A method for displaying the metallographic structure of an aluminum alloy clad plate

Abstract

This invention discloses a method for displaying the metallographic structure of an aluminum alloy composite plate, belonging to the field of metallographic sample preparation technology. The method for displaying the metallographic structure of an aluminum alloy composite plate using a metallographic etchant is characterized by the following steps: water-grinding of the aluminum alloy composite plate, mechanical polishing, electrolytic polishing, etching with a metallographic etchant, and finally, microstructural observation under a metallographic microscope. The metallographic etchant comprises sodium ethoxide, sodium hydroxide, potassium hydroxide, potassium permanganate, and water. The weight ratio of each component in the metallographic etchant is as follows: sodium hydroxide and potassium hydroxide 1-2 parts, sodium ethoxide 2-4 parts, potassium permanganate 8-12 parts, and water 220-240 parts. The weight ratio of sodium hydroxide to potassium hydroxide is 1-4:1-2. This invention uses a combination of sodium ethoxide, sodium hydroxide, potassium hydroxide, and potassium permanganate, which synergistically enhances the etching of the aluminum alloy composite plate and promotes the display of its metallographic structure.

Description

Technical Field

[0001] This invention belongs to the field of metallographic sample preparation technology, specifically relating to a method for displaying the metallographic structure of an aluminum alloy composite plate. Background Technology

[0002] With the continuous development of science and technology, single-component metals are no longer sufficient to meet the requirements of components used in specific environments. Metal-matrix composites, which combine the superior properties of multiple components, are expected to find applications in related fields. Among composite materials, metal-matrix composites are considered to have the greatest potential for large-scale industrial and commercial production due to their relatively simple manufacturing processes (such as extrusion or rolling) and stable performance. Because metal-matrix composites contain two or more metals, they can effectively leverage the performance advantages of each metal, maximizing strengths and minimizing weaknesses, making them an economical and practical new material with broad application prospects.

[0003] In the aluminum alloy category, 6082 and 2A14 aluminum alloys both belong to the heat-treatable strengthening series. 6082 aluminum alloy is mainly composed of elements such as Al, Mg, and Si, exhibiting moderate strength and ductility, and is primarily used in construction, piping, and automotive industries. 2A14 aluminum alloy, on the other hand, is mainly composed of elements such as Al, Cu, and Mg, possessing superior strength and ductility, and is mainly used in aerospace and other fields. Due to the higher Cu content in 2A14 aluminum alloy, its corrosion resistance differs significantly from that of 6082 aluminum alloy. For 6082 / 2A14 aluminum alloy composite plates, the strength and ductility of 6082 aluminum alloy are improved, but the differences in the constituent elements of 6082 and 2A14 aluminum alloys result in different corrosion resistances, which increases the difficulty of obtaining their metallographic structure.

[0004] Furthermore, the corrosion resistance of materials is not only related to their composition but also influenced by their processing conditions. For materials processed through extrusion, forging, and rolling, the microstructure exhibits numerous preferred orientations under external forces, and the texture, internal stress, and twinning within the microstructure all affect the corrosion resistance. Therefore, layered metallic composites place higher demands on metallographic testing techniques for clear and complete characterization of their microstructure. Summary of the Invention

[0005] To address the shortcomings of the prior art, this invention provides a method for metallographic display of aluminum alloy composite plates.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for displaying the metallographic structure of an aluminum alloy composite plate, characterized in that the method includes the following steps:

[0008] (1) Use 600-3000 grit silicon carbide sandpaper to water grind the aluminum alloy composite plate in sequence, and then perform mechanical polishing.

[0009] (2) The sample obtained in step (1) was ultrasonically cleaned in ethanol, dried and then electrolytically polished.

[0010] (3) After cleaning and drying the sample after step (2), immerse it in metallographic etching solution for etching, then wipe the sample surface with etching solution, rinse with water and ethanol in turn, dry it and observe the tissue under a metallographic microscope.

[0011] The metallographic etchant comprises sodium ethoxide, sodium hydroxide, potassium hydroxide, potassium permanganate, and water; the weight distribution of each component in the metallographic etchant is as follows: 1-2 parts sodium hydroxide and potassium hydroxide, 2-4 parts sodium ethoxide, 8-12 parts potassium permanganate, and 220-240 parts water; the weight ratio of sodium hydroxide to potassium hydroxide is 1-4:1-2.

[0012] This invention utilizes a compound of sodium ethoxide, sodium hydroxide, potassium hydroxide, and potassium permanganate to synergistically corrode aluminum alloy composite plates and promote the display of their metallographic structure. Sodium ethoxide is used in this invention to continuously decompose and generate hydroxide ions during the corrosion process, maintaining the alkalinity of the system and ensuring stability of the corrosion process. Furthermore, because the two aluminum alloys in the composite plate have different main element contents and types, their corrosion resistance also differs. For example, the main alloying elements in 6082 aluminum alloy are Al, Mg, Si, and Mn, while those in 2A14 aluminum alloy are mainly Al and Cu. Since 2A14 aluminum alloy contains a higher amount of Cu, its corrosion resistance is inferior to that of 6082 aluminum alloy. Therefore, this invention uses a mixed inorganic alkali, sodium hydroxide and potassium hydroxide, to provide the primary alkaline environment for the corrosion process, increasing the ionic disorder of the corrosion system, increasing the probability of particle collisions when the corrosion solution reacts with the composite plate matrix, and shortening the corrosion time. Furthermore, potassium permanganate was selected as a strong oxidant. When potassium permanganate reacts with the composite plate matrix in an oxidation-reduction reaction, it also further stains the etched grains. Due to the differences in corrosion resistance of the various aluminum alloys in the composite plate, the colors of the grains also show obvious contrast, which better reflects the characteristics of grain growth in different parts of the composite plate.

[0013] Through extensive experimental research, this invention has discovered that the ratio of sodium ethoxide, sodium hydroxide, potassium hydroxide, potassium permanganate, and water, within the limits specified in this invention, can uniformly corrode the composite plate and is beneficial for displaying the metallographic structure of the composite plate. However, if the concentrations of sodium ethoxide, sodium hydroxide, and potassium hydroxide are too high, the second phase in the composite plate will cause numerous corrosion pits due to differences in corrosion resistance. Simultaneously, if the content of the strong oxidant potassium permanganate is too high, it will catalyze the decomposition of sodium ethoxide too rapidly, weakening the effect of sodium ethoxide in maintaining the alkalinity of the corrosion system.

[0014] The aluminum alloy composite plate is generally produced by extrusion. During the composite deformation process, a large amount of internal stress accumulates within the material. During corrosion, the numerous dislocations and internal stresses remaining within the material severely hinder the corrosion process, affecting the stability of the metallographic corrosion. Therefore, this invention first macroscopically eliminates the oxide layer and various defects on the surface of the composite plate through mechanical polishing. Then, it further employs electrolytic polishing technology using anodic corrosion, which not only eliminates stress concentration on the composite plate surface but also removes micro-scratches, further improving the surface smoothness and providing a good surface for the subsequent chemical etching to reveal the grains.

[0015] In a preferred embodiment of the present invention, the purity of sodium ethoxide, sodium hydroxide, potassium hydroxide, and potassium permanganate is all analytical grade or higher.

[0016] In a preferred embodiment of the present invention, in step (1), the aluminum alloy composite plate is water-polished sequentially on silicon carbide sandpaper with meshes of 600, 1000, 1400, 2000, and 3000.

[0017] In a preferred embodiment of the present invention, the mechanical polishing process in step (1) includes: using a cashmere polishing cloth and polishing it under running water; the mechanical polishing speed is 300-450 r / min.

[0018] In a preferred embodiment of the present invention, in step (2), the electrolyte for electropolishing is composed of perchloric acid and ethanol; the volume ratio of perchloric acid to ethanol is 1:10.

[0019] In a preferred embodiment of the present invention, the concentration of perchloric acid is 70-72 wt%; and the concentration of anhydrous ethanol is ≥99.7 wt%.

[0020] In a preferred embodiment of the present invention, in step (2), the electropolishing temperature is -20℃ to -25℃, the electrolysis voltage is 15 to 20V, and the electrolysis time is 15 to 20s.

[0021] In a preferred embodiment of the present invention, in step (3), the etching time in the metallographic etching solution is 15-20 seconds.

[0022] As a preferred embodiment of the present invention, in step (3), the preparation method of the metallographic etching solution includes: adding an inorganic alkali, an organic alkali and an oxidant to water in sequence.

[0023] In a preferred embodiment of the present invention, in step (3), the sample surface is wiped with an etchant 5-10 times to fully color the sample.

[0024] Compared with existing technologies, the beneficial effects of this invention are as follows: On the one hand, this invention uses sodium ethoxide to continuously decompose and generate hydroxide ions, maintaining the alkalinity of the system and ensuring the stability of the corrosion process. On the other hand, considering the different corrosion resistance caused by the different types and contents of elements in the composite plate, this invention selects a mixture of inorganic alkalis, sodium hydroxide and potassium hydroxide, to provide the main alkaline environment for the corrosion process, increase the ionic disorder of the corrosion system, increase the probability of particle collisions when the corrosion solution reacts with the composite plate matrix, and shorten the corrosion time. Therefore, this invention combines organic alkali, inorganic alkali, and oxidant to synergistically enhance the corrosion of aluminum alloy composite plates and promote the display of the metallographic structure of the composite plates. Attached Figure Description

[0025] Figure 1 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing using the metallographic structure display method described in Example 1.

[0026] Figure 2 Metallographic diagram of an extruded 6082 / 2A14 aluminum alloy composite plate without heat treatment, processed by the metallographic structure display method described in Example 1.

[0027] Figure 3 Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Example 1.

[0028] Figure 4 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing using the metallographic structure display method described in Comparative Example 1.

[0029] Figure 5 Metallographic diagram of an extruded 6082 / 2A14 aluminum alloy composite plate that has not undergone heat treatment, after being processed by the metallographic display method described in Comparative Example 1.

[0030] Figure 6 Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Comparative Example 1.

[0031] Figure 7 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing with the metallographic structure display method described in Comparative Example 2.

[0032] Figure 8 The metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate without heat treatment after being processed by the metallographic display method described in Comparative Example 2.

[0033] Figure 9Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Comparative Example 2.

[0034] Figure 10 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing using the metallographic structure display method described in Comparative Example 3.

[0035] Figure 11 Metallographic diagram of an extruded 6082 / 2A14 aluminum alloy composite plate without heat treatment, processed by the metallographic display method described in Comparative Example 3.

[0036] Figure 12 Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Comparative Example 3.

[0037] Figure 13 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing with the metallographic structure display method described in Comparative Example 4.

[0038] Figure 14 The metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate without heat treatment after being processed by the metallographic display method described in Comparative Example 4.

[0039] Figure 15 Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Comparative Example 4.

[0040] Figure 16 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing with the metallographic structure display method described in Comparative Example 5.

[0041] Figure 17 Metallographic diagram of an extruded 6082 / 2A14 aluminum alloy composite plate without heat treatment, processed by the metallographic display method described in Comparative Example 5.

[0042] Figure 18 Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Comparative Example 5.

[0043] Figure 19 The image shows the metallographic structure of the heat-treated extruded 6082 / 2A14 aluminum alloy composite plate after processing using the metallographic structure display method described in Comparative Example 10.

[0044] Figure 20Metallographic diagram of an extruded 6082 / 2A14 aluminum alloy composite plate without heat treatment, processed by the metallographic display method described in Comparative Example 10.

[0045] Figure 21 Metallographic diagram of the extruded 6082 / 2A14 aluminum alloy composite plate after post-aging treatment, processed by the metallographic structure display method described in Comparative Example 10. Detailed Implementation

[0046] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0047] The aluminum alloy composite plate described in this embodiment and comparative example is a heat-treated extruded 6082 / 2A14 aluminum alloy composite plate, an untreated extruded 6082 / 2A14 aluminum alloy composite plate, or a post-aging extruded 6082 / 2A14 aluminum alloy composite plate; the above three types of aluminum alloy composite plates are respectively processed by the metallographic display method of the embodiment and comparative example.

[0048] Example 1

[0049] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 1g of sodium hydroxide, 1g of potassium hydroxide, 2g of sodium ethoxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0050] The metallographic structure display method for aluminum alloy composite plates described in this embodiment includes the following steps:

[0051] (1) Use 600, 1000, 1400, 2000 and 3000 grit silicon carbide sandpaper to water grind the aluminum alloy composite plate in sequence, and then polish it with cashmere polishing cloth under the condition of 300 r / min and running water rinsing.

[0052] (2) The sample obtained in step (1) is ultrasonically cleaned in ethanol, dried, and then placed in an electrolyte for electrolytic polishing. The electrolytic polishing is carried out at -20℃, the electrolysis voltage is 20V, and the electrolysis time is 15s. The electrolyte is prepared by mixing perchloric acid and anhydrous ethanol in a volume ratio of 1:10.

[0053] (3) After cleaning and drying the sample treated in step (2), immerse it in metallographic etching solution for 15 seconds. Then, use a degreased cotton ball dipped in etching solution to wipe the sample surface 5 times. Rinse with water and ethanol in sequence, and after drying, observe the tissue under a metallographic microscope.

[0054] according to Figure 1-3It can be seen that although the 6082 / 2A14 aluminum alloy composite plates are in different heat treatment states, their metallographic structure diagrams can clearly and completely show the shape and size of the grains and the grain boundaries. Moreover, the image color contrast is large, which can clearly compare the difference in grain size between the 6082 layer and the 2A14 layer of the composite plate, thus meeting the requirements for metallographic observation.

[0055] Example 2

[0056] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 0.7g sodium hydroxide, 1.3g potassium hydroxide, 2g sodium ethoxide, and 12g potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0057] The metallographic structure display method for aluminum alloy composite plates described in this embodiment includes the following steps:

[0058] (1) Use 600, 1000, 1400, 2000 and 3000 grit silicon carbide sandpaper to water grind the aluminum alloy composite plate in sequence, and then polish it with cashmere polishing cloth under the condition of 300 r / min and running water rinsing.

[0059] (2) The sample obtained in step (1) is ultrasonically cleaned in ethanol, dried, and then placed in an electrolyte for electrolytic polishing. The electrolytic polishing is carried out at -20℃, the electrolytic voltage is 20V, and the electrolytic time is 20s. The electrolyte is prepared by mixing perchloric acid and anhydrous ethanol in a volume ratio of 1:10.

[0060] (3) After cleaning and drying the sample treated in step (2), immerse it in metallographic etching solution for 20 seconds. Then, use a degreased cotton ball dipped in etching solution to wipe the sample surface 10 times. Rinse with water and ethanol in sequence, and after drying, observe the tissue under a metallographic microscope.

[0061] The aluminum alloy composite plate processed by the metallographic structure display method described in this embodiment can clearly show its microstructure, and the difference in grain size between the 6082 layer and the 2A14 layer of the composite plate can be clearly observed, meeting the requirements for metallographic observation.

[0062] Example 3

[0063] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 0.5g sodium hydroxide, 0.5g potassium hydroxide, 2g sodium ethoxide, and 10g potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0064] The metallographic structure display method of the aluminum alloy composite plate described in this embodiment is the same as that in Embodiment 1.

[0065] The aluminum alloy composite plate processed by the metallographic structure display method described in this embodiment can clearly show its microstructure, and the difference in grain size between the 6082 layer and the 2A14 layer of the composite plate can be clearly observed, meeting the requirements for metallographic observation.

[0066] Example 4

[0067] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 1.6g of sodium hydroxide, 0.4g of potassium hydroxide, 4g of sodium ethoxide, and 8g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0068] The metallographic structure display method of the aluminum alloy composite plate described in this embodiment is the same as that in Embodiment 1.

[0069] The aluminum alloy composite plate processed by the metallographic structure display method described in this embodiment can clearly show its microstructure, and the difference in grain size between the 6082 layer and the 2A14 layer of the composite plate can be clearly observed, meeting the requirements for metallographic observation.

[0070] Comparative Example 1

[0071] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 2.5 mL of nitric acid, 1.5 mL of hydrochloric acid, and 1 mL of hydrofluoric acid and adding them sequentially to 95 mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0072] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0073] according to Figure 4-6 As can be seen, Keller's reagent can clearly reveal the grains of the 2A14 layer in the 6082 / 2A14 aluminum alloy composite plate, but for the 6082 layer, apart from observing some corrosion pits, the shape and size of the grains cannot be observed. Figure 5 and 6 As can be seen above, the grain size of both the 6082 layer and the 2A14 layer in the 6082 / 2A14 aluminum alloy composite plate cannot be characterized.

[0074] Comparative Example 2

[0075] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 2g of sodium hydroxide and 5g of sodium fluoride and adding them sequentially to 93mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0076] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0077] from Figure 7-9It can be observed that in the 6082 / 2A14 aluminum alloy composite plate, apart from the grain shape of the 2A14 layer being vaguely observed, it is impossible to obtain further information such as the grain size and grain boundaries of the 2A14 layer; and the 6082 layer of the composite plate basically has no grain boundary display, making it impossible to distinguish the grain shape and size.

[0078] Comparative Example 3

[0079] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 2g of sodium hydroxide, 2g of potassium hydroxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0080] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0081] from Figure 10-12 It can be observed that during the corrosion process, due to the change in the alkalinity concentration of the system, only some characteristics of the grains in each layer of the composite plate can be reflected, resulting in incomplete metallographic display.

[0082] Comparative Example 4

[0083] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 2g of sodium hydroxide, 2g of sodium ethoxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0084] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0085] from Figure 13-15 It can be observed that during the corrosion process, only the solution-treated + aged composite plate and the post-aged composite plate show some grain characteristics. However, for the extruded composite plate, a large amount of darkening phenomenon appears on the sample surface. This is due to the non-uniformity of the corrosion process, which leads to uneven coloring of the strong oxidant potassium permanganate during the redox reaction.

[0086] Comparative Example 5

[0087] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 2g of potassium hydroxide, 2g of sodium ethoxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0088] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0089] from Figure 16-18It can be observed that during the corrosion process, only the solution-treated and aged composite plate exhibits some grain characteristics, while the post-aged and extruded composite plates show virtually no grain characteristics. This is due to the low corrosion activity and low ionic disorder in the system, which prevents the display of grain information in the composite plate.

[0090] Comparative Example 6

[0091] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 4g of potassium hydroxide and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0092] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0093] A etching solution containing only potassium hydroxide and the strong oxidant potassium permanganate has the same effect as an etching solution containing only sodium hydroxide and the strong oxidant potassium permanganate. In this etching system, the corrosive activity is low, and the concentration of the etching system cannot be kept constant. Therefore, only partial grain information of the composite board can be displayed, and the etching effect is unstable.

[0094] Comparative Example 7

[0095] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 1g of sodium hydroxide, 1g of potassium hydroxide, 5g of sodium ethoxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0096] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0097] When the content of organic base is too high, the hydroxide ions produced by its hydrolysis will indirectly affect the alkalinity concentration of the corrosion system. Therefore, its effect on stabilizing the alkalinity concentration of the corrosion system will be greatly reduced, which in turn affects the stability of the metallographic structure.

[0098] Comparative Example 8

[0099] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 2g of sodium hydroxide, 2g of potassium hydroxide, 2g of sodium ethoxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0100] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0101] When the content of inorganic alkali is too high, the alkalinity concentration in the corrosion system is too high, which will cause a large number of second phase particles in the composite plate to fall off, resulting in a large number of corrosion pits on the metallographic surface and affecting the imaging quality of the metallographic structure.

[0102] Comparative Example 9

[0103] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this embodiment includes: taking 1g of sodium hydroxide, 1g of potassium hydroxide, 2g of sodium ethoxide, and 15g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0104] The metallographic structure display method of the aluminum alloy composite plate described in this comparative example is the same as that in Example 1.

[0105] When the content of strong oxidant potassium permanganate is too high, it will not only accelerate the decomposition of organic base sodium ethoxide in the positive direction, weakening the effect of sodium ethoxide in maintaining the alkalinity of the corrosion system, but also deepen the color of the metallographic surface after the sample undergoes oxidation-reduction reaction, thus affecting the observation of grain boundaries.

[0106] Comparative Example 10

[0107] The preparation process of the metallographic etchant for the aluminum alloy composite plate described in this comparative example includes: taking 1g of sodium hydroxide, 1g of potassium hydroxide, 2g of sodium ethoxide, and 10g of potassium permanganate and adding them sequentially to 240mL of deionized water and stirring thoroughly to obtain the metallographic etchant.

[0108] The metallographic structure display method for the aluminum alloy composite plate described in this comparative example includes the following steps:

[0109] (1) Use 600, 1000, 1400, 2000 and 3000 grit silicon carbide sandpaper to water grind the aluminum alloy composite plate in sequence, and then polish it with cashmere polishing cloth under the condition of 300 r / min and running water rinsing.

[0110] (2) The sample obtained in step (1) was ultrasonically cleaned in ethanol, dried, and then immersed in metallographic etching solution for 15 seconds. Then, the sample surface was wiped 5 times with a degreased cotton ball dipped in etching solution. After rinsing with water and ethanol in turn, the sample was dried and then observed under a metallographic microscope.

[0111] from Figure 19-21 It can be observed that, due to the lack of an electrolytic polishing step, some stress marks from mechanical polishing are present on the surface of the etched composite board. This is particularly true for the 6082 layer in the composite board, where residual stress significantly affects the etching effect and consequently the display of its metallographic structure.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for displaying the metallographic structure of an aluminum alloy composite plate, characterized in that, The method includes the following steps: (1) Use 600 in sequence Aluminum alloy composite plates are water-ground on 3000-grit silicon carbide sandpaper and then mechanically polished. (2) The sample obtained in step (1) is ultrasonically cleaned in ethanol, dried and then electrolytically polished. (3) After cleaning and drying the sample treated in step (2), immerse it in metallographic etching solution for etching, then wipe the sample surface with etching solution, rinse with water and ethanol in turn, dry it and observe the tissue under a metallographic microscope. The metallographic etchant comprises sodium hydroxide, potassium hydroxide, sodium ethoxide, potassium permanganate, and water; the weight parts of each component in the metallographic etchant are 1-2 parts of sodium hydroxide and potassium hydroxide, 2-4 parts of sodium ethoxide, 8-12 parts of potassium permanganate, and 220-240 parts of water; the weight ratio of sodium hydroxide to potassium hydroxide is 1-4:1-2. In step (3), the etching time in the metallographic etching solution is 15~20s.

2. The metallographic structure display method for aluminum alloy composite plates as described in claim 1, characterized in that, In step (1), the mechanical polishing process includes: using a cashmere polishing cloth and polishing it under running water; the mechanical polishing speed is 300~450r / min.

3. The metallographic structure display method for aluminum alloy composite plates as described in claim 1, characterized in that, The electrolyte for electropolishing consists of perchloric acid and ethanol; the volume ratio of perchloric acid to ethanol is 1:

10.

4. The metallographic structure display method for aluminum alloy composite plates as described in claim 1, characterized in that, In step (2), the temperature for electropolishing is... 20℃~ 25℃, electrolysis voltage 15~20V, electrolysis time 15~20s.

5. The metallographic structure display method for aluminum alloy composite plates as described in claim 1, characterized in that, In step (3), the sample surface is wiped with an etchant 5 to 10 times to fully color the sample.

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