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Twinning-mediated plasticity has great potential for enhancing the strength and plasticity of Mg alloys, which is limited due to the lack of twin types. Here, we report a novel multistage twinning mode, i.e. the dominant twinning mode changes from single { 10 1 ¯ 2 } twins to the co-existence of { 10 1 ¯ 2 } and { 11 2 ¯ 6 } twins, in a deformed Mg-Al-Gd alloy. Introducing novel multistage twinning mode to accommodate strains appreciably along c-axes, combined with the interactions of high-density dislocations and dense twin boundaries, guarantees the high strain hardening of Mg alloys. These findings provide new insights into deformation mechanisms and mechanical properties of Mg-alloys. Introducing novel multistage twinning mode to accommodate strains appreciably along c-axes, combined with the interactions of high-density dislocations and dense twin boundaries, guarantees the high strain hardening of Mg alloys. [ABSTRACT FROM AUTHOR]

By introducing heterogeneous lamella-structure, we obtained a superior strength-ductility synergy in Mg-alloy associated with excellent strain-hardening ability, i.e. yield strength of ∼251 MPa, tensile strength of ∼393 MPa and elongation of ∼23%. By using advanced characterization techniques, we showed that strengthening was mainly caused by the non-uniform distribution of hetero-deformation induced (HDI) stress associated with grain-boundary disclinations, which are mediated by heterogeneous multi-grain interactions. Induced by grain-boundary disclinations and intergranular slip transfers, a variety of abnormal deformation modes have been activated，which contributed significantly to enhanced ductility. This work suggests a new avenue to evade strength-ductility trade-off dilemma in Mg-alloys. The heterogeneous lamella-structure leads to sustained strain-hardenability in Mg-alloy with unique accommodating deformation modes (extensive abnormal slips and feather-shaped twins), induced by grain-boundary disclinations and intergranular slip transfers. [ABSTRACT FROM AUTHOR]

• Through using a simple accumulative roll bonding process assisted by hard plates, we tailored a novel multiscale hetero-structure in Mg-9Al-1Zn (AZ91) alloy, consisting of bimodal-structured center-region and fine-grained surface-layer. The multiscale hetero-structured AZ91 alloy exhibits a high yield strength of ∼303 MPa, tensile strength of ∼400 MPa and elongation of ∼14.5 %. • The strain incompatibilities stimulated by the multiscale microstructural heterogeneities could influence the dominant deformation modes, and further activate diversified strain accommodation mechanisms, including non-Schmidt 〈 c + a 〉 dislocations. • A unique slip trace distribution has been developed in the fine grains around the basal-oriented coarse grain in bimodal-structured center-region, which effectively releases the micro-stress concentration. • High hetero-deformation induced (HDI) stress and HDI hardening could be attributed to the activation of multiple deformation modes, resulting in a mediated plastic deformation at high-stress-state and dislocation accumulation, which is beneficial to enhanced strength-ductility synergy. Most of the high-strength Mg alloys exhibit poor ductility at room temperature. Architecturing appropriate heterostructure in metallic materials gives rise to the breakthrough of the inherent strength-ductility trade-off dilemma. Here, we prepared a novel multiscale hetero-structure in Mg-9Al-1 Zn (AZ91) alloy, consisting of bimodal-structured center-region and fine-grained surface-layer, providing high strength and high ductility, i.e. yield strength of ∼303 MPa, tensile strength of ∼400 MPa, and elongation of ∼14.5 %. The multiscale microstructural heterogeneities were induced via a simple rolling process that combines the advantages of both accumulative rolling bonding (ARB) and hard plate rolling (HPR). By utilizing quasi-in-situ electron backscattered diffraction (EBSD)-digital image correlation (DIC) characterizations combined with the determination of dislocation/disclination distributions, it has been found that diversified strain accommodation mechanisms are stimulated by the strain incompatibilities near hetero-interfaces in the multiscale hetero-structure. In particular, non-basal slips have been activated largely in both the bimodal-structured center-region and fine-grained surface-layer. Moreover, a unique slip trace distribution has been observed in the fine grains adjacent to the basal-oriented coarse grain. Such a strain accommodation can better coordinate local strain incompatibility among the hetero-interface. The uniaxial loading–unloading–reloading tensile loop tests demonstrate that the multiscale heterogeneities impart a pronounced hetero-deformation induced hardening during tensile deformation. Multiple deformation modes, including the non-Schmid and non-basal slips, have been activated substantially in the multiscale hetero-structured Mg alloy, effectively relaxing local stress concentration and achieving stable plastic flow at a high-stress state, which is beneficial to improving strain-hardening ability and strength-ductility synergy. Our work could shed light on designing and processing strong and ductile Mg alloys, by tailoring proper microstructural heterogeneity to activate cooperated accommodating deformation modes. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract In the present work, we investigated the influence of deformation temperature on the formation of a bimodal microstructure and tensile properties of a Mg–9Al–1Zn (AZ91) alloy processed by a single pass hard plate rolling (HPR) with a thickness reduction of 55% followed by a short time annealing. Microstructural examinations by electron backscatter diffraction (EBSD) reveal that there exists a narrow deformation temperature window, i.e. it is only feasible to achieve a desired bimodal grain structure in the AZ91 alloy when HPRed at ∼350 °C. It is mainly because that partial dynamic recrystallization (DRX) occurs easily in the sample HPRed at ∼ 350 °C, facilitating the formation of a bimodal microstructure consisting of coarse un–recrystallized grains (>∼70 μm) and fine recrystallized grains (<∼5 μm). In contrast, reducing deformation temperature to ∼300 °C results in a coarse unrecrystallized microstructure containing substantial sub structure, while elevating the deformation temperature to ∼400 °C leads to an almost uniform recrystallized grain structure. Especially, the formation mechanism for the bimodal grain structure at the optimum deformation temperature is explored in terms of Schmidt factors analysis for basal slips (SF basal ) for grains of different size scales. Moreover, the 350 °C HPRed AZ91 sample exhibits a better combination of strength (ultimate tensile strength = ∼374 MPa) and ductility (elongation = ∼19.6%), as compared to the 300 and 400 °C samples. It is mainly attributed to the typical bimodal grain structure and the relatively high SF basal featured by the fine recrystallized grains as well as the nanometer spherical particles distributing in fine grain interiors. Graphical abstract Image 1 Highlights • A bimodal grain structure of Mg–9Al–1Zn alloy was achieved by tailoring rolling temperature during hard–plate rolling (HPR). • The formation of bimodal microstructure was explored in terms of Schmidt factors analysis for basal slips (SF basal ). • The formation of bimodal grain structure generated a simultaneous improvement of strength and ductility. [ABSTRACT FROM AUTHOR]

The present work revealed that equal-channel angular pressing (ECAP) deformation combined with appropriate annealing could represent as an efficient route to modify immiscible as-cast microstructure of a monotectic Al–8Bi alloy by a complete redistribution of immiscible Bi particles and grain refinement of alloy matrix. Especially, we found that the mean size of Bi particles in the 4-pass ECAPed Al–8Bi sample decreases after annealing at 200 °C for 8 h, due to inverse coarsening driven by the reduction of elastic energy and interfacial energy induced by morphology change and spatial distribution of Bi particles. [ABSTRACT FROM AUTHOR]

Abstract: The deformation behavior of a soft particle containing Al–8Bi hypermonotectic alloy during equal-channel angular pressing was studied. The size, shape and distribution of soft Bi particles are substantially modified via shearing, fragmentation, coalescence and ripening. It is found that the soft Bi particles have a strong influence on promoting refinement of Al grains via particle stimulated continuous dynamic recrystallization. The present work provides an effective methodology to obtain monotectic aluminium alloys with well-dispersed soft phase particles. [Copyright &y& Elsevier]

Abstract: The annealing response in a binary Al–7Mg alloy processed at room temperature by equal channel angular pressing (ECAP) has been investigated via X-ray diffraction (XRD), electron-probe micro analysis (EPMA) and electron backscattering diffraction (EBSD). After ECAP and subsequent annealing, Mg remains mainly homogeneously distributed in solid solution. A bimodal structure with ultrafine grains accompanied by micrometer-sized crystallites was developed after 3 passes. Upon annealing at ~275°C for 96h, extensive recovery was observed in the as-deformed material, leading to a relatively uniform microstructure; at ~300°C a discontinuous recrystallization initiated in less than 30s with subsequent grain growth clearly evident. Such remarkable thermal stability, i.e., slower recovery and recrystallization kinetics, of the present material, in contrast to other severely deformed commercial pure Al and Al–Mg alloys, is due mainly to the presence of high Mg solid solution contents, the formation of the bimodal structure consisting of both coarse crystallites and ultrafine grains. In addition, the possible Mg-containing precipitates during annealing might also retard the recrystallization kinetics. [Copyright &y& Elsevier]

• The superplastic response is studied in an Al–7Mg alloy with multi-scale microstructural heterogeneities. • The Al–7Mg exhibits enhanced thermal stability and superplasticity of ∼523% at 573 K and 1 × 10−3 s−1. • Enhanced thermal stability owes to cooperative effects of bimodal grain structure and mg segregation along GBs. • The high superplasticity is due to a cooperated mechanism involving dislocation slip accommodated by CDRX and GBS. Achieving high superplasticity in single-phase Al alloys remains a challenge, since the fine-grained structure required for superplastic deformation coarsens rapidly in the absence of dispersed second-phase particles during tensile deformation at elevated temperatures. This paper concentrates on the superplastic response of a high solid solution Al–7Mg alloy processed by equal-channel angular pressing (ECAP) under uniaxial tension. The ECAP-processed Al–7Mg alloy features multi-scale microstructural heterogeneities including a bimodal grain structure and Mg solute segregation along grain boundaries (GBs) of nano/ultrafine grains. To identify effects of multi-scale microstructural heterogeneities on superplastic deformation behavior of the high solid solution Al–7Mg alloy, microstructural evolutions are studied systematically by combing electron backscatter diffraction (EBSD), ASTAR-transmission electron microscopy (TEM) orientation imaging and atom probe tomography (APT). During deformation at the optimal tensile condition of 573 K and 1 × 10−3 s−1, the heterogeneous microstructure evolves to a stable uniform fine grain structure via continuous dynamic recrystallization (CDRX), and impressive superplasticity of ∼523% elongation is achieved. The high superplasticity is discussed in terms of the cooperated mechanism by dislocation slip accommodated by CDRX at the early tensile deformation stage and grain boundary sliding (GBS) at the late deformation stage. Our findings show that the evolution of microstructural heterogeneities in high solid solution Al–Mg alloys can be regulated, favoring for superplastic deformation, which offers an alternative strategy for developing low-cost Al alloys for enhanced mechanical properties. [Display omitted] [ABSTRACT FROM AUTHOR]

The coarse segregative eutectic phases, emerged in the twin roll casting (TRC) process of Mg strips, which cannot be resolved solely by controlling the processing variables or post heat treatment, are detrimental to the subsequent rolling deformation. Considering it, we introduce the pre-rolling steps on the TRC Mg-4Al-2Sn-1Zn (ATZ421) alloys, which is expected to facilitate the dissolution of these segregative phases by increasing distortion of crystal lattices and rolling stress, and further investigate the effect of a single pass or two passes pre-rolling on the microstructure evolution and tensile properties. It indicates that the pre-rolled alloy with two passes presents more uniform precipitates and higher twinning density in comparison with that using a single pass. The uniform distribution of precipitates in two passes pre-rolling is due to the increase in density of dislocations and deformed twins, which results in more distortion of crystal lattices with more stored energy, facilitating the diffusion of solutes. Moreover, the pre-rolling of two passes introduces more rolling stress into Mg matrix, which is beneficial for the crush of coarse eutectic phases, and further accelerates the sufficient dissolution of second phases. After the subsequent rolling and annealing processes, the sheet with pre-rolling deformation of two passes shows finer microstructure, which mainly benefits from the pinning effects of uniform nano-sized precipitates. As a result, the annealed sheet with two-pass pre-rolling deformation exhibits an advantageous combination of high strength and high ductility with fine microstructure, showing an ultimate tensile strength of ~297 MPa, a yield strength of ~ 205 MPa and an elongation of 25.0%. This work provides an effective method of dissolving the coarse segregative phases in the TRC Mg alloys with significant potential for industrial production. [ABSTRACT FROM AUTHOR]

• Plasticity can be achieved through multiple twinning modes and disclinations. • { 11 2 ¯ 6 } type extension twinning mode has been observed in mg alloys. • { 11 2 ¯ 6 } twins can be generated through reactions between twins and disclinations. • Three formation mechanisms of { 11 2 ¯ 6 } twins have been identified. Twinning-induced plasticity plays a critical role in determining the deformation behaviors of hexagonal close-packed metals (e.g., Mg and Ti), due to the lack of five independent slip systems required for a general deformation. In particular, twinning modes that can accommodate c-axis strain (tensile or compressive) are especially important, which are necessary complementary deformation modes to < a >-type dislocations. However, only limited types of extension twins, e.g., { 10 1 ¯ 2 } type twin, have been unambiguously identified in the literature, which is theoretically inadequate to accommodate a complex deformation with c-axis extension. Using topological defect theory, here we show that another extension twinning mode, { 11 2 ¯ 6 } twin, can be formed through reactions between disclinations and { 10 1 ¯ 2 } twins in Mg-alloys. Based on symmetry of the deformation space, we demonstrate that the { 11 2 ¯ 6 } twin originates from the inter-connection of correlated deformation paths, which can provide a tensile strain of 5.2% along c-axis and a compressive strain of 4.5% along 〈 11 2 ¯ 0 〉. { 11 2 ¯ 6 } twins can be formed through three formation mechanisms, i.e., direct formation, twin-twin intersection, and double twinning, which are validated by a combination of experimental characterizations and phase field simulations. Our work not only suggests a symmetry-based method to analyze twinning-induced plasticity, but also provides a new insight into the deformation mechanisms and mechanical properties of Mg-alloys. [Display omitted] [ABSTRACT FROM AUTHOR]

In the present work, Mg-9Al-1Zn-0.4Sn (AZT910) magnesium alloy sheets with a fine-grained structure (∼5 μm) and tilting basal texture were prepared by a 16-passes rolling process. Effect of tensile directions on properties and microstructural evolutions of the AZT910 alloy sheet at different temperatures, i.e. room temperature, 200 and 300 °C, respectively, were investigated by using three kinds of tensile specimens (rolling direction (RD), transverse direction (TD) and 45° towards RD). Experimental results showed that tensile properties exhibited a strong dependence on tensile directions at room temperature and 200 °C, while a negligible dependence at 300 °C. The anisotropic tensile properties imply that the deformation system of rolled AZT910 sheet consists of basal and non-basal slips at room temperature, and is a combination of basal slip, non-basal slip and grain boundary sliding/rotation (GBS) at 200 °C. The decrease of intensity and spreading of basal poles during tensile test and isotropic tensile properties indicates that GBS becomes the dominate deformation mechanism at 300 °C. The present work provides reference for the study of deformation behavior of novel superplastic magnesium alloy, and hence is of great significance for further application of wrought magnesium alloy. [ABSTRACT FROM AUTHOR]

In the present study, Mg-6Zn-1Zr (ZK60) alloy with a homogeneous fine-grained structure (~5 µm) was produced by hot extrusion. The influence of temperature on tensile properties anisotropy and the associated change in deformation mechanisms in the range of 25–275 °C of the fine-grained ZK60 alloy were investigated. Under room temperature, the fine-grained ZK60 alloy exhibited a high tensile strength of ~269–327 MPa and high ductility of ~15–39% when tested at three different directions, indicating a high anisotropy. With increasing testing temperature to 150 °C and further to 275 °C, the alloy showed a gradual decrease in anisotropy. Especially, the fine-grained ZK60 alloy exhibited superplasticity of ~376–434% when tested at 275 °C, which should be due to the increasing role of grain boundary sliding (GBS), as the strong basal texture associated with room temperature deformation became almost random at elevated temperatures. Moreover, the abrupt decrease in tensile anisotropy and associated change in texture with increasing temperature correlates closely to the transformation of deformation mode from a dislocation-dominated behavior to a GBS-mediated one. [ABSTRACT FROM AUTHOR]

This research elucidates discontinuous dynamic recrystallization (DDRX)-dependent high-temperature tensile properties and deformation mechanisms in simply extruded Al-7Mg alloys tailored by Sc/Zr ratios. The bimodal-grained Al-7Mg-0.4Sc alloy presents a high elongation to failure of ∼540% at 400 °C and 5 × 10−4 s−1. However, such superplastic behavior has not been observed in both coarse-grained Al-7Mg-0.1Sc-0.3Zr and Al-7Mg-0.3Sc-0.1Zr alloys. Thermally stable dispersed nano-sized Al 3 (Sc,Zr) particles strongly retard DDRX, accompanied by the retention of heterogeneous grain structure in Al-7Mg-0.1Sc-0.3Zr till fracture. The predominance of dislocation slip is proved by analyzing the evolution of texture and dislocations. In contrast, the bimodal grain structure evolves into a homogeneous fine one in Al-7Mg-0.4Sc with tensile deformation proceeding since coarsening Al 3 Sc precipitates play a weak role in restricting DDRX. The superplasticity in Al-7Mg-0.4Sc is achieved by cooperated mechanisms, i.e., grain boundary sliding (GBS) and dislocation slip as dominant mechanisms, which is accommodated by DDRX in the initial tensile deformation stage, followed by dislocation slip-accommodated GBS in the late stage. • Superplasticity with ∼540% elongation at 400 °C is obtained in bimodal-grained Al–7Mg-0.4Sc. • The superplasticity is associated with DDRX, which promotes a uniform fine grain structure and GBS prevailing. • Coarse-grained Al–7Mg-0.1Sc-0.3Zr has higher peak stress at 400 °C but without superplasticity. • Tiny Al 3 (Sc,Zr) particles retard DDRX, causing a heterogeneous grain structure and incompatible deformation. [ABSTRACT FROM AUTHOR]