Three-dimensional nondestructive testing method for micro thermal crack defects of rare earth magnesium alloy

Abstract

The application discloses a three-dimensional nondestructive testing method for micro hot crack defects of a rare earth magnesium alloy, and relates to a method for testing micro hot crack defects of a magnesium alloy. The application directly presents the hot crack defects in the rare earth magnesium alloy in a nondestructive testing mode based on three-dimensional computer reconstruction technology, which is beneficial to judging the sensitivity of the existing rare earth magnesium alloy material to the hot crack defects and qualitatively and quantitatively analyzing the number of the hot cracks. On the other hand, the formation mechanism of the hot crack defects in the rare earth magnesium alloy is revealed through the appearance and distribution state of the hot crack defects in the rare earth magnesium alloy. Furthermore, the application can be combined with destructive testing of actual castings to further evaluate whether the castings are qualified, the detection precision can reach 5 microns, even the hot cracks in the micron level can be recognized, the production efficiency is improved, and the cost is reduced.

Description

Technical Field

[0001] This invention relates to a method for detecting microscopic hot crack defects in magnesium alloys. Background Technology

[0002] Rare earth elements (REs) have solid solution strengthening and precipitation strengthening effects, which can alter the high-temperature tensile and creep properties of magnesium alloys and improve their corrosion resistance. Therefore, to significantly improve the performance of magnesium alloys, large amounts of REs are added to traditional magnesium alloys. However, with the large addition of REs, the casting performance of magnesium alloys declines sharply. The most prominent issue is that rare earth magnesium alloys are highly susceptible to hot cracking defects.

[0003] Hot cracking is a high-temperature cracking process caused by stress concentration during solidification. Hot cracks have an oxidized surface and a zigzag shape. Based on their formation, hot cracks can be classified as external cracks and internal cracks. External cracks often occur at corners of castings, where there are abrupt changes in cross-sectional thickness, or where localized slow solidification occurs and tensile stress is applied during solidification; they are mostly through-cracks. External cracks can be detected visually. However, internal cracks are difficult to detect because they occur inside the casting. When rare earth magnesium alloy castings with internal cracks are used, they can easily become a potential source of casting failure. Therefore, if internal hot crack defects in rare earth magnesium alloys are not accurately detected, they can lead to significant economic losses. Currently, apart from through-cracks (external type), which can be visually detected, other types of hot cracks are difficult to identify accurately. Furthermore, conventional non-destructive testing methods such as radiographic testing have millimeter-level accuracy, which is far from sufficient for internal hot cracks (the size of internal hot cracks is <1mm). Therefore, existing technologies cannot completely identify internal hot crack defects in rare earth magnesium alloy castings. Summary of the Invention

[0004] This invention, based on three-dimensional computer reconstruction technology, uses non-destructive testing to visually present the hot crack defects inside rare earth magnesium alloys. On the one hand, it helps to determine the sensitivity of existing rare earth magnesium alloy materials to hot crack defects and to perform qualitative and quantitative analysis of the number of hot cracks; on the other hand, it reveals the formation mechanism of hot crack defects in rare earth magnesium alloys by observing the morphology and distribution of hot crack defects.

[0005] The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys of the present invention is carried out according to the following steps:

[0006] I. Sampling

[0007] Samples were taken from rare earth magnesium alloy castings;

[0008] II. Layer-by-layer imaging using a three-dimensional X-ray microscope

[0009] The sample is placed in a three-dimensional X-ray microscope and photographed layer by layer to capture the internal information of the sample in the form of images.

[0010] III. Using data visualization software for 3D modeling

[0011] Import the photos obtained in step two into 3D image processing and analysis software for 3D modeling, and divide the model into different regions according to the different contrasts.

[0012] IV. Image Processing

[0013] In 3D image processing and analysis software, different regions in the 3D model are assigned color values ​​so that different regions display different colors, thereby improving the degree of differentiation and being used to calculate the volume ratio of thermal crack defects in the sample.

[0014] V. Calculation of the volume percentage of hot crack defects in the specimen

[0015] The volume of the hot crack defect region was calculated using 3D image processing and analysis software, and the volume ratio of the hot crack defect in the sample was also calculated.

[0016] VI. Calculation of the critical value of the proportion of hot crack defects

[0017] Take multiple rare earth magnesium alloy castings that fail the pressure test and performance evaluation, and take samples from these rare earth magnesium alloy castings. The sampling location is the failure location on the rare earth magnesium alloy castings during the pressure test and performance evaluation process. Calculate the volume ratio of hot crack defects in the sample according to the method in steps one to five. The minimum value among multiple calculation results is the critical value of the hot crack defect ratio.

[0018] VII. Three-dimensional non-destructive testing of rare earth magnesium alloy castings

[0019] Take a new rare earth magnesium alloy casting, calculate the volume ratio of hot crack defects in the sample according to steps one to five, and determine the scrapped casting and qualified casting based on the critical ratio of hot crack defects.

[0020] The principle and beneficial effects of this invention are as follows:

[0021] This invention utilizes three-dimensional computer reconstruction technology to identify hot crack defects in rare earth magnesium alloys, enabling the detection of internal cracks in castings. Furthermore, it can be combined with destructive testing of actual castings to further evaluate casting quality, achieving a detection accuracy of up to 5μm. Even micron-level hot cracks can be identified, improving production efficiency and reducing costs. Attached Figure Description

[0022] Figure 1 A schematic diagram showing the dimensions of a ZM6 alloy sample.

[0023] Figure 2 The 3D model obtained by importing a photo into Drogonfly software;

[0024] Figure 3 A schematic diagram of hot cracking defects in a three-dimensional model of ZM6 alloy;

[0025] Figure 4 This is a schematic diagram showing the distribution location of hot crack defects in the three-dimensional model of ZM6 alloy;

[0026] Figure 5 This is a morphological image of the ZM6 alloy sample cross-section after polishing. Detailed Implementation

[0027] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.

[0028] Specific Implementation Method 1: The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys in this implementation method is carried out according to the following steps:

[0029] I. Sampling

[0030] Samples were taken from rare earth magnesium alloy castings;

[0031] II. Layer-by-layer imaging using a three-dimensional X-ray microscope

[0032] The sample is placed in a three-dimensional X-ray microscope and photographed layer by layer to capture the internal information of the sample in the form of images.

[0033] III. Using data visualization software for 3D modeling

[0034] Import the photos obtained in step two into 3D image processing and analysis software for 3D modeling, and divide the model into different regions according to the different contrasts.

[0035] IV. Image Processing

[0036] In 3D image processing and analysis software, different regions in the 3D model are assigned color values ​​so that different regions display different colors, thereby improving the degree of differentiation and being used to calculate the volume ratio of thermal crack defects in the sample.

[0037] V. Calculation of the volume percentage of hot crack defects in the specimen

[0038] The volume of the hot crack defect region was calculated using 3D image processing and analysis software, and the volume ratio of the hot crack defect in the sample was also calculated.

[0039] VI. Calculation of the critical value of the proportion of hot crack defects

[0040] Take multiple rare earth magnesium alloy castings that fail the pressure test and performance evaluation, and take samples from these rare earth magnesium alloy castings. The sampling location is the failure location on the rare earth magnesium alloy castings during the pressure test and performance evaluation process. Calculate the volume ratio of hot crack defects in the sample according to the method in steps one to five. The minimum value among multiple calculation results is the critical value of the hot crack defect ratio.

[0041] VII. Three-dimensional non-destructive testing of rare earth magnesium alloy castings

[0042] Take a new rare earth magnesium alloy casting, calculate the volume ratio of hot crack defects in the sample according to steps one to five, and determine the scrapped casting and qualified casting based on the critical ratio of hot crack defects.

[0043] This embodiment has the following beneficial effects:

[0044] This embodiment utilizes three-dimensional computer reconstruction technology to identify hot crack defects in rare earth magnesium alloys, enabling the detection of internal cracks in castings. Furthermore, it can be combined with destructive testing of actual castings to further evaluate casting quality, achieving a detection accuracy of up to 5μm. Even micron-level hot cracks can be identified, improving production efficiency and reducing costs.

[0045] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the three-dimensional image processing and analysis software is Drogonfly.

[0046] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: the method for calculating the volume ratio of hot crack defects in the sample in step 5 is as follows: first, export the volume of all hot crack defect regions in the three-dimensional image processing and analysis software, and then divide the sum of the volumes of all hot crack defect regions by the volume of the sample to obtain the proportion of hot crack defects in the analyzed sample.

[0047] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the method for determining scrapped and qualified castings in step six is ​​as follows: If the volume percentage of hot crack defects in a new rare earth magnesium alloy casting exceeds a critical value for the proportion of hot crack defects, it is determined to be a scrapped casting; if the volume percentage of hot crack defects in a new rare earth magnesium alloy casting is below the critical value for the proportion of hot crack defects, it is determined to be a qualified casting. Based on this method, scrapped castings can be avoided only after testing, improving production efficiency and reducing costs.

[0048] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that the dimensions of the sample described in Step One are: diameter φ = 2-8 mm, height h = 6-14 mm.

[0049] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that the dimensions of the sample are: diameter φ = 2 mm and height h = 6 mm.

[0050] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the dimensions of the sample are: diameter φ = 8 mm and height h = 14 mm.

[0051] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that the dimensions of the sample are: diameter φ = 2 mm and height h = 14 mm.

[0052] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the dimensions of the sample are: diameter φ = 8 mm and height h = 6 mm.

[0053] Specific Implementation Method 10: This implementation method differs from Specific Implementation Methods 1 to 9 in that the dimensions of the sample are: diameter φ = 5mm and height h = 10mm.

[0054] Example:

[0055] The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys of the present invention is carried out according to the following steps:

[0056] I. Sampling

[0057] Samples were taken from rare earth magnesium alloy castings; the dimensions of the samples were: diameter φ = 5 mm, height h = 10 mm.

[0058] Samples such as Figure 1 As shown;

[0059] II. Layer-by-layer imaging using a three-dimensional X-ray microscope

[0060] The sample is placed in a three-dimensional X-ray microscope and photographed layer by layer to capture the internal information of the sample in the form of images.

[0061] III. Using data visualization software for 3D modeling

[0062] Import the photos obtained in step two into Drogonfly software for 3D modeling, and divide the model into different regions according to the different contrasts; Figure 2The 3D model obtained by importing the photo into Drogonfly software varies in its reflection, scattering, and absorption of X-rays due to the different atomic numbers of different elements. This is reflected in the 3D model as differences in brightness and contrast. After dividing the model into different regions based on the different contrasts, regions with similar gray levels are marked to separate different regions. For example, the bright areas are rare earth-containing precipitates, the dark areas are α-Mg matrix, and the black areas represent cavities where X-rays pass straight through, i.e., the black areas are where thermal cracks are located.

[0063] IV. Image Processing

[0064] In Drogonfly software, different regions in the 3D model are assigned color values ​​so that different regions display different colors to improve the distinction and to calculate the volume ratio of thermal crack defects in the sample.

[0065] Figure 3 A schematic diagram of hot cracking defects in a three-dimensional model of ZM6 alloy; Figure 4 This is a schematic diagram showing the distribution of hot crack defects in the three-dimensional model of ZM6 alloy. The ZM6 alloy sample section was polished by first grinding with 400# to 2000# sandpaper, and then polishing on a velvet polishing cloth at a speed of 300 r / min. Figure 5 This is a morphological image of the ZM6 alloy sample cross-section after polishing. The polishing process reveals the form, size, and characteristics of hot crack defects. Figures 3-5 As can be seen, this embodiment accurately located the thermal crack defect using 3D computer reconstruction technology, verifying the accuracy of analyzing thermal crack defects using this technology. It also proves that the initiation of thermal cracks is not limited to a single point, but rather involves multiple locations initiating simultaneously.

[0066] V. Calculation of the volume percentage of hot crack defects in the specimen

[0067] The volume of the hot crack defect region was calculated using Drogonfly software, and the volume ratio of hot crack defects in the sample was also calculated.

[0068] The method for calculating the volume ratio of hot crack defects in the sample is as follows: First, export the volume of all hot crack defect regions in Drogonfly software, i.e., the volumes of ID1 to ID31 in Table 1; then divide the sum of the volumes of all hot crack defect regions by the volume of the sample to obtain the proportion of hot crack defects in the analyzed sample.

[0069] Table 1 Quantitative statistics of hot cracking defects

[0070]

[0071]

[0072] The samples in Table 1 contain 31 hot crack initiation points, with volumes ranging from 5.65 × 10⁻⁶. -5 mm 3 Up to 0.761572575mm 3 Inconsistent. Overall, only the hot crack size > 0.1 mm was observed in ID=30 and ID=31. 3 , respectively corresponding to Figure 3 and Figure 4 The red and blue areas. The remaining 29 thermal cracks are smaller in size, in Figure 3 and Figure 4 The purple area is represented in the middle. In addition to volume, Table 1 also includes surface area and specific surface area (volume / surface area) to determine the morphology of hot cracks. Although the volumes of different hot cracks vary greatly (4-5 orders of magnitude), their specific surface areas are basically similar, ranging from 0.005 to 0.028. This indicates that the morphology of hot cracks of different volumes tends to be consistent, i.e., lamellar. This is due to the formation of hot cracks, which originate from the tearing of the intergranular liquid film. The hot cracks inherit the morphology of the liquid film, thus exhibiting a lamellar structure in three-dimensional space. Multiple hot crack initiation points work together to cause hot cracks in ZM6 alloy castings.

[0073] VI. Calculation of the critical value for the proportion of hot crack defects

[0074] Take three rare earth magnesium alloy castings that failed the pressure test and performance evaluation, and take samples from these rare earth magnesium alloy castings (sample 1-1, sample 1-2, and sample 1-3, respectively). The sampling location is the failure location on the rare earth magnesium alloy casting during the pressure test and performance evaluation. Calculate the volume ratio of hot crack defects in the sample according to the method in steps one to five. The minimum value among multiple calculation results is the critical value of the hot crack defect ratio.

[0075] The proportion of hot crack defects in sample 1-1 was 4.91%; the proportion of hot crack defects in sample 1-2 was 5.25%; and the proportion of hot crack defects in sample 1-3 was 3.11%. Therefore, the critical value for the proportion of hot crack defects was 3.11%.

[0076] VII. Three-dimensional non-destructive testing of rare earth magnesium alloy castings

[0077] Take a new rare earth magnesium alloy casting, calculate the volume ratio of hot crack defects in the sample according to the methods in steps one to five, and determine the scrapped casting and qualified casting based on the critical ratio of hot crack defects.

[0078] The method for determining scrapped and qualified castings is as follows: if the volume ratio of hot crack defects in a new rare earth magnesium alloy casting exceeds the critical value of the hot crack defect ratio, it is determined to be a scrapped casting; if the volume ratio of hot crack defects in a new rare earth magnesium alloy casting is lower than the critical value of the hot crack defect ratio, it is determined to be a qualified casting.

[0079] Three samples were taken from three different locations on the new rare-earth magnesium alloy casting: sample 2-1, sample 2-2, and sample 2-3. The test results were as follows: the proportion of hot crack defects in sample 2-1 was 6.22%; the proportion of hot crack defects in sample 2-2 was 4.32%; and the proportion of hot crack defects in sample 2-3 was 3.48%. The proportion of hot crack defects at each location on the new rare-earth magnesium alloy casting was greater than the critical value of 3.11%, therefore it was determined that the new rare-earth magnesium alloy casting would produce hot crack defects.

Claims

1. A three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys, characterized in that: The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys is carried out according to the following steps: I. Sampling Samples were taken from rare earth magnesium alloy castings; II. Layer-by-layer imaging using a three-dimensional X-ray microscope The sample is placed in a three-dimensional X-ray microscope and photographed layer by layer to capture the internal information of the sample in the form of images. III. Using data visualization software for 3D modeling Import the photos obtained in step two into 3D image processing and analysis software for 3D modeling, and divide the model into different regions according to the different contrasts. IV. Image Processing In 3D image processing and analysis software, different regions in the 3D model are assigned color values ​​so that different regions display different colors, thereby improving the degree of differentiation and being used to calculate the volume ratio of thermal crack defects in the sample. V. Calculation of the volume percentage of hot crack defects in the specimen The volume of the hot crack defect region was calculated using 3D image processing and analysis software, and the volume ratio of the hot crack defect in the sample was also calculated. VI. Calculation of the critical value of the proportion of hot crack defects Take multiple rare earth magnesium alloy castings that fail the pressure test and performance evaluation, and take samples from these rare earth magnesium alloy castings. The sampling location is the failure location on the rare earth magnesium alloy castings during the pressure test and performance evaluation process. Calculate the volume ratio of hot crack defects in the sample according to the method in steps one to five. The minimum value among multiple calculation results is the critical value of the hot crack defect ratio. VII. Three-dimensional non-destructive testing of rare earth magnesium alloy castings Take a new rare earth magnesium alloy casting, calculate the volume ratio of hot crack defects in the sample according to steps one to five, and determine the scrapped casting and qualified casting based on the critical ratio of hot crack defects.

2. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 1, characterized in that: The 3D image processing and analysis software is Drogonfly.

3. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 1, characterized in that: The method for calculating the volume ratio of hot crack defects in the sample in step five is as follows: First, export the volume of all hot crack defect areas in the three-dimensional image processing and analysis software, and then divide the sum of the volumes of all hot crack defect areas by the volume of the sample to obtain the proportion of hot crack defects in the analyzed sample.

4. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 1, characterized in that: The method for determining scrapped and qualified castings in step six is ​​as follows: if the volume ratio of hot crack defects in a new rare earth magnesium alloy casting exceeds the critical value of the proportion of hot crack defects, it is determined to be a scrapped casting; if the volume ratio of hot crack defects in a new rare earth magnesium alloy casting is lower than the critical value of the proportion of hot crack defects, it is determined to be a qualified casting.

5. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 1, characterized in that: The dimensions of the sample described in step one are: diameter φ = 2-8 mm, height h = 6-14 mm.

6. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 5, characterized in that: The dimensions of the sample are: diameter φ = 2 mm, height h = 6 mm.

7. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 5, characterized in that: The dimensions of the sample are: diameter φ = 8 mm, height h = 14 mm.

8. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 5, characterized in that: The dimensions of the sample are: diameter φ = 2 mm, height h = 14 mm.

9. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 5, characterized in that: The dimensions of the sample are: diameter φ = 8 mm, height h = 6 mm.

10. The three-dimensional non-destructive testing method for microscopic hot crack defects in rare earth magnesium alloys according to claim 5, characterized in that: The dimensions of the sample are: diameter φ = 5 mm, height h = 10 mm.

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