diffraction peaks are included in the statistics. If diffraction peaks are not automatically recognized by the software, they need to be added manually. After peak finding is completed, the data report is processed to obtain the FHWM values ​​of different diffraction peaks. This value is the full width at half maximum (FWHM) of the diffraction peak. After obtaining the accurate full width at half maximum (FWHM) value, the dislocation density corresponding to different diffraction planes and the total dislocation density inside the sample can be calculated using the following formula: In the formula: D is the full width at half maximum (FWHM) of the diffraction peak, b is the Burgers vector (the Burgers vector varies for different materials), and ρ is the dislocation density. Substituting the FWHM value and the Burgers vector into the above formula will give the dislocation density corresponding to a specific diffraction peak.

5. The method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness according to claim 1, characterized in that, The process of testing the surface microhardness of the processed sample includes: After the dislocation density test, the opposite side of the sample test surface is polished to remove surface scratches to ensure accurate hardness results. The Vickers hardness tester was selected as the testing instrument, and the specific conditions and parameters were set as follows: test force: 100gf, holding time: 15s, objective lens magnification: 40X. During the testing process, seven different locations were selected as test areas to obtain bright and clear indentation areas. After obtaining the test report, the maximum and minimum hardness values ​​are removed, and the average of the remaining five test values ​​is taken as the final hardness result of the current sample.

6. The method for evaluating residual stress in copper alloy rolling based on dislocation density and hardness according to claim 1, characterized in that, The residual stress inside the test sample includes: The side-tilt method was chosen as the residual stress testing method. The testing principle is that when there is residual stress in the sample, the interplanar spacing will change, and when Bragg diffraction occurs, the diffraction peaks will also shift accordingly. Moreover, the magnitude of the shift distance is related to the magnitude of the stress. The sample was irradiated several times with X-rays of wavelength λ at different incident angles, and the corresponding diffraction angles were measured. Find right The slope M can be used to calculate the stress. , It is the azimuth angle in any direction in space, that is, the angle between the incident ray and the perpendicular line of the test surface; After grinding and polishing, the sample is placed in a direction perpendicular to the stress test. First, a large-scale scan of the sample is performed to observe the diffraction peaks. In accordance with the requirements for residual stress measurement, different sample tilt angles were set to select four different ψ angles for measurement. After the test, the peak position was read using the half-width at half-maximum method with the Leptos software, and the sample's elastic modulus and Poisson's ratio were substituted into the data to process the data and calculate the fit. A straight line is used to obtain the residual stress in a specific direction of the specimen.

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