Extrusion Direction Research Articles

Equal channel angular sheet extrusion (ECASE) produces twinning heterogeneity in commercially pure titanium

Commercially pure grade 2 titanium in sheet form was processed by equal channel angular sheet extrusion (ECASE) up to two passes at room temperature. The ECASE process generated a heterogeneous state of deformation, mainly affecting the sheet metal edges´ vicinity. The deformation heterogeneity gave rise to notable microstructural changes throughout the sheet thickness with high densities of twins located around 600 μm from the sheet edges. At the same time, the middle zone was kept free of twins. The highest twin density generated with the ECASE process corresponds mostly to tension twins of type 101¯2101¯1 oriented towards the extrusion direction. The heterogeneous structure produced a material strength increase of 200 MPa, maintaining a uniform deformation zone of 10%. The good strength-ductility combination was related to a heterogeneous distribution of geometrically necessary dislocations (GNDs) between the hardest and softest areas. The edge areas presented greater GNDs of type ⟨a⟩ on the twins' exterior than in their interior while in the middle zone, the highest GND densities grouped around triple points and grain boundaries. It was found that the grains with the most significant capacity to nucleate twins and store GNDs were those with the c-axis of the crystals parallel to the normal direction (ND). According to the Hall-Petch relationship, the strength improvement of the heterogeneous material comes from the grain size reduction mainly due to twins induced by deformation around the edge areas.

Effects of trace Ag on precipitation behavior and mechanical properties of extruded Mg−Gd−Y−Zr alloys

The effects of trace Ag element on the precipitation behaviors and mechanical properties of the Mg−7.5Gd− 1.5Y−0.4Zr (wt.%) alloy by means of tensile test, X-ray diffractometry, scanning electron microscopy, electron backscattered diffractometry, and scanning transmission electron microscopy. There is an unusual texture (〈0001〉//extrusion direction) in the extruded Mg−Gd−Y−Zr alloys containing 0.5 wt.% Ag. During the aging periods at 225 °C, the addition of the trace Ag does not form new precipitates, just accelerates aging kinetics, and refines β′ precipitates, thereby increasing the number density of the β′ precipitates by Ag-clusters. Moreover, the Mg−Gd−Y−Zr alloy containing 0.5 wt.% Ag shows the most excellent synergy of strength and plasticity (408 MPa of ultimate tensile strength, 265 MPa of yield strength, and 12.9% of elongation to failure) after peak-aging.

Characterization of microstructure and texture of binary Mg-Ce alloy processed by equal channel angular pressing

The characterization of microstructure and texture development of binary Mg-0.3Ce (wt%) after equal-channel angular pressing (ECAP) processing via route Bc at 300 and 350 °C through 4 passes were investigated using electron backscatter diffraction (EBSD) measurements. The results demonstrated an effective grain refinement from millimeter range to 6.7 and 8.3 μm obtained after 4 passes at 300 and 350 °C, respectively. The grain refinement was obtained through dynamic recrystallization (DRX). At 300 °C, DRX occurred at low strain by twin-induced dynamic recrystallization (TDRX) and particle stimulated nucleation (PSN) mechanism and then converted with increasing strain to sub-grain development (SD) and grain boundary bulging dynamic recrystallization (GBBDRX). Besides, grain growth occurred during processing at 350 °C. The texture development strongly depends on the strain level, deformation temperature and DRX mechanisms. At 300 °C, a typical basal texture with a deviation of 40° towards extrusion direction was formed gradually up to 4 passes while a completely different texture was formed at 350 °C due to the large grain size.

Effects of extrusion ratio and direction on extruded Au nanowires investigated using molecular dynamics simulation

The effects of the extrusion ratio (diameter of the extrusion mold inlet divided by that of its outlet) and direction on extruded Au nanowires (NWs) are studied using molecular dynamics simulations based on the embedded-atom method. The effects are investigated in terms of atomic trajectories, common neighbor analysis, flow field, system pressure, and the extruded NW length-pressing ram displacement curve. The simulation results show that for the forward extrusion process, a smaller extrusion ratio leads to a larger diameter of the extruded NW and a smoother cross-sectional profile. Extruded NWs obtained at a smaller extrusion ratio have a higher face-centered cubic fraction and a less disordered structure due to lower system pressure. The adhesion effect between extruded NWs and mold outer walls increases with increasing extrusion ratio, resulting in an uneven appearance of extruded NWs and a decrease in their length. The backward extrusion process can produce amorphous NWs from crystal NWs. The forward extrusion process can produce NWs that are longer than those produced with the backward extrusion process.

Experimental investigations of the critical values of J-integral and crack tip opening displacement (CTOD) of high-density poly-ethylene PE100 elbow

The present study aims to characterize the cracking behaviour of high-density poly-ethylene (HDPE) pipe elbow. Experimental studies were performed to determine the mechanical behaviour of HDPE and study the anisotropy of the material. Tension tests were performed on compact tension (CT) specimens to identify the toughness value, expressed by the critical value of the J-integral JIc. These tests were carried out on specimens cut from a PE100 plate with a different orientation angle with respect to the extrusion direction. The testing results have shown that HDPE can be considered as an isotropic material. The methods used to calculate the JIc value resulted in different value. Due to these uncertainties, a study of a failure criteria using crack tip opening displacement (CTOD) was proposed and conducted. The combination of the J-integral and “CTOD” method gave the possibility to determine for the critical value of the J-integral as a value of the fracture toughness of the HDPE. The obtained results suggest that the value of 8.4 kJ/m2 can be considered as the JIc fracture toughness required to initiate the crack for the HDPE.

Formation of an abnormal texture in Mg-Gd-Y-Zn-Mn alloy and its effect on mechanical properties by altering extrusion parameters

The Mg-8Gd-4Y–1Zn–Mn (wt%) alloys prepared by semi-continuous casting and homogenizing treatment were extruded using different extrusion ratios and subsequent cooling processes. The microstructure, texture and mechanical properties of extruded alloys were investigated. The dynamic recrystallization process is promoted by increasing the extrusion ratio, while the static recrystallization process is suppressed by subsequent water cooling rather than air cooling. When the recrystallization ratio is relatively low, the non-recrystallized region showing a fiber <101‾0>Mg//extrusion direction (ED) texture component dominates the texture characteristic. With the increase of the recrystallization ratio, the recrystallized region exhibiting an abnormal <0001>Mg//ED texture gradually dominates the texture characteristic. The grain boundary energy anisotropy and the grain boundary mobility anisotropy are assumed to be changed by the Gd and Y addition, which affect the preferential growth of the abnormal <0001>Mg//ED oriented grains and eventually lead to the formation of abnormal texture component. The as-aged alloy extruded at the extrusion ratio of 6 followed by air cooling shows the highest strength. The extruded alloys with an intensive abnormal texture component exhibit the best mechanical isotropy in both as-extruded and as-aged conditions. The differences in strength along different directions are mainly resulted from the fiber strengthening.

Microstructure and properties evolution of Mg\u20132Y\u20130.6Nd\u20130.6Zr alloy rolled at room and liquid nitrogen temperature

The microstructure evolution, texture, mechanical behavior and twin deformation of the ECAPed Mg–2Y–0.6Nd–0.6Zr alloy at room and liquid nitrogen temperature were investigated by rolling samples. The ECAP processed material appeared the texture of 45° to the extrusion direction and its yield strength reached 93.6 MPa. The results showed that cryorolling encourages twinning in Mg–2Y–0.6Nd–0.6Zr alloy, enhancing the tensile strength and texture. Activation of {10–12} twinning during rolling was found to be more pronounced in the cryorolled samples than in the cold rolled samples owing to a lower temperature. As a result, the cryorolled samples had more twins than and cold rolled ones, the proportion of twin areas of room temperature rolling and ultra-low temperature rolling were: 2.45% and 4.23%.

Unveiling the microstructure evolution based on deformation mechanisms and dynamic recrystallization in as-extruded AZ31 Mg alloys during uniaxial compression

A series of uniaxial compression experiments were carried out on the as-extruded AZ31 Mg alloy with<10–10>-<11–20>//ED (extrusion direction) double fiber texture at 200–350 ℃. The microstructure evolution during the work hardening and dynamic softening stages were systematically investigated based on deformation mechanisms and dynamic recrystallization (DRX), respectively. Experimental and simulation results demonstrated that in the work hardening stage, the dominant deformation mechanisms were the basal<a>slip and {10−12} twinning at 250 ℃, while the basal<a>slip and prismatic<a>slip 350 ℃. The appearance of profuse {10−12} twins at 250 ℃ not only effectively refined the microstructure but also quickly promoted the formation of strong<0001>//CD (compression direction) texture. Moreover, the activation of twin variants was mainly dependent on their own Schmid factor that was higher in<10–10>//CD grains, resulting in the earlier disappearance of the<10–10>//ED texture component than the<11–20>//ED texture component. In contrast, owing to the limited of {10−12} twins, the samples at 350 ℃ exhibited a weak fiber texture with diffusely distributed of basal plane along the CD. In the dynamic softening stage, high temperature increased both the grain size and proportion of DRXed grains, resulting in a more homogeneous microstructure. More importantly, the continuous DRX (CDRX) transformed into discontinuous DRX (DDRX) as the temperature increased from 250 °C to 350 °C. The similar orientation between the new CDRXed grains and parent grains at 250 ℃ preserved the strong<0001>//CD texture, while at 350 ℃ the basal texture was significantly weakened due to the random orientation DDRXed grains and higher activation of pyramidal<c + a>slip. These findings are beneficial for the optimization of the temperature range of the MDF process.

Improved strength in wrought Mg–Y–Ni alloys by adjusting the block-shaped LPSO phase and plate-shaped γ′ phase

The microstructure and mechanical properties of two Mg–Y–Ni alloys with different volume fraction of block-shaped LPSO phase and different number densities of plate-shaped γ′ phase were investigated. The volume fraction of block-shaped LPSO phase increases with the content of Y and Ni in the Mg–Y–Ni alloys with Y/Ni atomic ratio of 1. The plate-shaped γ′ phase is formed in the matrix of the as-cast alloys and grows across the matrix during the preheating before extrusion, and its number density increases with increasing content of Y and Ni. After extrusion, the block-shaped LPSO phase is distributed along extrusion direction, and the plate-shaped γ′ phase can be observed in both non-dynamic recrystallized (non-DRXed) grains with strong basal texture and dynamic recrystallized (DRXed) grains with random texture. The increased volume fraction of LPSO phase improves the tensile yield strength of the as-extruded Mg–Y–Ni alloys, accompanied by the decrease in ductility. In addition to the obvious strengthening from the LPSO phase, the plate-shaped γ′ phase is also an effective strengthening phase which can hinder the movement of the slip systems in non-DRXed and DRXed grains of the Mg–Y–Ni alloys. The Mg94Y3Ni3 (at%) alloy containing the highest volume fraction of block-shaped LPSO phase and the highest number density of plate-shaped γ′ phase exhibits the superior tensile yield strength of 502 MPa after extrusion.

Anisotropy in tensile behavior of an extruded Mg-4.50Zn-1.13Ca (wt.%) alloy

Abstract The present study investigated anisotropy in tensile behavior of an extruded Mg-4.50Zn-1.13Ca (wt.%) alloy through tensile testing along different tilt angles relative to the extrusion direction. Results showed that the as-extruded Mg-4.50Zn-1.13Ca (wt.%) alloy exhibited anisotropy in tensile behavior due to the formation of basal texture. Basal slip, prismatic slip and tensile twinning were the dominant deformation modes depending on the tensile direction. Prismatic slip was the dominant deformation mode for samples with small tilt angle (θ = 0° and 22.5°). Basal slip was activated when the tilt angle was increased, which also resulted in the decrease of yield strength. Tensile twinning was responsible for the yielding of the samples with high tilt angles (θ = 67.5° and 90°). The ductility was significantly reduced at high tilt angle, which was mainly attributed to the appearance of tensile twinning during tensile deformation.

Texture role in the mechanical property improvement contributed by grain refinement for Mg-2.6Nd-0.55Zn-0.5Zr alloy subjected to extrusion process

This work successfully fabricated the fine-grained Mg-2.6Nd-0.55Zn-0.5Zr (wt%) alloy plates with the average grain sizes of 2.39–3.49 μm via the extrusion process. The microstructure evolution during extrusion process and the associated mechanical properties were investigated. Results showed that dynamic recrystallization (DRX) significantly refined the grain size and improved the microstructure homogeneity. Extrusion fragmentation effect on the coarse Mg12Nd particles contributed to the development of fine-grained uniform microstructure, especially at the lower extrusion temperature. Additionally, extrusion process turned the fiber basal texture into the double peak basal texture owing to the sequential deformation mode activation from basal slip and tension twinning to pyramidal <c+a> slip. Subsequent continuous DRX and particle-stimulated nucleation (PSN) recrystallization played a weakening effect on the double peak basal texture. Moreover, decreasing the extrusion temperature increased the activation difficulty of pyramidal <c+a> slip and weakened the effect of PSN on texture modification, leading the basal plane distribution along the extrusion direction to be strengthened. Fine-grained strengthening significantly improved the mechanical properties, but such strengthening capability was severely dependent on the texture. During tension deformation, the weak basal texture easily activated the basal slip whereas the strong basal texture needed to activate the prismatic slip. Hall-Petch analysis indicated that the higher yield stress in the strong basal texture was ascribed to the remarkable deformation mode strengthening (activation of prismatic slip) and the geometrical strengthening (higher Taylor factor). The weak basal texture was beneficial to improve the uniform elongation owing to the higher strain hardening ability, which was more obvious when the tension twinning was activated.

Effect of local texture and residual stress on the bendability of extruded 6000-series Al alloy profiles

In this study, X-ray cosα measurement was optimized with 3-axis oscillation to perform highly accurate measurements of residual stress in extruded Al alloy (A6061 and A6005C) profiles having preferred orientations and large grain sizes. In A6005C, a grain-growth region was observed just below the surface–bulk boundary and visualized via texture differences. The regions of preferred orientations corresponded well with the major changes in the residual stress as a function of depth from the surface. The boundary of the (110) and (100) textures corresponded well with the first local maximum in the von Mises stress (σvM) for both the alloys. The grain-growth region of A6005C corresponded to the region between the first and second local maxima of σvM. The principal stress (σ1) direction was almost parallel to the extrusion direction in the grain-growth region of A6005C. The changes in the σ1 direction with depth resulted in the observed anisotropic bending behavior.

Crack initiation and propagation characteristics of a dual‐phase Mg–Li alloy under high‐cycle and very‐high‐cycle fatigue regimes

AbstractUltralight Mg–Li alloys are promising aerospace materials as they are the lightest structural alloys at present; however, their fatigue behaviors remain to be explored. This work focuses on the fatigue strength and crack initiation behavior of an extruded dual‐phase Mg–Li alloy (LZ91) under high‐cycle and very‐high‐cycle fatigue regimes. The fatigue limit of LZ91 alloy at 109 cycles was determined to be 78 MPa, and the fatigue ratio is 0.46. Microstructural characterization demonstrates that fatigue cracks tend to initiate at β‐Li phase‐enriched regions. The α‐Mg phase presents a &lt; &gt; fiber texture with a basal plane that has low deformation in the extrusion direction and acts as an enhanced phase in relation to the β‐Li phase. Deformation discrepancies cause localized cyclic plasticity at the Li phase that leads to fatigue crack initiation.

Influence of microstructural characteristics on corrosion behavior of Mg–5Sn–3In alloy in Hank's solution

The microstructural observation, the mass loss test, potentiodynamic polarization measurements and corrosion morphology examinations were conducted to study the influence of microstructural characteristics on corrosion behavior of Mg–5Sn–3In alloys in Hank's solution after extrusion. The results show that the corrosion rate of the as-cast alloy is similar to that of as-extruded alloy; however, the local corrosion susceptibility is greatly weakened in the as-extruded alloy, especially in the extrusion direction. The relatively uniform corrosion morphology of the as-extruded alloy is attributed to refined Mg2Sn particles, uniform distribution of Mg2Sn particles and favorable crystal orientation. Meanwhile, the cytotoxicity tests confirm that the Mg–5Sn–3In alloy exhibits cytotoxicity of Grade 0–1 for NIH3T3 cells, suggesting an acceptable cytotoxicity of this alloy in the vitro assay.

High-Performance TiBw/Ti Composite Prepared by Hot Extrusion

The low ductility of the titanium matrix composites (TMCs) at room temperature has become a significant obstacle for the engineering applications. Therefore, to achieve excellent mechanical properties in TiBw/Ti composites, a processing route that hot extrusion on as-sintered TiBw/Ti composites was proposed. Comparing with the microstructure of as-extruded TiBw/Ti composite and as-sintered TiBw/Ti composite, it revealed that the alignment of TiB whiskers in composite changed from randomness to along the extrusion direction with the hot extrusion completing. Moreover, according to the mechanical property test results, the mechanical property of as-extruded TiBw/Ti composites enhanced at the same time (tensile strength of 789 MPa and plastic strain of 1.5% for as-sintered TiBw/Ti composites; tensile strength of 940 MPa and plastic strain of 18.1% for as-extruded TiBw/Ti composites). The obtained results provide a promising fabrication route for developing high-performance TiBw/Ti composites suitable for industrial applications.

Anisotropy deformation behaviour of extruded Mg-2Zn-Al-0.2Ca-0.2Mn-0.2Gd (wt.%) bar with bimodal structure

The anisotropy compression deformation behaviour of Mg-2Zn-Al-0.2Ca-0.2Mn-0.2Gd (wt.%) magnesium bar with bimodal structure were studied by compressing parallel and perpendicular to extrusion direction. EBSD technique was used to analyse the deformation behaviour, microstructure and texture evolution. The results show that Mg-2Zn-1Al-0.2Ca-0.2Mn-0.2Gd (wt.%) bar with special bimodal grain size but comparable texture characteristics with c-axes perpendicular to extrusion direction for both fine and coarse grains. The stress-strain curves and strain hardening rate response were significantly affected by the loading directions and initial texture. The anisotropy mechanical properties occurred due to different deformation behaviour. The dominant deformation mechanisms are basal slip in fine grains and extension twinning in coarse grains at initial deformation, however, the activation of prismatic slip and the unfavourable orientations for basal slip for sample compressing parallel extrusion direction contributes to the yield anisotropy. As the deformation continuing, twinning growth and basal slip dominant deformation. When loading perpendicular to extrusion direction, prismatic slip in fine grains also contributes to deformation to some extent. The c-axes of both samples turn to parallel to loading direction after compression.

Effect of Loading Direction on the Tensile Properties and Texture Evolution of AZ31 Magnesium Alloy

Samples were cut from an extruded AZ31 magnesium alloy bar for uniaxial tensile and EBSD characterization tests. The long axis and bar extrusion directions were 0° (T0 sample), 45° (T45 sample), and 90° (T90 sample). The effects of loading direction on the tensile behavior, microstructure, and texture evolution of the magnesium alloy were studied. Results show that the obvious mechanical anisotropy of tensile behavior is affected by the loading direction, and the T0 sample with a grain c-axis perpendicular to the extrusion direction has a strong basal texture and high flow stress and yield strength. The loading direction has a significant influence on the microstructure characteristics of different samples, especially the number of {10–12} tensile twins and {10–11} compression twins. Texture evolution results show that the loading direction and the effect of deformation mode on the deformation mechanism lead to variations in texture evolution: the basal slip and prismatic slip during the plastic deformation of the T0 specimen, the compression twin of the T45 specimen, and the tensile twin of the T90 specimen.

Effect of twins and plastic-deformation anisotropy of extruded magnesium alloy on fatigue crack growth and crack closure behavior

To study the effect of twins and plastic deformation anisotropy on the fatigue crack growth (FCG) behavior and crack closure behavior of extruded AZ31B magnesium alloys, two types of single-edge notched tensile specimens were prepared, with loading directions parallel (specimen E) and perpendicular (specimen T) to the extrusion direction (ED). FCG experiments using these specimens were performed at stress ratios R = 0.1 and −1, and cyclic speed of 10 Hz.In extruded magnesium alloy materials, the c-axis of the crystal is radially oriented on a plane perpendicular to the ED, indicating the generation of a strong texture.In the FCG experiment at R = −1 for specimen E, elongation in the c-axis direction occurred under compressive load, which generated {101‾2} <101‾1> tensile twins. The tensile twins increased the material deformation and fatigue crack opening distance. As a result, the effective stress intensity factor range ΔKeff increased, leading to the acceleration of the FCG velocity. At R = 0.1, tensile twins were not generated because the load waveform had no compressive load component; there was no change in ΔKeff and no acceleration of FCG.For specimen T at R = 0.1 and −1, tensile twin generation was expected because elongation in the c-axis direction occurred under tensile load. However, tensile twins did not occur, which is attributed to the effect of plastic deformation anisotropy. Therefore, for specimen T, the increase in ΔKeff and FCG acceleration did not occur, and no difference due to the R value was observed.

Strength–ductility balance of powder metallurgy Ti–2Fe–2W alloy extruded at high-temperature

This study aims to improve the mechanical properties of a Ti–2Fe base alloy by adding W solute and performing hot extrusion at a high temperature (1000 °C). W was added at 0, 1, 2, and 3 wt% using the powder metallurgy route and homogenization heat treatment. The as-extruded materials predominantly consisted of α phase with different microstructure morphologies; Ti–2Fe and Ti–2Fe–1W contained equiaxed α grains, while Ti–2Fe–2W and Ti–2Fe–3W showed equiaxed + acicular and acicular shape, respectively. Effective grain refinement was obtained in Ti–2Fe–2W (average grain size: ~1.64 μm), which greatly contributed to the strengthening. The solid solution of W was studied with X-ray powder diffraction, where a proportional increment of β lattice constant occurred as the W solute increased in the matrix (Ti–Fe). Additionally, electron backscatter diffraction analysis revealed that the W solution reduced the intensity of the prismatic texture along the extrusion direction. Based on the experimental evaluations, extruded Ti–2Fe–2W alloy exhibited a maximum yield strength of 925 MPa with excellent elongation 30% at room temperature, indicating a remarkable trade-off in strength and ductility.

Study on Bending Strength of Cementitious Composites Based on Fiber Alignment

The traditional cement-based composites can’t meet the needs of actual 3D printing, people are committed to get breakthroughs in printing materials and extrusion process. This paper introduces the preparation of fiber-reinforced concrete materials, determining the optimum content of glass fiber in composite cement-based materials, and studying the fiber alignment during extrusion. From the bending strength, the performance of 3D printed fiber concrete materials are comprehensively analyzed. As a result, the bending strength of the sample does increase to the fiber volume ratio. The composite cement-based material with 2 vol.-% aligned fiber can have an excellent flexural strength of 12.05MPa, and the samples along the extrusion direction are more excellent than that along the transverse direction.