Method for analyzing and detecting defects of large-size aluminum alloy round cast ingot

Abstract

The invention belongs to the technical field of aluminum alloy detection, and particularly relates to an analysis and detection method for defects of a large-size aluminum alloy round ingot, and the defect type can be determined through the detection method. Besides, the analysis and detection method provided by the invention has the advantages of being short in detection process, simple, capable of accurately and comprehensively representing the original characteristics of the defects in the cast ingot and the like, the defects can be prevented from entering the subsequent deformation processing procedure, the product yield is improved, the cost is reduced, and meanwhile, the optimization of the casting process can be effectively guided.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum alloy analysis and detection, and specifically relates to an analysis and detection method for defects of large-size aluminum alloy round ingots. Background Art

[0002] Aluminum alloys have the advantages of high specific strength, low density, good processing performance, corrosion resistance, fracture toughness, etc., and are widely used in aerospace, transportation, 3C and other fields. With the increasing demand for weight reduction of large forgings, the preparation and quality control of large-sized aluminum alloy round ingots have received widespread attention. Large-sized aluminum alloy round ingots are generally prepared by semi-continuous casting. Affected by factors such as raw materials and process conditions, semi-continuous casting round ingots may have defects such as looseness, pores, non-metallic inclusions, oxide film, cracks, etc. These defects will have a great impact on the subsequent deformation processing performance and the final use performance of the product. Therefore, it is of great significance to comprehensively detect and determine the types of defects in semi-continuous ingots and prevent defects from entering the subsequent deformation processing procedures, which is of great significance for optimizing and guiding the melting and casting process and improving the performance and yield of forgings.

[0003] For small-sized semi-continuous ingots, due to the fast cooling rate and relatively fine solidification structure, ultrasonic flaw detection methods can generally be used to detect the position and equivalent size of defects in the ingot, thereby preventing ingots containing excessive defects from entering the subsequent deformation processing process. For large-sized semi-continuous ingots, the solidification structure is usually coarse and uneven, which has a great impact on ultrasonic flaw detection. It is often impossible to obtain accurate defect position and equivalent size information, resulting in defects entering the subsequent deformation and heat treatment processes, affecting product performance and reducing the yield rate. Most existing defect detection methods can only be applied to aluminum alloy forgings or forging samples (for example, patent document 1: CN202311394337.0, patent document 2: CN201910022718.3), or use multi-channel water immersion flaw detection for detection (for example, patent document 3: CN202022287056.3), but these methods have problems such as long detection process, complex equipment, inability to fully characterize the original characteristics of defects in the ingot, and inability to analyze defects with smaller equivalent sizes.

[0004] By applying electromagnetic stirring during the semi-continuous casting process and precisely controlling the temperature field and composition field during the solidification of large-sized round ingots, fine-grained homogeneous ingots with flaw detection conditions can be obtained. However, the analysis and detection methods suitable for defects in large-sized aluminum alloy round ingots have yet to be developed. Summary of the invention

[0005] In view of the above problems, the present invention provides a method for analyzing and detecting defects in large-sized aluminum alloy round ingots, which can be used to accurately and comprehensively determine the original position, equivalent size, type and other characteristics of defects in large-sized ingots, and prevent defects from entering the deformation processing process, thereby improving product yield and reducing production costs, while providing direction for adjusting the smelting and casting processes. To achieve the above purpose, the technical solution of the present invention is as follows: A method for analyzing and detecting defects of large-size aluminum alloy round ingots comprises the following steps: Step 1: preparing an aluminum alloy round ingot by using an electromagnetic stirring semi-continuous casting process, then performing homogenization annealing on the round ingot, and then performing a car skin treatment; Step 2: using an ultrasonic flaw detector to determine the position and equivalent size of defects in the aluminum alloy round ingot behind the car body obtained in step 1 above, and using a cutting tool to obtain the round ingot containing the defective portion; Step 3: Processing the round ingot containing the defective part obtained in the above step 2 into an analysis and detection sample containing defects, and then exposing the defects on the fracture surface through plastic deformation; Step 4: Use a scanning electron microscope to analyze the structural morphology and element distribution of the defects on the fracture surface obtained in step 3 above to determine the defect type.

[0006] Preferably, in step 1, the specification of the aluminum alloy round ingot prepared by the electromagnetic stirring semi-continuous casting process is φ500~1100 mm, the homogenization annealing process is double-stage homogenization annealing, the primary annealing temperature is 450~475℃, the primary annealing time is 14~18 hours, the secondary annealing temperature is 465~490℃, the secondary annealing time is 8~12 hours; the car skin thickness is 3%~5% of the ingot diameter. For double-stage homogenization annealing, the primary annealing temperature is more preferably 460~470℃, the primary annealing time is more preferably 14~17 hours, the secondary annealing temperature is more preferably 480~490℃, and the secondary annealing time is more preferably 9~11 hours.

[0007] Preferably, in step 2, the position of the defect refers to the depth of the defect from the circumferential surface of the aluminum alloy round ingot and the length of the defect from the end surface of the aluminum alloy round ingot.

[0008] Preferably, in step 3, a defective rectangular test block with a size of about 50 mm×50 mm×150 mm is cut from the round ingot containing the defective part, and the defect is located at the center of the test block.

[0009] Preferably, in step 3, for defects with an equivalent size greater than 2 mm, a V-shaped groove is processed on a rectangular test block in a direction parallel to the defect, and a forging machine is used to break the rectangular test block at a speed of 0.5-1 mm / s, so that the defect is exposed on the fracture surface; for defects with an equivalent size of less than 2 mm, a tensile test bar with a parallel section diameter of φ5-15 mm is processed from the rectangular test block, so that the defect is located in the parallel section of the tensile test bar, and an electronic universal testing machine is used to test the defect at a speed of 0.000 25-0.000 50s. -1 The tensile test bar is broken at a strain rate so that the defects are exposed on the fracture surface.

[0010] Preferably, in step 4, a scanning electron microscope is used at an accelerating voltage of 5 to 20 V to obtain secondary electron images and energy spectrum test results of defective and non-defective positions on the fracture, and the types of defects are determined by comparison, the causes of the defects are analyzed, and the optimization of the smelting and casting processes is guided.

[0011] Compared with the existing analysis and detection methods, the advantages of the present invention are: (1) The present invention can be used to analyze and detect defects in large-sized aluminum alloy round ingots, prevent defects from entering subsequent deformation processing procedures, guide the optimization of the melting and casting process, improve product yield, and reduce costs.

[0012] (2) The present invention has a short detection process and a simple method. It can accurately and comprehensively characterize the original characteristics of defects in the ingot and can analyze defects with smaller equivalent sizes, providing new ideas and new directions for solving flaw detection problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Polarized microstructure of annealed φ880 mm 7050 ingot prepared by electromagnetic stirring semi-continuous casting method Figure 2 This is a macroscopic photo of the fracture surface of a tensile test bar with defects. Figure 3 The secondary electron image and energy spectrum scan results of the defective position in the fracture of the tensile test bar; among them, a is the microscopic morphology electron image of the defective position in the fracture, b is the Al element distribution map of the defective position, c is the Zn element distribution map of the defective position, d is the Cu element distribution map of the defective position, e is the Ti element distribution map of the defective position, f is the O element distribution map of the defective position, and g is the Mg element distribution map of the defective position. Figure 4 for Figure 3 Total spectrum of energy spectrum scan Figure 5 Schematic diagram of the energy spectrum test area at different accelerating voltages for (a) defective position and (b) non-defective position in the fracture of a tensile test bar DETAILED DESCRIPTION

[0014] In order to facilitate the understanding of the present invention, detailed descriptions are given in combination with embodiments. It should be noted that the following embodiments are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0015] Embodiment: In this embodiment, a method for analyzing and detecting defects of large-sized aluminum alloy round ingots comprises the following steps: Step 1: A φ880 mm 7050 aluminum alloy round ingot was prepared by semi-continuous casting using electromagnetic stirring (frequency of 3 Hz, stirring voltage of 10 V, stirring current of 80 A), and the fixed length of the ingot was 5000 mm. The round ingot was subjected to double-stage homogenization annealing, and the annealing process adopted was: the first-stage annealing temperature was 465°C, the first-stage annealing time was 16 h, the second-stage annealing temperature was 485°C, and the second-stage annealing time was 10 h. The metallographic structure of the annealed round ingot was analyzed, and its metallographic structure was as follows: Figure 1 As shown in the figure, it can be seen that the grain structure of the annealed ingot is fine and uniform, and the second phase is fully dissolved. Then the round ingot is rolled from φ880 mm to φ850 mm.

[0016] Step 2: Use an ultrasonic flaw detector to inspect the aluminum alloy round ingot behind the car body. The depth of the defect from the circumference of the aluminum alloy round ingot is 291 mm, the length of the defect from the two end faces of the aluminum alloy round ingot is 1348 mm and 3652 mm respectively, and the equivalent size of the defect is 1.25 mm. Mark the defect position and equivalent size on the ingot, and use a sawing machine to cut the round ingot containing the defective part.

[0017] Step 3: Cut a defective rectangular block of approximately 50 mm × 50 mm × 150 mm from the round ingot containing the defect, with the defect located at the center of the block. Process a tensile test bar with a parallel section diameter of φ12.5 mm from the rectangular block, with the defect located in the parallel section of the tensile test bar. Use an electronic universal testing machine to test the defective bars at 0.000 25 s. -1 The tensile test bar is broken at a strain rate so that the defects are exposed on the fracture surface. Figure 2 This is a macroscopic picture of the fracture sample of the above-mentioned tensile test bar. It can be clearly seen from the picture that the gray-black area in the circled part is the defect position, and the defect is located at the fracture.

[0018] Step 4: Use scanning electron microscopy to analyze the microstructure and element distribution of the defects on the fracture surface, and obtain the secondary electron image of the defect position of the above tensile test bar fracture sample (such as Figure 3 ) and the spectrum scan results (as shown Figure 4 as shown).

[0019] Figure 3Figure a shows that there are fewer deformation features at the defective location on the fracture. Figure 3 The presence of titanium element aggregation in e in the figure indicates the presence of a titanium-rich phase at the defect-containing position. Figure 3 f and Figure 3 There are oxygen and magnesium elements aggregated in g, and there is a corresponding relationship between the aggregated areas, indicating that there are magnesium oxides at the defect-containing positions.

[0020] Figure 5 The schematic diagram of the energy spectrum test area at different acceleration voltages (as shown in Table 1) at defective and non-defective positions in the fracture of the tensile test bar is shown in Table 1. The energy spectrum test results are shown in Table 1. In order to obtain the composition information closer to the surface of the sample, the energy spectrum test is carried out at a low acceleration voltage below 20eV, which can avoid the influence of the matrix on the composition test results and is suitable for characterizing surface defects with smaller thickness. The data of the test results at low acceleration voltage in Table 1 further show that the contents of oxygen, magnesium and titanium elements at the defective position are much higher than the contents of the corresponding components at the non-defective position, which can explain the presence of magnesium oxide and titanium-rich phase defects on the fracture surface. According to the type of the defect, it can be inferred that the formation of the defect is related to the process such as the addition method of magnesium ingot and the addition amount of aluminum titanium boron refiner. Therefore, in the actual production process, it can be considered to delay the addition time of magnesium ingot and reduce the addition amount of aluminum titanium boron refiner, which not only optimizes the melting and casting process, but also effectively controls product defects.

[0021]

[0022] It can be seen that the analysis and detection method of defects in large-scale aluminum alloy round ingots of the present invention can be used to accurately and comprehensively determine the original position, equivalent size, type and other characteristics of defects in large-scale ingots, and at the same time prevent defects from entering subsequent deformation processing procedures, which not only improves the product yield and reduces production costs, but also provides direction for the adjustment of smelting and casting processes, and effectively guides the optimization of smelting and casting processes. Therefore, the detection method of the present invention has a very broad application prospect in the field of aluminum alloy analysis and detection technology.

Claims

1. A method for analyzing and detecting defects of large-sized aluminum alloy round ingots, characterized in that: The steps include: Step 1: preparing an aluminum alloy round ingot by using an electromagnetic stirring semi-continuous casting process, then performing homogenization annealing on the round ingot, and then performing a car skin treatment; Step 2: using an ultrasonic flaw detector to determine the position and equivalent size of the defects in the aluminum alloy round ingot after the car body in step 1, and using a cutting tool to obtain the round ingot containing the defective part; Step 3: Processing the round ingot containing the defective part obtained in the above step 2 into an analysis and inspection sample containing defects, and exposing the defects on the fracture surface through plastic deformation; Step 4: Use a scanning electron microscope to analyze the structural morphology and element distribution of the defects on the fracture surface obtained in step 3 above to determine the defect type.

2. The method for analyzing and detecting defects in large-sized aluminum alloy round ingots according to claim 1, characterized in that: In the step 1, the specification of the aluminum alloy round ingot prepared by the electromagnetic stirring semi-continuous casting process is φ500~1100 mm, the homogenization annealing process is two-stage homogenization annealing, the primary annealing temperature is 450~475°C, the primary annealing time is 14~18 hours, the secondary annealing temperature is 465~490°C, and the secondary annealing time is 8~12h; the car skin thickness is 3%~5% of the ingot diameter.

3. The method for analyzing and detecting defects in large-sized aluminum alloy round ingots according to claim 1, characterized in that: In step 2, the position of the defect refers to the depth of the defect from the circumferential surface of the aluminum alloy round ingot and the length of the defect from the end surface of the aluminum alloy round ingot.

4. The method for analyzing and detecting defects in large-sized aluminum alloy round ingots according to claim 1, characterized in that: In the step 3, a defective rectangular test block with a size of 50 mm×50 mm×150 mm is cut from the round ingot containing the defective part, so that the defect is located at the center of the test block.

5. The method for analyzing and detecting defects in large-sized aluminum alloy round ingots according to claim 1, characterized in that: In the step 3, for defects with an equivalent size greater than 2 mm, a V-shaped groove is processed on the rectangular test block in a direction parallel to the defect, and the rectangular test block is broken by a forging machine at a speed of 0.5-1 mm / s, so that the defect is exposed on the fracture surface; for defects with an equivalent size of less than 2 mm, a tensile test bar with a parallel section diameter of φ5-15 mm is processed from the rectangular test block, so that the defect is located in the parallel section of the tensile test bar, and an electronic universal testing machine is used to test the defect at a speed of 0.000 25-0.000 50 s -1 The tensile test bar is broken at a strain rate so that the defects are exposed on the fracture surface.

6. The method for analyzing and detecting defects in large-sized aluminum alloy round ingots according to claim 1, characterized in that: In step 4, a scanning electron microscope is used to obtain secondary electron images and energy spectrum test results of defective and non-defective positions on the fracture surface at an acceleration voltage of 5 to 20 V, thereby comparing and determining the type of defect.

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