Severe Plastic Deformation Process Research Articles

Preparation of high performance 5083 aluminum alloy by alternate ring-groove pressing and torsion

A preparation process of high performance 5083 aluminum alloy sheet was proposed. The process is severe plastic deformation process of alternate ring-groove pressing and torsion based on cyclic stress state under warm conditions. The results show that when the temperature is 200 °C, the grain refinement effect after secondary deformation is the best, and the average grain size is refined from 24 to 12.5 μm. When the temperature is 300 °C, the mechanical properties of the sheet after one deformation are the best. Compared with those of the original sheet, the tensile strength (397 MPa) and breaking elongation (28.3%) are increased by 30% and 60%, respectively. The second phase particles and recrystallized grains improve the strength of the material by second phase strengthening and fine grain strengthening. The equiaxed recrystallized grains improve the plasticity and toughness of the material.

Compared microstructure and properties of an AlZnMgCu alloy processed by high pressure sliding and high-pressure torsion

Achieving high yield strength via submicrometer grain size and nanoscaled precipitation has been reached in 7### aluminum alloys thanks to severe plastic deformation (SPD) by High Pressure Torsion (HPT) process. Unfortunately, this technique has inherently strong limitations since only small parts can be processed and the plastic strain is not homogeneous. These limitations prevent large scale production of Ultra Fine Grain (UFG) materials for potential applications. A recent severe plastic deformation process, High Pressure Sliding (HPS) developed by Fujioka and Horita, allows to homogeneously deform large scale sheets by shear at higher speed. In this work, the competition between precipitation, grain growth and recrystallization during heat treatments after SPD was studied in depth for an AlZnMgCu alloys deformed by HPS with two deformation levels (γ ≈ 15 and γ ≈ 20) in order to investigate if the high mechanical properties obtained by HPT can be reached by HPS. Microstructures analyses after deformation and ageing were carried out by transmission electron microscopy and in situ small angle X ray scattering and then related to the mechanical behavior evaluated by tensile tests. Experimental data show very similar microstructures after HPS and HPT, with a good thermal stability thanks to the competition between precipitation, recrystallization and recovery. The obtained microstructural features lead to exceptional yield strength (>800 MPa) as compared to the classical aluminum alloys. This study is therefore very promising towards the aim of obtaining very high yield strength aluminum alloys suitable for applications.

Titanium-protein nanocomposites as new biomaterials produced by high-pressure torsion

The development of new biomaterials with outstanding mechanical properties and high biocompatibility has been a significant challenge in the last decades. Nanocrystalline metals have provided new opportunities in producing high-strength biomaterials, but the biocompatibility of these nanometals needs to be improved. In this study, we introduce metal-protein nanocomposites as high-strength biomaterials with superior biocompatibility. Small proportions of bovine serum albumin (2 and 5 vol%), an abundant protein in the mammalian body, are added to titanium, and two nanocomposites are synthesized using a severe plastic deformation process of high-pressure torsion. These new biomaterials show not only a high hardness similar to nanocrystalline pure titanium but also exhibit better biocompatibility (including cellular metabolic activity, cell cycle parameters and DNA fragmentation profile) compared to nano-titanium. These results introduce a pathway to design new biocompatible composites by employing compounds from the human body.

Achievement of high strength and good ductility in the large-size AZ80 Mg alloy using a designed multi-directional forging process and aging treatment

Most high-performance Mg alloy samples obtained by severe plastic deformation processes are difficult to implement in industrial utilization due to their small size. The strength of large samples developed using the multi-directional forging (MDF) process is significantly lower than that of small samples. This work developed a large commercial AZ80 alloy sample with dimensions of 100 × 100 × 140 mm3 using a two-step MDF process and artificial aging. The designed process is different from the reported MDF and aging processes. The T5 treated sample exhibits uniform mechanical properties with the ultimate tensile strength of 430 MPa (Engineering stress) and elongation to failure of 11.4%, reaching the level of wrought Mg-RE alloys. MDF at elevated temperatures improves the plasticity of the sample resulting in a good forgeability at 180 °C. The high density defects introduced by the MDF process include grain boundaries, dislocations and stacking faults (SFs) that accelerate the subsequent aging response. The good strength-ductility synergy is attributed to the simultaneous effect of an overall bimodal microstructure composed of fine grains and coarse grains, nanoscale β-Mg17Al12 precipitates, and a high density of dislocations and SFs. The designed process can benefit the general community of Mg alloys since the excellent mechanical properties do not rely on the strengthening mechanism due to the addition of specific elements. This work provides an effective way to develop large-size Mg alloy billets applied to load-bearing components.

Equal channel angular extrusion (ECAE): Die design, affecting variables and development of mechanical behavior and properties of bio-metals

There are numerous practices for producing nanocrystalline (NC) and ultrafine-grained (UFG) metals, composites, polymers and alloys; amongst which Equal Channel Angular Extrusion (ECAE) is one of the renowned techniques in metal forming processes under the severe plastic deformation process (SPD) in which a massive plastic strain is enforced on a bulk material. The novelty of this work is the design and fabrication of a split type of die specifically for carrying out ECAE on difficult-to-deform bio-metals. The die is designed for a channel angle of 120°. The study provides a detailed discussion of the pre and post-extrusion tests, process flowchart, and operational variables. This work offers a valuable opportunity to investigate the implications of the ECAE process for other challenging-to-deform metals. Additionally, the ultrafine-grained materials produced through ECAE have potential applications in industries such as automobile, power, and aerospace.

The influence of new severe plastic deformation on microstructure, mechanical, and corrosion properties of Mg-0.8Mn-0.5Ca alloy

In this research, the effect of accumulative extrusion bonding (AEB) on the microstructure and mechanical properties of Mg-0.8Mn-0.5Ca biocompatible alloy was investigated. The goal of this research was to develop the mechanical and corrosion properties of Mg-0.8Mn-0.5Ca alloy after ABE process as a novel severe plastic deformation process. The simulation of AEB process showed that the average effective strain per pass for channels with the internal angle of 120? was about 1.93. The average grain size was dramatically decreased from about 448.3 ?m for the homogenized alloy to 1.55 ?m for the 3-pass processed sample. Microstructural observations suggested a combination of continuous, discontinuous, and twinning-induced dynamic recrystallization as the major mechanisms of grain refinement. Tensile and compressive strengths were improved from 150 and 205 MPa to 330 and 301 MPa after three passes of AEB, indicating 2 and 1.5 times improvements, respectively. Tensile elongation decreased from 26% for the homogenized sample to 7.5% for the 3-pass processed sample due to the severe work-hardening, non-uniform strains, and inhomogeneous microstructure produced by the ABE process. Corrosion resistance in SBF solution was improved from 1.1 to 14.159 after three passes of ABE due to the presence of hydroxyapatite formed on the surface of the AEBed samples.

Properties and hardening behavior of equal channel angular extrusion processed Mg-Al binary alloys

We examined the competition between precipitation and grain-size refinement during equal channel angular extrusion (ECAE) of two fully solutionized coarse-grained Mg-Al alloys which was accomplished by using a “step-down” temperature method, up to 4 passes using the BC route. The extrudates show various levels of microstructural heterogeneity, especially at lower processing temperatures. Grain size refinement from hundreds of micrometers to a few micrometers was achieved by dynamic recrystallization (DRX). This is in conjunction with the formation of precipitates with a bimodal size distribution. One type is a few micrometers and found at grain boundaries, while the other precipitate type is a few hundred nanometers and found inside large parent grain remnants (PGR). The non-uniformity of the microstructure indicates that the ECAE deformation process is highly inhomogeneous. However, the presence of both fine grains and PGRs renders the extrudate with a higher capacity for actual strain hardening rate (ASHR: dσ/dε) comparable to that of the as-received materials. Dynamic compressive test results show a significant strength increase attributed to the precipitates, which is in addition to the strength improvement from grain size refinement (Hall-Petch Effect). These features validate the utility of ECAE for high-strength Mg alloy engineering. The work herein also provides microstructural insights to the severe plastic deformation (SPD) processing of Mg-Al alloys as well as a wealth of experimental data for the development of numerical models.

A Brief Review on Theoretical Models of Deformation Twinning at Locally Distorted Grain Boundaries

A brief review of the theoretical models which describe mechanisms of deformation twinning in nanocrystalline and ultrafine-grained materials is presented. In the framework of the models, formation of nanoscale deformation twins occurs at locally distorted grain boundaries that contain fragments being rich with grain boundary dislocations due to preceding severe plastic deformation processes. Within the review, mechanisms of deformation twinning at locally distorted grain boundaries represent (a) the consequent emission of partial dislocation; (b) the cooperative emission of partial dislocations; and (c) the generation of multiplane nanoscale shear.

Development and study of combined severe plastic deformation process

To increase the level of accumulated deformations during angular pressing, known routes are used, based on inter-transitional rotation of the workpiece at a certain angle before the next installation in a stamp. With the advent of relatively new methods for obtaining of bulk ultrafine-grained materials, the possibility of combining angular pressing and its rotation in accordance with a given route in one pass of the workpiece through intersecting channels of the die in accordance with a given route is studied, for which a technological process is developed and studied, in which equal-channel angular pressing and screw extrusion are combined. The computer simulation of the proposed process made it possible to reveal the features of the kinematics of the flow in the channels of the die, to predict the values of the contact pressure, power parameters and the resulting stresses and accumulated deformations in the volume of the pressed billet.

Functional gradation of aluminum alloy by impact of ballistics as severe plastic deformation process

In the present effort, impact of bullets fired at high speeds on a stationary target was used as a high strain-rate plastic deformation method to generate Functionally Graded Materials (FGMs). The bullet-shaped Aluminum alloy Al5052 specimens impacted the UHMWPE target at different projectile velocities ranging from 100 m/s to 750 m/s, to study the effect of the impact speed. Moreover, few of the projectiles impacted along the longitudinal axis whereas the remaining projectiles impacted with an obliquity to investigate the effect of leading-edge shape. The metallography of the projectile specimens fired at 750 m/s shows grain refinement from 70 ± 3 μm at the rear/ un-deformed point to 10 ± 1 μm at the front/ severely deformed point which is in the impact zone. Similar but of less magnitude variations were observed at other impact speeds also. The hardness variation was 45% (70 ± 3 HV at the rear surface to 102 ± 2 HV at the front face) at 750 m/s. Moreover, least variation in hardness and grain size was observed for projectile impacted at lowest velocity tested (100 m/s). Further, functionality in hardness and grain refinement was seen in graded direction due to shape of the projectile specimens, impact velocity, and target material. Depending upon the impact angles, axisymmetric (impacted normal to the longitudinal axis) or unsymmetrical (impacted at an angle) variation of grain refinement and hardness was observed.

Using high pressure torsion to process magnesium alloys for biological applications

The effect of high pressure torsion processing on mechanical properties and corrosion behavior of pure magnesium and Mg-Zn, Mg-Zn-Ca, Mg-Li-Y and Mg-Y-RE alloys is investigated. Micro-tomography and SEM characterization are used to estimate corrosion rate and evaluate non-uniform corrosion features. The results show that severe plastic deformation processing improves the strength of all magnesium alloys, but deformation localization can take place in the Mg-Zn-Ca and Mg-Y-RE alloys. The occurrence of deformation localization is associated with low strain rate sensitivity in these alloys and with severe corrosion localization. Pure magnesium and Mg-Zn and Mg-Li-Y alloys display good corrosion resistance with a low corrosion rate and maintain integrity after 28 days of immersion in Hank's solution.

Evolution of the grain structure of metals and alloys under intense plastic deformation: multilevel models

It is well known that the performance properties of products made of metals and alloys are determined mainly by the meso- and microstructure of the latter. The structure of materials is formed and undergoes significant changes in the processes of manufacturing parts and structures using thermomechanical processing methods. A very important parameter that determines the physical and mechanical characteristics of materials is the grain structure (size, shape, relative positions of grains and inclusions of various phases). In recent decades, in this regard, special attention has been paid to the processes of severe plastic deformation (SPD), which make it possible to obtain a submicro- and nanocrystalline grain structure, which provides a significant increase in the performance properties of products made of metals and alloys. The development of SPD technologies in modern conditions is unthinkable without mathematical modeling of the processes under consideration; the most important component in the development of such a "toolkit" are constitutive relations (or, more broadly, constitutive models). In connection with the foregoing, the latter should be able to describe the evolutionary structure at various scale levels. Until now, the practice of developers of materials processing technologies has been dominated by the use of macrophenomenological models based on classical continuum theories of plasticity, viscoplasticity, and creep. From the second half of the 20th century to the present, various improvements to the constitutive models of the above class have been proposed, in which additional parameters and kinetic equations are introduced for them, describing certain characteristics of the structure of materials. As a rule, such models make it possible to obtain an adequate picture of the changing structure, however, for specific materials and methods of thermomechanical treatment. At the same time, such models, unfortunately, do not have the necessary universality; when changing the material or processing method, they have to be significantly “customized” to specific conditions, up to a complete change in the relationships included in the model. A brief review of works devoted to the creation and application of models of this class is given in the previous article by the authors. The most promising and possessing a significant degree of universality, according to the authors, are currently multilevel constitutive models based on the introduction of internal variables and physical theories of plasticity (elastoviscoplasticity). A review of works that consider various aspects of the formulation, modification, numerical implementation and application of such models is proposed in this article. The main attention is paid to models focused on the description of changes in the structure of materials due to dislocation-disclination mechanisms; a brief note is given on models that take into account thermally activated diffusion mechanisms, due to which the processes of recovery and recrystallization are realized.

Evolution of the grain structure of metals and alloys under severe plastic deformation: continuum models

Products made of metals and alloys with a fine-grained structure, which have high physical, mechanical and operational characteristics, are becoming increasingly in demand in many technical and technological fields. The most common and efficient technologies for the production of parts from this class of materials are various processes of severe plastic deformation (SPD) (in general practice, at low homologous temperatures). At the same time, to achieve high degrees of deformation, a significant part of metals and alloys require increased processing temperatures, undergo significant heating during deformation processes, which may be accompanied by changes in the grain and subgrain structure due to recovery and recrystallization processes. An empirical approach to the development of SPD modes that ensure the formation of the necessary grain structure requires huge time and financial costs, and therefore considerable attention is paid by researchers in the field of solid mechanics and metal forming to approaches and methods of mathematical modeling. In connection with the foregoing, the number of publications on this subject has been intensively growing in recent years. The currently known models differ significantly in their approaches, the depth of penetration into the physics of processes, and the scope of consideration. The proposed brief review is focused on a qualitative analysis of works on this topic, a preliminary classification of existing models according to their purpose, versatility, and functionality. It seems possible to single out the two most common approaches to describing the change in the grain structure in the processes of thermomechanical processing of metals and alloys: continual (in most cases, single-level) and multilevel, based on the introduction of internal variables and physical theories. This review is devoted to the consideration of publications focused on the first of these approaches. Until now, the most common are macrophenomenological continuum models based on the analysis of experimental data conducted both in laboratories on macrosamples and in real production conditions. Models of this class are usually formulated in the form of operator relations over field quantities, they are relatively easy to implement due to their easy “embedding” into widely used commercial software packages, but they require significant costs for experiments to identify models, they are characterized by a low degree of versatility. Continuous theories are relatively less common, but still often used. These theories are based on the description of physical mechanisms and the evolution of the structure of metals and alloys in terms of continuum variables.

Fabrication of Copper of Harmonic Structure: Mechanical Property-Based Optimization of the Milling Parameters and Fracture Mechanism.

A severe plastic deformation process for the achievement of favorable mechanical properties for metallic powder is mechanical milling. However, to obtain the highest productivity while maintaining reasonable manufacturing costs, the process parameters must be optimized to achieve the best mechanical properties. This study involved the use of response surface methodology to optimize the mechanical milling process parameters of harmonic-structure pure Cu. Certain critical parameters that affect the properties and fracture mechanisms of harmonic-structure pure Cu were investigated and are discussed in detail. The Box-Behnken design was used to design the experiments to determine the correlation between the process parameters and mechanical properties. The results show that the parameters (rotation speed, mechanical milling time, and powder-to-ball ratio) affect the microstructure characteristics and influence the mechanical performance, including the fracture mechanisms of harmonic-structure pure Cu specimens. The best combination values of the ultimate tensile strength (UTS) and elongation were found to be 272 MPa and 46.85%, respectively. This combination of properties can be achieved by applying an optimum set of process parameters: a rotation speed of 200 rpm; mechanical milling time of 17.78 h; and powder-to-ball ratio of 0.065. The superior UTS and elongation of the harmonic-structure pure Cu were found to be related to the delay of void and crack initiation in the core and shell interface regions, which in turn were controlled by the degree of strength variation between these regions.

Strength and fracture mechanism of nanostructured metal materials for medical applications

In this paper we study titanium Grade4, magnesium alloy Mg-Zn-Ca, corrosion-resistant austenitic steel 08Kh18N9 for medical applications. The mechanical properties in tension, torsional strength, and cyclic crack resistance under different types of loading of steels are investigated. The results are compared for two states of steels: the initial coarse-grained (CG) state and ultrafine-grained (UFG) state produced by severe plastic deformation processing via equal-cannel angular pressing (ECAP). It is demonstrated that the ultrafine-grained materials have essentially better strength and lower sensitivity to cyclic overloads. It is concluded that all the studied UFG materials are more promising compared to CG ones for the manufacture of medical devices for various purposes, which experience various static and cyclic loads during operation.

An analytical model for predicting the extrusion force for the torsion extrusion process of metals

Torsion extrusion (TE) method as a severe plastic deformation (SPD) process can effectively refine the microstructures and improve the mechanical properties of materials. Accurate and rapid prediction of the extrusion force in the process of TE is an important problem in industry. This paper proposed an analytical model using upper bound method (UBM) for predicting the extrusion force in the TE process. The kinematically admissible velocity field is established based on a continuous spherical extrusion velocity field coupled with a torsional velocity field constrained in a conical die. The torsional angular velocities along the radial and axial directions are assumed with quadratic and cubic function, respectively, due to the radial and axial nonlinearity of torsional velocity in the deformation zone. In addition, considering its complexity, the shape of the deformation zone is mapped to a rectangular zone. By establishing the torsional velocity field in the mapped zone, the torsional velocity field of the deformation zone is obtained according to the mapping relation. The UBM model is validated by comparing the predicted extrusion force with the simulation results obtained from the finite-element method (FEM). Moreover, the influences of the friction factor, reduction ratio and die angle on the extrusion force were investigated as well.

Numerical-experimental study of die geometry in the constrained groove pressing of 6061 aluminum sheets

Nowadays, in line with the need of different industries to the materials with high strength to weight ratio, researchers have drawn attention to the processes of severe plastic deformation. The constrained groove pressing (CGP) is one of the most effective methods of severe plastic deformation to produce high-strength sheet metal using two dies with different shapes (grooved and flat). Despite the advantages of CGP in creating high accumulative plastic strain, this process leads to non-uniformity in mechanical properties of the sheet. This non-uniformity is one of the limitations of the CGP process which is considered in this study. Experimental and numerical studies were performed to investigate CGP process on 6061 aluminum alloy sheet up to two complete passes and the mechanical properties of the sheets were studied. Hardness testing was conducted on the worked material and the increase in the hardness of tested material in both longitudinal and thickness directions were observed. Also, it was shown that the non-uniformity in hardness distribution is correlated to the non-uniformity in the strain distribution. So, validated numerical model was used to develop the response surface method (RSM) and consequently to investigate the effect of geometric parameters in the grooved die on the strain uniformity. Finally, die geometry was optimized using the developed RSM model to produce a sample with more uniformity in strain and hardness distribution.

Manufacturing of high strength thin-walled aluminum 6063 tubes through severe plastic deformation combined with peak-aging treatment

Thin-walled aluminum tubes are widely used for different structural purposes, and therefore, the development of new methods for strengthening these elements is critical. This matter is especially true for aluminum alloys 6xxx since their maximum strengths projected through peak-aging are considerably lower than the similar strength of other wrought aluminum alloys like 2xxx and 7xxx. Although different works have proposed the imposition of severe plastic deformation for strengthening of 6xxx alloys, the application of this method for thin-walled tubes has been less studied due to the complexities of the severe plastic deformation processing of thin-walled tubes. In this study, the manufacturing of high-strength thin-walled aluminum 6063 tubes through the imposition of a new severe plastic deformation process and a subsequent post-aging treatment at two different temperatures is studied. For this purpose, the tension test is applied to measure the strength variation. Also, the electron backscattering diffraction equipped with scanning electron microscopy and the X-ray diffraction experiments are applied to investigate the microstructural evolution. Results show that the proposed approach can be successfully applied to the manufacturing of high-strength thin-walled aluminum 6063 tubes. Also, the strengthening effect of this procedure is attributed to an increase in the dislocation density and refinement of grains during the imposition of severe plastic deformation and an appearance of finer precipitates during the peak-aging treatment.

Microstructural evolution, shielding effectiveness, and the ballistic response of Mg/Al7075/B4C/Pb composite produced by combination of coating and severe plastic deformation (SPD) processes

Light-weight metal matrix composites reinforced by Pb and B4C are of interests in aerospace industry due to high strength to weight ratio and excellent shielding effectiveness. This paper investigates microstructure, shielding effectiveness, tensile properties, and high-velocity impact behavior of Mg/Al/B4C/Pb composite. In this composite, the B4C layer was deposited by electrophoretic deposition (EPD) on aluminum layers, then the sandwich with the stacking sequence of Mg/Al/B4C/Pb was fabricated through accumulative roll bonding (ARB). The optical microscopy (OM) and scanning electron microscopy (SEM) images illustrated that by increasing the cycles, all layers within composite experienced instabilities including necking and fracture. In addition, increasing the number of rolling cycles improved tensile properties, namely Young's modulus, elongation, yield, and ultimate strength. Furthermore, according to the results of the high-velocity impact test, by increasing the rolling cycle, less failure such as cracks and perforation was found on surfaces, indicating the enhanced ballistic resistance of composites. Plus, when composites were subjected to electron radiation, less relative doses of radiation were detected by dosimeter at higher rolling cycles which confirmed the attenuation of transmitted rays and then the enhancement of shielding effectiveness of composites.

An analysis of crystallographic texture and residual stresses of aluminium alloy RSA-501 after selected processes of twist extrusion (TE)

This study presents the residual stress analysis for the twist extrusion (TE) process after the experiment and numerical simulation and the analysis of the crystallographic texture changes and changes in hardness before and after the TE process for an RSA-501 aluminium alloy (Al; Mg5%; Mn1.5%; Sc0.8%; Zr0.4%).Crystallographic textures were obtained with the PANAlytical Empyrean X-ray diffractometer. The stresses were measured by applying the X-ray method with the use of using the PROTO iXRD diffractometer.The use of severe plastic deformation processes in the mass of the material leads to a significant change difference in the stress distribution in the workpiece and a change in texture compared to the reference material. The stress distribution in the sample cross-section and stress values varied and depended on the stage of the twisting process to which the surface was subjected. The highest stress (about 600 MPa) appears at the peaks of the front surface when exiting the twist area die TE. Higher stress values at the edges of the specimen are caused by friction (deformation) of the material against the die surface. The TE process strengthened the highest crystallographic texture background level was 49%.The conducted tests and the obtained results allow the determination of the process parameters and critical areas of the sample by carrying out a numerical simulation.Microhardness increases due to the TE process and the largest values were observed at the edges. This phenomenon is confirmed by the numerical simulation results presented in this paper.