A simplified method for low-magnification grain size detection of aluminum and aluminum alloy sheets and strips with equiaxed grains.

Abstract

This invention discloses a simplified method for detecting the low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains. First, standard samples with grain sizes from level one to eight are tested according to GB / T 3246.2-2012. These standard samples are then prepared into dumbbell-shaped tensile test specimens according to GB / T 228.1-2021, and each specimen is subjected to tensile testing. The resulting low-magnification grain size level is labeled after each fracture, serving as the standard sample. Next, aluminum and aluminum alloy sheets and strips with equiaxed grains are prepared into dumbbell-shaped tensile test specimens according to GB / T 228.1-2021. These specimens are then subjected to tensile testing to obtain the fractured specimen. The surface roughness of the fractured section is compared with that of the standard specimen. This comparison determines the low-magnification grain size level of the tested sample. This invention determines the grain size of the tested sample by comparing the surface roughness of the tested sample and the standard sample. It is simple to operate, safe to use, energy-saving, reduces the need for post-treatment with strong acids and alkalis, and is low-cost.

Description

I. Technical Field:

[0001] This invention belongs to the field of low-magnification grain size detection technology for aluminum strips and sheets, specifically relating to a simple method for low-magnification grain size detection of aluminum and aluminum alloy strips and sheets with equiaxed grains. II. Background Technology:

[0002] Currently, the inspection method for the microstructure of wrought aluminum and aluminum alloy products—specifically the low-magnification microstructure inspection method—is conducted in accordance with GB / T 3246.2-2012 (Inspection Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products Part 2: Low-Magnification Microstructure Inspection Method). This standard specifies the following methods for low-magnification grain size detection of aluminum and aluminum alloy sheets and strips:

[0003] 1) Sample preparation: Take strips 30mm wide and of varying lengths transversely;

[0004] 2) Immerse the sample in the following test solutions for several minutes. The test solution requirements are as follows: For samples of the 1XXX, 3XXX, 5XXX, and 8XXX series used for checking grain size, the surface to be inspected should be immersed in a strong mixed acid solution (2.1) or a strong mixed acid solution (2.2) at room temperature for an appropriate time, or repeatedly wipe the sample surface with an etchant, and then immediately rinse with water. This process can be repeated multiple times until the grains are clearly visible. For samples of the 2XXX, 4XXX, 6XXX, and 7XXX series used for checking grain size, the surface to be inspected should be immersed in a sodium hydroxide solution (2.3), a high-concentration mixed acid solution (2.4), or a strong mixed acid solution (2.2) at room temperature for an appropriate time, or repeatedly wipe the sample surface with an etchant, and then immediately rinse with water and nitric acid solution (2.5) until the grains are clearly visible. The test solutions described in 2.1 to 2.4 of the standard are as follows:

[0005] 2.1 Strong mixed acid solution: Mix hydrofluoric acid (ρ1.15g / mL), nitric acid (ρ1.40g / mL) and hydrochloric acid (ρ1.19g / mL) in a volume ratio of (1+5+15) until homogeneous.

[0006] 2.2 Strong mixed acid solution: Hydrofluoric acid (ρ 1.15 g / mL), nitric acid (ρ 1.40 g / mL), and hydrochloric acid (ρ 1.40 g / mL) are mixed.

[0007] Mix 1.19 g / mL of the product with water in a volume ratio of (1+5+15+42) until homogeneous.

[0008] 2.3 The concentration of the sodium hydroxide solution is 150 g / L to 250 g / L.

[0009] 2.4 High-concentration mixed acid solution: Mix hydrofluoric acid (ρ1.15g / mL), nitric acid (ρ1.40g / mL), hydrochloric acid (ρ1.19g / mL) and water in a volume ratio of (2+1+1+76).

[0010] 3) Grain size inspection: Samples with equiaxed grains should be evaluated according to the grain size grading standard.

[0011] The existing national standards for low-magnification testing use four test solutions: a mixture of hydrofluoric acid, nitric acid, and hydrochloric acid, or highly corrosive solutions such as sodium hydroxide solution. This standard requires etching the sample, and the etchant is an acid or alkali reagent that is currently under strict control. This poses safety and cost issues. The etchant method is dangerous and sometimes requires multiple etchings and wiping. More importantly, the etchant is difficult to dispose of after use, causing pollution and harming the environment. III. Summary of the Invention:

[0012] The technical problem this invention aims to solve is to address the shortcomings of the existing national standard GB / T 3246.2-2012, "Methods for Inspecting the Microstructure of Wrought Aluminum and Aluminum Alloy Products." This invention provides a simplified method for detecting the low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains. This simplified method eliminates the need for strong acid and alkali etching of the sample, allowing for indirect determination of the low-magnification grain size of the aluminum alloy. The grain size of the test sample is determined by comparing the surface roughness of the test sample with that of a standard sample. This method solves the problems existing in the prior art and is simple to operate, safe to use, energy-saving, reduces the need for strong acid and alkali post-treatment, and is low in cost.

[0013] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0014] This invention provides a simple method for detecting the low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains. The simple detection method includes the following steps:

[0015] (1) Preparation of standard samples:

[0016] 1) Test samples with grain sizes from grade I to grade VIII according to the low magnification microstructure test method specified in GB / T 3246.2-2012 Test Method for Microstructure of Wrought Aluminum and Aluminum Alloy Products, Part 2;

[0017] 2) Prepare dumbbell-shaped tensile specimens from the samples tested in step 1) according to GB / T228.1-2021 standard for tensile testing of metallic materials;

[0018] 3) The dumbbell-shaped tensile samples prepared in step 2) were broken on a universal tensile testing machine. After breaking, the corresponding low-magnification grain size level was marked and used as standard samples.

[0019] (2) Preparation of the sample to be tested:

[0020] 1) In accordance with GB / T228.1-2021 standard for tensile testing of metallic materials, aluminum and aluminum alloy sheet and strip samples with equiaxed grains were made into dumbbell-shaped tensile specimens;

[0021] 2) The tensile sample prepared in step 1) is broken on a universal tensile testing machine to obtain the fractured sample of the test sample. The surface roughness of the parallel section of the obtained fractured sample is compared with that of the standard sample obtained in step (1). The low magnification grain size level of the test sample is determined by comparison.

[0022] According to the above-mentioned simplified test method for low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains, the total length Lt of the dumbbell-shaped tensile test sample is 180±1mm, the parallel length Lc is 75±2mm, the width b0 of the parallel length of the tensile test sample is 12.5±0.05mm, and the transition arc radius R of the tensile test sample is 20~22mm (the accuracy and shape tolerance of the sample after processing conform to GB / T228.1-2021).

[0023] According to the above-mentioned simple test method for low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains, when tensile testing is performed on a universal tensile testing machine, the displacement speed of the crossbeam of the tensile testing machine is 2 mm / minute.

[0024] According to the above-mentioned simplified detection method for low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains, the grain size level of the sample being tested is equiaxed grains, and its state is any one of the fully annealed O state, H111 state, T4 state and T6 state in aluminum alloy states.

[0025] According to the above-mentioned simple detection method for low-magnification grain size of aluminum and aluminum alloy plates and strips with equiaxed grains, when the surface roughness of the parallel section of the obtained fractured sample is compared with that of the standard sample obtained in step (1), the tested sample and the standard sample are the same type of aluminum and aluminum alloy, in the same state, and the crossbeam displacement speed of the tensile testing machine is the same when they are stretched.

[0026] In the simplified detection method of the present invention, when the surface roughness of the sample being tested is close to or finer than that of the standard primary grain sample, the low-magnification grain level of the sample being tested is identified as a low-magnification primary grain; when the surface of the sample being tested after stretching is rougher than the primary grain surface but finer than the secondary grain sample, it is identified as a secondary grain; and so on.

[0027] The detection principle of this invention, which indirectly determines low-magnification grain size based on the surface roughness of the sample after tensile fracture, is as follows:

[0028] The surface roughness generated during the deformation of aluminum alloy specimens is mainly influenced by two factors: the internal microstructure of the specimen and the external tensile conditions. The influence of material microstructure on surface roughness is primarily due to the grain size within the material, while the tensile conditions mainly refer to the elongation after stretching. During polycrystalline deformation, the orientation of each grain relative to the force axis varies in terms of softness and hardness, resulting in different deformation sequences and amounts. Softly oriented grains exhibit larger deformation, while hard-oriented grains show smaller deformation. Furthermore, the deformation is uneven within each grain, typically with greater deformation in the grain center and smaller deformation at and near grain boundaries. The smaller difference in strain between the grain interior and near grain boundaries in fine grains contributes to a more uniform deformation transition and maintains a smooth surface. Conversely, the larger difference in strain between the grain interior and near grain boundaries in coarse grains makes it difficult for the deformation between grains to coordinate, resulting in uneven deformation. Therefore, the anisotropy of grain mechanical behavior macroscopically creates an uneven surface structure, forming the defect of "surface roughness." The greater the stretching amount, the greater the difference in deformation between the surface and the core, i.e., the more uneven the deformation. Research results reveal a direct correlation between surface roughness and grain size; the coarser the grains, the rougher the surface after stretching. Similarly, the surface roughness of a grain-size material after stretching is also directly proportional to the stretching amount; the greater the stretching amount, the rougher the surface after stretching. In this invention, the sample is broken on a tensile testing machine, which is equivalent to giving the material a maximum tensile deformation. This maximizes the surface change after stretching, making it easier to examine the surface roughness after breakage and thus, by comparing it with a standard sample, to briefly determine its low-magnification grain size.

[0029] The positive and beneficial effects of this invention are:

[0030] 1) The simplified detection method of this invention does not require strong acid or alkali etching of the sample to indirectly determine the low-magnification grain size of the aluminum alloy. Therefore, the detection method of this invention is more environmentally friendly, conforms to the current concept of energy conservation and environmental protection, and has significant social benefits.

[0031] 2. The technical solution of this invention determines the grain size of the test sample by comparing the surface roughness of the test sample and the standard sample. Therefore, the method of this invention solves the problems existing in the prior art.

[0032] 3. The method of the present invention is simple to operate, safe to use, energy-saving, reduces the post-treatment of strong acids and alkalis, and has low cost.

[0033] In summary, this invention has significant economic and social benefits. IV. Description of the attached drawings:

[0034] Figure 1 A schematic diagram of the dumbbell-shaped tension sample of this invention;

[0035] Figure 1In the figure, Lt is the total length of the tension sample, Lc is the parallel length, b0 is the width of the parallel length of the tension sample, and R is the radius of the transition arc in the tension sample.

[0036] Figure 2 This is a schematic diagram of the dumbbell-shaped tension sample made according to Embodiment 1 of the present invention.

[0037] Figure 3 This is a schematic diagram of the low-magnification grain size level of the standard sample prepared in Example 1 of the present invention.

[0038] Figure 4 This is a schematic diagram of a dumbbell-shaped tensile sample prepared from the test sample in Embodiment 1 of the present invention.

[0039] Figure 5 This is a schematic diagram of the sample after it was broken in Embodiment 1 of the present invention.

[0040] Figure 6 for Figure 5 A magnified view of a portion of the image.

[0041] Figure 7 This is a schematic diagram of a dumbbell-shaped tensile sample prepared from the test sample in Embodiment 2 of the present invention.

[0042] Figure 8 This is a schematic diagram of the sample after it was broken in Embodiment 2 of the present invention.

[0043] Figure 9 for Figure 8 A magnified view of a portion of the image. V. Detailed Implementation Methods:

[0044] The present invention will be further illustrated below with reference to the embodiments, but this does not limit the scope of protection of the technical solution of the present invention.

[0045] Example 1:

[0046] This invention provides a simplified low-magnification grain size detection method for aluminum and aluminum alloy sheets and strips with equiaxed grains (taking 6061 aluminum alloy T6 temper sheet as an example). The detailed steps are as follows:

[0047] (1) Preparation of standard samples:

[0048] 1) Test samples with grain sizes from grade I to grade VIII according to the low magnification microstructure test method specified in GB / T 3246.2-2012 Test Method for Microstructure of Wrought Aluminum and Aluminum Alloy Products, Part 2;

[0049] 2) The 6061-T6-3.0mm specimens tested in step 1) were prepared into dumbbell-shaped tensile specimens according to GB / T228.1-2021 Standard for Tensile Testing of Metallic Materials (see Appendix for details). Figure 2 );

[0050] In the obtained dumbbell-shaped tensile specimen, the total length Lt of the specimen is 180 mm, the parallel length Lc is 75 mm, the width b0 of the parallel length of the specimen is 12.5 mm, and the radius R of the transition arc in the specimen is 20 mm.

[0051] 3) The dumbbell-shaped tensile specimens prepared in step 2) were broken on a universal tensile testing machine at a crossbeam displacement speed of 2 mm / min. After breaking, the corresponding low-magnification grain size level was marked as the standard specimen (see Appendix for details). Figure 3 );

[0052] (2) Preparation of the sample to be tested:

[0053] 1) In accordance with GB / T228.1-2021 Standard for Tensile Testing of Metallic Materials, dumbbell-shaped tensile specimens were prepared from aluminum and aluminum alloy sheet and strip samples with equiaxed grains (6061 aluminum alloy T6-1.0mm thick) (see attached document for details). Figure 4 );

[0054] The total length of the tensile specimen is Lt, which is 180 mm; the parallel length is Lc, which is 75 mm; the width of the parallel length of the tensile specimen is b0, which is 12.5 mm; and the radius of the transition arc in the tensile specimen is R, which is 20 mm.

[0055] 2) The tensile sample prepared in step 1) is subjected to tensile testing on a universal tensile testing machine at a crossbeam displacement speed of 2 mm / min; the fractured sample is obtained (see attached diagram). Figure 5 The surface roughness of the parallel segments of the obtained fractured sample and the standard sample obtained in step (1) are compared. After comparison, the low magnification grain size level of the tested sample is determined to be first-level grain.

[0056] Example 2:

[0057] The present invention provides a simplified method for detecting the low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains (taking 6061 aluminum alloy in T6 condition as an example). This method is essentially the same as Example 1, except that:

[0058] (2) Preparation of the sample to be tested:

[0059] 1) In accordance with GB / T228.1-2021 Standard for Tensile Testing of Metallic Materials, dumbbell-shaped tensile test specimens were prepared from 6061 aluminum alloy T6-3.0mm strip samples with equiaxed grains (see attached document for details). Figure 7 ):

[0060] The total length of the dumbbell-shaped tension specimen is Lt, which is 180 mm; the parallel length is Lc, which is 75 mm; the width of the parallel length of the tension specimen is b0, which is 12.5 mm; and the radius of the transition arc in the tension specimen is R, which is 20 mm.

[0061] 2) The tensile sample prepared in step 1) is subjected to tensile testing on a universal tensile testing machine. The crossbeam displacement speed of the tensile testing machine is 2 mm / min, and the fractured sample is obtained (see Appendix for details). Figure 8 The surface roughness of the parallel segments of the obtained fractured sample and the standard sample obtained in step (1) are compared. After comparison, it is determined that the low magnification grain size level of the tested sample is secondary grain.

Claims

1. A simplified method for detecting the low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains, characterized in that, The simplified detection method includes the following steps: (1) Preparation of standard samples: 1) Test samples with grain sizes from grade I to grade VIII according to the low magnification microstructure test method specified in GB / T 3246.2-2012 Test Method for Microstructure of Wrought Aluminum and Aluminum Alloy Products, Part 2; 2) Prepare dumbbell-shaped tensile specimens from the samples tested in step 1) according to GB / T228.1-2021 standard for tensile testing of metallic materials; In the obtained dumbbell-shaped tension specimen, the total length Lt of the tension specimen is 180±1mm, the parallel length Lc is 75±2mm, the width b0 of the parallel length of the tension specimen is 12.5±0.05mm, and the transition arc radius R in the tension specimen is 20~22mm; 3) The dumbbell-shaped tensile specimens prepared in step 2) were broken on a universal tensile testing machine. The crossbeam displacement speed of the tensile testing machine was 2 mm / min. After breaking, the corresponding low-magnification grain size level was marked and used as standard specimens. (2) Preparation of the test sample: 1) In accordance with GB / T228.1-2021 standard for tensile testing of metallic materials, aluminum and aluminum alloy sheet and strip samples with equiaxed grains were made into dumbbell-shaped tensile specimens; In the obtained dumbbell-shaped tension specimen, the total length Lt of the tension specimen is 180±1mm, the parallel length Lc is 75±2mm, the width b0 of the parallel length of the tension specimen is 12.5±0.05mm, and the transition arc radius R in the tension specimen is 20~22mm; 2) The tensile sample prepared in step 1) is broken on a universal tensile testing machine. The displacement speed of the crossbeam of the tensile testing machine is 2 mm / min. The broken sample is obtained. The surface roughness of the parallel section of the obtained broken sample is compared with that of the standard sample obtained in step (1). The low magnification grain size level of the tested sample is determined by comparison.

2. The simplified method for detecting low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains according to claim 1, characterized in that: The grain size of the sample being tested is equiaxed, and its state is any one of the fully annealed O state, H111 state, T4 state, and T6 state in the aluminum alloy state.

3. The simplified method for detecting the low-magnification grain size of aluminum and aluminum alloy sheets and strips with equiaxed grains according to claim 1, characterized in that: When comparing the surface roughness of the parallel section of the obtained fractured sample with the standard sample obtained in step (1), the tested sample and the standard sample are the same type of aluminum and aluminum alloy, in the same state, and the crossbeam displacement speed of the tensile testing machine is the same when they are stretched.

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