A metal material rapid upsetting testing machine and testing method

Abstract

The present invention provides a metal material rapid upset testing machine and testing method, which belongs to the technical field of metal material mechanical property detection. The method is based on cutting cylindrical specimens in three orthogonal directions, synchronously measuring radial and axial strains through axial compression and calculating the plastic anisotropy index; screening the main direction according to the index distribution and adjusting the strain rate and height reduction rate, dividing the temperature range in combination with the thermal deformation characteristics of the material, and correcting the process parameters; adopting two-stage compression, pausing after the completion of the first stage, and adjusting the parameters in the second stage to complete the remaining compression and record the dynamic response. This method effectively suppresses the interference of grain boundary slip differences and dynamic recrystallization on the anisotropy index by quantifying multi-directional plastic flow characteristics, optimizing main direction parameters, and temperature coefficient correction and compressing specimens in stages, thereby solving the plastic flow evaluation deviation caused by the imbalance between texture orientation and thermodynamic response in traditional single compression tests.

Description

Technical Field

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

[0002] As the core basic material of modern industry, the mechanical properties of metal materials directly affect the structural design and safety and reliability of key fields such as aerospace, automobile manufacturing, and energy equipment. With the widespread application of advanced forming technologies such as additive manufacturing and rolling processes, the internal microstructure of metal materials has shown significant anisotropic characteristics, such as grain orientation distribution, grain boundary density differences, and directional arrangement of defects. 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 a 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, specifies the basic procedures and parameter requirements for upset forging tests of metallic materials, primarily for evaluating the mechanical properties of homogeneous materials. However, when upset forging tests are performed on metal materials with significant anisotropy, the test results often deviate significantly from the actual application performance. For example, additively manufactured titanium alloys exhibit significantly lower plastic flow capacity in the build direction due to obstruction by columnar grain boundaries compared to the horizontal direction, while rolled aluminum alloys exhibit more pronounced radial expansion in the thickness direction due to the dominance of minor-axis grain slip. Traditional upset forging tests employ uniaxial compressive loading with fixed strain rates and height reduction rates, ignoring the differences in the material's plastic flow coordination in different directions. Furthermore, when the specimen is subjected to compressive loading during the test, the grain boundary migration, dynamic recrystallization, and grain slip mechanisms of anisotropic materials exhibit asymmetric responses depending on the loading direction, resulting in deviations between the actual strain distribution and theoretically calculated values. This deviation not only affects the accuracy of material property characterization but also may obscure the inherent relationship between microstructural evolution and macroscopic mechanical behavior, limiting the reliability of material process optimization and engineering applications.

[0004] To address these issues, an upset forging test method is urgently needed that can systematically identify and correct for differences in the plastic flow of anisotropic materials. Through multi-directional data acquisition, dynamic parameter adjustment, and temperature effect compensation, this method can accurately quantify the anisotropic characteristics of the material and establish a cross-scale correlation with the microstructure, 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 metal material rapid upset testing machine and a testing method.

[0006] To achieve the above object, the present invention adopts the following technical solution: a metal material rapid upsetting test method, comprising the following steps:

[0007] Based on cutting cylindrical specimens in three orthogonal directions of metal materials, the true radial strain and true axial strain in each direction are simultaneously measured by axial compression of the specimens to calculate the plastic anisotropy index;

[0008] The main directions are selected according to the distribution of plastic anisotropy index in each direction, and the strain rate and height reduction rate in the main directions are adjusted;

[0009] 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;

[0010] Based on the corrected strain rate and height reduction rate, the corrected mechanical behavior data were obtained by compressing the specimen in the main direction in two stages. The first stage completed the main part of the total compression, and the second stage completed the remaining compression and recorded the dynamic response parameters.

[0011] Furthermore, the diameter of the cylindrical specimen ranges from 5 to 200 mm, and the ratio of height to diameter is 1.5 to 2.0;

[0012] Furthermore, the three orthogonal directions include a processing direction, a first direction perpendicular to the processing direction, and a second direction perpendicular to the processing direction and the first direction; wherein, the processing direction is the direction of dominant deformation during the material manufacturing process; the first direction is a horizontal direction perpendicular to the processing direction; and the second direction is a vertical direction perpendicular to the processing direction and the first direction.

[0013] Furthermore, the true radial strain is calculated by the diameter change of the specimen before and after compression, the true axial strain is calculated by the height change 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.

[0014] Furthermore, the screening method for the main direction is that the plastic anisotropy index deviates from the average value of the three directions by the largest magnitude and the standard deviation contribution rate exceeds a preset threshold;

[0015] Furthermore, the method for adjusting the strain rate and height reduction rate in the main direction includes reducing the strain rate or increasing the height reduction rate when the plastic anisotropy index in the main direction is lower than the average value; and increasing the strain rate or reducing the height reduction rate when the plastic anisotropy index in the main direction is higher than the average value.

[0016] Furthermore, the strain rate correction is based on the relationship between the material deformation activation energy and the test temperature to calculate the temperature compensation coefficient, and the height reduction rate correction is based on the coupling effect of material thermal expansion and thermal softening to calculate the correction coefficient.

[0017] Furthermore, the temperature range is divided into low temperature zone, medium temperature zone and high temperature zone; the low temperature zone is dominated by dynamic recovery effect, the medium temperature zone is dominated by phase transformation or grain boundary sliding effect, and the high temperature zone is dominated by dynamic recrystallization effect.

[0018] Furthermore, the first stage of the two-stage compression completed 70% to 80% of the total height reduction, and the second stage completed the remaining 20% to 30%. A pause time was set between the stages to stabilize data acquisition. The strain rate was fine-tuned in the second stage according to the dynamic recrystallization state.

[0019] Furthermore, when the metal material is an additively manufactured titanium alloy, the main direction is the build direction, the baseline strain rate is set to 3-5 / s, and the baseline height reduction rate is set to 50% to 55%.

[0020] Furthermore, 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%.

[0021] Another technical solution provided by the present invention is a metal material rapid upset testing machine used for the above-mentioned testing method, comprising:

[0022] Positioning module, used to position and clamp the specimen;

[0023] Axial loading module for performing single or two-stage axial compression on the specimen;

[0024] Strain measurement module, used to measure the radial strain and axial strain of the specimen;

[0025] The control module is 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.

[0026] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0027] This invention provides a rapid upset testing machine and method for metal materials. By cutting cylindrical specimens along the material processing direction and two orthogonal directions, dynamically adjusting the principal direction parameters based on the plastic anisotropy index, compensating for temperature effects using a thermodynamic model, and employing two-stage segmented compression control, this method achieves precise quantification of the anisotropic plastic flow characteristics of metal materials and suppresses temperature interference. This method systematically reduces the deviation in overall performance evaluation caused by abnormal plastic flow in the material's principal direction, while also adapting to the dynamic changes in thermal deformation behavior under different temperature conditions. This method provides highly reliable data support for material processing optimization and performance evaluation under extreme operating conditions.

[0028] The present invention cuts the specimen along the machining direction and its two orthogonal directions and simultaneously measures the true radial strain and axial strain. It then uses the standard deviation contribution rate to select the main direction, adjusts the strain rate or height reduction rate parameters, and specifically balances the differences in plastic flow capacity in each direction. Conventional unidirectional compression tests ignore the grain orientation distribution characteristics and are unable to effectively identify differences in material anisotropy, resulting in evaluation results that deviate from reality. The present invention significantly reduces the impact of plastic flow anomalies in the main direction on overall performance characterization through multi-directional data acquisition and optimization of main direction parameters, significantly enhancing the correlation between anisotropy evaluation results and microstructural characteristics.

[0029] The present invention divides the temperature interval based on the thermodynamic constitutive model and 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 sliding effects on the test data. Conventional test methods lack a temperature-strain coupling correction mechanism, which can easily lead to inaccurate plastic flow measurements due to thermal softening or hardening under high or low temperature environments. The present invention uses a temperature compensation module to correct parameters in real time, significantly improving the stability of test data within a wide temperature range, especially in high dynamic recrystallization temperature ranges or low deformation activation energy conditions. It can accurately capture the law of the evolution of material anisotropy characteristics with temperature, and meet the needs of material performance evaluation in extreme environments in fields such as aerospace.

[0030] Dynamic adjustment of principal direction parameters and temperature compensation correction are deeply coupled through a parameter control module. In high-temperature tests, the strain rate and reduction rate are simultaneously optimized based on real-time temperature data, extending the second-stage compression pause time to balance dynamic recrystallization and grain boundary hindrance effects. In low-temperature tests, this synergistically suppresses the tendency of grain short-axis slip and enhances the regulatory effect of grain boundary strengthening on plastic flow. This combination effectively corrects principal direction plastic flow anomalies across a wide temperature range, significantly improving the correlation between anisotropy index and microstructural characteristics. It also ensures that test data under conditions of high-temperature rapid deformation or low-temperature high strain rates are both highly accurate and stable, providing a cross-scale performance mapping relationship for the design of materials for complex working conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0032] Figure 1 The present invention is a flow chart of a rapid upsetting test method for metal materials. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0035] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying 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 therefore cannot be understood 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 understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, features defined as "first", "second", etc. may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0036] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "installed," "connected," and "connected" should be understood in a broad sense. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0037] All materials not otherwise specified were purchased commercially or prepared by conventional methods in the art. Ti-6Al-4V titanium alloy (titanium alloy TC4 rod) was purchased from Shanghai Muran Industrial Development Co., Ltd.; 6061-T6 aluminum alloy (6061-T6 aluminum rod) was purchased from Shanghai Yuhang Aluminum Co., Ltd.

[0038] Exemplary methods:

[0039] like Figure 1 As shown, a metal material rapid upsetting test method includes the following steps:

[0040] S1. Based on the cutting of cylindrical specimens in three orthogonal directions of metal materials, the true radial strain and true axial strain in each direction are simultaneously measured by axial compression of the specimens to calculate the plastic anisotropy index;

[0041] S2. Select the main direction according to the distribution of plastic anisotropy index in each direction, and adjust the strain rate and height reduction rate of the main direction;

[0042] 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;

[0043] S4. Based on the corrected strain rate and height reduction rate, the specimen in the main direction is compressed in two stages to obtain the corrected mechanical behavior data. The first stage completes the main part of the total compression, and the second stage completes the remaining compression and records the dynamic response parameters.

[0044] Below, each step will be described in detail.

[0045] Step S1 cuts cylindrical specimens from anisotropic metal materials along the machining direction, transverse direction, and normal direction; applies an axial compressive load to the specimen on a rapid upsetting testing machine to a preset deformation amount, and simultaneously measures the diameter expansion and height reduction of the specimen during the compression process; and calculates the plastic anisotropy index R in the three directions based on the true strain formula to characterize the differences in the plastic flow characteristics of the material under different loading directions.

[0046] Anisotropic materials have a directional distribution of their microstructure due to the manufacturing process, causing their mechanical properties (strength and plasticity) to vary significantly with the loading direction. For example, in rolled aluminum alloys, flattened grains align along the rolling direction, while in additively manufactured titanium alloys, columnar grains grow along the deposition direction. This step quantifies the differences in the plastic flow capacity of anisotropic metal materials in three orthogonal directions (the machining direction and its two perpendicular directions) through rapid upset forging tests (strain rate ≥ 1 / s). This calculation establishes the plastic anisotropy index (R) and establishes a correlation between the material's anisotropic characteristics and microstructure, providing benchmark data for subsequent parameter optimization.

[0047] The three orthogonal directions in additively manufactured Ti-6Al-4V include the build direction (Z-axis, perpendicular to the deposited layer), the horizontal transverse direction (X-axis), and the horizontal longitudinal direction (Y-axis). The build direction is the processing direction. Columnar grains in additively manufactured Ti-6Al-4V grow along the Z-direction (build direction). Grain boundaries hinder dislocation slip during Z-direction compression, resulting in lower plastic flow in this direction. In contrast, the X / Y-direction, due to weaker lateral connections between grains, is more susceptible to radial expansion during compression.

[0048] The three orthogonal directions of rolled aluminum alloy 6061-T6 are the rolling direction (L-axis, the main direction of sheet extension), the transverse direction (T-axis, the width of the sheet), and the thickness direction (S-axis, the thickness of the sheet). The rolling direction is the processing direction. The flattened grains of rolled aluminum alloy 6061-T6 are aligned along the L-axis. During compression in this direction, grain boundary strengthening inhibits radial flow. However, in the S-axis (thickness direction), radial expansion during compression is more pronounced due to the weaker resistance along the minor axis of the grains.

[0049] In this step, cylindrical specimens are cut along the three aforementioned directions using a wire-cut or precision milling machine. The specimens have a diameter range of 5-200mm, a height-to-diameter ratio of 1.5-2.0, an end face parallelism error of ≤0.02mm, and a surface roughness Ra of ≤0.8μm. The cylindrical specimens are then placed in a rapid upsetting testing machine and compressed at a strain rate of 1-13 / s, ending at a height reduction rate of 40-60%. The height and diameter of the compressed specimens are recorded. Radial strain is measured in real time using a laser displacement sensor to scan the mid-section diameter of the specimen, with a sampling frequency of ≥1kHz and an accuracy of ±0.01mm. Axial strain is recorded using the testing machine's displacement sensor to record the compression displacement, simultaneously calibrating the system's elastic deformation error.

[0050] The logarithmic ratio of the absolute value of the deformed size to the original size is used as the true strain to calculate the true radial strain and true axial strain. The true radial strain is expressed as ,in is the original diameter of the specimen, is the maximum diameter after compression; the true axial strain is expressed by the formula ,in is the original height of the sample, is the height after compression. Based on the true radial strain and true axial strain, the plastic anisotropy index is , reflecting the ratio of radial to axial plastic flow capacity.

[0051] In a specific embodiment, a Φ10mm×15mm cylindrical specimen is cut from a Ti-6Al-4V titanium alloy deposited block formed by selective laser melting along the Z direction (construction direction), X direction (horizontal transverse direction), and Y direction (horizontal longitudinal direction), using slow wire cutting to ensure directional accuracy; the end face is electrolytically polished to a roughness of Ra=0.4μm to eliminate the interference of surface microcracks on deformation. The Ti-6Al-4V titanium alloy cylindrical specimens are placed in the testing machine in turn, and the specimens with an original height of 15mm are compressed to a height of 7.5mm at a strain rate of 5 / s at room temperature of 25°C, with a height reduction rate of 50%. The diameter d of the Z-direction specimen after compression is 12.8mm, and the true radial strain is 0. is 0.246 and the true axial strain The plastic anisotropy index is -0.693. is 0.355; the diameter d of the X-axis specimen after compression is 14.2 mm, and the true radial strain is 0.352 and the true axial strain The plastic anisotropy index is -0.693. is 0.508; the diameter d of the Y-axis specimen after compression is 14.6 mm, and the true radial strain is 0.379 and the true axial strain The plastic anisotropy index is -0.693. The plastic anisotropy index R value is ranked as follows: > > The plastic flow capacity in the Y direction (horizontal longitudinal direction) is the strongest, while the plastic flow capacity in the Z direction (building direction) is the weakest. This is because during the selective laser melting process of Ti-6Al-4V titanium alloy, the rapid laser solidification leads to the formation of coarse columnar crystals in the Z direction, with grain boundaries parallel to the building direction. During compression, the Z-direction grain boundaries hinder dislocation slip, significantly inhibiting radial flow. In the X / Y directions, the interlaced interlayer molten pools form fine-grained regions, resulting in stronger plastic flow capacity.

[0052] In another specific embodiment, Φ12mm×18mm cylindrical specimens were cut from rolled aluminum alloy 6061-T6 plates along the rolling direction (L), transverse direction (T), and thickness direction (S), and the end faces were ground to Ra=0.6μm. The aluminum alloy 6061-T6 cylindrical specimens were placed in a testing machine and compressed from an original height of 18mm to a height of 9.9mm at a strain rate of 3 / s at room temperature of 20°C, with a height reduction rate of 45%. The diameter d of the specimen after compression in the L direction was 13.5mm, and the true radial strain is 0.118 and the true axial strain The plastic anisotropy index is -0.606. is 0.53; the diameter d of the T-axis specimen after compression is 14.1 mm, and the true radial strain is 0.160 and the true axial strain The plastic anisotropy index is -0.606. is 0.58; the diameter d of the specimen after compression in the S direction is 14.8 mm, and the true radial strain is 0.210 and the true axial strain The plastic anisotropy index is -0.606. The plastic anisotropy index R value is ranked as follows: > > The plastic flow capacity is strongest in the thickness direction (S) and weakest in the rolling direction (L). This is because the rolling process flattens the grains of aluminum alloy 6061-T6 along the L direction. During compression in the L direction, grain boundary strengthening inhibits lateral flow. The S direction is more susceptible to radial expansion due to its weaker resistance along the minor axis of the grains.

[0053] Based on the distribution of the plastic anisotropy index (R value) in the three directions in step S1, the principal direction (the direction with the largest R value deviation from the mean) is selected. By adjusting the strain rate or height reduction rate parameters in this direction, the difference in plastic flow capacity between it and the other two directions is reduced, thereby systematically reducing the impact of the overall anisotropy of the material. Step S2 selects the principal direction based on the R value distribution and standard deviation contribution rate in step S1. The microscopic mechanism of the plastic flow anomaly (such as grain boundary obstruction and grain slip) is analyzed, and the strain rate or height reduction rate parameters are adjusted in the opposite direction to bring the R value of the corrected principal direction closer to the mean of the other directions.

[0054] The principal direction is the direction in which the R-value deviates most from the mean among the three orthogonal directions. This direction indicates abnormal plastic flow (excessive or insufficient plastic flow). It is usually the direction with the maximum or minimum R-value or the main processing direction of the material. By calculating the standard deviation of the R-values in the three directions, the direction with a contribution of more than 50% is selected as the principal direction.

[0055] By adjusting the strain rate and height reduction rate in the principal direction, the R value approaches the average of the other two directions. If the R value in the principal direction is too low (weak plastic flow), reduce the strain rate to 50-80% of the baseline value or increase the height reduction rate by +5-15% to promote plastic coordination. If the R value in the principal direction is too high (strong plastic flow), increase the strain rate to 120-150% of the baseline value or reduce the height reduction rate by -5-15% to suppress radial flow.

[0056] In a specific embodiment, the plastic anisotropy index R value of the Ti-6Al-4V titanium alloy formed by selective laser melting includes the Z-direction plastic anisotropy index 0.355, X-direction plastic anisotropy index is 0.508 and the Z-direction plastic anisotropy index The R value in the Z direction deviates the most from the mean (Δ=0.115), contributing 60% of the standard deviation, and is selected as the main direction. This is because the R value in the Z direction (building direction) is too low due to the obstruction of columnar grain boundaries. It is necessary to reduce the strain rate or increase the height reduction rate, and extend the deformation time to promote grain boundary sliding, thereby improving To make it close to the three-dimensional average, the strain rate in the Z direction was reduced from 5 / s to 3 / s (a 40% decrease), and the height reduction rate was increased from 50% to 55% (a 10% increase). Reducing the strain rate prolongs the deformation time and promotes dislocation slip at the Z-direction columnar grain boundaries; increasing the height reduction rate increases the deformation amount and activates more slip systems.

[0057] In another specific embodiment, the plastic anisotropy index R value of the rolled aluminum alloy 6061-T6 includes the L-direction plastic anisotropy index 0.195, T-direction plastic anisotropy index is 0.264 and the S-direction plastic anisotropy index The R value in the three directions is 0.347, with a mean of 0.269 and a standard deviation of 0.076. The S-direction has the largest deviation from the mean (Δ=0.078), contributing 51% of the standard deviation and is therefore selected as the primary direction. This is because the R value in the S-direction (thickness direction) is too high due to the tendency of the minor axis of the grains to slip, necessitating an increased strain rate or a reduced height reduction rate to shorten the deformation time to suppress lateral flow. Therefore, the S-direction strain rate was increased from 3 / s to 5 / s (a 67% increase), while the height reduction rate was reduced from 45% to 40% (an 11% decrease). Increasing the strain rate and shortening the deformation time suppressed lateral slip in the S-direction grains, while reducing the height reduction rate limited the depth of plastic deformation and reduced flow advantage.

[0058] Step S3, based on the reference parameters (strain rate and height reduction rate) in the principal directions from step S2, divides the temperature correction intervals according to the material's thermal deformation characteristics (dynamic recrystallization temperature, thermal expansion coefficient, etc.). Temperature-dependent correction factors are defined based on the thermodynamic constitutive model to correct the strain rate and height reduction rate. This step introduces a temperature variable to further modify the test parameters to compensate for or exploit the effect of temperature on the plastic flow of anisotropic materials, ensuring that the high and low temperature test conditions accurately characterize the material's anisotropic characteristics.

[0059] In the low-temperature range of 20-400°C for Ti-6Al-4V titanium alloy, the β phase is more stable and the columnar grain boundary barrier effect is slightly weakened. In the medium-temperature range of 400-800°C, the α+β two-phase region is in place, dynamic recovery initiates, and anisotropic differences are partially reduced. In the high-temperature range of 800-950°C, the β phase dominates, dynamic recrystallization is significant, and anisotropy rapidly weakens. In the low-temperature range of 20-200°C for 6061-T6 aluminum alloy, work hardening dominates, and anisotropic differences gradually weaken with increasing temperature. In the medium-high-temperature range of 200-400°C, dynamic recovery is enhanced, and the slip resistance along the minor axis (S) of the grains is reduced.

[0060] The strain rate correction is equal to the base strain rate multiplied by the strain rate temperature compensation coefficient. Use the formula , Q is the deformation activation energy (260 kJ / mol for Ti-6Al-4V and 172 kJ / mol for 6061-T6), R is the gas constant (8.314 J / (mol·K)), is the room temperature reference temperature (taken as 298 K).

[0061] The height reduction rate correction is equal to the base reduction rate multiplied by the height reduction rate correction factor. Use the formula , is the thermal softening-expansion coupling coefficient (0.12 for Ti-6Al-4V and 0.10 for 6061-T6).

[0062] In a specific embodiment, the strain rate of Ti-6Al-4V titanium alloy is 3 / s at 25°C and the height reduction rate is 55%. Based on the temperature correction calculation at 785°C, the strain rate temperature compensation coefficient is 0.64, height reduction rate correction factor is 1.14, the corrected strain rate is 1.92s -1 The corrected height reduction rate is 62.7%. Reducing the strain rate to 1.92 / s can reduce the damage to the Z-direction columnar grains caused by dynamic recrystallization and preserve anisotropy. Increasing the reduction rate to 62.7% can exploit high-temperature plasticity, but it is important to ensure that the instability threshold is not exceeded.

[0063] In another specific embodiment, the strain rate of 6061-T6 aluminum alloy is 5 / s at 25°C and the height reduction rate is 40%. Based on the temperature correction calculation at 415°C, the strain rate temperature compensation coefficient is 0.95, height reduction rate correction factor is 1.08, the corrected strain rate is 4.75s -1 The corrected height reduction rate is 43.2%. Maintaining a high strain rate suppresses lateral slip of S-direction grains and prevents anisotropic rebound; the reduction rate is slightly increased to 43.2% to compensate for thermal softening while avoiding grain coarsening.

[0064] Based on the strain rate and height reduction rate corrected in step S3, step S4 conducts a two-stage rapid upsetting test to obtain the real mechanical behavior data of the material under rapid deformation conditions at a constant temperature, including flow stress, strain hardening rate, and fracture strain, etc., to provide subsequent benchmark data without anisotropic interference. This step divides the total compression stroke into two stages, sets a pause time between the stages to stabilize data acquisition, and maintains or fine-tunes the strain rate in the two stages based on the strain rate and height reduction rate corrected in step S3; and simultaneously records the axial load, displacement, radial expansion, and strain rate sensitivity parameters of each stage. Among them, the total stroke reduction rate is the percentage reduction of the original height of the specimen to the total height after compression, and the stage compression ratio is the ratio of the single-stage compression to the total stroke reduction.

[0065] Preferably, the first stage completes 70%-80% of the total reduction, quickly completes most of the plastic deformation, and avoids temperature rise or microstructure changes caused by long-term loading; the second stage completes the remaining 20%-30%, controls the final forging deformation, and captures the mechanical response of the high strain area. The strain rate can be fine-tuned by ±5% based on step S3; the pause time between the first stage and the second stage is 0.5-2 seconds to ensure data stability and eliminate instantaneous elastic recovery.

[0066] Collect axial data including load-displacement curves, true stress ( , is the initial cross-sectional area of the specimen), true strain ( ); radial data includes real-time measurement of diameter expansion by laser displacement sensor and calculation of radial strain ; The strain rate sensitivity index m is calculated by the difference in the two-stage rate, which describes the dependence of the material flow stress on the strain rate. The formula is , is the flow stress, is the strain rate; monitor the crack initiation and fracture morphology of the sample surface and calculate the fracture strain , is the height of the specimen at fracture.

[0067] In a specific embodiment, a Z-direction additive manufacturing Ti-6Al-4V titanium alloy specimen was compressed in two stages at a strain rate of 1.92 / s and a height reduction rate of 50%. In the first stage, the specimen was compressed to a height of 10.5 mm (a reduction rate of 30%, accounting for 70% of the total reduction), with a strain rate of 1.92 / s and a pause of 1 second; in the second stage, the specimen was compressed to a final height of 7.5 mm (a reduction rate of 20%, accounting for 30% of the total reduction), with a strain rate maintained at 1.92 / s. The measured flow stress in the first stage was 1083.2 MPa, the flow stress in the second stage was 1136.5 MPa, the strain rate sensitivity index m was 0.008, and the fracture strain was 0. is 0.725.

[0068] In another specific embodiment, an L-rolled aluminum alloy 6061-T6 specimen was compressed in two stages at a strain rate of 4.75 / s and a height reduction rate of 45%. In the first stage, the specimen was compressed to a height of 12.6 mm (a reduction rate of 30%, accounting for 70% of the total reduction), at a strain rate of 4.75 / s, and paused for 0.5 seconds; in the second stage, the specimen was compressed to a final height of 9.9 mm (a reduction rate of 15%, accounting for 30% of the total reduction), and the strain rate was fine-tuned to 4.99 / s. The measured flow stress in the first stage was 247.6 MPa, the flow stress in the second stage was 258.9 MPa, the strain rate sensitivity index m was 0.005, and the fracture strain was 0. It is 0.595.

[0069] Example structure:

[0070] A metal material rapid upset testing machine, used in the above exemplary method, comprises the following structure:

[0071] Positioning module, used to position and clamp the specimen;

[0072] Axial loading module for performing single or two-stage axial compression on the specimen;

[0073] Strain measurement module, used to measure the radial strain and axial strain of the specimen;

[0074] The control module is 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.

[0075] Experimental Example 1:

[0076] In this experimental example, the control group was set up according to the existing standard YB / T5293-2022, including:

[0077] (1) A Φ10 mm × 15 mm cylindrical specimen was cut along the Z direction of the additively manufactured Ti-6Al-4V material and placed in a rapid upsetting testing machine, compressed to 7.5 mm in a single cycle at a constant temperature of 25 °C and a strain rate of 5 / s, with a height reduction rate of 50%;

[0078] (2) A Φ12 mm × 18 mm specimen was cut along the rolling direction L of the rolled aluminum alloy 6061-T6 and placed in a rapid upsetting testing machine, compressed to 7.5 mm in a single cycle at a constant temperature of 20 °C and a strain rate of 3 / s, with a height reduction rate of 45%.

[0079] In this experimental example, the experimental group was set up according to the exemplary method, including:

[0080] (3) A Φ10 mm × 15 mm cylindrical specimen was cut along the Z direction of the additively manufactured Ti-6Al-4V material and placed in a rapid upsetting testing machine. The specimen was compressed in two stages at a constant temperature of 785 °C and a strain rate of 1.92 / s, with a pause of 1 s in between. In the first stage, the specimen was compressed to a height of 9.0 mm (height reduction rate of 40%), and in the second stage, the specimen was compressed to a height of 5.6 mm (height reduction rate of 62.7%).

[0081] (4) A Φ12 mm × 18 mm specimen was cut along the rolling direction L of the rolled aluminum alloy 6061-T6 and placed in a rapid upsetting testing machine. The specimen was compressed in two stages at a constant temperature of 415 °C, with a pause of 0.5 s in between. In the first stage, the specimen was compressed to a height of 12.6 mm at a strain rate of 4.75 / s (height reduction rate of 30%), and in the second stage, the specimen was compressed to a height of 9.9 mm at a strain rate of 5.22 / s (height reduction rate of 43.2%).

[0082] The flow stress, strain rate sensitivity and fracture strain of the above four groups of samples were tested respectively, and the results are shown in the following table:

[0083] Table 1 Comparison table of test results

[0084]

[0085] In rapid upset forging tests of metal materials, differences in plastic flow capacity caused by anisotropy can significantly interfere with the authenticity of mechanical behavior. In the additive manufacturing Ti-6Al-4V titanium alloy build direction (Z direction), dislocation slip is strongly hindered because the columnar grain boundaries are parallel to the compression axis. The plastic anisotropy index R value is only 0.355, significantly lower than the 0.508 and 0.547 in the horizontal transverse (X direction) and longitudinal (Y direction) directions. This is because the coarse columnar crystal structure formed during laser melting acts as a barrier to dislocation movement in the Z direction during compression, resulting in restricted radial expansion. If only relying on a single parameter adjustment, such as simply reducing the strain rate, although the deformation time can be extended to promote grain boundary slip, it cannot simultaneously solve the problem of dynamic recrystallization destroying the columnar crystal structure at high temperatures.

[0086] By reducing the strain rate, increasing the height reduction rate, and performing staged compression, the experimental group reduced the Z-direction strain rate from 5 / s to 1.92 / s. This prolonged the deformation time, allowing columnar grain boundaries to migrate and dynamically recover at a high temperature of 785°C, activating non-basal slip systems. Simultaneously, the height reduction rate was increased from 50% to 62.7%, increasing the deformation volume to force more slip systems into motion and alleviate the grain boundary hindrance effect. In the first stage of staged compression, 70% of the reduction was achieved quickly at 1.92 / s, utilizing dynamic recovery to release local stress. In the second stage, the remaining 30% of the deformation was completed at a constant rate, suppressing high-temperature-induced grain coarsening. Data showed that the optimized Z-direction flow stress gradient decreased from 1198.7 MPa in a single compression to 1083.2 MPa and 1136.5 MPa in two stages. The fracture strain increased from 0.693 to 0.725, while the strain rate sensitivity exponent, m, 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. Single parameter adjustment cannot achieve such multi-scale coupled optimization.

[0087] For rolled aluminum alloy 6061-T6, the R value in the thickness direction (S direction) is as high as 0.347, significantly deviating from the 0.195 in the rolling direction (L direction) due to the low resistance to short-axis slip of the grains. The flattening of the grains caused by the rolling process makes lateral flow in the S direction more likely during compression. Increasing the strain rate alone, while suppressing short-axis slip, can exacerbate work hardening and local necking. The experimental group increased the S-direction strain rate from 3 / s to 5.22 / s, shortening the deformation time to limit the dominance of short-axis slip; fine-tuned the height reduction rate from 45% to 43.2% to balance the thermal softening effect; and in the staged compression, the first stage of the compression was completed at 4.75 / s to complete 70% of the deformation, and the second stage was accelerated to 5.22 / s to enhance the rate suppression effect. The data show that the S-direction flow stress gradient was optimized from 283.4 MPa to 247.6 MPa and 258.9 MPa, and the m-value decreased from 0.022 to 0.005. Although the fracture strain decreased slightly from 0.606 to 0.595, the contribution of the anisotropy standard deviation was compressed from 51% to 15%. This process is essentially a combination of high strain rate inhibition of slip and dynamic recovery of equilibrium microstructure evolution. Adjusting the strain rate or reduction rate alone cannot simultaneously achieve flow stress smoothing and anisotropy weakening.

[0088] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A metal material rapid upsetting test method, characterized in that: The following steps are involved: Based on cutting cylindrical specimens in three orthogonal directions of metal materials, the true radial strain and true axial strain in each direction are simultaneously measured by axial compression of the specimens to calculate the plastic anisotropy index; The main directions are selected according to the distribution of plastic anisotropy index in each direction, and the strain rate and height reduction rate in the main directions are adjusted; 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; Based on the corrected strain rate and height reduction rate, the corrected mechanical behavior data are obtained by compressing the specimen in the main direction in two stages. The first stage completes the main part of the total compression, and the second stage completes the remaining compression and records the dynamic response parameters. The true radial strain is calculated by the diameter change of the sample before and after compression, the true axial strain is calculated by the height change of the sample before and after compression, and the plastic anisotropy index is the ratio of the true radial strain to the true axial strain; 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.

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

3. The test method according to claim 1, characterized in that The screening method for the main direction is that the plastic anisotropy index deviates from the average value of the three directions by the largest amount and the standard deviation contribution rate exceeds a preset threshold; The method for adjusting the strain rate and height reduction rate in the main direction includes reducing the strain rate or increasing the height reduction rate when the plastic anisotropy index in the main direction is lower than the average value; and increasing the strain rate or reducing the height reduction rate when the plastic anisotropy index in the main direction is higher than the average value.

4. 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; the low temperature zone is dominated by a dynamic recovery effect, the medium temperature zone is dominated by a phase transformation or grain boundary sliding effect, and the high temperature zone is dominated by a dynamic recrystallization effect.

5. The test method according to claim 1, characterized in that 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 stages to stabilize data collection. The strain rate is fine-tuned in the second stage according to the dynamic recrystallization state.

6. The test method according to claim 1, characterized in that 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%.

7. The test method according to claim 1, characterized in that 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%.

8. A metal material rapid upset testing machine, used to implement the testing method according to any one of claims 1 to 7, characterized in that: include: Positioning module, used to position and clamp the specimen; Axial loading module for performing single or two-stage axial compression on the specimen; Strain measurement module, used to measure the radial strain and axial strain of the specimen; The control module is 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.

Images