Average Misorientation Angle Research Articles

Crystallographic orientation and slip behavior of powder metallurgy Ti–6Al–4V via multi-directional forging

In this study, we present a microstructural and mechanical analysis of Ti–6Al–4V alloys processed by low-temperature multi-directional forging at 900 °C, achieving near-theoretical density (99.9%), with a tensile strength of 1070 MPa and elongation of 14.9%. The microstructure is defined by both continuous and discontinuous dynamic recrystallization occurring simultaneously, related to an increase in dislocation density. Significantly, this study reveals the interaction between crystallographic orientation and spheroidization during the forging process. Specifically, changes in crystallographic orientation include the asynchronous formation of new subgrains/grains, the disruption of the Burgers orientation relationship, and rotation around the <11 2‾ 0>axis, which not only increases the orientation differences between α lamellae but also enhances the spheroidization process. Moreover, our findings demonstrate that during deformation, the activation of basal and pyramidal slip systems is favored over prismatic slip, indicating that the forging process has enhanced slip activity. The average misorientation angle and the fraction of high-angle grain boundaries are quantified, providing a detailed characterization of the evolved microstructure. This study adopts a new perspective to examine the microstructural evolution during the multidirectional forging process in powder metallurgy, presenting findings that elucidate how multidirectional forging effectively controls.

Thermal restoration kinetics and microstructural evolution of an Mg-RE alloy during annealing by quasi-in-situ observation

Quasi-in-situ electron backscatter diffraction method is applied to properly investigate thermal restoration kinetics and microstructural evolution of a commercial WE54 alloy after 10 % engineering pre-strain and post-annealing at 500 °C for 10, 35, and 70 min. Results show a reduction in the average grain orientation spread can effectively evaluate the restoration kinetics compared to other characteristics like average grain size or average misorientation angle. For microstructural evolution, nucleation behavior and abnormal grain growth of recrystallization nuclei as well as evolution of deformation twin have been investigated in detail. Low-angle grain boundary network due to the recovery effect provides recrystallization nuclei in the early stage of annealing, after which both continuous and discontinuous recrystallization nuclei are observed near deformation twin boundaries and original high-angle grain boundaries. Afterwards, grains with a tilting angle of 30° from the transverse direction grow abnormally, replacing the deformed grains, deformation twins, and part of some recrystallized grains. In addition, some twins can grow into the adjacent grains while de-twinning also occurs depending on twin orientations during thermal restoration.

Effects of rolling process and microstructure on the brittle crack initiation and arrest of a marine steel under low‐temperature

AbstractThe effects of the rolling process and microstructure on the brittle crack initiation and arrest of marine steel were systematically investigated. The microstructures of two steel plates produced by different rolling processes were observed and analyzed. The results demonstrated that the rolling process significantly influenced the microstructure. As the rolling temperature decreased, the grain size decreased, the high‐angle grain boundary (HAGB) content increased, and the average grain misorientation angle increased. The brittle crack initiation and the arrest abilities were evaluated by initiation fracture toughness and crack arrest toughness, respectively. The initiation fracture toughness and crack arrest toughness increased with the decreasing grain size and the increasing content of HAGBs. Finally, the influence of microstructure on the brittle crack initiation and arrest ability was explained from two aspects: (1) the critical event of crack initiation at low temperatures, and (2) the hindering effect of HAGB on the propagation of brittle cracks.

In-situ EBSD study of deformation behavior of nickel-based superalloys during uniaxial tensile tests

In this paper, we study the deformation behavior of nickel-based superalloys by in-situ EBSD and uniaxial tensile tests. This study mainly focuses on the microstructure evolution in the same area of the sample during deformation, including the evolution of various types of grain boundaries, geometrically necessary dislocations, grain orientations and texture, and their effect on the mechanical properties. The results show that the rotation of grains is closely related to their initial orientation during deformation. The lattice of grain is rotated to a certain extent to accommodate the more favorable orientation under low strain, leading to higher Schmid factors for the sample. Under large stresses, the grains occur deformation, multiple slip systems start simultaneously or alternately and the Schmid factors value gradually tends to stabilize at a lower level. Meanwhile, the texture orientation density of the initial Rotating cubic {001} < 110 > texture, α-fiber (RD//<110 >) texture, and γ-fiber (ND // <111 >) gradually decrease or even disappears, while the texture orientation density of Copper {112} < 111 > and Goss {011} < 100 > increases during uniaxial tensile deformation for Cr20Ni80 alloy. Grain rotation may be a result of large strain due to stress triaxiality and resulting plane stress condition owing to specimen dimension, which is beneficial to improve the plastic deformability of the alloy. Interestingly, with the increase of strain, the average misorientation angle first decreases and then increases, which is associated with the dislocation density. In addition, serious torsion occurs in the grains during this process, forming a large number of substructures. These substructures result in grain refinement and the Hall-Petch effect. In fact, during the deformation process, multiple strengthening mechanisms act in coordination, leading to an increase in the strength of the alloy.

A New Method for Evaluating the Accuracy of the Orientation Measured by Different Kikuchi Pole Combinations in Kikuchi Patterns

Abstract In this study, high-precision coordinates of Kikuchi poles were obtained for orientation calculation by locating the lattice plane traces of Kikuchi patterns of stainless steel. Orientation can be measured by selecting three noncoincident Kikuchi poles in a Kikuchi pattern, and different combinations of Kikuchi poles provide different orientation solutions. The “deviation” defined in this study and the orientation calculation error of each combination are generally positively correlated. Therefore, the deviation can be used to evaluate the accuracy of the orientation calculation for each combination without the theoretical orientation, and can also be used as a criterion for selecting Kikuchi pole combinations for orientation calculations. The results show that the average misorientation angles for all combinations are 1.983° (orientation a), 2.768° (orientation b), and 2.175° (orientation c) before the screening of the Kikuchi pole combinations by deviation. For each pattern, the first five combinations with the smallest deviation are selected, and the average misorientation angles of these combinations are 0.791° (orientation a), 0.789° (orientation b), and 0.910° (orientation c). The orientation calculation errors are reduced by 60, 71, and 58%, respectively. The accuracy of the orientation calculation is greatly improved, thus avoiding the appearance of orientation solutions with large errors.

Effects of Al3(Sc1-xZrx) nano-particles on microstructure and mechanical properties of friction-stir-welded Al-Mg-Mn alloys

Microstructure and mechanical properties of friction-stir-welded Al−5.50Mg−0.45Mn and Al−5.50Mg− 0.45Mn−0.25Sc−0.10Zr (wt.%) alloys were investigated by tensile tests and microscopy methods. The results show that the yield strength, ultimate tensile strength and elongation of the Al−Mg−Mn joint are (191±3) MPa, (315±1) MPa and (4.8±1.9)%, respectively. The corresponding values of the Al−Mg−Mn−Sc−Zr joint are (288±5) MPa, (391±2) MPa and (3.4±1.0)%. The Al−Mg−Mn−Sc−Zr joint has smaller grain size, lower average misorientation angle and higher low-angle grain boundary fraction than the Al−Mg−Mn joint. Both the two joints fracture at the weld nugget zone (WNZ), and Al3(Sc1−xZrx) nano-particles with a mean size of (9.92±2.69) nm still remain in this “weakest zone”. Theoretical calculation indicates that nano-particles can provide Orowan and grain boundary strengthening in WNZ, increasing the yield strength of the Al−Mg−Mn joint by 97 MPa.

Microstructural Evolution of SK85 Pearlitic Steel Deformed by Heavy Cold Rolling.

The microstructural evolution of SK85 pearlitic steel cold-rolled up to a 90% rolling reduction was characterized by scanning electron microscopy with electron backscattered diffraction (EBSD) and X-ray diffraction (XRD). SK85 steel exhibits excellent cold rolling performance. The interlamellar spacing of pearlite is refined obviously and a tensile strength of 2318 MPa can be reached for SK85 steel after 90% rolling reduction, an increase of 83% from 1264 MPa before rolling. The EBSD observation indicates that the {001} <110> texture becomes pronounced at a 90% rolling reduction in cold-rolled Sk85 steel. A propagation and multiplication of dislocations occur during rolling as the kernel average misorientation (KAM) angles significantly increase from 0.72° to 2.11°. The XRD analysis reveals that bcc ferrite is transformed into a bct structure at a 90% rolling reduction. The strengthening mechanism was discussed.

Achieving High Tensile Strength of Heat-Resistant Ni-Fe-Based Alloy by Controlling Microstructure Stability for Power Plant Application

A new, wrought Ni-Fe-based alloy with excellent creep rupture life has been developed for 700 °C-class advanced ultra-supercritical (A-USC) steam turbine rotor application. In this study, its tensile deformation behaviors and related microstructure evolution were investigated. Tensile tests were carried out at room temperature, 700 °C, and 750 °C. The results show that the Ni-Fe-based alloy has excellent yield strength at 700 °C, which is higher than that of some other Ni-based/Ni-Fe-based alloys. The fracture surface characteristics indicate trans-granular and intergranular fracture modes at room temperature, 700 °C, and 750 °C. However, the intergranular fraction mode became dominant above 700 °C. Dynamic recrystallization occurred at 700 °C and 750 °C with increasing average misorientation angles. The volume fraction of the γ′ precipitate was around 20%, and the average size of the γ′ precipitates was around 30 μm, which had no noticeable change after the tensile tests. The predominant deformation mechanisms were planar slip at room temperature, bypassing of the γ′ precipitates by the Orowan mechanism, and dislocation shearing at 700 °C and 750 °C. The tensile properties, fracture characteristics, and deformation mechanisms have been well-correlated. The results are helpful in providing experimental evidence for the development and optimization of high-temperature alloys for 700 °C-class A-USC applications.

Effects of billet heating temperature and extrusion speed on the microstructures and mechanical properties of the longitudinal welds in aluminum alloy profiles with complex cross-section

The effects of billet heating temperature and extrusion speed on the microstructures and mechanical properties of longitudinal welds in the aluminum alloy profiles with complex cross-section were studied. The results show that as the billet heating temperature or extrusion speed gradually increases, the average grain size shows a decreasing trend, the average grain boundary misorientation angle shows an increasing trend, and the density of dislocations increases first and then decreases. The elongation (EL) shows a trend of increasing first and then decreasing. Higher billet heating temperature contributes to increase the ultimate tensile strength (UTS) and yield strength (YS) of the longitudinal welds, while extrusion speed has little effect. Poor welding quality is the main factor leading to the low mechanical properties of the longitudinal welds. When the welding quality is higher, the interaction between dislocations and precipitation phases has an important impact on the mechanical properties of the longitudinal welds. The longitudinal welds of the profiles studied in this work have the highest EL and the largest UTS when the combinations of the billet heating temperature and the extrusion speed are 490 °C × 3.5 mm/s and 520 °C × 3.5 mm/s, respectively.

Comparison Study of Hot Deformation Behavior and Microstructure Evolution of Rack Steels with and without Segregation

In order to compare the hot deformation behavior and microstructure evolution of the rack steels with and without segregation, hot compression tests are carried out in the temperature range of 1173–1423 K and the strain rate range of 0.01–10 s−1 on a DIL805A/D quenching and deformation dilatometer. The flow stress, constitutive relation, processing map, and microstructure characterization are investigated. The results show that the flow stress increases with the increase of strain rate and the decrease of deformation temperature. The calculated activation energy (Q) and stress exponent (n) for the segregated samples are 395.245 kJ mol−1 and 6.046, which are higher than segregated samples, showing 376.815 kJ mol−1 and 5.930. The processing maps show that the workability of the nonsegregated steel is significantly more excellent than segregated steel. The segregated steel shows a higher kernel average misorientation angle and local strain. Complete dynamic recrystallization occurs at a high strain rate, and high deformation temperature can refine the grains.

Inherited multimodal microstructure evolution of high-fracture-toughness Mg-Zn-Y-Al alloys during extrusion for the consolidation of rapidly solidified ribbons

The mechanisms of multimodal microstructure evolution and the effects of microstructural factors on mechanical properties must be elucidated to design new alloys with superior properties. In this study, high-fracture-toughness and ductile Mg96.75Zn0.85Y2.05Al0.35 alloys were developed using rapidly solidified (RS) ribbon-consolidation technique, and the inherited multimodal microstructure evolution during plastic flow consolidation of the RS ribbons was investigated. The use of extrusion for plastic flow consolidation of the heat-treated RS ribbons produced a multimodal microstructure consisting of the worked grains with high Kernel average misorientation (KAM) angles (Group 1), the ultrafine dynamically recrystallized (DRXed) grains with intermediate KAM angles (Group 2), and the fine DRXed grains with low KAM angles (Group 3). Groups 1 and 2 contribute to the alloy strengthening, while Group 3 contributes to improving ductility with strain-hardening, resulting in enhancement of the fracture toughness. To form the multimodal microstructure, it was necessary to apply plastic flow with equivalent strains of >2.3 to the heat-treated RS ribbons possessing duplex microstructures with different dispersions of the long-period stacking ordered phase.

Modulating heat input to optimize corrosion and synergistic cavitation erosion-corrosion behavior of Ni201 cladding layer by cold metal transfer

The effects of heat input (HI) on the microstructure, microhardness, corrosion resistance and cavitation erosion resistance of cold metal transfer (CMT) Ni201 cladding layers were studied. The Ni201 cladding layers present a γ single-phase austenite structure, which exhibit a columnar to equiaxed transition (CET) transformation along the temperature gradient direction of approximately parallel energy input. As HI increases, the microstructure tends to become coarsen and the dilution rate increases, resulting in lattice distortion of γ phase. The Ni201 cladding layer has a strong γ-fiber texture in the 〈100〉 orientation as indicated by the EBSD analysis. With the increase of HI, the grain size and Schmidt factor increase, while the average misorientation angle decreases. The microhardness of Ni201 cladding layer exhibits a general downward trend from 198.3 HV to 171.7 HV with the increase of HI, while the abnormal increase of the microhardness of S3 sample is caused by solution strengthening and precipitation strengthening. In addition, the coarsening microstructure and diffusion of elements such as Fe intensifies the galvanic corrosion reaction, leading to a downward trend in the corrosion resistance of cladding layers. Synergistic cavitation erosion-corrosion is used to detect the self-repair and re-passivation behavior of the passivation film during the cavitation erosion process of the Ni201 cladding layers. Increasing the HI leads to an increase in the mean depth of erosion rate (MDER) of Ni201 cladding layers from 3.6 μm·h−1 to 5.5 μm·h−1, which is attributed to deterioration of the passivation film quality and the reduction of the mechanical property. Finally, the synergistic cavitation erosion-corrosion mechanism of Ni201 cladding layers is proposed according to the analysis results. The CMT Ni201 cladding layers fabricated in this paper exhibit a great potential for anti-corrosion application in ocean engineering.

Characterization of the deformation bands in AA1100 deformed by plane forging and return-plane forging

In this study, the deformation bands (DBs) in AA1100 after plane forging (PF) and return-plane forging (R-PF) during multi-axis diagonal forging (MADF) were observed using microtexture analysis. Typical texture components (plane-strain texture components) observed in face-centered cubic (FCC) materials deformed by plane-strain compression were developed in the PF specimen. Blurry bands with an orientation relationship of mainly LAGBs were developed in the deformed grains in the PF specimen. Slip trace analysis and Schmid factor (SF) calculations revealed the correlation between the blurry bands and the slip behavior. Regions of matrix and DBs inside the deformed grains of the R-PF specimen were distinguished mostly by their HAGBs. The heterogeneity of the Taylor factor (M) values that occurred within the blurry bands and their surrounding regions induced the development of the DBs in the R-PF specimen. The heterogeneities of the deformation behavior between the inside and the outside of the blurry bands that developed in the grains of the PF specimen during the R-PF were a direct reason for the generation of DBs in the deformed grains of the R-PF specimen. The transmission-EBSD (t-EBSD) technique revealed that the average misorientation angle inside the DBs was higher than that inside the matrix.

Evolution of the microstructure and mechanical properties of interstitial-free steel during multi-axial diagonal forging

In this study, sound workpieces made of interstitial-free (IF) steel were manufactured by performing up to 4 cycles without the occurrence of forging defects via the use of a new multi-axis diagonal forging (MADF-ver2) process at room temperature. The microstructure that was developed in the deformed specimens was experimentally analyzed and compared. As the number of cycles increased, the average grain size gradually decreased, and both the average misorientation angle and the fraction of high-angle grain boundaries (HAGBs) continued to increase. As the number of cycles increased, the change in average geometrically necessary dislocation (GND) density was insignificant due to the occurrence of dynamic recovery. The effects of microstructural factors on the hardness, yield strength, and total elongation of the deformed specimens were investigated. The ultrafine-grained structure formed by MADF-ver2 continuously increased the hardness and yield strength with increases in the number of cycles. On the other hand, total elongation was not dependent on the number of cycles, and this independence was mainly the result of insignificant changes in the average GND density due to the dynamic recovery that occurred throughout the specimen.

Effect of the magnitude of sub-boundary angles on the abnormal grain growth rate of Goss grains in Fe-3%Si steel

In spites of extensive studies, the selective abnormal grain growth (AGG) of Goss grains in Fe-3%Si steel remains still unclear. Here, the effect of the magnitude of sub-boundary angles on AGG behavior was investigated both by computer simulations and experiments. In 3-dimensional Monte Carlo simulations of grain growth based on the realistic grain boundary energy distribution data, the grains of Goss orientation, which are given the sub-boundaries, grew abnormally and smaller sub-boundary energies resulted in larger Goss grains. Additionally, a Fe-3%Si steel, after primary recrystallization, was heated to 1050 °C to induce AGG. Measurements of sub-boundary angles for three different sizes of abnormally growing Goss grains by synchrotron X-ray microdiffraction after the initial stage of secondary recrystallization showed that the misorientation of the sub-boundary angles was 0.41° for the small Goss grain of 734 μm. Moreover, the average misorientation of sub-boundary angles was 0.33° for the medium Goss grain of 1050 μm and 0.25° for the large Goss grain of 2978 μm. In contrast, the average misorientation angles of the sub-boundaries after the final stage of secondary recrystallization were only 0.05°. The results indicate that the sub-boundary angle is a determining parameter for the size of abnormally growing grains. • The effect of sub-boundary angle on abnormal grain growth behavior was investigated. • In the simulations, the Goss grains with small sub-boundary energies grew larger. • In the experiments, the large Goss grains tended to have small sub-boundary angles. • The sub-boundary angle should be a key parameter of abnormally growing Goss grains.

Grain Scale Investigation of the Mechanical Anisotropic Behavior of Electron Beam Powder Bed Additively Manufactured Ti6Al4V Parts

Numerous factors, including variable grain structures and different inherent defects, impact the mechanical behavior of Ti6Al4V parts fabricated using metal Additive Manufacturing (AM) processes. This study focuses on an in-depth analysis of how different microstructural features, such as crystallographic texture, grain size, grain boundary misorientation angles, and inherent defects, as byproducts of the electron beam powder bed fusion (EB-PBF) AM process, impact its anisotropic mechanical behavior. Standard tensile testing, conducted on samples produced at different orientations relative to the build table, showed significant anisotropy in elastic-plastic constitutive characteristics. Furthermore, X-ray computed tomography (CT) and electron back-scattered diffraction (EBSD) analyses were conducted on as-built samples to assess the effects of inherent defects and microstructural anomalies on such behavior. The samples arranged vertically and parallel to build direction had an average porosity of 0.05%, while the horizontally built samples, which were perpendicular to the build direction, had an average porosity of 0.17%. Moreover, the vertical samples showed larger grain sizes, with an average of 6.6 µm, wider α lath sizes, a lower average misorientation angle, and subsequently lower strength values than the other two horizontal samples. Among the three strong preferred grain orientations of the α phases, &lt;1 1 2¯ 1&gt; and &lt;1 1 2¯ 0&gt; were dominant in the horizontally built samples, whereas the &lt;0 0 0 1&gt; orientation was dominant in vertically built samples. Finally, larger grain sizes and higher beta-phase volume ratios were observed in the areas located at distances further away from the build plate. This was possibly due to the change in thermal gradients, cooling rates, and some thermal annealing phenomena resultant from the elevated build chamber temperature.

Multilevel model of polycrystals: application to assessing the effect of texture and grains misorientation on the critical deformation of the dynamic recrystallization initiation

The current state of materials constitutive models and the computer technology development make it possible to numerically implement complex multilevel models that allow describing the material structure evolution. In this regard, it is possible to formulate optimal control problem for metal forming processes in order to create the required performance characteristics of finished products and their ingots. To solve this problem in this study, the effective multilevel modeling approach is used to describe the thermomechanical treatment of polycrystalline materials. The model is based on this approach with the introduction of internal variables, in which the carriers and physical mechanisms of the processes of hot intense plastic deformation are explicitly considered. At deformation temperatures order of 0.5 homologous and above, recrystallization process have a special effect on the formation and change of the grain and defect material structure. The paper considers the problem of determining the critical deformation of dynamic recrystallization initiation, that depending on the material texture and the mutual misorientation of neighboring grains. Numerical experiments of the multilevel model are used to simulate two stages of inelastic deformation for this purpose. At the first stage, cold inelastic deformation by simple shear and compression is considered, that leading to the formation of a corresponding texture. At the second stage, uniaxial hot tension deformation is considered. The initial distribution of crystallographic grain orientation is assumed to be uniform. Two variants of the grains mutual misorientation with the prescribed increased and decreased values of the average misorientation angles are considered. The recrystallization process is not explicitly modeled. The current model is intended to assess the recrystallization critical deformation. It is shown that the mutual misorientation of grains, rather than texture, has the most influence on the critical deformation. An increase in the angle of grains mutual misorientation contributes to an earlier start of the dynamic recrystallization process. The formation of a deformation texture leads to a decrease in the angle of mutual misorientation, and, accordingly, to a decrease in dynamic recrystallization intensity. Despite this, with an increase of deformation, the driving force of recrystallization (the average value of the difference of stored energy between neighbor grains) is increases, which leads to the implementation of dynamic recrystallization.

Влияние температуры равноканального углового прессования на формирование мелкозернистой структуры в сплаве Al-3 %Cu

Тhe effect of the temperature of equal channel angular pressing (ECAP) on the microstructural changes in a model alloy Al-3 %Cu was investigated. ECAP of the as- homogenized and preliminary overaged alloy with an initial grain size ranging from 200 to 400 μm was performed by route A up to effective strains 8 –12 under isothermal conditions in the temperature range 150 – 400°C (0.45 – 0.75 Tm). ECAP at 150°C led to the significant refinement of the grain structure of the alloy. New fine grains were predominantly formed due to fragmentation of the original grains by the development of mutually intersected deformation- / microshear bands, which initially had the medium-angle misorientations (from 5 to 15°). The number of bands, as well as their boundary misorientations, gradually increased during deformation, leading to the development of crystallites surrounded by high-angle boundaries in accordance with the mechanism of continuous dynamic recrystallization. After 8 ECAP passes, a partially recrystallized structure was obtained in the material, containing regions of (ultra)fine grains with an average size of about 1.2 μm and arrays of the fragmented structure. The average misorientation angle in such the structure was as high as 23.2° and the fraction of high-angle boundaries was about 50 %. Precipitates of Θ (Al2Cu)-phase present in the alloy hindered the dynamic and static recovery and grain growth at the elevated ECAP temperature, and so stabilized the forming grain structure. The increase of the ECAP temperature to 400°C postponed the formation of the fine-grain structure to higher strains and resulted in increase in the average size of new grains to 15 μm, as well as decreased the fraction of high-angle boundaries to 30 % and the average misorientation angle of intercrystallite boundaries to 16.2°. The main reasons for the suppression of the fine-grain structure formation with increasing the ECAP temperature were the occurrence of a more uniform deformation in the earlier stages of processing and the gradual dissolution of the Θ-phase that stabilized the alloy structure.

Effect of hot rolling on microstructure, crystallographic texture, and hardness of AZ31 alloy

In this study, relationships between microstructure, texture, and hardness of hot-rolled AZ31 alloy were investigated. It was found that the grain size decreased into the ultra-fine domain after 60% hot deformation, reaching a grain size of 1 μm. Several dynamic recrystallization (DRX) mechanisms activated after 40% and 60% deformations including discontinuous dynamic recrystallization (DDRX), twin dynamic recrystallization (TDRX), continuous dynamic recrystallization (CDRX), and particle stimulated nucleation (PSN). With increasing the thickness reduction, the intensity of basal texture first increased, then slightly decreased, and finally significantly increased to 15.7 multiple of random density. The average misorientation angle decreased when the thickness reduction increased owing to the formation of a very strong {0001} basal texture. With increasing the strains, the average microhardness increased because of decreasing grain size and increasing twin fraction and shear band density. There were no differences between the hardness values of RD–TD and RD–ND planes for AZ31 samples after 10% and 40% hot rolling and these samples were isotropic. After 60% deformation, the hardness of the RD–TD plane (73.5 HB) was higher than that of the RD–ND one (68.4 HB) that resulted in hardness anisotropy due to the generation of very strong basal texture.

A comparative study on deformation mechanisms, microstructures and mechanical properties of wide thin-ribbed sections formed by sideways and forward extrusion

Extruded profiles/sections are increasingly used in the transport industry for lightweight structures. In this paper, a wide thin-ribbed aluminium profile with asymmetric Z-shape, was manufactured by a novel sideways extrusion process proposed by the authors. A comparative study was conducted by utilising the direct/forward extrusion process at the same extrusion temperature and speed, in which the different process mechanics, resulting microstructures and mechanical properties of profiles have been investigated by experiments and finite element modelling. It was revealed that, compared with sideways extrusion, although the design of a die pocket in forward extrusion induces preform and avoids the use of the large-diameter billet and extrusion container/press needed for extruding wide profiles, it requires a greater extrusion force due to work-piece upsetting necessary to fill the die pocket and leads to a lower effective strain in the profile rib. EBSD characterisation of the regions with an equal effective strain indicated that an increased shear strain is more efficient for obtaining fine grains with a higher average misorientation angle. In the same region of the profile rib made from the two different processes, sideways extrusion results in greater grain refinement due to greater effective strains, and a slightly greater texture intensity was found due to the intensive shear deformation. Tensile tests on formed profiles revealed that sideways extrusion leads to a higher yield strength (YS) and ultimate tensile strength (UTS) but a relatively lower elongation to failure, due to the combined effects of grain refinement, GND and texture intensity enhancement. Compared with the billet, the profile formed by forward and sideways extrusion has a YS increased by about 60% and 79% respectively, and an UTS increased by about 74% and 80% respectively in the extrusion direction, demonstrating an advantage of the sideways extrusion process in improving material strength under the same extrusion condition.