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Here, we present a high ductility of the Be–Al alloy manufactured by investment casting. It was superior to most Be–Al based alloys reported so far, exhibiting high yield strength of 53∼58 MPa, ultimate tensile strength of 111∼117 MPa, and high tensile strain of 14.1–18.8 %. The many < c + a> dislocations in the Be phase were primarily responsible for the exceptionally high mechanical characteristics. A high Schmid factor for pyramidal slip led to slip transfer between the Be grains and Al grains, which may contribute to relieving stress concentration and delaying early fracture.The profuse activated pyramidal < c + a> dislocations could render the unusual high tensile strain. The high strength was attributed to both the good interfacial strength and the constraint of hard Be phase, which makes the soft Al phase strong like the hard Be phase. It demonstrates the strong texture microstructure design of the Be phase had a synergistic improvement in the strength-ductility balance, suggesting that this could be a useful tactic for enhancing the mechanical characteristics of Be–Al alloys.

Pyramidal dislocations in magnesium (Mg) and other hexagonal close-packed metals play an important role in accommodating plastic strains along the c-axis. Bulk single crystal Mg only presents very limited plasticity in c-axis compression, and this behavior was attributed to out-of-plane dissociation of pyramidal dislocations onto the basal plane and resulted in an immobile dislocation configuration. In contrast, other simulations and experiments reported in-plane dissociation of pyramidal dislocations on their slip planes. Thus, the core structure and mode of dissociation of pyramidal dislocations are still not well understood. To better understand the dissociation behavior of pyramidal dislocations in Mg at room temperature, in this work, atomistic simulations were conducted to investigate four types of pyramidal dislocations at 300 K: edge and screw Py-I on {101¯1}, edge and screw Py-II on {112¯2} by using a modified embedded atom method (MEAM) potential for Mg and anisotropic elasticity dislocation model. The results show that when energy minimization was performed before relaxation, in-plane dissociation of edge dislocations on respective pyramidal plane could be obtained at room temperature for all four types of dislocation. Without energy minimization, the edge dislocations dissociated out-of-plane onto the basal plane. Calculations of potential energy and hydrostatic stress of individual atoms at the edge dislocation core show that the extraordinarily high energy and atomic stresses in the as-constructed dislocation structures caused the out-of-plane dissociation onto the basal plane. The core structures of all four types of pyramidal dislocation after in-plane dissociation were analyzed by computing the distribution of the Burgers vector.

The common problem of low tensile yield strength (TYS) prevails in high ductility dilute-alloying Mg-RE alloys prepared by traditional hot extrusion. The design strategy of heterostructures in the microstructure of Mg alloys can effectively improve the strength-ductility synergy in mechanical properties, which is expected to break the trade-off dilemma between strength and ductility. In this work, we successfully prepared a series of high ductility as-extruded Mg-Gd-Zn-Zr alloys with all elongations (ELs) greater than 26.0% at room temperature. By controlling the extrusion process and thus introducing heterogeneous fiberous structure, we finally obtained a superior Mg-1.5Gd-0.5Zn-0.5Zr (wt.%) alloy with strength-ductility synergy, which exhibits a TYS of 246 MPa, ultimate tensile strength (UTS) of 274 MPa and an EL of 29.0%. The microstructure examination for the alloy with the heterostructure reveals that the structure consists of alternating filamentous deformed-grain and fine-grain layers. The overall fine grains in the microstructure, a large amount of nanoprecipitates and the relatively high density of residual dislocations contribute to the high TYS of the alloy. The alloy maintaining high ductility is attributed to the activation of multiple slip systems, especially the active and mobile dislocations, the inhibition of the P-type dislocation to B-type dislocation transition, {10 1¯ 2} tensile twinning generated early during tensile testing, and full intergranular slip transfers caused by high geometric compatibility. The present work can further promote the development of dilute-alloying Mg-RE alloys with high strength-ductility synergy.

High strength–ductility synergy is difficult to achieve in Mg alloys. Although high strength has been achieved through considerable alloying addition and low-temperature extrusion, these techniques result in low ductility (2%–5%). In this work, a novel low-alloy Mg–Ca-based alloy that overcomes this strength–ductility trade-off is designed. The alloy has an excellent tensile yield strength (∼425 MPa) and exhibits a reasonably high elongation capacity (∼11%). A microstructure examination reveals that a high density of submicron grains and nano-precipitates provides the alloy high strength, and the leaner alloy additions and higher extrusion temperatures initially improve ductility. As a result, the density of residual dislocations is reduced, and the formation of low-angle grain boundaries (LAGBs) is enhanced. With fewer residue dislocations, it becomes less probable for the newly activated mobile dislocations to be impeded and transformed into an immobile type during the subsequent tensile test. The LAGBs function as potential sites to emit new dislocations, thus enhancing the dislocation–multiplication capability. More importantly, they can induce evident sub-grain refinement hardening and guarantee that the alloy achieves high strength. The findings lead to a controllable Mg alloy design strategy that can simultaneously afford high strength and ductility. Image, graphical abstract [ABSTRACT FROM AUTHOR]

The dramatic characteristics of serrated flow, i.e., Portevin-Le Châtelier (PLC) effect was observed in AlN/AZ91 composites under uniaxial compression testing at 350 °C with a strain rate of 0.05 s−1. The results show that the PLC effect mainly originates from the repeated shearing of extension twins by pyramidal dislocations in favorably orientated grains, while the profuse activation of extension twins and pyramidal dislocations was induced by AlN particles, which provides new insights into the PLC effect in magnesium-based materials. • Portevin-Le Châtelier (PLC) effect was observed in AlN/AZ91 composites. • PLC effect mainly originates from the repeated shearing of extension twins by pyramidal dislocations. • The activation of extension twins and pyramidal dislocations was induced by AlN reinforcement particles. • Extension twins sheared by Pyr. II < c + a > dislocations were characterized in AlN/AZ91 composites. [ABSTRACT FROM AUTHOR]

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Room-temperature tensile behavior and associated deformation mechanisms of multiple-axial forged (MAFed) pure Mg has been investigated. The as-MAFed Mg, with a coarsely recrystallized structure, exhibited a balanced strain-hardening behavior with strain, resulting in extraordinary mechanical properties with high ultimate stress (~200 MPa) and extensive true strain (~0.30). The observation on the microstructural evolution suggests that the balanced strain-hardening behavior is correlated with de-twinning behavior cooperated with pyramidal dislocations at the plastic straining stage.

Stacking fault (SF) is critically important for both the strength and ductility improvement in Mg alloys, whereas understanding the controlling factors of inducing deformation SFs is insufficient due to the complexity. In this study, deformation mechanism of the calcium-containing Mg alloys is examined under different Ca concentrations and strain rates. It is found that the SFs activations in Mg alloys are closely associated with twining migrations. Increasing both Ca concentration and strain rate promotes deformation twinning, which in turn contributes to the higher density of SFs formations. [ABSTRACT FROM AUTHOR]

Room-temperature tensile behavior and associated deformation mechanisms of multiple-axial forged (MAFed) pure Mg has been investigated. The as-MAFed Mg, with a coarsely recrystallized structure, exhibited a balanced strain-hardening behavior with strain, resulting in extraordinary mechanical properties with high ultimate stress (~200 MPa) and extensive true strain (~0.30). The observation on the microstructural evolution suggests that the balanced strain-hardening behavior is correlated with de-twinning behavior cooperated with pyramidal dislocations at the plastic straining stage. [ABSTRACT FROM AUTHOR]