Modeling of high-temperature deformation of commercial pure aluminum (1050)

The high-temperature deformation of commercial pure aluminum (Al) (1050) was investigated by performing tensile tests in the temperature range of 473–673 K at initial strain rates of 0.01–0.2 s⁻¹. The tests were carried out to derive constitutive equations capable of describing the flow stress of the material in terms of the strain, strain rate, activation energy, and finally, the deformation temperature. The present experimental results reveal that the temperature range could be divided into two regimes based on the change of the stress exponent and the activation energy with temperature of deformation. The constitutive equations are derived using a regression technique. Good correlation has been obtained between the experimental values of the flow stress and those predicted using the derived constitutive equations.     

Effect of Nb particles on the flow behavior of TiAl alloy

High temperature compressive deformation behaviors of PM-TiAl alloy containing Nb particles (Ti–45Al–5Nb–0.4W/2Nb (at. %)) were investigated at temperatures ranging from 1050 °C to 1200 °C, and strain rates from 0.001 s⁻¹ to 1 s⁻¹. The flow curves were employed to develop constitutive equations, and the apparent activation energy of deformation Q was determined as 447.35 kJ/mol. A revised processing map was constructed on the basis of the flow stress, which can accurately describe the deformation behaviors and predict the optimum hot forging condition. The addition of 2% Nb particles reduces the peak stress and increases the activation energy of TiAl-based intermetallic, however, it increases the instable domain in the processing map.     

High-temperature deformation behavior and processing map of 7050 aluminum alloy re]20101008

The high-temperature deformation behavior and processing map of 7050 aluminum alloy were investigated by tensile tests conducted at various temperatures (340, 380, 420, and 460 °C) with various strain rates of 10⁻⁴, 10⁻³, 10⁻², and 0.1 s⁻¹. The results show that the instability region with a peak power dissipation efficiency of 100 % occurs at the low deformation temperature region of 340 °C to 380 °C and high strain rates (>10⁻³ s⁻¹). The 7050 aluminum alloy exhibited a continuous dynamic recrystallization domain with power dissipation efficiency of 35% to 60 % in the deformation temperature range of 410 °C to 460 °C and the strain rate range of 10⁻⁴–10⁻³ s⁻¹. The domain with a power dissipation efficiency of 35 % to 50 % occurring at high deformation temperatures and strain rates was interpreted to represent dynamic recovery. Dynamic recovery and continuous dynamic recrystallization provide chosen domains for excellent hot workability.     

The Effect of Deformation Heating on Restoration and Constitutive Equation of a Wrought Equi-Atomic NiTi Alloy

In this study, a set of constitutive equation corrected for deformation heating is proposed for a near equi-atomic NiTi shape memory alloy using isothermal hot compression tests in temperature range of 700 to 1000 °C and strain rate of 0.001 to 1 s⁻¹. In order to determine the temperature rise due to deformation heating, Abaqus simulation was employed and varied thermal properties were considered in the simulation. The results of hot compression tests showed that at low pre-set temperatures and high strain rates the flow curves exhibit a softening, while after correction of deformation heating the softening is vanished. Using the corrected flow curves, the power-law constitutive equation of the alloy was established and the variation of constitutive constants with strain was determined. Moreover, it was found that deformation heating introduces an average relative error of about 9.5% at temperature of 800 °C and strain rate of 0.1 s⁻¹. The very good agreement between the fitted flow stress (by constitutive equation) and the measured ones indicates the accuracy of the constitutive equation in analyzing the hot deformation behavior of equi-atomic NiTi alloy.     

Deformation behavior of TC6 alloy in isothermal forging

Isothermal compression of the TC6 alloy was carried out in a Thermecmaster-Z (Wuhan Iron and Steel Corporation, P.R. China) simulator at deformation temperatures of 800∼1040 °C, strain rates of 0.001∼50.0 s⁻¹, and maximum height reduction of 50%. The deformation behavior of the TC6 alloy in isothermal forging was characterized based on stress-strain behavior and kinetic analysis. The activation energy of deformation obtained in the isothermal forging of the TC6 alloy was 267.49 kJ/mol in the β phase region and 472.76 kJ/mol in the α+β phase region. The processing map was constructed based on the dynamic materials model, and the optimal deformation parameters were obtained. Constitutive equations describing the flow stress as a function of strain rate, strain, and deformation temperature were proposed for the isothermal forging of the TC6 alloy, and a good agreement between the predicted and experimental stress-strain curves was achieved.     

A study of the strain rate microstructural response and wear of metals

Titanium (Ti) and copper (Cu) pins were slid against alumina in a pin-on-disk machine at a load of 50 N and sliding speeds varying from 0.1 to 4 ms⁻¹. The evolution of the microstructure in the subsurface of the material and the wear rate was co-related to the strain rate microstructural response of the material in uniaxial compression, at different strain rates (0.1–100 s⁻¹) and temperatures (298–673 K). The strain rates and temperatures in the plastically deforming zone near the surface of the pins were determined using noniterative methods. The strain rates were found to be in the region of 100 s⁻¹ near the surface and decreases as one moves into the sub-surface of the pin. The temperatures increased as the speed increased. These estimated strain rates and temperatures were superimposed on the strain rate microstructural response maps of these materials. The uniaxial compression test results of Ti showed adiabatic shear banding as a microstructural mechanism that evolves at high strain rates (≥10 s⁻¹) and lower temperatures (<575 K). Adiabatic shear bands are sites of easy crack nucleation and propagation. When Ti is slid at low speeds the near surface region of the pins deform in the adiabatic shear banding regions in the strain rate microstructural response map. At such speeds the wear rate is found to be high and reduces as the sliding speed is increased, when the material undergoes a more homogeneous deformation. The microstructural response of Cu under uniaxial compression showed that the material undergoes flow banding at intermediate strain rates (1 s⁻¹) and temperatures of up to 473 K. The subsurface microstructure of the pins slid at low speeds showed subsurface cracking and sheet like debris formation. This happen at lower speeds because the flow banding and crack nucleation is expected in the subsurface where the strain rates and temperatures are lower. The present test results show a clear relation to exist between the strain rate response of the material in uniaxial compression and its subsurface microstructural evolution and wear rate.     

The hot formability of an Al-Cu-Mg-Fe-Ni forging disk

The high temperature formability of AA2618-T61 forged disk was studied by means of tensile test over temperatures and strain rates ranging from 100 to 400°C and 3 × 10⁻⁵ −3 × 10⁻³ s⁻¹, respectively. The constitutive equations of the material were calculated based on an Arrhenius-type equation and the ductility of the material was evaluated considering elongation and percent reduction of area. The results showed that both kinds of softening mechanisms, dynamic recovery and dynamic recrystallization, occurred during high temperature deformation of the alloy. Strain rate sensitivity of the material was evaluated in all the deformation conditions and the obtained values were used to calculate the apparent activation energy.     

Development of high strain rate equations for stainless steels

The dynamic response of four types of stainless steel sheet was investigated at different strain rates from 10⁻² up to 10³ s⁻¹. The results from the tensile tests were used to evaluate the parameters in three different multiplicative strain rate equations of the type used in crashworthiness calculations. A new type of sigmoid constitutive equation is proposed for one grade of stainless steel.     

Study on the Hot Workability of SiCp/Al Composites Based on a Critical Strain Map

We used the isothermal compression test (conducted in a Gleeble-3500 system) to study the hot deformation behaviors of SiCp/Al composites over a wide range of temperatures (623-773 K) and strain rates (0.001-10 s^?1). A 3D hot-processing map was constructed based on the Malas stability criteria and experimental data. An artificial neural network model of four hot work quality characteristic parameters (strain rate sensitivity m, its derivative m′, temperature sensitivity s, and its derivative s′) were established. A new hot-processing map, known as a hot-processing critical strain map, has been proposed based on the smallest strain prior to instability. Two optimized processing regions at 623-660 K, 0.05-0.075 s^?1 and 720-773 K, 0.04-0.18 s^?1 were determined based on this map.     

Hot deformation mechanisms in Ti-5.5Al-1Fe alloy

The mechanisms of hot deformation in the alloy Ti-5.5Al-1Fe have been studied in the temperature range 750 to 1150 °C and with the true strain rate varying from 0.001 to 100 s⁻¹ by means of isothermal compression tests. At temperatures below β transus and low strain rates, the alloy exhibited steady-state flow behavior, while, at high strain rates, either continuous flow softening or work hardening followed by flow softening was observed. In the β region, the deformation behavior is characterized by steady-state behavior at low strain rates, yield drops at intermediate strain rates, and oscillations at high strain rates. The processing maps revealed two domains. (1) In the temperature range 750 to 1050 °C and at strain rates lower than 0.01 s⁻¹, the material exhibits fine-grained superplasticity. The apparent activation energy for superplastic deformation is estimated to be about 328 kJ/mole. The optimum conditions for superplasticity are 825 °C and 0.001 s⁻¹. (2) In the β region, a domain occurs at temperatures above 1100 °C and at strain rates from 0.001 to 0.1 s⁻¹ with its peak efficiency of 47% occurring at 1150 °C and 0.01 s¹. On the basis of kinetic analysis, tensile ductility, and grain size variation, this domain is interpreted to represent dynamic recrystallization (DRX) of β phase. The apparent activation energy for DRX is estimated to be 238 kJ/mole. The grain size (d) is linearly dependent on the Zener-Hollomon parameter (Z) per the equation

Deformation Behavior of AZ31 Magnesium Alloy During Tension at Moderate Temperatures

The mechanical properties and deformation mechanisms have been studied by tension testing at temperatures between 373 and 523 K and at strain rates ranging from 10⁻¹ to 10⁻³ s⁻¹. The experimental results show that the plasticity improves significantly with temperature and decreases obviously with increasing strain rate. When the temperature is below the recrystallization temperature, twinning and dislocation slip have been proven to be the dominant model of plastic deformation. With the temperature increasing, some DRXed grains can be observed at the twinned regions and grain boundaries, suggesting that both twinning-induced DRX and continuous DRX occurred in the deformation process.     

Mechanical analysis of woven composites at high strain rates and its application to predicting impact behavior

The deformation behavior of woven composites at high strain rates was analyzed using a constitutive equation developed to describe the nonlinear, anisotropic/asymmetric and rate-dependent mechanical behavior of woven composites. The rate-dependent nonlinear behavior of woven composites was characterized at high strain rates (1 s⁻¹ to 100 s⁻¹) using a tensile testing method first proposed in this research. The material properties for the developed constitutive equation were determined and subsequently used in a finite element analysis of the deformation behavior of woven composites at high strain rates. Finally, the impact behavior of woven composites was predicted using the constitutive equation and the results were compared with experiments, showing that the current constitutive equation including the characterization method is adequate to describe the deformation behavior of woven composites at high strain rates up to impact level.     

Development of Processing Map for 7075 Al/20% SiCp Composite

The hot deformation behavior and microstructure evolution of 7075 Al/20% SiC_p composite have been studied using the processing map. Compression tests were carried out in the temperature range of 300-500 °C and at the strain rate range of 0.001-1.0 s⁻¹. The stable and unstable regions in the map were verified with the microstructural observations of the deformed compression specimens. The “stable” regions, i.e., dynamic recrystallization and “unstable” regions such as debonding of SiC particles, matrix crack, and adiabatic shear band formation were identified from the processing map and compared with the reported microstructural observations of the deformed compression specimens. The optimum hot working conditions for this composite were identified.     

Superplastic Behavior of Al-4.5Mg-0.46Mn-0.44Sc Alloy Sheet Produced by a Conventional Rolling Process

This article describes the superplastic behavior of the Al-4.5Mg-0.46Mn-0.44Sc alloy. The investigated alloy was produced by casting and was conventionally processed to form a sheet with a thickness of 1.9 mm and an average grain size of 11 μm. The superplastic properties of the alloy were investigated using a uniaxial tensile testing with a constant cross-head speed and with a constant strain rate in the range 1 × 10⁻⁴ to 5 × 10⁻² s⁻¹ at temperatures from 390 to 550 °C. The investigations included determinations of the true-stress, true-strain characteristics, the maximum elongations to failure, the strain-rate sensitivity index m, and the microstructure of the alloy. The m-values determined with the strain-rate jump test varied from 0.35 to 0.70 in the temperature interval from 390 to 550°C and strain rates up to 2 × 10⁻² s⁻¹. The m-values decreased with increased strain during pulling. The elongations to failure were in accordance with the m-values. They increased with the temperature and were over 1000%, up to 1 × 10⁻³ s⁻¹ at 480 °C and up to 1 × 10⁻² s⁻¹ at 550 °C. A maximum elongation of 1969% was achieved at an initial strain rate of 5 × 10⁻³ s⁻¹ and 550 °C. The results show that the addition of about 0.4 wt.% of Sc to the standard Al-Mg-Mn alloy, fabricated by a conventional manufacturing route, including hot and cold rolling with subsequent recrystallization annealing, results in good superplastic ductility.     

Characterization of hot deformation behavior of as-forged TiAl alloy

The deformation behavior of as-forged Ti–43Al–9V–Y alloy was investigated by hot compression tests in the temperature range of 1100–1225 °C and strain rate range of 0.01–0.5 s⁻¹. The results show that the alloy exhibits negative temperature sensitivity and positive strain rate sensitivity. The stress exponent (n = 3.02) and the apparent activation energy (Q = 342.27 kJ/mol) of the present alloy are lower than that of previous reported TiAl alloys, which suggests that the as-forged Ti–43Al–9V–Y alloy exhibits better deformability at low temperatures and high strain rates. A processing map for hot working was developed on the basis of a dynamic material model. The deformation mechanisms were analyzed by the processing map. The optimum processing condition at the strain of 0.6 is 1180–1210 °C/0.01–0.05 s⁻¹. A crack-free Ti–43Al–9V–Y sheet was prepared by hot rolling at these optimized parameters. EBSD results show that dynamic recrystallization is more likely to occur for γ phase.     

Study on high strain rate superplasticity of A 6061Al alloy composite reinforced with 30 Vol.% AlN particulate

An investigation on the superplastic behavior of 30 vol.% AlNp/6061Al composite prepared by powder metallurgy (PM) techniques was carried out. Superplastic tensile tests of the composite were performed at strain rates ranging from 10° to 10⁻³ s⁻¹ and at temperatures from 823 to 893 K. A fine-grained structure prior to superplastic testing was obtained by hot rolling after extrusion. The highest total elongation to failure of 438% was achieved at a temperature of 863 K and at an initial strain rate of 1.67×10⁻¹ s⁻¹ and the highest value of the strain rate sensitivity index (m) was 0.42 for the composite. Differential thermal analysis (DTA) was used to investigate the possibility of any partial melting in the vicinity of optimum superplastic temperatures. The formation of a liquid phase is attributed to the melting of the Al-Si eutectic phase at the surface of the AlN particulates at elevated temperatures, as determined by electron probe microanalysis (EPMA). The influence of the microstructure and the fracture behavior on the superplastic behavior of the composite was studied by transmission electronic microscopy (TEM) and scanning electron microscopy (SEM). A large number of matrix filaments were present at the fracture surfaces of the specimens when superplastic deformation of the composite was performed under the optimum superplastic test conditions. The presence of dislocations and fine recrystallized grains in the test specimens suggested that they play an important role in the high-strain-rate superplasticity for this composite.     

Superplastic-like behavior of Al-high Si alloys produced from rapidly solidified powders and ribbons

The high temperature tensile properties of hyper-eutectic Al-Si alloys were studied at temperatures between 683 and 813 K at initial strain rates between 8.3X10⁻⁴ and 4.2X10⁻¹s⁻¹. The alloys were prepared from prealloyed powders and ribbons, which were respectively fabricated by the centrifugal atomization and melt spinning, through the hot extrusion process at an extrusion ratio of 110:1. The extruded alloy bars prepared from the powders and ribbons, i.e. the powder-extruded and ribbon-extruded bars, have homogenous micro-structures with the fine silicon particles dispersed in the aluminum matrices for the Al-25Si and Al-15Si alloys. The maximum elongation-to-failure of the powder-extruded bar and the ribbon-bar are almost equal, 150%, for the Al-25Si alloy, In the Al-15Si alloy, the ribbon-extruded bar has superior elongation compared to the powder-extruded bar, that is, these are respectively 520% and 400%. The maximum elongation was attained at the relatively high strain rate of 10⁻²s⁻¹ independent of the silicon content and solidification process.     

High temperature deformation behavior of Ti−6Al−4V alloy with and equiaxed microstructure: a neural networks analysis

The hot deformation behavior of Ti−6Al−4V alloy with an equiaxed microstructure was investigated by means of Artificial Neural Networks (ANN). The flow stress data for the ANN model training was obtained from compression tests performed on a thermo-mechanical simulator over a wide range of temperature (from 700°C to 1100°C) with strain rates of 0.0001 s⁻¹ to 100 s⁻¹ and true strains of 0.1 to 0.6. It was found that the trained neural network could reliably predict flow stress for unseen data. Workability was evaluated by means of processing maps with respect to strain, strain rate, and temperature. Processing maps were constructed at different strains by utilizing the flow stress predicted by the model at finer intervals of strain rates and temperatures. The specimen failures at various instances were predicted and confirmed by experiments. The results establish that artificial neural networks can be effectively used for generating a more reliable processing map for industrial applications. A graphical user interface was designed for ease of use of the model.     

Constitutive relationship of IN690 superalloy by using uniaxial compression tests

The hot deformation behavior of IN690 superalloy was characterized in a temperature range of 1273-1473 K and a strain rate range of 0.01-10 s-1 using uniaxial compression tests on process annealed material.The constitutive relations between flow stress and effective strain,effective strain rate as well as deformation temperature were studied.It can be concluded that the flow stress significantly reduces with the deformation temperature of IN690 superalloy increasing.Whereas,there is a significant increase of flow stress when the strain rate increases from 0.1 s-1 to 10 s-1.Based on the hyperbolic-sine Arrhenius-type equation,a constitutive equation considering compensation of strain was developed.The activation energy and the material constants(Q,n and ln A) decrease as the deformation strain increases.The strain dependent term is successfully incorporated in the constitutive equation through a quartic equation.A good agreement between the experimental data and the predicted results has been achieved,indicating that the proposed constitutive equation and the methods of determing the material constants are suitable to model the high temperature deformation behavior of IN690 superalloy.     

Upper bound analysis of deformation and dynamic ageing behavior in elevated temperature equal channel angular pressing of Al-Mg-Si alloys

In the present study, the plastic deformation and dynamic strain ageing behavior of Al-6082 (Al-Mg-Si) alloy treated with elevated temperature equal channel angular pressing (ECAP) were investigated using upper bound analyses. Tensile tests were carried out over wide ranges of temperature and strain rate in order to evaluate the dynamic ageing conditions. ECAP processing was then experimentally performed at temperatures from room temperature up to 200 °C under various strain rates ranging between 10⁻⁴s⁻¹ and 10⁻¹s⁻¹. The upper bound analysis solutions and the experimental results are comparable. A theoretical dynamic ageing region was found to be in the temperature range of 90 °C to 260 °C, which is in agreement with the experimental observations in the temperature range of 75 °C to 175 °C.