Rapid displaying method for macrostructure of large-size multiphase brass cast ingot

Abstract

The invention discloses a method for rapidly displaying a macrostructure of a large-size multiphase brass cast ingot. The method comprises the following steps: cutting a sample from the large-size multiphase brass cast ingot, and mechanically cutting a detection surface of the sample until the surface roughness Ra is less than or equal to 1.2 microns; preparing an HNO3 solution with the mass fraction of 45-55% as a corrosive liquid; the method comprises the following steps: uniformly pouring a prepared HNO3 solution on a detection surface of a sample, covering the detection surface with the HNO3 solution to form a complete liquid film, standing and corroding for 10-20 seconds, immediately scrubbing the detection surface, wiping the detection surface with absorbent cotton, repeating for 1-2 times until the detection surface clearly shows a macrostructure, wiping the surface with absorbent cotton, and collecting an image of the detection surface by adopting a high-resolution scanner. The method is easy and convenient to operate, good in reproducibility and suitable for industrial application, the whole corrosion process only needs 20-40 seconds, and the macroscopic structure of the large-size multiphase brass cast ingot can be clearly, uniformly, completely and efficiently shown.

Description

Technical Field

[0001] This invention belongs to the field of metal material testing and metallographic analysis technology, specifically relating to a method for rapid visualization of the macrostructure of large-size multiphase brass ingots. Background Technology

[0002] Copper and copper alloys are widely used due to their excellent properties. The macrostructure of their ingots (such as grain size, morphology, dendrite distribution, and defect distribution) directly affects the performance and quality of the processed materials. Therefore, accurately and efficiently displaying their macrostructure is crucial for optimizing production processes and controlling quality.

[0003] Currently, the main methods for revealing the macrostructure of metals include chemical etching and machining, but both of these methods have certain limitations when applied to brass ingots with complex compositions.

[0004] Chemical etching methods: Traditionally, ferric chloride hydrochloric acid solution and ammonium persulfate solution are commonly used as etching agents for brass. However, for multiphase brass containing lead, these etching agents have significant drawbacks: 1) Ferric chloride hydrochloric acid solution easily causes excessive blackening of the β phase (CuZn phase), obscuring dendritic details, and has poor selectivity for etching the lead phase (Pb), easily causing lead phase detachment or contamination, forming difficult-to-remove stains or holes on the test surface, interfering with microstructure judgment; 2) Ammonium persulfate solution easily forms an oxide contamination film on the sample surface, reducing microstructure contrast and resulting in insufficient clarity; 3) Existing chemical etching methods generally suffer from long etching times (usually requiring several minutes or even longer), large reagent consumption, and cumbersome operation procedures. For large brass ingots, especially large brass ingot cross-sections with diameters exceeding 200 mm, it is difficult to ensure uniform etching.

[0005] Machining methods, such as precision turning, have environmental advantages, but their limitations are: 1) The process is complex and has extremely stringent requirements for machine tool accuracy, tool geometry parameters, and cutting parameters (such as speed and feed rate), requiring high technical skills from operators; 2) This method is effective in revealing the microstructure of high-purity single-phase materials, but for multiphase brass (including α phase, β phase, and lead phase, etc.), its ability to reveal the microstructure by relying on the contrast of cutting lines is insufficient, making it difficult to clearly distinguish the distribution of different phases and dendrite morphology; 3) The equipment investment cost is high and it lacks universality.

[0006] Existing technologies lack a method for revealing the macrostructure of large-size, multiphase brass ingots, making it difficult to simultaneously achieve rapid, uniform, and clear revealing results. The fundamental reason for this is the failure to achieve precise coordination between various processes and parameters. Therefore, there is an urgent need in the field for a method that can overcome these shortcomings and is particularly suitable for rapidly and clearly revealing the macrostructure of large-size, multiphase brass ingots. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for rapid visualization of the macrostructure of large-size multiphase brass ingots that is simple to operate, has good reproducibility, and is suitable for industrial applications, in order to overcome the shortcomings of the prior art. This method precisely coordinates the surface roughness (Ra ≤ 1.2 μm), nitric acid solution concentration (45-55%), and corrosion operations with short-time, multiple, and interspersed cleaning. The entire corrosion process takes only 20-40 seconds, achieving clear, uniform, complete, and efficient visualization of the macrostructure of large-size multiphase brass ingots.

[0008] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a method for rapid visualization of the macrostructure of large-size multiphase brass ingots, comprising the following steps: S1. Sampling and surface pretreatment: Samples are cut from large-sized multiphase brass ingots, and the test surfaces of the samples are machined to a surface roughness Ra ≤ 1.2 μm; S2. Preparation of etching solution: Prepare an HNO3 solution with a mass fraction of 45-55% as the etching solution; S3. Corrosion treatment: Pour the prepared HNO3 solution evenly onto the test surface of the sample, so that the HNO3 solution covers the test surface to form a complete liquid film. After standing for corrosion for 10-20 seconds, immediately brush the test surface and then wipe the test surface with degreased cotton. S4. Repeat the operation and image acquisition: Repeat step S3 1-2 times until the macroscopic tissue is clearly visible on the detection surface. After wiping the surface with degreased cotton, use a high-resolution scanner to acquire the image of the detection surface.

[0009] The method of this invention processes the test surface of the sample to a surface roughness Ra ≤ 1.2 μm through mechanical cutting. This parameter provides an ideal reaction substrate for the subsequent chemical etching step. If the roughness is too large (e.g., Ra > 1.5 μm), the micro-grooves on the surface are too deep, and the etchant is prone to stagnation, leading to localized over-etching and the formation of contamination marks. If the roughness is too small (e.g., Ra < 0.5 μm), although the surface is smoother, the processing cost increases significantly, and an overly dense surface layer is not conducive to the initial uniform wetting and slight, uniform adhesion of the etchant, which may prolong the etching time or lead to uneven etching.

[0010] This invention uses a 45-55% (w / w) HNO3 solution as the etching solution. Its etching mechanism lies between that of low-concentration and high-concentration nitric acid, enabling rapid and uniform etching of large-sized multiphase brass. The 45-55% (w / w) HNO3 solution avoids the blurring of details caused by the slow, selective etching of low-concentration nitric acid, while also avoiding the problem of the dense passivation film formed by the vigorous reaction of high-concentration nitric acid, which can obscure the microstructure. The 45-55% (w / w) HNO3 solution forms a moderately thick, easily peelable etching product film on the detection surface, creating a "lifting" effect during subsequent brushing. This allows for clear, uniform, complete, and efficient exposure of the macrostructure and its contours, while avoiding excessive interference with the β-phase and lead phase.

[0011] In the corrosion treatment step of this invention, by forming a complete liquid film of HNO3 solution covering the detection surface, the instantaneous uniformity and consistency of the chemical environment on large-sized detection surfaces can be ensured. Simultaneously, this invention controls the corrosion treatment time to 10-20 seconds, which is an optimized result based on the synergistic effect between the surface roughness obtained in step S1 and the nitric acid concentration selected in step S2. The corrosion treatment method of this invention ensures that the corrosion reaction proceeds fully while effectively avoiding the loss of microstructural details due to over-corrosion.

[0012] This invention innovatively employs a precise synergy between short-duration, multiple, and intermittent cleaning (i.e., brushing and wiping immediately after each etching step) etching operation and image acquisition steps, achieving stepwise precise control of etching depth: the first etching forms the preliminary outline of the macrostructure, while the second etching further deepens and sharpens grain boundary and phase boundary details, thereby significantly improving the contrast and clarity of the microstructure display. After finally wiping the inspection surface with degreasing cotton, a high-resolution scanner is immediately used to acquire images of the inspection surface, thus obtaining high-quality macrostructure images of large-size multiphase brass ingots.

[0013] Preferably, the chemical composition of the brass ingot, by mass fraction, is: Cu 54-61%, Pb 0.5-3.5%, Fe ≤ 0.65%, P ≤ 0.01%, total impurity elements ≤ 2.0%, and the balance is Zn.

[0014] Preferably, the diameter of the detection surface of the sample is ≥200 mm. The method of the present invention is particularly suitable for the uniform and rapid development of macroscopic structures in large cross-sections with a diameter of 200 mm or more.

[0015] Preferably, the machining parameters in step S1 are: lathe speed 600-800 r / min, feed rate 0.1-0.2 mm / r, and depth of cut 1.5-2.5 mm. More preferably, the machining parameters are: lathe speed 700 r / min, feed rate 0.15 mm / r, and depth of cut 2 mm.

[0016] Preferably, the HNO3 solution in step S2 is prepared by mixing a 66% HNO3 solution with distilled water.

[0017] Preferably, the mass fraction of the HNO3 solution in step S2 is 50%.

[0018] Preferably, the thickness of the liquid film formed in step S3 is 0.5-2.0 mm.

[0019] Preferably, the tool used for brushing in step S3 is a nylon brush, and the rinsing medium is tap water.

[0020] Compared with the prior art, the present invention has the following advantages: (1) The method of the present invention precisely coordinates the surface roughness (Ra ≤ 1.2 μm), nitric acid solution concentration (45-55%), and short-time, multiple, and intermittent cleaning corrosion operations to achieve clear, uniform, complete, and efficient visualization of the macrostructure of large-size multiphase brass ingots. The method of the present invention can clearly and uniformly visualize the dendritic structure of large-size multiphase brass ingots, and has good differentiation between α phase, β phase, and lead phase, avoiding problems such as phase transformation blackening, stains, or contamination films caused by traditional etchants.

[0021] (2) The method of the present invention requires only 20-40 seconds for the entire corrosion process of large-size multiphase brass ingot samples. Compared with the corrosion time of several minutes to tens of minutes required by the traditional method, the efficiency is significantly improved, the detection cycle is greatly shortened, and the reagent consumption of the method of the present invention is small, the waste liquid is easy to treat, and there is no need to use high-risk or easily polluting reagents such as hydrofluoric acid and ferric chloride. At the same time, the requirements of the mechanical cutting process of the method of the present invention are within the economic and reasonable range, and the overall cost is low.

[0022] (3) The method of the present invention is simple to operate and has good reproducibility. It is suitable for industrial applications, especially for the rapid display of the macrostructure of large-size multiphase brass ingots on the production site, providing a reliable and efficient solution for online quality monitoring in industrial production. Attached Figure Description

[0023] Figure 1 The image shows a scanned image of the macrostructure of a brass ingot obtained in Example 1. Figure 2This is a scanning image of the macrostructure of a brass ingot obtained after etching for 15 seconds in step S3 of Comparative Example 1. Figure 3 This is a scanning image of the macrostructure of a brass ingot obtained after etching for 2 minutes in step S3 of Comparative Example 2; Figure 4 This is a scanning image of the macrostructure of a brass ingot obtained after etching for 40 seconds in step S3 of Comparative Example 3. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0025] Example 1: A brass ingot with a diameter of 200 mm was tested. Its chemical composition, by mass fraction, was: Cu 58%, Pb 2.0%, Fe 0.3%, with the balance being Zn and trace impurities. The rapid visualization method for its macrostructure included the following steps: S1. Sampling and Surface Pretreatment: Samples were cut from large-sized multiphase brass ingots, and the test surfaces of the samples were machined by mechanical cutting. The lathe speed was 700 r / min, the feed rate was 0.15 mm / r, the cutting depth was 2 mm, and the surface roughness Ra = 1.0 μm was achieved. S2. Preparation of etching solution: Dilute a 66% HNO3 solution with distilled water to prepare a 50% HNO3 solution as the etching solution. S3. Corrosion treatment: Pour the prepared HNO3 solution evenly onto the test surface of the sample, so that the HNO3 solution covers the test surface to form a complete liquid film with a thickness of 1.0 mm. After standing for 15 seconds for corrosion, immediately use a nylon brush dipped in tap water to gently brush the test surface, and then wipe the test surface with degreased cotton. S4. Repeat the operation and image acquisition: Repeat step S3 once. The macroscopic structure of the detection surface is clearly visible. After wiping the surface with degreased cotton, acquire the image of the detection surface using a high-resolution flatbed scanner (1200 dpi). Figure 1 The image shown is a macroscopic tissue scan with high contrast and clear dendritic structure.

[0026] The entire corrosion process in Example 1 took only about 30 seconds.

[0027] Comparative Example 1: A sample was taken from a large-sized multiphase brass ingot with the same chemical composition and diameter as in Example 1, and its macrostructure was visualized. The only difference between Comparative Example 1 and Example 1 was the cutting parameters used in step S1, resulting in a surface roughness Ra = 2.2 μm on the sample's test surface after machining. The results showed that when the sample was treated using the method of Comparative Example 1, after etching for 15 seconds in step S3, obvious uneven corrosion spots and flow marks appeared on the sample's test surface. The microstructure was blurred in some areas, and blemishes appeared at the lead phase locations. The macrostructure scanning image is shown below. Figure 2 The clarity is poor. If step S4 is continued, the tissue visualization will be even worse.

[0028] Comparative Example 2: Samples were taken from a large-sized multiphase brass ingot with the same chemical composition and diameter as in Example 1, and macroscopic microstructure was visualized. The only difference between Comparative Example 2 and Example 1 was that in step S2, a 20% HNO3 solution was used as the etching solution. The results showed that when the sample was treated using the method of Comparative Example 2, after etching for 15 seconds in step S3, almost no microstructure was visible on the test surface. Extending the etching time to 2 minutes and then brushing and wiping resulted in... Figure 3 The image shown is a macroscopic tissue scan image. (By...) Figure 3 It is evident that the dendritic outline remains indistinct, and the lead phase has been selectively dissolved and detached, forming numerous micropores that severely damage the integrity of the structure.

[0029] Comparative Example 3: Samples were taken from a large-sized multiphase brass ingot with the same chemical composition and diameter as in Example 1, and the macrostructure was visualized. The only difference between Comparative Example 3 and Example 1 was that in step S2, the single etching time was extended to 40 seconds, and the operation was not repeated (i.e., only one etching was performed). The results showed that, after etching the sample for 40 seconds in step S3 using the method of Comparative Example 3, followed by brushing and wiping, the resulting... Figure 4 The image shown is a macroscopic tissue scan image. (By...) Figure 4 As can be seen, the sample's detection surface is generally black and dark, the dendritic structure becomes blurred due to excessive etching, a large amount of detail is lost, and the structure contrast is low, making it unsuitable for accurate structure analysis.

[0030] Conclusion: A comparison of Example 1 and Comparative Examples 1-3 shows that only by employing the process parameter combination defined in this invention, and through precise coordination of surface roughness Ra ≤ 1.2 μm, nitric acid solution concentration of 45-55%, and short-duration, multiple, and intermittent cleaning corrosion operations, can the clear, uniform, complete, and efficient visualization of the macrostructure of large-size multiphase brass ingots be achieved. Deviation from any single parameter will lead to a significant decrease in the visualization effect of the ingot's macrostructure, which fully demonstrates the close synergy and non-obviousness of the parameters in the technical solution of this invention.

Claims

1. A method for rapidly revealing the macrostructure of large-size multiphase brass ingots, characterized in that, Includes the following steps: S1. Sampling and surface pretreatment: Samples are cut from large-sized multiphase brass ingots, and the test surfaces of the samples are machined to a surface roughness Ra ≤ 1.2 μm; S2. Preparation of etching solution: Prepare an HNO3 solution with a mass fraction of 45-55% as the etching solution; S3. Corrosion treatment: Pour the prepared HNO3 solution evenly onto the test surface of the sample, so that the HNO3 solution covers the test surface to form a complete liquid film. After standing for corrosion for 10-20 seconds, immediately brush the test surface and then wipe the test surface with degreased cotton. S4. Repeat the operation and image acquisition: Repeat step S3 1-2 times until the macroscopic tissue is clearly visible on the detection surface. After wiping the surface with degreased cotton, use a high-resolution scanner to acquire the image of the detection surface.

2. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1, characterized in that, The chemical composition of the brass ingot, by mass fraction, is: Cu 54-61%, Pb 0.5-3.5%, Fe ≤ 0.65%, P ≤ 0.01%, total impurity elements ≤ 2.0%, and the balance is Zn.

3. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1, characterized in that, The diameter of the test surface of the sample is ≥200 mm.

4. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1, characterized in that, The parameters for machining in step S1 are: lathe speed 600-800 r / min, feed rate 0.1-0.2 mm / r, and depth of cut 1.5-2.5 mm.

5. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1, characterized in that, In step S2, the HNO3 solution is prepared by mixing a 66% HNO3 solution with distilled water.

6. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1 or 5, characterized in that, The mass fraction of the HNO3 solution in step S2 is 50%.

7. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1, characterized in that, The thickness of the liquid film formed in step S3 is 0.5-2.0 mm.

8. The method for rapid visualization of the macrostructure of large-size multiphase brass ingots according to claim 1, characterized in that, In step S3, the tool used for scrubbing is a nylon brush, and the rinsing medium is tap water.

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