Bimodal grain structure formation and strengthening mechanisms in Mg-Mn-Al-Ca extrusion alloys

The effects of small additions of calcium (0.1%and 0.5%~1) on the dynamic recrystallization behavior and mechanical properties of asextruded Mg-1Mn-0.5Al alloys were investigated.Calcium microalloying led to the formation of Al_(2)Ca in as-cast Mg-1Mn-0.5Al-0.1Ca alloy and both Mg_(2)Ca and Al_(2)Ca phases in Mg-1Mn-0.5Al-0.5Ca alloy.The formed Al_(2)Ca particles were fractured during extrusion process and distributed at grain boundary along extrusion direction (ED).The Mg_(2)Ca phase was dynamically precipitated during extrusion process,hindering dislocation movement and reducing dislocation accumulation in low angle grain boundaries (LAGBs) and hindering the transformation of high density of LAGBs into high angle grain boundaries (HAGBs).Therefore,a bimodal structure composed of fine dynamically recrystallized (DRXed) grains and coarse un DRXed regions was formed in Ca-microalloyed Mg-1Mn-0.5Al alloys.The bimodal structure resulted in effective hetero-deformation-induced (HDI) strengthening.Additionally,the fine grains in DRXed regions and the coarse grains in un DRXed regions and the dynamically precipitated Mg_(2)Ca phase significantly enhanced the tensile yield strength from 224 MPa in Mg-1Mn-0.5Al to335 MPa and 352 MPa in Mg-1Mn-0.5Al-0.1Ca and Mg-1Mn-0.5Al-0.5Ca,respectively.Finally,a yield point phenomenon was observed in as-extruded Mg-1Mn-0.5Al-x Ca alloys,more profound with 0.5%Ca addition,which was due to the formation of (■) extension twins in un DRXed regions.

Influence of different extrusion processes on mechanical properties of magnesium alloy

AZ31 Mg alloy sheets were processed by the conventional symmetrical extrusion(CSE)and the asymmetric extrusion(ASE).Progressive-asymmetric extrusion(PASE)and severe strain-asymmetric extrusion(SASE)were employed for ASE processes.The texture at near-surface and mid-layer zones of ASE sheets was diverse penetrating the normal direction(ND).This was attributed to an additional asymmetric shear strain deformation during the ASE process.(0002)basal planes of PASE sheets tilt to the shear deformation direction.Meanwhile,the basal texture intensity of PASE sheets has been weakened compared with one in CSE sheets.Grain refinement and tilted weak basal texture obtained by SASE process dramatically enhances the room temperature strength and plasticity of the extruded AZ31 magnesium alloy sheets.The microstructure and mechanical responses were examined and discussed.

Stability of twins in Mg alloys-A short review

In this article,the stability of twins,especially{10–12}twins,in Mg alloys was critically reviewed.In the last decade,pre-twinning is considered to be an effective method for adjusting the microstructure and properties of wrought Mg alloys.Especially,formation of twin-texture can remarkably improve formability of rolled Mg alloys.However,the stability of{10–12}twins determines the effect of this method.Previous work revealed that initial{10–12}twins may either grow or shrink under further deformation,and may be removed by static recrystallization under thermal effect.It is considered that improving the stability of twin structure could enhance the contribution of twin-texture on subsequent plastic formability.Based on this background,stress stability and thermal stability of{10–12}twin structure were summarized and reviewed in this article.Finally,a few critical scientific problems in this research field were pointed out.©2020 Published by Elsevier B.V.on behalf of Chongqing University.

Comparison of microstructures and mechanical properties of composite extruded AZ31 sheets

The microstructures and mechanical properties of the composite extruded AZ31/AZ31 and AZ31/4047 Al sheets were investigated and made a comparison to the conventional extruded AZ31 sheet.Owing to the introduced intense shear deformation at the interface during the composite extrusion,grain refinement and tilted texture were detected in AZ31 layers of the AZ31/AZ31 and AZ31/4047 Al sheets,while the conventional extruded AZ31 sheet exhibited a relative coarse,inhomogeneous microstructure and strong basal texture.The compressiontension yield ratio was increased gradually from the AZ31 to the AZ31/AZ31 and AZ31/4047 Al sheets.Besides,the AZ31/4047 Al sheet could successfully accomplish the whole bending forming process at room temperature,while the AZ31 and AZ31/AZ31 sheets were both bend-formed to failure with significant cracks in the outer tensile region under the identical bending parameters.Moreover,under the same bending strain,both the outward offset degree of strain neutral layer and the sheet thickening were more serious in the AZ31/4047 Al composite sheet than those of the AZ31 and AZ31/AZ31 sheets.The foremost reason was the quite wide gap of material properties between Mg alloy AZ31 layer(tensile loading in the outer region)and Al 4047 layer(compressive loading in the inner region).

Microstructure and mechanical behavior of the Mg-Mn-Ce magnesium alloy sheets

The microstructural evolution and mechanical behavior of Mg-Mn-Ce magnesium alloy were investigated in the present study.Mg alloy was prepared with metal model casting method and subsequently hot extruded at 703 K with the reduction ratio of 101:1.The grains were dynamically recrystallized after the extrusion process.Moreover,the(0002)pole figure of Mg-Mn-Ce alloy developed a splitting of pronounced basal texture.The mechanical properties were different due to different angles between c-axis and loading direction(0°,45°and 90°)in the tensile tests.This significantly induces an asymmetry in the yield behavior.The Mg-Mn-Ce alloy exhibits a classical dimple structure as a result of slip accumulation and ductile tear.

The effects of orientation control via tension-compression on microstructural evolution and mechanical behavior of AZ31 Mg alloy sheet

The grain orientation control via twinning activity on deformation features is of great significance to offer a key insight into understanding the deformation mechanism of Mg alloy sheets.The{10–12}twinning were performed by pre-strain paths,i.e.,tension(6%)and compression(5%)perpendicular to the c-axis along extrusion direction(ED),to investigate the microstructural evolution and mechanical properties of AZ31 Mg alloy sheets.The distinction in the texture evolution and strain hardening behavior was illustrated in connection with the pre-strain paths for the activities of twinning and slip.The result shows that the activation of the deformation mode was closely bound up with the grain orientation and the additional applied load direction.The{10–12}twin-texture components with c-axis//ED were generated by precompression,which can provide an appropriate alternative to accommodate the thin sheet thickness strain and enhance the room temperature formability of Mg alloy sheet.

The genetic architecture of growth traits in Salix matsudana under salt stress

Willow(Salix)is one of the most important ornamental tree species in landscape plants.One species,Salix matsudana,is widely used as a shade tree and border tree because of its soft branches and plump crown.Some varieties of S.matsudana were salt tolerant and could grow normally in coastal regions.However,the molecular mechanisms of salt tolerance for S.matsudana have been less clear.Here,we addressed this issue by performing a mapping experiment containing 195 intraspecific F1 progeny of S.matsudana,derived from salt-sensitive‘yanjiang’and salt-tolerant‘9901’,grown by cuttings in a 100 mM NaCl solution.Growth performance of these progeny under salt stress was investigated,displaying marked genotypic variability with the coefficients of variance of 28.64–86.11%in shoot and root growth traits.We further mapped specific QTLs contributing to these differences to the Salix genome.Of the 204 QTLs identified,a few were detected to explain a remarkably larger portion of the phenotypic variation than many others.Many detected QTLs were found to reside in the region of candidate genes of known biological function.The discovery of growth QTLs expressed under salt stress provides important information for marker-assisted breeding of salt tolerant Salix varieties and founds the basis for the application of S.matsudana in coastal afforestation.

Energy partitioning and evapotranspiration in a black locust plantation on the Yellow River Delta,China

Plantations of woody tree species play a crucial role in ecological security along coastal zones.Understanding energy partitioning and evapotranspiration can reveal land–atmosphere interaction processes.We investigated energy fluxes,evapotranspiration,and their related biophysical factors using eddy covariance techniques in a black locust(Robinia pseudoacacia L.)plantation in 2016,2018,and 2019 on the Yellow River Delta.Downward longwave radiation offsets 84–85%of upward longwave radiation;upward shortwave radiation accounted for 12–13%of downward shortwave radiation.The ratio of net radiation to downward radiation was 18–19%over the three years.During the growing season,latent heat flux was the largest component of net radiation;during the dormant season,the sensible heat flux was the dominant component of net radiation.The seasonal variation in daily evapotranspiration was mainly controlled by net radiation,air temperature,vapor pressure deficit,and leaf area index.Black locust phenology influenced daily evapotranspiration variations,and evapotranspiration was greater under sea winds than under land winds because soil water content at 10-cm depth was greater under sea winds during the day.Seasonal patterns of daily evaporative fraction,Bowen ratio,crop coefficient,Priestley–Taylor coefficient,surface conductance,and decoupling coefficient were mainly controlled by leaf area index.The threshold value of daily surface conductance was approximately 8 mm sover the plantation.

Enhanced mechanical properties of Mg-3Al-1Zn alloy sheets through slope extrusion

A novel extrusion approach,entitled slope extrusion(SE),was employed to manufacture AZ31(Mg-3Al-1 Zn,wt%)alloy sheets.The microstructures,textures,and mechanical properties were investigated,compared with those of the AZ31 sheet fabricated by conventional extrusion(CE).Through the combination of finite element simulation and actual experiment,the ultimate results indicated that significant grain refinement(from 9.1 to 7.7 and 5.6μm)and strong basal texture(from 12.6 to 17.6 and 19.5 mrd)were achieved by the SE process.The essence was associated with the additional introduced inclined interface in the process of SE,which could bring about more asymmetric deformation and stronger accumulated strain along the ND when compared with the process of CE.As a consequence,the SE sheets exhibited a higher yield strength(YS)and ultimate tensile strength(UTS)than the counterparts of the CE sheet,which was mainly assigned to the synergistic effects from grain refining and texture strengthening.

Size structure of urban agglomerations in China:rationality evaluation,patterns, and implications

This paper establishes a diagnostic model for assessing the rationality of size structure of urban agglomerations(UAs) in China. The model is designed to determine from a three-dimensional index including size distribution index(SDI), size compactness index(SCI), and size efficiency index(SEI). The spatio-temporal pattern of size structure involving the studied 19 UAs and its implications are explored. The results indicate that size structure of China's UAs advanced from a low rationality development stage to a moderate rationality development stage in 1995-2015.Among them, the SDI and SEI were reasonably high, and the SCI was relatively low. Spatially, the high rationality UAs were distributed across eastern China, while the low rationality UAs were located in western China. UAs with positive size structure possessed typically a dual-or multicenter urban structure, while UAs with negative size structure usually presented as a single-center structure. The evolutionary trajectories of rationality of size structure of UAs can be summarized as four different stages. Our findings suggest that, in addition to consolidating the status of national-level UAs, the development of regional-level UAs should be promoted. Also, the fostering focus and direction should be oriented toward an UA with dual-or multicenter spatial structure.

Liquid crystal model of vesicle deformation in alternating electric fields

Considering the efects of osmotic pressure,elastic bending,Maxwell pressure,surface tension,as well as fexo-electric and dielectric properties of phospholipid membrane,the shape equation for sphere vesicle in alternation(AC)electric feld is derived based on the liquid crystal model by minimizing the free energy due to coupled mechanical and AC electrical felds.Besides the efect of elastic bending,the infuence of osmotic pressure and surface tension on the frequency dependent behavior of vesicle membrane in AC electric feld is also discussed.Our theoretical results for membrane deformation are consistent with corresponding experiments.The present model provides the possibility to further disclose the frequency-depended behavior of biological cells in the coupled AC electric and diferent mechanical felds.

黄河三角洲滨海草带建设的饲草基础生物学问题

根据滨海盐碱地区土壤盐渍化程度开展人工种草,建设滨海草带,发展盐碱地生态草牧业,可解决草粮争地的矛盾,服务国家大粮食安全。该文综述了黄河三角洲地区饲草轮作、稻麦轮作及林草间作等盐碱地滨海草带示范栽培模式,讨论了滨海草带耐盐机制、耦合高产优异生产性状分子模块育种及饲草高附加值产业发展等方面的基础生物学问题,并给出解决策略和实现路径。

Influence of minor Ce additions on the microstructure and mechanical properties of Mg-1.0Sn-0.6Ca alloy

The microstructure and mechanical properties of Mg-Sn-Ca-Ce alloys with different Ce contents(0.0,0.2,0.5,1.0 wt%)were studied at room temperature.Ce additions to ternary Mg-Sn-Ca alloy resulted in grain refinement as well as a change in the category of second phase from CaMgSn to(Ca,Ce)Mg Sn and Mg12Ce.The volume fraction of second phase increased with rising Ce content,which aggravated the restriction of DRXed grain growth during the extrusion process and eventually led to texture weakening of as-extruded Mg-Sn-Ca based alloys.In terms of plasticity,owing to vigorously activated basal slip and homogeneous distributed tensile strain in tension,the tensile ductility of as-extruded alloys reached the maximum value of 27.6%after adding 0.2 wt%Ce,which enhanced by about 26%than that of ternary MgSn-Ca alloy.However,further Ce additions(0.5 and 1.0 wt%)would coarsen the second phase particles and then impair ductility.The tension-compression yield asymmetry of as-extruded Mg-Sn-Ca ternary alloy was alleviated greatly via Ce additions,due to the joint effects of grain refinement,increased amount of strip distributed second phase particles and texture weakening.

Texture control by {10-12} twinning to improve the formability of Mg alloys: A review

Texture control of wrought Mg alloys, particularly in rolled Mg alloy sheets, has been an important research topic for the past several decades because it has significant influence on stretch formability at room temperature. For Mg alloys, {10-12} twinning can be easily activated and causes a 86.3° lattice rotation. Thus, pre-twinning deformation is considered as an effective and low-cost method for texture control in wrought Mg and its alloys. Furthermore, it has been verified that texture control via pre-twinning deformation can remarkably improve stretch formability of rolled Mg alloy sheets. In this review, recent researches on texture control via twinning deformation and its influence on stretch formability will be critically reviewed. The main contents include the micro-mechanism and impact factors of control in twin-orientation, plastic processing techniques of pre-inducing twins and the application of pre-induced twins in improvement of stretch formability. Finally, further research directions on this field were proposed.

Effect of free-end torsion on microstructure and mechanical properties of AZ31 bars with square section

In this study,a rolled AZ31 bar with square section was used.The reciprocating torsion was performed to maintain the shape of the sample.The microstructure evolution of AZ31 bar during torsion and its influence on compressive anisotropy were investigated in detail.Results showed that reciprocating torsion can simultaneously enhance yield strength in three compressive directions,and reduce compressive anisotropy.Reciprocating torsion generated profuse dislocations and{10–12}twin boundaries to harden the micro-hardness and yield strength.Reciprocating torsion can also generate new texture component which is mainly from the orientation of newly generated{10–12}twins.The new twin-structures will be responsible for the reduction in compressive anisotropy.Moreover,uneven deformation features in twisted sample were systematically investigated.

Transformation of Laves phases and its effect on the mechanical properties of TIG welded Mg-Al-Ca-Mn alloys

The effects of Al content and Ca/Al mass ratio on the microstructure and mechanical properties of tungsten inert gas(TIG)welded Mg-2Ca-x Al-0.5Mn(x=0,1,5)alloy joints were studied in present work.Results showed that increasing Al content was effective in reducing the dendrite spacing at the fusion zone(FZ)edge.The Laves phases in the FZ and the heat-affected zone(HAZ)can be changed from Mg_(2)Ca to(Mg,Al)_(2)Ca with the decrease of Ca/Al ratio,and the(Mg,Al)_(2)Ca could be further transformed to Al_(2)Ca under welding thermal cycle.Furthermore,dynamic dissolution and precipitation of Laves phases and Al_(8)Mn_(5)phases occurred in the HAZ,resulting in a gradient microstructure and hardness peak in this area.The tensile properties of the joints were significantly improved with the increase of Al content,which was mainly due to the modification of Laves phases.

Diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couples

The diffusion behavior and reactions between Al and Ca in Mg alloys by diffusion couple method were investigated. Results demonstrate that Al_2Ca is the only phase existing in the diffusion reaction layers.The volume fraction of Al_2Ca in diffusion reaction layers increases linearly with temperature. The standard enthalpy of formation for intermetallic compounds was rationalized on the basis of the Miedema model. Al-Ca intermetallic compounds were preferable to form in the Mg-Al-Ca ternary system under the same conditions. Over the range of 350–400?C, the structure of Al_2Ca is more stable than that of Al_4Ca, Al_(14)Ca_(13) and Al_3Ca_8. The growth constants of the layer Ⅰ, layer Ⅱ and entire diffusion reaction layers were determined. The activation energies for the growth of the layer Ⅰ, layer Ⅱ and entire diffusion reaction layers were(80.74 ± 3.01) k J/mol,(93.45 ± 2.12) k J/mol and(83.52 ± 1.50) k J/mol, respectively.In layer Ⅰ and Ⅱ, Al has higher integrated interdiffusion coefficients D^(Int, layer)ithan Ca. The average effective interdiffusion coefficients D_(Al)^(eff) values are higher than D_(Ca)^(eff) in the layer Ⅰ and Ⅱ.

血液病患者中GSTA1基因多态性分析及其对GST酶活性的影响（英文）

谷胱甘肽硫转移酶(GSTs)是体内重要的药物代谢酶,且存在基因多态性的现象。本研究调查了170例血液病患者的GST酶活性和GSTA1基因多态性,并探讨了它们之间的关系。通过PCR-RFLP技术分析患者的GSTA1基因多态性,DNA测序仪确定启动子区域中的四个突变位点(-631,-567,-69和-52)的碱基序列;通过测量CDNB和GSH之间催化反应的速率来计算患者的GST酶活性。结果显示,男性和女性的平均GST活性分别为5.20±0.13和5.17±0.12 nmol/min/mL,差异不显著(P=0.91)。基因型GSTA1*A*A、GSTA1*A*B和GSTA1*B*B的频率分别为75.3%,22.9%和1.8%;等位基因GSTA1*A和*B频率为86.8%和13.2%。通过卡方检验,男性和女性之间的基因型频率分布没有显着差异(P=0.743)。杂合突变基因型的平均GST活性(4.83±0.76 nmol/min/mL)低于野生基因型(5.34±1.26 nmol/min/mL, P=0.018),高于纯合突变基因型(3.32±0.07 nmol/min/mL,P=0.022)。这些发现可能有助于改善血液病患者的个体化治疗,并促进血液病精准医学的发展。

Brain-targeted polymersome codelivery of siRNA and temozolomide for effective glioblastoma chemo-RNAi synergistic therapy

Temozolomide (TMZ) is a clinically approved drug for glioblastoma (GBM) therapy. However, as a result of methylguanine-DNA-methyltransferase (MGMT), which is able to repair damaged DNA-damage repairing, TMZ usually yields unsatisfactory therapeutic effects. Small interfering RNA (siRNA) is a potential alteration tool for sensitivity of TMZ by targeting DNA repair enzymes. However, a suitable TMZ and siRNA codelivery system that can effectively and actively co-deliver siRNA/TMZ into the brain tumor is lacking. In this study, we constructed an angiopep-2 decorated polymersomal delivery system to co-deliver TMZ/siRNA for synergistic GBM therapy. This targeted polymersomal nanomedicine not only enhanced the circulation time of siRNA/TMZ in blood but also improved their blood-brain barrier (BBB) crossing and GBM targeting ability. Moreover, when we co-administered siRNAs specific to retinoblastoma binding protein 4 (RBBP4) together with TMZ in GBM cells, these RBBP4- specific siRNA (siRBBP4) modulated the sensitivity of TMZ by regulating MGMT, and thus showed a powerful synergistic anti-tumor effect. We demonstrated that angiopep-2 decorated polymersomal siRBBP4/TMZ co-loaded nanomedicines are capable of inhibiting tumor growth and significantly improved life expectancy of orthotropic GBM bearing mice. Overall, our study suggests that such a polymersomal TMZ/siRNA codelivery system provides a robust and potent nanoplatform for targeted GBM chemo-RNAi therapy.