Hot Plane Strain Compression Research Articles

Flow stress behavior, constitutive modeling, processing map and microstructure evolution in hot deformation of Fe-7.1Al-0.7Mn-0.4C-0.3Nb alloy

The automotive industry has experienced rapid growth, with lightweight materials becoming a significant research focus. Among these materials, low-density Fe–Mn–Al–C alloys show promise for this kind of application. To optimize the hot workability parameters of these alloys for practical applications, it is essential to explore the hot deformation behavior of these alloys. In this study, we investigated the hot deformation behavior of the low-density alloy Fe-0.77Mn-7.10Al-0.45C-0.31Nb using hot plane-strain compression tests for several deformation temperatures (850, 950, 1050, and 1150 °C) and nominal strain rates (0.01, 1, and 10 s−1). Unusual flow stress curves were observed for low (0.01 s−1) and intermediate (1 s−1) strain rates, with discontinuous yielding and multiple stress peaks. This high-temperature behavior is associated with non-homogeneous strain partitioning in duplex microstructure (δ-ferrite + γ). Using the Zenner-Hollomon constitutive modeling approach, we estimated the thermal activation energy for hot deformation as 297 kJ/mol from the experimental peak flow stresses. Additionally, processing maps and microstructure correlation analysis revealed that the alloy exhibits good hot workability in the 975–1075 °C temperature range under low and intermediate strain rates (0.01–0.3 s−1). Under these processing conditions, the δ-ferrite microstructure is submitted to dynamic recovery, while the austenitic phase undergoes dynamic recrystallization.

Texture weakening and grain refinement behavior of the extruded Mg-6.03Zn-0.55Zr alloy during hot plane strain compression

A series of hot plane strain compression (PSC) experiments of the extruded Mg-6.03Zn-0.55Zr alloy were conducted on the Gleeble-3500 machine with strain rates of 0.01 s−1 to 10 s−1 and temperatures ranging from 300 °C to 500 °C to reveal the microstructure evolution during the secondary process. The effects of grain refinement and texture modification which were easily affected by the deformation mechanism and dynamic recrystallization (DRX) were systematically studied. Experimental results showed that the main deformation mechanism during PSC was basal <a> slip (74.3 %–94.9 %) and assisted by prismatic <a> slip (4.8 %–21.1 %) and pyramidal <c+a> slip (0.3 %–4.6 %). Since the pyramidal <c+a> slip and prismatic <a> slip were more preferred to activate owing to the significant decrease of critical resolved shear stress (CRSS) at a higher temperature, the activation of non-basal slip promoted the c-axes of the grains deviated from compression direction which weakened the basal fiber texture. Moreover, the activation of non-basal slip could promote DRX behavior to some extent. Further analysis of the DRX mechanism showed that the continuous DRX (CDRX) by continuous rotation of low angle grain boundaries was dominant at lower temperatures and higher strain rates, while discontinuous DRX (DDRX) which nucleated at the grain boundaries played a more and more important role as the temperature increased and strain rate decreased. After characterizing the orientations of the DRXed grains, the CDRXed grains owned a similar grain orientation with the deformed grain while the DDRXed grains exhibited a fairly dispersed distribution, indicating that the weakening effect of the basal texture was greater with a higher DDRX fraction.

Estimation of peak stress of AM30 magnesium alloy during hot plane strain compression

This paper presents the results of an analysis of the hot deformation flow behaviour of magnesium alloy AM30. The true stress–strain curve's experimental results are used to plot the hardening curve. The critical strain value and maximum softening strain value are calculated using the hardening curve. The estimation of peak stress is done by employing the constitutive Arrhenius hyperbolic equation. Material constants are determined using exponential and power equations.The estimated peak stress compared with the experimental peak stress and good agreement between both the stress value is found.

Microstructural and Textural Investigation of an Mg-Zn-Al-Ca Alloy after Hot Plane Strain Compression.

The formability of magnesium alloys can be significantly improved by Ca as an alloying addition. Compared to conventional alloy sheets such as AZ31, texture modification can be found in rolled Mg-Ca sheets, which reveal a randomized orientation distribution. The hot deformation behavior of a twin-roll cast and homogenized Mg-2Zn-1Al-0.3Ca (ZAX210) alloy was characterized during hot compression at a temperature of 350 °C and strain rates of 0.1 s-1 and 10 s-1. Electron backscatter diffraction (EBSD) analysis was performed in order to describe the microstructural and texture evolution. The ZAX210 alloy exhibits a pronounced dynamic recrystallization (DRX) behavior during compression at high strain rates, while at lower strain rates DRX hardly occurred. This effect can be attributed to different DRX mechanisms that take place as a function of strain rate. At low strain rates, DRX occurred locally at the grain boundaries of the original microstructure, forming a so-called necklace structure. Increasing strain rate results in an increased fraction of recrystallized grains from 18% (0.1 s-1) to 39% (10 s-1). The microstructure revealed that twin boundaries act as nucleation sites for the DRX (TDRX). The recrystallized areas exhibit a weaker texture compared to the deformed microstructure.

Microstructural and textural investigation of an Mg–Dy alloy after hot plane strain compression

Abstract The microstructure and texture development in a Mg–0.41Dy (wt%) alloy after plane strain compression (PSC) at 300 °C under a strain rate of 10−2 and 10−4 s−1 up a final true strain of −1.2 were investigated using electron backscatter diffraction (EBSD) and X-ray diffraction. At high strain rate of 10−2 s−1, the microstructure exhibited massive twins mainly {10 1 ¯ 2} extension, {10 1 ¯ 1} contraction and {10 1 ¯ 3}-{10 1 ¯ 2} double twin due to the random texture of the as-cast alloy. Meanwhile, at a low strain rate of 10−4 s−1, the microstructure was characterized by dynamic recrystallization at the {10 1 ¯ 2} extension, {10 1 ¯ 1} contraction twins and grain boundaries. Twin dynamic recrystallization (TDRX), rotational dynamic recrystallization (RDRX) and discontinuous dynamic recrystallization (DDRX) were the main mechanisms responsible for the formation of recrystallized grains. The texture was characterized by the formation of three fibers: basal , 1 ¯ 0>// CD and 2 ¯ 0> // CD where CD is the compression direction. Moreover, the texture was less sensitive to the deformation conditions since the recrystallized grains showed the same orientation than twins. The changes of the mechanical properties of the alloy were ascribed to the resulting microstructure due to the twinning and dynamic recrystallization.

Dynamic recrystallization behaviour of AlxCoCrFeNi high entropy alloys during high-temperature plane strain compression

AlxCoCrFeNi high entropy alloys (HEAs) with Al molar ratios of 0.3, 0.6 and 0.9 were subjected to hot plane strain compression testing at varying strain rates and strains in the temperature range of 930–1030 °C. A detailed analysis of the flow curves and microstructural evolution of these alloys was conducted under different hot working conditions. Very slow dynamic recrystallization kinetics and a relatively high activation energy of hot deformation (Q=549 kJ/mol) were found for the Al0.3CoCrFeNi FCC HEA. The main restoration mechanism for this alloy was the formation of new grains through strain-induced migration of the grain boundaries. Increasing the Al content to 0.6 and 0.9 molar ratio changed the microstructure to a duplex one comprising of FCC and BCC phases. A complex restoration behaviour was observed for the FCC phase in the duplex structures consisting of discontinuous dynamic recrystallization at the vicinity of the interphases, and a gradual evolution of substructures resembling continuous dynamic recrystallization within the grains in regions far from interphases. The main softening mechanism within the BCC phase in the duplex microstructures was continuous dynamic recrystallization, characterised by a progressive conversion of low-misoriented subgrains into grains bounded by a mixture of low and high angle grain boundaries.

Effect of Zener–Holloman Parameter on the Prior Austenite Grain size in a 12Cr-10Ni Precipitation-Hardenable Stainless Steel

Hot isothermal plane strain compression (PSC) tests were carried out on a 12Cr-10Ni martensitic precipitation-hardenable (PH) stainless steel, in the temperature range of 750-1050 °C, to study microstructural evolution during large strain deformation. The nature of stress–strain curves varies with Zener–Holloman parameter (Z) with specimens deformed at high Z showing steady-state behavior and those deformed at lower Z showing flow softening. Prior austenite grain size (PAGS), d, exhibited a strong correlation to Z showing a bilinear behavior represented as: d = (1803.9)Z−0.094 for high Z deformation and d = (1456.2)Z−0.058 for low Z deformation. Based on the above study, it is recommended to thermomechanically process 12Cr-10Ni steel at Z ≥ 1022 for obtaining products with good strength–toughness balance.

On the evolution and modelling of Cube texture during dynamic recrystallisation of Ni–30Fe–Nb–C model alloy

A combination of electron back–scattering diffraction and visco–plastic self–consistent (VPSC) –based dynamic recrystallisation (DRX) modelling was used to investigate the texture evolution in a Ni–30Fe–Nb–C model alloy subjected to hot plane strain compression to a true strain of 1.2 at temperatures of 925 °C and 1075 °C. Typical of hot rolled face centred cubic materials (in the absence of DRX), deformation at 925 °C led to the development of β–fibre orientations along with a weaker Cube ({001}〈100〉) component. This Cube orientation intensifies and dominates the final texture with the occurrence of DRX during deformation at 1075 °C. The VPSC model successfully predicted the experimental textures at 925 °C (without DRX) and 1075 °C (with DRX), by accounting for non–octahedral {011}〈110〉 slip activity at high temperatures and by using a physically more realistic grain–matrix interaction scheme intermediate between the Taylor and Sachs models. Our simulations show that the dominance of the Cube orientation in the DRX texture at 1075 °C can be ascribed to its higher stored energy and subsequently higher probability of nucleation, combined with its stabilisation due to the activation of non–octahedral {011}〈110〉 slip.

Continuous dynamic recrystallization (CDRX) model for aluminum alloys

The control of a microstructure, during and after hot forming, is crucial to tailor optimum mechanical properties for specific applications. Recrystallization is a key process which may contribute to a great extent to microstructure development. Dynamic recrystallization is becoming an attracting research area to investigate novel hot forming routes in order to maximize the performance of aluminum products while shortening the time required for manufacturing. A continuous dynamic recrystallization (CDRX) mathematical model was developed by Gourdet–Montheillet (GM) to predict the inherent phenomena of an AA1200 alloy. In the present work, the original GM model has been extended and applied to study CDRX in a 5052 aluminum alloy. The proposed model embodies a solid solution and second phase strengthening, through newly estimated kinetic factors and a kinetic constant, respectively, to discern the CDRX behavior of 5052 aluminum alloy compared to AA1200. The latter kinetic constant relies on the Kocks–Mecking–Estrin (KME) theory. The input law of the fraction of high angle boundaries (f HAB), as a function of strain (e) (but independent of temperature and strain rate), is defined as the best fitting function of the experimental data. The results are presented in terms of stress–strain curves, dislocation density, and (sub) grain size, as these are important design parameters from an industrial and engineering viewpoint. The model has been validated successfully, from both a qualitative and quantitative point of view, against various literature data sources and tests (e.g., hot compression, hot plane strain compression, and equal channel angular pressing) pertaining to the 5052 alloy and other similar Al–Mg alloys.

Modeling constitutive relationship of 6013 aluminum alloy during hot plane strain compression based on Kriging method

Hot plane strain compression tests of 6013 aluminum alloy were conducted within the temperature range of 613–773 K and the strain rate range of 0.001–10 s−1. Based on the corrected experimental data with temperature compensation, Kriging method is selected to model the constitutive relationship among flow stress, temperature, strain rate and strain. The predictability and reliability of the constructed Kriging model are evaluated by statistical measures, comparative analysis and leave-one-out cross-validation (LOO-CV). The accuracy of Kriging model is validated by the R-value of 0.999 and the AARE of 0.478%. Meanwhile, its superiority has been demonstrated while comparing with the improved Arrhenius-type model. Furthermore, the generalization capability of Kriging model is identified by LOO-CV with 25 times of testing. It is indicated that Kriging method is competent to develop accurate model for describing the hot deformation behavior and predicting the flow stress even beyond the experimental conditions in hot compression tests.

Global modeling for elevated temperature flow behavior of 6013 aluminum alloy during two-pass deformation

AbstractTwo-pass hot plane strain compression tests of 6013 aluminum alloy were conducted at different temperatures, strain rates, and holding times. Using the experimental data, four popular metamodel types – Kriging, radial basis function, polynomial regression and artificial neural network – were investigated as potential methods for global modeling of the flow behavior during two-pass deformation. The global model developed from the Kriging method was superior in terms of the accuracy and stability of the prediction. Furthermore, this model was successfully used to predict not only the two-pass deformation behavior beyond the experimental conditions, but also the multipass deformation behavior. It is proved that the Kriging method is an effective and reliable approach to develop a global model for optimization of the hot forming process.

Constitutive analysis of 6013 aluminum alloy in hot plane strain compression process considering deformation heating integrated with heat transfer

Hot plane strain compression tests of 6013 aluminum alloy were conducted at temperatures ranging from 613 to 773 K and strain rates ranging from 10-3 to 10 s-1. A novel model is developed to describe the temperature rise considering deformation heating integrated with heat transfer in tests. The experimental flow stress data are corrected by the proposed novel model. Based on the corrected flow stress, the modified power function constitutive model is developed considering the coupled effects of deformation temperature and strain rate on flow stress. Meanwhile, another two widely used models, temperature-compensated power function and straincompensated hyperbolic sine constitutive model, are also established for the studied 6013 aluminum alloy. Finally, the three constitutive models are compared from the aspects of accuracy, stability and efficiency. It is found that the experimental flow stress is significantly affected by the temperature rise. Furthermore, the influence of heat transfer on temperature rise cannot be ignored. When the constitutive model is established, the coupled effects of deformation temperature and strain rate on flow stress should be considered. The modified power function constitutive model is the best one in describing the flow behavior among the three models.

Orientation dependence of the substructure characteristics in a Ni–30Fe austenitic model alloy deformed in hot plane strain compression

The present work examines in detail the substructure and texture characteristics in a Ni–30Fe austenitic model alloy subjected to deformation by plane strain compression (PSC) at temperatures between 700 and 900°C to strains between 0.2 and 1 using a strain rate of 1s−1. The flow curves display characteristics typical of limited dynamic recrystallization. The deformed matrix texture is similar to that expected for rolling/PSC deformation of face-centred cubic metals while the comparatively weaker dynamic recrystallization texture is dominated by the Cube component. The non-Cube deformed matrix grains contain “organized”, self-screening arrays of microbands aligned along the slip planes with high Schmid factors. By contrast, the Cube deformed matrix grains exhibit more “random” cell substructure with a low density of superimposed larger-angle dislocation walls. These walls are related to {111} slip planes at low strains, but tend to follow the rigid body rotation toward the compression plane at large strains.

Microtexture tracking of sub-boundary evolution during hot deformation of aluminium

Abstract The microstructure and microtexture evolution of the same 3 grains around a triple point has been followed during hot plane strain compression by electron backscattered diffraction (EBSD) up to a strain of 1.2. A large grained model alloy of Al–0.1 wt% Mn was deformed in the form of a split sample in channel die compression at 400 °C by 3 repeated cycles, each involving EBSD grain orientation mapping, hot deformation and quenching. Detailed substructure maps of 3 grains on an inner surface demonstrates that their dislocation substructure develops up to a strain of about 0.5 then stabilises at approximately constant size, disorientation distribution and boundary alignment. The results are consistent with the repolygonisation model of steady state sub-boundary creation and dissolution during hot deformation.

Mapping microstructure inhomogeneity using electron backscatter diffraction in 316L stainless steel subjected to hot plane strain compression tests

The microstructure inhomogeneity in 316L stainless steel subjected to hot plane strain compression tests has been assessed using electron backscatter diffraction (EBSD). Two variables were investigated: the effect of strain rate and the effect of friction at the tool/specimen interface. Tests were performed isothermally at 950°C at nominal equivalent tensile strain rates of 0·01 and 1 s−1. Low and high friction conditions have been simulated by applying both a glass based lubricant and a boron nitride spray respectively. Results suggest that friction causes a variation in microstructure from the surface to the midplane of the deformed specimen. Several methods used to quantify and represent this inhomogeneity are presented in the present paper. Electron backscatter diffraction measurement issues are discussed. A grain size mapping method using a two-dimensional moving average has been developed to overcome the difficulties associated with the visualisation of measurement results over large areas on EBSD maps. It has proved to be a powerful tool for the spatial statistics of large quantity data obtained by EBSD.

Microtexture tracking in hot-deformed polycrystalline aluminium: Comparison with simulations

The average rotations of 157 individual grains measured in an Al–0.1%Mn polycrystal deformed in hot plane-strain compression to a strain of 1.2 have been compared to the predictions from several crystal plasticity models. The Taylor model successfully predicts the distributions of the rotation angles, but overestimates the rate of evolution of the rotation axes, which explains the overestimation of the final texture. The model also provides a first-order agreement for the rotation axes and the final components of the individual grains. The discrepancies are related to the influence of grain interaction. The main mechanisms of texture development at the level of the individual grains are identified through an analysis of their orientation trajectories. The introduction of local grain interactions, which produce a rotation variability at constant orientation, is shown to weaken texture development.

Behaviour of oxide scales in hot steel strip rolling

The behaviour of oxide scales in the finishing Hot Strip Mill is simulated by the hot Plane Strain Compression Test (PSCT). Compared with the ideal case of homogeneous plastic co-deformation of the oxide layer and the underlying metal, different types of defects are described: delamination at the interface or within the oxide layer; interfacial plastic instability due to the jump of the mechanical properties; perpendicular, through-thickness cracks where the axial strain parallel to the interface dominates, followed by micro-extrusion of metal between the fragments; oblique cracks followed by sliding along the lips, where shear dominates. The Finite Element Method (FEM) is used to bring elements of interpretation, as to which conditions determine each mechanism. Conclusions for the behaviour in hot rolling are sketched.

Modeling the Flow Behavior, Recrystallization, and Crystallographic Texture in Hot-Deformed Fe-30 Wt Pct Ni Austenite

The present work describes a hybrid modeling approach developed for predicting the flow behavior, recrystallization characteristics, and crystallographic texture evolution in a Fe-30 wt pct Ni austenitic model alloy subjected to hot plane strain compression. A series of compression tests were performed at temperatures between 850 °C and 1050 °C and strain rates between 0.1 and 10 s−1. The evolution of grain structure, crystallographic texture, and dislocation substructure was characterized in detail for a deformation temperature of 950 °C and strain rates of 0.1 and 10 s−1, using electron backscatter diffraction and transmission electron microscopy. The hybrid modeling method utilizes a combination of empirical, physically-based, and neuro-fuzzy models. The flow stress is described as a function of the applied variables of strain rate and temperature using an empirical model. The recrystallization behavior is predicted from the measured microstructural state variables of internal dislocation density, subgrain size, and misorientation between subgrains using a physically-based model. The texture evolution is modeled using artificial neural networks.

The microstructures of polycrystalline Al–0.1Mg after hot plane strain compression

The microstructures of Al–0.1Mg polycrystals deformed in plane strain compression at temperatures of 20–400 °C have been investigated by electron backscatter diffraction. At all temperatures, the microstructures are characterized by two types of banded substructure, primary bands of aligned low angle boundaries whose alignment to the rolling plane is a function of strain and temperature, and secondary bands which develop into grain-scale shear bands with increasing strain. Several aspects of the deformation microstructures, including the orientation dependence of subgrain parameters and the inhomogeneity of the microstructure, differ from those of single crystals of similar orientation, and this it attributed to local grain interactions.

Modelling hot plane strain compression test Part 3 – Effect of asymmetric conditions

Finite element analysis has been used to study possible causes of asymmetrical deformation in plane strain compression tests and their consequences. It is shown that U shaped or Z shaped distortion of the specimens can arise from temperature gradients, lateral offset of the tools and non-uniform lubrication, which causes different coefficients of friction at the top and bottom tools, or a changing coefficient of friction across the width of the tools. When the tools are rigid, the stress–strain curves are the same as for specimens deformed symmetrically under the same mean, but uniform conditions. With changing friction conditions across the width of the tools, the lateral load generated can be sufficiently large to cause lateral displacement of the tools in experimental practice. Computation with the top tool free to rotate leads to severe asymmetry and a small reduction in the level of the stress–strain curve.