Method for analyzing reasons of parabolic lines on surface of low-aluminum-zinc-aluminum-magnesium after punch forming

Abstract

The invention discloses a reason analysis method for parabolic lines on the surface of low-aluminum-zinc-aluminum-magnesium after punch forming, and belongs to the technical field of plating layer analysis and detection. The method comprises the following steps: (1) taking a zinc-aluminum-magnesium plate with parabolic lines on the surface after stamping, and cutting two round samples; (2) taking a round sample, and putting the round sample into the display agent until the cross grain defect is clearly displayed on the surface of the sample plate; (3) putting the sample plate in the step (2) under a scanning electron microscope to observe the cross grain defect and the spacing; and (4) another round sample is taken and subjected to a tensile test, obvious parabolic lines exist on the surface after stretching, and the test result fully shows that the parabolic lines on the surface of the zinc-aluminum-magnesium plate after punch forming are caused by transverse line defects existing in the original plate. According to the method, the cross grain defects of the original plate and the stamped parabolic grains are subjected to correlation research, the parabolic grains after stamping forming are precisely traced, the production problem can be precisely positioned, the original plate is guided to be managed and controlled in advance, cost is reduced, efficiency is improved, and the method is rapid, simple, accurate and low in cost.

Description

Technical Field

[0001] This invention relates to the field of coating analysis and testing technology, specifically to a method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping. Background Technology

[0002] Low-aluminum-zinc-aluminum-magnesium coated steel sheets, as a novel material, have shown great potential in the automotive, home appliance, and construction industries due to their high corrosion resistance and surface quality. With the promotion of green building materials and lightweight materials, the replacement of traditional materials by low-aluminum-zinc-aluminum-magnesium coated steel sheets in multiple fields is accelerating. As the technology matures and costs are optimized, its market penetration rate is expected to continue to increase.

[0003] With the rapid development of industries such as automobiles and home appliances, the requirements for the surface quality of stamped metal sheets are becoming increasingly stringent. After stamping, low-aluminum-zinc-aluminum-magnesium coated sheets often exhibit parabolic defects on the surface, which not only affects the appearance of the product but may also reduce its corrosion resistance and mechanical properties.

[0004] To determine the cause of the parabolic streaks on the surface after stamping, scanning electron microscopy (SEM) was used to observe the original low-aluminum-zinc-aluminum-magnesium coated sheet before stamping, but no defects were observed. Analysis using SEM combined with energy dispersive spectroscopy (EDS) showed no abnormalities in composition. Cross-sectional metallographic analysis also showed no abnormalities. These methods were insufficient to determine the cause of the parabolic streaks. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for analyzing the causes of parabolic lines on the surface of low-aluminum-zinc-aluminum-magnesium stamping. This method can clearly show the transverse defects on the surface of the original plate, and then determine through tensile forming test that the parabolic line defects on the surface of the low-aluminum-zinc-aluminum-magnesium plate are caused by the regular transverse defects on the surface of the original plate. It has the characteristics of low detection cost, speed, simplicity and accuracy.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping includes the following steps: (1) Wire cutting to obtain samples: Take a 210mm×300mm zinc-aluminum-magnesium plate with parabolic lines on the surface after stamping, and cut two circular samples with a size of 95±0.05mm using a metallographic cutting machine. (2) Displaying transverse defects on the original plate: Take a circular sample after wire cutting in step (1), put it in the display agent for 3-10 minutes, and take it out after the transverse defects are clearly displayed on the surface of the sample. Rinse it clean with alcohol. The display agent is made by adding 2-8 mL of 5% copper sulfate aqueous solution to 100 mL of water. (3) Observation under scanning electron microscope: Cut 10mm×10mm-15mm×15mm sample blocks from the sample in step (2) using a shearing machine, rinse them with alcohol, and observe the transverse defects and spacing under a ZEISS scanning electron microscope. (4) Tensile forming verification: Take another circular sample from step (1), clean the surface, apply lubricating oil evenly to the upper and lower surfaces, select the mold according to the sample thickness, select the constant blanking force mode, the blanking force is 10-15 kN, the load is controlled at 1-3 kN, the punch speed is 15-25 mm / min, and a tensile test is carried out. After stretching, there are obvious parabolic patterns on the surface. The test results fully demonstrate that the parabolic patterns on the surface of the zinc-aluminum-magnesium plate after stamping are caused by the transverse defects in the original plate.

[0007] Preferably, in step (2), the ZEISS scanning electron microscope uses a high voltage of 15KV and the mode is HDBSD.

[0008] Uneven passivation film causes transverse striation defects on the surface of the original plate. These defects are not observable using conventional testing methods. This invention focuses on the correlation between transverse striation defects in the original plate and stamping parabolic striations. Determining a one-to-one correspondence between the formation of parabolic striations and transverse striation defects after stamping requires specific experimental parameters and methods, as well as cross-validation with multi-dimensional data. The experimental method created in this invention can achieve this goal. The innovative indicator and detection method, combined with unique correlation research, accurately determine the cause of parabolic striation formation, precisely locate production problems, optimize detection applications, and provide innovative extensions. Furthermore, it fills the detailed gap in defect tracing in the production process, which is of great significance for actual production quality control.

[0009] The principle of the indicator of this invention is as follows: a copper sulfate solution can undergo a displacement reaction with the zinc in the zinc layer of a galvanized sheet. The passivation film (such as a chromate film) on the surface of the galvanized sheet is a dense protective layer that can prevent the copper sulfate solution from reacting with the underlying zinc layer. However, there is a "passivation film barrier difference." A complete and thick passivation film can prevent the reaction, while defective areas or thin passivation films cannot block it. Thus, defects are revealed through precipitates, reflecting differences in film thickness.

[0010] The above technical solution has the following advantages compared with the existing technology: 1. The display agent of the present invention can fully display the horizontal defects of the original board, and has the characteristics of being simple, accurate, fast and low cost.

[0011] 2. The method of this invention studies the correlation between the transverse defects of the original plate and the parabolic patterns after stamping, accurately traces the source of the parabolic patterns after stamping, and verifies the display of the transverse defects of the original plate and the formation process of the parabolic patterns after stamping. It can accurately locate production problems, guide the early control of the original plate, reduce costs and increase efficiency, and is fast, simple, accurate and low cost. Attached Figure Description

[0012] Figure 1a Photograph of the original plate surface in Example 1; Figure 1b The photograph shown in Example 1 shows the result after the horizontal striation defect was detected. Figure 2 The image shown is a scanning electron microscope image of the transverse striation defect in Example 1. Figure 3 This is a photograph of the surface after stretching in Example 1; Figure 4 The image shown in Comparative Example 1 was observed using a direct scanning electron microscope. Figure 5 The results of cross-sectional metallographic analysis are for Comparative Example 1; Figure 6a Photograph of the original plate in Example 2; Figure 6b The photograph shown in Example 1 shows the result after the horizontal striation defect was detected. Figure 7 The image shown is a scanning electron microscope image of the transverse striation defect in Example 2. Figure 8 This is a photograph of the surface after stretching in Example 2; Figure 9a Photograph of the original plate surface in Example 3; Figure 9b The photograph shown in Example 1 shows the result after the horizontal striation defect was detected. Figure 10 The image shown is a scanning electron microscope image of the transverse striation defect in Example 3. Figure 11 This is a photograph of the surface after stretching in Example 3. Detailed Implementation

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0014] A method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping is as follows: (1) Wire cutting to obtain samples: Take a 1.0mm zinc-aluminum-magnesium plate (grade DC53D+ZM) 210mm×300mm with parabolic lines on the surface after stamping, and cut two circular samples with a size of 95.05mm using a metallographic cutting machine. (2) Displaying transverse defects on the original plate: Take a circular sample after wire cutting in step (1) and place it in the following display agent: 2 mL of 5% copper sulfate aqueous solution is added to 100 mL of water. Let it stand for 10 minutes until the transverse defects caused by uneven passivation film are clearly displayed on the sample surface. Then, take it out and rinse it with alcohol. See the original plate and the photos after the defects are displayed. Figure 1a and Figure 1b .

[0015] (3) Observation under scanning electron microscope: Cut a 10mm×10mm sample from step 2 using a shearing machine, rinse it with alcohol, and observe it under a ZEISS scanning electron microscope. The high voltage is set to 15KV, and the mode is set to HDBSD mode. The cross-shaped defects caused by the uneven passivation film and the spacing of the cross-shaped defects caused by the uneven passivation film are clearly shown, which are 504.5 μm and 361.8 μm. See Figure 2 .

[0016] (4) Tensile forming verification: Take another circular sample from step 1, clean the surface, apply lubricating oil evenly to the upper and lower surfaces, select a suitable mold according to the sample thickness, select the constant blank holder force mode, the blank holder force is 10 kN, the load is controlled at 1 kN, the punch speed is 15 mm / min, and a tensile test is performed. The test results show that parabolic patterns can be clearly displayed on the surface of the stamped part, which fully demonstrates that the parabolic patterns on the surface of the zinc-aluminum-magnesium plate after stamping are caused by the transverse defects caused by the uneven passivation film in the original plate. The surface after tensile forming shows Figure 3 .

[0017] Comparative Example 1: Images of the original plate observed directly by scanning electron microscopy, showing no transverse striation defects caused by uneven surface passivation film. Direct scanning electron microscopy was used to observe the parabolic lines on the surface of the zinc-aluminum-magnesium plate after stamping. However, it failed to reveal transverse defects caused by uneven passivation film. The procedure is as follows: (1) Take a 1.0mm zinc-aluminum-magnesium plate (grade DC53D+ZM) with parabolic patterns on the surface after stamping, and cut an 8×10mm sample using a shearing machine.

[0018] (2) Place the sample in a beaker containing alcohol, clean the surface with ultrasonic for 5 minutes, then remove it and dry it with a hair dryer.

[0019] (3) When observed under a scanning electron microscope, no characteristic morphology was found. Direct observation under a scanning electron microscope could not reveal the transverse defects caused by uneven thickness of the passivation film. The results are shown in the figure. Figure 4 .

[0020] Comparative Example 2: Cross-sectional metallographic methods cannot observe transverse striation defects. Cross-sectional metallography can only observe the zinc-aluminum-magnesium phase structure of the coating, but cannot determine the cause of the parabolic lines on the surface after stamping. This includes wire cutting of samples, hot mounting, grinding, polishing, etching, and metallographic microscopy observation, specifically: (1) Sampling: Take a 1.2mm zinc-aluminum-magnesium plate (grade DC51D+ZM) with parabolic patterns on the surface after stamping, and cut a sample with a size of 8mm×8mm using wire cutting. (2) Hot mounting: The sample from step 1 is placed vertically into the mounting machine for mounting, which takes 10 minutes.

[0021] (3) Grinding: After mounting, the sample is coarsely ground with 280# metallographic sandpaper until the scratches are in the same direction. After rotating 90°, it is finely ground with 600# sandpaper until the previous scratch disappears. After rotating 90° again, it is finely ground with 800# sandpaper until the previous scratch disappears. This process takes 10 minutes.

[0022] (4) Then polishing is performed, specifically: water and 2.5μm high-efficiency metallographic polishing agent are sprayed evenly onto a 250mm pressure-sensitive adhesive woolen polishing cloth, and then polished for 2 minutes at a speed of 600 rpm.

[0023] (5) Corrosion: Specifically, after polishing, corrode with 0.1% nitric acid alcohol for 3 seconds, rinse with alcohol and blow dry.

[0024] (5) Metallographic microscopy revealed only the zinc-aluminum-magnesium coating; the cause of the parabolic lines on the surface after stamping could not be identified. See details... Figure 5 . Example 2

[0025] A method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping is as follows: (1) Wire cutting to obtain samples: Take a 1.2mm zinc-aluminum-magnesium plate (grade DC51D+ZM) with parabolic lines on the surface after stamping, and cut two circular samples with a size of 95mm using wire cutting. (2) Displaying transverse defects on the original plate: Take a circular sample after wire cutting in step (1) and place it in the following display agent: 8 mL of 5% copper sulfate aqueous solution + 100 mL of water. Let it stand for 3 minutes until the transverse defects caused by uneven passivation film are clearly displayed on the sample surface. Then, take it out and rinse it with alcohol. See the original plate and the photos after the defects are displayed. Figure 6a and Figure 6b .

[0026] (3) Observation under scanning electron microscope: Cut a 15mm×15mm sample from the sample in step 2 using a shearing machine, rinse it with alcohol, and observe it under a ZEISS scanning electron microscope. The high voltage is set to 15KV, and the mode is set to HDBSD mode. The cross-stripping defects caused by the uneven passivation film can be clearly shown, and the spacing of the cross-stripping defects caused by the uneven passivation film is 405.5 μm and 341.7 μm, respectively. See Figure 7 .

[0027] (4) Tensile forming verification: Take another circular sample from step 1, clean the surface, apply lubricating oil evenly to the upper and lower surfaces, select a suitable mold according to the sample thickness, select the constant blank holder force mode, the blank holder force is 15 kN, the load is controlled at 3 kN, the punch speed is 25 mm / min, and a tensile test is performed. The test results show that parabolic patterns can be clearly displayed on the surface of the stamped part, which fully demonstrates that the parabolic patterns on the surface of the zinc-aluminum-magnesium plate after stamping are caused by the uneven thickness of the passivation film of the original plate. After tensile forming, the surface shows Figure 8 . Example 3

[0028] A method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping is as follows: (3) Wire cutting to obtain samples: Take a 1.5mm zinc-aluminum-magnesium plate (grade DC52D+ZM) with parabolic lines on the surface after stamping. Take a 210mm×300mm zinc-aluminum-magnesium plate and cut two circular samples with a size of 94.95mm using a metallographic cutting machine. (2) Displaying transverse defects on the original plate: Take a circular sample after wire cutting in step (1) and place it in the following display agent: 5 mL of 5% copper sulfate aqueous solution + 100 mL of water. Let it stand for 6 minutes until the transverse defects caused by uneven passivation film are clearly displayed on the sample surface. Then, take it out and rinse it with alcohol. See the original plate and the photos after the defects are displayed. Figure 9a and Figure 9b .

[0029] (3) Observation under scanning electron microscope: Cut a 12mm×12mm sample from the sample in step 2 using a shearing machine, rinse it with alcohol, and observe it under a ZEISS scanning electron microscope. The high voltage is set to 15KV, and the mode is set to HDBSD mode. The cross-shaped defects caused by the uneven passivation film can be clearly shown, and the spacing of the cross-shaped defects caused by the uneven passivation film is 405.5 micrometers. See Figure 10 .

[0030] (4) Tensile forming verification: Take another circular sample from step 1, clean the surface, apply lubricating oil evenly to the upper and lower surfaces, select a suitable mold according to the sample thickness, select the constant blank holder force mode, the blank holder force is 13 kN, the control load is 2 kN, the punch speed is 20 mm / min, and a tensile test is performed. The test results show that parabolic patterns can be clearly displayed on the surface of the stamped part, which fully demonstrates that the parabolic patterns on the surface of the zinc-aluminum-magnesium plate after stamping are caused by the uneven thickness of the passivation film of the original plate. After tensile forming, the surface shows Figure 11 .

[0031] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping, characterized in that: Includes the following steps: (1) Wire cutting to obtain samples: Take a 210mm×300mm zinc-aluminum-magnesium plate with parabolic lines on the surface after stamping, and cut two circular samples with a size of 95±0.05mm using a metallographic cutting machine. (2) Displaying transverse defects on the original plate: Take a circular sample after wire cutting in step (1), put it in the display agent for 3-10 minutes, and take it out after the transverse defects are clearly displayed on the surface of the sample. Rinse it clean with alcohol. The display agent is made by adding 2-8 mL of 5% copper sulfate aqueous solution to 100 mL of water. (3) Observation under scanning electron microscope: Cut 10mm×10mm-15mm×15mm sample blocks from the sample in step (2) using a shearing machine, rinse them with alcohol, and observe the transverse defects and spacing under a ZEISS scanning electron microscope. (4) Tensile forming verification: Take another circular sample from step (1), clean the surface, apply lubricating oil evenly to the upper and lower surfaces, select the mold according to the sample thickness, select the constant blanking force mode, the blanking force is 10-15 kN, the load is controlled at 1-3 kN, the punch speed is 15-25 mm / min, and a tensile test is carried out. After stretching, there are obvious parabolic patterns on the surface. The test results fully demonstrate that the parabolic patterns on the surface of the zinc-aluminum-magnesium plate after stamping are caused by the transverse defects in the original plate.

2. The method for analyzing the causes of parabolic lines on the surface after low-aluminum, zinc, aluminum, and magnesium stamping as described in claim 1, characterized in that: In step (2), the ZEISS scanning electron microscope is set to 15KV high voltage and HDBSD mode.

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