Twin Growth Research Articles

Three-dimensional study of grain scale tensile twinning activity in magnesium: A combination of microstructure characterization and mechanical modeling

Tensile twinning is a main deformation mode in hexagonal close packed structure metals, so it is important to comprehensively understand twinning mechanisms which are not fully disclosed using 2D or small volume 3D characterization techniques. A large area 3D electron backscatter diffraction (EBSD) measurement and crystal plasticity modeling were carried out to investigate the tensile twinning behaviors in a magnesium (Mg) alloy. The results showed that tensile twinning activity was underestimated using conventional 2D EBSD scans. When compressed to yield point, the examined twin frequency with 2D was lower than that using 3D EBSD. The effects of Schmid factor (SF) on twinning were investigated. Almost all high Schmid factor (SF>0.35) grains were twinned. A surprising high twin frequency of 82% in middle SF (0.35>=SF>=0.15) grains was observed, which was unexpected since the middle SF grains were believed to be unfavorable for twinning. The twin frequency in low SF (SF<0.15) grains was slightly increased from 2D to 3D EBSD due to the small volume of twins. The shear stress maintained a high level and was homogeneously distributed in high SF grains, facilitating twin nucleation and growth. The shear stress was distributed heterogeneously within the middle SF grains, and twins were nucleated within areas with positive shear stress. The shear stress in low SF grains was not favorable for twinning and twins occurred in the vicinity of stress accumulation. Twinning activities in the same grain varied on different layers. It was attributed to the stress fluctuation derived from grain environment changes.

How to grow single-crystalline and epitaxial NiTi films in (100)- and (111)-orientation

Understanding the martensitic microstructure in nickel–titanium (NiTi) thin films helps to optimize their properties for applications in microsystems. Epitaxial and single-crystalline films can serve as model systems to understand the microstructure, as well as to exploit the anisotropic mechanical properties of NiTi. Here, we analyze the growth of NiTi on single-crystalline MgO(100) and Al2O3(0001) substrates and optimize film and buffer deposition conditions to achieve epitaxial films in (100)- and (111)-orientation. On MgO(100), we compare the transformation behavior and crystal quality of (100)-oriented NiTi films on different buffer layers. We demonstrate that a vanadium buffer layer helps to decrease the low-angle grain boundary density in the NiTi film, which inhibits undesired growth twins and leads to higher transformation temperatures. On Al2O3(0001), we analyze the orientation of a chromium buffer layer and find that it grows (111)-oriented only in a narrow temperature range around 500 ∘C. By depositing the Cr buffer below the NiTi film, we can prepare (111)-oriented, epitaxial films with transformation temperatures above room temperature. Transmission electron microscopy confirms a martensitic microstructure with Guinier Preston-zone precipitates at room temperature. We identify the deposition conditions to approach the ideal single crystalline state, which is beneficial for the analysis of the martensitic microstructure and anisotropic mechanical properties in different film orientations.

Twin density and twin thickness evolution in sputtered Al–Mg alloys

Twinned Al–Mg alloys have been reported. However, the role of Mg solute in facilitating the formation of growth twins remains unclear. By using a precession-assisted crystal orientation mapping technique (PACOM) coupled with transmission electron microscopy (known as ASTAR), we examined the evolution of twin boundaries in Al, Al–1Mg, and Al–2.2Mg (at. %) films. The twinned grain fraction elevates with increasing film thickness until it reaches a peak when the film thickness is 120–160 nm. The Al–Mg alloys exhibited greater twinned grain fractions than pure Al. To investigate the fluctuation of twinned grain fraction, two types of twin boundaries were classified including intergranular and intragranular twins. The initial increase in twin density is attributed to the impingement of twinned grains during island coalescence and the twinned grains are more likely to survive during the grain growth process. Whereas the decrease in twinned grain fraction in thicker films is related to the removal of intragranular twins, and a lack of formation mechanisms of new twins.

Molecular dynamics simulation of twin nucleation and growth in Ni-based superalloys

Micro-twinning is the major creep deformation mechanism in most Ni-based superalloys at temperatures above 700 °C. Nevertheless, many aspects of twin nucleation and growth remain unexplored. The Kolbe mechanism for micro-twinning is currently widely accepted in the community to explain these processes, based on post mortem TEM characterization and indirect theoretical estimations. However, this does not mean that other mechanisms cannot contribute to creep. Molecular dynamics (MD) simulations offer an alternative possibility to probe different creep mechanisms. In this work, we use MD simulations to demonstrate that a qualitatively different mechanism for nucleation and growth of twins can be competitive with the Kolbe mechanism in the intermediate temperature regime of 600 °C–800 °C. The proposed mechanism is closely related to the formation mechanism of super intrinsic stacking faults (SISFs) originally introduced by Condat and Decamps in 1987.

Unveiling deformation twin nucleation and growth mechanisms in BCC transition metals and alloys

Twinning provides critical stress-relieving and flaw tolerance in body-centred cubic (BCC) transition metals (TMs) when dislocation plasticity is suppressed. Twin nucleation and growth mechanisms have been studied for over half a century without a consensus. Here, we use a reduced-constraint slip method to unveil the path to twin nucleation, growth and associated energy barriers in the entire BCC TM family. Twinning is surprisingly but essentially controlled by a normalized energy difference η between the hexagonal close-packed (HCP) and BCC structures in elemental TMs, and can be effectively tuned and quantitatively predicted by first-principles calculations in TM alloys. Fracture mechanics theory with η-based barriers enables predictions of critical solute concentrations to activate twinning and reverse ductile-to-brittle transitions in BCC TMs, as demonstrated in WRe alloys. The computational approach provides a unified and quantitative method to predict twinning and a practical tool for rapid screening of alloy compositions ensuring ductile behaviour.

Mechanisms of nucleation and defect growth in undercooled melt containing oxide clusters

Mechanisms governing the nucleation and defect growth during solidification of undercooled aluminum (Al) in the presence of oxide clusters are studied by molecular dynamics (MD) simulations. Without serving as heterogeneous nucleation sites or changing the overall average grain size, Al oxides (Al2O3) induce localized variations in nanostructures away from the oxide surfaces. Thermodynamic modeling of solidification based on the terrace-ledge model suggests that the non-wetting nature of the liquid Al- solid Al2O3 interface prevents formation of perfect and twinned structures on oxide surfaces. Delayed crystal nucleation and steady-state solidification followed by a sharp growth of smaller grains are identified to trigger variations in crystal orientation selection and increase the localized fraction of twinned structures in regions between oxide surfaces. Finally, our investigation of formation of growth twin boundaries provides the first computational evidence that both layer-by-layer additions and formation-decomposition of grain boundaries mechanisms govern the formation of five-fold twin boundaries during solidification of Al.

Growth Twins and Premartensite Microstructure in Epitaxial Ni-Mn-Ga Films

Magnetic shape memory alloys have been examined intensively due to their multifunctionality and multitude of physical phenomena. For both areas, epitaxial films are promising since the absence of grain boundaries is beneficial for applications in microsystems and they also allow to understand the influence of a reduced dimension on the physical effects. Despite many efforts on epitaxial films, two particular aspects remain open. First, it is not clear how to keep epitaxial growth up to high film thickness, which is required for most microsystems. Second, it is unknown how the microstructure of premartensite, a precursor state during the martensitic transformation, manifests in films and differs from that in bulk.Here, we focus on micrometer-thick austenitic Ni-Mn-Ga films and explain two distinct microstructural features by combining high-resolution electron microscopy and X-ray diffraction methods. First, we identify pyramid-shaped defects, which originate from {1 1 1} growth twinning and cause the breakdown of epitaxial growth. We show that a sufficiently thick Cr buffer layer prevents this breakdown and allows epitaxial growth up to a thickness of at least 4 µm. Second, premartensite exhibits a hierarchical microstructure in epitaxial films. The reduced dimension of films results in variant selection and regions with distinct premartensite variants, unlike its microstructure in bulk.

Effect of long-period ordered stacking on twinning behavior and mechanical properties of Mg-Al-Y alloy during uniaxial hot compression

Two alloys with (T4-4h) and without (T4-8h) long-period stacking ordered (LPSO) phase were obtained by solution treatment of as-cast Mg-1Al-12Y alloy at 540 ℃ for 4 h and 8 h, respectively. The compressive tests (300 – 450 ℃, ε=0.01s−1) showed that the strengthening effect of LPSO in T4-4h alloy gradually disappeared with temperature increase. In addition, the corresponding compression deformation behavior of the two alloys was also investigated by electron backscatter diffraction (EBSD). It was found that the twinning of the two alloys was dominated by {101¯2} extension twins, and the large amount of lamellar LPSO in T4-4 h alloy inhibited the activation and growth of twins. The [0001] // compression direction (CD) texture formed after deformation is mostly attributed to the activation and growth of extension twins. By analyzing the activated twin variants, it was found that the activation of twin variants mainly depended on Schmid factor (SF). For twin variants with smaller SF, they may be activated due to local stress concentration. Based on the analysis results of in-grain misorientation axis (IGMA) and SF, the deformation mechanism of the alloys at elevated temperature is dominated by basal slip and non-basal slip. The stronger mechanical properties of T4-4h alloy than those of T4-8h are attributed to the obstruction of non-basal slip movement by LPSO.

Twin-twin geometric structure effect on the twinning behavior of an Mg-4Y-3Nd-2Sm-0.5Zr alloy traced by quasi-in-situ EBSD

We studied the microstructure evolution of Mg-4Y-3Nd-2Sm-0.5Zr alloy by quasi-in-situ electron backscatter diffraction (EBSD) along with several strains under compression tests, which provided direct evidence for the influence of different twin-twin geometric structure on the twinning behavior. The results showed that the mechanical properties of the alloy were higher than traditional magnesium alloys (the maximum compressive strength reaches 402.5 MPa) due to the strengthening effect of Sm and Nd elements addition on solution strengthening, precipitation strengthening, and grain refinement. Combined with the quasi-in-situ EBSD technique, two different twin-twin geometric structures, ‘parallel structure’ and ‘cross structure’, were observed directly in the alloy. In the later stage of deformation, for ‘parallel structure’, residual stress and a large number of dislocations mainly existed in the twin boundary and tip position. For the ‘cross structure’, there was a lot of dislocation density in the interior of twins after fusion. The twin growth rate of ‘parallel structure’ was much faster than that of ‘cross structure’ because the stress of twins was mainly concentrated on the tip of twin. When the movement for the tip of twin was blocked, the growth rate of twin would be obviously decreased. Moreover, the ‘cross structure’ was easy to produce closed space. Due to the constraints of surrounding twins, the confined space was easy to stress concentration, thus inhibiting the growth of twins. At the same time, the ‘cross structure’ of twins needed a more external force to continue to deform, which also served as a strengthening structure.

Influences of lattice strain and SiGe buffer layer thickness on electrical characteristics of strained Si/SiGe/Si(110) heterostructures

In previous studies, we reported on significantly high hole mobility in a strained Si/SiGe/Si(110) heterostructure pMOSFET. In this study, we investigated impact of strain on the hole mobility in this structure. 20-nm thick (110)-oriented strained Si films with different strain levels were formed using solid-source molecular beam epitaxy. A positive correlation between the hole mobility and the strain of the Si layer is verified. It is also shown that formation of growth twins and strain relaxation of SiGe layer in the [1‾10] direction deteriorate the hole mobility. The maximum mobility enhancement factor obtained in this study is about 3. In addition, the influence of the SiGe layer thickness on the off-state leakage current in pMOSFET operation is discussed. It is found that the upper part of the thick SiGe samples includes cause of the leakage current, indicating change of conductivity with the progress of the crystal growth of SiGe layer. This phenomenon is related to the formation process of the crystalline defects. Another finding is the existence of a current path through the substrate, which suggests a defect-assisted current flow across the SiGe/n-Si(110) junction.

The influence of gadolinium concentration on the twin propagation rate in magnesium alloys

Ultra-high-speed camera (UHSC) imaging was used for the study of the influence of gadolinium (Gd) content on the longitudinal growth of twins in Mg-Gd binary alloys. The results clearly indicate that the twin propagation rate is of the order of 101 m/s and slows down with increasing Gd concentration. Concurrent molecular dynamics (MD) simulations reveal that the presence of Gd atoms enhances the formation of stacking faults (SFs), which hinder twin propagation as effectively as twin boundary pinning by Gd solutes. As a result, the twin tip exhibits intermittent motion at the microscopic level.

Maternal weight, blood lipids, and the offspring weight trajectories during infancy and early childhood in twin pregnancies.

The intrauterine environment has a profound and long-lasting influence on the health of the offspring. However, its impact on the postnatal catch-up growth of twin children remains unclarified. Therefore, this study aimed to explore the maternal factors in pregnancy associated with twin offspring growth. This study included 3142 live twin children born to 1571 mothers from the Beijing Birth Cohort Study conducted from 2016 to 2021 in Beijing, China. Original and corrected weight-for-age standard deviation scores of the twin offspring from birth to 36months of age were calculated according to the World Health Organization Child Growth Standards. The corresponding weight trajectories were identified by the latent trajectory model. Maternal factors in pregnancy associated with the weight trajectories of the twin offspring were examined after adjustment for potential confounders. Five weight trajectories of the twin children were identified, with 4.9% (154/3142) exhibiting insufficient catch-up growth, 30.6% (961/3142), and 46.8% (1469/3142) showing adequate catch-up growth from different birth weights, and 15.0% (472/3142) and 2.7% (86/3142) showing various degrees of excessive catch-up growth. Maternal short stature [adjusted odds ratio (OR) = 0.691, 95% confidence interval (CI) = 0.563-0.848, P = 0.0004] and lower total gestational weight gain (GWG) (adjusted OR = 0.774, 95% CI = 0.616-0.972, P = 0.03) were associated with insufficient catch-up growth of the offspring. Maternal stature (adjusted OR = 1.331, 95% CI = 1.168-1.518, P < 0.001), higher pre-pregnancy body mass index (BMI) (adjusted OR = 1.230, 95% CI = 1.090-1.387, P < 0.001), total GWG (adjusted OR = 1.207, 95% CI = 1.068-1.364, P = 0.002), GWG rate (adjusted OR = 1.165, 95% CI = 1.027-1.321, P = 0.02), total cholesterol (TC) (adjusted OR = 1.150, 95% CI = 1.018-1.300, P = 0.03) and low-density lipoprotein-cholesterol (LDL-C) (adjusted OR = 1.177, 95% CI = 1.041-1.330) in early pregnancy were associated with excessive growth of the offspring. The pattern of weight trajectories was similar between monochorionic and dichorionic twins. Maternal height, pre-pregnancy BMI, GWG, TC and LDL-C in early pregnancy were positively associated with excess growth in dichorionic twins, yet a similar association was observed only between maternal height and postnatal growth in monochorionic twins. This study identified the effect of maternal stature, weight status, and blood lipid profiles during pregnancy on postnatal weight trajectories of the twin offspring, thereby providing a basis for twin pregnancy management to improve the long-term health of the offspring.

Twinning in Hexagonal Close-Packed Materials: The Role of Phase Transformation

Twinning is a major mechanism of plastic deformation in hexagonal close-packed (hcp) structures. However, a mechanistic understanding of twin nucleation and growth has yet to be established. This paper reviews the recent progress in the understanding of twinning in hcp materials—particularly the newly discovered phase transformation-mediated twinning mechanisms—in terms of crystallographical analysis, theoretical mechanics calculations, and numerical simulations. Moreover, the relationship between phase transformation-mediated twinning mechanisms and twinning dislocations are presented, forming a unified understanding of deformation twinning. Finally, this paper also reviews the recent studies on transformation twins that are formed in hcp martensite microstructures after various phase transformations, highlighting the critical role of the mechanical loading in engineering a transformation twin microstructure.

Forming mechanism of growth twins and microstructure evolution on improvement of strength and toughness properties by β-eutectoid element in Ti-7Mo-4Al-4Zr-3Nb-2Cr-xFe alloys

To form growth twins and simultaneously improve strength and toughness by using a β-eutectoid element, Ti-7Mo-4Al-4Zr-3Nb-2Cr-xFe alloys were prepared. The phase composition, morphology of growth twins, tensile properties and fracture toughness were tested. Also, the formation of growth twins and the strength-toughness mechanism were studied. The results show that α and β phases exist after heat treatment. The relative content of β phase increases from 6.1 % to 12.5 % with increasing Fe content. Dislocation entanglements and dislocation walls appear at the α/β interface. There are two kinds of α phases, which are αp and αs phases. The growth twin with a width of ∼20 nm is found in αs phase due to the mismatch with the matrix lattice during solidification process. The smallest size of αp phase is at 1.0 wt% Fe. As the stable element of the β phase, Fe increases the phase transformation resistance from β phase to α phase to limit the growth of α phase. When Fe content increases from 0 to 1.5 wt%, tensile strength increases from 1107 to 1314 MPa. By increasing Fe content from 0 to 1.0 wt%, fracture toughness and elongation increase from 64 to 80 MPa·m1/2 and 5.4–7.1 %, respectively. The strength and toughness of the alloys increase simultaneously within 0–1.0 wt%Fe. The solution strengthening of Fe, the refinement of αp phase, and the formation of growth twins and dislocation walls are the main reasons for the improvement in strength and toughness.

Growth of twins conceived using assisted reproductive treatments up to 5 years old: a national growth cohort.

Do twins conceived through assisted reproductive treatments (ART) grow differently from naturally conceived (NC) twins in early life? Assessments at 6-8 weeks old and at school entry show that ART twins conceived from frozen embryo transfer (FET) grow faster than both NC twins and ART twins conceived from fresh embryo transfer (ET). Singletons born from fresh ET grow more slowly in utero and in the first few weeks of life but then show postnatal catch-up growth by school age, compared to NC and FET babies. Evidence on early child growth of ART twins relative to NC twins is inconsistent; most studies are small and do not distinguish FET from fresh ET cycles. This cohort study included 13528 live-born twin babies conceived by ART (fresh ET: 2792, FET: 556) and NC (10180) between 1991 and 2009 in Scotland. The data were obtained by linking Human Fertilisation and Embryology Authority ART register data to the Scottish Morbidity Record (SMR02) and Scottish child health programme datasets. Outcome data were collected at birth, 6-8 weeks (first assessment), and school entry (4-7 years old) assessments. The primary outcome was growth, measured by weight at the three assessment points. Secondary outcomes were length (at birth and 6-8 weeks) or height (at school entry), BMI, occipital circumference, gestational age at birth, newborn intensive care unit admission, and growth rates (between birth and 6-8 weeks and between 6-8 weeks and school entry). All twins in the linked dataset (born between 1991 and 2009) with growth data were included in the analysis. To determine outcome differences between fresh ET, FET, and NC twins, linear mixed models (or analogous logistic regression models) were used to explore the outcomes of interest. All models were adjusted for available confounders: gestational age/child age, gender, maternal age and smoking, Scottish Index of Multiple Deprivation, year of treatment, parity, ICSI, and ET stage. In the primary birth weight models, the average birth weight of fresh ET twins was lower [-35 g; 95% CI: (-53, -16)g] than NC controls, while FET twins were heavier [71 g; 95% CI (33, 110) g] than NC controls and heavier [106 g; 95% CI (65, 146) g] than fresh ET twins. However, the difference between FET and NC twins was not significant when considering only full-term twins (≥37 weeks gestation) [26 g; 95% CI (-30, 82) g], while it was significantly higher in preterm twins [126 g; 95% CI (73, 179) g]. Growth rates did not differ significantly for the three groups from birth to 6-8 weeks. However, FET twins grew significantly faster from 6 to 8 weeks than NC (by 2.2 g/week) and fresh ET twins (by 2.1 g/week). By school entry, FET twins were 614 g [95% CI (158, 1070) g] and 581 g [95% CI (100, 1063) g] heavier than NC and fresh ET twins, respectively. Length/height and occipital frontal circumference did not differ significantly at any time point. Although the differences between ART and NC reflect the true ART effects, these effects are likely to be mediated partly through the different prevalence of mono/dizygotic twins in the two groups. We could not explore the mediating effect of zygosity due to the unavailability of data. The confounding variables included in the study were limited to those available in the datasets. Live-born twins from FET cycles are heavier at birth, grow faster than their fresh ET and NC counterparts, and are still heavier at school entry. This differs from that observed in singletons from the same cohort, where babies in the three conception groups had similar weights by school entry age. The results are reassuring on known differences in FET versus fresh ET and NC twin outcomes. However, FET twins grow faster and are consistently larger, and more ART twins depict catch-up growth. These may lead to an increased risk profile for non-communicable diseases in later life. As such, these twin outcomes require careful evaluation using more recent and comprehensive cohorts. This study was funded by the EU H2020 Marie Sklodowska-Curie Innovative Training Networks (ITN) grant Dohartnet (H2020-MSCA-ITN-2018-812660). The authors have no competing interests to declare. N/A.

Modes of strain accommodation in Cu-Nb multilayered thin film on indentation and cyclic shear

Two-phase layered thin films with a high density of semi-coherent interfaces exhibit excellent mechanical properties and thermal stability. In this study, a magnetron-sputtered Cu-Nb dual-layered thin film (∼500 nm for Cu and ∼150 nm for Nb) having an amorphous interface between Cu and Nb with a high density of aligned growth twins in Cu is subjected to severe surface deformation. The material is loaded using indentation and cyclic shear under tribological testing. The strain accommodation in the subsurface microstructure after deformation varies based on the local structure and deformation mode. Grain refinement and crack formations in the stressed region of the Nb layer and localized crystallization of the amorphous interface are observed after indentation and scratch testing. Pronounced detwinning of growth twins in the Cu layer under the cyclic shear strain leaves large dislocations sites and loops which are observed both by high-resolution transmission electron microscopy and experiment-guided molecular dynamic (MD) simulations. Our simulations provided insights into understanding the pathway for the detwinning process under cyclic shear loading.

An experimental and crystal plasticity investigation of anisotropic compression behaviour of Mg-Sn-Ca alloy

The ductility of Magnesium alloys is often limited due to the strong basal texture. Initial attempts were made to reduce the intensity of the basal textures by adding rare earth(RE) elements. However, owing to the cost and scarcity of RE elements, alloys with calcium and tin were recently introduced. Among them, Mg-2Sn-2Ca alloys are the most promising, with high strength reported in the extruded condition. In this work, we report, for the first time, the mechanical properties of the alloy in the sheet form. In plane mechanical anisotropy in compressive behaviour is studied along with the detailed characterisation of texture, microstructure and the deformation twins in the material. Unlike strongly basal textured Mg alloys, deformation twinning was also observed in samples loaded along the normal direction. Crystal plasticity simulations were performed to confirm the slip and twin activity. Furthermore, a detailed analysis of deformation twins revealed that the so called Schmid twins accommodate strain by both twin growth and slip, whereas the non-Schmid twins accommodate the strain exclusively by crystallographic slip.

Deformation dynamics in pre-strained Mg–3Al–1Zn alloy: An in situ synchrotron X-ray study

The effects of preexisting dislocations generated via pre-strain on deformation twinning in a textured magnesium alloy are investigated via real-time, in situ, synchrotron X-ray imaging and diffraction. One sample is stretched along the rolling direction (RD, perpendicular to the c-axis) to introduce dislocations, and then compressed along RD. For comparison, an as-received sample is directly compressed along RD. Bulk stress–strain curves (macroscale), strain fields (mesoscale) and X-ray diffraction patterns (microscale) are obtained simultaneously. Postmortem electron backscatter diffraction characterizations are performed as a complement. The {101̄2} extension twinning in both samples can boost strain hardening rate by slowing down the strain localization process. However, the dislocations generated with pre-strain interact with the twin boundaries, and obstruct twin motion and growth. Therefore, strain localization mitigation due to twinning in the pre-strained sample is reduced compressed to its counterpart.

Mg-3Al-1Zn alloy deformed along different strain paths: Role of latent hardening

The mechanical properties of magnesium alloy AZ31 were investigated experimentally with visco-plastic self-consistent modeling. Tension, compression and plane strain compression (PSC) tests were performed along 3 directions of a hot rolled plate, and the material parameters input in the model were fitted with the uniaxial stress-strain curves. The critical resolved shear stress (CRSS) for tension twinning was modeled with a modified Voce hardening law first decreasing, and then increasing with strain, that could reproduce better the flow stress for twin-predominant deformation. Such CRSS evolution may better model twin nucleation, propagation and growth. Firstly simulations were carried out assuming latent hardening coefficients for slip by other slip systems equal to self-hardening. Then different heterogeneous latent hardening were used, whose values were based on dislocation dynamics simulations from the literature. This study shows that equal self and latent hardening can reproduce the stress strain curves and plastic anisotropy as well as heterogeneous mode on mode latent hardening. Discrepancies between simulations and experimental results from PSC are explained by an under-estimation of twinning for some PSC strain paths.

Effects of pre-aging on microstructure evolution and deformation mechanisms of hot extruded Mg–6Zn–1Gd–1Er Mg alloys

Abstract The influence of pre-aging treatment on the microstructure, texture and mechanical properties of the Mg–6Zn–1Gd–1Er (wt.%) alloy was investigated. The microstructure analysis shows that the presence of pre-aging is beneficial to { 10 1 ¯ 2 } twin nucleation at the early stage of extrusion and inhibits the growth of twins and promotes the formation of [ 10 1 ¯ 0 ] -fiber texture components, thus accelerating the complex process of recrystallization. In the middle stage of extrusion, the extruded samples under the condition of solid solution were subjected to dynamic precipitation during severe shear deformation. The precipitation of the second phase particles followed the particle stimulating nucleation (PSN) mechanism, which increased the volume fraction of DRX grains during extrusion. In the extruded samples under the peak-aged condition, the particles appear dissolved during the severe shear deformation strain, which slows down the DRX process. In the later stage of extrusion, the small rod-shaped particles followed the PSN mechanism, and finally formed the strong fiber texture. The extruded alloy exhibits the strongest mechanical properties under the peak-aged state, with ultimate tensile strength (UTS) of 346 MPa, tensile yield strength (TYS) of 217 MPa, and elongation to failure (EL) of 13.6%. The improvement of mechanical properties is mainly attributed to the existence of strong fiber texture, small rod-shaped and block-shaped phases.