A method for determining dendrite channel permeability

Abstract

The present invention belongs to the technical field of metal alloy casting, and specifically relates to a method for determining the permeability of dendrite channels. The present invention includes the steps of: corroding the surface of the alloy, performing a polishing process to obtain a low-magnification tissue image with a clear dendrite interface outline, and using a two-dimensional imager to obtain a high-definition low-magnification tissue image of the metal; measuring the primary and secondary dendrite arm spacings and the segregation area ratio by image processing software, extracting the dendrite outline by image processing software, and calculating the fractal dimension of the dendrite outline morphology according to the box counting method; and calculating the permeability of the columnar crystal region, the columnar crystal to equiaxed crystal transition region (CET), and the dendrite channel in the equiaxed crystal region. The permeability of the dendrite channel can quantitatively predict the flow resistance of the liquid phase between dendrites during the solidification process of the metal, thereby achieving control of the liquid phase flow rate and flow direction during the solidification process. This provides guidance for regulating the three-dimensional density of the actual solidification structure of the metal and thereby finely controlling segregation.

Description

Technical Field

[0001] The invention belongs to the technical field of metal alloy casting, and particularly relates to a method for determining dendrite channel permeability. Background Art

[0002] During the solidification process of metal alloys, the transition from a completely liquid phase to a completely solid phase is not instantaneous. Instead, a two-phase region of solid and liquid coexists, known as the mushy zone. The mushy zone consists of a dendritic solid phase and a solute-rich liquid phase, and the liquid-solid transition gradually completes. To prevent the formation of micropores during cooling and shrinkage, the shrinkage of the metal alloy in the mushy zone must be compensated by the flow of liquid metal in the interdendritic channels. Simultaneously, macrosegregation (large-scale compositional inequalities ranging in size from millimeters to centimeters to even meters) also forms in the mushy zone. In most cases, this is caused by the flow of the solute-rich liquid phase in the interdendritic channels driven by contraction, geometry, solid-phase deformation, or gravity. For typical dendritic structures, the dendritic region can be treated as a porous medium, and Darcy's law can be used to estimate the flow of liquid in the interdendritic channels. Using Darcy's law requires the permeability of the interdendritic flow channels; that is, the flow of the solute-rich liquid phase in the interdendritic channels can be expressed in terms of permeability. Therefore, the calculation of the permeability during the actual solidification process of the metal helps to understand the interdendritic liquid flow, thereby providing guidance for the refined control of segregation defects.

[0003] Researchers primarily use two conventional methods to estimate the permeability of interdendritic channels: direct experimental measurement and numerical analysis. However, experimental methods are time-consuming and costly, and are difficult to perform for metals or alloys with high melting points. Furthermore, numerical analysis struggles to accurately estimate the permeability of actual alloys due to the complex changes in dendrite morphology during solidification. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for determining the permeability of dendrite channels. The present invention provides a new method for determining the permeability of dendrite channels based on the actual cast structure characteristics of metals, which makes up for the shortcomings of methods for calculating the permeability of dendrite channels such as direct experimental measurement and numerical analysis.

[0005] In order to achieve the above object, the present invention provides the following technical solutions:

[0006] The present invention provides a method for determining dendrite channel permeability, comprising the following steps:

[0007] Dendrite corrosion is performed on the surface of the alloy sample to obtain a treated sample; the treated sample has a macrostructure with a dendrite interface profile; the macrostructure is a columnar crystal region macrostructure, a columnar crystal to equiaxed crystal transition region macrostructure, or an equiaxed crystal region macrostructure;

[0008] acquiring a low-magnification tissue image of the treated sample;

[0009] Image processing software was used to analyze the acquired low-magnification tissue images;

[0010] When the macrostructure is a columnar crystal region macrostructure, the analysis includes: measuring the primary dendrite arm spacing, segregation area, and total area in the macrostructure image; and calculating the segregation area ratio from the segregation area and the total area.

[0011] When the macrostructure is a columnar crystal to equiaxed crystal transition zone macrostructure or an equiaxed crystal zone macrostructure, the analysis includes: measuring the primary dendrite arm spacing, the secondary dendrite arm spacing, the segregation area, and the total area in the macrostructure image; and calculating the segregation area ratio from the segregation area and the total area;

[0012] The fractal dimension of dendrite outlines in low-magnification tissue images was obtained according to the box counting method;

[0013] When the macrostructure is a columnar crystal region macrostructure, the permeability of the dendrite channel in the columnar crystal region is obtained according to the segregation area ratio, the primary dendrite arm spacing, and the fractal dimension of the dendrite profile;

[0014] When the low-magnification structure is a low-magnification structure in the columnar crystal to equiaxed crystal transition zone or an equiaxed crystal zone low-magnification structure, the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition zone or the equiaxed crystal zone is obtained according to the segregation area ratio, the primary dendrite arm spacing, the secondary dendrite arm spacing and the fractal dimension of the dendrite profile.

[0015] Preferably, the permeability of the dendrite channel in the columnar crystal region is obtained by the formula shown in Formula 1:

[0016]

[0017] In formula 1, Kc is the permeability of the dendrite channel in the columnar crystal region, m 2 ; R seg is the segregation area ratio; λ1 is the primary dendrite arm spacing, m; D is the fractal dimension of the dendrite outline.

[0018] Preferably, the permeability of the columnar crystal to equiaxed crystal transition region or the dendrite channel in the equiaxed crystal region is obtained as shown in Formula 2:

[0019]

[0020] In formula 1, Ke is the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition region or the equiaxed crystal region, m 2 ; R segis the segregation area ratio; λ1 is the primary dendrite arm spacing, m; λ2 is the secondary dendrite arm spacing, m; D is the fractal dimension of the dendrite outline.

[0021] Preferably, the dendrite corrosion is performed using a metal low-magnification corrosion method.

[0022] Preferably, the dendrite corrosion directly obtains an initial treatment sample; and further comprises polishing the surface of the initial treatment sample to obtain the treatment sample.

[0023] Preferably, the polishing is: polishing the corroded surface of the initial treatment sample with metallographic sandpaper until the dendrite structure is exposed; the mesh number of the metallographic sandpaper is 800 mesh.

[0024] Preferably, the acquisition is performed by using a two-dimensional imager.

[0025] Preferably, the low-magnification tissue image is a tissue image that can be observed with the naked eye or a microscope with a magnification of ≤10 times.

[0026] Preferably, the method for obtaining the fractal dimension of the dendrite outline is: extracting the dendrite outline in the low-magnification tissue image using computer software; calculating the fractal dimension of the dendrite outline according to the box counting method; the computer software is Matlab.

[0027] Preferably, the image processing software is Image-ProPlus.

[0028] The present invention provides a method for determining the permeability of a dendrite channel, comprising the following steps: performing dendrite corrosion on the surface of an alloy sample to obtain a treated sample; the treated sample has a low-magnification structure with a dendrite interface profile; the low-magnification structure is a columnar crystal region low-magnification structure, a columnar crystal to equiaxed crystal transition region low-magnification structure, or an equiaxed crystal region low-magnification structure; obtaining a low-magnification structure image of the treated sample; analyzing the obtained low-magnification structure image using image processing software; when the low-magnification structure is a columnar crystal region low-magnification structure, the analysis comprises: measuring the primary dendrite arm spacing, segregation area, and total area in the low-magnification structure image; calculating the segregation area ratio from the segregation area and the total area; when the low-magnification structure is a columnar crystal to equiaxed crystal transition region low-magnification structure or an equiaxed crystal region low-magnification structure The analysis includes: measuring the primary dendrite arm spacing, secondary dendrite arm spacing, segregation area and total area in the low-magnification tissue image; calculating the segregation area ratio from the segregation area and the total area; obtaining the fractal dimension of the dendrite outline in the low-magnification tissue image according to the box counting method; when the low-magnification tissue is a columnar crystal region low-magnification tissue, obtaining the permeability of the dendrite channel in the columnar crystal region according to the segregation area ratio, the primary dendrite arm spacing and the fractal dimension of the dendrite outline; when the low-magnification tissue is a columnar crystal to equiaxed crystal transition region low-magnification tissue or an equiaxed crystal region low-magnification tissue, obtaining the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition region or the equiaxed crystal region according to the segregation area ratio, the primary dendrite arm spacing, the secondary dendrite arm spacing and the fractal dimension of the dendrite outline. The present invention uses the segregation area ratio Rseg (the ratio of the segregation area to the total area of the analysis region) in the macrostructure of an actual metal sample as the liquid fraction in the mushy zone. Furthermore, the present invention uses fractal dimension to quantitatively characterize the complexity of dendrite profile morphology. Consequently, the present invention uses the segregation area ratio and fractal dimension to replace the liquid volume fraction and tortuosity coefficient in conventional permeability formulas to calculate dendrite permeability. The method provided by the present invention can calculate the permeability of dendrite channels during the solidification process of actual metal alloys. The analysis region and range can be flexibly selected, allowing for the calculation of dendrite permeabilities for different dendrite types, including columnar crystals, columnar-to-equiaxed transition regions (CETs), and regional dendrite permeabilities of equiaxed crystals.

[0029] The present invention can quantitatively predict the flow resistance of the liquid phase between dendrites by calculating the permeability of the dendrite channel. The greater the permeability of the dendrite, the smaller the flow resistance of the liquid phase between dendrites; conversely, the greater the permeability of the dendrite. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a low-magnification microstructure diagram of columnar crystals, the transition area from columnar crystals to equiaxed crystals, and the equiaxed crystal area;

[0031] Figure 2 is the dendrite permeability of columnar crystals, the transition region from columnar crystals to equiaxed crystals, and the equiaxed crystal region;

[0032] Figure 3 The calculation process of fractal dimension of dendrite outline; Figure 3 (a) is the original low-magnification tissue image. Figure 3 (b) is the low-magnification tissue outline. Figure 3 (c) in the figure is the box counting method to calculate the fractal dimension. Figure 3 (d) in the figure is the relationship diagram between lnN(r) and lnr. DETAILED DESCRIPTION

[0033] The present invention provides a method for determining dendrite channel permeability, comprising the following steps:

[0034] Dendrite corrosion is performed on the surface of the alloy sample to obtain a treated sample; the treated sample has a macrostructure with a dendrite interface profile; the macrostructure is a columnar crystal region macrostructure, a columnar crystal to equiaxed crystal transition region macrostructure, or an equiaxed crystal region macrostructure;

[0035] acquiring a low-magnification tissue image of the treated sample;

[0036] Image processing software was used to analyze the acquired low-magnification tissue images;

[0037] When the macrostructure is a columnar crystal region macrostructure, the analysis includes: measuring the primary dendrite arm spacing, segregation area, and total area in the macrostructure image; and calculating the segregation area ratio from the segregation area and the total area.

[0038] When the macrostructure is a columnar crystal to equiaxed crystal transition zone macrostructure or an equiaxed crystal zone macrostructure, the analysis includes: measuring the primary dendrite arm spacing, the secondary dendrite arm spacing, the segregation area, and the total area in the macrostructure image; and calculating the segregation area ratio from the segregation area and the total area;

[0039] The fractal dimension of dendrite outlines in low-magnification tissue images was obtained according to the box counting method;

[0040] When the macrostructure is a columnar crystal region macrostructure, the permeability of the dendrite channel in the columnar crystal region is obtained according to the segregation area ratio, the primary dendrite arm spacing, and the fractal dimension of the dendrite profile;

[0041] When the low-magnification structure is a low-magnification structure in the columnar crystal to equiaxed crystal transition zone or an equiaxed crystal zone low-magnification structure, the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition zone or the equiaxed crystal zone is obtained according to the segregation area ratio, the primary dendrite arm spacing, the secondary dendrite arm spacing and the fractal dimension of the dendrite profile.

[0042] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0043] In this study, the permeability of dendrite channels can quantitatively predict the flow resistance of the liquid phase between dendrites during metal solidification, thereby enabling control of the liquid phase flow rate and direction during solidification. This provides guidance for regulating the three-dimensional density of the actual solidified metal structure and thereby finely controlling segregation.

[0044] The present invention performs dendrite corrosion on the surface of an alloy sample to obtain a treated sample; the treated sample has a macrostructure with a dendrite interface profile; the macrostructure is a columnar crystal region macrostructure, a columnar crystal to equiaxed crystal transition region macrostructure, or an equiaxed crystal region macrostructure.

[0045] In the present invention, the dendrite corrosion is preferably performed using a metal low-magnification corrosion method.

[0046] In a specific embodiment of the present invention, the metal macrocorrosion method is the method described in GBT226-2015 "Macrostructure and Defect Acid Etching Test Method for Steel".

[0047] In the present invention, the dendrite corrosion directly obtains the initial treatment sample; the present invention preferably further comprises performing surface polishing on the initial treatment sample to obtain the treatment sample.

[0048] In the present invention, the polishing is preferably performed by polishing the corroded surface of the initial treatment sample with metallographic sandpaper until the dendrite structure is exposed. In the present invention, the mesh number of the metallographic sandpaper is preferably 800 mesh.

[0049] After obtaining the treated sample, the present invention obtains a low-magnification tissue image of the treated sample;

[0050] In the present invention, the acquisition is preferably performed by using a two-dimensional imager. The present invention has no special requirements on the specific implementation of using a two-dimensional imager to acquire low-magnification tissue images of the processed sample.

[0051] In the present invention, the low-magnification tissue image is preferably a low-magnification tissue image that can be observed with the naked eye or a microscope with a magnification of ≤10 times.

[0052] After obtaining the low-magnification tissue image, the present invention uses image processing software to analyze the acquired low-magnification tissue image; when the low-magnification tissue is a columnar crystal region low-magnification tissue, the analysis includes: measuring the primary dendrite arm spacing, segregation area and total area in the low-magnification tissue image; and calculating the segregation area ratio from the segregation area and the total area; when the low-magnification tissue is a columnar crystal to equiaxed crystal transition region low-magnification tissue or an equiaxed crystal region low-magnification tissue, the analysis includes: measuring the primary dendrite arm spacing, secondary dendrite arm spacing, segregation area and total area in the low-magnification tissue image; and calculating the segregation area ratio from the segregation area and the total area.

[0053] In the present invention, dendrites can be divided into columnar crystals and equiaxed crystals according to their morphology. The macrostructure of the alloy is generally composed of a columnar crystal region (the tissue morphology in this region is all columnar crystals), a columnar crystal to equiaxed crystal transition region (the tissue morphology in this region is the coexistence of columnar crystals and equiaxed crystals) and an equiaxed crystal region (the tissue morphology in this region is all equiaxed crystals). When dendrites grow, they will first grow in one direction (trunk, primary dendrite arms), and then branches (secondary dendrite arms) will grow on the trunk, similar to the growth of trees. After the dendrites grow out, they will not completely fill the entire space. There will be gaps between the dendrites, and the unsolidified liquid phase will flow in these gaps, which are called interdendritic channels.

[0054] The present invention has no special requirements on the specific implementation method of measuring low-magnification tissue images using image processing software.

[0055] In a specific embodiment of the present invention, the image processing software is Image-ProPlus.

[0056] The present invention obtains the fractal dimension of the dendrite outline in the low-magnification tissue image according to the box counting method.

[0057] In the present invention, the method for obtaining the fractal dimension of the dendrite outline is preferably: extracting the dendrite outline in the low-magnification tissue image using computer software; and calculating the fractal dimension of the dendrite outline according to the box counting method.

[0058] In the present invention, the computer software is preferably Matlab.

[0059] After obtaining the segregation area ratio, the primary dendrite arm spacing, the secondary dendrite arm spacing and the fractal dimension of the dendrite outline, when the low-magnification structure is a columnar crystal region low-magnification structure, the present invention obtains the permeability of the dendrite channel in the columnar crystal region based on the segregation area ratio, the primary dendrite arm spacing and the fractal dimension of the dendrite outline; when the low-magnification structure is a columnar crystal to equiaxed crystal transition region low-magnification structure or an equiaxed crystal region low-magnification structure, the present invention obtains the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition region or the equiaxed crystal region based on the segregation area ratio, the primary dendrite arm spacing, the secondary dendrite arm spacing and the fractal dimension of the dendrite outline.

[0060] In the present invention, the permeability of the dendrite channel in the columnar crystal region is obtained by the formula shown in Formula 1:

[0061]

[0062] In formula 1, Kc is the permeability of the dendrite channel in the columnar crystal region, m 2 ; R seg is the segregation area ratio; λ1 is the primary dendrite arm spacing, m; D is the fractal dimension of the dendrite outline.

[0063] In the present invention, the permeability of the columnar crystal to equiaxed crystal transition region and the dendrite channel of the equiaxed crystal region is obtained as shown in Formula 2:

[0064]

[0065] In formula 1, Ke is the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition region or the equiaxed crystal region, m 2 ; R seg is the segregation area ratio; λ1 is the primary dendrite arm spacing, m; λ2 is the secondary dendrite arm spacing, m; D is the fractal dimension of the dendrite outline.

[0066] In the present invention, dendrite channel permeability is a parameter that describes the resistance of a porous medium to fluid flow. It is an important parameter affecting the flow rate of liquid metal in the mushy zone and is closely related to the shape of the interdendritic channel. The permeability of the interdendritic channel mainly depends on the dendrite arm spacing, the liquid phase volume fraction, and the curvature coefficient of the flow channel. However, the liquid phase volume fraction is difficult to measure during the actual metal solidification process. The solute-enriched liquid phase in the mushy zone will form segregation after the metal solidifies.

[0067] The present invention can control the flow rate and flow direction of the liquid phase by adjusting the solidification parameters. This provides a direction for controlling the three-dimensional density of the actual solidification structure and thereby finely controlling segregation. At the same time, the present invention calculates the permeability of the inter-dendritic channel based on the low-magnification tissue image of the actual metal, so the permeability of different types of dendrite regions can be calculated by selecting different solidification positions of the metal. In summary, compared with the existing methods, the present invention has the following beneficial results: the permeability of the dendrite channel in the actual metal solidification process can be calculated, the analysis area and range can be flexibly selected, and the calculation of the permeability of different types of dendrite regions (columnar crystals, CET and equiaxed crystals) can be realized and is easy to implement.

[0068] In order to further illustrate the present invention, the technical solution provided by the present invention is described in detail below with reference to the accompanying drawings and embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0069] Example 1

[0070] 1) In this embodiment, 82B cord steel is used as an example. First, the metal surface of the 82B cord steel is subjected to a macroscopic etching treatment according to the metal macroscopic etching method described in GBT226-2015 "Macroscopic Structure and Defects of Steel - Acid Etching Method". The specific type of etchant, etching time, and etching temperature can be determined based on the selected metal with reference to GBT226-2015 "Macroscopic Structure and Defects of Steel - Acid Etching Method".

[0071] 2) Then, the corroded metal surface was polished with 800-grit metallographic sandpaper to obtain a low-magnification microstructure image with clear dendrite interface contours, and a high-definition low-magnification microstructure image of the metal was obtained using a two-dimensional imager; Figure 1 Shown are low-magnification microstructure images of different solidification zones of 82B cord steel.

[0072] 3) After obtaining a low-magnification microstructure image of the metal, the dendrite arm spacing and segregation area ratio were measured using the existing image processing software Image-Pro Plus. The dendrite arm spacing includes the primary and secondary dendrite arm spacings. The segregation area ratio refers to the ratio of the segregation area to the total area of the analysis region. The remainder of the low-magnification microstructure image excluding dendrites is considered segregation. Specific values are shown in Table 1.

[0073] 4) Calculation of dendrite outline fractal dimension: First, we need to extract the dendrite outline from the low-magnification tissue image through Matlab programming. The process is shown in Figure 3 , Figure 3 (a) is the original low-magnification tissue image. Figure 3 (b) is the low-magnification tissue outline. Figure 3 (c) in the figure is the box counting method to calculate the fractal dimension. Figure 3 (d) in the figure is the relationship between lnN(r) and lnr. The fractal dimension is then calculated using the box counting method; the specific values are shown in Table 1.

[0074] 5) After obtaining the dendrite arm spacing, segregation area ratio, and fractal dimension, the permeability of the dendrite channel in the columnar crystal region was calculated using Formula 1, and the permeability of the dendrite channel in the columnar to equiaxed transition region (CET) and the equiaxed crystal region was calculated using Formula 2. Specific values are shown in Table 1. Furthermore, the present invention achieves the calculation of the permeability of different types of dendrite regions by selecting different solidification positions of the metal. Figure 2 Shown are the permeability values for different dendrite type regions (columnar, CET, and equiaxed).

[0075]

[0076]

[0077] In formulas 1 and 2: Kc—permeability of dendrite channel in columnar crystal region, m 2 ;

[0078] Ke—CET and permeability of dendrite channel in equiaxed crystal region, m 2 ;

[0079] R seg —segregation area ratio;

[0080] λ1—primary dendrite arm spacing, m;

[0081] λ2—secondary dendrite arm spacing, m;

[0082] D—Fractal dimension of dendrite outline.

[0083] Table 1 Specific values of permeability calculation process

[0084]

[0085] Although the above embodiment provides a detailed description of the present invention, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the scope of protection of the present invention.

Claims

1. A method for determining dendrite channel permeability, characterized in that: The following steps are involved: Dendrite corrosion is performed on the surface of the alloy sample to obtain a treated sample; the treated sample has a macrostructure with a dendrite outline; the macrostructure is a columnar crystal region macrostructure, a columnar crystal to equiaxed crystal transition region macrostructure, or an equiaxed crystal region macrostructure; acquiring a low-magnification tissue image of the treated sample; Image processing software was used to analyze the acquired low-magnification tissue images; When the macrostructure is a columnar crystal region macrostructure, the analysis includes: measuring the primary dendrite arm spacing, segregation area, and total area in the macrostructure image; and calculating the segregation area ratio from the segregation area and the total area. When the macrostructure is a columnar crystal to equiaxed crystal transition zone macrostructure or an equiaxed crystal zone macrostructure, the analysis includes: measuring the primary dendrite arm spacing, the secondary dendrite arm spacing, the segregation area, and the total area in the macrostructure image; and calculating the segregation area ratio from the segregation area and the total area; The fractal dimension of dendrite outlines in low-magnification tissue images was obtained according to the box counting method; When the macrostructure is a columnar crystal region macrostructure, the permeability of the dendrite channel in the columnar crystal region is obtained according to the segregation area ratio, the primary dendrite arm spacing, and the fractal dimension of the dendrite profile; The formula for obtaining the permeability of the dendrite channel in the columnar crystal region is shown in formula (1): In formula (1): Kc is the permeability of the dendrite channel in the columnar crystal region, m 2 ; R seg is the segregation area ratio; λ1 is the primary dendrite arm spacing, m; D is the fractal dimension of the dendrite outline; When the macrostructure is a columnar crystal to equiaxed crystal transition zone macrostructure or an equiaxed crystal zone macrostructure, the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition zone or the equiaxed crystal zone is obtained according to the segregation area ratio, the primary dendrite arm spacing, the secondary dendrite arm spacing, and the fractal dimension of the dendrite profile; The formula for obtaining the permeability of the columnar crystal to equiaxed crystal transition region or the dendrite channel in the equiaxed crystal region is shown in formula (2): In formula (2), Ke is the permeability of the dendrite channel in the columnar crystal to equiaxed crystal transition region or the equiaxed crystal region, m 2 ; R seg is the segregation area ratio; λ1 is the primary dendrite arm spacing, m; λ2 is the secondary dendrite arm spacing, m; D is the fractal dimension of the dendrite outline.

2. The method for determining the dendrite channel permeability according to claim 1, wherein: The dendrite corrosion is performed by adopting a metal low-magnification corrosion method.

3. The method for determining the dendrite channel permeability according to claim 1, wherein: The dendrite corrosion directly obtains the initial treatment sample; and further comprises polishing the surface of the initial treatment sample to obtain the treatment sample.

4. The method for determining the dendrite channel permeability according to claim 3, wherein: The polishing is as follows: using metallographic sandpaper to polish the corroded surface of the initial treatment sample until the dendrite structure is exposed; the mesh number of the metallographic sandpaper is 800 mesh.

5. The method for determining dendrite channel permeability according to claim 1, characterized in that: Acquisition: Acquired using a two-dimensional imager.

6. A method for determining dendrite channel permeability according to claim 1 or 5, characterized in that: The low-magnification tissue image is a tissue image that can be observed with the naked eye or a microscope with a magnification of ≤10 times.

7. The method for determining dendrite channel permeability according to claim 1, characterized in that: The method for obtaining the fractal dimension of the dendrite outline is as follows: using computer software to extract the dendrite outline in the low-magnification tissue image; and calculating the fractal dimension of the dendrite outline according to the box counting method; the computer software is Matlab.

8. The method for determining dendrite channel permeability according to claim 1, characterized in that: The image processing software is Image-Pro Plus.

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