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In this study, a lower electric current (1.0–2.0 A/mm2) was applied during hot compression of Ti 2 AlNb alloys, and the mechanical response, microstructure evolution, and electroplasticity mechanism were investigated. The results showed that the maximum flow stress drop could reach 18.7 % after applying a lower electric current of 2.0 A/mm2, which confirms the existence of electroplasticity. The stress drop increased with increasing electric current density. However, the flow stresses of the samples in the isothermal compression test and those subjected to a 1.0 A/mm2 electric current compression test were similar, indicating that there is a threshold value for the electroplasticity effect on flow stress. The lower strain hardening rate caused by the electric current confirmed the electroplasticity effect, promoting the softening effect. Additionally, the lower average activation energy Q , affected by the electric current, implied the improvement of the deformability of the alloy due to the deformation mechanism of dynamic recovery (DRV), dynamic globularization, or dynamic recrystallization (DRX). The gradual reduction of dislocation density with increasing electric current density resulted in the stress drop, which can be ascribed to the directional drifting electrons colliding with dislocations, which promoted the movement of dislocations by arranging the dislocations in parallel. The local high temperature induced by the local Joule heating effect at the O lamella had a strong promoting effect on the globularization of the O lamella by producing uniform lattice distortion/local strain at the O/B2 interface. With increasing furnace temperature, the drifting electrons accelerated the transformation of LAGBs to HAGBs which promoted the appearance of dynamic recrystallization grains. • The maximum flow stress drop could reach 18.7 % after applying a lower electric of 2.0A/mm2 during hot compression. • The lower average activation energy Q which indicates the improvement of deformability of the Ti 2 AlNb alloys. • The stress drop was related to the effect of electric current on the dislocation evolution, the globularization and DRX. • The electric current promoted globularization of the O lamella by producing uniform lattice distortion/local strain. [ABSTRACT FROM AUTHOR]

In situ oriented TiB whisker reinforced TA15 matrix composites (TiBw/TA15) exhibited an improvement of tensile properties. The strain hardening after yield point was almost counteracted by the reduced effective cross-sectional area caused by the whisker fracture, thus resulting in a large yield strength ratio. [ABSTRACT FROM AUTHOR]

Multi-pass lowered-temperature rolling was applied on the friction stir welded ZK61 magnesium alloy sheets not only for fabricating wide high-performance wrought magnesium alloy sheets, but also for reducing the sheet inhomogeneity including the microstructure and mechanical properties induced by friction stir welding. Results showed that obvious microstructure inhomogeneity including plannar texture anisotropy between the base metal and the stir zone were introduced in the friction stir welded ZK61 alloy sheets, but can be strikingly weakened by hot rolling deformation via multiple dynamic recrystallization. These led to a uniform fine-grained structure of about 8 µm in average grain size and similar (0002) basal texture in the final 1.4 mm thick sheets, and brought a continuous improvement in the associated property differences, where the relatively lower yield strength in base metal zone was strongly correlated with spreading (0002) texture while higher values in stir zone with stable intense (0002) texture. Moreover, the experimental and calculated Hall–Petch relationships were investigated to explain the different evolution of yield strength between the base metal and the stir zone. Meanwhile, enhanced fracture elongations larger than 20% in both the base metal zone and the stir zone were primarily attributed to grain refinement. [ABSTRACT FROM AUTHOR]

In situ synthesized TiB whisker reinforced 3.5 vol% TiBw/Ti6Al4V composites have been synthesized by pre-sintering and hot extrusion with steel cup processes. The effects of pre-sintering temperature and time on densification behavior and mechanical properties of the as-extruded composites were investigated. The results indicated that as-extruded TiBw/Ti64 composite sintered at 1100 °C had the highest relative density of 99.4% along with ultimate tensile strength of 1352 MPa and elongation of 4.72%. With increasing pre-sintering temperature from 900 to 1100 °C, the in situ synthesized TiB whiskers which construct a quasi-continuous network microstructure produced by pre-sintering and hot extrusion techniques grow rapidly, while the relative density of the composites increases obviously. At the same time, the fracture type changes from brittle fracture to the hybrid-fracture characteristic of plastic fracture and brittle fracture. The strengthening effects can attribute to the matrix refine and the in-situ reaction TiB whiskers reinforcement due to pre-sintering and hot extrusion plastic deformation. The results also suggest that the optimal pre-sintering and hot extrusion with steel cup techniques are sintered at 1100 °C for 1 h in consideration of the comprehensive properties and the cost. [ABSTRACT FROM AUTHOR]

This work realized the texture tailor of Mg-2.6Nd-0.55Zn-0.5Zr (wt.%) alloy sheets via the hot extrusion on the billets subjected to different solution times from 0 h to 16 h. The solution treatment of 530 °C could effectively dissolve the coarse Mg 12 Nd particles. But abundant small second phase particles again developed after hot extrusion owing to the solid solution decline of Nd in magnesium matrix and the strain induced precipitation. The occurrence of dynamic recrystallization during hot extrusion improved the microstructure homogeneity and refined the grain sizes to 4.2–5.7 μm. Additionally, the activations of basal slip, prismatic slip and pyramidal slip together promoted the development of double peak basal texture in the hot-extruded sheets. However, this kind of texture was weakened by the particle-stimulated nucleation recrystallization and its weakening degree gradually decreased with the prolongation of solution time. This made the sheet with the long solution time more likely retain the strong deformation basal texture. Such strong basal texture increased the activation fraction of prismatic slip along the extrusion direction (ED), producing the higher yield stress and the lower uniform elongation. Influenced by this, the anisotropies in the yield stress and the uniform elongation between the ED and the transverse direction (TD) were obviously weakened. Besides, the activation of tension twinning greatly increased the uniform elongation and decreased the yield stress. [ABSTRACT FROM AUTHOR]

The microstructures evolution, texture characteristics and mechanical properties of Mg-2.5Nd-0.5Zn-0.5Zr alloy processed by high strain rate rolling (HSRR) at different temperature were systematically investigated in the current study. The results showed that the initial material was approximately equiaxed grains (23.8 μm) with a large number of divorced eutectic Mg 12 Nd phases precipitated along grain boundaries in a continuous network. After HSRRed, the microstructure was obviously refined, and uniform distributed. The average grain size was refined to 3.63 μm (R673), 2.71 μm (R648) and 2.17 μm (R623), respectively, and corresponding percentage of recrystallization were 46.1%, 49.3% and 63.9%, respectively. R623, R648 presented a strong (0002) basal surface bimodal texture in the RD direction but this texture was in the TD direction in R673, all of which preferential orientation was at 66.3–90° region. An excellent combination of ultimate tensile strength (324 ± 2 MPa), the yield strength (298 ± 3 MPa) and the elongation (6.9 ± 1.5%) were achieved in a fine-grained (2.17 ± 1.17 μm) Mg-2.5Nd-0.5Zn-0.5Zr alloy prepared by HSRR at 623 K. The higher yield strength can be obtained by refinement strengthening, dislocation strengthening, precipitation strengthening and texture strengthening. • Fine-grained alloy sheets with superior properties (298 MPa for tensile yield strength) were achieved by HSRR. • The texture evolution, grain size refining mechanism and strengthening mechanism were analyzed in detail. • Mg-2.5Nd-0.5Zn-0.5Zr alloy sheet was prepared by the high strain rate rolling. [ABSTRACT FROM AUTHOR]

The evolution of microstructure and texture in a single rolling pass was investigated at rolling temperature of 250 ℃. Based on the analysis of microstructure evolution, thickness reduction of 31% was identified as a critical deformation strain for the occurrence of continuous dynamic recrystallization (CDRX) in this work. CDRX strikingly refined the grain size and improved the microstructure homogeneity. The results based on intragranular misorientation axis analysis showed that the activation of abundant stochastic stored dislocations with a broad range of orientations developed in CDRX was the main reason of the transformation from <10−10>//RD texture to randomized texture along <10−10>-<11−20> arc in inverse pole figure. Microhardness distribution was mainly influenced by the fraction of deformed grains. Grain refinement increased yield stress and uniform elongation, while weaker texture only increased uniform elongation. [ABSTRACT FROM AUTHOR]

ZK60 magnesium alloy sheets with various texture states were successfully fabricated by controlling the rolling temperature in multi-pass lowered-temperature rolling. The microstructure including texture and the mechanical properties of the resulting sheets were investigated. Results showed that dynamic recrystallization (DRX) during current rolling process could be realized at lower deformation temperature when the thickness reduction per pass was larger than 30%, and with its help, the grain size was significantly refined and the microstructure homogeneity strikingly improved. In this circumstance, deformation temperature mainly influenced the texture state of the resulting sheets, implying that with the increase of deformation temperature the distribution of (0002) basal planes remained stable along the rolling direction but gradually increased along the transverse direction. The calculation results about the friction stress for various deformation modes indicated that the changing ratios of the critical resolved shear stress (CRSS) for the non-basal slip to that for basal slip resulted in this texture difference. Additionally, for the samples with the dominant deformation mode of basal slip, the yield stress gradually decreased and the uniform elongation increased with the weakening of basal texture. However, if dominant deformation mode changed, an abrupt change would occur in their values. This change of yield stress came from the change of CRSS, while uniform elongation from strain hardening rate. [ABSTRACT FROM AUTHOR]

Tension/compression symmetrical ZK61 magnesium alloy rod with fine grain and weak texture was achieved by compression-extrusion process. The formation mechanism of fine grain and weak texture was analyzed by investigating the microstructure and texture evolution during compression-extrusion process. In compression stage, {10–12} twinning deformation was activated greatly, which brought about significant grain refinement and formation of <0002>∥ED texture. As extrusion process going on, twinning gradually decreased and basal slip dominated the following deformation. Texture oriented into single annular shape by subsequent twinning in early extrusion and the annulation rotated toward ED gradually then merged into fiber texture by basal slip in late extrusion. Besides, texture was weakened by grain boundary slip and non-basal slip. With DRXed grain orientations similar to that of the deformed parent grains, Discontinuous dynamic recrystallization played a dominant role in grain refinement during extrusion stage, but the refinement was relatively minor compared to twining refinement in compression stage. Finally, magnesium alloy with fine grain and weak texture was achieved. The benefit of this microstructure and texture characteristic upon mechanical properties was the great enhancement of compressive yield strength, from the suppression of twinning when compressed. Therefore, tension/compression asymmetry was greatly improved by compression-extrusion process. • Tension/compression asymmetry was eliminated by compression-extrusion process. • Sharp grain refinement relied on twin deformation in early stage of the process. • Grain boundary slip and non-basal slips together contributed to texture weakening. [ABSTRACT FROM AUTHOR]

Abstract In this paper, 2.5 vol% TiBw/TA15 composites were fabricated by low-energy milling and subsequent powder extrusion. After low-energy milling process, the fine TiB 2 powders were adhered on the surface of the spherical TA15 powders. Next, the blended powders were extruded at 1100 °C with extrusion ratio of 10:1. The Widmanstatten α + β microstructure with thickness of 550–620 nm in α phase was obtained and the strong (0001) α //ED and (101) α //ED texture was formed after powder extrusion. The TiB whiskers (TiBw) twisted along the extrusion direction and led to the 'wall' structure. High-temperature tensile behavior of this studied composites was investigated at 800–950 °C with strain rate of 0.001–0.1 s−1. According to the stress-strain curves, the activation energy (Q) was calculated to be 325 kJ mol−1, higher than the TA15 matrix, which is due to the combined effect of phase morphology, extrusion texture and TiBw reinforcements. In addition, the tensile strain has effect on microstructure evolution. Static spheroidizing has been processed in the grip area of tensile sample. As the tensile strain increased, the volume fraction of and the average grain size α phase decreased. Moreover, voids nearby the TiBw reinforcements were observed due to the incoordination deformation between TiBw and TA15 matrix. [ABSTRACT FROM AUTHOR]

Abstract High-performance magnesium alloy rods with mechanical isotropy were fabricated by a designed compression-extrusion process to better adapt for industrial massive manufacture. To be specific, yield strengths over 240 MPa in both tension and compression were obtained, highlighting the improvement of tension/compression asymmetry. After investigation, tension deformation in the later compression-extrusion was dominated by slip similar to that in the as-received rod. A slight decrease in yield strength was observed in spite of remarkable grain refinement, mainly caused by the weakening of {0002} fiber texture that enhanced the activation of basal slip. On the contrary, compression deformation was initially induced by {10−12} twinning, responsible for the rather low yield strength, but it gradually shifted to slip particularly after twinning exhausted. The twinning-induced deformation was significantly suppressed by both texture weakening and grain refining, resulting in a significantly increased tendency in yield strength. Both the yield strengths could be well estimated by texture modified Hall-Petch relationships. Additionally, excellent ductility of ~35% in elongation was simultaneously achieved due to the combined contribution of texture weakening and grain refinement, indicating good secondary formability. Moreover, the addition of rare earth element could further enhance the uptrending tendency of yield strengths, which was mainly due to dispersed reinforcement. [ABSTRACT FROM AUTHOR]

Three ZK60 resulting sheets with same grain size but various texture states were successfully fabricated by a combination process of hot rolling, cold rolling and annealing treatment. Subsequently, standard Erichsen tests were performed on these resulting sheets which possessed orthotropic basal texture exhibiting an egg-shaped asymmetric distribution of basal poles from the normal direction. Combining with the analysis of strain hardening ability obtained from uniaxial tension test, it could be concluded that the magnesium alloy sheets with orthotropic basal texture presented anisotropy in strain hardening ability, and their stretch formability was dependent on the strong texture in one direction of magnesium alloy sheets. That was to say, texture weakened only in single direction could not improve the stretch formability. This conclusion was supported more by the direction of crack propagation which was parallel to the weak texture direction of magnesium alloy sheet. [ABSTRACT FROM AUTHOR]

Three ZK60 resulting sheets with same grain size but various texture states were successfully fabricated by a combination process of hot rolling, cold rolling and annealing treatment. Subsequently, standard Erichsen tests were performed on these resulting sheets which possessed orthotropic basal texture exhibiting an egg-shaped asymmetric distribution of basal poles from the normal direction. Combining with the analysis of strain hardening ability obtained from uniaxial tension test, it could be concluded that the magnesium alloy sheets with orthotropic basal texture presented anisotropy in strain hardening ability, and their stretch formability was dependent on the strong texture in one direction of magnesium alloy sheets. That was to say, texture weakened only in single direction could not improve the stretch formability. This conclusion was supported more by the direction of crack propagation which was parallel to the weak texture direction of magnesium alloy sheet. [ABSTRACT FROM AUTHOR]

In order to reduce the cyclic tension-compression asymmetry and cyclic hardening that exists widely in magnesium alloys, ZK61magnesium alloys with different texture intensities and grain sizes were fabricated by conventional extrusion and compression-extrusion process. It was found that the compression-extrusion process had a remarkable effect on the texture weakening and grain refining, which significantly improved monotonic tension-compression asymmetry and cyclic tension-compression asymmetry. Under their combined effects, the {10–12} twinning-detwinning behavior of ZK61 magnesium alloy during cyclic tension-compression deformation was effectively suppressed, resulting in a remarkable reduction of the difference of peak stresses in tension and compression. In the meantime, shape asymmetry embodied in a concave-up characteristic of the cyclic hysteresis loops was almost eliminated as the weakening of the detwinning-prismatic slip transition. Twinning-promoted dislocation pile-up and twinning-induced grain segmentation were significantly attenuated with texture weakening and grain refining, leading to a substantial weakening of cyclic hardening. Eventually, ZK61 magnesium alloy with low cyclic tension-compression. • Low cyclic tension-compression asymmetry achieved via compression-extrusion process. • {10–12} twinning-detwinning suppressed by basal texture weakening and grain refining. • Inhibition of detwinning-prismatic slip transition lowered cyclic asymmetry. • Gentle dislocation propagation correlated with basal slip retarded cyclic hardening. • Cyclic hardening quantified by a texture-modified dislocation strengthening formula. [ABSTRACT FROM AUTHOR]

A novel <0001>//ED (<0001>) texture was obtained in Mg-9Gd-5Y-0.5Zr alloy by hot extrusion at 350 °C. The formation mechanism of <0001> texture during extrusion was studied by independent analysis of plastic deformation mechanism, recrystallized (DRXed) behavior, and grain growth. The results showed that the plastic deformation mechanism was dominated by the traditional basal slip, resulting in a strong <10-10>//ED (<10-10>) basal texture at the initial stage of extrusion. The <10-10> texture was gradually weakened by the random nucleation of DRXed behavior dominated by discontinuous dynamic recrystallization (DDRX) and supplemented by continuous dynamic recrystallization (CDRX). Finally, the <0001> texture was formed due to the preferential growth of the low-energy <0001>//ED grains during grain growth process. Compared with the formation of conventional <10-10> texture by hot extrusion in the Mg–Gd series alloys, the formation of the <0001> texture in the as-extruded Mg-9Gd-5Y-0.5Zr alloy achieved outstanding room temperature ductility and hardening ability. The elongation (EL) and uniform elongation (UEL) reached 31.5% and 20.2%, respectively. • A novel <0001> texture (<0001>//ED) was obtained in Mg-9Gd-5Y-0.5Zr alloy by hot extrusion at 350 °C. • Microstructure and texture evolution during hot extrusion were demonstrated. • The formation mechanism of <0001> texture during extrusion was studied. • The strength and ductility of Mg–Gd series alloys with <10-10> and <0001> textures were compared. [ABSTRACT FROM AUTHOR]

In this study, the starting materials of the fine-grained Mg-Nd-Zn-Zr alloy with a grain size of ∼2.78 μm were prepared by hot extrusion with an extrusion ratio of 19.63 at 400 °C. The superplastic behavior and microstructure evolution of the fine-grained extruded Mg-Nd-Zn-Zr alloy was studied in the temperature ranges of 350 °C–500 °C and the strain rate ranged from 1 × 10−2 s−1 to 5 × 10−4 s−1. Results showed that the maximum elongation of 1015.50% was obtained at 450 °C with 5 × 10−4 s−1, and high strain rate superplasticity (HSRS) was achieved at 400 °C and 450 °C with 1 × 10−2 s−1. Moreover, theoretical calculations revealed that deformation mechanisms were grain boundary slip (DBS), m = 0.42–0.52 at 350 °C–450 °C, and solute drag creep (SDC), m = 0.37 at 500 °C. Meanwhile, there were regulated by grain boundary diffusion or lattice diffusion. In the last stage of deformation, due to grain growth and significant strain, plenty of geometrically necessary dislocations (GNDs) and {10–12} twins were generated in the grain, resulting in stress concentration. Because the stress concentration could not be eliminated in time, cavities were formed at the second phase particles and trigeminal grain boundaries. Various types of fracture, such as ductile fracture, microvoid accumulation fracture, and so on, resulted from the growth and connection of cavities. [ABSTRACT FROM AUTHOR]

This work investigated the asymmetry evolutions in the microstructure and the plastic deformation behavior between the entire tension and compression for AZ31 magnesium alloy by combining the experiment and visco-plastic self-consistent (VPSC) model. Large yield stress asymmetry between the tension and the compression existed at the onset of plastic deformation, but such stress asymmetry slightly increased first and then gradually decreased to 1.01 with the increase of logarithmic plastic strain. This kind of asymmetry variation was ascribed to the microstructure evolution asymmetry. Compared to the tension deformation, tension twin boundaries migrated more easily in the compression deformation owing to the appropriate crystal orientation, producing more obvious fraction variation of tension twin boundary and the intersection of different tension twin variants. The VPSC model clarified the texture evolution asymmetry between the tension and the compression by the contribution of each deformation mechanism to the macroscopic strain, revealing that prismatic slip activation in the tension triggered the development of ⟨ 10 1 ‾ 0 ⟩ / / L D (LD: loading direction) type texture while abundant tension twinning in the compression laid the foundation of ⟨ 0002 ⟩ / / L D type texture. Additionally, owing to the deformation mechanism transformation from basal slip to prismatic slip in tension deformation, the attenuation degree in the strain hardening rate was gradually weakened, while in compression deformation, the participation of elastic deformation contributed to the increasing stage of strain hardening rate after the exhaustion of tension twinning. In addition, the geometrical orientation factor and deformation mechanism factor together contributed to the decline of flow stress asymmetry. [ABSTRACT FROM AUTHOR]

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 Mg 12 Nd 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 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 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. [ABSTRACT FROM AUTHOR]