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The low microalloying content and high yield strength of 365 MPa have been achieved simultaneously in extruded Mg–Ce–Al alloy which is mainly ascribed to the unexpected grain refinement (mean size of ∼420 nm). It is found that adding tiny Al (0.05 wt.%) into Mg–0.2 wt.% Ce alloy can promote the formation of Ce–Al-enriched segregation along dislocations and grain boundaries which can effectively counterbalance the thermally activated dislocation recovery and thus guarantee grain refinement. The ultra-fined grains are mainly related to both linear and planar cosegregation of solutes, rather than the traditional planar segregations and/or nanoprecipitations at grain boundaries. A new mechanism of linear/planar cosegregation of solutes for ultrafine DRXed grains formation in Mg alloys has been found, rather than traditional planar segregations and/or nanoprecipitations at grain boundaries. [ABSTRACT FROM AUTHOR]

This work reported the effect of extrusion speeds on the microstructures and mechanical properties of Mg-Ca binary alloy. The results showed that yield strength of the as-extruded Mg-1.2 wt.% Ca alloys decrease from ∼ 360 MPa to ∼ 258 MPa as the ram speed increases from 0.4 mm/s to 2.4 mm/s, and the elongation increases from ∼ 3.9% to ∼ 12.2%. The microstructure changes from bimodal grain feature to the complete dynamical recrystallization (DRX) with increase of the extrusion speed. The ultrafine DRXed grains in size of ∼0.85 µm, the numerous nano-Mg 2 Ca particles dispersing along the grain boundaries and interiors, as well as the high density of residual dislocations, should account for the high strength. It is believed that the high degree of dynamic recrystallization and the resulting texture randomization play the critical roles in the ductility enhancement of the high-speed extruded Mg alloys. [ABSTRACT FROM AUTHOR]

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]

Ultrahigh strength is achieved in low-cost Mg-4Sm-0.6Zn-0.4Zr alloy by a traditional extrusion process, with tensile yield strength over 450 MPa, which exceeds the majority of heavy rare-earth (RE) alloyed Mg-RE extrusion alloys. The alloy showed a typical bimodal microstructure, consisting of fine recrystallized grains with random orientations and coarse hot-worked grains with strong basal texture. And profuse Mg 3 Sm particles were dynamically precipitated in recrystallized grains boundary as well as hot-worked grains interior during extrusion. The ultrahigh yield strength of the alloy is closely related to the combined effect of fine recrystallized grains, highly textural hot-worked grains, and numerous nanoscale particles, independent of the accepted age-hardening in those heavy RE containing Mg alloys. Low cost, high strength, and simple extrusion process make the present alloy gets more fantastic potential in industrial applications than other Mg-RE extrusion alloys. [ABSTRACT FROM AUTHOR]

An ultra-high strength and low-cost magnesium wrought alloy, Mg-1Ca-1Al-0.3Zn-0.4Mn (wt%), has been fabricated by conventional extrusion, with yield strength of ~435 MPa, the ultimate tensile strength of ~449 MPa and the elongation of ~4.2%. Mono-dispersive nano-precipitations, e.g., the Al 2 Ca phase and AlMn phase, have been induced during extrusion, which can effectively pin pyramidal dislocation motions in grain interiors and thus provide substantial nucleation sites for dynamic recrystallization in present Ca-containing Mg alloys. Simultaneously, these fine-precipitates distributing at the new grain boundaries can prevent their growths, which thus guarantee the ultra-fine grains formation (300–500 nm). After heat treatment, a higher number density of nano Al 2 Ca and AlMn phases can be further precipitated, which results in the alloy still maintaining the ultra-high strength of ~444 MPa. The multiple roles of the same nano-precipitations in both promoting the ultrafine grains formation and affording precipitation hardening have been clarified in present Mg wrought alloy. • Ultra-high strength of ~449 MPa was achieved in the low-cost Mg-1Ca-1Al-0.3Zn-0.4Mn (wt%) wrought alloy. • Ultra-fine grain size (300–500 nm) was achieved due to ther fine-precipitates distributing at the new grain boundaries. • A higher number density of nano-precipitations could afford extra precipitation hardening effect after heat treatment. [ABSTRACT FROM AUTHOR]

In this work, the trace Ce atoms have been added into the low-alloyed Mg-Al-Ca matrix, and the microstructure and mechanical properties have been investigated. For the Mg-Al-Ca ternary alloy, the tensile yield strength (TYS) would be decreased from ~ 321 MPa at 260 °C (extrusion temperature) to ~ 294 MPa at 290 °C. In contrast, the Mg-Al-Ca-Ce alloy can still exhibit the high YS of ~ 350 MPa and elongation of ~ 12.1% at higher extrusion temperature of 290 °C. Microstructure characterization shows that the Ce addition can effectively induce the solute segregations along both dislocations and grain boundaries in Mg-Al-Ca-Ce alloy, which thus leads to the finer grain size of 0.7 ~ 0.8 µm at a wide range of extrusion temperature. Formation of subgrain with strong texture, residual dislocations due to segregation and profuse nano-precipitations can together contribute to the high yield strength of Mg-Al-Ca-Ce alloy. More importantly, the trace Ce atoms can promote the activation of non-basal dislocations in Mg matrix and also the weakened texture in DRXed grains. As a result, the ductility is also simultaneously improved by the trace addition of Ce atom into Mg-Al-Ca based alloy. The relevant results can shed light on designing the new high strength and low-alloyed Mg alloys. • Simultaneous improvement of strength and ductility is achieved through trace Ce addition into dilute Mg-Al-Ca alloys. • Solute segregations along both dislocations and grain boundaries can be achieved by the addition of Ce. • Finer grain size of 0.7–0.8 µm at a wide range of extrusion temperature is obtained in the new Mg-Al-Ca-Ce alloy. [ABSTRACT FROM AUTHOR]

In this work, the role of Al addition in modifying the microstructure and mechanical properties of the Mg-1.0Ca- x Al (x = 0.6, 1.0 wt%; termed as XA10 and XA11, respectively) based alloys has been systematically investigated. Microstructural examination showed that, when the Al content is low, the Al and Ca atoms were inclined to segregate to the dislocation lines in the XA10 sample. As a result, the mobility of dislocation was restrained and the dynamic recovery behavior was hindered, which leads to a low degree of dynamic recrystallization. When the Al content is high, in contrast, no apparent Ca/Al segregations along dislocations have been found in XA11-0 extrusion billet during the whole stages of processing, which results in the enhanced dislocation mobility. Consequently, the recovery of dislocations and dynamic recrystallization rate can be largely enhanced at the earlier stage of extrusion. More importantly, subsequently formed high density Guinier-Preston (G.P.) zones and nano-disk Al 2 Ca phases in the high-Al content Mg sample can play an effective role in inhibiting the growth of subgrains and dynamically recrystallized (DRXed) grains, which enhance the thermal stability of high density low angular grain boundaries (LAGBs) in the later extrusion stage. The high density nano-disk phases, high volume fraction of DRXed grains, as well as the high density LAGBs in the un-DRXed grains, can together contribute to both high strength and good elongation of the XA11 sample. The findings lead to the controllable Mg-Ca based alloy designing strategy that can improve the strength and ductility simultaneously. • An excellent strength-ductility synergy was achieved at dilute alloying content. • The dynamic recrystallization behavior of the low-alloyed Mg-Ca-Al based alloy was investigated. • The segregation of Ca/Al atoms to dislocations take place preferentially at lower Al content. • The high density nano-disk phases, DRXed grains, as well as the LAGBs in the un-DRXed grains were observed in higher Al content. [ABSTRACT FROM AUTHOR]