Metal material rapid upsetting test machine and test method

Abstract

The invention provides a metal material rapid upsetting testing machine and a testing method, and belongs to the technical field of metal material mechanical property detection. According to the method, a cylindrical sample is cut based on three orthogonal directions, radial and axial strains are synchronously measured through axial compression, and a plastic anisotropy index is calculated; screening a main direction according to exponential distribution, adjusting a strain rate and a height reduction rate, dividing a temperature interval in combination with thermal deformation characteristics of a material, and correcting process parameters; two-stage compression is adopted, pause is performed after the first stage is completed, and the second stage adjusts parameters to complete residual compression amount and records dynamic response. According to the method, by quantifying multi-direction plastic flow characteristics, optimizing main direction parameters, correcting temperature coefficients and compressing samples in stages, the interference of grain boundary slippage difference and dynamic recrystallization on anisotropy indexes is effectively inhibited; the problem of plastic flow evaluation deviation caused by imbalance of texture orientation and thermodynamic response in a traditional single compression test is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical property testing of metal materials, and particularly relates to a rapid upsetting testing machine and testing method for metal materials. Background Art

[0002] As the core basic material of modern industry, the mechanical properties of metal materials directly affect the structural design and safety reliability in key fields such as aerospace, automotive manufacturing, and energy equipment. With the wide application of advanced forming technologies such as additive manufacturing and rolling processes, the microstructure inside metal materials exhibits significant anisotropic characteristics, such as grain orientation distribution, grain boundary density difference, and defect oriented arrangement. These characteristics lead to significant differences in the plastic flow ability, strength response, and fracture behavior of the material under different loading directions. Therefore, how to accurately quantify the mechanical properties of anisotropic materials and establish the correlation with microstructural characteristics has become one of the core challenges in the field of materials science and engineering.

[0003] The current standard YB / T5293 - 2022 stipulates the basic process and parameter requirements for the upsetting test of metal materials, mainly for the mechanical property evaluation of homogeneous materials. However, when actually conducting the upsetting test on metal materials with obvious anisotropy, the test results often deviate significantly from the actual application performance. For example, in the building direction of additive manufacturing titanium alloy, the plastic flow ability is significantly lower than that in the horizontal direction due to the hindrance of columnar grain boundaries, while in the thickness direction of rolled aluminum alloy, the radial expansion is more obvious due to the short axis slip advantage of grains. The traditional upsetting test ignores the difference in plastic flow coordination of the material in different directions by applying unidirectional compression loading and fixing the strain rate and height reduction rate. In addition, during the test, when the specimen is subjected to compressive load, the grain boundary migration, dynamic recrystallization, and grain slip mechanisms of anisotropic materials will show asymmetric responses due to different loading directions, resulting in the deviation of the true strain distribution from the theoretical calculated value. This deviation not only affects the characterization accuracy of material properties, but also may obscure the internal relationship between microstructural evolution and macroscopic mechanical behavior, restricting the reliability of material process optimization and engineering applications.

[0004] To address the above problems, there is an urgent need for an upsetting test method that can systematically identify and correct the plastic flow differences of anisotropic materials. Through multi-directional data acquisition, dynamic parameter adjustment, and temperature effect compensation, the anisotropic characteristics of the material can be accurately quantified, and the cross-scale correlation with the microstructure can be established, thereby providing a reliable basis for material design and process optimization under complex working conditions. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a rapid upsetting testing machine and testing method for metal materials.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a rapid upsetting test method for metal materials, comprising the following steps: Cut cylindrical specimens based on three orthogonal directions of the metal material, synchronously measure the true radial strain and true axial strain in each direction by axially compressing the specimens, and calculate the plastic anisotropy index; Screen the main direction according to the distribution of the plastic anisotropy index in each direction, and adjust the strain rate and height reduction rate of the main direction; Divide the temperature range based on the hot deformation characteristics of the material, and correct the strain rate and height reduction rate of the main direction; Based on the corrected strain rate and height reduction rate, obtain the corrected mechanical behavior data by two-stage compression of the main direction specimens. The first stage completes the main part of the total compression amount, and the second stage completes the remaining compression amount and records the dynamic response parameters.

[0007] Further, the diameter range of the cylindrical specimen is 5 - 200 mm, and the ratio of height to diameter is 1.5 - 2.0; Further, the three orthogonal directions include the processing direction, the first direction perpendicular to the processing direction, and the second direction perpendicular to the processing direction and the first direction; wherein, the processing direction is the direction that dominates the deformation during the material manufacturing process; the first direction is the horizontal direction perpendicular to the processing direction; the second direction is the vertical direction perpendicular to the processing direction and the first direction.

[0008] Further, the true radial strain is calculated by the change in diameter of the specimen before and after compression, the true axial strain is calculated by the change in height of the specimen before and after compression, and the plastic anisotropy index is the ratio of the true radial strain to the true axial strain.

[0009] Further, the screening method for the main direction is that the amplitude of the plastic anisotropy index deviating from the average value of the three directions is the largest and the standard deviation contribution rate exceeds the preset threshold; Further, the adjustment method for the strain rate and height reduction rate of the main direction includes when the plastic anisotropy index of the main direction is lower than the average value, reducing the strain rate or increasing the height reduction rate; when the plastic anisotropy index of the main direction is higher than the average value, increasing the strain rate or reducing the height reduction rate.

[0010] Further, the strain rate correction calculates the temperature compensation coefficient based on the relationship between the material deformation activation energy and the test temperature, and the height reduction rate correction calculates the correction coefficient based on the coupling effect of material thermal expansion and thermal softening.

[0011] Further, the temperature range is divided into a low temperature zone, a medium temperature zone, and a high temperature zone; the low temperature zone is dominated by the dynamic recovery effect, the medium temperature zone is dominated by the phase transformation or grain boundary slip effect, and the high temperature zone is dominated by the dynamic recrystallization effect.

[0012] Further, the first stage of the two-stage compression completes 70% to 80% of the total height reduction, and the second stage completes the remaining 20% to 30%. A pause time is set between the stages for stabilizing data acquisition, and the second stage fine-tunes the strain rate according to the dynamic recrystallization state.

[0013] Further, when the metal material is an additively manufactured titanium alloy, the main direction is the building direction, the reference strain rate is set to 3 - 5 / s, and the reference height reduction rate is set to 50% to 55%.

[0014] Further, when the metal material is a rolled aluminum alloy, the main direction is the thickness direction, the reference strain rate is set to 4 - 6 / s, and the reference height reduction rate is set to 40% to 45%.

[0015] Another technical solution provided by the present invention: A rapid upsetting testing machine for metal materials, used for the above test method, includes: A positioning module for positioning and clamping the specimen; An axial loading module for performing single or two-stage axial compression on the specimen; A strain measurement module for measuring the radial strain and axial strain of the specimen; A control module, signal-connected to the axial loading module and the strain measurement module, for calculating the plastic anisotropy index and adjusting the strain rate and height reduction rate of the axial loading module.

[0016] The present invention solves the defects existing in the background technology and has the following beneficial effects: The present invention provides a rapid upsetting testing machine and test method for metal materials. By cutting cylindrical specimens along the material processing direction and its two orthogonal directions, dynamically adjusting the main direction parameters based on the plastic anisotropy index, compensating for the temperature influence by combining the thermodynamic model, and adopting two-stage segmented compression control, the accurate quantification of the anisotropic plastic flow characteristics of metal materials and the suppression of temperature interference are achieved. This method can systematically reduce the deviation of the overall performance evaluation caused by abnormal plastic flow in the main direction of the material, and at the same time adapt to the dynamic changes of the hot deformation behavior under different temperature conditions, providing high-reliability data support for material processing process optimization and extreme working condition performance evaluation.

[0017] The present invention cuts specimens along the processing direction and its two orthogonal directions and synchronously measures the true radial strain and axial strain, and combines the standard deviation contribution rate to screen the main direction, adjust the strain rate or height reduction rate parameters, and specifically balance the differences in plastic flow capabilities in each direction. Due to ignoring the grain orientation distribution characteristics, the traditional single-direction compression test cannot effectively identify the anisotropic differences of materials, resulting in the evaluation results deviating from the actual situation. Through multi-directional data acquisition and optimization of the main direction parameters, the present invention significantly reduces the influence of abnormal plastic flow in the main direction on the overall performance characterization, and greatly enhances the correlation between the anisotropic evaluation results and the microstructural characteristics.

[0018] Based on the thermodynamic constitutive model, the present invention divides the temperature range, defines the strain rate compensation coefficient and the height reduction rate correction coefficient, and combines the two-stage compression control module to dynamically adjust the compression rate and stroke at high or low temperatures, effectively suppressing the interference of thermal expansion, dynamic recrystallization and grain boundary slip effects on the test data. Due to the lack of a temperature-strain coupling correction mechanism, conventional test methods are prone to inaccurate measurement of plastic flow due to thermal softening or hardening in high or low temperature environments. The present invention corrects the parameters in real time through the temperature compensation module, significantly improving the stability of test data in a wide temperature range. Especially in the high dynamic recrystallization temperature range or under low deformation activation energy conditions, it can accurately capture the law of the evolution of material anisotropy characteristics with temperature, meeting the requirements for material performance evaluation in extreme environments such as aerospace.

[0019] The dynamic adjustment of the main direction parameters and the temperature compensation correction are deeply coupled through the parameter control module. In high-temperature tests, the strain rate and reduction rate are synchronously optimized according to the real-time temperature data, and the compression pause time in the second stage is extended to balance the dynamic recrystallization and grain boundary hindrance effects; in low-temperature tests, the tendency of short-axis slip of grains is synergistically suppressed, and the regulation effect of grain boundary strengthening on plastic flow is enhanced. The combination of the two effectively corrects the abnormal plastic flow in the main direction within a wide temperature range, significantly improving the correlation between the anisotropy index and the microstructural characteristics, and at the same time ensuring that the test data under high-temperature rapid deformation or low-temperature high-strain rate conditions have both high precision and high stability, providing a cross-scale performance mapping relationship for material design under complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings; Figure 1 It is a flowchart of a rapid upsetting test method for metal materials. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

[0022] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, the present invention may be practiced in other ways than those specifically described herein. Therefore, the scope of protection of the present invention is not limited by the specific embodiments disclosed below.

[0023] In the description of the present application, it should be understood that the orientation or positional relationships indicated by the terms "center", "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. are based on the orientation or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as limiting the scope of protection of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Therefore, the features defined with "first", "second", etc. may explicitly or implicitly include one or more of such features. In the description of the present invention, unless otherwise specified, the meaning of "a plurality" is two or more.

[0024] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", and "connected" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood through specific situations.

[0025] The materials not specifically described below are all obtained through commercial purchase or prepared by conventional methods in the art. Among them, the Ti-6Al-4V titanium alloy (titanium alloy TC4 rod) is purchased from Shanghai Muran Industrial Development Co., Ltd.; the 6061-T6 aluminum alloy (6061-t6 aluminum rod) is purchased from Shanghai Yuhang Aluminum Industry Co., Ltd.

[0026] Exemplary method: As Figure 1 shown, a rapid upsetting test method for metal materials includes the following steps: S1. Cut cylindrical specimens based on three orthogonal directions of the metal material, synchronously measure the true radial strain and true axial strain in each direction by axially compressing the specimens, and calculate the plastic anisotropy index; S2. Screen the main direction according to the distribution of the plastic anisotropy index in each direction, and adjust the strain rate and height reduction rate of the main direction; S3. Divide the temperature range based on the thermal deformation characteristics of the material, and correct the strain rate and height reduction rate in the main direction; S4. Based on the corrected strain rate and height reduction rate, compress the specimen in the main direction through two-stage compression to obtain the corrected mechanical behavior data. The first stage completes the main part of the total compression amount, and the second stage completes the remaining compression amount and records the dynamic response parameters.

[0027] Next, each step will be introduced in detail.

[0028] In step S1, cylindrical specimens are cut from the anisotropic metal material along the processing direction, transverse direction, and normal direction; an axial compression load is applied to the specimen on a rapid upsetting testing machine until the preset deformation amount, and the diameter expansion amount and height reduction amount of the specimen are measured synchronously during the compression process; based on the true strain formula, the plastic anisotropy index R in three directions is calculated respectively to characterize the differences in plastic flow characteristics of the material under different loading directions.

[0029] Due to the directional distribution of the microstructure caused by the manufacturing process of the anisotropic material, its mechanical properties (strength, plasticity) change significantly with the loading direction. For example, in rolled aluminum alloy, the flattened grains are arranged along the rolling direction, and in additive manufacturing titanium alloy, the columnar grains grow along the deposition direction. This step quantifies the differences in plastic flow capabilities of anisotropic metal materials in three orthogonal directions (processing direction and its two perpendicular directions) through rapid upsetting tests (strain rate ≥ 1 / s), calculates the plastic anisotropy index R, and establishes the correlation between the anisotropic characteristics of the material and the microstructure, providing benchmark data for subsequent parameter optimization.

[0030] The three orthogonal directions of additive manufacturing Ti-6Al-4V include the build direction (Z-axis, i.e., the vertical direction of the deposition layer), the horizontal transverse direction (X-axis), and the horizontal longitudinal direction (Y-axis), where the build direction is the processing direction. The columnar grains of additive manufacturing Ti-6Al-4V grow along the Z-direction (build direction), and the grain boundaries hinder dislocation slip during Z-direction compression, resulting in lower plastic flow ability in this direction; while in the X / Y direction, due to the weak transverse connection of grains, radial expansion is more likely to occur during compression.

[0031] The three orthogonal directions of rolled aluminum alloy 6061-T6 include the rolling direction (L-axis, the main direction of sheet extension), the transverse direction (T-axis, the width direction of the sheet), and the thickness direction (S-axis, the thickness direction of the sheet), where the rolling direction is the processing direction. The flattened grains of rolled aluminum alloy 6061-T6 are arranged along the L-direction, and the grain boundary strengthening effect inhibits radial flow during L-direction compression, while in the S-direction (thickness direction), due to the weaker resistance in the short-axis direction of the grains, radial expansion is more significant during compression.

[0032] In this step, a cylindrical specimen is cut along the above three directions using wire cutting or a precision milling machine. The diameter ranges from 5 to 200 mm, the height-to-diameter ratio is 1.5 to 2.0, the end face parallelism error is ≤ 0.02 mm, and the surface roughness Ra is ≤ 0.8 μm. The cylindrical specimens are successively placed in a rapid upsetting testing machine, and the specimens are compressed at a strain rate of 1 - 13 / s. The termination condition is a height reduction rate of 40 - 60%. Record the height and diameter of the specimen after compression. Among them, the radial strain is scanned in real-time by a laser displacement sensor for the diameter change in the middle of the specimen, the sampling frequency is ≥ 1 kHz, and the accuracy is ± 0.01 mm; the axial strain is recorded by the displacement sensor of the testing machine for the compression displacement, and the elastic deformation error of the synchronous calibration system is calibrated.

[0033] Take the absolute value logarithmic ratio of the deformed size to the original size as the true strain, and calculate the true radial strain and the true axial strain. The true radial strain is calculated using the formula , where is the original diameter of the specimen, is the maximum diameter after compression; the true axial strain is calculated using the formula , where is the original height of the specimen, is the height after compression. Based on the true radial strain and the true axial strain, the plastic anisotropy index is , reflecting the ratio of the plastic flow ability in the radial direction to the axial direction.

[0034] In a specific embodiment, cylindrical specimens with a diameter of Φ10 mm × 15 mm are cut from a selective laser melted formed Ti-6Al-4V titanium alloy deposition block along the Z-direction (building direction), X-direction (horizontal transverse), and Y-direction (horizontal longitudinal). A slow wire cutting is used to ensure the direction accuracy; the end face is treated by electrolytic polishing, and the roughness Ra = 0.4 μm to eliminate the interference of surface microcracks on deformation. The Ti-6Al-4V titanium alloy cylindrical specimens are successively placed in the testing machine. At room temperature of 25 °C and a strain rate of 5 / s, the specimen with an original height of 15 mm is compressed to a height of 7.5 mm, and the height reduction rate is 50%. After compression, the diameter d of the Z-direction specimen is 12.8 mm, the true radial strain is 0.246 and the true axial strain is -0.693, and the plastic anisotropy index is 0.355; after compression, the diameter d of the X-direction specimen is 14.2 mm, the true radial strain is 0.352 and the true axial strain is -0.693, and the plastic anisotropy index is 0.508; after compression, the diameter d of the Y-direction specimen is 14.6 mm, the true radial strain is 0.379 and the true axial strain is -0.693, the plastic anisotropy index is 0.547. The R value sorting of the plastic anisotropy index is > > . The plastic flow ability in the Y direction (horizontal longitudinal direction) is the strongest, and the plastic flow ability in the Z direction (building direction) is the weakest. This is because during the selective laser melting forming process of Ti-6Al-4V titanium alloy, rapid laser solidification results in the formation of coarse columnar grains in the Z direction, and the grain boundaries are parallel to the building direction. When compressed, the grain boundaries in the Z direction hinder the dislocation slip, significantly inhibiting the radial flow; in the X / Y direction, due to the interlaced molten pools between layers, a fine grain area is formed, and the plastic flow ability is relatively strong.

[0035] In another specific embodiment, cylindrical specimens with a diameter of Φ12mm and a height of 18mm are cut along the rolling direction (L), transverse direction (T), and thickness direction (S) of the rolled aluminum alloy 6061-T6 plate, and the end faces are ground to Ra = 0.6μm. The aluminum alloy 6061-T6 cylindrical specimens are successively placed in the testing machine, and at room temperature of 20°C and a strain rate of 3 / s, the specimen with an original height of 18mm is compressed to a height of 9.9mm, and the height reduction rate is 45%. After compression, the diameter d of the specimen in the L direction is 13.5mm, the true radial strain is 0.118 and the true axial strain is -0.606, and the plastic anisotropy index is 0.53; after compression, the diameter d of the specimen in the T direction is 14.1mm, the true radial strain is 0.160 and the true axial strain is -0.606, and the plastic anisotropy index is 0.58; after compression, the diameter d of the specimen in the S direction is 14.8mm, the true radial strain is 0.210 and the true axial strain is -0.606, and the plastic anisotropy index is 0.61. The R value sorting of the plastic anisotropy index is > > . The plastic flow ability in the thickness direction (S) is the strongest, and the plastic flow ability in the rolling direction (L) is the weakest. This is because the rolling process makes the grains of the aluminum alloy 6061-T6 arrange flatly along the L direction. When compressed in the L direction, the grain boundary strengthening effect inhibits the transverse flow; in the S direction, due to the weaker resistance in the short axis direction of the grains, radial expansion is more likely to occur.

[0036] Based on the distribution of plastic anisotropy indices (R-values) in three directions in step S1, the main direction (the direction with the largest deviation of the R-value from the mean) is selected. By adjusting the strain rate or height reduction rate parameter in this direction, the difference in plastic flow ability between this direction and the other two directions is reduced, systematically reducing the influence of the overall anisotropy of the material. In step S2, the main direction is selected according to the R-value distribution and standard deviation contribution rate in step S1, and the microscopic mechanism of its abnormal plastic flow (such as grain boundary hindrance, grain slip) is analyzed, and the strain rate or height reduction rate parameter is adjusted in the reverse direction to make the R-value of the corrected main direction approach the mean value of the other directions.

[0037] The main direction refers to the direction with the largest deviation of the R-value from the mean among the three orthogonal directions, reflecting the abnormal plastic flow ability (too strong or too weak) in this direction. It is usually the direction of the maximum or minimum value of the R-value, or the main direction of material processing. By calculating the standard deviation of the R-values in the three directions, the direction with a standard deviation contribution rate exceeding 50% is selected as the main direction.

[0038] By adjusting the strain rate and height reduction rate in the main direction, its R-value is made to approach the average value of the other two directions. If the R-value of the main direction is too low (weak plastic flow), the strain rate is reduced to 50 - 80% of the reference value or the height reduction rate is increased by +5 - 15% to promote plastic coordination; if the R-value of the main direction is too high (strong plastic flow), the strain rate is increased to 120 - 150% of the reference value or the height reduction rate is reduced by -5 - 15% to inhibit radial flow.

[0039] In a specific embodiment, the plastic anisotropy index R-value of selective laser melting formed Ti-6Al-4V titanium alloy includes the Z-direction plastic anisotropy index of 0.355, the X-direction plastic anisotropy index of 0.508, and the Z-direction plastic anisotropy index of 0.547. The three-way mean is 0.47 and the standard deviation is 0.096. The R-value in the Z-direction deviates from the mean the most (Δ = 0.115), contributing a standard deviation rate of 60%, and is selected as the main direction. This is because the R-value in the Z-direction (the building direction) is too low due to the hindrance of columnar grain boundaries, and the strain rate needs to be reduced or the height reduction rate needs to be increased, and the deformation time needs to be extended to promote grain boundary slip, so as to increase it to be close to the three-way mean. Therefore, the Z-direction strain rate is reduced from 5 / s to 3 / s (a decrease of 40%), and the height reduction rate is increased from 50% to 55% (an increase of 10%). Reducing the strain rate and extending the deformation time promote the dislocation slip of the columnar grain boundaries in the Z-direction; increasing the height reduction rate increases the deformation amount and activates more slip systems.

[0040] In another specific embodiment, the plastic anisotropy index R-value of rolled aluminum alloy 6061-T6 includes the L-direction plastic anisotropy index is 0.195, the plastic anisotropy index in the T direction is 0.264, and the plastic anisotropy index in the S direction is 0.347. The three-direction average value is 0.269, and the standard deviation is 0.076. The R value in the S direction deviates from the average value the most (Δ = 0.078), contributing a standard deviation rate of 51%, and is selected as the main direction. This is because the R value in the S direction (thickness direction) is too high due to the easy slip of the short axis of the grains. It is necessary to increase the strain rate or reduce the height reduction rate and shorten the deformation time to inhibit the transverse flow. Therefore, the strain rate in the S direction is increased from 3 / s to 5 / s (an increase of 67%), and the height reduction rate is reduced from 45% to 40% (a decrease of 11%). Increasing the strain rate shortens the deformation time and inhibits the transverse slip of the S-direction grains; reducing the height reduction rate limits the depth of plastic deformation and reduces the flow advantage.

[0041] Step S3 is based on the reference parameters (strain rate and height reduction rate) of the main direction in step S2, and divides the temperature correction interval according to the material hot deformation characteristics (dynamic recrystallization temperature, thermal expansion coefficient, etc.); defines a temperature-dependent correction coefficient based on the thermodynamic constitutive model to correct the strain rate and height reduction rate. In this step, by introducing a temperature variable, the test parameters are further corrected to compensate for or utilize the influence of temperature on the plastic flow of anisotropic materials, ensuring that the test conditions at high / low temperatures can accurately characterize the anisotropic characteristics of the materials.

[0042] The low-temperature region of Ti-6Al-4V titanium alloy is 20 - 400 °C, the β-phase stability is enhanced, and the columnar grain boundary hindrance effect is slightly weakened; the medium-temperature region is 400 - 800 °C, the α+β two-phase region, dynamic recovery starts, and the anisotropy difference is partially reduced; the high-temperature region is 800 - 950 °C, the β-phase is dominant, dynamic recrystallization is significant, and the anisotropy weakens rapidly. The low-temperature region of 6061-T6 aluminum alloy is 20 - 200 °C, work hardening is dominant, and the anisotropy difference gradually weakens with the increase of temperature; in the medium-high temperature region of 200 - 400 °C, dynamic recovery is enhanced, and the slip resistance in the short axis direction (S direction) of the grains decreases.

[0043] The strain rate correction is equal to the reference strain rate multiplied by the strain rate temperature compensation coefficient. The strain rate temperature compensation coefficient is expressed by the formula , Q is the deformation activation energy (260 kJ / mol for Ti-6Al-4V, 172 kJ / mol for 6061-T6), R is the gas constant (8.314 J / (mol·K)), is the reference temperature at room temperature (298K).

[0044] The height reduction rate correction is equal to the reference reduction rate multiplied by the height reduction rate correction coefficient. The height reduction rate correction coefficient is expressed by the formula , is the thermal softening - expansion coupling coefficient (0.12 for Ti - 6Al - 4V and 0.10 for 6061 - T6).

[0045] In a specific embodiment, for Ti - 6Al - 4V titanium alloy at 25°C, the strain rate is 3 / s and the height reduction rate is 55%. Based on temperature correction calculation at 785°C, the strain rate temperature compensation coefficient is 0.64, and the height reduction rate correction coefficient is 1.14. Then the corrected strain rate is 1.92 s -1 , and the corrected height reduction rate is 62.7%. Reducing the strain rate to 1.92 / s can reduce the damage of dynamic recrystallization to the Z - direction columnar grains and retain anisotropy; increasing the reduction rate to 62.7% utilizes high - temperature plasticity, but it is necessary to ensure that it does not exceed the critical instability value.

[0046] In another specific embodiment, for 6061 - T6 aluminum alloy at 25°C, the strain rate is 5 / s and the height reduction rate is 40%. Based on temperature correction calculation at 415°C, the strain rate temperature compensation coefficient is 0.95, and the height reduction rate correction coefficient is 1.08. Then the corrected strain rate is 4.75 s -1 , and the corrected height reduction rate is 43.2%. Maintaining a high strain rate inhibits the transverse slip of S - direction grains and prevents the rebound of anisotropy; slightly increasing the reduction rate to 43.2% compensates for thermal softening while avoiding grain coarsening.

[0047] Step S4, based on the corrected strain rate and height reduction rate in step S3, obtains the true mechanical behavior data of the material under rapid deformation conditions at a constant temperature through a two - stage rapid upsetting test, including flow stress, strain hardening rate, fracture strain, etc., providing benchmark data without anisotropy interference for the follow - up. This step divides the total compression stroke into two stages, sets a pause time between the stages to stabilize data acquisition, and maintains or finely tunes the strain rate in the two stages according to the corrected strain rate and height reduction rate in step S3; synchronously records the axial load, displacement, radial expansion amount, and strain rate sensitivity parameters in each stage. Among them, the total stroke reduction rate is the reduction percentage of the original height of the specimen to the total height after compression, and the stage compression amount ratio is the ratio of the single - stage compression amount to the total stroke reduction amount.

[0048] Preferably, in the first stage, 70%-80% of the total reduction amount is completed, most of the plastic deformation is quickly completed, and temperature rise or microstructural changes caused by long-term loading are avoided; in the second stage, the remaining 20%-30% is completed, the final forging deformation amount is controlled, the mechanical response in the high-strain area is captured, and the strain rate can be finely adjusted by ±5% based on step S3; there is a pause time of 0.5-2 seconds between the first stage and the second stage to ensure data stability and eliminate instantaneous elastic recovery.

[0049] Collect axial data including load-displacement curves, true stress ( , is the initial cross-sectional area of the specimen), true strain ( ); radial data includes the diameter expansion measured in real time by a laser displacement sensor, and the radial strain is calculated; the strain rate sensitivity index m is calculated through the two-stage rate difference, which describes the dependence of the material flow stress on the strain rate, and is calculated by the formula , is the flow stress, is the strain rate; monitor the surface crack initiation and fracture instant morphology of the specimen, and calculate the fracture strain , is the height of the specimen at fracture.

[0050] In a specific embodiment, a Z-direction additive manufacturing Ti-6Al-4V titanium alloy specimen is compressed in two stages at a strain rate of 1.92 / s and a height reduction rate of 50%. In the first stage, it is compressed to a height of 10.5 mm (reduction rate of 30%, accounting for 70% of the total reduction amount), the strain rate is 1.92 / s, and a pause of 1 second; in the second stage, it is compressed to the final height of 7.5 mm (reduction rate of 20%, accounting for 30% of the total reduction amount), and the strain rate is maintained at 1.92 / s. The flow stress in the first stage is measured to be 1083.2 MPa, the flow stress in the second stage is 1136.5 MPa, the strain rate sensitivity index m is 0.008, and the fracture strain is 0.725.

[0051] In another specific embodiment, an L-direction rolled aluminum alloy 6061-T6 specimen is compressed in two stages at a strain rate of 4.75 / s and a height reduction rate of 45%. In the first stage, it is compressed to a height of 12.6 mm (reduction rate of 30%, accounting for 70% of the total reduction amount), the strain rate is 4.75 / s, and a pause of 0.5 second; in the second stage, it is compressed to the final height of 9.9 mm (reduction rate of 15%, accounting for 30% of the total reduction amount), and the strain rate is finely adjusted to 4.99 / s. The flow stress in the first stage is measured to be 247.6 MPa, the flow stress in the second stage is 258.9 MPa, the strain rate sensitivity index m is 0.005, and the fracture strain is 0.595.

[0052] Exemplary Structure: A rapid upset forging testing machine for metal materials, which is used for the above exemplary method, includes the following structure: A positioning module for positioning and clamping specimens; An axial loading module for performing single-stage or two-stage axial compression on specimens; A strain measurement module for measuring the radial strain and axial strain of specimens; A control module, which is signal-connected to the axial loading module and the strain measurement module, for calculating the plastic anisotropy index and adjusting the strain rate and height reduction rate of the axial loading module.

[0053] Experimental Example 1: In this experimental example, a control group was set up with reference to the existing standard YB / T5293-2022, including: (1) Cut a Φ10mm×15mm cylindrical specimen along the building direction Z of additive manufacturing Ti-6Al-4V, place it in the rapid upset forging testing machine, and compress it once at a constant temperature of 25°C and a strain rate of 5 / s to 7.5mm, with a height reduction rate of 50%; (2) Cut a Φ12mm×18mm specimen along the rolling direction L of rolled aluminum alloy 6061-T6, place it in the rapid upset forging testing machine, and compress it once at a constant temperature of 20°C and a strain rate of 3 / s to 7.5mm, with a height reduction rate of 45%.

[0054] In this experimental example, an experimental group was set up with reference to the exemplary method, including: (3) Cut a Φ10mm×15mm cylindrical specimen along the building direction Z of additive manufacturing Ti-6Al-4V, place it in the rapid upset forging testing machine, and compress the specimen in two stages at a constant temperature of 785°C and a strain rate of 1.92 / s, with a 1s pause in the middle. In the first stage, compress it to a height of 9.0mm (height reduction rate 40%), and in the second stage, compress it to a height of 5.6mm (height reduction rate 62.7%); (4) Cut a Φ12mm×18mm specimen along the rolling direction L of rolled aluminum alloy 6061-T6, place it in the rapid upset forging testing machine, and compress the specimen in two stages at a constant temperature of 415°C, with a 0.5s pause in the middle. In the first stage, compress it at a strain rate of 4.75 / s to a height of 12.6mm (height reduction rate 30%), and in the second stage, compress it at a strain rate of 5.22 / s to a height of 9.9mm (height reduction rate 43.2%).

[0055] The flow stress, strain rate sensitivity, and fracture strain of the above four groups of specimens were detected respectively, and the results are shown in the following table: Table 1 Comparison Table of Test Results

[0056] In the rapid upsetting test of metal materials, the differences in plastic flow ability caused by anisotropy will significantly interfere with the authenticity of mechanical behavior. In the building direction (Z-direction) of the additive manufacturing Ti-6Al-4V titanium alloy, due to the columnar grain boundaries being parallel to the compression axis, dislocation slip is strongly hindered, and the plastic anisotropy index R value is only 0.355, significantly lower than 0.508 and 0.547 in the horizontal transverse direction (X-direction) and longitudinal direction (Y-direction). This is because of the coarse columnar grain structure formed during the laser melting process, where the grain boundaries become barriers to dislocation movement during Z-direction compression, resulting in limited radial expansion. If only relying on single-parameter adjustment, such as simply reducing the strain rate, although it can extend the deformation time to promote grain boundary slip, it cannot simultaneously solve the problem of the destruction of the columnar grain structure by dynamic recrystallization at high temperatures.

[0057] The experimental group reduced the Z-direction strain rate from 5 / s to 1.92 / s by reducing the strain rate, increasing the height reduction rate, and segmented compression, extending the deformation time, enabling the columnar grain boundaries to migrate and dynamically recover at a high temperature of 785°C, activating the non-basal slip system; at the same time, the height reduction rate was increased from 50% to 62.7%, increasing the deformation amount to force more slip systems to operate and alleviating the grain boundary hindrance effect. In the first stage of segmented compression, 70% of the reduction amount was quickly completed at 1.92 / s, using dynamic recovery to release local stress; in the second stage, the rate was maintained to complete the remaining 30% of the deformation, inhibiting grain coarsening caused by high temperature. The data shows that after optimization, the Z-direction flow stress gradient decreased from 1198.7 MPa in single compression to 1083.2 MPa and 1136.5 MPa in two stages, the fracture strain increased from 0.693 to 0.725, and at the same time, the strain rate sensitivity index m value decreased from 0.035 to 0.008. These changes are essentially the result of the synergistic effect of grain boundary migration, dislocation rearrangement, and thermal activation mechanisms, and such multi-scale coupling optimization cannot be achieved by single-parameter adjustment.

[0058] For rolled aluminum alloy 6061-T6, the R value in the thickness direction (S direction) is as high as 0.347 due to the low resistance of the short axis slip of the grains, which significantly deviates from 0.195 in the rolling direction (L direction). The flattening of the grains caused by the rolling process makes it easier for the S direction to flow laterally during compression. If only the strain rate is increased, the short axis slip can be suppressed, but the work hardening and local necking will be aggravated. The experimental group increased the S direction strain rate from 3 / s to 5.22 / s, shortened the deformation time and limited the advantage of the short axis slip of the grains; fine-tuned the height reduction rate from 45% to 43.2% to balance the thermal softening effect; in the segmented compression, the first stage completed 70% deformation at 4.75 / s, and the second stage was accelerated to 5.22 / s to strengthen the rate suppression effect. The data show that the S-direction flow stress gradient is optimized from 283.4MPa to 247.6MPa and 258.9MPa, and the m value is reduced from 0.022 to 0.005. Although the fracture strain is slightly reduced from 0.606 to 0.595, the contribution rate of the anisotropy standard deviation is compressed from 51% to 15%. This process is essentially a comprehensive manifestation of high strain rate inhibition of slip and dynamic recovery of balanced organizational evolution. Adjusting the strain rate or reduction rate alone cannot achieve both smooth flow stress and anisotropic weakening.

[0059] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A rapid upsetting test method for metal materials, characterized in that, It includes the following steps: Cut a cylindrical specimen based on three orthogonal directions of the metallic material, synchronously measure the true radial strain and true axial strain in each direction by axially compressing the specimen, and calculate the plastic anisotropy index; Screen the main direction according to the distribution of the plastic anisotropy index in each direction, and adjust the strain rate and height reduction rate of the main direction; Divide the temperature range based on the hot deformation characteristics of the material, and correct the strain rate and height reduction rate of the main direction; Based on the corrected strain rate and height reduction rate, obtain the corrected mechanical behavior data by two-stage compressing the specimen in the main direction. The first stage completes the main part of the total compression amount, and the second stage completes the remaining compression amount and records the dynamic response parameters.

2. The test method according to claim 1, characterized in that, The diameter range of the cylindrical specimen is 5 - 200 mm, and the ratio of height to diameter is 1.5 - 2.0; The three orthogonal directions include the processing direction, the first direction perpendicular to the processing direction, and the second direction perpendicular to the processing direction and the first direction; among them, the processing direction is the direction that dominates the deformation during the material manufacturing process; the first direction is the horizontal direction perpendicular to the processing direction; the second direction is the vertical direction perpendicular to the processing direction and the first direction.

3. The test method according to claim 1, wherein, The true radial strain is calculated by the change in diameter of the specimen before and after compression, the true axial strain is calculated by the change in height of the specimen before and after compression, and the plastic anisotropy index is the ratio of the true radial strain to the true axial strain.

4. The test method according to claim 1, wherein The screening method for the main direction is that the amplitude of the plastic anisotropy index deviating from the average value of the three directions is the largest and the standard deviation contribution rate exceeds the preset threshold; The adjustment method for the strain rate and height reduction rate of the main direction includes when the plastic anisotropy index of the main direction is lower than the average value, reducing the strain rate or increasing the height reduction rate; when the plastic anisotropy index of the main direction is higher than the average value, increasing the strain rate or reducing the height reduction rate.

5. The test method according to claim 1, characterized in that, The strain rate correction calculates the temperature compensation coefficient based on the relationship between the material deformation activation energy and the test temperature, and the height reduction rate correction calculates the correction coefficient based on the coupling effect of material thermal expansion and thermal softening.

6. The test method according to claim 1, characterized in that, The temperature range is divided into a low-temperature zone, a medium-temperature zone, and a high-temperature zone; in the low-temperature zone, the dynamic recovery effect dominates, in the medium-temperature zone, the phase transformation or grain boundary slip effect dominates, and in the high-temperature zone, the dynamic recrystallization effect dominates.

7. The test method according to claim 1, characterized in that, In the first stage of the two-stage compression, 70% to 80% of the total height reduction amount is completed, and in the second stage, the remaining 20% to 30% is completed. A pause time is set between stages for stable data acquisition, and the strain rate is fine-tuned according to the dynamic recrystallization state in the second stage.

8. The test method according to claim 1, wherein When the metallic material is an additive manufacturing titanium alloy, the main direction is the building direction, the reference strain rate is set to 3 - 5 / s, and the reference height reduction rate is set to 50% to 55%.

9. The test method according to claim 1, characterized in that, When the metallic material is a rolled aluminum alloy, the main direction is the thickness direction, the reference strain rate is set to 4 - 6 / s, and the reference height reduction rate is set to 40% to 45%.

10. A rapid upset forging testing machine for metal materials, which is used to implement the testing method described in any one of claims 1-9, and is characterized in that, It includes: A positioning module for positioning and clamping the specimen; An axial loading module for performing single-stage or two-stage axial compression on the specimen; A strain measurement module for measuring the radial strain and axial strain of the specimen; A control module, which is signal-connected to the axial loading module and the strain measurement module, is used to calculate the plastic anisotropy index and adjust the strain rate and height reduction rate of the axial loading module.

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