TD-split Texture Research Articles

Effects of Sn and Mn additions on microstructural characteristics and tensile properties of Mg-1Gd alloy

Effects of Sn, Mn, and their combined additions on microstructural characteristic and tensile properties of extruded Mg-1Gd (G1) alloy are explored. Compared to the sole Sn or Mn addition, an excellent grain refining is happened with the Sn and Mn combined addition. The average grain size of G1, Mg-1Gd-0.8Sn (GS10), Mg-1Gd-0.7Mn (GM10) and Mg-1Gd-0.8Sn-0.7Mn (GSM100) alloys is ∼21.3, 10.1, ∼12.8 and ∼6.8 μm, respectively. The sole Mn addition enhances the strength and ductility of G1 alloy. The forming the fine α-Mn particles and grain refining are attributed to the improved properties of GM10 alloy. The sole Sn addition increases the yield strength of G1 alloy along extrusion direction (ED), but it decreases along transverse direction (TD), The inhomogeneous distribution of coarse GdMgSn particles and formation of TD-split texture should play an important role. The combined effects of Sn and Mn additions guarantee high strength-ductility synergy of GSM100 alloy. The GSM100 alloy exhibits the ultimate strength, yield strength and ductility of ∼276, ∼158 MPa and 24.7 % along ED, and ∼253, ∼157 MPa and 17.5 % along TD, respectively. The jointly effect of the fine grains, a lot of fine GdMgSn and α-Mn particles, the texture weakening and Sn solute atom contributes to the enhancement of properties of GSM100 alloy.

Microstructure and texture transformation of unidirectional rolled 3% Y2O3p/ZGK200 composites during annealing

The microstructure and texture transformation of unidirectional rolled 3% Y2O3p/ZGK200 composites were investigated after annealing at 300 °C for 5–60 min. The results showed that the deformed grains transformed into fine recrystallized grains which continuously grew up during annealing. Correspondingly, the elliptical annular texture changed into a non-basal texture tilted along the transverse direction (TD) with the reduced texture intensity, the widened distribution and the increased tilting angle of TD-split texture. The recrystallized texture was influenced by preferential grain nucleation and preferential grain growth of recrystallized grains with c-axis tilted 45–70° and 70–90° from normal direction (ND) during annealing. The Y2O3 particles could promote a higher tilting angle while the w-phases could also promote recrystallized grains. In addition, co-segregation of Zn/Gd resulted in TD-split texture after annealing. Meanwhile, the recrystallized grains with c-axis tilted 45–70° from ND showed preferential growth, which was attributed to the reduced store energy and increased low energy grain boundary such as 73° [10−10].

Effect of unidirectional rolling and cross-rolling on microstructure and mechanical anisotropy of Mg-Gd-Y-Ag-Zr plates

Mg-10Gd-2Y-0.4Ag-0.4Zr (wt%) alloy plates are prepared by Unidirectional Rolling (UR) and Cross-Rolling (CR). The effects of these two methods on the microstructure and mechanical anisotropy of the plates are investigated in detail by combining microstructure characterization and room temperature tensile tests. The results show that the UR plate has a finer grain size and obvious dynamic precipitation response, with many dynamically precipitated β phase particles distributed along the rolling direction and forming particle strips. The CR plate has experienced more dynamic recovery, and the driving force of dynamic recrystallization is decreased, resulting in larger grain size. However, the more dynamic recovery reduces the dynamic precipitation response and leads to a more uniform microstructure, and hardly finds dynamic precipitated β phase particles in the CR plate. The texture component of the UR plate is the basal texture and TD-split texture, while that of the CR plate is the basal texture and rare RT-split texture. The TD-split texture and the anisotropic distributed particle strips in the UR plate caused a strong mechanical anisotropy. While the yield anisotropy and elongation anisotropy of the CR plate are reduced simultaneously due to the more uniform microstructure and rare RT-split texture.

Insights into the microstructures and mechanical properties of magnesium–calcium–transition elements: A combined experimental and simulation study

Small amounts of transition elements: Ti, Mn, Fe, Co, and Ni, have been added to a Mg–0.1Ca (wt%) alloy to elucidate their additions on the microstructure and room temperature (RT) mechanical properties. Only Ni was effective in weakening the texture intensity and thus led to the improvement in RT formability and ductility, whereas the other elements were basically no effect. The microstructural characterization by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in conjunction with energy-dispersive X-ray spectrometry (EDS) and numerical simulation using a grain boundary (GB) phase model indicates that the Ca and Ni co-segregated to the GB of the Ni-containing alloy, while the GB of the other alloys was enriched with Ca only. Further investigations by a correlative electron backscatter diffraction and STEM-EDS reveal that the transverse direction (TD) oriented GBs had significantly lower concentration of Ca and Ni compared to the basal-oriented GBs, which resulted in the development of the TD-split texture in the Ni-containing alloy. A compositionally optimized Mg–0.1Ca–0.1Ni (wt%) alloy showed a large index Erichsen value of 8.5 mm in the sheet form, and exhibited a high tensile yield strength of 238 MPa with a moderate fracture elongation of 14% in the form of an extruded rod. Due to the addition of small amounts of alloying elements, the newly developed Mg–0.1Ca–0.1Ni alloy had an excellent thermal conductivity of 154 W/(m·K) which is even higher than that of a commercial 5052 Al alloy.

Influence of aluminum content on microstructure and performance of Mg-Zn-Ca-Al-Mn magnesium alloys

The influences of Al content on microstructure, mechanical properties, stretch formability and thermal conductivity of Mg-1.5Zn-0.3Ca-xAl-0.2Mn (x: 0.2, 0.5, 1, 1.25, 1.5, 2, wt%) alloys were investigated. With increasing the Al content from 0.2 wt% to 2 wt%, the texture changed from the TD-split texture to the quadrupolar texture at the Al content of 1.25 wt%, and finally became the RD-split texture with an increased texture intensity. The change of texture can be attributed to the formation of Al2Ca phase, which weakens the segregation of Ca at grain boundaries due to the decreased amount of Ca solute atoms in the α-Mg matrix. In addition, Al-Mn precipitates changed from a spherical shape to a rod shape accompanied by a largely increased Al/Mn ratio and a decreased amount of precipitates, when the Al content was increased to be larger than 1 wt%. The 0.2–1.5 wt% Al added alloys exhibited excellent stretch formability with the Erichsen values of 8.4–9.1 mm, which were much larger than that (6.8 mm) of the 2 wt% Al added alloy due to texture effect. The 1 wt% Al added alloy had the largest Erichsen value of 9.1 mm, while the 0.2 wt% and 2 wt% Al added alloys exhibited much higher yield strength (165 and 171 vs. 144 MPa). The thermal conductivity continuously decreased with increasing the Al content. Compared to the 2 wt% Al added alloy, the 0.2 wt% Al added alloy exhibited a much higher thermal conductivity (140 vs. 105 W/(m·K)) benefiting from the low concentration of Al solute atoms in the α-Mg matrix. Consequently, a combination of strong mechanical strength, excellent stretch formability and high thermal conductivity was achieved in the low Al-containing alloys with 0.2–0.5 wt% Al.

The effect of Gd on the microstructure evolution and mechanical properties of Mg-4Zn-0.6Ca alloy

In this work, the effect of Gd on the microstructure evolution and mechanical properties of Mg–4Zn–0.6Ca–xGd (x = 0, 0.3, 0.6 and 1, wt%) alloys were investigated systematically. The results show that Mg-4Zn-0.6Ca alloy was composed of α-Mg, Mg7Zn3 and Ca2Mg6Zn3 phase. The W-phase (Mg3Zn3Gd2) was synthesized after addition of Gd. The dynamic recrystallization was restrained and the average grain size decreased after 0.6 wt% Gd addition, causing the increase of unrecrystallized region. In addition, the volume fraction of second phase increased with increasing Gd content up to 1 wt%, and the effect of particles stimulated nucleation (PSN) was enhanced, resulting in a decrease in unrecrystallized region. The addition of Gd promoted the occurrence of the overall texture split and TD-split texture component, causing decreased basal texture intensity. An optimal mechanical property of Mg–4Zn–0.6Ca–1Gd alloy, with the yield and ultimate tensile strength of 240 MPa and 297 MPa, respectively, was achieved. The values were increased by 82 MPa and 37 MPa, respectively, compared with that of Mg–4Zn–0.6Ca alloy. In initial deformation stage, strain-hardening rate of alloys decreased with increase of Gd content. Mg-4Zn-0.6Ca-0.6Gd alloy possessed the lowest strain-hardening rate because of fine grain size. However, strain-hardening rate was increased when Gd content was increased to 1 wt%, which may be related to decreased texture intensity and presence of many second phases. This work reveals the effect of co-addition of minor Ca and Gd on the microstructure evolution and mechanical properties of Mg-Zn alloys, which provides theoretical basis for the development of high strength Mg alloy.

Formation mechanism of high-strain bands in commercially pure titanium

In textured α-Ti, band-like high-strain regions at approximately 45° to the loading direction are commonly observed under tensile deformation. Herein, such high-strain regions were called high-strain bands (HSB), and the reasons for the formation mechanism of HSBs were investigated by a uniaxial tensile test and crystal plasticity finite element (CPFE) analyses. First, we conducted a uniaxial tensile test of commercially pure titanium (CP–Ti) with a TD-split texture, where aggregates of (0001) split and incline in the transverse direction, and changes in strain distributions with deformation were observed by digital image correlation. The strain distributions showed that HSBs of approximately 45° to the loading direction were formed from the initial stage of deformation. Second, a geometric model including crystal orientation information was constructed from the crystal orientation map of the CP-Ti specimen obtained by electron back-scattered diffraction, and the cause of the formation of HSBs was investigated by CPFE analysis. The stress–strain relationship and strain distributions obtained by CPFE analysis correlated well with those obtained experimentally, and the HSBs were successfully reproduced. Finally, CPFE analyses were conducted when the loading conditions, critical resolved shear stress (CRSS), or elastic constants were changed. These results show that the HSBs formed from the initial stage of deformation and the distributions formed by elastic deformation changed depending on the elastic anisotropy. However, the distribution of HSBs after plastic deformation was unchanged by elastic anisotropy. This may be because the directions of easy deformation by elastic and plastic deformation coincided. Elastic anisotropy did not affect the distributions of HSBs formed by plastic deformation, and elastic and plastic deformations were predominantly determined by elastic constants and CRSS, respectively. Curved HSBs were also observed when plastic deformation-resistant regions occupied a large area in the specimen. In this case, the distributions of HSBs, caused by elastic deformation did not coincide with those of the plastic deformation.

Static recrystallization behavior of the cold-rolled Mg-1Al-1Zn-0.1Ca-0.2Y magnesium alloy sheet

In this study, we investigated the static recrystallization behavior and basal texture change from rolling direction (RD)-split (c-axes of grains toward the RD) to transverse direction (TD)-split (c-axes of grains toward the TD) of the cold-rolled Mg-1Al-1Zn-0.1Ca-0.2Y (AZXW1100) alloy during annealing. The cold-rolled AZXW1100 alloy sheet contained highly deformed shear bands (SBs), corresponding to 58 % of the total area, which caused rapid recrystallization at the beginning of annealing. The fine recrystallized grains nucleated in the SBs, and the intersection of the twins grew larger while consuming the deformed matrix grains, which did not recrystallize even at the late stage of annealing and were consumed by the surrounding recrystallized grains nucleated on the SBs. Owing to the difference in the recrystallization initiation time between the SB and deformed matrix grains, the recrystallized grains nucleated in the SBs guided the overall recrystallization behavior. Additionally, quasi-in-situ electron backscattered diffraction analyses clearly showed that among the recrystallized grains nucleated at the SBs, the grains with TD texture components became larger through preferential growth, whereas those with RD texture components did not grow and disappeared. Owing to this preferential grain growth, the texture intensity in the RD decreased and that in the TD was maintained, resulting in the formation of a diamond-like or TD-split texture. In this study, the co-segregation of Al, Zn, and Ca atoms along the grain boundaries and the formation of nanoscale Al8Mn5 particles were found to reduce boundary mobility and, consequently, hinder grain growth. These results can explain the texture change from a strong RD-split to a weak TD-split during annealing.

Unveiling the rolling texture variations of α-Mg phases in a dual-phase Mg-Li alloy

LZ91 Mg-Li alloy plates with three types of initial texture were rolled by 70% reduction at both room temperature and 200 °C to explore the rolling texture formation of α-Mg phase. The results showed that the rolling texture is largely affected by the initial texture. All the samples exhibited two main texture components as RD-split double peaks texture and TD-split double peaks texture after large strain rolling. The intensity of the two texture components was strongly influenced by the initial orientation and rolling temperature. Extension twinning altered the large-split non-basal orientation to a near basal one at low rolling strain. The basal orientation induced by twinning is unstable, which finally transmitted to the RD-split texture. The strong TD-split texture formed due to slip-induced orientation transition from its initial orientation. The competition between prismatic 〈a〉 and basal slip determined the intensity and tilt angle of the TD-split texture. By increasing the rolling temperature, the TD-split texture component was enhanced in all three samples. Limitation of extension twinning behavior and the promotion of prismatic slip at elevated temperature are the main reasons for the difference in hot and cold rolling texture.

Understanding the mechanisms of texture evolution in an Mg-2Zn-1Ca alloy during cold rolling and annealing

A TD-split basal texture with two peaks highly tilted from the normal direction (ND) towards the transverse direction (TD) is usually developed in Mg-Zn-Ca plates and can effectively improve ductility and formability. In the present study, the texture evolution during cold rolling and subsequent annealing of a Mg-2Zn-1Ca plate with initial TD-split texture was investigated, and new insights into the mechanisms of texture evolution were obtained. The results show that a dumbbell-shaped basal texture transformed into an elliptical shape after 41% cold rolling. The random distribution of prismatic planes became preferred with <101¯0> largely parallel to the rolling direction (RD). Crystal plasticity simulations revealed that basal slip was the predominant deformation mode, and inclined basal poles toward the ND. The activation of other non-basal slips would retard this tendency. Prismatic slip with a relative activity of 20% to 30% preserved the pre-existing TD-split texture after a high rolling reduction of 41%. Pyramidal <c+a> slip prevented the formation of basal fiber and lead to a spreading of basal poles toward the RD mainly at strains over 29%. After full recrystallization, the elliptical TD-split basal texture became a dumbbell-shaped TD-split texture. Grain nucleation was observed at grain boundaries (GBN mechanism), within deformation twins (DTN mechanism), and near precipitates (PSN mechanism). GBN and DTN mainly developed a TD-split basal-texture. Instead of the formation of random orientations as considered previously, PSN produced a TD-split basal-texture, and the basal poles exhibited a much wider distribution with high angle of the peaks off the ND. The grains nucleated by GBN, DTN, and PSN did not exhibit preferred growth, and consequently, the texture hardly changed during subsequent grain growth.

Effect of annealing temperature on microstructure and mechanical properties of cold-rolled commercially pure titanium sheets

The strength of traditional commercially pure titanium (CP-Ti) alloys often fails to meet the demand of structural materials. In order to enhance their mechanical properties, the cold-rolled CP-Ti alloys were annealed at different temperatures, and the recrystallization behavior and texture evolution were investigated. It was found that the bimodal microstructure (equiaxed and elongated grains) was formed after partial recrystallization, and the corresponding sample exhibited an excellent combination of ultimate tensile strength (702 MPa) and total elongation (36.4%). The recrystallization nucleation of CP-Ti sheets occurred preferentially in the high strain and the high-angle grain boundaries (HAGBs) regions. Meanwhile, the internal misorientations of the deformed heterogeneous grains increased and transformed into HAGBs, which further promoted the recrystallization nucleation. The main recrystallization texture was basal TD-split texture transformed from cold-rolled basal RD-split texture, and the oriented nucleation played a dominated role during recrystallization.

Local slip activities in polycrystalline α-Ti depending on textures and strain rates

It is possible that strain localization in polycrystalline α-Ti leads to the fracture, and it is crucial to evaluate the local slip activities for individual slip systems depending on their textures and loading conditions. In this study, the effects of textures and strain rates on local slip activities were investigated using the crystal plasticity finite element method. For the analysis, microstructural models of α-Ti with the following three textures were employed: aggregates of (0001) axes are (i) splitting in rolling direction (RD-split texture), (ii) splitting in transverse direction (TD-split texture), and (iii) aligned in normal direction (basal texture). For each texture model, two variations in the crystal orientation distributions were considered, namely, small and large scatterings of crystal orientations in the (0001) axes by normal random numbers. The differences in the strain rate sensitivities of the critical resolved shear stresses (CRSSs) among slip systems were also considered. Tensile loading was applied by a forced displacement in the RD with two strain rate conditions of 1.0 × 10−4 s−1 and 1.0 × 10−1 s−1. Local non-prismatic slips were easier to operate in the models with basal and RD-split textures than with the TD-split texture. The slip strains for non-prismatic slip systems were higher at higher strain rates, while activities in the prismatic slips decreased with an increase in strain rates. The mechanism of the exchange of slip system activities can be explained by strain redistribution between hard and soft regions and changes in CRSS as a function of strain rates.

Dependence of compressive creep behavior on the loading direction of an extruded Mg sheet with an extremely dilute yttrium addition

In this work, the dependence of compressive creep behavior on loading direction was investigated using an extruded Mg sheet with an extremely dilute yttrium addition (0.2 wt%Y) and a split texture. The compressive creep tests were conducted at 393 K under applied stress ranging from 50 MPa to 100 MPa, with the loading direction parallel to the extrusion direction (ED), transverse direction (TD) and normal direction (ND), respectively. It was shown that the creep behavior of this dilute alloy had obvious dependence on the loading direction. The creep resistance ranked as a high-to-low sequence of ND > TD > ED. The creep mechanisms for all loading directions were revealed to be independence on the applied stress. Normal {101‾2} twinning, independent prismatic slip and pyramidal <c + a > slip were all detected in the ED sample. Differently, the TD and ND samples shared identical creep mechanisms, including anomalous {101‾2} twinning, cross-slip and pyramidal <c + a > slip. For the ED sample, the easy twin penetration and independent prismatic slip collaboratively conspired to the poor creep resistance. For the TD and ND samples, the successive work hardening induced by anomalous {101‾2} twins and the solute segregation at grain boundaries contributed to the high creep resistance. Although the creep resistance has long been thought to proportionate to the yield stress, this work discovered that the sample with low yield stress could possess high creep resistance in a TD-split texture. Henceforth, the findings are definitely helpful for the microstructure designs of heat-resistant Mg alloys.

Simulation-aided analysis on mechanical properties of dilute Mg-Zn-Ca alloy sheets

The relationship between Zn content and room temperature (RT) mechanical properties of dilute Mg-xZn-0.1Ca (x = 0.1, 0.2,0.3, 0.5, 1.5, 2.5 in wt%) alloy sheets was investigated. The index Erichsen (IE) value, an indicator of stretch formability, was found to increase significantly from 6.6 mm to 8.4 mm by increasing the Zn content from 0.2 wt% to 0.3 wt%. Visco-Plastic Self-Consistent (VPSC) simulation revealed there was no apparent difference in the relative activity of deformation modes in Mg-0.2Zn-0.1Ca and Mg-0.3Zn-0.1Ca alloys. On the other hand, electron back-scattered diffraction observation showed that a component having basal poles tilted towards the transverse direction (TD) began to appear when 0.3 wt% of Zn was added, and the typical TD-split texture was developed when the Zn content was increased to more than 1.5 wt%. Therefore, the rapid improvement of RT formability observed in this study can be attributed to the formation of TD-split texture. In addition to this, the efficient scheme for parameter fitting required to use VPSC simulation was also proposed in this study.

An exceptional ductility of AZ31 magnesium alloy sheet achieved by consecutive multi-pass cooperative lowered-temperature rolling

In this study, a novel technique of consecutive multi-pass cooperative lowered-temperature rolling (CMCLR) was proposed for the first time, with the purpose of preparing high performance wrought magnesium alloys. Based on this, a highly ductile magnesium alloy sheet could be effectively produced from ingot. The corresponding microstructure could directly evolve from coarse dendrites to equiaxed grains with an average size of ∼5 μm, which was attributed to the intense dynamic recrystallization (DRX) during isothermal deformation. The equivalent strain gradually decreased from the surface to the interior and edge of the rolled sheet due to the anisotropic plastic deformation. Instead, the temperature of the core of the sheet was slightly higher than that of the surface due to the deformation heat effect. The basal texture in the RD-TD plane generally weakened in the form of the splitting of basal texture toward the RD and the broadening of basal plane away from the pole center due to texture randomization dominated by DRXed grains. The exceptional ductility of more than 28.7% together with acceptable ultimate tensile strength of not less than 267 MPa was ascribed to the progressive work hardening as a result of seamless switching of multiple deformation modes, i.e., basal dislocation-slip-mediated deformation was preferentially operated and then was substituted by twinning-controlled deformation and non-basal dislocation-slip-dominated deformation. The selection of {101‾2} twin variants agreed well with geometrical compatibility factor (m’) criterion instead of Schmid’s law. The activated twin variants nearly engulfed the whole parent grains for the sake of preserving compatible deformation continuity at ambient temperature, giving rise to the formation of TD-split texture. Comparatively, the {101‾2} twinning could randomize the basal texture via reorienting grain orientations which in turn facilitated the reactivation of dislocation slip systems in the case of high temperature deformation.

The preferential growth and related textural evolution during static recrystallization in a cold-rolled Mg–Zn–Gd alloy

The grain growth process plays an important role in the texture formation in magnesium alloys. The microstructural and micro-textural evolution of a cold-rolled Mg–Zn–Gd alloy during annealing at 350 °C for 60–190 min were tracked by quasi-in-situ electron backscatter diffraction method. The results show that grain growth takes place gradually with the annealing time increasing. Moreover, the TD-split texture maintains the texture type but alters in three aspects - the increased tilting angle, the decreased pole intensity and the widened distribution of high-intensity area. Grains with their c-axis tilting 45–70° from normal direction show preferential growth which is closely associated with the texture changes. The original grain size advantage is one of the important factors leading to the growth advantage, some grain boundaries, such as 50–60° [ 1 ¯ 2 1 ¯ 0 ], 50–60° [ 2 ¯ 7 5 ¯ 0 ], 60–70° [ 1 ¯ 2 1 ¯ 0 ] (∑18b), and 70–80° [ 10 1 ¯ 0 ] (∑10) are also considered to be related to this preferential growth.

Development of low-alloyed Mg–Zn–Ca–Sn–Mn alloy with high strength-ductility synergy by sub-rapid solidification and hot rolling

Achieving high strength-ductility synergy is a great challenge in low-alloyed Mg alloys. In this work, a new Mg–1.0Zn–0.45Ca–0.35Sn–0.2Mn (wt.%, ZXTM1000) alloy was designed and fabricated by sub-rapid solidification (SRS) to overcome the dilemma. After hot rolling and annealing, the new alloy sheet exhibited an excellent tensile yield strength (YS, ∼270 MPa) and elongation (∼21%). Microstructure characterization revealed that the high YS was mainly attributed to the fine grains (∼3 μm) and high density of spherical Ca2Mg6Zn3, Mg2Ca, and α-Mn precipitates. Moreover, the homogeneous grain size distribution, weakened TD-split texture and the activation of multiple types of slips contributed to the enhanced ductility. The findings demonstrate an effective way to fabricate low-alloyed Mg alloys with high strength and ductility by combining the SRS and hot rolling.

A combined experimental and numerical study on room temperature formable magnesium–silver–calcium alloys

Abstract This work investigated effects of silver (Ag) content on the microstructure, texture and mechanical properties of magnesium–silver–calcium alloys by a combined experimental and numerical approach. A series of ternary magnesium–silver–calcium alloys with Ag concentrations between 0.3 and 12 wt% were prepared by hot-extrusion, hot-rolling followed by annealing. As-rolled sheets showed rolling direction split textures with double peaks irrespective of the Ag content. A new component where (0002) basal poles tilted from the normal direction toward the transverse direction (TD) appeared when the Ag content was increased to 1 wt% after annealing. The Mg–xAg–0.1Ca (x = 0.3, 1, 2 and 3) alloys showed excellent room temperature (RT) formability, which could be mainly ascribed to weak basal textures developed after annealing. When the Ag content was increased to 6 wt%, a weak TD-split texture with a homogeneous fine-grained microstructure was developed, which resulted in excellent RT formability and high strength. In contrast, the Mg–12Ag–0.1Ca alloy showed much lower RT formability and ductility in comparison with Mg–Ag–Ca alloys with lower Ag concentrations due to the presence of coarse AgMg4 particles. Visco-plastic self-consistent simulation results revealed that the activity of prismatic slip was increased with increasing the Ag content and the enhanced activity of prismatic during rolling may partially lead to the formation of TD-split texture in the formable Mg–Ag–Ca alloys during annealing.

Comparison of the Mechanical Properties and Forming Behavior of Two Texture-Weakened Mg-Sheet Alloys Produced by Twin Roll Casting

The influence of rolling and annealing on the resulting mechanical properties and forming behavior of Mg-Zn-RE and Mg-Zn-Ca alloys produced via twin roll casting is investigated. After hot rolling followed by an annealing treatment, both alloys develop a fine-grained microstructure with average grain sizes less than 10 µm. A distinctive development of a texture with a pronounced split of the basal poles in the transverse direction, so called TD-split, is observed in both alloys during the annealing. Due to the fine microstructure and weak texture, which enhances the activation of basal slip, both alloys show large ductility with fracture strain higher than 30%. However, due to the TD-split texture, a high asymmetry of the yield stress is observed, where the yield stress in rolling direction is significantly higher than the yield stress along 45° and the transverse direction. Both alloys show high stretch formability at room temperature with Erichsen indices around 7. Despite a low planar anisotropy and high stretch formability, the Mg-Zn-RE alloy shows undesirable earing behavior, while the Mg-Zn-Ca alloy fractures during warm deep drawing. Moreover, the deep drawing operation using the as-rolled sheet of Mg-Zn-RE alloy can be successfully done. It is observed that the earing behavior can be effectively reduced by deviating from the TD-split texture. In this regard, cold rolling was explored to reduce the anisotropy of the ductile and formable alloy.

Study on the evolution pattern of grain orientation and misorientation during the static recrystallization of cold-rolled Mg-Zn-Gd alloy

The recrystallization process has been reported to be responsible for the formation of non-basal texture in Mg-RE and Mg-Zn-RE alloy. The microstructure, macro-texture, grain orientation and misorientation evolution have been characterized during annealing at 150–480 °C to understand the evolution of non-basal texture from a cold-rolled elliptical annular texture to a TD-split texture with double peaks tilting away from ND to TD. The results show that static recrystallization (SRX) begins to take place at 200 °C, and an almost fully recrystallized microstructure is obtained at 300 °C and obvious grain growth from 300 °C to 400 °C. Meanwhile, during the SRX process, the R texture component disappears while the T (−45°) texture component is enhanced, turning into the TD-split texture, and the specific crystal direction parallel to RD rotates from [011¯0] to [1¯21¯0]. The misorientation relationship between SRXed grains and the matrix depends on the nucleated location based on the electron backscattered diffraction (EBSD) results. Furthermore, most SRXed grains formed by different ways have T orientation. During grain growth period, several special grain boundaries are preserved. Meanwhile, coarse grains have T orientation and [1¯21¯0]//RD orientation, showing a preferred grain growth tendency. It is referred that the texture evolution during SRX is mostly related to preferred grain growth which may be caused by the special misorientation or/and the segregation of Zn and Gd solute atoms on special grain boundaries.