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Effect of different rolling reductions on the microstructure and mechanical properties of Mg-6Al-3Zn-0.1Mn wt.% alloys were investigated by means of scanning electron microscopy (SEM), electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that after rolling the as-extruded Mg-Al-Zn-Mn alloy, more second phases are dynamically precipitated. The grains are also gradually refined with increasing the total reduction due to the dynamic recrystallization, and the average grain sizes are estimated to be ∼7.2 μm, ∼3.7 μm, ∼1.2 μm for the as-extruded Mg alloy, ∼34% and ∼60% rolled samples, respectively. On the other hand, the high-density contraction twins have been activated in as-rolled Mg samples, which can effectively separate the Mg matrix and a similar grain refinement effect can be afforded. Moreover, the dislocations are significantly multiplied during the rolling process. Consequently, the tensile strength of the Mg alloy is gradually increased, and the ∼60% rolled Mg alloy exhibits the optimal mechanical properties, with the ultimate tensile strength (UTS) of ∼363 MPa and the elongation of ∼7.2%. • Ultra-fined grain size of ∼1.2 μm was produced in AZM630 alloy by combining extrusion and rolling. • The tensile yield strength of as-rolled Mg alloy is up to 327 MPa with high elongation of 7.2%. • Dislocation tangles and contraction twin boundaries effectively improved both the strength and ductility. [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]

In this work, the neutron poison element of boron (B) has been successfully added into the AlNbTiZr based multiprincipal element alloy (MPEA) via the arc melting method, and a new class of nuclear fuel materials based on the MPEAs with both high strength, and neutron poison property has been developed. The mechanical results show that both the AlNbTiZr and AlNbTiZrB samples exhibit the high yield strength of 790 ~ 800 MPa under compressive condition, and 720 ~ 750 MPa under tension. With a minor addition of B element, the ductility of AlNbTiZrB sample is largely deteriorated, exhibiting the compressive ductility of ~ 35 % and tensile ductility of only ~ 1 %. The X-ray diffraction (XRD), Calculation of Phase Diagram (CALPHAD) and transmission electron microscopy (TEM) characterizations demonstrate the formation of numerous feather-like TiB precipitates in AlNbTiZrB sample, which lead to the largely deteriorated tensile ductility in B-containing sample. Despite of that, the compressive ductility can yet reach as high as ~ 35 %, and excellent yield strength can be also obtained. Consequently, the present B-containing MPEA can act as a new promising candidate for future nuclear-fuel materials. • A new boron-containing AlNbTiZrB multiprincipal element alloy (MPEA) has been successfully developed. • AlNbTiZrB samples exhibit the high yield strength of ~ 800 MPa under compression, and also ~ 720 MPa under tension. • The poor tensile ductility in AlNbTiZrB can be ascribed to the existence of numerous feather-like TiB precipitates. • The present B-containing MPEA can act as a new promising candidate for future nuclear-fuel materials. [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 microstructure and mechanical properties of the as-extruded and as-annealed Mg-0.8Ca-xMn-0.2Ce (x = 0.4, 0.7) wt% alloys, which are named as XME04 and XME07, have been investigated. An ultra-high strength of ~428 MPa can be achieved in as-extruded XME04 sample due to the high proportion of as-deformed grains and also high density of residual dislocations. The high Mn addition in as-extruded XME07 alloy can promote the dynamical recrystallization and induce more nano-precipitations. More nano-Mn precipitates in XME07 alloy can effectively hinder grain growth during extrusion and contribute to the finer grains. As a result, more precipitation of nano-phases, finer grains, and lower density of residual dislocations together account for the higher thermal stability in XME07 alloy than that in XME04 alloy. A novel Mg-0.8Ca-0.7Mn-0.2Ce wt% alloy with an excellent thermal stability has been developed. After annealing at 300 °C for 6 h, the yield strength of this alloy can still maintain at ~322 MPa. The relevant results can provide important guidance for developing novel Mg wrought alloys with both ultra-high strength and also high thermal stability. • Ultra-high strength of ~428 MPa was achieved in the low-cost Mg-0.8Ca-0.4Mn-0.2Ce (wt%) wrought alloy. • The Mn addition can promote dynamical recrystallization and induce more nano-precipitations. • A novel Mg-0.8Ca-0.7Mn-0.2Ce wt% alloy with an excellent thermal stability has been produced. [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]