5182 aluminum alloy metallographic corrosion liquid and metallographic corrosion method

Abstract

The invention belongs to the technical field of aluminum alloy metallographic corrosion, particularly relates to a 5182 aluminum alloy metallographic corrosive liquid and a corrosion method thereof, and aims to solve the problems that an existing corrosive liquid is fixed in formula and is difficult to adapt to 5182 aluminum alloys in different states. The corrosive liquid is composed of hydrofluoric acid, nitric acid and hydrochloric acid, and precise corrosion is achieved through hydrofluoric acid concentration gradient regulation and control. The hydrofluoric acid can selectively dissolve a compact oxidation film and a grain boundary phase on the surface of the aluminum alloy. Nitric acid mainly plays a role in uniformly corroding matrix metal; the hydrochloric acid enhances the hydrogen ion concentration through synergy, promotes the reaction efficiency of nitric acid and hydrofluoric acid, and improves the corrosion uniformity. The method breaks through the adaptation limitation of a traditional fixed formula, the components are simplified, the cost is low, and the precise corrosion requirement of the 5182 aluminum alloy can be met only by adjusting the concentration of hydrofluoric acid.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy metallographic corrosion technology, specifically relating to a 5182 aluminum alloy metallographic corrosion solution, a rapid corrosion method, and a metallographic detection method. Background Technology

[0002] Among the 5XXX series aluminum alloys, 5182 aluminum alloy belongs to the Al-Mg series. The Mg content in 5182 aluminum alloy is relatively high. This alloy has high strength, especially fatigue strength, high plasticity and corrosion resistance. It cannot be strengthened by heat treatment and is often used in automobile manufacturing, shipbuilding and transportation, aerospace and other fields.

[0003] The microstructure of aluminum alloys (such as grain size and morphology) significantly affects their strength, ductility, and other properties. Therefore, clear observation of the microstructure of aluminum alloys is of substantial importance. Traditionally, Keller's reagent is often used for metallographic etching of aluminum alloys, allowing observation of the microstructure under a microscope after etching. However, due to the strong corrosion resistance of 5182 aluminum alloy, traditional etching solutions such as Keller's reagent are not ideal for etching the grain boundaries of 5182 aluminum alloy, often resulting in over-etching of the matrix or failure to clearly display the grain boundaries. Currently, methods for observing the microstructure of aluminum alloy materials include electrolytic polishing with polarization and EBSD (electron backscatter diffraction). However, these methods are costly, highly dependent on equipment, time-consuming, and cumbersome. Therefore, exploring a low-cost, simple, efficient, and effective grain boundary etching solution for 5182 aluminum alloy is crucial. Summary of the Invention

[0004] This invention aims to overcome the shortcomings of existing etching solutions with fixed formulations that are difficult to adapt to different states of 5182 aluminum alloys. It provides a metallographic etching solution and method that achieves precise etching through gradient control of hydrofluoric acid concentration, is low-cost, and easy to operate. To solve the above-mentioned technical problems, this invention provides a metallographic etching solution for 5182 aluminum alloys based on gradient control of hydrofluoric acid concentration and its method. This etching solution is composed of hydrofluoric acid, nitric acid, and hydrochloric acid. Each component works synergistically during the etching process, specifically: hydrofluoric acid selectively dissolves the dense oxide film and grain boundary phases on the aluminum alloy surface; nitric acid mainly plays a role in uniformly etching the base metal; and hydrochloric acid, by synergistically enhancing the hydrogen ion concentration, promotes the reaction efficiency of nitric acid and hydrofluoric acid, and improves the uniformity of etching. By controlling the gradient of hydrofluoric acid concentration, the limitations of traditional fixed-formula etching solutions are overcome, enabling precise etching to be achieved for the grain size differences of aluminum alloys in different processing states (such as annealing, hot rolling, and cold rolling). Simultaneously, the composition remains simplified (containing only hydrofluoric acid, nitric acid, and hydrochloric acid), reducing production costs. During operation, only the concentrations of hydrofluoric acid, nitric acid, and hydrochloric acid need to be adjusted to meet diverse analytical needs, significantly improving analytical efficiency and the reliability of corrosion results. Through these advantages, this invention provides a more economical, efficient, and accurate solution for the metallographic analysis of 5182 aluminum alloy, possessing significant practical application value.

[0005] To solve the above problems, the technical solution adopted in the embodiments of the present invention is as follows:

[0006] This invention discloses a metallographic etching solution for 5182 aluminum alloy, the composition and volume percentage of which are: 2-5 ml hydrofluoric acid, 2-4 ml nitric acid, 1-2 ml hydrochloric acid, and the remainder is water, with a total solution volume of 100 ml.

[0007] The mass fractions of the hydrofluoric acid, nitric acid, and hydrochloric acid are 40%, 65-68%, and 36-38%, respectively.

[0008] A method for improving the metallographic corrosion of 5182 aluminum alloy sheets, using the aforementioned metallographic etching solution, is as follows:

[0009] 1) Preparation of metallographic etching solution: First, add water to a beaker, then add 2-5 ml of hydrofluoric acid (40% by mass), 2-4 ml of nitric acid (65% by mass), and 1-2 ml of hydrochloric acid (38% by mass). Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution.

[0010] 2) Sample preparation: The aluminum alloy sample is cold-mounted with epoxy resin and epoxy resin curing agent, and removed after the mounted sample has solidified.

[0011] 3) Mechanical grinding: Use sandpaper of different grits to grind the sample surface from coarse to fine in sequence to remove the grinding marks from the previous processing;

[0012] 4) Polishing: First, polish with 0.5μm alumina metallographic polishing agent and velvet polishing cloth for 1-2 minutes, then use diamond polishing spray with a particle size of 0.25μm for fine polishing for 1-2 minutes. When the sample surface shows a mirror gloss and no scratches are observed under an optical microscope, the polishing is complete. After polishing, rinse with anhydrous ethanol.

[0013] 5) Corrosion: The above-mentioned corrosive liquid is evenly dripped onto the polished sample surface. The corrosion time is 30-40 seconds. Ensure that the corrosive liquid completely covers the sample to ensure the uniformity of corrosion.

[0014] 6) Rinsing: After corrosion is complete, rinse quickly with distilled water, then rinse the sample surface with anhydrous ethanol, and dry with a hair dryer.

[0015] 7) Metallographic examination: The corroded metallographic sample is placed under a metallographic microscope for observation.

[0016] Compared with the prior art, the beneficial effects provided by the embodiments of the present invention are:

[0017] First, this etching solution exhibits excellent etching effects on 5182 aluminum alloy, clearly revealing grain boundaries and grain size. It is also simple to operate and requires minimal testing equipment and conditions. Second, the reagent is readily available and inexpensive, facilitating large-scale application. Finally, this etching solution effectively corrodes alloys that are difficult to treat with traditional reagents, significantly increasing the area and extent of grain boundary corrosion, improving the accuracy of grain size detection, and aiding in the study of the impact of grain structure on material properties. Attached Figure Description

[0018] Figure 1 The image shows the metallographic microstructure obtained by etching in Example 1.

[0019] Figure 2 The image shows the metallographic microstructure obtained by etching in Example 2.

[0020] Figure 3 The image shows the metallographic microstructure obtained by etching in Example 3.

[0021] Figure 4 The image shows the metallographic microstructure obtained by etching in Example 4.

[0022] Figure 5 The image shows the metallographic microstructure obtained by etching in Example 5. Detailed Implementation

[0023] To clarify the purpose, technical solution, and advantages of this invention, a detailed description will be provided below with reference to specific embodiments. This invention provides a method for preparing an etching solution for grain boundary corrosion of 5182 aluminum alloy.

[0024] Example 1

[0025] 1) Preparation of metallographic etching solution: First, add 70 ml of water to a beaker, then add 2 ml of hydrofluoric acid (40% by mass), 2.5 ml of nitric acid (65% by mass), and 1.5 ml of hydrochloric acid (38% by mass) in sequence. Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution.

[0026] 2) Sample preparation: The aluminum alloy sample is cold-mounted with epoxy resin and epoxy resin curing agent, and removed after the mounted sample has solidified.

[0027] 3) Mechanical grinding: Use sandpaper of different grits to grind the sample surface in sequence from coarse to fine. The sandpaper grades used are 120#, 200#, 400#, 600#, 800#, 1000#, and 2000#, in order to remove the grinding marks from the previous processing. Each time the sandpaper is changed, the sample needs to be rotated 90° so that the grinding directions are intersected to ensure the surface flatness.

[0028] 4) Polishing: First, polish with 0.5μm alumina metallographic polishing agent and velvet polishing cloth for 1-2 minutes, then polish with diamond polishing spray with a particle size of 0.25μm for 1-2 minutes. When the sample surface shows a mirror gloss and no polishing marks are observed under an optical microscope, the polishing is complete. After polishing, rinse with anhydrous ethanol.

[0029] 5) Corrosion: The above-mentioned corrosive liquid is evenly dripped onto the polished sample surface. The corrosion time is 30-40 seconds. Ensure that the corrosive liquid completely covers the sample to ensure the uniformity of corrosion.

[0030] 6) Rinsing: After corrosion is complete, rinse quickly with distilled water, then rinse the sample surface with anhydrous ethanol, and dry with a hair dryer.

[0031] 7) Metallographic Examination: The etched metallographic sample was observed under a metallographic microscope. The metallographic structure of the etched sample is shown below. Figure 1 .

[0032] Example 2

[0033] 1) Preparation of metallographic etching solution: First, add 70 ml of water to a beaker, then add 3 ml of hydrofluoric acid (40% by mass), 2.5 ml of nitric acid (65% by mass), and 1.5 ml of hydrochloric acid (38% by mass) in sequence. Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution.

[0034] 2) Sample preparation: Same as in Example 1;

[0035] 3) Mechanical polishing: Same as in Example 1;

[0036] 4) Polishing: Same as in Example 1;

[0037] 5) Corrosion: Same as in Example 1;

[0038] 6) Rinsing: Same as in Example 1;

[0039] 7) Metallographic examination: Same as in Example 1; the metallographic structure of the sample after corrosion is shown in Figure 1. Figure 2 .

[0040] Example 3

[0041] 1) Preparation of metallographic etching solution: First, add 70 ml of water to a beaker, then add 4 ml of hydrofluoric acid (40% by mass), 2.5 ml of nitric acid (65% by mass), and 1.5 ml of hydrochloric acid (38% by mass) in sequence. Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution.

[0042] 2) Sample preparation: Same as in Example 1;

[0043] 3) Mechanical polishing: Same as in Example 1;

[0044] 4) Polishing: Same as in Example 1;

[0045] 5) Corrosion: Same as in Example 1;

[0046] 6) Rinsing: Same as in Example 1;

[0047] 7) Metallographic examination: Same as in Example 1; the metallographic structure of the sample after corrosion is shown in Figure 1. Figure 3 .

[0048] Example 4

[0049] 1) Preparation of metallographic etching solution: First, add 70 ml of water to a beaker, then add 5 ml of hydrofluoric acid (40% by mass), 2.5 ml of nitric acid (65% by mass), and 1.5 ml of hydrochloric acid (38% by mass) in sequence. Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution.

[0050] 2) Sample preparation: Same as in Example 1;

[0051] 3) Mechanical polishing: Same as in Example 1;

[0052] 4) Polishing: Same as in Example 1;

[0053] 5) Corrosion: Same as in Example 1;

[0054] 6) Rinsing: Same as in Example 1;

[0055] 7) Metallographic examination: Same as in Example 1; the metallographic structure of the sample after corrosion is shown in Figure 1. Figure 4 .

[0056] Comparative Example

[0057] 1) Preparation of metallographic etching solution: First, add 70 ml of water to a beaker, then add 1 ml of hydrofluoric acid (40% by mass), 2.5 ml of nitric acid (65% by mass), and 1.5 ml of hydrochloric acid (38% by mass) in sequence. Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution.

[0058] 2) Sample preparation: Same as in Example 1;

[0059] 3) Mechanical polishing: Same as in Example 1;

[0060] 4) Polishing: Same as in Example 1;

[0061] 5) Corrosion: Same as in Example 1;

[0062] 6) Rinsing: Same as in Example 1;

[0063] 7) Metallographic examination: Same as in Example 1; the metallographic structure of the sample after corrosion is shown in Figure 1. Figure 5 .

[0064] Metallographic samples of 5182 aluminum alloy from Examples 1 to 4 and the comparative example were observed under a 400x metallographic microscope. The metallographic structures of the 5182 aluminum alloy from Examples 1 to 5 and the comparative example were compared and observed. The results showed that the metallographic structure of the sample after the comparative example treatment ( Figure 5The grain boundaries are blurred, not fully visible, and have low distinguishability. The metallographic structures of the samples treated in Examples 1 and 2 are shown below. Figure 1 and Figure 2 The grain boundaries are blurred and cannot be fully displayed. Example 4: Metallographic structure of the treated sample ( Figure 4 The grain boundaries were excessively dissolved, resulting in excessive corrosion. The sample treated in Example 3 (…) Figure 3 It can clearly show grain boundaries and grain size, improve the accuracy of grain size detection, and is easy to operate with low requirements for detection equipment and conditions. This helps to study the influence of grain structure on material properties and makes it easier to carry out subsequent microstructure analysis and evaluation.

[0065] Finally, it should be noted that the above specific embodiments are merely examples illustrating the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail through examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to specific solutions without departing from the spirit and scope of the technical solutions of the present invention. Any such modifications or substitutions should be considered to be included within the scope of the claims of the present invention.

Claims

1. A metallographic etching solution for 5182 aluminum alloy, characterized in that: Its composition and volume percentage are: 2-5 ml hydrofluoric acid, 2-4 ml nitric acid, 1-2 ml hydrochloric acid, and the remainder is water, with a total solution volume of 100 ml. The mass fractions of the hydrofluoric acid, nitric acid and hydrochloric acid are 40%, 65-68% and 36-38%, respectively.

2. A method for improving the metallographic corrosion of 5182 aluminum alloy sheets, comprising using the aforementioned metallographic etching solution for etching, the process of which is as follows: 1) Preparation of metallographic etching solution: First, add water to a beaker, then add 2-5 ml of hydrofluoric acid (40% by mass), 2-4 ml of nitric acid (65% by mass), and 1-2 ml of hydrochloric acid (38% by mass). Continue adding water to the beaker until the total volume of the mixture is 100 ml. Finally, stir thoroughly with a glass rod to ensure the solution is homogeneous, thus obtaining a high-concentration acid metallographic etching solution. 2) Sample preparation: The aluminum alloy sample is cold-mounted with epoxy resin and epoxy resin curing agent, and removed after the mounted sample has solidified. 3) Mechanical grinding: Use sandpaper of different grits to grind the sample surface from coarse to fine in sequence to remove the grinding marks from the previous processing; 4) Polishing: First, polish with 0.5μm alumina metallographic polishing agent and velvet polishing cloth for 1-2 minutes, then use diamond polishing spray with a particle size of 0.25μm for fine polishing for 1-2 minutes. When the sample surface shows a mirror gloss and no scratches are observed under an optical microscope, the polishing is complete. After polishing, rinse with anhydrous ethanol. 5) Corrosion: The above-mentioned corrosive liquid is evenly dripped onto the polished sample surface. The corrosion time is 30-40 seconds. Ensure that the corrosive liquid completely covers the sample to ensure the uniformity of corrosion. 6) Rinsing: After corrosion is complete, rinse quickly with distilled water, then rinse the sample surface with anhydrous ethanol, and dry with a hair dryer. 7) Metallographic examination: The corroded metallographic sample is placed under a metallographic microscope for observation.

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