A method for observing grain distribution of aluminum alloy

Abstract

The present invention provides a method for observing the distribution of aluminum alloy grains, which specifically includes the following steps: S1, mechanical polishing, by sequentially using 400-2000 mesh sandpaper and 3μm and 0.5μm polishing paste to perform step-by-step fine processing on the surface of the aluminum alloy sample until there is no obvious scratch on the surface; S2, electrolytic polishing; S3, anodic coating; S4, polarizing microscope observation, placing the coated sample under a polarizing microscope, observing and recording the distribution, size and morphology of the grains within a magnification range of 200× to 1000×. The present invention can significantly improve the contrast of the grain boundary and the accuracy of observation by optimizing the polishing, electrolysis and observation steps, has the advantages of simple operation, good repeatability and wide application range, and is suitable for microstructure analysis of aluminum alloys.

Description

Technical Field

[0001] The present invention relates to a method for observing grain distribution, and more specifically to a method for observing grain distribution of aluminum alloy. Background Art

[0002] Aluminum alloys are widely used in aerospace, automobile manufacturing, construction engineering and other fields due to their light weight, high strength and excellent corrosion resistance. However, the performance of aluminum alloys is largely affected by their internal grain structure. The size and distribution of grains directly determine the mechanical properties (such as strength, ductility and fatigue life) and corrosion resistance of the material. Therefore, how to efficiently and accurately observe and analyze the grain distribution of aluminum alloys has become an important topic in material research and quality control.

[0003] The existing aluminum alloy grain observation technology has the following limitations:

[0004] ① The polishing process is unstable: Mechanical polishing and chemical polishing have high requirements on the flatness and uniformity of the sample surface. Different process parameters may lead to deviations in grain observation results.

[0005] ② Complex sample preparation: including mechanical polishing, electrolytic polishing and anodic coating steps, the operation is cumbersome and time-consuming, and it relies heavily on equipment accuracy and operator experience.

[0006] ③ Limited observation effect: Although polarizing microscope has great advantages in observing grain distribution, insufficient contrast may occur when accurately identifying certain tiny grains or grain boundaries in complex alloy systems.

[0007] ④High technical requirements: The traditional electrolytic polishing liquid formula and electrolytic conditions have a significant impact on the treatment effect of the sample, but there is no unified standard in the existing literature, which makes the experimental repeatability poor.

[0008] Therefore, further optimization is needed. Summary of the invention

[0009] In view of the problems existing in the prior art, the present invention proposes a method combining mechanical polishing, electrolytic polishing, anodic coating and polarizing microscope observation. By optimizing the process parameters of each processing step, including the selection of mechanical polishing particle size, the composition ratio of the electrolyte, and the control of the electrolytic voltage and current, the specific scheme is as follows:

[0010] A method for observing the grain distribution of an aluminum alloy, the method comprising the following steps:

[0011] S1. Mechanical polishing: Use 400 mesh, 800 mesh, 1200 mesh, 1500 mesh and 2000 mesh sandpaper to polish the aluminum alloy sample in turn; use 3μm and 0.5μm polishing paste to finely polish the sample surface until there is no obvious scratch on the surface;

[0012] S2. Electrolytic polishing: prepare electrolyte; electrolytic polish the sample under the conditions of constant voltage of 20V and controlled current of 0.1-0.2A, and the electropolishing time is 10-15 seconds;

[0013] S3, anodic coating: prepare electrolyte; under the condition of constant voltage of 20V and controlled current of 0.2-0.3A, perform anodic coating on the sample for 120 seconds;

[0014] S4. Polarizing microscope observation: Place the coated sample under a polarizing microscope, adjust the microscope light source and polarizer; observe and record the distribution, size and morphology of the sample grains at a magnification of 200× to 1000×.

[0015] Furthermore, in the mechanical polishing step S1, the grinding time of each type of sandpaper is 3 to 5 minutes, and the use time of the polishing paste is 10 minutes and 5 minutes respectively.

[0016] Furthermore, in the S2 electrolytic polishing step, the electrolyte is perchloric acid and anhydrous ethanol in a volume ratio of 1:9, and the electropolishing time is preferably 12 seconds.

[0017] Furthermore, in the S3 anode coating step, the electrolyte is fluoroboric acid and pure water in a volume ratio of 5:200, and the coating time is 120 seconds.

[0018] Furthermore, the observation magnification of the polarizing microscope in S4 is 500×.

[0019] Furthermore, the electrolytic polishing and anode coating steps both use a DC regulated power supply, the sample is fixed as the anode, and the voltage and current control accuracy error does not exceed ±5%.

[0020] Furthermore, in S2 electrolytic polishing, the sample was the anode and the stainless steel was the cathode;

[0021] Furthermore, in the S3 anode coating, the sample is the anode and the stainless steel is the cathode.

[0022] Beneficial effects:

[0023] The present invention provides a method for observing the grain distribution of aluminum alloys. By optimizing the steps and parameters of mechanical polishing, electrolytic polishing, anodic coating and polarizing microscope observation, efficient and accurate observation of the grain distribution of aluminum alloys is achieved, which has the following beneficial effects:

[0024] (1) By controlling the sandpaper grit and grinding time of mechanical polishing, combined with fine polishing of 3μm and 0.5μm polishing pastes, the surface of the sample is flat, smooth, and scratch-free, providing a high-quality foundation for subsequent electrolytic polishing and coating. The use of efficient electrolytic polishing technology significantly improves the surface finish of the sample, while avoiding microscopic defects that may be introduced by mechanical processing, ensuring the accuracy of the grain distribution observation results.

[0025] (2) By performing anodic coating after electrolytic polishing, a uniform and stable film is formed on the surface, which significantly improves the contrast of the grain boundary and makes up for the problem of insufficient contrast in polarizing microscope observation in the traditional method. The optimized electrolyte ratio is fluoroboric acid:pure water=5:200 and the voltage and current parameters are optimized to ensure the uniformity and stability of the film, which is suitable for aluminum alloy samples of different sizes and shapes.

[0026] (3) Observation using a polarizing microscope. By adjusting the light source and the angle of the polarizer, combined with the high-contrast surface after the anodic coating, the size, distribution and morphology of the grains can be clearly and intuitively displayed. The magnification range of the polarizing microscope is 200× to 1000× to meet different resolution requirements and can be flexibly adjusted to meet different analysis needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the grain distribution diagram a of aluminum alloy.

[0028] Figure 2 It is the grain distribution diagram of aluminum alloy b.

[0029] Figure 3 It is the grain distribution diagram of aluminum alloy c. DETAILED DESCRIPTION

[0030] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with examples. The examples are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0031] Example:

[0032] A method for observing the grain distribution of aluminum alloy comprises the following specific steps:

[0033] S1: Mechanical polishing

[0034] Sample preparation: Select an aluminum alloy sample with a size of 20mm×20mm×5mm and clean the surface to remove oil and oxides.

[0035] Polishing steps:

[0036] Use 400 mesh, 800 mesh, 1200 mesh, 1500 mesh and 2000 mesh sandpaper to polish the surface of the sample.

[0037] The grinding time of each type of sandpaper is controlled within 3 to 5 minutes, during which the sandpaper is kept in full contact with the sample surface, and pure water is used as a lubricant.

[0038] Polishing steps:

[0039] Use 3μm polishing paste and polish on a polishing machine for 10 minutes to remove fine scratches on the surface of the sample;

[0040] The surface was further fine-polished using 0.5 μm polishing paste for 5 min until the surface was smooth and free of visible scratches.

[0041] S2: Electrolytic polishing

[0042] Preparation of electrolyte: Mix perchloric acid and anhydrous ethanol in a volume ratio of 1:9, stir well to obtain electrolyte.

[0043] Electrolysis steps:

[0044] Add the prepared electrolyte into the electrolytic cell;

[0045] Use a DC regulated power supply with a constant voltage of 20V and a current control range of 0.1 to 0.2A;

[0046] The sample was fixed as the anode, the stainless steel as the cathode, and the electro-throwing time was 12 seconds;

[0047] After completion, rinse the sample surface with anhydrous ethanol, then rinse with pure water and blow dry.

[0048] S3: Anodic coating

[0049] Electrolyte preparation: Mix fluoroboric acid and pure water in a volume ratio of 5:200, stir well to obtain a coated electrolyte.

[0050] Lamination steps:

[0051] Add the prepared coating electrolyte into the electrolytic cell;

[0052] Use a DC regulated power supply with a constant voltage of 20V and a current controlled within the range of 0.2 to 0.3A;

[0053] The sample was fixed as the anode, the stainless steel as the cathode, and the coating time was 120 seconds;

[0054] After completion, rinse the sample surface with pure water and then blow dry it with a hair dryer at low temperature.

[0055] S4: Polarized light microscope observation

[0056] Sample preparation: Place the coated sample on the stage of the polarizing microscope.

[0057] Observation steps:

[0058] Adjust the light source brightness and polarizer angle of the microscope to select the appropriate contrast effect;

[0059] The grain distribution, size and morphology of the sample surface were observed and recorded at a magnification of 500×. Figure 1 , 2 , as shown in 3;

[0060] If further analysis is required, the magnification can be changed to 200× or 1000× for additional observation of the local area.

[0061] result

[0062] Through the above steps, the surface of the aluminum alloy sample is smooth and flat, the grain boundary is clearly displayed under the polarizing microscope, and the distribution, size and morphology of the sample grains can be accurately observed and recorded. This method ensures the stability of sample preparation and the high accuracy of observation results, and is suitable for quality control and scientific research of aluminum alloy materials.

[0063] As a further improvement, the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for observing the grain distribution of aluminum alloy, characterized in that: The method comprises the following steps: S1. Mechanical polishing: Use 400 mesh, 800 mesh, 1200 mesh, 1500 mesh and 2000 mesh sandpaper to polish the aluminum alloy sample in turn; use 3μm and 0.5μm polishing paste to finely polish the sample surface until there is no obvious scratch on the surface; S2. Electrolytic polishing: prepare electrolyte; electrolytic polish the sample under the conditions of constant voltage of 20V and controlled current of 0.1-0.2A, and the electropolishing time is 10-15 seconds; S3, anodic coating: prepare electrolyte; under the condition of constant voltage of 20V and controlled current of 0.2-0.3A, perform anodic coating on the sample for 120 seconds; S4. Polarizing microscope observation: Place the coated sample under a polarizing microscope, adjust the microscope light source and polarizer; observe and record the distribution, size and morphology of the sample grains at a magnification of 200× to 1000×.

2. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: In the mechanical polishing step S1, the grinding time of each type of sandpaper is 3 to 5 minutes, and the use time of the polishing paste is 10 minutes and 5 minutes respectively.

3. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: In the S2 electrolytic polishing step, the electrolyte is perchloric acid and anhydrous ethanol in a volume ratio of 1:9, and the electropolishing time is preferably 12 seconds.

4. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: In the S3 anode coating step, the electrolyte is fluoroboric acid and pure water in a volume ratio of 5:200, and the coating time is 120 seconds.

5. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: The observation magnification of the polarizing microscope in the S4 is 500×.

6. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: The electrolytic polishing and anode coating steps both use a DC regulated power supply, the sample is fixed as the anode, and the voltage and current control accuracy error does not exceed ±5%.

7. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: In S2 electrolytic polishing, the sample is the anode and the stainless steel is the cathode.

8. The method for observing the grain distribution of aluminum alloy according to claim 1, characterized in that: In the S3 anode coating, the sample is the anode and the stainless steel is the cathode.

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