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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]

Tailoring recrystallization via particle-stimulated nucleation (PSN) and pinning effects from secondary phase particles effectively weakens textures, which is still challenging for low-alloyed rare earth-free Mg alloys. Herein, the texture of a dilute cold-rolled Mg-2.2Al-0.33Ca (wt.%) alloy is found to reduce with the appearance of transverse direction (TD) texture components during static recrystallization. The texture transition is mainly attributed to the preferential growth of TD-oriented recrystallized grains, resulting from the preferential segregation of Al and Ca atoms on basal-oriented grain boundaries with low misorientation angles. The findings provide an in-depth understanding of texture modification in Mg alloys. The anisotropic co-segregation of Al and Ca on grain boundaries is responsible for the texture weakening of a dilute Mg-Al-Ca alloy, which provides a strategy for texture modification in such alloys. [ABSTRACT FROM AUTHOR]

Achieving high strength-ductility synergy in hard-to-deform high-alloyed Mg-Gd-Y-Zn-Zr alloys by rolling remains a great challenge. In this work, a Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr (wt.%) alloy sheet possessing a high yield strength (YS) of ∼385 MPa, ultimate tensile strength (UTS) of ∼420 MPa and elongation of ∼19% was achieved via a single-pass hard-plate rolling (HPR) process. The high YS is mainly from amounts of submicron FGs and strong interactions between densely distributed γ′ precipitates and pyramidal dislocations in CGs. The activation of multiple slip systems, HDI-hardening effect, and crack suppression effect from γ′ particles, endow the excellent ductility. The hard-to-deform WE94 alloy sheet exhibiting a superior strength-ductility synergy has been prepared by a single-pass HPR process. The bimodal grain structure containing substantial ultrafine grains coupling with inhomogeneously-distributed nano-scale precipitates accounts for the superior mechanical properties. [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]

Unraveling the varied modification mechanisms of trace elements under diverse cooling rates is of great importance to regulate the morphology of primary Mg2Si in hypereutectic Al-Mg2Si alloys. In the present work, the modification mechanisms of Sr and Sb in Al-20Mg2Si alloys under different cooling rates are discussed in detail. Increasing the cooling rates from ~ 50 to 76 °C/s to ~ 213 to 230 °C/s leads to the morphology transition of primary Mg2Si from hoppers to dendrites, which is attributed to a smaller constitutional zone with the increase of temperature gradients introduced by high cooling rates. The addition of 0.15 wt pct Sr modifies the morphology of primary Mg2Si phase to cubes at cooling rates of ~ 50 to 76 °C/s and ~ 213 to 230 °C/s with the same modification mechanism, i.e., by increasing nucleation driving force for primary Mg2Si and the adsorption-poisoning effect. In contrast, the modification mechanisms of Sb are different under varying cooling rates. At low cooling rates of ~ 50 to 76 °C/s, Sb modifies the morphology of primary Mg2Si to be truncated octahedrons by introducing Mg3Sb2 particles as heterogeneous nuclei and the substitution of Sb to Si in Mg2Si crystals. At high cooling rates of ~ 213 to 230 °C/s, primary Mg2Si grows coarser with a dendrite morphology due to solute trapping, which changes the modification mechanism to substitution alone. Moreover, it is interesting that at cooling rates of ~ 213 to 230 °C/s, primary and eutectic Mg2Si particles in the Al-20Mg2Si-0.15Sr alloy are refined simultaneously, which greatly suppresses the crack formation and propagation. Accordingly, the ultimate tensile strength and elongation to failure are increased to ~ 242 MPa and ~ 5.6 pct compared to the unmodified alloy (~ 188 MPa and ~ 1.4 pct, respectively). [ABSTRACT FROM AUTHOR]

Achieving appreciable strain-aging hardening coupling with fine-grain strengthening remains a critical challenge in dilute Mg alloys, as high-temperature solid-solution, utilized to impart high-level solutes for strain-aging, inevitably causes grain coarsening and great strength loss. Herein, we report a rapid dislocation-mediated solute repartitioning behavior upon aging in a low-temperature annealed Mg–1.0Zn–0.45Ca–0.33Sn–0.2Mn (wt.%) alloy. Thereby, appreciable strain-aging hardening (YS increment of ∼30 MPa) coupling with fine-grain (grain size of ∼2.5 µm) strengthening accounts for a high yield strength (∼297 MPa) and ductility (∼20%). It suggests a feasible avenue to develop strong dilute Mg alloys by combining strain-aging hardening and fine-grain strengthening. By manipulating solute distribution while keeping a fine-grain structure, appreciable strain-aging hardening response coupling with fine-grain strengthening guarantees the development of strong dilute Mg alloy. [ABSTRACT FROM AUTHOR]

Herein, the influence of equal channel angular pressing (ECAP) routes, i.e., A and Bc, on the microstructure and texture evolution of a Mg–3.7Al–0.7Zn–0.8Sn–0.4Mn (wt%) alloy is investigated by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and X‐ray diffraction (XRD). It is found that with increasing the number of ECAP passes, the area fraction of the dynamically precipitated secondary‐phase particles increases, whereas particle size becomes larger. After four and six passes of ECAP via route A, shear deformation induced by ECAP promotes the incline of c‐axes toward extrusion direction (ED). The optimum room temperature (RT) mechanical properties (yield strength of ≈225 MPa, ultimate tensile strength of ≈312 MPa, and elongation to fracture of ≈31.9%) are obtained after four passes of ECAP at 200 °C via route A. The improved strength results from fine dynamic recrystallization (DRX)/ed grains, nanoscale secondary‐phase particles, and basal texture. Herein, it is indicated that Mg–Al–Zn–Sn alloys have great potential as low‐cost high‐strength‐ductility wrought Mg alloys. [ABSTRACT FROM AUTHOR]

• Primary Mg2Si is modified from dendrites to truncated octahedrons with 0.5 wt% Be-Sb. • Be-Sb modifies Mg 2 Si by controlling the nucleation and growth process simutaneouly. • The formation of Mg 3 Sb 2 enhances heterogenous nucleation sites of primary Mg 2 Si. • Be refines the primary Mg 2 Si by adsorption-poisoning mechanism. • 0.5 wt% Be-Sb modified alloy exhibits an improvement in mechanical properties. Modifying the primary Mg 2 Si phase in hypereutectic Al-Mg 2 Si system with controllable sizes and morphologies is difficult to realize by the single addition of elements, which can only enhance nucleation or control its growth process via adsorption-poisoning. This research provides insights into modification mechanisms of the co-addition of Sb and Be in an Al-20Mg 2 Si alloy to refine the primary Mg 2 Si phase by controlling the nucleation and growth process simutaneouly. With 0.5 wt% Be-Sb, truncated octahedrons with rounded corners are obtained, along with the size refinement from ~150 µm to ~10 µm. The formation of Mg 3 Sb 2 particles significantly refines the primary phase by acting as heterogeneous nucleation sites during solidification. Meanwhile, Be could adsorb on the Mg 2 Si surfaces and restrain the advanced growth of Mg 2 Si<100> direction, which contributes to the final morphology of the primary phase. The formation of truncated octahedrons with rounded corners contributes to an improvement in elongation to failure (from ~0.7% to ~1.9%) and ultimate tensile strength (from ~142 MPa to ~198 MPa) comparing to the unmodified alloy, which relieves the stress concentration and restrains the crack source. This study offers a simple methodology to prepare Al-Mg 2 Si alloys reinforced with close to spherical Mg 2 Si particles, which is critical to design lightweight Al-Mg 2 Si alloys with improved performance. [ABSTRACT FROM AUTHOR]

Regulating the solute atoms to form dense nano-sized precipitates is an essential strategy to enhance the strength of Mg alloys, wherein the maximum strength improvement is usually achieved by artificial aging at low temperatures (150-250 °C) for several to dozens of hours. In the present study, we found that a Mg-1.04Zn-0.52Ca-0.27Sn-0.18Mn (wt.%, ZXTM1100) alloy exhibits a substantial yield strength (YS) increment of ∼81 MPa after undergoing cyclic deformation (CD) at room temperature. Moreover, the impressive YS improvement only reduces the elongation to failure from ∼18% to ∼16%. To explore the strengthening mechanisms, the microstructure evolutions of cyclically deformed ZXTM1100 alloy have been systematically investigated by multi-length scale characterization techniques, including synchrotron X-ray diffraction, transmission electron microscopy (TEM), and correlative transmission electron microscopy and atom probe tomography (TEM-APT). It has been found that the strength increment mainly originates from the dynamic formation of a high density (∼5.7 × 1024 m-3) of multi-type solute clusters (e.g. Zn-Ca, Zn-Ca-Mn, and Zn-Zn), which can strengthen the alloy by ∼70 MPa. For the first time, such a high strengthening effect from the formation of solute clusters has been reported in a dilute Mg alloy. The accelerated solute clustering process can be rationalized when considering the supersaturated non-equilibrium vacancies produced by CD treatment. Our work not only demonstrates the pronounced cluster strengthening effect in a dilute Mg alloy, but also could provide new insights into the development of Mg alloys with high strength-ductility synergy. [Display omitted] [ABSTRACT FROM AUTHOR]

The Hall-Petch (H–P) relation for bimodal-grained Mg–Al–Zn alloys consisting of both ultra-fine grains (UFGs)/fine grains (FGs) and coarse grains (CGs) is discussed separately for yield stress and flow stress according to different deformation behaviors of UFGs/FGs and CGs. The yield behavior is controlled by basal dislocation slip of UFGs/FGs and twinning of CGs collectively. Thereafter, non-basal slip is activated in basal-oriented CGs as deformation proceeds. Considering the synergy effect of UFGs/FGs and CGs, we present modified H–P relations for bimodal-grained Mg–3Al–1Zn (AZ31) and Mg–9Al–1Zn (AZ91) alloys containing either few or numerous dispersed particles, respectively, by which the calculated strengths depict experimental values well. Image 1 • The strengthening mechanism and deformation behavior of bimodal-grained Mg alloys are discussed. • The yield behavior is controlled by basal slip and twinning collectively, followed by non-basal slip in basal-oriented CGs. • A quantitative Hall-Petch relation is built to predict the yield strength of bimodal-grained AZ31 and AZ91 alloys. [ABSTRACT FROM AUTHOR]