Non-basal Slip Research Articles

Development of high strength-ductility Mg-Er extruded alloys by micro-alloying with Mn

This work systematically investigated the influence of the micro-Mn addition on the microstructures and mechanical properties of Mg-Er alloys. To investigate their deformation mechanisms during tensile testing, electron back-scattered diffraction, transmission electron microscopy, slip trace analysis, and visco-plastic self-consistent polycrystal constitutive (VPSC) modeling were used. The study showed that the as-solid solution samples only consist of the α-Mg phase. All samples exhibit a complete dynamic recrystallized (DRXed) microstructure with an average grain size of 2.79 µm after hot extrusion. The ductility first increases from 26.02 % to 35.34 % and then remains unchanged with the increment of Mn content. Meanwhile, the yield strength significantly increases from 95 MPa to 200 MPa. According to VPSC results, the initial slip resistance (τ0) difference between prismatic and basal slips decreases from 109 MPa to 92 MPa and τ0 between pyramidal and basal slip systems from 129 MPa to 112 MPa. Both the VPSC and two-beam diffraction results confirmed that pyramidal<c+a>slip and<a>slip were activated during tensile deformation. The quantitative analysis of the slip trace line verified that the volume of non-basal slip reached 65 % when the content of Mn was increased to 0.9 wt%. Mn in solid solution increased the activity of pyramidal<c+a>and prismatic<a>dislocations during deformation, which is beneficial for accommodating c-axis strain. Consequently, the ambient ductility of Mg-2Er alloy with Mn addition is improved.

Quasicrystal-strengthened biomedical magnesium alloy fabricated by laser additive manufacturing

Magnesium (Mg) alloy, particular Mg-zinc (Zn) series alloy, owns great potential as implant materials, despite it shows uncontrollable corrosion rate and inadequate mechanical performance. Herein, alloying treatment with rare earth yttrium (Y) was adopted to improve the overall performance of Mg-Zn-Zr alloy. In detail, Mg-Zn-Y-Zr (ZW61) parts were fabricated using laser additive manufacturing. Results showed that Y addition had contributed to the formation of quasicrystal I-phase (Mg3Zn6Y), which could serve as weak cathode and alleviate the occurrence of micro-galvanic corrosion within Mg matrix. Meanwhile, Y addition also promoted the development of compact corrosion film, which further delayed the corrosion of Mg matrix. Thus, laser-processed ZW61 parts showed a considerably reduced corrosion rate of 0.67 mm/year. More importantly, the quasicrystal I-phase contributed to a more significant Orowan strengthening effect, as it exhibited a near-coherent interface with α-Mg. Besides, rare earth Y decreased the energy of stacking faults, and thereby activated numerous non-basal slip systems during deformation, as proved by TEM observation. Thus, as-built ZW61 part showed simultaneously improved strength and plasticity. Furthermore, in vitro cell testing proved its favorable biocompatibility. Our research exhibited that laser-processed ZW61 was a competitive candidate for orthopedics device application.

Effect of grain size on superplastic deformation behavior of Zn-0.033 Mg alloy

Zn alloys reveal excellent biological degradability and compatibility, suitable mechanical properties, and unique anti-atherosclerotic properties, which make them suited for miniaturized medical implants. Superplastic forming is a promising method to fabricate high-performance microparts with difficult-to-deform materials. However, the effect of grain size on superplasticity in Zn alloys and the underlying mechanisms still need to be determined. In this research, Zn-0.033 Mg (in wt.%) alloy with different grain sizes from 1.53 to 36.17 μm was obtained by equal-channel angular pressing and heat treatment, and its mechanical performance was evaluated by uniaxial tensile tests in the temperature range of 453–533 K and the strain rate range of 0.001–0.01 s−1. Experimental results indicated that the flow stress is significantly reduced with increasing deformation temperature, and the elongation is effectively improved with the reduction in strain rate. Furthermore, the Zn-0.033 Mg alloy with a grain size of 1.53 μm exhibited a superplastic deformation with an elongation of 376 ± 79% at 453 K and 0.001 s−1. Two distinguishing deformation stages were observed during the superplastic deformation. In the early stage, the ∼85 ± 5°/ <1‾1‾20> twins significantly emerged, leading to subsequent dynamic recrystallization by high-angle grain boundary migration. In the steady-state stage, the non-basal dislocation slip was significantly activated via changing the grain orientation from hard to soft orientation with the aid of continuous dynamic recrystallization. The fracture mechanisms were further discussed based on the fracture surface analysis, indicating that the ultrafine-grained structures can accommodate the nucleation and growth of cavities by grain boundary sliding, enabling low-temperature superplasticity. These findings can grant a new insight and understanding of the superplastic mechanism of Zn alloys and shed light on the manufacture of high-performance Zn alloys for medical implants.

Elimination of in-plane mechanical anisotropy and enhancement of strength-ductility of rolled Mg sheets via electric-associated twinning and recrystallization

A novel method referred as electric-associated corrugated wide limit alignment (E-CWLA) was proposed to address the contradiction between strength and plasticity of hot-rolled Mg sheets. The counterpart without electricity was known as CWLA. A huge number of tensile twins (TTs) was induced in CWLAed sample R300, and dynamic recrystallization (DRX) occurs. Strong transverse direction (TD)-titled texture accounts for the huge difference in yielding strength between different loading directions, which are closely related to Schmid factors of prismatic <a> and pyramidal <c+a> slips, resulting in different ultimate tensile strength (UTS) and ductility of R300 along different directions. E-CWLAed sample E300 presents good in-plane mechanical isotropy with the maximum UTS of 272.1 MPa, yielding strength of 213.6 MPa and elongation of 22.7%, increasing by 32%, 53% and 83% compared with the as-received sheets, respectively. Regardless loading direction, basal and non-basal slips possess similar SFs and greatly facilitates uniform plastic deformation and mechanical isotropy of E300. The special microstructure including lots of fine grains, some large grains and TTs results in a bimodal basal texture with very weak TD-titled component promotes its good deformation compatibility. Electricity contributes little to TTs formation of E300, and its thermal effect promoting dislocation mobility and DRX and the athermal effect increasing DRX nucleation rate are responsible for final grain size distribution.

Revealing the dynamic recrystallization mechanism, extrusion deformation mechanism, and tensile deformation behavior of Mg–6Al–1Zn–1.1Sc alloy

In this study, extruded deformed billet and extruded rod of Mg–6Al–1Zn–1.1Sc (wt. %) alloy were characterized by optical microscopy (OM) and electron backscatter diffraction (EBSD). The room temperature tensile properties and deformation behavior of extruded alloy were investigated using a universal testing machine and the visco-plastic self-consistent (VPSC) model. The results indicated that the coarse deformed grains (DGs) progressively disappeared and the degree of dynamic recrystallization (DRX) of the alloy increased as the sampling position approached the outlet of the extrusion die. In addition, the grain boundary strengthening induced by DRX increased the corresponding Vickers hardness. DRX mechanisms during extrusion included discontinuous DRX, continuous DRX, twin-induced DRX, and particle-stimulated nucleation (PSN). The EBSD-based in-grain misorientation axes (IGMA) analysis revealed that the slip modes within DGs were dominated by prismatic slip in the early stages of extrusion and by multiple slip modes in the later stages. The yield strength, ultimate tensile strength, and elongation of the extruded alloy were 172.4 MPa, 290.1 MPa, and 26.9%, respectively. The combination of grain boundary strengthening, texture strengthening, and secondary phase strengthening resulted in the high yield strength. The VPSC model well simulated the tensile deformation of the extruded alloy with (0001)//ED (extrusion direction) fiber texture. The superior plasticity of the extruded alloy was ascribed to the high Schmid factor (SF) of the non-basal slip and the activation of the non-basal slip facilitated by the reduction in the ratio of the critical resolved shear stress (CRSS) between the non-basal slip and the basal slip.

Underlying slip/twinning activities of Mg-xGd alloys investigated by modified lattice rotation analysis

The inconsistencies regarding the fundamental correlation between Gd content and slip (twinning) activities of Mg alloys appeal further investigations. However, the traditional slip dislocations analysis by TEM is time-consuming, and that by SEM/EBSD cannot recognize the partial slip modes. These urge a more efficient and comprehensive approach to easily distinguish all potential slip modes occurred concurrently in alloy matrix. Here we report a modified lattice rotation analysis that can distinguish all slip systems and provide statistical results for slip activities in Mg alloy matrix. Using this method, the high ductility of Mg-Gd alloy ascribed to the enhanced non-basal slips, cross-slip, and postponed twinning activities by Gd addition is quantitatively clarified.

The influence of the LPSO on the deformation mechanisms and tensile properties at elevated temperatures of the Mg-Gd-Zn-Mn alloys

The introduction of long period stacking ordered (LPSO) phase is an effective way to improve the performance of the magnesium alloys at elevated temperatures. In this paper, the hot tensile behaviors of two Mg-4Gd-1Zn-0.5Mn (wt.%) alloys with different lamellar LPSO volume fractions under the strain rate of 2.2 × 10–4 s –1 and at varied temperatures (150 °C–250 °C) were investigated. With the increasing of the deformation temperatures, the peak stresses of the alloy with lower volume fraction of the LPSO decreased (denoted as LL alloy). The hot tensile mechanical properties of the alloy with higher volume fraction of the LPSO (denoted as HL alloy) are significantly higher than those of LL alloy. When the deformation temperature was 250 °C, the LL alloys significantly underwent dynamic recrystallization (DRX) and the DRX dominated by discontinuous dynamic recrystallization (DDRX). However, the HL alloys did not have obvious DRX due to the lamellar LPSO hindering the grain boundary migration. The basal fiber texture of the alloy was produced after hot tensile. The deformation of the LL alloys was dominated by prismatic <a> slip during the hot deformation while the deformation of the HL alloys was dominated by the prismatic <a> slip and pyramidal <c+a> slip. The pyramidal <c+a> slip was activated by the Young's moduli mismatch between the α-Mg matrix and LPSO. Lamellar LPSO has an positive effect on strengthening the mechanical properties of the alloy which is attributed to the hinder of LPSO to non-basal slip, the prick function of kink to basal slip and the inhibition of LPSO to DDRX.

Investigations on the tensile deformation of pure Mg and Mg–15Gd alloy by in-situ X-ray synchrotron radiation and visco-plastic self-consistent modeling

In this study, the texture evolutions of two Mg materials during tension are explored. In-situ X-ray synchrotron and Visco-Plastic Self-Consistent (VPSC) modeling are employed to investigate the different deformation modes between pure Mg and Mg–15Gd (wt.%) alloy. These two materials with a strong extrusion texture show large different slip/twinning activity behaviors during tensile deformation. The basal 〈a〉 slip has the highest contribution to the initial stage of plastic deformation for pure Mg. During the subsequent plastic deformation, the prismatic slip is dominant due to the strong ED // 〈100〉 fiber texture. In contrast, the deformation behavior of Mg–15Gd alloy is more complex. Twinning and basal slip are dominant at the early stage of plastic deformation, but further deformation results in the increased activation of prismatic and pyramidal slips. In comparison to pure Mg, the ratios of the critical resolved shear stress (CRSS) between non-basal slip and basal slip of the Mg–15Gd alloy are much lower.

Developing a Mg alloy with ultrahigh room temperature ductility via grain boundary segregation and activation of non-basal slips

Poor room temperature (RT) ductility is an inherent disadvantage of magnesium (Mg) alloys, which limits their wide application. Grain refinement is an accepted method to improve ductility and strength simultaneously. However, obtaining ultrafine grains (about 1 μm and below) usually requires severe deformation processes, which is not conducive to be widely used. Here, by utilizing a distinctive design strategy, i.e., introducing beneficial solute to achieve grain boundary (GB) segregation and effectively reduce the critical resolved shear stress (CRSS) ratio between non-basal slips and basal slip, thus efficiently activating non-basal slips, we obtained a Mg-0.3Er (at%) alloy with moderate-fine grains (∼8 μm) having elongation near 50% at RT. Based on the results of in-situ electron back-scatter diffraction and slip trace analysis, and weak beam dark-field observation, we confirmed that minor Er element and appropriate fine grains would contribute to the activation of considerable non-basal dislocations and the suppression of twinning. In addition, through energy dispersive spectrometry element analyses for systematic investigation, we found that the GB segregation level of the alloy annealed at 300 °C is higher than that of the alloy annealed at 360 °C. The higher GB segregation level would impact the cohesion strength and be conducive to activate more non-basal dislocations to accommodate local stress, thus suppressing the GB cracking and finally improving the ductility. This study not only suggests an effective way for large-scale development of high ductility Mg alloys at RT, but also provides a new insight to elucidate the origins of ultrahigh ductility by revealing the fraction of non-basal slips and the level of GB segregation.

Clarifying the deformation modes and strengthening mechanisms of Mg-11Gd-5Y-2Zn-0.7Zr with outstanding high-temperature mechanical properties

The mechanical properties of as-extruded Mg-11Gd-5Y-2Zn-0.7Zr (GWZ1152) alloy were systematically studied with respect to their microstructures at room and high temperatures. It exhibited excellent ultimate tensile strength (UTS) of 365 MPa at room temperature (RT), while it maintained relatively high UTS as the temperatures increased to 250 °C (342 MPa), 300 °C (337 MPa) and 350 °C (278 MPa) with a strain rate of 1.85 × 10−3 s−1. The microstructural characterizations revealed that such outstanding heat resistance is mainly attributed to (i) the fine dynamic recrystallized (DRXed) grains and strongly textured un-DRXed grains, (ii) the block-shaped LPSO phase and the nano-scale β precipitates, (iii) the nano-spaced basal LPSO/SFs. Compared to other heat-resistant Mg alloys, our intrinsic chemistry properties contribute to the superior high-temperature mechanical properties of GWZ1152 alloy. For the deformation modes at RT, the dislocations were mainly generated and accumulated on the block-shaped LPSO, followed by cracking and propagation. At 250 °C and 300 °C, non-basal slip inside the coarse un-DRXed was generated, the cracks and fractures were initiated along the slip trace. The main deformation mechanism of GWZ1152 alloy at 350 °C was grain boundary sliding, cracks usually occurred at grain boundaries.

Microstructure and High-Temperature Mechanical Properties of Mg-1Al-12Y Alloy Containing LPSO Phase

This paper describes our study on the effect of the long-period stacking order (LPSO) phase on the comprehensive mechanical properties of the as-cast Mg-1Al-12Y (wt. %) alloy. The microstructure and tensile mechanical properties of as-cast alloy and solution treatment alloy were evaluated. The results showed that α-Mg matrix, Al2Y phase and β-Mg24Y5 phase were present in the as-cast alloy. After solution treatment, the β-Mg24Y5 phase in the alloy was dissolved and the LPSO phase was precipitated. The solution treatment did not cause grain growth or Al2Y phase change, but the comprehensive mechanical properties of the alloy were significantly improved. This was mainly due to the precipitation of the LPSO phase in the solid solution alloy. In addition, the dissolution of the β-Mg24Y5 phase after solution treatment could also improve the mechanical properties. The improvement of the comprehensive mechanical properties of solution treatment alloys at room temperature was due to the dispersion strengthening caused by the intragranular LPSO phase dispersed within the alloy, which had a good blocking effect on the movement of dislocations. The ductility of the solid-solution alloy was greatly improved at a high temperature while maintaining high strength because the LPSO phase is kinked, the dislocation density was reduced, and more non-basal slip was activated during the high-temperature tension.

Microstructure evolution and mechanical properties of cup-shaped specimens prepared by rotary backward extrusion

Rotary backward extrusion (RBE) has been proven to be a useful method for preparing high-performance cup-shaped specimens. However, previous relevant studies aimed to investigate small samples. In this paper, large cup-shaped specimens were prepared by RBE at rotary speeds of 0.35 r/min and 0.9 r/min. The microstructural evolution and properties were analyzed for different regions of the cup wall. The results showed that the obtained microstructure became finer from the outer to inner region, and increasing the rotary speed improved the deformation uniformity and mechanical properties. Continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) actively contributed to hot deformation. High recrystallization effectively weakened the texture intensity, and the inner region at a rotary speed of 0.9 r/min showed an abnormal texture; this phenomenon was attributed to the activation of nonbasal slip brought by high strains and rare earth contents. Refinement strengthening was a major mechanism during RBE; the highest recrystallization of the region reached 93.1%, and its yield strength (YS), ultimate strength (UTS), and elongation (EL) values were ∼219.3 MPa, ∼298.2 MPa, ∼15.2%, respectively.

Texture evolution and effect on mechanical properties of repetitive upsetting-extruded and heat treatment Mg-Gd-Y-Zn-Zr alloy containing LPSO phases

The texture evolution mechanism of Mg-13.1Gd-3.9Y–2Zn-0.4Zr (wt%) alloys during reciprocating upsetting extrusion (RUE) and subsequent heat treatment were investigated in this study. The relationship between texture weakening and deformation mechanism during multi-pass deformation was further discussed. The results show that the strong (0001)∥ED basal texture was formed after RUE, which decreases with the increase of deformation passes; the texture type had no obvious change after T5 treatment, and the texture intensity decreases significantly after T6 treatment. The high proportion of deformed grains determines the formation of strong basal texture after a single pass deformation. Due to the strong anisotropy of LPSO phases, deformed grains with different initial orientations participate in deformation through kinking or activation of basal slip and prismatic <a> slip, respectively, and have different effects on the final texture components. With the strain increases (2 P), the deformed grains are consumed by DRXed grains with random texture, and the non-basal slip of DRXed grains became the main deformation mechanism. After T6 heat treatment, the < 112̅0 > fiber texture components were formed in the sample, which is due to the random nucleation and preferential growth of recrystallized grain during solution treatment. The mechanical properties of the alloys are significantly improved after RUE deformation, but the improvement on ED is better than that on TD. The mechanical properties of the alloys are improved by T5 or T6 heat treatment. The anisotropy of the former is still maintained, while that of the latter is basically eliminated.

The evolution of microstructure and texture of AZ80 and AZ80-LaMM magnesium alloy wheel hubs processed by single-pass radial forging

In this paper, 1.5 wt% La-rich Mish Metal (LaMM) was added to AZ80 magnesium alloy, and microstructure evolution, texture development of AZ80 wheel hub were studied by single-pass radial forging, so as to provide basic data for the preparation of magnesium alloy wheel hub with uniform microstructure and excellent mechanical properties. A detailed microstructure analysis was performed using the optical microscopy (OM) and electron back-scatter diffraction (EBSD). The result shows that the LaMM greatly improves the refinement ability and deformation uniformity of AZ80 wheel hub, and the volume fraction of DRX is greatly increased, which is attributed to the increase of recrystallized nucleation cores in the RE (rare earth) phase bands through the effect of particle stimulated nucleation (PSN). The texture of the wheel hub is gradually weakened along the forming direction due to the increasing strain and dynamic recrystallization (DRX) degree. The larger cumulative strain can promote the activation of the non-basal slip systems and the generation of dislocations, which ultimately promotes the emergence of dynamic recrystallized (DRXed) grains and weakens the texture. The texture of AZ80 wheel hub is weakened by LaMM, which changes the DRX mechanism of spokes and lower rim part, promotes the occurrence of DRX, and produces more non-basal slip. Some of the grains are biased towards the basal plane, which is more conducive to grain slip, while the other DRXed grains are also deflected due to non-basal plane slip. The hardness values of AZ80-LaMM wheel hub are larger and more uniform than those of AZ80 wheel hub. This can be attributed to the fact that the RE phases inhibit the grain growth, keep the microstructure stable and produce better grain refinement.

Influence of strain rate on grain refinement and texture evolution under complex shear stress conditions

The effects of different complex shear stress conditions on grain refinement and texture evolution of Mg-13Gd-4Y-2Zn-0.5Zr alloy were investigated. With increasing strain rate, the average grain size of compression-shear (CS) and compression-torsion (CT) samples are decreased, and the grain size of dynamic recrystallization (DRX) grains is also decreased. This is because that the precipitation number of β phases is increased, and the hindering effect on grain growth can be significantly enhanced. The DRX fractions of CS and CT samples are decreased with increased strain rate. The low DRX fraction at high strain rate is related to the insufficient time for grains to nucleate. The DRX process can be promoted by the PSN mechanism of second phases, and the grain growth can be restricted by the pinning effect. At the same time, the texture strength is enhanced as the strain rate increased. Besides, the kinking degree of lamellar long-period stacking ordered (LPSO) phases is increased. Under complex shear stress conditions, non-basal slip, especially pyramidal slip, is easily activated and the texture is deflected greatly. Compared with the CS samples, CT samples have smaller average grain size, higher DRX fraction, and lower texture strength for a certain strain rate. This is because that the equivalent stress of the CT sample is larger, the stress triaxiality is smaller, so more serious dislocations are piled up near grain boundaries and second phases. At the same time, since CT sample was sheared with torsion, the dislocation movement path can be called “rotational dislocation accumulation”, and the longer distribution path of the CT sample is generated, so more sub-grains and low-angle grain boundaries (LAGBs) are formed. Compared with the CS sample, more huge-angle grain boundaries (HAGBs) and DRX grains are formed from grain boundary to grain interior, so better grain refinement effect is achieved.

Ameliorating the edge cracking behavior of Mg-Mn-Al alloy sheets prepared by multi-pass online heating rolling

Low-cost Mg-1Mn-0.5Al (MA10) alloys with good comprehensive strength and ductility have been developed and have the potential to substitute commercial AZ31 alloys. Thus, the rollability in terms of the edge cracking behavior of MA10 alloy sheets was investigated by multi-pass online heating rolling at different temperatures. The microstructure evolution was characterized by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results reveal that edge cracking is significantly improved with increasing temperature due to the more uniform microstructure, higher degree of recrystallization, more homogeneous strain distribution, and more activation of non-basal slips at the edge. The maximum basal texture intensity at the edge of MA10 rolled sheets is obviously increased with increasing temperature, which can be attributed to the increased numbers of grains with basal orientation after multi-pass online heating rolling.

Ductility enhancement by activating non-basal slip in as-extruded Mg alloys with dilute Sc addition

This work systematically investigates the impact of the dilute Sc addition on microstructures and mechanical properties in Mg alloys. Electron back scattered diffraction, slip traces analysis, transmission electron microscopy, and visco-plastic self-consistent polycrystal constitutive (VPSC) modeling were performed to investigate the deformation mechanisms in the tensile testing, especially the activation of <c+a> slip. The results showed that as-solid solution samples only consisted of α-Mg phase. After extrusion, all samples exhibited a similar average grain size. With the increment of the Sc content, the ductility of the samples was significantly improved, which failure elongation (FL) of Mg-xSc (x = 0.3, 0.6, 0.9 wt.%) alloys improved from 14.4% to 24.8%. The yield strength of each alloy is similar, about 200 MPa. VPSC results indicated that the difference value of the initial slip resistance (τ0) between prismatic slip and basal slip decreases from 63 MPa to 49 MPa, and the difference value of τ0 between pyramidal slip and basal slip decreases from 72 MPa to 57 MPa. The VPSC and the two-beam diffraction results confirmed that the pyramidal <c+a> slip and prismatic <a> slip were activated in tensile testing. The quantitative analysis of the slip trace line verified that the volume of non-basal slip reached 49.5% when the Sc content increased to 0.9 wt.%. Therefore, the addition of Sc in solid solution increased the amount of pyramidal <c+a> and prismatic <a> dislocation activities during the deformation process, which was beneficial to coordinate the c-axis strain, and finally improved ductility of Mg alloy.

Effect of Mn addition on the microstructure, mechanical, and corrosion properties of an extruded biodegradable Zn-0.2Mg alloy

In this study, the effect of Mn addition on microstructural evolution, mechanical properties, and biocorrosion behaviors of as-extruded Zn-0.2 Mg alloy as candidates for degradable biomaterials were investigated. The microstructural observations indicated that the addition of Mn element significantly refined α-Zn grains, and the average size decreased from 17.23 μm to 7.14 μm. Moreover, Mn-rich intermetallic precipitated alongside eutectic Mg2Zn11 phases. A result of electron backscattered diffraction indicated that manganese has caused grains to rotate 19°, facilitating the activation of non-basal slip as the Schmid factor increases. Mechanical test results showed that the yield strength (YS), ultimate tensile strength (UTS), and elongation (El) of Zn-0.2Mg-0.5Mn alloy is improved by 35.92%, 31.51%, and 6.65%, respectively, compared with Zn-0.2 Mg alloy. The main mechanisms responsible for the improvement of mechanical properties were higher volume fraction of the particles, grain refinement, texture modification, and deformation twining formed by Mn addition. The electrochemical test in SBF solution at human body temperature revealed that the corrosion rate of Mn-containing alloy increased from 0.664 mm/year to 0.87 mm/year compared to the base alloy. It is evident from these results that the Zn-0.2Mg-0.5Mn alloy has a great deal of potential as a cardiovascular stent material.

Cerium-activated non-basal slip improves ductility of magnesium alloy

Biodegradable magnesium (Mg) possesses satiable elastic modulus and favorable biocompatibility, but poor plasticity limited its clinical application in bone repair field. In this work, rare-earth cerium (Ce) was introduced in Mg powder via mechanical alloying (MA). Under sustainable impact of huge compelling force, the Mg and Ce powders welded together and generated much crystal defects, which reduced the energy barrier of solute atom diffusion, thus obtaining Mg-Ce supersaturated solid solution powder. Afterwards, the MA-processed powder was shaped into parts by powder metallurgy. The supersaturated Ce weakened the texture and triggered<c+a> dislocation on pyramidal planes, which accelerated the cross-slip of dislocation and gave birth to sufficient slip system during deformation. As a result, the Mg-Ce/MA part showed a high ductility with elongation of ∼18.1%. In addition, the in vitro cell testing showed that Ce addition exerted no obvious negative effect on the biocompatibility. This work showed the feasibility of MA and powder metallurgy in fabricating high performance RE-Mg alloy towards to future biomedical application.

The effect of grain size on deformation modes and deformation heterogeneity in a rolled Mg–Zn–Ca alloy

Grain refinement could promote the activation of non-basal slip and enhance the strength and ductility of Mg alloy simultaneously. In this work, the grain size effect on deformation modes and deformation heterogeneity and its relations to crystallographic orientation in a rolled Mg–1.58Zn–0.1Ca alloy sheet with a weakened transverse direction (TD) spread texture were investigated via intragranular misorientation axis (IGMA) and high resolution-digital image correlation (HR-DIC) measurement. The results indicate that a decrease of the grain size from 55 to 13 μm increased the yield strength (YS) by 56.9%, from 72 MPa to 113 MPa, for the TD samples, but only by 8% for the rolling direction (RD) samples, from 125.7 to 135.7 MPa. Moreover, grain refinement enhanced the elongation by 76.4% for the TD samples, from 11% to 19.1%, and merely by 26.5% for the RD samples, from 16.6% to 21%. The transition in dominant deformation modes due to grain size decreasing can be summarized as: for the RD samples: basal slip → prismatic slip; for the TD samples: basal slip + tension twinning → prismatic slip. The enhanced activity of prismatic slip in the fine-grained (FG)-TD and FG-RD samples can be ascribed to the reduced ratio of critical resolved shear stress (CRSS)prismatic/CRSSbasal. For both the RD and TD samples, grain refinement facilitated deformation homogeneity, which could be related to the enhanced activity of basal slip and non-basal slip, as well as the resulting improved deformation compatibility across grain boundary.