Extrusion Axis Research Articles

Cyclic fibre texture in hot extruded Ni50Mn29Ga21

Abstract The cyclic texture in polycrystalline 5M Ni50Mn29Ga21 magnetic shape-memory alloy fabricated by hot extrusion was investigated with high-energy synchrotron radiation, neutron diffraction, and electron backscatter diffraction. Combination of these techniques reveals that the texture of the hot extruded sample is quite complex. It is composed of components related to the radial direction and rotated around the extrusion axis. Additionally, the dominant texture components change from the centre to the edge of the rod. The recrystallized grains contain many twins with the trace of the twin boundaries preferentially aligned along the extrusion and radial direction showing the cyclic nature of the texture and microstructure. The results are discussed with respect to deformation mode, phase transformations, starting grain structure, and texture.

Polyoxymethylene orientation by equal‐channel multiple angular extrusion

AbstractThe effect of conditions and routes of deformation in the course of equal‐channel multiple‐angular extrusion (ECMAE) on physical and mechanical properties of polyoxymethylene (POM) have been studied. As deformation routes, Route C (shear planes are parallel, and the simple shear direction of every deformation zone is changed through 180°) and Route E (shear planes are turned through ±45° around the extrusion axis and the normal to the axis, and simple shear direction is changed through 180° or ±90° with respect to the deformation zone) were selected. It has been shown that ECMAE provides the increase of modulus of elasticity E more than twice, tensile strength σT increases in four times. At the same time, strain at break εb is reduced by 1.5%. The value of the achieved effects depends on the accumulated deformation and the selected deformation route. The best set of physical and mechanical characteristics was observed in the case of Route E. According to SEM data, Route C results in partial pore healing and E provides total pore healing both in longitudinal and transversal direction. The observed effects are related to orientation order formation, increase of cristallinity degree and reduction of structure imperfection of extrudates. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Microstructure and properties of Mg-12Gd-3Y-0.5Zr alloys processed by ECAP and extrusion

Equal channel angular pressing (ECAP) processing and conventional extrusion (Ex) were applied to the Mg-12Gd-3Y-0.5Zr (wt%) magnesium alloy in order to evaluate the potential improvement in the mechanical properties. The ECAP experiment was conducted at 380 °C in a die having an included angle of 90° between two channels by the Bc route with the billet rotated by 90° about its longitudinal axis. Subsequently, some billets were processed by conventional extrusion at 300 °C. The microstructures were examined by X-ray diffraction (XRD), optical microscopy and transmission electron microscopy (TEM). The experimental results indicate that the grain size is refined effectively, but the basal planes are highly inclined (about 40°) from the extrusion axis introduced by ECAP, which impairs the grain boundary strengthening effect. The conventional extrusion, following the ECAP, can modify the grains in hard orientation. Based on grain boundary strengthening due to ECAP and texture strengthening due to Ex, the strength is improved effectively. The enhanced activity of the non-basal slips, due to the refined grains and the reduction in c/a ratio, is responsible for good ductility and high strain hardening rate in samples obtained by the two-step process.

Texture and mechanical behavior evolution of age-hardenable Mg–Nd–Zn extrusions during aging treatment

Three magnesium alloys containing different Nd and Zn were extruded and heat treated. The addition of Nd gives rise to the RE texture (c-axis oriented at an angle lower than 90° to the extrusion axis) in extruded Mg rods, reducing yield strength, improving tension–compression asymmetry and enhancing ductility. The Zn addition, on the other hand, weakens the RE texture by rotating the c-axes of the grains away from the extrusion axis, and also leads to the formation of a significant amount of Mg–Nd–Zn intermetallics at grain boundaries and triple points for concentrations above 0.2 wt.%. Heat treatment after extrusion causes significant age hardening as well as makes the grains reorient and further improvement on yield symmetry together. When the effect of age-hardening is included, the Mg–3.0Nd–0.2Zn–Zr (wt.%) extrusion is found to provide the best combination of strength, ductility and tension–compression asymmetry.

Structural homogeneity and low-temperature micromechanical properties of ultrafine-grained AZ31 magnesium alloy

The degree of microstructural homogeneity of ultrafine-grained (UFG) AZ31 magnesium alloy produced by a special thermomechanical process including four cycles of equal-channel angular pressing (ECAP, route Bc) is studied by the microindentation method. The defect structure of the UFG alloy is quite homogeneous. Texture owing to ECAP showed up as a lower average microhardness measured in a plane perpendicular to the extrusion axis than that measured in a plane containing that axis, and in a slight dependence of the microhardness on the location of the indent on the billet surface. The microhardness of the initial coarse-grained alloy is close to that of the UFG samples measured in a plane perpendicular to the extrusion axis. Tensile deformation of the samples over a wide temperature range of 4.2–295 K increased the microhardness in the region of the neck by more than 30%. The temperature dependence of the microhardness over 77–295 K is indicative of thermally activated plastic deformation in AZ31 alloy. The mechanism for deformation of the alloy appears to be interactions between dislocations and local defects of impurity origin.

Grain size effects on deformation twinning in an extruded magnesium alloy tested in compression

Ambient temperature compression tests with concurrent acoustic emission (AE) measurements have been performed on a hydrostatically extruded, fine-grained, round bar of alloy AZ31 parallel to the extrusion axis. A multiple increase in the AE count rates to peak intensities was detected with increasing strain. An analysis of the samples tested to specific values of strain using electron backscattering diffraction revealed that (10–12) twins first appear in large grains and that only with increasing strain do smaller grains tend to twin.

The role of networking in the optical anisotropy of hot-extruded calcium phosphate glass

We have investigated the structural modifications that occur concomitantly with the generation of optical anisotropy in the binary glass with nominal starting composition 0.51(CaO)0.49(P 2O 5) as a result of hot-extrusion processes. Micro-Raman and X-ray-fluorescence micro-analysis have been used to map the structure and composition along the directions parallel and orthogonal to the extrusion axis, with respect to which we have detected birefringence and refractive index modifications up to 10 −3. The results show an annular region, midway between the axis and the outer side, in which Ca is slightly depleted and the phosphate chains are shortened and packed through crosslinking sites in anisotropic arrangement.

Elevated-Temperature Mechanical Behavior of As-Cast and Wrought Ti-6Al-4V-1B

This work studied the effect of processing on the elevated-temperature [728 K (455 °C)] fatigue deformation behavior of Ti-6Al-4V-1B for maximum applied stresses between 300 to 700 MPa (R = 0.1, 5 Hz). The alloy was evaluated in the as-cast form as well as in three wrought forms: cast-and-extruded, powder metallurgy (PM) rolled, and PM extruded. Processing caused significant differences in the microstructure, which in turn impacted the fatigue properties. The PM-extruded material exhibited a fine equiaxed α + β microstructure and the greatest fatigue resistance among all the studied materials. The β-phase field extrusion followed by cooling resulted in a strong α-phase texture in which the basal plane was predominately oriented perpendicular to the extrusion axis. The TiB whiskers were also aligned in the extrusion direction. The α-phase texture in the extrusions resulted in tensile-strength anisotropy. The tensile strength in the transverse orientation was lower than that in the longitudinal orientation, but the strength in the transverse orientation remained greater than that for the as-cast Ti-6Al-4V. The ratcheting behavior during fatigue is also discussed.

Texture induced anisotropy in extruded Ti–6Al–4V–xB alloys

The tensile properties of extruded Ti–6Al–4V–xB alloys (wt.%) were evaluated in an orientation perpendicular to the extrusion direction at room-temperature and 455°C. The extrusion process preferentially oriented the basal plane of α-Ti perpendicular to the extrusion axis. This strong α-phase texture resulted in tensile anisotropy. The tensile strength in the transverse orientation was lower than that in the longitudinal orientation, but it remained greater than that for the as-cast Ti–6Al–4V. The TiB phase was aligned in the extrusion direction and increased B content was found to weaken the α-phase texture, causing a weakening of tensile anisotropy. Debonding was not observed during the tensile tests in the transverse orientation, indicating a strong interface bond exists between the TiB phase and the two-phase (α+β) Ti–6Al–4V matrix.

Microstructural development of the hot extruded magnesium alloy AZ31 under cyclic testing conditions

Abstract A study of the internal strain (stress) evolution during uni-axial cyclic deformation along the prior extrusion axis with fully reversed total constant strain amplitudes εA (0.5% < εA < 5%) was investigated by using in-situ high energy synchrotron X-ray diffraction. The deformation is dominated by {1012} 〈1011〉 twinning and detwinning mechanisms within the textured hot extruded magnesium alloy AZ31. The results show a strong load partitioning between the internal stresses of (1010) and (1120) parent grains and of the (0002) twinned daughter grains that are relaxed. Following the evolution of the twinning/detwinning behavior and the hkil dependent microstresses as a function of cycling numbers, two different regimes were observed whereby it was found that the transition between these regimes is marked by an applied strain amplitude of eA = 0.625%.

Axi-symmetric forward spiral extrusion, a kinematic and experimental study

A modified axi-symmetric forward spiral extrusion process has been proposed here to allow for a near zero area reduction process. The axi-symmetric forward spiral extrusion, AFSE, can be carried out through a die with a number of engraved spiral grooves. This paper investigates the kinematics of the AFSE process. A velocity field is derived using principle of mass conservation along the extrusion axis. The proposed model has been developed to calculate strain components in the deformation zone during the process. An experimental method has been designed which uses composite lead samples with embedded copper wires to trace the strain path to verify the proposed velocity field. A good agreement between experimental results and the proposed analytical model was observed. The proposed velocity field, verified by experimental results, shows that the deformation develops away from the AFSE die–sample interface. A linear gradient of velocity in the radial direction was observed which is in good agreement with the proposed velocity field. Based on the estimated strains, velocity gradient, and nearly no change in sample cross section during AFSE, the process seems to have good potential for application as a new severe plastic deformation process in both continuous and batch modes.

Grain Refinement of Magnesium Alloy AZ31 under Torsion Extrusion with a Square-Hole Die

Grain refinement and crystal orientation of magnesium alloy AZ31 under torsion extrusion with a square-hole die are investigated. The optimum temperature and ratio of the die rotation speed to the extrusion speed were clarified, resulting in uniformly distributed fine grains with sizes in the range 1- m over the entire cross section of the worked specimen. The crystal orientation of the specimen was determined by electron backscatter diffraction and compared with that of a conventionally extruded specimen. In the case of torsion extrusion, a very strong <0001> texture was observed along the extrusion axis, especially in the center region of the cross section. In contrast, the <0001> direction of many grains in the conventionally extruded specimen tended to be perpendicular to the extrusion axis.

Investigation of tensile–compressive yield asymmetry and the role of deformation twin in extruded pure magnesium

Abstract An asymmetry in tensile–compressive yield behaviour of extruded 99.95 % pure magnesium at two different strain rates was investigated. The yield asymmetry was observed at both strain rates, and the compressive yield strengths were over 50 % lower than the corresponding tensile yield strengths. Examinations with transmission electron microscopy revealed that twin bands were observed in compression specimens, and the twinning system was {0112}<0111>. Fibre structures (or textures) were examined using both X-ray pole-figures, which enabled one to identify that the extrusion axis was parallel to <1010> directions. The Schmid factors on slip systems and the twinning system were estimated, i. e., the Schmid factor for {1101}<1120> slip system was maximum in tension, and that for the twinning system was highest in compression. The origin of the yield asymmetry in extruded pure magnesium is associated with both the highest Schmid factor for the twinning system in compression and the critical resolved shear stress for twinning, which is lower than that for slip.

Fabrication of bimetallic rods consist of a Zr-based bulk metallic glass and a crystalline copper by co-extrusion

In this preliminary work, we demonstrated rod-type Zr 44Ti 11Cu 9.8Ni 10.2Be 25 (LM1B) bulk metallic glass/crystalline copper composites fabricated by co-extrusion. The co-extrusion tests were carried out at three different temperature-punch speed combinations within supercooled liquid region of the LM1B bulk metallic glass. The influence of process conditions on the homogeneity of the area fraction between core and sleeve along the extrusion axis, the existence and thickness of the interface layer with or without defect, and overall strength of this bimetallic compound was systematically investigated by various experiments.

The microstructure, tensile, and shear deformation behavior of an AZ31 magnesium alloy after extrusion and equal channel angular pressing

The shear punch testing (SPT) technique and the uniaxial tension tests were employed to evaluate the mechanical properties of the equal channel angularly pressed (ECAPed) AZ31 magnesium alloy. After extruding, the material was ECAPed for 1, 2, and 4 passes using route B C. The grain structure of the material was refined from 20.2 to 1.6 μm after 4 passes of ECAP at 200 °C. The 4 pass ECAPed alloy showed lower yield stress and higher ductility as compared to the as-extruded condition, indicating that texture softening has overcome the strengthening effects of grain refinement. The same trends in strength and ductility were also observed in shear punch testing. Similar shear strength and ductility values of the samples taken perpendicular to the extrusion direction (ED) and normal direction (ND) after 4 passes of ECAP indicated that {0 0 0 2} basal planes were inclined (∼45°) to the extrusion axis. The shear punch testing technique was found to be a useful method for verifying directional mechanical properties of the miniature samples of the ECAPed magnesium alloys.

Orientation dependent slip and twinning during compression and tension of strongly textured magnesium AZ31 alloy

Over recent years there have been a remarkable number of studies dealing with compression of magnesium. A literature search, however, shows a noticeably less number of papers concerned with tension and a very few papers comparing both modes, systematically, in one study. The current investigation reports the anisotropic deformation behavior and concomitant texture and microstructure evolution investigated in uniaxial tension and compression tests in two sample directions performed on an extruded commercial magnesium alloy AZ31 at different Z conditions. For specimens with the loading direction parallel to the extrusion axis, the tension–compression strength anisotropy was pronounced at high Z conditions. Loading at 45° from the extrusion axis yielded a tension–compression strength behavior that was close to isotropic. During tensile loading along the extrusion direction the extrusion texture resists twinning and favors prismatic slip (contrary to compression). This renders the shape change maximum in the basal plane and equal to zero along the c-axis, which resulted in the orientation of individual grains remaining virtually intact during all tension tests at different Z conditions. For the other investigated sample direction, straining was accommodated along the c-axis, which was associated with a lattice rotation, and thus, a change of crystal orientation. Uniaxial compression at a low Z condition (400 °C/10 −4 s −1) yielded a desired texture degeneration, which was explained on the basis of a more homogeneous partitioning of slip systems that reduces anisotropy and enhanced dynamic recrystallization (DRX), which counteracts the strong deformation texture. The critical strains for the nucleation of DRX in tensiled specimens at the highest investigated Z condition (200 °C/10 −2 s −1) were found to range between 4% and 5.6%.

Principles of ECAP–Conform as a continuous process for achieving grain refinement: Application to an aluminum alloy

Equal-channel angular pressing (ECAP) combined with the Conform process provides a solution for the continuous production of ultrafine-grained materials. Rods of a commercial Al-6061 alloy were processed by ECAP–Conform at room temperature for up to a total of four passes. Microstructural observations showed significant grain refinement but with elongated grains after four passes with average widths of ∼150 nm and lengths of ∼1.2 μm when viewed on the longitudinal planes. Microhardness measurements after a single pass revealed inhomogeneities both on the cross-sectional planes and along the rod. After processing through four passes there was reasonable homogeneity throughout the rod. Measurements of the shear strengths in two orthogonal directions perpendicular to the extrusion axis showed significant strengthening after ECAP–Conform and there was no evidence for any plastic anisotropy after processing through four passes.

Anisotropy of creep resistance in extruded magnesium

Creep deformation of extruded magnesium, prepared via a powder metallurgical route with a final hot extrusion, is examined in the temperature range of 473–623 K. The greatest creep resistance is observed in specimens with the stress axis parallel to the extrusion axis and the lowest at declinations between 45° and 90°. Most of this orientation dependence can be accounted for by the variation in the resolved shear stress on the basal slip planes.

The role of Zr-rich cores in strength differential effect in an extruded Mg–Zn–Zr alloy

This work examines the effects of extrusion parameters namely ratio and temperature on recrystallization behavior of a Mg–Zn–Zr alloy, and their consequent effects on anisotropy in the mechanical properties. Upon extrusion, the characteristic Zr-rich cores that do not recrystallize form the so-called “soft stringers” which are deformed bands elongated in the extrusion direction and curled around the extrusion axis. At higher extrusion ratio, there is more twinning contribution and the DRX response is improved, making the recryatallized grains finer and increasing the proportion of recrystallized Zr-rich cores. A basal texture after extrusion and the directional activation of tensile twinning cause anisotropy in the mechanical properties. In addition, the microstructural features such as large unrecrystallized regions and coarse crystallized grains also contribute in the strength differential effect. Further slip in the strain-hardened unrecrystallized grains is inhibited while twin activation under favorable orientation becomes easier in the coarse recrystallized grains. A higher proportion of large unrecrystallized and coarse crystallized gains in the case of lower extrusion ratio result in a much higher strength differential effect (∼100 MPa) in comparison to the one caused by the crystallographic texture only (∼25 MPa).

The effect of processing on the 455 °C tensile and fatigue behavior of boron-modified Ti–6Al–4V

This work investigated the effect of nominal boron (B) additions of 0.1 wt.% and 1.0 wt.% on the elevated-temperature (455 °C) fatigue deformation behavior of Ti–6Al–4V (wt.%) for maximum applied stresses between 250 and 550 MPa ( R = 0.1, 5 Hz). The alloys were evaluated in the as-cast condition as well as the cast-and-extruded condition. Boron additions resulted in a dramatic refinement of the as-cast grain size, and larger boron additions resulted in larger titanium-boride (TiB) phase volume percents. For the as-cast alloys, the B-containing alloys exhibited longer average fatigue lives than those for Ti–6Al–4V, which was suggested to be related to their increased strength and stiffness due to the addition of the strong and stiff TiB phase. The longest average fatigue lives were exhibited by the Ti–6Al–4V–0.1B alloy, which also exhibited the greatest elongation-to-failure value. The extrusions, which were performed in the β-phase field, resulted in a significantly smaller grain size, a smaller α-colony size, and finer α-lath width compared to that for the as-cast B-modified alloys. The TiB whiskers were aligned in the extrusion direction and the α-phase was also strongly textured such that the basal plane was predominately oriented perpendicular to the extrusion axis. Together these microstructural features were responsible for the significantly higher 455 °C yield strength, ultimate tensile strength, and fatigue strength exhibited by the cast-and-extruded alloys compared with the as-cast alloys. In the extruded condition, B-addition did not improve the tensile or fatigue strength.