Basal Pole Figures Research Articles

Improving the stretch formability of a heat-treatable magnesium–aluminum–calcium–manganese alloy by copper addition at the parts-per-million-level

Dilute magnesium–aluminum–calcium–manganese alloys have a quick age-hardening response and thus show higher strength after short periods of artificial aging; however, their room temperature formability is rather low. Here, we report that the addition of a small amount of copper (Cu) could substantially increase the Erichsen value of a Mg–0.5Al–0.5Ca–0.3Mn (wt.%) alloy due to the formation of a weakened sheet texture and variation in the distribution of (0002) basal pole figure. Specifically, the 0.03 wt% (300 parts-per-million) Cu-containing alloy showed a large index Erichsen value of 7.4 mm, which was noticeably higher than that of the Cu-free alloy (5.2 mm). Further investigation of the microstructure by transmission electron microscopy revealed that Cu co-segregated with Al and Ca at the grain boundaries, which played a critical role for the formation of the weaker basal texture and finer microstructure in the Cu-containing alloys. Owing to the small amount of the Cu addition, the resultant Mg–0.5Al–0.5Ca–0.3Mn–0.03Cu alloy showed a large thermal conductivity of 131 W/(m·K) in a solution treated condition. Subsequent artificial aging at 170 °C for 8 h (T6) not only improved the thermal conductivity to 141 W/(m·K) but also increased the tensile yield strength from 127 to 181 MPa. The improvement in both thermal conductivity and tensile yield strength by the T6-treatment is associated with the precipitation of densely distributed single-atomic layer Guinier–Preston zones lying parallel to the (0002) basal plane.

Effects of the Al Content on the Evolution of Quadruple Basal Textures in Mg-xAl-1Zn-0.1Mn-0.1Ca-0.2Y Alloy Sheets Processed via Cold Rolling and Annealing

The effects of the Al content on the texture evolution of Mg-xAl-1Zn-0.1Ca-0.2Y alloy sheets fabricated via hot rolling, cold rolling, and subsequent annealing were systematically investigated. A lower Al content led to a higher number of free Ca solute atoms that contributed to co-segregation with Zn, delaying the recrystallization of the cold-rolled sheets during annealing and changing the basal pole figure shape of the annealed sheets. A quadruple basal texture, in which the positions of the four basal poles were developed at tilt angles of ±25° to the rolling direction (RD) and ±40° to the transverse direction (TD) from the normal direction, was obtained in the annealed Mg sheets. A smaller amount of Al caused an increase in the intensity of the main peaks along the TD but a decrease in the intensity along the RD. As a result, the texture of the annealed sheets gradually changed from RD-split to diamond and TD-split in the (0002) pole figure, as shown by the relative comparison of pole intensities in both directions. This texture change strongly affects the Schmid factor for the basal slip. For the alloys with an off-basal texture investigated in this study, as the maximum intensity of the basal poles increased, the average Schmid factor of the basal planes also increased, making the basal slip easier.

Hot Rectangular Extrusion Textures of Six Mg‐Alloys Via Neutron Diffraction

Due to the high quality and statistics utilizing neutron diffraction for texture analyses, the crystallographic texture variation of six Mg‐alloys is described in detail (AM20–AZ31–AZ61–AZ91–ZC71–WE43). More or less in all cases, the crystallographic texture is composed of some ideal texture components such as {0001} <10–10> and {10–10} <11–20> and fiber components such as <0001> // ND and <10–10> // ED. There is a dependency of the existence and texture sharpness of texture components with alloying elements such as the amount of Al. ZC71 is special with one dominating texture component {10–10} <11–20>. WE43 shows the split of the central pole in the basal pole figure but texture components are identical to other alloys without the tilt.

Prediction of the plastic anisotropy of magnesium alloys with synthetic textures and implications for the effect of texture on formability

Crystallographic texture is a well-known microstructural feature influencing the formability of magnesium alloys. However, the effects of individual texture characteristics common after thermomechanical processing have not been isolated due to the experimental challenge associated with varying them independently. Similarly, the effect of the propensity for twinning on formability, which both accommodates deformation and reorients the crystal, have not been systematically studied. This study uses synthetic sheet textures in conjunction with a viscoplastic self-consistent (VPSC) polycrystal plasticity model to predict deformation and formability behavior. The VPSC model was first parameterized based on experimental mechanical data and textures from fine-grained thixomolded and thermomechanically processed AZ61L. Subsequently, synthetic textures were generated to examine the effects of basal peak intensity, prismatic plane distribution, and asymmetry of the basal pole figure peak. Of these texture characteristics, basal peak strength is the most important predictor of forming behavior, with prismatic plane distribution and c-axis anisotropy resulting in comparatively weak effects. In the second part of the study, the effective critical resolved shear stress for twinning was varied, resulting in poorer forming behavior with easier twin activation. In both cases, increasing prismatic slip activity was deleterious to the predicted forming behavior.

Calcium and zirconium as texture modifiers during rolling and annealing of magnesium–zinc alloys

Rolling experiments were carried out on a ternary Mg–Zn–Ca alloy and its modification with zirconium. Short time annealing of as-rolled sheets is used to reveal the microstructure and texture development. The texture of the as-rolled sheets can be characterised by basal pole figures with split peak towards the rolling direction (RD) and a broad transverse angular spread of basal planes towards the transverse direction (TD). During annealing the RD split peaks as well as orientations in the sheet plane vanish whereas the distribution of orientations tilted towards the TD remains. It is shown in EBSD measurements that during rolling bands of twin containing structures form. During subsequent annealing basal orientations close to the sheet plane vanish based on a grain nucleation and growth mechanism of recrystallisation. Orientations with tilt towards the TD remain in grains that do not undergo such a mechanism. The addition of Zr delays texture weakening.

Microstructure and Texture Evolution During Sub-Transus Thermomechanical Processing of Ti-6Al-4V-0.1B Alloy: Part I. Hot Rolling in (α + β) Phase Field

In the current study, the evolution of microstructure and texture has been studied for Ti-6Al-4V-0.1B alloy during sub-transus thermomechanical processing. This part of the work deals with the deformation response of the alloy by rolling in the (α + β) phase field. The (α + β) annealing behavior of the rolled specimen is communicated in part II. Rolled microstructures of the alloys exhibit either kinked or straight α colonies depending on their orientations with respect to the principal rolling directions. The Ti-6Al-4V-0.1B alloy shows an improved rolling response compared with the alloy Ti-6Al-4V because of smaller α lamellae size, coherency of α/β interfaces, and multiple slip due to orientation factors. Accelerated dynamic globularization for this alloy is similarly caused by the intralamellar transverse boundary formation via multiple slip and strain accumulation at TiB particles. The (0002)α pole figures of rolled Ti-6Al-4V alloy shows “TD splitting” at lower rolling temperatures because of strong initial texture. Substantial β phase mitigates the effect of starting texture at higher temperature so that “RD splitting” characterizes the basal pole figure. Weak starting texture and easy slip transfer for Ti-6Al-4V-0.1B alloy produce simultaneous TD and RD splittings in basal pole figures at all rolling temperatures.

Microstructure and texture evolution of MgZnCe magnesium alloys sheets and associated restoration mechanisms during annealing

The texture evolution in four MgZnCe alloys was compared to that of Mg3Al1Zn (AZ31) alloy following rolling and subsequent isothermal annealing. All the as-cast and homogenized alloys were rolled through two stages that can be characterized as rough rolling and finish rolling, respectively. To investigate the effect of finish rolling temperature, one finish rolling pass with 65% reduction in thickness was performed at 300°C and 450°C. Of the studied compositions, the Mg1Zn1Ce, which had the highest Ce/Zn ratio, showed the weakest as-rolled texture and homogenous shear banding/twinning. Changing the Zn content changed particle size and, in alloys subject to texture weakening, the static recrystallization mechanism altered. On annealing, the maximum intensity of basal pole figures decreases as recrystallization progresses. The Mg1Zn1Ce (with the highest Ce/Zn), texture weakening is maintained even after full recrystallization, when grain coarsening occurs. However, in the Mg4Zn1Ce and AZ31 alloys, texture strengthening occurs when grain coarsening occurs, and the double split basal peak is replaced by a single peak. In these two alloys, grain coarsening is also accompanied by a bimodal grain size whereas in the Mg1Zn1Ce alloy, the grain coarsening leads to a uniform grain size. It is concluded that the differences between the Ce bearing alloys are related to Zn; increasing Zn decreases the solubility of Ce, which can influence the texture changes.

Texture weakening and static recrystallization in rolled Mg–2.9Y and Mg–2.9Zn solid solution alloys

The microstructure and texture evolution in the Mg–2.9Y and Mg–2.9Zn solid solution alloys were investigated following rolling and subsequent isothermal annealing. The Mg–2.9Y alloy was hot rolled, and the Mg–2.9Zn alloy was rolled at room temperature in order to evaluate the possibility of attaining texture weakening by the suppression of dynamic recrystallization (DRX) and promotion of static recrystallization (SRX). It was found that texture weakening can be attained in Mg even in the absence of Y when there is no DRX, and SRX occurs during annealing. In solid solution, Y suppresses DRX during hot rolling, and retards the kinetics of SRX and grain coarsening in Mg. In the two alloys, the orientation of statically recrystallized grains at bands/twins (TSRX grains) is close to that of double and compression twins, exhibiting a much more evenly distributed and slightly wider orientation than that of basal parent grains and twins. In both Mg–2.9Zn and Mg–2.9Y alloys, a continuous texture weakening is observed with the progress of SRX, which results in a bimodal microstructure consisting of small TSRX grains and larger ones. With the increase in grain size during coarsening, the maximum intensity of basal pole figures rises linearly, with the slope of the lines being nearly identical in the two alloys. This texture strengthening was ascribed to the consumption of small TSRX grains by larger ones.

Neutronographic Texture Analysis of Zirconium Based Alloys

Neutron diffraction is a very powerful tool in texture analysis of zirconium based alloys used in nuclear technique. Textures of five samples (two rolled sheets and three tubes) were investigated by using basal pole figures, inversion pole figures, and ODF distribution function. The texture measurement was performed at diffractometer KSN2 on the Laboratory of Neutron Diffraction, Department of Solid State Engineering, Faculty of Nuclear Sciences and Physical Engineering, CTU in Prague. Procedures for studying textures with thermal neutrons and procedures for obtaining texture parameters (direct and inverse pole figures, three dimensional orientation distribution function) are also described. Observed data were processed by software packages HEXAL and GSAS. Our results can be summarized as follows: i) All samples of zirconium alloys show the distribution of middle area into two maxima in basal pole figures. This is caused by alloying elements. A characteristic split of the basal pole maxima tilted from the normal direction toward the transverse direction can be observed for all samples, ii) Sheet samples prefer orientation of planes (100) and (110) perpendicular to rolling direction and orientation of planes (002) perpendicular to normal direction, iii) Basal planes of tubes are oriented parallel to tube axis, meanwhile (100) planes are oriented perpendicular to tube axis. Level of resulting texture and maxima position is different for tubes and for sheets. The obtained results are characteristic for zirconium based alloys.

Microstructure, mechanical properties and texture evolution of AZ31 alloy containing trace levels of strontium

The effect of low levels of Sr (0.01, 0.03, 0.05 wt.%) on the microstructure, mechanical properties and texture of AZ31 magnesium alloy has been investigated. Thermodynamic modeling has been used to study the effect of Sr on phase precipitation at different temperatures. Cooling curve analysis reveals a decrease in solidification superheat with the addition of 0.03 wt.% Sr to AZ31. The as-cast microstructures of the alloys have been studied using optical microscopy (OM) and electron probe micro analysis (EPMA). Results show the refining effect of Sr on the grain size and on the β-Mg17Al12 precipitates through growth poisoning and inoculation, respectively. To investigate the mechanical properties of the alloys, as-cast samples were compression tested at elevated temperatures. Hot compression peak stress (σmax) and critical strain before recrystallization (εc) initially drop but then increase. σmax first decreases due to the depletion of Al from solid solution and then increases when the amount of the Al–Sr precipitates reach a significant amount. εc drops due to the acceleration of dynamic recrystallization kinetics as a result of grain refinement. It increases with increasing Sr when the concentration Sr in solid solution is increased leading to dislocation pinning and retardation of recrystallization. X-ray texture measurements on the hot compressed and extruded samples show a decrease in maximum intensity of the basal pole figures with increasing Sr as a result of reduced twining and the changes in Al and Sr concentrations in solid solution.

Hot rolling of binary Ti–Nb alloys Part 1: evolution of microstructure and texture

Abstract This work describes the development of texture during hot rolling of three binary alloys, namely Ti-8Nb, Ti-12Nb and Ti-16Nb. The alloys have been unidirectionally hot rolled at 800°C and air cooled. The alloy Ti-8Nb consists of the α (cph) and small volume fraction of β (bcc) phases while the alloys Ti-12Nb and Ti-16Nb show the presence of α n (orthorhombic) and small volume fractions of β phases in as-cast and hot rolled conditions. The Ti-8Nb alloy exhibits nearly c-type texture in terms of basal pole figure in 40% hot rolled condition with a strong and inhomogeneous [0001]⊩ND fibre. Subsequent rolling reductions change texture and weaken the fibre present in 40% hot rolled specimen. The Ti-12Nb alloy exhibits c-type texture in 60% hot rolled specimen with a strong [001]⊩ND fibre. The overall texture of 80% hot rolled specimen is weak and different in terms of basal pole figure. The development of texture during hot rolling of the alloy Ti-16Nb is different from that of Ti-12Nb alloy even though the texture of 80% hot rolled specimens of both the alloys are nearly the same. The high overall intensity of texture in alloy Ti- 16Nb in the 80% hot rolled specimen can be attributed to the presence of a large volume fraction of β phase in comparison to that of the alloy Ti-12Nb.

Evolution of texture in pure magnesium during rolling

Abstract This work describes the development of texture in cast pure magnesium during unidirectional rolling, multi-step reverse rolling and multi-step cross rolling at different temperatures. The unidirectionally and the multi-step reverse hot-rolled plates exhibit mainly an asymmetric R-type texture with basal-pole split. Hot-rolled plates were also cold-rolled to a small reduction (10 %) by taking small strips of the RD-ND and TD-ND planes with two different initial textures. The shape and location of the main texture components in basal pole figures and ODF plots depend on the hot-rolling temperature and on the mode of rolling. The textures obtained in this study are compared with those of pure magnesium reported in literature.

The Structural Evolution of an Orthogneiss‐fold Within the Reitzenhainer Rotgneisstruktur (Erzgebirge Mts., GDR)

The crystallographic preferred orientations of quartz in gneiss taken from different spots of a recumbent fold structure in the Erzgebirge Mts. (southern GDR) are studied by means of neutron time‐of‐flight diffraction. A single component texture has been found for all specimens, with quartz c‐axes parallel to the tectonic a‐direction. The variations in texture sharpness are related to different deformation conditions of the samples. A fabric rotation of 30° has been found from the limb to the crest of the fold on the basis of () and () pole figures. The basal pole figures of quartz derived from an ODF analysis compared well with optical U‐stage measurements. The determined fabrics are discussed taking into account model calculations of experimentally deformed quartzites and geological informations.

チタン板の降伏条件式の粒度依存性

Planar anisotropy of the yield stress and the plastic strain ratio obtained by uniaxial tensile tests has been analyzed for titanium sheets with grain sizes ranging from 10 to 140 μ. The results obtained are as follows:(1) Planar anisotropy of the yield stress and the plastic strain ratio of the titanium sheet under the uniaxial stress can be explained in terms of the yield criterion,(This article is not displayable. Please see full text pdf.) \ oindentwhere σX, σY and τXY, τXZ, τYZ ware referred to the principal axis of the anisotropy proposed by the authors.(2) It can safely be said that the position of the Z-axis is located at an angle θ on the basal pole figure where the basal pole intensity was maximum. This position can also be predicted from the plastic strain ratio in the rolling direction.(3) In the same material, the parameter q in the above equation decreases with an increase in grain size, but its dependence on grain size differs for the other materials.(4) The q value was determined from the following equation when the position of Z-axis on the basal pole figure was determined:(This article is not displayable. Please see full text pdf.) (5) The yield criterion proposed here coincides with that of Hill when the plastic strain ratio r (in the rolling direction, the 45° direction and the 90° direction) has been measured precisely.