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The present work revealed a potential to control the static recrystallization kinetics through regulating the feature of pre-existing Mg17Al12 particles in Mg-Al-Zn alloys. The AZ31 (Mg-3Al-1Zn) with rarely dispersoids exhibits the fastest recrystallization rate, while the AZ61 (Mg-6Al-1Zn) with only fine particles (∼100 nm) recrystallizes slower than AZ91 (Mg-9Al-1Zn) containing Mg17Al12 precipitates with scattered size distribution (ranging from less than 100 nm to above 0.6 μm). Especially, we found that coarse Mg17Al12 particles in AZ91 are easier to trigger particle stimulated nucleation (PSN) at 275 °C than 175 °C, which compensates the strong recrystallization inhibition of fine dispersoids, leading to the recrystallization dramatically transforms from retarded to accelerated.

Bake-hardening (BH) processing is an efficient way to rapidly increase the strength of solution-treated Mg alloys, which is attributed to GP-zone strengthening or dislocation pinning caused by solute segregation. Here we report a new hardening mechanism of BH in Mg–2Zn-0.5Ca (wt. %) alloy, i.e., twin boundary pinning, which could obtain enhanced strength-ductility synergy, with a flow stress of ∼200 MPa (increased from ∼141 MPa) and an elongation to failure of ∼17% (increased from ∼12%). Microstructure analyses show that the co-segregation of Zn and Ca atoms at 10 1 ¯ 2 twin boundaries can impede twin boundary migration, which effectively suppresses crack propagation and therefore improves the ductility. Meanwhile, the twin boundary pinning obviously increases strength in conjunction with the pinning effects of co-segregated Zn and Ca atoms at dislocations. Such a twin boundary pinning mechanism suggests that BH technique can be generally applied to develop high-performance Mg alloys with enhanced strength and ductility.

A remarkable natural aging (NA) hardening response induced by pre-strain treatment, i.e. an evident increment of flow stress from ~138 MPa to ~163 MPa within only 48h, was observed in a dilute Mg–1.0Zn–0.45Ca–0.33Sn–0.2Mn (wt.%, ZXTM1000) alloy sheet. The pre-strain deformation introduces profuse basal dislocations and supersaturated non-equilibrium vacancies, favoring the solute diffusion process and therefore resulting in a heterogeneous solute distribution for energy minimization. The retarded dislocation movement by co-segregation of Zn and Ca atoms is responsible for the strengthening effect. This work sheds light on the appreciable NA phenomenon previously unexpected in dilute Mg alloys assisted by the introduction of crystal defects, and the associated microstructure evolutions at ambient temperature provide a novel strategy for the design of high-performance low-cost Mg alloys.

A novel Mg-5.34Al-2.23Zn-1.73Sn (wt%, AZT522 for short) alloy with high strength-ductility synergy was designed and fabricated via simple hot rolling and annealing treatment to compete with the commonly used Mg-9Al-1Zn-0.2Mn (wt%, AZ91) alloy. Different from the coarse microstructure of the as-cast AZ91 alloy, the as-cast AZT522 alloy has much finer microstructure, which consists of finer dendrites and smaller second phase particles. Hot rolling was carried out on the solution-treated alloys to effectively refine the microstructure and improve the mechanical properties. The results suggest that the AZT522 alloy shows better rolling formability. Then, the hot-rolled AZT522 alloy was annealed at the optimized parameter, i.e., 225 °C/1.5 h, leading to uniform fine grains with an average size of ~2.3 µm and numerous near-spherical precipitates (Mg17Al12 and Mg2Sn) with a mean diameter of ~90 nm. Benefiting from the fine annealing microstructure, the novel AZT522 alloy finally exhibited high tensile properties at room temperature, i.e., ultimate tensile strength (UTS) of ~343 MPa, yield strength (YS) ~271 MPa, and elongation to failure (δf) ~16%, which is a much better combination of strength and ductility than the annealed AZ91 alloy. This novel AZT522 alloy may provide a new insight to develop commercial high strength and ductility Mg alloys.

Herein, a new Mg-Zn-Ca-Y wrought alloy designed by micro-alloying of Ca and Y and subjected to an appropriate processing technique that showed an excellent combination of high strength and ductility at room and elevated temperatures. Density functional theory calculation indicates that Y atoms can incorporate into Ca2Mg6Zn3 phases by replacing Ca atoms, which increases the number density of the Ca2Mg6Zn3 phase and refine their size. The pinning effect of precipitates hinders grain growth and leads to a fine average grain size (~2.5 μm), which also results in high tensile properties. Meanwhile, the solid-soluted Zn, Ca, and Y elements, numerous nano-precipitates and Luders elongation promote the dislocation accumulation during further tensile deformation, which enhances both strain hardening and strain hardening rate, leading to a high elongation. Moreover, the annealed ZXW600 alloy exhibits high strength at high temperatures (≤ 120 °C), which is attributed to the strong pinning effect of fine particles. This work will be helpful for the development of new high-alloyed Mg-Zn based wrought alloys with high performance and extensive application in industries.

Wrought Mg–Zn–Zr alloys with a strong basal texture usually exhibit highly anisotropic plastic behavior, resulting in premature fracture during deformation at room temperature. In the present study, we prepared a Mg–1Zn–0.2Zr (ZK10) alloy sheet by multi-pass hot rolling and annealing, tailoring the basal texture and reducing the plastic anisotropy with the addition of dilute Ca. Microstructural characterizations of the tensile-deformed alloys show that pyramidal slip and 10 1 ¯ 2 twinning are more easily formed in the Ca-containing alloy compared with those in the ZK10 alloy. The weakened basal texture involving Ca addition leads to promoted activation of 10 1 ¯ 2 twinning, without significant impact on the Schmid factor distribution of pyramidal slip. Simulation results of the visco-plasticity self-consistent model further indicate that Ca reduces the ratio of critical resolved shear stress for pyramidal slip and 10 1 ¯ 2 twinning versus basal slip, leading to a significant improvement in ductility. This work may provide a new strategy to develop wrought Mg alloys with enhanced ductility.

The dependence of abnormal grain growth (AGG) on initial solidification microstructure in the Al-Mg-Si-Fe alloy was investigated. The AGG was more prone to occur during annealing in the sample following the sub-rapid solidification (SRS, cooling rate ~ 200 K/s) route as compared to the counterpart undergoing conventional solidification (CS, ~18 K/s). It was verified to be closely related to the {100} 〈310〉 grain clusters containing high-mobility grain boundaries based on quasi in-situ microstructure analysis and the refined Mg2Si particles that can be easily dissolved in the SRS sample. This research provides insights for better understanding the close relationship between the AGG and SRS process.

Achieving high strength-ductility synergy is a great challenge in low-alloyed Mg alloys. In this work, a new Mg–1.0Zn–0.45Ca–0.35Sn–0.2Mn (wt.%, ZXTM1000) alloy was designed and fabricated by sub-rapid solidification (SRS) to overcome the dilemma. After hot rolling and annealing, the new alloy sheet exhibited an excellent tensile yield strength (YS, ∼270 MPa) and elongation (∼21%). Microstructure characterization revealed that the high YS was mainly attributed to the fine grains (∼3 μm) and high density of spherical Ca2Mg6Zn3, Mg2Ca, and α-Mn precipitates. Moreover, the homogeneous grain size distribution, weakened TD-split texture and the activation of multiple types of slips contributed to the enhanced ductility. The findings demonstrate an effective way to fabricate low-alloyed Mg alloys with high strength and ductility by combining the SRS and hot rolling.

In this study, we are pleased to report a low-alloyed Mg–1.0Zn–0.45Ca–0.35Sn–0.2Mn (wt. %) alloy sheet fabricated by hot rolling, showing superplastic deformation ability with tensile elongation of ~410%±30% at 573 K and 1 × 10−3 s−1. The superplasticity is co-dominated by grain boundaries sliding (GBS) and solute drag creep. Unlike high-alloyed Mg alloys with dispersed precipitates, this low-alloyed system keeps its fine-grained microstructure by the co-segregation of Zn and Ca atoms at grain boundaries (GBs) coupled with a few precipitates. Although the co-segregation of Zn and Ca atoms at GBs are not favored for GBS, the resulting superior thermostability is of great importance to achieve superplastic deformation. Thus, we put forward a new path in achieving superplasticity in low alloyed Mg alloys by using a complementary thermodynamic and kinetic stabilization approach.

The development of wrought Mg alloys with high alloying contents is greatly restricted by the negative influence of coarse aggregative second phases originating from the casting process. In the present work, we reported a high-performance Mg-5Al-2Sn-2Zn-0.5Bi (wt%, ATZB5220) alloy fabricated by combining sub-rapid solidification (SRS) and controlled hot rolling. The microstructure of the as-cast alloy was greatly refined by the SRS with a high cooling rate (~350 °C/s). The micro-segregation of different alloying elements was also alleviated by the SRS to varying degrees. The improvement degrees of micro-segregation for Al and Sn solutes were much higher compared with Zn and Bi. The SRS sample obtained more uniform and finer (~3 μm) grains than the conventional solidified counterpart after hot rolling (a reduction of ~70%) and annealing treatment, which mainly benefited from the finer as-cast microstructure under the SRS. Eventually, the high-alloyed ATZB5220 sample following the SRS route showed a good combination of strength and ductility, exhibiting an ultimate tensile strength (UTS) of ~356 MPa, yield strength (YS) of ~267 MPa, and elongation to failure (δf) of ~13%. This work provides a novel strategy to fabricate high-performance Mg alloy sheets with high alloying contents.

The microstructure, mechanical properties and corrosion behavior of hot&ndash, rolled Mg&ndash, xSn&ndash, 1Zn&ndash, 0.5Ca (x = 1, 3 and 5 wt.%) alloys were investigated for possible application as biodegradable implants. The hot&ndash, 0.5Ca alloys consisted of &alpha, Mg matrix and Mg2Sn phase. The number of the Mg2Sn particles significantly increased and the grains were gradually refined (14.2 &plusmn, 1.5, ~10.7 &plusmn, 0.7 and ~6.6 &plusmn, 1.1 &mu, m), while the recrystallized fraction significantly decreased with the increase in the Sn content, the Mg&ndash, 1Sn&ndash, 0.5Ca alloy was almost completely recrystallized. Ultimate tensile strength (UTS) and tensile yield strength (TYS) increased slightly, reaching maximum values of 247 MPa and 116 MPa, respectively, for the Mg&ndash, 5Sn&ndash, 0.5Ca alloy, and the elongation decreased with the increase in the Sn content, the Mg&ndash, 0.5Ca alloy showed the highest elongation (15.3%). In addition, immersion tests and electrochemical measurements in Hank&rsquo, s solution revealed that the corrosion rates of Mg&ndash, 0.5Ca alloys increased with the increase in the Sn content. A model of the corrosion behavior was discussed for hot&ndash, 0.5Ca alloys in Hank&rsquo, s solution. Among the Mg&ndash, 0.5Ca (x = 1, 3 and 5 wt.%) alloys, Mg&ndash, 0.5Ca alloy exhibits optimal corrosion resistance and appropriate mechanical properties.