Dynamic Material Model Research Articles

Optimization of hot backward extrusion process parameters for flat bottom cylindrical parts of Mg-8Gd-3Y alloy based on 3D processing maps

Based on three-dimensional processing maps and numerical simulation, a demo flat bottom cylindrical part (with outer diameter of 235 mm, wall thickness of 34 mm, and height of 255 mm) of high strength Mg-Gd-Y magnesium alloy was hot backward extruded by adding an outer flange to increase the overall deformation amount and strain uniformity. Firstly, on the basis of dynamic material model and Murty instability criterion, isothermal compression stress-strain curves of cast-homogenized Mg-8Gd-3Y alloy were used to construct the processing maps. The processing maps show that the formable domain is relatively narrow: at lower strain rates ranging from 0.001 to 0.006 s−1, and the suitable temperature is from 350 to 450 °C; and at higher strain rates ranging from 0.006 to 0.1 s−1, and the temperature is from 410 to 450 °C. Then, the processing maps were integrated into a finite element software to simulate the forming process of cylindrical parts, and the influences of deformation temperature and velocity on the power dissipation efficiencies of different positions of flanged cylindrical parts were mainly discussed. The simulation results indicate that the average strain of flanged cylindrical parts reaches 30.07% and is larger than that of unflanged cylindrical parts, and the standard deviation of the strain of flanged cylindrical parts is 19.35% and less than that of unflanged cylindrical parts. The optimal process parameters corresponding to the maximum power dissipation efficiency are the temperature of 430 °C and velocity of 1 mm/s. Finally, under the optimal forming condition, the hot backward extrusion experiments of flanged cylindrical parts were conducted. The experimental results exhibit that the flanged cylindrical parts could be properly formed with good surface quality, and have relatively uniform microstructures and mechanical properties. The difference of tensile strength between the bottom and cylindrical body is less than 5 MPa, and the hardness difference is less than 1.6 HV.

Deformation Behavior and Cavitation of AA2017 at Elevated Temperatures

In this work, deformation behavior of AA2017-T4 at elevated temperatures was studied employing uni-axial tensile and creep experiments. Tensile tests were carried out at temperatures varying 150–500 °C under different strain rates then, a combination of neural network and dynamic material modeling was utilized to construct the processing maps. Furthermore, creep experiments were conducted to assess inelastic deformation behavior of the alloy at temperatures between 150 and 225 °C and stresses in the range of 150 to 230 MPa. Microstructural evaluations were carried out for determination of microstructural changes and formation of voids and cavities within the samples. The results showed that dynamic precipitation could occur during deformation at temperatures 175–225 °C leading to negative strain-rate sensitivity at true strains larger than 0.1. The main softening process was detected as dynamic recovery at temperatures higher than 250 °C however, dynamic recrystallization could also occur at low strain rates and temperatures higher than 400 °C. The activation energies for hot deformation were computed as 380.6 kJ mole−1 at 250–350 °C and it was reduced to 224.7 kJ mole−1 for the range of 350–500 °C. This showed the hard particle could significantly change rate of flow softening. The creep activation energy was determined as 169.5 kJ while the stress-exponent varied between 5.5 and 10.1 at temperatures between 150 and 225 °C indicating that dynamic recovery controlled by dislocation climb could be the governing creep mechanism.

Development of Processing Maps for Hot Deformation: Algorithm and Common Errors

The development of processing maps using the dynamic materials modeling (DMM) approach is a widely used method for choosing the appropriate process parameters for the thermomechanical processing of any material. This paper highlights the correct algorithm for developing the processing map by calculating the metallurgical power dissipation efficiency (η) and the newly proposed binary instability parameter (β). Further, common errors that can arise during the computations, and their consequences are also highlighted.

Prediction and Prevention of Cracks in Free-Cutting Stainless Steel Bar Forming

A three high planetary mill is used to produce bismuth-containing stainless-steel bars with high production efficiency. However, due to the influence of bismuth metal properties, the selection of processing parameters must be optimized to avoid the generation of cracking in the bar core. To solve this contradiction and find a suitable processing zone, the thermal simulation experiment of bismuth-containing stainless-steel material was carried out first to determine the constitutive relationship of the material. Three-roll planetary rolling experiments were carried out to determine the crack-producing region. Based on the Brozzo ductile fracture criterion, the fracture threshold of bismuth-containing austenitic stainless-steel bars in three-roll planetary rolling was determined by the finite element (FE) simulation. Five key process parameters were selected, with five factors and four levels of the orthogonal test designed. Through FE simulations, the possibility of cracking of stainless-steel bars with bismuth austenites in different technologic conditions was judged, and a set of optimal technologic parameters was obtained. Based on range analysis, the influence of various process parameters on bar cracking was discussed. Then, based on the dynamic material model and Murty criterion, the processing map of free-cutting austenitic stainless containing bismuth was established. It was found that the optimum process parameters were consistent with the processable range of the hot-working chart. Finally, the field rolling was carried out with the optimum process parameters, showing that there was no crack in the bar.

Constitutive Equation and Hot Processing Map for Tensile Test of Mg-13Gd-4Y-2Zn-0.5Zr Alloy at Elevated Temperature

The high temperature tensile behavior of Mg-13Gd-4Y-2Zn-0.5Zr alloy was investigated at deformation temperature of 400-520 °C and strain rate of 0.001-0.5 s-1, and the stress-strain curves were obtained by using INSTRON 3382. The high temperature tensile constitutive model and hot processing map of the alloy were established, and the reliability of the hot processing map was further verified by analyzing the microstructure of the deformed alloy. The results showed that the dynamic recrystallization (DRX) occurred of Mg-13Gd-4Y-2Zn-0.5Zr alloy during the tensile tests under high temperature conditions, and its peak stress decreased with the increase of deformation temperature or strain rate. The Arrhenius equation can be used to fit the rheological behavior of the alloy. The thermal deformation activation energy Q was 259.13kJ/mol, and the maximum error between the model and the experimental data was less than 9%. It can be concluded that the optimum deformation parameters of the alloy were temperature of 500-520 °C and strain rate of 0.01-0.001 s-1 based on the dynamic material model and hot processing map.

Study on rheological behavior and microstructural evolution of Al-6Mg-0.4Mn-0.15Sc-0.1Zr alloy by isothermal compression

The effects of trace amounts of Sc/Zr on rheological properties and microstructural evolution of the Al-6Mg-0.4Mn-0.15Sc-0.1Zr alloy under different deformation conditions were studied by isothermal compression tests at deformation temperatures of 280 °C ∼ 460 °C and strain rates of 0.001 ∼ 10 s−1. A constitutive model based on the hyperbolic sine function was established. The dependence of the flow stress on strain, strain rate, and deformation temperature was described. Using experimental data and dynamic material model, machining diagrams of the alloy with strains of 0.3 and 0.5 were obtained, and the hot workability of the alloy was verified. The results showed that the deformation temperature and strain rate had significant effects on the deformation behavior of the alloy. The flow stress of the alloy increased with the increase in strain rate and decreased with the increase in deformation temperature. Under high-temperature and low-strain-rate conditions, the alloy tended to undergo dynamic recrystallization, and the volume fraction and grain size increased with the increase in deformation temperature and the decrease in strain rate. Based on the analysis of the microstructural evolution, the construction of the machining diagram, and the solution of the rheological constitutive equation, suitable values of the deformation temperature were determined to be 380 °C ~ 460 °C. Moreover, suitable values of the strain rate were determined to be 0.001 and 0.3 s−1. The deformation activation energy of 161.28 kJ mol−1 was obtained.

Constitutive behavior and hot workability of multi-direction forged T2 copper during hot compression deformation

The hot deformation behavior of a multi-direction forged (MDFed) T2 copper was investigated by the isothermal compression test at deformation temperatures between 673 and 1173 K and strain rates between 0.001 and 10 s− 1. The results reveal that the deformation characteristics of the flow stress are sensitive to the hot deformation parameters. The deformation activation energy of the MDFed copper under the test conditions was calculated as 195.601 kJ/mol. The constitutive behavior was described by a two-stage constitutive model, which is based on the stress–dislocation relation and kinetics of dynamic recrystallization (DRX). Based on the dynamic material model, the three-dimensional (3D) processing maps were established to identify the instability regions and optimal hot processing parameters. It is found that DRX occurred in all the stability and instability regions, and the optimal processing conditions are in the temperature range of 923–1023 K and strain rate range of 0.1–1 s− 1, which indicates a feature of incomplete DRX. Moreover, the grains overgrew at high deformation temperatures and low strain rates, resulting in a poor workability for the MDFed copper.

Synthesizing and Hot Deformation Behavior of Novel Al-X Wt.% Zn Alloys for Advanced Casting Industries

The present paper investigates the synthesizing routes and best method to explain the hot deformation behavior of novel Al-x wt.% Zn alloys (x = 0, 10, 20, 30, 40 and 50 wt.%). Based on several synthesizing routes, it was studied that the liquid metallurgy route followed by squeeze casting and extrusion is the best manufacturing method of the novel Al-Zn castings. These novel Al-Zn casting alloys would give more benefits as it possesses lower value of melting temperature; which is best suited for die-casting parts. To explore the mechanical behavior of Al-Zn castings, hot deformation studies by developing the processing map is best method by which complete information related to these alloys bahaviour could be obtained. From the literature, it was found that the hot workability behavior can be examined by developing the processing map using dynamic material modelling (DMM) and constitutive models (sine-hyperbolic Arrhenius kinetic rate equation). The step by step procedure to be followed for hot deformation analysis was explained in this work. From this analysis, the peak flow stress, stability region, instability region, power dissipation efficiency, activation energy and dynamic recrystallization region can be explored. In addition, as a pilot study related to these Al-Zn alloy, several castings, namely, pure Aluminium(Al), Al-10Zn, Al-20Zn, Al-30Zn, Al-40Zn, and Al-50Zn were successfully casted using electric furnace and then all these castings were squeezed followed by extruded to have improved densification. The hardness of casted samples was revealed that Al-40Zn casting exhibited a vicker’s hardness strength (VHS) of 1326 MPa which was 4 times higher than pure Al.

Hot Deformation Characteristics and 3-D Processing Map of a High-Titanium Nb-Micro-alloyed Steel.

Hot deformation behavior of a high-titanium Nb-micro-alloyed steel was investigated by conducting hot compression tests at the temperature of 900–1100 °C and the strain rate of 0.005–10 s−1. Using a sinh type constitutive equation, the apparent activation energy of the examined steel was 373.16 kJ/mol and the stress exponent was 6.059. The relations between Zener–Hollomon parameters versus peak stress (strain) or steady-state stress (strain) were successfully established via the Avrami equation. The dynamic recrystallization kinetics model of the examined steel was constructed and the validity was confirmed based on the experimental results. The 3-D atomic distribution maps illustrated that strain can significantly affect the values of power dissipation efficiency and the area of instability domains. The 3-D processing maps based on a dynamic material model at the strains of 0.2, 0.4, 0.6 and 0.8 were established. Based on traditional and 3-D processing maps and microstructural evaluation, the optimum parameter of for a high-titanium Nb-micro-alloyed steel was determined to be 1000–1050 °C/0.1–1 s−1.

Effect of grinding parameters on microstructure evolution of TC21 titanium alloy with bimodal starting microstructure

Abstract This study aims to investigate the deformation behavior of two-phase titanium alloy Ti–6Al–3Mo–2Zr–2Sn–2Nb–1Cr (TC21) during grind hardening (GH) process. According to dynamic material modeling (DMM) combine Kumar’s instability criterion, the processing maps were constructed to discuss processing properties of material. Results suggest that the ideal processing region is in the temperature of 880 °C, strain rate range 10−3-0.03s−1. The evolution mechanism of α phase was revealed using TEM microstructural analysis under different grinding conditions. It is interesting that, some secondary-precipitated α phase with approximate orientation usually combine to form lamellar α colonies, while some ones with different orientations split to short rod-like or globular structure particularly at higher grinding depth. The optimum grinding parameters for TC21 is at grinding depth range 60–90 μm, wheel speed of 20 m s−1 followed by aging treatment. Most of all, the GH technology has a significantly advantage than heat treatment for exhibiting higher micro-hardness and lower friction coefficient.

Hot deformation behavior and workability of a Ni–Co based superalloy

Abstract The hot deformation behavior of a new Ni–Co based alloy was investigated by the isothermal compression tests in a temperature range of 1060–1180 °C and a strain rate range of 0.01–10 s−1 under a true strain of 0.693. The results show that the flow stress, corrected by friction and adiabatic heating, increases with the decreasing temperature and increasing strain rate. Considering the dissolution of the γ′ precipitates during hot deformation, the Arrhenius-type constitutive equations were established segmentally via fitting the corrected flow stress data. The activation energies for the γ+γ′ dual-phase region and the γ single-phase region of the alloy are 671 and 391 kJ mol−1, respectively. The reason for higher activation energy of the γ+γ′ dual-phase region is that γ′ ((Ni,Co)3(Al,Ti)) precipitates hinder dislocation slip and harden the alloys during hot deformation. The processing map based on the dynamic material model (DMM) was also constructed. According to the analysis of microstructural evolution, dynamic recrystallization (DRX) occurs under all deformation conditions. The optimum hot deformation processing conditions for the γ+γ′ dual-phase region are 1060–1070 °C/0.01–0.02 s−1 or 1070–1141 °C/0.01–1 s−1. In addition, the optimal processing parameter for the γ single-phase region is 1141–1175 °C/0.01–10 s−1 (except a part of flow instability domain).

Processing map and hot deformation behavior of Ta-particle reinforced TiAl composite

Abstract The hot deformation behavior of a Ta-particle reinforced TiAl composite was studied. Ti–48Al–2Cr–2Nb– 0.2W(at.%)/20vol.%Ta metal matrix composite was fabricated by spark plasma sintering. The deformation behavior was investigated by hot compression tests at the temperature ranging from 1050 to 1200 °C and the strain rate ranging from 1×10−3 to 1 s−1. The constitutive equation containing true strain variables was established. The values of activation energy Q under different strain degrees are between 240 and 280 kJ/mol, which are lower than that of pure TiAl. Based on dynamic material modeling, the processing maps at various strain degrees were established, and the optimized parameters for hot working are 1050–1100 °C and 0.005–0.01 s−1. The microstructural evolution during deformation was characterized, which indicated that the dynamic recrystallization plays an important role in this process.

Dynamic Recrystallization Behavior and Processing Map of the 6082 Aluminum Alloy.

Multiple hot-compression tests were carried out on the 6082 aluminum (Al) alloy using a Gleeble-1500 thermal simulation testing machine. Data on flow stresses of the 6082 Al alloy at deformation temperatures of 623 to 773 K and strain rates from 0.01 to 5 s−1 were attained. Utilizing electron backscatter diffraction (EBSD) and a transmission electron microscope (TEM), the dynamic recrystallization behaviors of the 6082 Al alloy during hot compression in isothermal conditions were explored. With the test data, a hot-working processing map for the 6082 Al alloy (based on dynamic material modeling (DMM)) was drawn. Using the work-hardening rate, the initial critical strain causing dynamic recrystallization was determined, and an equation for the critical strain was constructed. A dynamic model for the dynamic recrystallization of the 6082 Al alloy was established using analyses and test results from the EBSD. The results showed that the safe processing zone (with a high efficiency of power dissipation) mainly corresponded to a zone with deformation temperatures of 703 to 763 K and strain rates of 0.1 to 0.3 s−1. The alloy was mainly subjected to continuous dynamic recrystallization in the formation of the zone. According to the hot-working processing map and an analysis of the microstructures, it is advised that the following technological parameters be selected for the 6082 Al alloy during hot-forming: a range of temperatures between 713 and 753 K and strain rates between 0.1 and 0.2 s−1.

Hot deformation behavior and processing map of Mg-12Gd-1MM-0.6Zr magnesium alloy

The hot deformation behavior of Mg-12Gd-1MM-0.6Zr (wt.%) magnesium alloy was tested by Gleeble-1500D hot simulator with reduction of 60% and strain rates from 0.001 to 1 s−1 at the temperature range from 753 to 793 K. The results show that the flow stress is influenced by both, temperatures and strain rates. At constant temperatures, flow stress is increased with strain rate, while at constant strain rates, it decreased with temperature. The constitutive equation of Mg-12Gd-1MM-0.6Zr alloy during hot compression was constructed by the linear regression analysis. Average activation energy and stress exponent were 227.94 kJ/mol and 2.87, respectively. The processing map was plotted and analyzed via the dynamic material model. The most proper ranges for hot deformation temperature and strain rate were found to be 763 to 783 K and 0.01 to 0.1 s−1, respectively.

Determination of Hot Extrusion Parameters in a Spray-Formed Ultrahigh-Strength Aluminum Alloy

To determine a suitable industrial extrusion process, the hot deformation behavior of a spray-formed ultrahigh-strength aluminum alloy was studied with a series of isothermal compression tests. The temperature range was from 340 to 480 °C, while the strain rates ranged from 0.001 to 1 s−1. The flow stress behavior was studied, and the activation energy map showed the deformation difficulty degree under different compression conditions. The dynamic materials model processing map displayed three high-efficiency domains and two low-efficiency domains. As a result of the microstructure observations, it was determined that the high-efficiency domains were related to dynamic recrystallization, superplasticity and cracking. The optimum processing conditions were at intermediate temperatures from 410 to 430 °C and strain rates from 0.008 to 0.06 s−1. In light of the extrusion calibration, the practical extrusion condition was determined to be 410 °C/0.03 s−1. The surface morphology and microstructure after practical hot extrusion were consistent with the prediction by the processing maps and calibration.

Hot deformation behavior of the AA6016 matrix composite reinforced with in situ ZrB2 and Al2O3 nanoparticles

The hot deformation tests of in situ ZrB2 and Al2O3 nanoparticles reinforced AA6016 matrix composite were studied at deformation temperature of 300 °C–450 °C and strain rate of 0.001–1 s−1. In this paper, the ZrB2 and Al2O3 nanoparticles were successfully prepared by direct melt reaction method firstly. Based on experimental results, the flow stress increased rapidly with the increasing true strain and decreased with the increasing temperature. Constitutive equation of the composite can be established based on the Arrhenius constitutive model. The processing map based on dynamic material model showed two stable processable domains: Domain A(300–360 °C/0.08–0.01 s−1), which was controlled by dynamic recovery and domain B(410–430 °C/0.37–1 s−1), which was typical dynamic recrystallization structure. The microstructural changes of the samples after deformed were observed through optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). It was concluded that these two kinds of reinforced particles can greatly promote recrystallization nucleation at high temperatures. Thus, domain B is optimum hot processing window.

The analysis of flow behavior of Ti-6Al-2Sn-4Zr-6Mo alloy based on the processing maps

The paper presents the analysis of hot deformation behavior of Ti-6Al-2Sn-4Zr-6Mo (Ti-6246) alloy using the theory of dynamic material modeling (DMM) based on hot compression tests performed to a total true strain of 1 at the strain rates from 0.01 to 100 s−1 and at the temperatures within the range between 800 and 1100 °C. The processing maps according to the Prasad’s criterion were developed. The analysis of the processing maps allowed for the placement of domains describing the areas of potentially favorable combinations of hot deformation parameters. The microstructure observations of the investigated alloy specimens after hot deformation in stability and instability areas were conducted. The optimal processing parameters for numerical modeling of Ti-6246 alloy forging were selected based on processing maps. After complex analysis of the obtained results, microstructural observations and numerical modeling of forging of selected part, the forging tests of Ti-6246 alloy were realized. The obtained product quality assessment was carried out by computed tomography non-destructive testing.

Hot deformation behavior and processing map of Zr-4 alloy

The hot deformation behavior of Zr-4 alloy at the deformation temperature range of 750–1000 °C and the strain rate range of 0.001–10 s−1 was studied on a Gleeble-3500 thermal simulator. The results show that the flow stress increases with the increasing strain rates or the decreasing deformation temperature. Based on the experimental data, the strain-compensated constitutive equation was established to predict flow stress during different strains, strain rates and temperatures. Meanwhile, the hot deformation activation energy of Zr-4 alloy was respectively calculated to be 224.31 kJ/mol, 593.50 kJ/mol and 345.71 kJ/mol in α single-phase region, α+β two-phase region and β single-phase region, which are obviously much higher than the activation energy of pure zirconium (113 kJ/mol). It indicates that the main deformation mechanism is not the dynamic recovery but other deformation mechanisms. According to the dynamic material model and Murty instability criterion, Murty processing maps have been constructed at the true strain of 0.6 and 1.2. Moreover, by combining microstructural observations, the areas of 750–880 °C/0.01–0.32 s−1 and 900–1000 °C/0.03–1 s−1 are identified to be the optimum hot working parameters.

Characterization of hot deformation behavior of 30Si2MnCrMoVE low-alloying ultra-high-strength steel by constitutive equations and processing maps

Isothermal compression tests of as-forged 30Si2MnCrMoVE low-alloying ultra-high-strength steel were carried out on a Gleeble 3500 thermal simulator at the deformation temperatures of 950–1150 °C and strain rates of 0.01–10 s−1. Based on the classical stress–dislocation density relationship and the kinematics of the dynamic recrystallization, the constitutive equations of the work hardening dynamical recovery period and dynamical recrystallization period were developed by using the work hardening curve and Avrami equation, which shows good agreement with the experimental value. Processing maps at the strain of 0.90 were constructed based on dynamic material model and were analyzed combined with microstructure observation under different conditions. The optimum parameter based on the processing maps was obtained and verified by a supplementary experiment. The power dissipation maps and instability maps at strains of 0.05–0.90 were also constructed, and the evolution law was analyzed in detail. The established constitutive equation and hot processing maps can provide some guidance for hot working process.

Hot Deformation Characteristics of 18Cr-5Ni-4Cu-N Stainless Steel Using Constitutive Equation and Processing Map

The hot deformation of 18Cr-5Ni-4Cu nitrogen-alloyed austenitic stainless steel was tested with a Gleeble-1500D simulator in the temperature range of 1273–1473 K and in the strain rate range of 0.01–10 s−1. The Zener-Hollomon parameter method was used to construct a constitutive equation for high-temperature plastic deformation. The energy dissipation diagram of the material was calculated based on dynamic material modelling (DMM). The microstructural variations were characterized via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) with energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The thermodynamic calculation results showed that the addition of nitrogen to 18Cr-5Ni-4Cu steel promoted the formation of Cr2N and gas phases and expanded the austenite phase region; these results were consistent with the XRD test results of the solid solution sample. The hot deformation activation energy after nitrogen addition was 556.46 kJ∙mol−1. The processing map predicted that the optimum hot working regimes were in the temperature range of 1416–1461 K, where ln ε ˙ was 0.75–1 on the power dissipation map. At high temperatures and a small strain rate, dynamic recrystallization easily occurred. The TEM analyses showed that nano-scale M23C6 and Cr2N precipitated at the grain boundary, and NbC with a diameter of approximately 150 nm appeared along the grain boundary, resulting in grain boundary strengthening. The phase precipitation results were consistent with the Thermo-Calc calculation results. The nitrogen solid solution in the steel promoted the precipitation of nitrides, which caused grain boundary strengthening. Thus, the grain boundary stress increased and wedge-shaped grain boundary cracks formed.