Thin shear boundary layers in flow of hot aluminium

2020

In the extrusion of clad composite materials with different flow stresses are usually used. This causes an inhomogeneous material flow which can induce sleeve or core fracture. In the present study, the material flow during indirect extrusion of copper-clad aluminum (CCA) rods was analyzed by means of experimental and numerical investigations throughout the process. In order to provide material models for the numerical analysis hot compression tests of the aluminum alloy EN AW-1080A and the copper alloy CW004A were carried out. The indirect extrusion was performed using a conical die with a semi die angle of 45° and an extrusion ratio of 14.8:1. The container was heated to 330°C, while billet, die, and ram were kept at room temperature. The extrusion trial was then modeled with the FEM based software DEFORM 2D. Cross sections were taken from the extruded rod and compared to the corresponding sections of the simulation with regard to the development of the equivalent copper cross sec...

Metallurgical Transactions B Process Metallurgy, 1987

This paper deals with an investigation into the flow of aluminum powder billet during hot extrusion at low reduction ratios through square edge die under axisymmetric conditions. Analytical studies using the finite element method as well as the experimental observations are reported for various low reduction ratios ranging from 1.3:1 to 3.2:1 at extrusion temperatures, 300, 400, and 500 °C; friction effects have also been included. Extrusion pressures, velocity vectors, average pressure contours, and effective strain-rate contours are obtained using a velocity-pressure relationship. Analytical extrusion pressures agree quite well with experimental values. Metallographic investigations of the longitudinal section of partially extruded billets reveal very clearly the flow of the material in the different regions, viz., inside the container, near the die and the extruded portion, and are correlated with analytical results.

Mechanics Research Communications, 2009

In this research, the plastic flow behavior of Al-6%Mg alloy was studied by analyzing the results of hot compression tests in a range of temperature and strain rate. Then, an artificial neural network (ANN) model was trained at which the temperature, strain-rate, and strain parameters were used as the input layer and the flow stress as the output. The comparison of the predicted and experimental results of stress-strain curve proved the prediction capability of the ANN model.

Metals

Stress-strain curves of the EN AW 6082 aluminium alloy with 1.2 Si-0.51 Mg-0.75 Mn (wt.%) were determined by the uniaxial compression tests at temperatures of 450–550 °C with a strain rate of 0.5–10 s−1. The initial structure state corresponded to three processing types: as-cast structure non-homogenized or homogenized at 500 °C, and the structure after homogenization and hot extrusion. Significantly higher flow stress appeared as a result of low temperature forming of the non-homogenized material. Hot deformation activation energy Q-values varied between 99 and 122 kJ·mol−1 for both homogenized materials and from 200 to 216 kJ·mol−1 for the as-cast state, while the Q-values calculated from the measured steady-state stress were always higher than those calculated from the peak stress values. For the extruded state of the 6082 alloy, the physically-based model was developed to reliably predict the flow stress influenced by dynamic softening, temperature, strain rate, and true strain ...

Metallurgical and Materials Transactions A, 2005

A thoroughly tested, high-temperature channel-die compression (CDC) rig is described for simulating hot plane strain compression of metallic alloys up to 500 °C. The equipment is currently used to characterize the flow stress and microstructure evolution in hot-rolled Al alloys. It has been validated by several tests involving (1) metallographic analysis of deformed samples; (2) flow stress comparisons with the same, or similar alloys deformed in conventional uniaxial or plane strain compression; and (3) microstructure and texture measurements. The use of modern lubricants enables one to obtain accurate flow stresses and true plane strain deformations that are homogeneous over 80 pct of the sample. The equipment also features rapid heating and cooling systems to minimize thermallyinduced microstructure changes. Some results on high-temperature slip systems, hot deformation textures, and microstructures, and the behavior of constituent particles are outlined to illustrate the advantages of the technique.

Journal of Materials Engineering and Performance, 2014

In order to study flow stress behavior for hot working of a typical Al-Zn-Mg-Cu alloy, experimental stressstrain data obtained from isothermal hot compression tests at strain rates of 0.004, 0.04, and 0.4 s 21 and deformation temperatures of 400, 450, 500, and 520°C were used to develop the constitutive equation. The peak stress decreased with increasing deformation temperature and decreasing strain rate. The effects of temperature and strain rate on deformation behavior were represented by Zener-Hollomon parameter in an exponent-type equation. Employing an Arrhenius-type constitutive equation, the influence of strain has been incorporated by considering the related material constants as functions of strain. The accuracy of the developed constitutive equations has been evaluated using standard statistical parameters such as correlation coefficient and average absolute relative error. The results indicate that the proposed straindependent constitutive equation gives an accurate and precise estimate of the flow stress in the relevant temperature range.

Key Engineering Materials, 2011

In this work a numerical method for the simulation of extrusion processes with modeling of microstructure is presented. Extensive testing was done to provide a basis for the verification of simulation results. Circular rods of AA6005A were extruded by backward and forward extrusion with different extrusion ratios, billet temperatures and product velocities. The extruded rods were cooled either by water or at air to distinguish between dynamic and static recrystallization. Temperature and strain-rate dependent yield stresses were determined from hot compression tests. Special friction tests on cylindrical specimens under high hydrostatic stresses at high temperatures have been performed and the parameters of a friction model were identified from the experiments. The recrystallized volume fraction and grain sizes in the extruded rods were analyzed by means of optical micrographs. The obtained results were used to determine the parameters of a recrystallization model which was implemen...

Materials Science and Engineering: A, 2011

The present investigation has been conducted in order to develop a rational approach able to describe the changes in flow stress of AA7075-T6 aluminum alloy with deformation temperature and strain rate, when this material is deformed at temperatures in the range of 123-298 K at strain rates in the range of 4 × 10 −4 to 5 × 10 −2 s −1 . The constitutive formulation that has been advanced to accomplish these objectives represents a simplified form of the mechanical threshold stress (flow stress at 0 K) model developed at Los Alamos National Laboratory (Los Alamos, New Mexico, USA). Thus, it is assumed that the current flow stress of the material arises from both athermal and thermal barriers to dislocation motion. In the present case, the effect of three thermal barriers has been considered: solid solution, precipitation hardening and work-hardening. The first two effects do not evolve during plastic deformation, whereas the last one is considered as an evolutionary component of the flow stress. Such an evolution is described by means of the hardening law earlier advanced by [20]. The law is implemented in differential form and is integrated numerically in order to update the changes in strain rate that occur during tensile tests carried out both at constant and variable crosshead speed. The extrapolation of the hardening components from 0 K to finite temperatures is accomplished by means of the model earlier advanced by Kocks (1976) [19]. The results illustrate that the constitutive formulation developed in this way is able to describe quite accurately both the flow stress and work-hardening rate of the material, as well as temperature and strain rate history effects that are present when deformation conditions change in the course of plastic deformation. The evaluation of the ductility of the alloy indicates that the changes in this property are mainly determined by deformation temperature rather by strain rate. When deformation temperature decreases from 298 to 123 K, ductility also decreases from ∼35 to 24%. However, despite these relatively small variations, significant changes in the fracture morphology could be observed on the fracture surfaces of the examined specimens, with the predominance of a mixed ductile-brittle mechanism at lower temperatures.

2010

In industrial practice of hot forging, i.e. extrusion-type forging, abrupt changes in strain rate during the deformation of the material occur. For accurate numerical simulation of a forging process, the experimental investigation of the effect of the transient change in strain rate on plastic flow behaviour is necessary. The present paper deals with the investigation of this effect on the flow stress of an Al-Zn-Mg-Cu alloy during its deformation at 450 °C. During continuous uniaxial compression loading of a cylindrical specimen, the strain rate was abruptly increased or decreased from its initial value at engineering strain of ∼26 %. From the beginning of the upsetting up to the strain of ∼26 % the value of the strain rate was constant and equal to either 1 s -1 or 10 s -1 . At the strain of ∼26 % the value of the strain rate was either increased to 10 s -1 or decreased to 1 s -1 . The results of the experimental investigations were used to determine the isothermal flow stress-strain curves of the Al-Zn-Mg-Cu alloy. On the basis of these curves, the strain rate sensitivity index m as a function of true strain as well as temperature was determined.

2008

for introducing the present topic and for his inspiring guidance, constructive criticism and valuable suggestion throughout this project work. We would like to express our gratitude to Dr.K.C.Patra (Head of the Department), for his valuable suggestions and encouragements at various stages of the work. We are also thankful to all the staff in Department of Civil Engineering for providing all joyful environments in the lab and helping us out in different ways. Last but not least, our sincere thanks to all our friends who have patiently extended all sorts of help for accomplishing this undertaking.