DRXed Grains Research Articles

Microstructure and mechanical property of a novel heat-resistant Mg-Ca-Mn based alloy

In this work, the microstructure and mechanical properties at both room temperature (RT) and 250 °C of an as-extruded Mg-Ca-Mn based alloy have been systematically investigated. When the extrusion temperature is as low as 260 °C (XMNdAZ-260 sample), the solute segregation at the grain boundary (GB) is few, and the ultra-fine dynamic recrystallized (DRXed) grains can be formed, which thus leads to an ultra-high yield strength (YS) of ∼426 MPa, and a limited elongation (EL) of ∼1.8% at RT. With increasing the extrusion temperature to 300 °C (XMNdAZ-300 sample), the DRXed grains have grown to some extent, and the YS is decreased to ∼373 MPa at RT, accompanied with a reasonable EL of ∼8.9%. Interestingly, the XMNdAZ-300 sample exhibits a much higher ultimate tensile strength (UTS) of ∼271 MPa at 250 °C, as compared with XMNdAZ-260 sample having UTS of only ∼224 MPa at 250 °C. The obvious solute segregation along GBs played an important role in enhancing high temperature strength via suppressing GB sliding. With the exposure time increasing, most of the GB segregation evolves to nano-precipitations, which thus leads to the strength loss at 250 °C, UTS of ∼190 MPa in 96 h-aged sample. Nevertheless, heat-resistant properties of present Mg alloys are superior to the commercial counterparts, which provides an important insight into developing novel heat-resistant Mg alloys via constructing solute segregation at GBs.

Effects of deformation temperatures on microstructures, aging behaviors and mechanical properties of Mg-Gd-Er-Zr alloys fabricated by hard-plate rolling

In this investigation, a high-strength Mg-12Gd-1.0Er-0.5Zr (wt.%) alloy sheet was produced by hot extrusion (HE) and subsequent hard-plate rolling (HPR) at different temperatures. The results indicate that the microstructures of these final-rolled sheets are inhomogeneous, mainly including coarse deformed grains and dynamic recrystallized (DRXed) grains, and the volume fraction of these coarse deformed grains increases as the rolling temperature increases. Thus, more DRXed grains can be found in R-385 °C sheet, resulting in a smaller average grain size and weaker basal texture, while the biggest grains and the highest strong basal texture are present in R-450 °C sheet. Amounts of dynamic precipitation of β phases which are mainly determined by the rolling temperature are present in these sheets, and its precipitation can consume the content of Gd solutes in the matrix. As a result, the lowest number density of β phase in R-450 °C sheet is beneficial to modify the age hardening response. Thus, the R-450 °C sheet displays the best age hardening response because of a severe traditional precipitation of β' (more) and βΗ /βΜ (less) precipitates, resulting in a sharp improvement in strength, i.e. ultimate tensile strength (UTS) of ∼ 518 ± 17 MPa and yield strength (YS) of ∼ 438±18 MPa. However, the elongation (EL) of this sheet reduces greatly, and its value is ∼ 2.7 ± 0.3%. By contrasting, the EL of the peak-aging R-385 °C sheet keeps better, changing from ∼ 4.9 ± 1.2% to ∼ 4.8 ± 1.4% due to a novel dislocation-induced chain-like precipitate which is helpful to keep good balance between strength and ductility.

A new strong and ductile multicomponent rare-earth free Mg–Bi-based alloy achieved by extrusion and subsequent short-term annealing

A new multicomponent rare-earth free low-alloyed Mg-1.0Bi-1.0Mn-1.0Al-0.5Ca-0.3Zn (wt.%) alloy is prepared by low-temperature and low-speed extrusion. The as-extruded sample has an ultra-high yield strength (∼425 MPa) but low elongation-to-failure (∼2.1%) mainly due to a bimodal grain structure containing ultra-fine recrystallized (DRXed) grains and large-sized unDRXed regions with a strong basal fiber texture feature, accompanied by a certain amount of micro-scale second phases (Al8Mn5 and Mg2Bi2Ca) and the uniformly distributed nano-scale α-Mn particles. More importantly, the excellent strength-ductility synergy is realized in the annealed samples after appropriate short-term annealing, and the yield strength and elongation-to-failure can reach ∼378 MPa and ∼16.8%, respectively. The effective inhibition of grain growth by grain boundary co-segregation of solutes and pinning effect of α-Mn nanoparticles is crucial for the annealed samples to maintain the relatively high strength. The formation of a new heterogeneous fibrous structure containing fine/coarse DRXed grains and thin fibrous unDRXed regions, along with weak basal fiber texture and low-density residual dislocations, is a key factor for the annealed sample to significantly enhance the ductility. Hence, such a new high strong and ductile low-alloyed Mg–Bi-based alloy will be helpful for enriching high performance low-cost wrought Mg alloy series to achieve extensive applications in industries.

Improvement in tensile strength of extruded Mg–5Bi alloy through addition of Sn and its underlying strengthening mechanisms

Through an investigation of the microstructure and mechanical properties of extruded Mg–5Bi– x Sn (BT5 x, x = 0, 2, 4, and 6 wt%) alloys, this study demonstrates that the addition of Sn to an Mg–5Bi binary alloy significantly improves the tensile strength of the extruded alloy. All the extruded alloys exhibit a typical basal fiber texture and a partially dynamically recrystallized (DRXed) microstructure consisting of fine DRXed grains and coarse unDRXed grains. As the Sn content increases from 0 wt% to 6 wt%, the average size of the DRXed grains decreases from 4.2 to 2.8 μm owing to the increase in the amount of precipitates via their grain-boundary pinning effect. The extruded B5 and BT52 alloys contain numerous Mg 3 Bi 2 precipitates, but their size and number density are smaller and higher, respectively, in the latter alloy. Numerous Mg 2 Sn precipitates as well as Mg 3 Bi 2 precipitates are present in the extruded BT54 and BT56 alloys, and the number density of the Mg 2 Sn precipitates is higher in the latter alloy because of its higher Sn content. The addition of 2 wt% Sn to the B5 alloy significantly improves the yield strength (YS) and ultimate tensile strength (UTS) of the extruded alloy—by 76 and 57 MPa, respectively. This drastic improvement is the combined outcome of enhanced grain-boundary hardening, precipitation hardening, and solid-solution hardening effects induced by the refined DRXed grains, numerous precipitates, and Sn solute atoms, respectively. The further addition of 2 wt% or 4 wt% Sn to the BT52 alloy leads to moderate increments in the YS and UTS of the extruded alloy. Specifically, each addition of 2 wt% Sn increases the YS and UTS by ~26 and ~20 MPa, respectively, which is attributed mainly to the additional precipitation hardening effect induced by the Mg 2 Sn precipitates.

Analysis of Abnormal Texture and Strengthening Mechanisms of Extruded Mg–Gd–Y–Nd–Zr Alloy

The formation mechanism of an abnormal texture with <0001> orientation parallel to the extrusion direction (<0001>//ED) and strengthening mechanisms in the extruded Mg–Gd–Y–Nd–Zr alloy are investigated. When extruded at a ratio of 25, the abnormal texture is accompanied by a completely dynamic recrystallized (DRXed) microstructure, and its intensity increases with increasing extrusion temperature. When the extrusion ratio is reduced to 9, the multiple texture components are formed, accompanied by nonuniform microstructures. Rare‐earth (RE) elements segregating at the grain boundary or existing as a secondary phase affect the activation of nonbasal slips and preferential growth of DRXed grains. The formation mechanisms of abnormal texture are completed DRX, the operation of pyramidal <c + a> slip, and growth advantage. The strengthening mechanisms in the extruded Mg–Gd–Y–Nd–Zr alloy mainly include solid solution strengthening, grain boundary strengthening, and precipitate strengthening, among which solid solution strengthening plays a key role. The trade‐off between the three strengthening mechanisms results in the stability of the mechanical properties of the extruded Mg–Gd–Y–Nd–Zr alloy under various extrusion conditions.

Crystal plasticity model of induction heating-assisted incremental sheet forming with recrystallisation simulation in cellular automata

To relate the thermomechanical behaviour and microstructural evolution of the heat-assisted incremental sheet forming (SPIF) for Ti–6Al–4 V sheet, multi-scale models based on crystal plasticity finite element model (CPFEM), representative elementary volume (RVE), and cellular automaton (CA) were established in this article. An experimental-scale CPFEM was built in advance to provide macrograin level strain, strain rate, and temperature output data, which were then used in RVE and CA as inputs to simulate the microstructural evolution throughout the SPIF process. The output results include the pole figures, dynamic recrystallisation (DRX) maps, and statistics results of the alpha (α) phase of the Ti–6Al–4 V (α-Ti) alloy from stage to stage throughout the 700 ^circ{rm C} SPIF. The obtained statistics results of dislocation density, grain orientation angles, and grain size were verified with electron backscatter diffraction (EBSD). The CA analysis of the DRX progress at the upper, centre, and lower regions of the deformed workpiece has discovered that the incremental increase of the strain rate has significant effects on the dislocation density that produced a proportional relationship to the DRX percentage. The results revealed that the strain rate has strong domination in affecting the slip of grains orientation, which overcomes the effect of temperature increase in this SPIF process. Furthermore, it was found that a large amount of DRXed grains were generated at the grain boundaries, which reduced the mean grain size and increased the DRX percentage, which produced an inversely proportional relationship to the dislocation density. The thermomechanical behaviour on the SPIF workpiece was increased incrementally, which is insufficient for DRX initiation in the upper region, and the behaviour was enhanced at the centre and lower region, which can be corresponded to the microstructural evolution throughout the process.

Achieving high strength-ductility synergy in dilute Mg-Al-Ca alloy by trace Ce addition

In this work, the trace Ce atoms have been added into the low-alloyed Mg-Al-Ca matrix, and the microstructure and mechanical properties have been investigated. For the Mg-Al-Ca ternary alloy, the tensile yield strength (TYS) would be decreased from ~ 321 MPa at 260 °C (extrusion temperature) to ~ 294 MPa at 290 °C. In contrast, the Mg-Al-Ca-Ce alloy can still exhibit the high YS of ~ 350 MPa and elongation of ~ 12.1% at higher extrusion temperature of 290 °C. Microstructure characterization shows that the Ce addition can effectively induce the solute segregations along both dislocations and grain boundaries in Mg-Al-Ca-Ce alloy, which thus leads to the finer grain size of 0.7 ~ 0.8 µm at a wide range of extrusion temperature. Formation of subgrain with strong texture, residual dislocations due to segregation and profuse nano-precipitations can together contribute to the high yield strength of Mg-Al-Ca-Ce alloy. More importantly, the trace Ce atoms can promote the activation of non-basal dislocations in Mg matrix and also the weakened texture in DRXed grains. As a result, the ductility is also simultaneously improved by the trace addition of Ce atom into Mg-Al-Ca based alloy. The relevant results can shed light on designing the new high strength and low-alloyed Mg alloys. • Simultaneous improvement of strength and ductility is achieved through trace Ce addition into dilute Mg-Al-Ca alloys. • Solute segregations along both dislocations and grain boundaries can be achieved by the addition of Ce. • Finer grain size of 0.7–0.8 µm at a wide range of extrusion temperature is obtained in the new Mg-Al-Ca-Ce alloy.

Microstructures and mechanical properties of Mg–6Zn–1Y–0.85Zr alloy prepared at different extrusion temperatures and speeds

The influence of extrusion temperature and speed on the microstructures and mechanical properties of the as-extruded Mg–6Zn–1Y–0.85Zr (ZWK610) alloy was inquired by indirect extrusion at three ram speeds (1, 3 and 6 mm/s) and extruding temperatures (250, 300 and 350 °C). The extruded alloy organization mainly consists of equiaxed finely dynamic recrystallized (DRXed) grains, elongated coarse un-DRXed grains and massive W–Mg3Y2Zn3 and I–Mg3Zn6Y phases. The increasing extrusion temperature and speed result in larger DRXed grains, higher DRXed volume fractions and fewer second phase volume fractions. Mechanical properties drop with increasing extrusion temperature and speed. The extruded alloy prepared at low temperature and speed reveals a lower DRXed volume fraction, a finer DRXed grain size and a higher phase volume fraction because a large number of depressively distributed particles could inhibit the grain boundary migration and pin the dislocations effectively. Excellent mechanical properties were acquired at 250 °C and 1 mm/s, with ultimate tensile and tensile yield strengths of 410 MPa and 365 MPa, respectively, while the elongation is 7.1%.

Effect of LPSO orientation on the compression behavior and workability of the Mg-5Gd-3Y–1Zn-0.5Zr alloy

To investigate the effect of LPSO orientation on the compression behavior and workability of Mg alloys, a Mg-5.3Gd-3.3Y-1.1Zn-0.5Zr (wt%) alloy was extruded to obtain the bimodal microstructure with a certain amount of directionally arranged LPSO phases. The subsequent compression tests indicate that the values of activation energy of deformation (Q) are approaching (180–194 kJ/mol) along different orientations (ED, 45°, and TD), which are much lower compared with the as-homogenized Mg-Gd-Y-Zn-Zr alloys due to the sufficient initial grain boundaries (I-GBs). Enhanced kinking and DRX at kink bands at the higher Zener-Hollomon (Z) parameters result in the slight decrease of Q and the movement of optimal processing domains for the ED orientation. The I-GBs overshadow the effect of LPSO orientation via kinking deformation on the DRX ratio and workability. The increase of Z parameter tends to reduce the DRXed grain size and the homogeneity of both the microstructure and hardness. Different α-Mg and LPSO orientations of the extruded alloy induce the anisotropy of peak flow stress (σp) during compression and the extraordinary elliptical shape of the compressed TD specimens. This work provides useful information for the industrial production of wrought LPSO-containing Mg alloys.

Achieving high strength and rapid degradation in Mg-Gd-Ni alloys by regulating LPSO phase morphology combined with extrusion

In this study, Mg-13.2Gd-4.3Ni alloys containing continuous bulk-shaped long-period stacking ordered (LPSO), lamellar LPSO, and a small amount of eutectic phase were prepared, and the evolution of microstructure at different extrusion temperatures and its influence on mechanical and degradation properties as well as corrosion mechanism were investigated. Preheating before extrusion can effectively promote the precipitation of lamellar LPSO in matrix. EX400 with higher volume fraction of non-DRXed grains exhibited higher strength, which was mainly due to strong texture, high dislocation density, and high volume fraction of lamellar LPSO. The EX420 with higher volume fraction of DRXed grains showed higher degradation rate, which was mainly due to the higher density of grain boundary. The EX400 exhibited excellent comprehensive properties with tensile yield strength (TYS) of 334 MPa, ultimate tensile strength (UTS) of 484 MPa and elongation (EL) of 7.4%, ultimate compressive strength (UCS) of 638 MPa and compressive yield strength (CYS) of 443 MPa, degradation rate of 86.1 mg/cm2/h at 93 °C in 3 wt.% KCl solution.

Hot-deformation kinetics analysis and extrusion parameter optimization of a dilute rare-earth free magnesium alloy

The fundamental research on thermo-mechanical conditions provides an experimental basis for high-performance Mg-Al-Ca-Mn alloys. However, there is a lack of systematical investigation for this series alloys on the hot-deformation kinetics and extrusion parameter optimization. Here, the flow behavior, constitutive model, dynamic recrystallization (DRX) kinetic model and processing map of a dilute rare-earth free Mg-1.3Al-0.4Ca-0.4Mn (AXM100, wt.%) alloy were studied under different hot-compressive conditions. In addition, the extrusion parameter optimization of this alloy was performed based on the hot-processing map. The results showed that the conventional Arrhenius-type strain-related constitutive model only worked well for the flow curves at high temperatures and low strain rates. In comparison, using the machine learning assisted model (support vector regression, SVR) could effectively improve the accuracy between the predicted and experimental values. The DRX kinetic model was established, and a typical necklace-shaped structure preferentially occurred at the original grain boundaries and the second phases. The DRX nucleation weakened the texture intensity, and the further growth caused the more scattered basal texture. The hot-processing maps at different strains were also measured and the optimal hot-processing range could be confirmed at the deformation temperatures of 600∼723 K and the strain rates of 0.018∼0.563 s−1. Based on the optimum hot-processing range, a suitable extrusion parameter was considered as 603 K and 0.1 mm/s and the as-extruded alloy in this parameter exhibited a good strength-ductility synergy (yield strength of ∼ 232.1 MPa, ultimate strength of ∼ 278.2 MPa and elongation-to-failure of ∼ 20.1%). Finally, the strengthening-plasticizing mechanisms and the relationships between the DRXed grain size, yield strength and extrusion parameters were analyzed.

Unexpected effect of pre-aging prior to extrusion on microstructure and mechanical properties of extruded Mg–8Sn–6Zn–0.1Mn alloy

Pre-aging prior to extrusion (AE), aiming to achieve high strength without sacrificing ductility, has shown considerable potential in Mg-Sn alloys containing low content of Zn element. For Mg–8Sn–6Zn–0.1Mn alloy containing high contents of Sn and Zn elements, however, an unexpected decrease in mechanical properties after AE treatment is observed and comprehensively investigated in this paper. We demonstrate that after pre-aging treatment, the size and volume fraction of bulk Mg2Sn particles are not decreased as expected, but some fine particles are segregated around the bulk Mg2Sn phases due to high contents of Sn and Zn in this alloy. The bulk phases are prone to facilitate the occurrence of particle-stimulated nucleation and continuous dynamic recrystallization mechanisms during extrusion. Since pre-aging treatments produce a high number of fine particles, these particles exert a pinning or drag effect on grain boundaries, inhibiting the nucleation of dynamic recrystallization, which reduce the volume fraction of dynamic recrystallized grains (DRXed). Unexpectedly, solution-extruded (SE) alloy has finer and higher volume fraction of DRXed grains than AE alloy. Additionally, the fine particles produced by dynamic precipitation in SE alloy are densely distributed and smaller than those in AE alloy. The coarse particles in AE alloy serve as the crack initiation sites under external force, and reduce the ductility of the alloy. Consequently, SE alloy with excellent strength-ductility synergy can be attributed to a combination of refinement of grain structure and fine densely distributed particles.

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

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

Superior elevated-temperature strength of Mg–Y–Sn alloys with thermostable multi-scale precipitates and grain structure

The newly developed Mg–Y–Sn extrusions are prepared by adding Sn (0.6 and 1.5 wt%) to Mg–6Y. The optimized Mg–6Y-1.5Sn exhibited superior elevated-temperature strength up to 300 °C, charactered by the pronounced strain hardening. Specifically, the yield stress and ultimate tensile strength of this alloy at 300 °C are 186 ± 3 MPa and 328 ± 7 MPa, respectively, which are 64% and 93% higher than that of the highly RE-alloyed WE54. Sn addition to Mg–6Y introduces a large number of thermal-stable micron/nano-scale Sn3Y5 precipitates. Mg–6Y-1.5Sn, which contained more nano-scale precipitates, exhibited better elevated-temperature strength than that of Mg–6Y-0.6Sn. The grain structure transitioned from a uniformed equiaxial grain in Mg–6Y to a thermal-stable multiscale grain structure in Mg–6Y-0.6/1.5Sn, which consisted of fiber textured un-DRXed area with high dislocation density and randomly orientated DRXed grains with low dislocation density. The exceptional elevated-temperature strength strongly correlated to the combined thermal-stable multiscale precipitates and grain structures.

Corrosion behaviors of hot-extruded Mg96Y2Zn2 alloy in transverse and longitudinal directions: Guidance for parameters selection

The hot-extruded Mg alloys containing long period stacking ordered (LPSO) phase suffered from the difference of corrosion behavior between transverse and longitudinal sections. To fathom out the mechanism of the difference and improve the overall corrosion resistance, the extruded Mg96Y2Zn2 alloys are prepared through different ram speed. Dynamic recrystallization was achieved in extruded Mg96Y2Zn2 alloys and the LPSO phases were elongated along the extrusion direction (ED). The results indicates that the basal texture can be strengthened by increasing the ram speed, since the volume fraction of dynamically recrystallized (DRXed) grains is reduced. As a result of the extruded Mg96Y2Zn2 alloys did not undergo passivation during corrosion, the decrease in grain size led to an increase in corrosion rate. The peeling off of LPSO strips with larger size caused more serious damage to the alloys. The existence of texture and huge LPSO strips lead to the difference of corrosion properties in the two directions. Therefore, larger DRXed grains with a higher volume fraction and finer scaled LPSO strips are beneficial to the corrosion properties of extruded Mg96Y2Zn2 alloys. Parameters have the same effects as low ram speed are conducive to improve corrosion resistance.

Tensile behavior at various temperatures of the Mg-Gd-Y-Zn-Zr alloys with different initial morphologies of LPSO phases prior to extrusion

The tensile behavior at (−100)-300 °C of the extruded and peak-aged Mg-5Gd-3Y-xZn-0.5Zr (x = 1 and 2 wt%, designated as VWZ531K and VWZ532K) alloys was investigated in the aspects of microstructural evolution, deformation modes, mechanical properties, etc. The higher Zn content endows the VWZ532K alloy with more intragranular lamellar LPSO phases and larger interdendritic ones at the initial homogenized status, which induces the lower DRX ratio, finer DRXed grain size, and negligible aging hardening response subsequently. During extrusion, precipitation of intragranular LPSO phases occurred in the VWZ531K alloy and partial DRXed grains formed a special texture component with the c-axis aligning parallel to the extrusion direction. However, the VWZ532K alloy experienced the dissolution of intragranular LPSO and dynamic precipitation of β phases. During tensile tests, deformation modes (including twinning, basal slip and non-basal slip) were modified by the testing temperature, grain orientation, LPSO morphology, etc. Compared with the β′ precipitates, LPSO phases are more thermostable to maintain the high-temperature strength, which induce the higher tensile yield strength of the peak-aged VWZ532K alloy (182 MPa) at 300 °C. The larger volume fraction of tension twins and lamellar LPSO phases result in the abnormal high elongation (17.9%) at −100 °C for the VWZ531K alloy.

Dynamic recrystallization behavior of the equiatomic FeCoCrNi high-entropy alloy during high temperature deformation

The hot deformation behavior of a FeCoCrNi high-entropy alloy was investigated in this work. The tests were carried out at 900–1100 °C, under strain rates of 0.001–0.1 s−1 and the effect of friction between specimen and tool on flow stress curves under different deformation conditions was analyzed and modified. The experimental results were employed to determine the constitutive equation with strain-dependent material constants for modeling and for prediction of flow stress at different deformation conditions, using the data obtained from the Sellars–Tegart–Garofalo equation. Microstructural studies revealed that dynamic recrystallization was the primary softening mechanism, resulting in significant microstructural reconstitution and fine grains formation. A complete-recrystallized microstructure with a high proportion of annealing twin boundary was obtained in the specimen hot compressed at 1000 °C/0.01 s−1, so that the average grain size was 22 μm, compared to the initial grain size of 42 μm. The increase of the size and fraction of the DRXed grains during hot deformation decrease the alloy hardness. The dynamic recrystallization parameters such as critical, peak, and steady-state stress, and strain were determined using the work hardening rate analysis. Moreover, the activation energy for deformation of the alloy was determined to be 417 kJ mol−1. The results also indicated that the critical stress and strain for initiating dynamic recrystallization were inversely proportionate to deformation temperature and the strain rate. Furthermore, increasing the deformation temperature resulted in grain growth, whereas increasing the strain rate led to grain refinement. The critical stress and strain were dependent on the Zener–Hollomon (Z) parameter via a power relation with exponents of 0.14 and 0.12, respectively.

Hot deformation behavior, processing map, microstructure evolution and dynamic recrystallization mechanism of Mg-5Al-0.6Sc alloy

In this study, the hot compression test of as-cast Mg-5Al-0.6Sc alloy was performed on Gleeble-3500 simulator, and the effect of deformation temperature (T: 250–400 °C) and strain rate (ε̇: 0.001 –1 s−1) on hot deformation mechanism of the alloy were systematically investigated. The thermal deformation behavior, microstructure evolution, texture and dynamic recrystallization (DRX) mechanism of the alloy were analyzed in detail by combining the constitutive equation, processing map and electron backscatter diffraction (EBSD) technology. The results demonstrated that the flow stress decreased with the increase of T and decrease of ε̇. The established constitutive equation could accurately predict the hot deformation behavior of the alloy, and the calculated average activation energy (Q) is 144.58 kJ/mol. Based on processing map, the optimal processing area is within 300–350 °C, 0.001 s − 1 and 350–400 °C, 0.001 s−1 - 0.01 s−1. The microstructure at 350 °C and 0.001 s−1 is more uniform and exhibits low residual stress level. The increase of T and decrease of ε̇ are both conducive to the occurrence of DRX. DRX mechanism includes discontinuous DRX (DDRX), continuous DRX (CDRX), deformation twin induced DDRX and CDRX. In addition, both DRXed grains and unDRXed grains showed typical<0001>// CD texture. Combined with the in-grain misorientation axis (IGMA) analysis, when T is 250 °C and 300 °C, the deformation is dominated by basal<a>dislocations and prismatic<a>dislocations, and the proportion of twinning and DRX is extremely low. When T is 350 °C and 400 °C, the pyramidal Ⅱ<c+a>dislocations is activated greatly, and the DRX fraction increases significantly, which become the predominant deformation mechanism.

Microstructural characterization and mechanical response of the extruded ZK61 magnesium alloy under dynamic and quasi-static loading

The microstructural characterization and mechanical behavior of the extruded ZK61 alloy were examined under dynamic and quasi-static loading at 623 K. The microstructure showed that an adiabatic shear band (ASB, ~10 μm in width) was formed under dynamic loading at 3.6 × 103 s−1 due to severe local plastic deformation and it was composed of ultra-fine grains (~0.46 μm). By comparison, the shear deformation of quasi-static loading was located in an area (~200 μm in width) with equiaxed grains (~4 μm). The texture analysis of the shear regions showed a stable orientation that all the (0002) basal plane was parallel to the shear direction (SD) and the orientation mainly aggregated near 〈10−13〉//SD, while a weak peak around 〈0001〉//SD appeared with a strain rate of 1.0 × 10−3 s−1. The main recrystallization mechanism during quasi-static deformation was discontinuous dynamic recrystallization (DDRX) which nucleated at the grain boundaries by absorbing surrounding high-density dislocations. However, the formation of the DRXed grains within the ASB during dynamic deformation was attributed to rotational dynamic recrystallization (RDR) that the sub-grain boundaries tilted nearly 30° to generate new grains driven by the grain boundary energy. For mechanical responses, the stress-strain curve of dynamic loading showed high yield stress and long working-hardening stage, while the strain-hardening and thermal-softening in quasi-static curves reached a dynamic balance.

The microstructure evolution and abnormal yield asymmetry of extruded Mg-10Gd-0.5Zr alloy

The Mg-10Gd-0.5Zr alloy had a bimodal microstructure and abnormal yield asymmetry (CYS/TYS = 1.4) after extrusion. In this paper, we discussed the origin of this asymmetry and researched the microstructure and texture variation after tensile and compression using EBSD analysis. The deformed grains exhibited intensive basal texture (<10-10>//ED), while the fine DRXed grains showed weak or even random texture. The maximum MUD value of unDRXed grains increased during tension and decreased due to twinning during compression. It was found that the dislocation slip dominated both tensile and compressive deformation. The deformed grains mainly occurred prismatic <a> slip and the DRXed grains were basal slip. Numerous DRXed grains undertaken the main deformation task. Suppression of extension twinning and strain localization were the secondary and main reasons for this abnormal yield asymmetry.