Metallographic detection method for magnesium-aluminum dissimilar metal welded joint
By using a combination of caustic soda, acetic acid, and phosphoric acid solutions, along with a grinding process, the problem of uneven corrosion in magnesium-aluminum alloy welded joints was solved, enabling accurate metallographic testing of magnesium-aluminum dissimilar metal welded joints and improving testing efficiency and effectiveness.
Patent Information
- Application Number
- CN202511156905.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-08-18
- Publication Date
- 2025-11-21
AI Technical Summary
Existing technologies cannot simultaneously achieve a moderate corrosion state in the macroscopic metallographic inspection of magnesium alloy and aluminum alloy welded joints, resulting in poor inspection results and affecting welding quality assessment and defect analysis.
The aluminum alloy structure was etched with caustic soda solution, the magnesium alloy structure was etched with acetic acid solution, and finally etched with phosphoric acid solution. Combined with polishing, this process ensured the effective removal of corrosion products from the surfaces of each alloy.
It enables accurate metallographic testing of magnesium-aluminum dissimilar metal welded joints, simplifies the operation, improves testing efficiency and effectiveness, and meets the needs of quality assessment.
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Figure CN120992285A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metallographic testing technology, specifically relating to a metallographic testing method for magnesium-aluminum dissimilar metal welded joints. Background Technology
[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.
[0003] Aluminum alloys are currently the main material for high-speed train bodies because they combine necessary strength, rigidity, excellent corrosion resistance, good processability (especially extrusion molding), high safety, and excellent recyclability.
[0004] Magnesium alloys, as the lightest metallic structural materials, possess advantages such as high specific strength, good shock absorption, and easy recyclability. Their application and exploration are underway in non-load-bearing structural components and functional parts of rail transit vehicles, such as interior trim, equipment housings and supports, door system components, driver's cab control panel components, and auxiliary structural components. Achieving effective joining between magnesium and aluminum alloys will help promote the application of magnesium alloy components in high-speed trains. The rail transit industry primarily uses friction stir welding to join magnesium and aluminum alloys, and the quality of the weld joint directly determines the reliability of train safety operation. Macroscopic metallographic inspection is one of the most important inspection methods for weld joints.
[0005] Magnesium alloys and aluminum alloys exhibit significantly different corrosion resistance. Aluminum alloys possess excellent natural barrier protection due to their dense, stable, and self-healing Al2O3 film, resulting in superior corrosion resistance. In contrast, magnesium alloys have a loose, unstable, and easily soluble MgO / Mg(OH)2 film, coupled with their extremely low corrosion potential, leading to poor corrosion resistance. When performing metallographic testing on welded joints of aluminum and magnesium alloys, using acidic solutions during corrosion testing increases the risk of galvanic corrosion in magnesium alloys, making them more prone to over-corrosion. Aluminum alloys, on the other hand, show less corrosion, preventing both alloys from simultaneously achieving a suitable corrosion level. Similarly, using alkaline solutions to corrode magnesium-aluminum dissimilar metal welded joints results in corrosion of the aluminum alloy while the magnesium alloy remains uncorroded, again failing to yield a properly corroded welded joint.
[0006] When the corrosion levels of two materials differ significantly, it not only interferes with the identification of welding defects and weld morphology, but also directly leads to excessive color difference on both sides of the joint during photography, affecting the display effect of metallographic images. Existing technologies struggle to solve these technical problems. Summary of the Invention
[0007] To address the shortcomings of existing technologies, the purpose of this invention is to provide a macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints. This method solves the problems of difficult macroscopic metallographic inspection and poor metallographic image display in magnesium-aluminum dissimilar metal welded joints.
[0008] To achieve the above objectives, the present invention is implemented through the following technical solution: A macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: The test surface of the magnesium-aluminum dissimilar metal welded joint sample to be tested is ground to ensure that the roughness meets the requirements. The aluminum alloy structure was corroded by immersing the sample in a caustic soda solution. Then, the sample was etched with acetic acid solution to corrode the magnesium alloy structure; Finally, the surface of the sample to be tested was etched using a phosphoric acid solution. After the etching is complete, clean, dry, and observe the sample.
[0009] The beneficial effects achieved by one or more embodiments of the present invention described above are as follows: First, the sample is etched with a caustic soda solution. At this time, the magnesium alloy structure does not react, and the aluminum alloy structure surface can be selectively etched to effectively control the degree of corrosion on the aluminum alloy surface. During this process, corrosion products are generated on the aluminum alloy surface. Then, the sample is etched with an acetic acid solution, which can selectively corrode the magnesium alloy surface. Moreover, the acetic acid solution can effectively dissolve the corrosion products on the aluminum alloy surface. When the sample is wiped with a phosphoric acid solution afterward, the corrosion products on the sample surface can be quickly removed, while effectively reducing the corrosion time to prevent the magnesium alloy surface from being over-corroded.
[0010] This invention effectively solves the problems of difficult macroscopic metallographic inspection and poor metallographic image display of magnesium-aluminum dissimilar metal welded joints. It also has the advantages of simple operation, good corrosion effect and high inspection efficiency, which can meet the needs of quality assessment of magnesium-aluminum dissimilar metal welded joints and help promote the research and development of magnesium alloy welding technology. Attached Figure Description
[0011] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0012] Figure 1 This is a corrosion effect diagram from Example 1; Figure 2 This is a diagram showing the corrosion effect in Comparative Example 1; Figure 3This is a diagram showing the corrosion effect in Comparative Example 2. Detailed Implementation
[0013] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0014] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, unless otherwise expressly indicated by the invention, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof. For ease of description, the words "up," "down," "left," and "right" appearing in this invention only indicate that they are consistent with the up, down, left, and right directions of the accompanying drawings themselves, and do not limit the structure. They are merely for the purpose of facilitating the description of this invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.
[0015] Terminology Explanation Section: Macroscopic metallographic testing is a commonly used non-destructive or micro-destructive testing method in the field of materials science or engineering. It is generally a technique that uses the naked eye or a low-magnification magnifying glass (usually less than 50x) to observe the surface or cross-section of a metallic material (or other solid material) after appropriate preparation (such as cutting, grinding, polishing, or etching) in order to evaluate its overall structure, macroscopic defects and inhomogeneities.
[0016] Aluminum alloys are alloys made with aluminum as the base material and the addition of certain amounts of other alloying elements (such as copper, magnesium, silicon, zinc, manganese, etc.). They are one type of lightweight metal material. They retain the lightweight properties of aluminum (density approximately 2.7 g / cm³). 3 It is only 1 / 3 the weight of steel, and through alloying treatment, its mechanical properties such as strength, hardness, and wear resistance are significantly improved. At the same time, it has good electrical and thermal conductivity, corrosion resistance, and processability.
[0017] Magnesium alloys are alloys with magnesium as the base material, incorporating other alloying elements such as aluminum, zinc, manganese, and zirconium. They belong to the category of lightweight metals. Their density typically ranges from 1.7 to 2.0 g / cm³. 3 Magnesium alloys are among the lowest density metallic structural materials currently used in practical applications. They possess advantages such as high specific strength and specific stiffness, good vibration damping, strong electromagnetic shielding, and easy recycling, but their corrosion resistance and heat resistance are relatively weak.
[0018] Friction stir welding is a solid-state joining technique that uses a high-speed rotating stirring head to generate heat through friction with the materials being welded. This heat brings the materials in the welding area to a plastic state, and then a solid-state bond is achieved under the mechanical stirring and extrusion of the stirring head. Its principle is to soften the material through frictional heat rather than melting it, thus effectively avoiding defects such as porosity and cracks common in traditional fusion welding. It is particularly suitable for welding low-melting-point lightweight metals such as aluminum alloys and magnesium alloys.
[0019] Sodium hydroxide solution is an aqueous solution of sodium hydroxide, also known as caustic soda solution, lye solution, etc., and is a strongly alkaline solution.
[0020] Acetic acid solution is an aqueous solution of acetic acid, also known as acetic acid solution. It is a common organic weak acid solution. In water, it partially ionizes into hydrogen ions and acetate ions. It has the general properties of acids and can react with active metals, bases, carbonates, etc., but it has a relatively weak corrosive effect on metals.
[0021] Etching is a corrosion method in which the sample to be tested is placed in a chemical agent and the surface of the metal sample is selectively corroded by the chemical agent or electrochemical method.
[0022] As described in the background section, existing technologies suffer from significant differences in corrosion resistance between magnesium alloys and aluminum alloys. Conventional metallographic testing methods cannot simultaneously corrode the microstructures of both magnesium and aluminum alloys to an appropriate level, resulting in poor macroscopic metallographic testing of magnesium-aluminum dissimilar metal welded joints. This negatively impacts joint quality assessment and defect analysis. To address these technical problems, this invention proposes a macroscopic metallographic testing method for magnesium-aluminum dissimilar metal welded joints, comprising the following steps: The test surface of the magnesium-aluminum dissimilar metal welded joint sample to be tested is ground to ensure that the roughness meets the requirements. The aluminum alloy structure was corroded by immersing the sample in a caustic soda solution. Then, the sample was etched with acetic acid solution to corrode the magnesium alloy structure; Finally, the surface of the sample to be tested was etched using a phosphoric acid solution. After the etching is complete, clean, dry, and observe the sample.
[0023] The principle of using caustic soda solution to corrode the aluminum alloy structure in a sample is as follows: The oxide film (Al2O3) on the surface of aluminum alloy will first react with sodium hydroxide to generate soluble sodium tetrahydroxyaluminate (NaAl(OH)4). The reaction equation is: Al2O3 + 2NaOH + 3H2O = 2NaAl(OH)4. After the oxide film is removed, the exposed aluminum substrate continues to react with sodium hydroxide and water to generate sodium tetrahydroxyaluminate and release hydrogen gas. The reaction equation is: 2Al + 2NaOH + 6H2O = 2NaAl(OH)4 + 3H2↑. During the reaction, aluminum and oxide film in the aluminum alloy can react rapidly with the alkali, while the second phase and impurity phases in the aluminum alloy, such as Mg2Si and AlFeSi, will react with the alkali. The resulting corrosion products are insoluble in the alkali and eventually remain on the surface of the aluminum alloy.
[0024] The principle of using acetic acid solution to corrode the structure of magnesium alloys is as follows: Acetic acid (CH3COOH), being a weak acid, ionizes to release H+. + The ions undergo a displacement reaction with the base metal magnesium (Mg) in the magnesium alloy: Mg + 2CH3COOH → (CH3COO)2Mg + H2↑; the generated magnesium acetate [(CH3COO)2Mg] is easily soluble in water, causing the magnesium alloy surface to be continuously dissolved, while releasing hydrogen gas.
[0025] Magnesium alloys often contain alloying elements such as aluminum, zinc, and manganese, as well as impurity phases. These components form micro-batteries with the magnesium matrix. As a reactive metal, magnesium preferentially loses electrons and is oxidized to Mg. 2+ This causes elements such as aluminum, zinc, and manganese in magnesium alloys to remain undissolved and form corrosion products on the surface of the magnesium alloy.
[0026] Corrosion products remaining on the surface of aluminum and magnesium alloys can affect the accuracy of metallographic testing, so they need to be removed.
[0027] When caustic soda is used to corrode aluminum alloy first, and then acetic acid is used to corrode magnesium alloy, caustic soda has no effect on magnesium alloy, while acetic acid can corrode and dissolve the corrosion products on the surface of aluminum alloy to a certain extent, making the corrosion products on the surface of aluminum alloy thinner and looser. When phosphoric acid solution is used for wiping, the corrosion product layer can be quickly wiped clean.
[0028] Phosphoric acid, as a moderately strong acid, can remove alkaline corrosion products from aluminum alloy surfaces and also remove substances from magnesium alloy surfaces that are insoluble in the weak acid acetic acid. Furthermore, phosphoric acid exhibits relatively mild corrosion at room temperature, minimizing excessive erosion of the substrate while removing corrosion products, thus ensuring the accuracy of metallographic analysis results.
[0029] If the sample is first etched with acetic acid and then with caustic soda, the magnesium alloy is selectively corroded during acetic acid etching, while the aluminum alloy is selectively corroded during caustic soda etching. Furthermore, the caustic soda solution has limited dissolution effect on the corrosion products on the magnesium alloy surface, and the corrosion products on the aluminum alloy surface cannot be dissolved or weakened. If phosphoric acid is used for etching, the number of etching cycles and the time required increase, inevitably leading to over-corrosion of the magnesium alloy, especially at the weld seam, which affects the accuracy of metallographic analysis.
[0030] In some embodiments, the sample is polished with 320# and 600# sandpaper in sequence to ensure that the surface roughness of the test surface is Ra0.1~0.2μm.
[0031] Grinding can eliminate scratches, burrs, oxide layers, and plastic deformation layers generated during sample cutting and processing, avoiding interference from these surface damages with subsequent low-magnification microstructure observation. By grinding with sandpaper from coarse to fine, the sample surface is gradually made smooth, ensuring that the etchant can act evenly on the metal matrix and reducing uneven corrosion caused by surface irregularities. Grinding can remove the surface work-hardened layer, exposing the true metal structure inside the sample, providing an accurate structural basis for subsequent corrosion and microscopic observation.
[0032] In some embodiments, the concentration of the caustic soda solution is 50-200 g / L. For example, it can be 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, or 200 g / L; preferably 100-150 g / L.
[0033] The concentration of caustic soda solution mainly affects the corrosion process of aluminum alloys in terms of corrosion rate, surface condition, and process controllability. Higher caustic soda concentration leads to a faster corrosion rate, which can improve the efficiency of metallographic specimen preparation to some extent. However, excessively high caustic soda concentration makes the corrosion process difficult to control, increases sodium hydroxide carryover, and raises production costs. Conversely, excessively high caustic soda concentration results in a slower corrosion rate, affecting the efficiency of metallographic specimen preparation.
[0034] Preferably, the etching time of the sample with caustic soda solution is 1-5 min, such as 1 min, 1.1 min, 1.2 min, 1.3 min, 1.4 min, 1.5 min, 1.6 min, 1.7 min, 1.8 min, 1.9 min, 2 min, 2.1 min, 2.2 min, 2.3 min, 2.4 min, 2.5 min, 2.6 min, 2.7 min, 2.8 min, 2.9 min, 3.0 min, 3.1 min, 3.2 min, 3.3 min, 3.4 min, 3.5 min, 3.6 min, 3.7 min, 3.8 min, 3.9 min, 4.0 min, 4.1 min, 4.2 min, 4.3 min, 4.4 min, 4.5 min, 4.6 min, 4.7 min, 4.8 min, 4.9 min, or 5.0 min; preferably 2-3 min.
[0035] In some embodiments, the volume ratio of acetic acid to water in the acetic acid solution is 1:5-20, such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, or 1:20; preferably 1:6-10.
[0036] Acetic acid dissociates in water to produce H+. + Magnesium in magnesium alloys undergoes an anodic dissolution reaction. When the acetic acid concentration is low, such as <5%, the buffering capacity of the low-concentration acetic acid solution is weak, and the local pH value is prone to fluctuation, which may lead to pitting corrosion or non-uniform corrosion.
[0037] When the acetic acid concentration is appropriate, the proportion of undissociated CH3COOH molecules in the solution increases. These molecules can adsorb onto the magnesium alloy surface to form a protective film (such as magnesium acetate complex), inhibiting H2O. + The contact surface slows down corrosion, thus effectively preventing excessive corrosion of magnesium alloys. Furthermore, at this time, the acetic acid solution is in the CH3COOH / CH3COO... - The buffer pair provides a more stable pH value, which is more conducive to uniform corrosion.
[0038] When the acetic acid concentration is too high, the viscosity of the high-concentration acetic acid solution increases, hindering ion diffusion, and H+... + The reduced migration rate and the formation of a dense layer of adsorbed organic molecules or salt deposits on the surface hinder the corrosion reaction. If the protective layer is uneven, it may lead to pitting corrosion and other problems, resulting in uneven corrosion and affecting the accuracy of metallographic analysis.
[0039] Preferably, the etching time of the sample with acetic acid solution is 10-50s, more preferably 20-30s.
[0040] After etching the metallographic sample with acetic acid, it needs to be removed and cleaned. This cleaning process also requires a certain amount of time. If the acetic acid solution contains H+... + Excessive acetic acid concentration results in insufficient etching time for complete corrosion. During the cleaning process after metallographic sample removal, the magnesium alloy continues to corrode, making the process difficult to control and prone to over-corrosion. Therefore, adjusting the acetic acid concentration and appropriately extending the etching time allows for better control of the etching progress.
[0041] In some embodiments, the volume ratio of phosphoric acid to water in the phosphoric acid solution is 1:5-15, preferably 1:6-10.
[0042] Preferably, the time for etching the sample with phosphoric acid solution is 5-30s, more preferably 10-20s.
[0043] The present invention will be further described below with reference to the embodiments.
[0044] In the following examples and comparative examples, the magnesium alloy test plates used were all of grade YGB27-H112, the aluminum alloy test plates were all of grade 6005A-T6, the backing plates were all of grade 5083P-O, and the welding method was friction stir welding.
[0045] Example 1 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn.
[0046] (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 120 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 100 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 100 ml / L; the etching time was 10 s, and the temperature was room temperature. (7) The metallographic specimen was cleaned and dried, and the low-magnification microstructure of the weld joint was observed using a stereomicroscope. The metallographic specimen after corrosion showed good visualization of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure. The corrosion effect of the metallographic specimen in Example 1 is shown in [reference needed]. Figure 1 .
[0047] Example 2 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 100 g / L; the etching time is 4 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 110 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 100 ml / L; the etching time was 10 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0048] Example 3 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 80 g / L; the etching time is 5 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 120 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 100 ml / L; the etching time was 10 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0049] Example 4 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 50 g / L; the etching time is 8 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 110 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 120 ml / L; the etching time was 20 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0050] Example 5 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 150 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 130 ml / L; the etching time is 20 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 150 ml / L; the etching time was 20 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0051] Example 6 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 140 g / L; the etching time is 4 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 150 ml / L; the etching time is 15 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 150 ml / L; the etching time was 20 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0052] Example 7 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 140 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 80 ml / L; the etching time is 40 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 90 ml / L; the etching time was 30 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0053] Example 8 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 70 g / L; the etching time is 6 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 120 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 110 ml / L; the etching time was 30 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. The metallographic specimens after corrosion show good imaging of the magnesium alloy microstructure, weld microstructure, and aluminum alloy microstructure.
[0054] Comparative Example 1 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test side facing up in the beaker and etch the metallographic sample with Köhler reagent (water, concentrated nitric acid, concentrated hydrochloric acid and hydrofluoric acid in a volume ratio of 95:2.5:1.5:1); etching time: 60s, room temperature; (3) The sample was removed, cleaned, and dried. The low-magnification microstructure of the weld joint was observed using a stereomicroscope. After corrosion, the aluminum alloy microstructure of the metallographic specimen showed good corrosion, while the magnesium alloy microstructure and weld microstructure showed excessive corrosion. The corrosion effect of the metallographic specimen in Comparative Example 1 is shown in [reference needed]. Figure 2 .
[0055] Comparative Example 2 A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn; (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; acetic acid solution ratio: 10mL-C2H4O2+90ml-H2O; etching time: 30s, room temperature; (3) The sample was removed, cleaned, and dried. The low-magnification microstructure of the weld joint was observed using a stereomicroscope. After corrosion, the magnesium alloy and weld microstructures of the metallographic specimen showed good corrosion, while the aluminum alloy microstructure showed insufficient corrosion. The corrosion effect of the metallographic specimen in Comparative Example 2 is shown in [reference needed]. Figure 3 .
[0056] Depend on Figure 1 As can be seen, the magnesium alloy and aluminum alloy microstructures in Example 1 exhibit moderate corrosion, with minimal color difference. The welded joint shows good imaging across all areas, allowing for observation and analysis of each region. Figure 2It can be seen that the aluminum alloy in Comparative Example 1 exhibits moderate corrosion, while the magnesium alloy shows excessive corrosion, resulting in a significant color difference between the two and making effective observation of the microstructure on the magnesium alloy side impossible. Figure 3 It can be seen that the magnesium alloy in Comparative Example 2 has a moderate degree of corrosion, but the aluminum alloy has too little corrosion. The color difference between the two is large, making it impossible to effectively observe the microstructure on the aluminum alloy side.
[0057] Comparative Example 3 The difference from Example 1 is that steps (2) and (4) are interchanged, while the rest is the same as in Example 1. Specifically: A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn.
[0058] (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 100 ml / L; the etching time is 30 s, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 120 g / L; the etching time is 3 min, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 100 ml / L; the etching time was 10 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. After corrosion, the aluminum alloy microstructure of the metallographic specimens showed good corrosion, while the magnesium alloy microstructure and weld microstructure showed slightly excessive corrosion.
[0059] Comparative Example 4 The difference from Example 1 is that the acetic acid solution is replaced with a 1% HF solution; all other aspects are the same as in Example 1. A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn.
[0060] (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 120 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with a 1% HF solution; the etching time is 30s, at room temperature. (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 100 ml / L; the etching time was 10 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. After corrosion, the aluminum alloy microstructure of the metallographic specimens showed good corrosion, while the magnesium alloy microstructure and weld microstructure showed excessive corrosion.
[0061] Comparative Example 5 The difference from Example 1 is that the acetic acid solution is replaced with a 3% (v / v) nitric acid ethanol solution; all other aspects are the same as in Example 1. A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn.
[0062] (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 120 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with a 3% nitric acid ethanol solution; the etching time is 30s, at room temperature. (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with phosphoric acid solution; the concentration of phosphoric acid solution was 100 ml / L; the etching time was 10 s, and the temperature was room temperature. (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. After corrosion, the aluminum alloy microstructure of the metallographic specimens showed good corrosion, while the magnesium alloy microstructure and weld microstructure showed excessive corrosion.
[0063] Comparative Example 6 The difference from Example 1 is that the step of etching the metallographic sample with phosphoric acid solution in step (6) is omitted; all other steps are the same as in Example 1. A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn.
[0064] (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 120 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 100 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) Clean and dry the metallographic specimen, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. After corrosion, a layer of corrosion products remains on the test surface of the metallographic specimen, which affects the observation effect.
[0065] Comparative Example 7 The difference from Example 1 is that the phosphoric acid solution in step (6) is replaced with a 1% HF solution; all other aspects are the same as in Example 1. A metallographic inspection method for magnesium-aluminum dissimilar metal welded joints includes the following steps: (1) Use 320# and 600# sandpaper to polish the test surface of the sample in turn.
[0066] (2) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with caustic soda solution; the concentration of sodium hydroxide in the caustic soda solution is 120 g / L; the etching time is 3 min, at room temperature; (3) Remove the sample, clean it, and dry it; (4) Place the sample with the test surface facing up into the beaker and etch the metallographic sample with acetic acid solution; the concentration of acetic acid solution is 100 ml / L; the etching time is 30 s, at room temperature; (5) Remove the sample, clean it, and dry it; (6) The metallographic sample was etched with a 1% HF solution; the etching time was 10s, at room temperature; (7) Clean and dry the metallographic specimens, and observe the low-magnification microstructure of the weld joint using a stereomicroscope. After corrosion, the aluminum alloy microstructure of the metallographic specimens showed good corrosion, while the magnesium alloy microstructure and weld microstructure showed excessive corrosion.
[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints, characterized in that: Includes the following steps: The test surface of the magnesium-aluminum dissimilar metal welded joint sample to be tested is ground to ensure that the roughness meets the requirements. The aluminum alloy structure was corroded by immersing the sample in a caustic soda solution. Then, the sample was etched with acetic acid solution to corrode the magnesium alloy structure; Finally, the surface of the sample to be tested was etched using a phosphoric acid solution. After the etching is complete, clean, dry, and observe the sample.
2. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 1, characterized in that: The sample was polished with 320# and 600# sandpaper in sequence to ensure that the surface roughness was Ra0.1~0.2μm.
3. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 1, characterized in that: The concentration of the sodium hydroxide solution is 50-200 g / L.
4. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 3, characterized in that: The concentration of the sodium hydroxide solution is 100-150 g / L.
5. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 3, characterized in that: The etching time of the sample with caustic soda solution is 1-5 minutes, preferably 2-3 minutes.
6. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 1, characterized in that: In the acetic acid solution, the volume ratio of acetic acid to water is 1:5-20.
7. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 6, characterized in that: In the acetic acid solution, the volume ratio of acetic acid to water is 1:6-10.
8. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 6, characterized in that: The etching time of the sample with acetic acid solution is 10-50s, preferably 20-30s.
9. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 1, characterized in that: In the phosphoric acid solution, the volume ratio of phosphoric acid to water is 1:5-15, preferably 1:6-10.
10. The macroscopic metallographic inspection method for magnesium-aluminum dissimilar metal welded joints according to claim 9, characterized in that: The time for etching the sample with phosphoric acid solution is 5-30s, preferably 10-20s.