Quantitative analysis method for exfoliation corrosion resistance of aluminum alloy material

Abstract

The invention discloses a quantitative analysis method for exfoliation corrosion resistance of an aluminum alloy material, and belongs to the technical field of exfoliation corrosion resistance detection of aluminum alloy. The method comprises the following steps: (1) establishing a corresponding relation between a corrosion grade and a microscopic corrosion layer depth range; (2) uniformly dividing a to-be-tested surface of the aluminum alloy sample into a plurality of alternately distributed test surfaces and non-test surfaces, and coating the non-test surfaces with protective coatings; (3) preparing a corrosion solution according to alloy types and standard requirements, and carrying out a corrosion test; and (4) after the corrosion test is completed, cutting a section sample at the position where the surface exfoliation corrosion is most serious, measuring the depth of a corrosion layer, and determining the corrosion level by comparing the established corresponding relationship between the corrosion level and the depth range of the microscopic corrosion layer. According to the method, a numerical value corresponding relationship is established between the exfoliation corrosion level of the aluminum alloy and the actual exfoliation corrosion depth, and the exfoliation corrosion state of the surface of the aluminum alloy and the depth of a microscopic corrosion layer are associated, so that quantitative analysis of the exfoliation corrosion level is realized.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy exfoliation corrosion performance detection, and in particular to a quantitative analysis method for the exfoliation corrosion resistance of an aluminum alloy material. Background Art

[0002] The exfoliation corrosion performance test of aluminum alloy is an accelerated exfoliation corrosion test method. Under certain conditions, the test material is fully immersed in a corrosive solution for a certain period of time, and then the material's sensitivity to exfoliation is evaluated by visual detection or metallographic observation. At present, the evaluation method generally adopts the method of comparing with the standard spectrum and confirming the corrosion level, that is, according to the visual corrosion morphology of the sample surface, it is divided into N (no obvious corrosion), P (pitting corrosion) and E (exfoliation corrosion) levels. Different degrees of exfoliation corrosion levels can be divided into EA, EB, EC and ED. However, this visual evaluation method is greatly affected by the subjective factors of the tester, and the consistency of the evaluation results is poor. Different testers often give different evaluation levels for the same sample, and it is impossible to quantitatively evaluate the exfoliation corrosion performance. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a quantitative analysis method for the exfoliation corrosion resistance of aluminum alloy materials, which can quantitatively and accurately evaluate the exfoliation corrosion performance of aluminum alloy materials.

[0004] The technical solution adopted by the present invention is: The present invention provides a method for quantitatively analyzing the exfoliation corrosion resistance of an aluminum alloy material, comprising the steps of: (1) Prepare calibration samples that meet the requirements of the standard for macroscopic assessment of different corrosion levels by comparing the spectra, cut cross-sectional samples at the location with the most severe surface corrosion, measure the depth of the corrosion layer, and establish the corresponding relationship between the corrosion level and the depth range of the microscopic corrosion layer; (2) Take the aluminum alloy test piece and cut it into test specimens with a width of 30-50 mm and a length of 100-300 mm. Clean the oil stains on the surface of the test specimen, rinse it with clean water, and dry it for later use. Then divide the test surface of the test specimen evenly into several alternating test surfaces and non-test surfaces, and apply a protective coating on the non-test surface. (3) Prepare the corrosion solution according to the alloy type and standard requirements, place the test sample horizontally with the test surface facing up and completely immersed in the solution, and conduct the corrosion test according to the standard requirements; (4) After the corrosion test is completed, cut a cross-sectional specimen at the location where the surface exfoliation corrosion is most serious, mount the specimen, grind and polish it, measure the depth of the corrosion layer, and record it. Determine the corrosion grade based on the measured depth of exfoliation corrosion and the established correspondence between the corrosion grade and the depth range of the microscopic corrosion layer.

[0005] Furthermore, in step (2), the test surface includes a test area located on the surface to be tested and a side area close to the test area of ​​the surface to be tested.

[0006] Furthermore, in step (2), the height of the side area of ​​the test surface is 2-3 mm.

[0007] Furthermore, in step (2), the protective coating is strippable chloroprene rubber or acid-resistant insulating varnish.

[0008] Furthermore, when the cross-sectional sample is cut at the location where the surface exfoliation corrosion is most severe in step (4), the cutting plane is perpendicular to the test area of ​​the test surface located on the surface to be tested and parallel to the length direction of the sample.

[0009] Furthermore, when a cross-sectional sample is cut at the location where the surface exfoliation corrosion is most severe in step (4), the cross-sectional sample cut includes a test surface and a non-test surface.

[0010] Furthermore, when testing the depth of the corrosion layer in step (4), a metallographic microscope is used to measure the vertical distance between the original surface position of the protective coating and the deepest position of the exfoliation corrosion depth as the depth of the corrosion layer.

[0011] Furthermore, when testing the corrosion layer depth in step (4), it is necessary to measure at least 5 locations and take the average value.

[0012] The beneficial effects of the present invention are: The present invention provides a method for quantitatively analyzing the exfoliation corrosion resistance of an aluminum alloy material. By establishing a numerical correspondence between the exfoliation corrosion grade of the aluminum alloy and the actual exfoliation corrosion depth, the exfoliation corrosion state of the aluminum alloy surface and the depth of the microscopic corrosion layer are correlated, thereby achieving quantitative analysis of the exfoliation corrosion grade of the aluminum alloy and being able to more accurately evaluate the exfoliation corrosion resistance of the aluminum alloy material. In addition, the present invention also improves the method for preparing exfoliation corrosion test specimens, by applying a corrosion-resistant protective coating to the specimens at intervals, thereby retaining the position of the original surface of the specimens, which is used as a benchmark for measuring the exfoliation corrosion depth, thereby improving the accuracy of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0014] Figure 1 It is a schematic diagram of sample preparation of exfoliation corrosion specimens of the present invention; Figure 2It is a schematic diagram of the sampling position of the exfoliation corrosion metallographic specimen of the present invention; Figure 3 It is a metallographic detection diagram of the exfoliation corrosion depth of the EA-level exfoliation corrosion sample of the present invention; Figure 4 It is a metallographic detection diagram of the exfoliation corrosion depth of the EB-level exfoliation corrosion sample of the present invention; Figure 5 This is a metallographic detection diagram of the exfoliation corrosion depth of the EC-level exfoliation corrosion sample of the present invention; Figure 6 This is a metallographic detection diagram of the exfoliation corrosion depth of the ED-level exfoliation corrosion sample of the present invention.

[0015] Markings in the figure: 1. Test surface; 11. Test area of ​​the surface to be tested; 12. Side area of ​​the test area close to the surface to be tested; 2. Non-test surface; 3. Metallographic inspection surface. DETAILED DESCRIPTION

[0016] The present invention provides a quantitative analysis method for the exfoliation corrosion resistance of aluminum alloy materials. In order to make the purpose, technical solution and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0017] This embodiment provides a quantitative analysis method for the exfoliation corrosion resistance of aluminum alloy materials. Taking a certain 7xxx aluminum alloy as an example, the steps are as follows: (1) For the 7xxx aluminum alloy, several calibration specimens that meet the macroscopic assessment of corrosion levels from EA to ED were prepared according to the standard requirements for spectrum comparison, and cross-sectional specimens were cut at the location where the surface corrosion was most serious, and the depth of the corrosion layer was measured, as shown in Table 1. Based on the test data in Table 1 above, a corresponding relationship table between the corrosion level and the microscopic corrosion layer depth range was established, as shown in Table 2.

[0018] Table 1 Test results of calibration samples

[0019] Table 2 Correspondence between exfoliation corrosion grade and microscopic corrosion layer depth

[0020] It should be noted that when establishing a correspondence table between corrosion grade and exfoliation corrosion depth based on the test results of calibration samples, statistical analysis is performed separately for different grades, that is, the minimum and maximum values ​​are determined based on the exfoliation corrosion depth range corresponding to several calibration samples of a certain corrosion grade, and the minimum value of the corrosion grade is adjusted and the maximum value is increased based on experience and the minimum and maximum values ​​of the exfoliation corrosion depth range corresponding to several calibration samples of adjacent corrosion grades, to ensure the continuity of the exfoliation corrosion depth range of the determined corrosion grade.

[0021] (2) Take the aluminum alloy test piece and cut it into test pieces with a width of 50 mm and a length of 200 mm. The thickness is the original thickness, which is 20 mm. Clean the oil stains on the surface of the test piece, rinse it with clean water, and dry it for later use. Evenly divide the test surface of the test piece into 10 alternately distributed test surfaces 1 and non-test surfaces 2. The test surface 1 includes a test area 11 located on the test surface and a side area 12 close to the test area of ​​the test surface, and the height of the side area of ​​the test surface is 2.5 mm. The non-test surface is coated with a protective coating, which is a strippable chloroprene rubber, so as to retain the position of the original surface of the sample, which is used as a reference for measuring the depth of exfoliation corrosion. The aluminum alloy test piece prepared in this step is as follows: Figure 1 shown.

[0022] (3) Prepare a corrosion solution according to the type of alloy and standard requirements, place the test sample horizontally with the test surface facing upward and completely immersed in the solution, and perform a corrosion test according to the standard requirements; this embodiment is 7xxx aluminum alloy, and the corrosion solution preparation process is as follows: weigh 234g NaCl and 50g KNO3, dissolve them in deionized water, add 0.1mol HNO3, and dilute to 1L with deionized water to obtain a corrosion solution with a pH of about 0.4; perform a corrosion test according to ASTM G34, the test temperature is: 25℃±3℃, the corrosion time is: 7XXX, 48h; after the test is carried out for 5h, 24h, and 48h, the corrosion condition of the sample is checked, and the test surface should not be damaged and the sample is not cleaned during the inspection.

[0023] (4) If Figure 2As shown, after the corrosion test is completed, a cross-sectional sample is cut at the location where the surface exfoliation corrosion is most serious, and when the cross-sectional sample is cut at the location where the surface exfoliation corrosion is most serious, the cutting plane is perpendicular to the test area located on the test surface and parallel to the length direction of the sample, and the cutting plane is the metallographic detection surface 3, and the cut cross-sectional sample includes the test surface and the non-test surface; the cut cross-sectional sample is mounted and then ground and polished, and the depth of the corrosion layer is measured. It is necessary to measure at least 5 positions and take the average value, which specifically refers to selecting at least 5 positions with large corrosion layer depths in the cut cross-sectional sample using a metallographic microscope for measurement and taking the average value, and when testing the corrosion layer depth at each position, the vertical distance between the original surface position of the protective coating and the position with the deepest exfoliation corrosion depth is measured on the metallographic detection surface 3 using a metallographic microscope as the corrosion layer depth; then the corrosion level is determined according to the measured exfoliation corrosion depth and in accordance with the established correspondence between the corrosion level and the microscopic corrosion layer depth range.

[0024] In addition, in the above step (1), the calibration sample is prepared according to the sample preparation method of the above step (2), the corrosion solution is prepared according to the above step (3), and the exfoliation corrosion depth is measured according to the measurement method of the above step (4). Moreover, in practical applications, the corresponding relationship between the corrosion grade and the corrosion depth of different series of aluminum alloys can be established in advance through experiments. When it is necessary to perform exfoliation corrosion rating on the aluminum alloy material in the later stage, the exfoliation corrosion test can be directly performed according to the steps (2)-(4) of the present invention and the corrosion depth can be detected, and then the corrosion grade of the aluminum alloy can be determined according to the corresponding relationship between the corrosion grade and the corrosion depth of the series of aluminum alloys.

[0025] Based on the established correspondence between the corrosion grade and the depth range of the microscopic corrosion layer, this embodiment tests the exfoliation corrosion depth of four 7xxx samples. The metallographic detection photos of the exfoliation corrosion depth at one position of each sample are shown in FIG. Figure 3-6 In this embodiment, each sample was tested 5 times, and the average values ​​were 150.3μm, 525.4μm, 615.8μm, and 2276.2μm, respectively. According to the corrosion layer depth measurement results, combined with the established correspondence between the corrosion level and the microscopic corrosion layer depth range, the corrosion levels of the four samples were judged to be EA, EB, EC, and ED, respectively.

[0026] It should be noted that some parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0027] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A quantitative analysis method for the exfoliation corrosion resistance of aluminum alloy materials, characterized in that: Includes steps: (1) Prepare calibration samples that meet the requirements of the standard for macroscopic assessment of different corrosion levels by comparing the spectra, cut cross-sectional samples at the location with the most severe surface corrosion, measure the depth of the corrosion layer, and establish the corresponding relationship between the corrosion level and the depth range of the microscopic corrosion layer; (2) Take the aluminum alloy test piece and cut it into test specimens with a width of 30-50 mm and a length of 100-300 mm. Clean the oil stains on the surface of the test specimen, rinse it with clean water, and dry it for later use. Then divide the test surface of the test specimen evenly into several alternating test surfaces and non-test surfaces, and apply a protective coating on the non-test surface. (3) Prepare the corrosion solution according to the alloy type and standard requirements, place the test sample horizontally with the test surface facing up and completely immersed in the solution, and conduct the corrosion test according to the standard requirements; (4) After the corrosion test is completed, cut a cross-sectional specimen at the location where the surface exfoliation corrosion is most serious, mount the specimen, grind and polish it, measure the depth of the corrosion layer, and record it. Determine the corrosion grade based on the measured depth of exfoliation corrosion and the established correspondence between the corrosion grade and the depth range of the microscopic corrosion layer.

2. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 1, characterized in that: In step (2), the test surface includes a test area located on the surface to be tested and a side area of ​​the test area close to the surface to be tested.

3. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 2, characterized in that: The height of the side area of ​​the test surface in step (2) is 2-3 mm.

4. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 1, characterized in that: In the step (2), the protective coating is a strippable chloroprene rubber or an acid-resistant insulating varnish.

5. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 2, characterized in that: When cutting a cross-sectional sample at the location where the surface exfoliation corrosion is most severe in the step (4), the cutting plane is perpendicular to the test area of ​​the test surface located on the surface to be tested and parallel to the length direction of the sample.

6. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 5, characterized in that: When a cross-sectional sample is cut at the location where the surface exfoliation corrosion is most severe in the step (4), the cross-sectional sample cut includes a test surface and a non-test surface.

7. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 1, characterized in that: In the step (4), when testing the depth of the corrosion layer, a metallographic microscope is used to measure the vertical distance between the original surface position of the protective coating and the deepest position of the exfoliation corrosion depth as the depth of the corrosion layer.

8. The method for quantitatively analyzing the exfoliation corrosion resistance of aluminum alloy materials according to claim 1, characterized in that: When testing the corrosion layer depth in step (4), it is necessary to measure at least 5 locations and take the average value.

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