An evaluation method for semi-solid slurry technology of aluminum alloy

Abstract

A method for evaluating semi-solid slurry preparation technology for aluminum alloys involves sampling and conducting tensile tests on billets prepared using a semi-solid slurry preparation method and rapidly cooled with water at a solid fraction of 70%, and castings prepared under the same experimental conditions but without the semi-solid slurry preparation step, according to the GB / T 228-2002 standard. The two sets of tensile strengths are then processed using descending order, median-rank algorithm, and Origin software to obtain the slope K and correlation coefficient R. 2 The intercept B; using Excel's iterative programming solution, the position parameter γ, shape parameter β, and scale parameter η are obtained, and then the expected tensile strength T of the specimen is calculated. R Based on the difference in mechanical property consistency between the two sets of data, the modulus Y = K / K 1 The difference in tensile strength T = T R -T R 1 This invention evaluates semi-solid pulping technology. By providing a quantifiable assessment of the advantages and disadvantages of semi-solid pulping methods, it offers a reliable comparative method for rheological casting research.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology and relates to an evaluation method for semi-solid pulping technology of pure aluminum and aluminum alloys. Background Technology

[0002] Semi-solid slurry rheocasting has attracted widespread attention from experts and scholars since its inception. This technology combines the advantages of liquid forming and solid forming, enabling the production of products with complex structures and mechanical properties close to forgings, while also offering low production costs, making it suitable for large-scale industrial production. Over the past half-century, scholars both domestically and internationally have developed semi-solid slurry preparation processes such as SSR (semi-solid rheocasting), CRP (Continuous rheocasting process), TRC (New rheocasting process), SCP (Serpentine channel pouring process), and SEED (Swirled enthalpy equilibration device).

[0003] Theoretically, castings prepared using semi-solid slurry as a rheoforming material have advantages such as low defects, high density, high mechanical properties, and high consistency. However, to date, the actual mechanical properties of castings obtained by various processes and production technologies, both domestically and internationally, especially the consistency of mechanical properties, are far lower than theoretical values, failing to fully realize the technical advantages of semi-solid slurry rheoforming. This discrepancy between theory and actual performance can be attributed to entrapment traps generated during the semi-solid slurry preparation process. These defects originate from surface turbulence generated during intense stirring or melt transfer in the semi-solid slurry preparation process, which can lead to the entrapment of gases or oxide films on the aluminum alloy surface into the melt. Due to the high viscosity of semi-solid slurry, these defects are extremely difficult to remove or eliminate in subsequent processing, ultimately resulting in defects such as cracks and bubbles in the casting, causing significant damage to the consistency of the casting's mechanical properties.

[0004] Currently, most quality assessments of semi-solid pulping methods, both domestically and internationally, focus only on the spheroidization and homogenization of the pulp's internal microstructure. Entrainment defects are assessed using only qualitative methods, typically metallographic microscopy and scanning electron microscopy, which analyze their morphology, composition, and characteristics. This assessment approach is only applicable to the specific pulping method used in the researcher's experiment, exhibiting poor repeatability and universality. It also ignores the differences in the number of entrapment defects introduced by different pulping methods. There is currently no universally applicable method for assessing the number of entrapment defects across all semi-solid pulping processes.

[0005] Technical solution

[0006] The purpose of this invention is to address the shortcomings of existing technologies by proposing an evaluation method for aluminum alloy semi-solid pulping technology. This method utilizes simple and standardized mathematical and statistical techniques to evaluate the advantages and disadvantages of various semi-solid pulping methods. It is suitable for quantitatively assessing the impact of entanglement defects on the consistency of mechanical properties and the expected values ​​of casting mechanical properties of various semi-solid pulping technologies, and for evaluating the merits of different semi-solid pulping techniques.

[0007] This invention is achieved through the following technical solutions.

[0008] The evaluation method for aluminum alloy semi-solid pulping technology described in this invention includes the following steps:

[0009] (1) Prepare the pulp according to existing semi-solid pulping technologies, including mechanical stirring, electromagnetic oscillation, serpentine channel method or low temperature shearing method;

[0010] (2) Determine the temperature at which the solid fraction of the semi-solid slurry is 70% according to the alloy composition. When the semi-solid slurry is cooled to this temperature, the semi-solid slurry billet is water-quenched rapidly to retain the entrapment defects in the slurry to the greatest extent.

[0011] (3) Tensile test specimens shall be prepared by randomly sampling from the cooled semi-solid billet in accordance with the national standard GBT228-2002 for tensile test specimens, with a sample quantity ≥30.

[0012] (4) Arrange and number the tensile strengths of the tensile specimens in descending order, specifying the total number of data samples as n, the sample number as i, and the tensile strength as t. i ;

[0013] (5) Calculate the F(i) value for each sample using the median rank algorithm:

[0014]

[0015] (6) x i =ln(t) i ), Import the data into Origin plotting software, create a scatter plot, and fit all data points to a straight line to obtain the slope K and the correlation coefficient R (which measures the degree of linear correlation between the data). 2 and intercept B;

[0016] (7) Under the same experimental conditions as the above semi-solid pulping technology, the semi-solid pulping step is omitted. After the aluminum alloy ingot is melted, it is directly water-quenched and rapidly cooled to obtain a tensile specimen. Steps (3)-(6) are repeated to obtain the slope K. 1 Correlation coefficient R 2 1 and intercept B 1 ;

[0017] (8) Check the correlation coefficient R 2 R 2 1 The value of R is determined. 2 R 2 1 If all values ​​are greater than or equal to 0.8, it indicates that the tensile strength distribution of the tensile specimen conforms to the Weibull distribution; therefore, the evaluation method of this invention can be used for evaluation.

[0018] (9) Calculate the mechanical property consistency difference modulus Y = K / K 1 ;

[0019] The closer the Y value is to 1, the less damage the semi-solid pulping technology causes to the consistency of mechanical properties. When the Y value is greater than 0.95, it means that the semi-solid pulping technology causes almost no damage to the consistency of mechanical properties. When the Y value is between 0.85 and 0.95, it means that the semi-solid pulping technology causes some damage to the consistency of mechanical properties. When the Y value is between 0.7 and 0.85, it means that the semi-solid pulping technology causes very significant damage to the consistency of mechanical properties. When the Y value is less than 0.7, it means that the semi-solid pulping technology has serious design flaws.

[0020] (10) The tensile strength t i Import the values ​​into column A of the Excel chart, import the sample numbers into column B, import the median rank F(i) into column C, and create the formula C2 = (B2 - 0.3) / (30 + 0.4). Import the tensile strength difference values ​​into column D and create the formula D2 = A2 - γ0 (γ0 is the minimum tensile strength value rounded down). Create the formula E2 = 1 - C2. Import xi into column F and create the formula F2 = LN(D2). Import yi into column G and create the formula G2 = LN(LN(1 / E2)). Use functions to calculate the slope K, intercept B, and correlation coefficient R of xi and yi. 2 Set the shape parameter β = K, the scale parameter η = Exp(B / K), and the position parameter γ = γ0, and input them in column form, using the correlation coefficient R. 2 With the objective function, the initial value γ0 is a variable cell with constraints (0-γ0). A solver is used to perform a maximum time of 100 seconds and 100 iterations to obtain the initial value γ0, slope K, intercept B, and correlation coefficient R. 2 Shape parameter β, scale parameter η, position parameter γ;

[0021] (11) Calculate the expected tensile strength T of the tensile specimen under semi-solid pulping conditions according to the following formula. R Z represents the specified reliability, which is generally defined as 0.9 to 1;

[0022]

[0023] (12) Under the same experimental conditions as the above semi-solid pulping technology, the semi-solid pulping step is omitted, and the aluminum alloy ingot is directly subjected to water quenching and rapid cooling after melting. Following the above steps (10) and (11), the expected value of the tensile strength T of the tensile specimen after direct water quenching and rapid cooling is obtained. R 1 ;

[0024] (13) Calculate the tensile strength difference T = T R -T R 1 The larger the T value, the greater the contribution of the semi-solid pulping technology to the expected mechanical properties. If the T value is negative, it indicates that the semi-solid pulping technology has serious design flaws.

[0025] The advantage of this invention lies in the fact that it can obtain the expected mechanical properties of a large batch of castings and comparable expected mechanical property consistency values ​​through testing and statistical analysis of only a small number of random samples. This method allows for the quantitative evaluation of the merits of semi-solid slurry preparation methods, providing a reliable comparative tool for rheological casting research and solving the long-standing problem of being unable to quantitatively compare and only qualitatively analyze semi-solid slurry preparation methods in the field of research. Furthermore, this invention is also applicable to the quantitative analysis of the effects of melt purification, grain refinement, or modification methods during the smelting process. Through comparison, the contribution of various melt treatment methods to mechanical properties and their consistency can be effectively evaluated. Detailed Implementation

[0026] The present invention will be further illustrated by the following embodiments.

[0027] According to embodiments of the present invention, an assessment parameter is provided that can measure the degree of damage to the consistency of mechanical properties of castings caused by a semi-solid slurry preparation method by only preparing a small number of tensile samples.

[0028] According to embodiments of the present invention, evaluation parameters are provided that can measure the contribution of semi-solid slurry preparation methods to the tensile strength of castings using only a small number of samples.

[0029] Example

[0030] (1) The pulp was prepared using the RSF semi-solid pulping method;

[0031] To prevent sticking during billet transfer, the inner surface of the crucible is pre-treated: ① Polish the inner wall of the crucible with sandpaper, using 200 grit, 400 grit, and 800 grit in that order; ② Prepare a zinc oxide suspension at a ratio of 100 ml / 10 g, and use a brush to evenly coat the inner wall of the crucible, completely covering it; ③ Place the crucible in a forced-air drying oven at 200℃ for 3 hours to remove moisture from the crucible wall. This ensures that the zinc oxide is evenly distributed on the inner wall, isolating it from the molten aluminum alloy and preventing adhesion and shear deformation during billet removal; ④ Heat the crucible to 700℃, add the aluminum alloy ingot (with surface oxide film removed), and melt the ingot.

[0032] (2) Determine the temperature at which the solid fraction of the semi-solid slurry is 70% according to the alloy composition. Use a balance body with the same composition as the aluminum alloy ingot and a weight of 1 / 12 of the aluminum alloy liquid to insert into the molten aluminum alloy liquid for rotational stirring and cooling. When the semi-solid slurry is cooled to the temperature at which the solid fraction is 70%, the semi-solid slurry billet is water quenched and rapidly cooled to retain the entrapment defects in the slurry to the greatest extent.

[0033] (3) Tensile specimens were prepared by randomly sampling from the cooled semi-solid billet in accordance with the national standard GBT228-2002 for tensile test specimens. The sample quantity was 30.

[0034] (4) Arrange and number the tensile strengths of the tensile specimens in descending order, specifying the total number of data samples as n, the sample number as i, and the tensile strength as t. i ;

[0035] (5) Calculate the F(i) value for each sample using the median rank algorithm:

[0036]

[0037] (6) Let xi = ln(t) i ), Import the data into Origin plotting software, create a scatter plot, and fit all data points to a straight line to obtain the slope K and correlation coefficient R. 2 The parameters such as the intercept B are shown in the table below;

[0038] Drawing B Weight Unweighted intercept -121.22411 ± 4.54817 slope 21.50975 ± 0.81068 Sum of Squares of Residuals 1.58892 Pearson's r 0.98069 R squared (COD) 0.96175 Adjusted R-squared 0.96038

[0039] (7) Repeat step (1), and directly water quench the aluminum alloy ingot after melting, and repeat steps (3)-(6) to obtain the slope K of the tensile specimen. 1 =26.23, correlation coefficient R 2 1 =0.96515;

[0040] (8) Check the correlation coefficient R 2 R 2 1 The value of R determines 2 R 2 1 All values ​​are greater than or equal to 0.8, indicating that the mechanical properties of the castings obtained by RSF slurry preparation technology and water quenching rapid cooling are consistent with the Weibull distribution, and the evaluation method of this invention can be used for evaluation.

[0041] (9) Calculate the mechanical property consistency difference modulus Y = K / K 1 ;

[0042] A Y-value closer to 1 indicates less damage to the consistency of mechanical properties caused by the semi-solid pulping technology. A Y-value greater than 0.95 indicates almost no damage to the consistency of mechanical properties. A Y-value between 0.85 and 0.95 indicates some damage to the consistency of mechanical properties. A Y-value between 0.7 and 0.85 indicates significant damage to the consistency of mechanical properties. A Y-value less than 0.7 indicates a serious design flaw in the pulping technology. In this embodiment, a Y-value of 0.82 indicates that the RSF semi-solid pulping method significantly damages the consistency of mechanical properties.

[0043] (10) The tensile strength t i Import the values ​​into column A of the Excel chart, import the sample numbers into column B, import the median rank F(i) into column C and create the formula C2 = (B2 - 0.3) / (30 + 0.4), import the tensile strength difference values ​​into column D and create the formula D2 = A2 - γ0 (γ0 is the minimum tensile strength value rounded down), create the formula E2 = 1 - C2, import xi into column F and create the formula F2 = LN(D2), import yi into column G and create the formula G2 = LN(LN(1 / E2)), and use functions to calculate the slope K, intercept B, and correlation coefficient R of xi and yi. 2 Set the shape parameter β = K, the scale parameter η = Exp(B / K), and the position parameter γ = γ0, and input them in column form, using the correlation coefficient R. 2 With the objective function, the initial value γ0 is a variable cell with constraints (0-γ0). A solver is used to perform a maximum time of 100 seconds and 100 iterations to obtain the initial value γ0, slope K, intercept B, and correlation coefficient R. 2 The shape parameter β, scale parameter η, and position parameter γ are shown in Table 2 (Table 1 shows the parameters before the planning solution).

[0044] Table 1 Before Programming Solution

[0045]

[0046]

[0047] Table 2 shows the results after solving the programming problem.

[0048]

[0049]

[0050] (11) Calculate the expected value of the tensile strength T of the specimen according to the following formula. R Z represents the specified reliability, which is generally defined as 0.9 to 1. In this embodiment, the calculation is performed with a reliability of 0.95 to obtain the T value of the tensile specimen prepared by the RSF slurry technology. R =260.16;

[0051]

[0052] (12) Repeat step (1) and directly perform water quenching after the aluminum alloy ingot is melted. According to steps (3)-(10), obtain the expected value of tensile strength T under rapid water quenching conditions. R 1 The T calculated in this embodiment R 1 =238.44;

[0053] (13) Calculate the tensile strength difference T = T R -T R 1 In this embodiment, the difference in tensile strength obtained by water quenching and rapid cooling after using RSF semi-solid pulping technology and direct water quenching and rapid cooling was calculated to be T = 21.72. This proves that RSF semi-solid pulping technology improves the tensile strength of tensile specimens and quantifies the contribution of RSF semi-solid pulping technology to the tensile strength of castings.

Claims

1. An evaluation method for aluminum alloy semi-solid pulping technology, characterized in that: Includes the following steps: (1) Prepare the pulp according to existing semi-solid pulping technology, including mechanical stirring, electromagnetic oscillation, serpentine channel method or low temperature shearing method; (2) Determine the temperature at which the solid fraction of the semi-solid slurry is 70% according to the alloy composition. When the semi-solid slurry is cooled to this temperature, the semi-solid slurry blank is water-quenched rapidly to retain the entrapment defects in the slurry to the greatest extent. (3) Tensile test specimens shall be prepared by randomly sampling from the cooled semi-solid billet in accordance with the national standard GBT228-2002 for tensile test specimens, and the sample quantity shall be ≥30. (4) The tensile strength of the tensile specimen is arranged in descending order and numbered, and the total number of data samples is set as n, the sample number is i, and the tensile strength is t i ; (5) Calculate the F(i) value for each sample using the median rank algorithm: (6) x i =ln(t i ), y i =ln(ln( Import the data into Origin plotting software, create a scatter plot, and fit all data points to a straight line to obtain the slope K and correlation coefficient R. 2 and intercept B; (7) Under the same experimental conditions of the semi-solid slurry technology, the semi-solid slurry step is omitted, and the tensile specimen is obtained by water quenching and rapid cooling after the aluminum alloy ingot is melted, and steps (3)-(6) are repeated to obtain the slope K 1 , the correlation coefficient R 2 1 , and the intercept B 1 ; (8) Check the correlation coefficient R 2 R 2 1 The value of R is determined. 2 R 2 1 If all values ​​are greater than or equal to 0.8 and the tensile strength distribution of the tensile specimen conforms to the Weibull distribution, then this evaluation method shall be used to evaluate the semi-solid pulping technology. (9) Calculate the modulus of mechanical property consistency difference Y=K / K 1 ; The closer the Y value is to 1, the less damage the semi-solid pulping technology causes to the consistency of mechanical properties; when the Y value is greater than 0.95, the semi-solid pulping technology has almost no damage to the consistency of mechanical properties; when the Y value is between 0.85 and 0.95, the semi-solid pulping technology has some damage to the consistency of mechanical properties; when the Y value is between 0.7 and 0.85, the semi-solid pulping technology has a very significant damage to the consistency of mechanical properties. A Y value less than 0.7 indicates a serious design flaw in the semi-solid pulping technology. (10) The tensile strength t i Import the values ​​into column A of the Excel chart, import the sample numbers into column B, import the median rank F(i) into column C, and create the formula C2=(B2-0.3) / (n+0.4). Import the tensile strength difference values ​​into column D and create the formula D2=A2-γ0, where γ0 is the minimum tensile strength value rounded down. Create the formula E2=1-C2. Import xi into column F and create the formula F2=LN(D2). Import yi into column G and create the formula G2=LN(LN(1 / E2)). Use functions to calculate the slope K, intercept B, and correlation coefficient R of xi and yi. 2 Set the shape parameter β=K, the scale parameter η=Exp(B / K), and the position parameter γ=γ0, and input them in column form, using the correlation coefficient R. 2 With the objective function, the initial value γ0 is a variable cell with constraints (0-γ0). A solver is used to perform a maximum time of 100 seconds and 100 iterations to obtain the initial value γ0, slope K, intercept B, and correlation coefficient R. 2 Shape parameter β, scale parameter η, position parameter γ; (11) Calculate the expected tensile strength T of the tensile specimen under semi-solid pulping conditions according to the following formula. R Where Z is the specified reliability, which is defined as 0.9~1; (12) Under the same experimental conditions as the above semi-solid pulping technology, the semi-solid pulping step is omitted, and the aluminum alloy ingot is directly subjected to water quenching and rapid cooling after melting. According to the above steps (10) and (11), the expected value of the tensile strength T of the tensile specimen after direct water quenching and rapid cooling is obtained. R 1 ; (13) Calculate the difference in tensile strength T = T R -T R 1 The larger the T value, the greater the contribution of the semi-solid pulping technology to the expected mechanical properties. If the T value is negative, the semi-solid pulping technology has serious design flaws.

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