Effects of different volume fraction of long-period stacking ordered(LPSO)phase on the microstructure,mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn(x=1 wt%,2 wt%,4 wt%and y=2 wt%,4 wt%,8 wt%)al...Effects of different volume fraction of long-period stacking ordered(LPSO)phase on the microstructure,mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn(x=1 wt%,2 wt%,4 wt%and y=2 wt%,4 wt%,8 wt%)alloys were studied by an optical microscope,a scanning electron microscope,texture analysis,a transmission electron microscope and tensile testing.The results reveal that the volume fraction of LPSO phase increases from ZW12 to ZW24 to ZW48 alloys with the elevating Zn and Y content but constant Y/Zn value,and the mechanical strength of the LPSO-containing Mg-Zn-Y-Mn system is gradually improved when increasing LPSO phases.With the highest volume fraction of LPSO phase,ZW48 alloy presents the highest ultimate tensile strength(UTS)of 427 MPa along the extrusion direction(ED)when compared with those of ZW12 alloy with the UTS of 307 MPa and ZW24 alloy with the UTS of 347 MPa.Moreover,the elongation ratio of ZW48 alloy is maintained to moderate 9.9%,which is also the highest among three studied alloys.On the other hand,texture analysis demonstrates that the basal texture of the a-Mg phase in the ZW48 alloy is significantly weakened by the generation of more LPSO phases.On the contrary,a high texture intensity of a-Mg phase and obvious mechanical anisotropy can be observed for the ZW12 alloy.However,mechanical anisotropy still exists in the ZW48 alloy containing massive LPSO phases,which is attributed primarily to the zonal distribution of large LPSO along the ED.展开更多
The LPSO phase can effectively enhance the mechanical properties of Mg alloys.To investigate the impact of different LPSO phase contents and morphologies on the mechanical properties and strengthening mechanisms of Mg...The LPSO phase can effectively enhance the mechanical properties of Mg alloys.To investigate the impact of different LPSO phase contents and morphologies on the mechanical properties and strengthening mechanisms of Mg-Y-Al alloys under room temperature deformation,this study prepared Mg-12Y-1Al(WA121)alloys containing Bulk-LPSO(B-LPSO),Lattice-LPSO(L-LPSO),and Needle-like LPSO(N-LPSO)with different contents through different heat-treatment processes.The results indicate that with the increase in heat treatment time,the contents of B-LPSO phases remain essentially unchanged,and the contents of L-LPSO and N-LPSO phases gradually increase.The increase in N-LPSO phase content is the most pronounced,with the highest content(7.29%)observed in the alloy treated for 4.5 h.Moreover,the alloy treated for 4.5 h exhibits the best mechanical properties,with ultimate tensile strength(UTS),tensile yield strength(TYS),and elongation(EL)values of 177 MPa,139 MPa,and 4.27%,respectively.Compared to the as-cast alloy,UTS,TYS,and EL increased by 9.94%,11.2%,and 27.1%,respectively.The study reveals that all three LPSO phases exhibit excellent dislocation hindering effects,effectively enhancing strength of the alloy.Additionally,the N-LPSO phase,due to its dense distribution,forms numerous dislocation channels within the grains,dispersing stress concentration within the grains to improve plasticity of the alloy.Furthermore,the interaction between the N-LPSO phase and the other phases in the alloy can also enhance plasticity of the alloy.Therefore,the alloy treated for 4.5 h demonstrates a synergistic improvement in strength and plasticity.Research has revealed that the precipitation mechanism of the N-LPSO phase in the as-cast WA121 alloy involves the formation of an Al-rich region adjacent to the needle-like Mg_(24)Y_(5) phase.Subsequently,the Y element provided by the dissolving Mg_(24)Y_(5) phase reacts with this region,ultimately leading to the formation of the needle-like LPSO phase.展开更多
The heterostructure preparation in Mg-rare earth(RE)alloy has attracted much attention due to the excellent enhancement of strength and ductility.However,the effect of heterostructure composition on mechanical propert...The heterostructure preparation in Mg-rare earth(RE)alloy has attracted much attention due to the excellent enhancement of strength and ductility.However,the effect of heterostructure composition on mechanical properties in Mg-RE alloy is still not clear.In this work,three types of heterostructures with different composition induced by lamellar 14H long period stacking ordered(LPSO)phase were achieved in the Mg-Gd-Y-Zn-Zr alloys after cyclic extrusion and compression(CEC).The heterostructure was mainly composed of dynamic recrystallization(DRX)grains,deformed coarse grains,multiscale LPSO phase(blocky,granular,lamellar LPSO phase).The strength and ductility of Mg-Gd-Y-Zn-Zr alloy with heterostructure were simultaneously improved.The DRX behavior during CEC process was largely affected by the lamellar LPSO phase.The lamellar LPSO with large spacing(∼92 nm)and low thickness(∼13.46 nm)is easy to occur kinking behavior and the zigzag kinking area can serve as nucleation sites to promote DRX behavior.While the lamellar LPSO phase with high thickness(∼23.41 nm)and similar spacing(∼82 nm)was ruptured into granular LPSO phase and thus increase the volume fraction of granular LPSO phase,which made a great contribution to DRX behavior by particle stimulated nucleation.The main deformation mechanism of solution treatment+furnace cooling(SF)sample during CEC process is dominated by the multiple slips composed of basal slips,prismatic slips and pyramidal slips.For the solution treatment+air cooling(SA)sample and solution treatment+ageing treatment(ST)sample,the activation of basal slips is the critical deformation mechanism.The main contribution to yield strength is from the grain boundary,dislocation and hetero-deformation induced(HDI)strengthening.Moreover,the HDI strengthening in the SF and SA sample after CEC deformation is much larger than that of ST sample due to the distinct heterostructure composition.展开更多
The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forgin...The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.展开更多
Suitable heat treatment processes were adopted to regulate the precipitation of the lamellar LPSO phase andβ′phase in Mg−Gd−Y−Zn−Zr−Nd alloy.The effects of lamellar LPSO phase andβ′phase on the mechanical properti...Suitable heat treatment processes were adopted to regulate the precipitation of the lamellar LPSO phase andβ′phase in Mg−Gd−Y−Zn−Zr−Nd alloy.The effects of lamellar LPSO phase andβ′phase on the mechanical properties and damping capacity of the alloy were studied systematically.Experimental results demonstrate that the lamellar LPSO phase is more conducive to dynamic recrystallization processes,leading to a high degree of recrystallization and a weak texture intensity,resulting in a higher plasticity and damping capacity.After aging treatment,theβ′precipitates exhibit pronounced aging strengthening and increase the number of mobile interfaces,thus enhancing the strength and damping capacity at the same time.Through regulating lamellar LPSO and agedβ′phase,the alloy achieves high strength and high damping capacity:ultimate tensile strength of 498 MPa,yield strength of 371 MPa and damping capacity of 0.02 at strain amplitude of 1×10^(−3).展开更多
The microstructural evolution of a 18R single phase （S 18） alloy during annealing at 773 K for 100 h was investigated in order to reveal the formation mechanism of 14H phase. The results showed that the as-cast S 18...The microstructural evolution of a 18R single phase （S 18） alloy during annealing at 773 K for 100 h was investigated in order to reveal the formation mechanism of 14H phase. The results showed that the as-cast S 18 alloy was composed of 18R phase （its volume fraction exceeds 93%）, W particles and α-Mg phase. The 18R phase in S18 alloy was thermally stable and was not transformed into 14H long period stacking ordered （LPSO） phase during annealing. However, 14H lamellas formed within tiny α-Mg slices, and their average size and volume fraction increased with prolonging annealing time. Moreover, the 14H phase is nucleated within α-Mg independently on the basis of basal stacking faults （SFs）. The broadening growth of 14H lamellas is an interface-controlled process which involves ledges on basal planes, while the lengthening growth is a diffusion-controlled process and is associated with diffusion of solute atoms. The formation mechanism of 14H phase in this alloy could be explained as α-Mg＇→α-Mg＋14H.展开更多
This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium （Y） element. The addition of Y resulted in the ...This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium （Y） element. The addition of Y resulted in the formation of ternary 1 （Mg3YZn6）, W （Mg3Y2Zn3） and LPSO （Mg12YZn） phases which subse- quently reinforced alloys ZM31 ＋ 0.3Y, ZM31 ＋ 3.2Y and ZM31 ＋ 6Y, where the value denoted the amount of Y element （in wt%）. Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion （CTE）, which was derived to be 1.38 x 10^-5 K^-1 and 2.35 x 10^-5 K^-1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and crE mismatch were the predominant strengthening mechanisms in the ZM31＋0.3Y and ZM31 ＋ 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 ＋ 6Y alloy.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.展开更多
The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavi...The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavior,fracture toughness and strain rate sensitivity(SRS)of materials within micro/nanoscale.Firstly,a nanomechanical model was developed for extracting hardness(H),young’s modulus(E)and yield stress(σY)from the characteristic load points which were subsequently analyzed by atomic force microscope(AFM)images.The elasticity data and AFM data were then utilized for determination of plastic deformation in constituent phases.The displacement of the indentation gets the highest value for Mg matrix and between precipitates,depth is more in LPSO rather than that of MgRE.The serrated flow or the behavior of shear bands may originate from the side effect of the interface region in Mg alloys with precipitates.It can be deduced that the KIC produced by both L method and energy-based calculation are both reliable for KIC approximation.The maximum load in simulation withμ=0.2 friction is marginally lesser than that of the frictionless(μ=0)one while elastic recovery of indentation withμ=0.2 is higher to some extent.展开更多
Casting magnesium alloys hold the greatest share of magnesium application products due to their short processing period, low cost and near net shape forming. Compared with conventional commercial magnesium alloys or o...Casting magnesium alloys hold the greatest share of magnesium application products due to their short processing period, low cost and near net shape forming. Compared with conventional commercial magnesium alloys or other Mg–RE-based alloys, the novel Mg–RE–TM cast alloys with long period stacking ordered(LPSO) phases usually possess a higher strength and are promising candidates for aluminum alloy applications. Up to now, two ways: alloying design and casting process control(including subsequent heat treatments), have been predominantly employed to further improve the mechanical properties of these alloys. Alloying with other elements or ceramic particles could alter the solidifi cation pattern of alloys, change the morphology of LPSO phases and refi ne the microstructures. Diff erent casting techniques(conventional casting, rapidly solidifi cation, directional solidifi cation, etc.) introduce various microstructure characteristics, such as dendritic structure, nanocrystalline, metastable phase, anisotropy. Further heat treatments could activate the transformation of various LPSO structures and precipitation of diverse precipitates. All these evolutions exert great impacts on the mechanical properties of the LPSO-containing alloys. However, the underlying mechanisms still remain a subject of debate. Therefore, this review mainly provides the state of the art of the casting magnesium alloys research and the accompanying challenges and summarizes some topics that merit future investigation for developing high-performance Mg–RE–TM cast alloys.展开更多
The microstructure and damping capacities of MgZnxYi.33x(x=l-4at.%)alloys were discussed and researched.The main phase composition of the alloys consists of a_Mg and long-period stacking ordered(LPSO)phase.Due to incr...The microstructure and damping capacities of MgZnxYi.33x(x=l-4at.%)alloys were discussed and researched.The main phase composition of the alloys consists of a_Mg and long-period stacking ordered(LPSO)phase.Due to increasedLPSO phase,grain size was refined.LPSO phase was advantageous to the damping properties of the Mg-Zn-Y alloys.Mg-7%Zn-12.8%Y has the highest damping capacity up to0.04.Due to stacking fault probability,the LPSO phase in the Mg-Zn-Yalloys could be new damping source to dissipate energy so as to contribute to the improvement of damping capacities.展开更多
The microstructure of the precipitated phases of Mg95.sGd3Zn1Zro.2 alloys with long-period stacking ordered structure before and after heat treatment is discussed. The corrosion properties of the as-cast （F）, solid-...The microstructure of the precipitated phases of Mg95.sGd3Zn1Zro.2 alloys with long-period stacking ordered structure before and after heat treatment is discussed. The corrosion properties of the as-cast （F）, solid-solution （T4） and aging-treated （T6） alloys in 1% NaC1 solution are studied. The hydrogen evolution and electrochemical measurements display that the as-cast Mg95.sGd3Zn1Zro.2 alloy with the continuous network eutectic phase exhibits the greatest corrosion resistance, while T6 sample with some needle-like phases and the particle phases is the worst among the three alloys. It is proposed to be mainly related to the amount, composition, microstructure and distribution of the precipitated phases.展开更多
The microstructures and strengthening mechanisms of the Mg-8.2 Gd-4.6 Y-1.5 Zn-0.4 Zr(wt%) alloy with long-period stacking ordered(LPSO),β’ and γ type phases were systematically studied.The results show that the LP...The microstructures and strengthening mechanisms of the Mg-8.2 Gd-4.6 Y-1.5 Zn-0.4 Zr(wt%) alloy with long-period stacking ordered(LPSO),β’ and γ type phases were systematically studied.The results show that the LPSO with lamellar and block structures forms near the grain boundaries.The grains are clearly refined,and the 18 R LPSO phase is oriented along the extrusion direction after extrusion.Some particles also precipitate from the Mg matrix dynamically.The extruded alloy exhibits a remarkable agehardening response,and mechanical properties,with a tensile strength(TS) of 449 MPa,yield strength(YS) of 362 MPa,and elongation of 7.9% obtained in the peak-aged alloy.The strengthening mechanisms of the alloy in different states are discussed.Grain boundary and precipitation strengthening are the main strengthening mechanisms for the peak-aged alloy.展开更多
In this work,as-cast Mg-Ni-Y alloys were proposed to develop a feasible material for fracturing balls,and their mechanical performance and corrosion behavior were systematically investigated.Long period stacking order...In this work,as-cast Mg-Ni-Y alloys were proposed to develop a feasible material for fracturing balls,and their mechanical performance and corrosion behavior were systematically investigated.Long period stacking order(LPSO)phase was firstly introduced to improve both the mechanical properties and degradation rate of magnesium alloys.With the increase of LPSO phase,the compressive strength was improved significantly,while the elongation of the alloys decreased owing to the relatively brittle nature of LPSO phase.Due to the higher corrosion potential of LPSO phase,the LPSO phase can accelerate the corrosion process by providing more micro-couples.However,the LPSO phase would serve as the corrosion barrier between the corrosion medium and the matrix when the contents of LPSO phase are too high in Mg92.5Ni3Y4.5 and Mg87.5Ni5Y7.5 alloys.As-cast Mg97.5Ni1Y1.5 alloy with satisfactory mechanical properties and rapid degradation rate was successfully developed,exhibiting a high degradation rate of 6675 mm/a(93℃)in 3 wt.%KCl solution and a favorable ultimate compressive strength of 410 MPa.The degradation rate of Mg97.5Ni1Y1.5 alloy is 2-5 times of the current commercial magnesium alloy fracturing materials.展开更多
Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy(wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-densit...Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy(wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-density stacking faults, differentially spaced lamellar intragranular 14H-LPSO phases, and network intergranular 18R-LPSO phases with high-density intragranular stacking faults. Effects of these featured LPSO phases and stacking faults on dynamic recrystallization(DRX) behavior were investigated via hot compression. Promoted DRX behavior via particle stimulated nucleation(PSN) is introduced by coexisting intergranular island 18R and 14H LPSO phases and intragranular wide spacing lamellar 14H-LPSO phases, contributing the highest DRX fraction of 42.6%. Conversely, it is found that DRX behavior with network intergranular 18R-LPSO phases and dense intragranular stacking fault is considerably inhibited with the lowest fraction of 22.8%. That is, the restricted DRX due to dislocations pinning by stacking faults overwhelms the enhanced DRX behavior via PSN of island intergranular 18R and 14H LPSO phases. Specially, compared with dense intragranular lamellar 14H-LPSO phases, high-density stacking faults exert a larger inhibition effect on DRX behavior.展开更多
The influence of solid solution treatment on the microstructure and corrosion resistance of as-cast Mg_(95.5)Zn_(1.5)Y_(3)alloy is characterized.The microstructure of the as-cast Mg_(95.5)Zn_(1.5)Y_(3)alloy mainly con...The influence of solid solution treatment on the microstructure and corrosion resistance of as-cast Mg_(95.5)Zn_(1.5)Y_(3)alloy is characterized.The microstructure of the as-cast Mg_(95.5)Zn_(1.5)Y_(3)alloy mainly consisted ofα-Mg,W(Mg_(3)Zn_(3)Y_(2))phase,and the long period stacking ordered(LPSO)(Mg_(12)ZnY)phase.After solid solution treatment,most of the W phase disappears gradually with increasing solution treatment time,with only a small amount of W phase distributed as particle.The LPSO phase slightly dissolved into substrate,and its morphology transitions from blocky shape to rod shape.Solid solution treatment of Mg_(95.5)Zn_(1.5)Y_(3)exhibits excellent corrosion resistance,because the Y and Zn atoms became enriched in the matrix and the changed morphologies of the LPSO and W phases were modified through heat treatment.The alloy created with solid solution treatment at 520℃for 10 hours exhibits corrosion potential of−1.419 V,suggesting a significant improvement in corrosion performance.展开更多
The long-period stacking ordered phases(LPSOs) in Mg-Ni-Y system have been attracting great interest as effective strengthening components because of their unique structural characteristics and deformation mechanism.H...The long-period stacking ordered phases(LPSOs) in Mg-Ni-Y system have been attracting great interest as effective strengthening components because of their unique structural characteristics and deformation mechanism.However,the phase relationships in LPSOs are complicated and unclear,which restricts the design of advanced magnesium-based alloys.The aim of the present work is to experimentally determine the phase equilibria relationships focusing on LPSOs and establish the thermodynamic description for Mg-Ni-Y system.Four types of LPSOs,that is,14H,12R,18R and 10H,are confirmed through equilibrated alloys and high-resolution transmission electron microscopy(HR-TEM).The formation enthalpies of LPSOs(14H,12R,18R and 10H) are calculated based on density functional theories(DFT) calculations.A new ternary compound,termed as τ phase,is observed for the first time which is likely to be the distorted structure of 12R as determined from the TEM image which shows a 12-layer closed packing plane distance of 3.252nm and a shear angle of 83.2°between(0002) and(10■0) planes.Based on the determined phase equilibria relationship,the Mg-Ni-Y system is assessed and a selfconsistent description is obtained where the LPSOs are modeled as the stoichiometric compounds.The comparison between the calculation result and experimental data suggests the accuracy of the present thermodynamic database in the Mg-rich corner.展开更多
It is a long-term challenge to further improve the corrosion resistance while ensuring the strength of magnesium(Mg)alloys.Revealing the effect of potential fluctuation on the micro-galvanic corrosion and the subseque...It is a long-term challenge to further improve the corrosion resistance while ensuring the strength of magnesium(Mg)alloys.Revealing the effect of potential fluctuation on the micro-galvanic corrosion and the subsequent film formation is important for understanding the corrosion mechanism of Mg alloys with multiple strengthening phases/structures.Here,we prepared the high-strength Mg-14.4Er-1.44Zn-0.3Zr(wt.%)alloys containing hybrid structures,i.e.,elongated long-period stacking ordered(LPSO)blocks+intragranular stacking faults(SFs)/LPSO lamellae.The Mg alloy with elongated LPSO blocks and intragranular LPSO lamellae(EZ-500 alloy)obtains good corrosion resistance(2.2 mm y^(–1)),while the Mg alloy containing elongated LPSO blocks and intragranular SFs(EZ-400 alloy)shows a significantly higher corrosion rate(6.9 mm y^(–1)).The results of scanning Kelvin probe force microscopy(SKPFM)show the elongated LPSO blocks act as cathode phase(87 mV in EZ-400 alloy),and the SFs serve as the weak anode(30 mV in EZ-400 alloy),resulting in high potential fluctuation in EZ-400 alloy.On the contrary,both elongated blocks and intragranular lamellae are cathodic LPSO phase(67–69 mV)in EZ-500 alloy,leading to a lower potential fluctuation.Quasi in-situ atomic force microscope(AFM)observation indicates that high potential fluctuation would cause strong micro-galvanic corrosion,and subsequently leads to the failure in rapid formation of corrosion film,finally forming a loose and porous film,while relatively low potential fluctuation could result in more uniform corrosion mode and facilitate the rapid formation of protective film.Therefore,we propose that it is an effective way to develop high-strength corrosionresistant Mg alloys by controlling the potential fluctuation to form a“uniform potential”strengthening microstructure。展开更多
The Mg–Zn–Y–Zr alloys with long-period stacking-ordered(LPSO)and W eutectic phases were investigated to develop new magnesium casting alloys.The temperatures for T6 heat treatment were selected based on the hardnes...The Mg–Zn–Y–Zr alloys with long-period stacking-ordered(LPSO)and W eutectic phases were investigated to develop new magnesium casting alloys.The temperatures for T6 heat treatment were selected based on the hardness and electrical conductivity measurements.The hot tearing susceptibility of the alloys with LPSO phase is lower than that of the alloys with W phase,which is associated with the freezing range of the alloys.However,the investigated alloys displayed the same fluidity.Under T6 conditions,increasing the Y content in the alloys resulted in increased yield strength,whereas other tensile properties were similar for the alloys.The corrosion resistance was higher for the alloys with LPSO phase compared to that of the alloys with W phase.Mg−2.5Zn−3.7Y−0.3Zr(mass fraction,%)alloy with LPSO phase possessed high castability and mechanical properties,with a corrosion rate of 2 mm/year.展开更多
Achieving high strength in Mg alloys is usually accompanied by ductility loss.Here,a novel Mg97Y1Zn1Ho1 at.%alloy with a yield strength of 403 MPa and an elongation of 10%is developed.The strength-ductility synergy is...Achieving high strength in Mg alloys is usually accompanied by ductility loss.Here,a novel Mg97Y1Zn1Ho1 at.%alloy with a yield strength of 403 MPa and an elongation of 10%is developed.The strength-ductility synergy is obtained by a comprehensive strategy,including a lamella bimodal microstructure design and the introduction of nano-spaced solute-segregated 14H long-period stacking-ordered phase(14H LPSO phase)through rare-earth Ho alloying.The lamella bimodal microstructure consists of elongated un-recrystallized(un-DRXed)coarse grains and fine dynamically-recrystallized grains(DRXed regions).The nano-spaced solute-segregated 14H LPSO phase is distributed in DRXed regions.The outstanding yield strength is mainly contributed by grain-boundary strengthening,18R LPSO strengthening,and fiberlike reinforcement strengthening from the nano-spaced 14H LPSO phase.The high elongation is due primarily to the combined effects of the bimodal and lamellar microstructures through enhancing the work-hardening capability.展开更多
A yield phenomenon was firstly reported in an extruded Mg-6.8Y-2.5Cu alloy and the corresponding microstructure was also investigated in this work,The cast alloy is mainly composed ofα-Mg,18R long period stacking ord...A yield phenomenon was firstly reported in an extruded Mg-6.8Y-2.5Cu alloy and the corresponding microstructure was also investigated in this work,The cast alloy is mainly composed ofα-Mg,18R long period stacking order(LPSO)phase,eutectic phase(Mg_(20)Cu_(4)Y_(1)),and Mg_(2)Cu phase.The 18R LPSO phase at the dendritic grain boundary transforms into the 14H LPSO phase in the grain interior during homogenization.After extrusion,the grain size of the homogenized alloy is remarkably refined to-3.69μm and the second phase is significantly broken and distributed in the extrusion direction.Tensile testing curves of the extrude alloy at room temperature indicate that the yield strength and ultimate tensile strength increase while the elongation of the alloy decreases with increasing strain rate.Interestingly,a yield plateau fo rms and gradually decreases with increasing strain rate.The yield phenomenon is related to the dislocation multiplication and the interaction between the movable dislocations and solute atoms.展开更多
基金Project supported by Guangdong Basic and Applied Basic Research Foundation(2024A1515030065,2023A1515012299)Guangzhou Science and Technology Planning Project(2024A04J6299,202201011454)+2 种基金Young Talent Support Project of Guangzhou Association for Science and Technology(QT2024-012)the National Natural Science Foundation of China(52101283)National College Students Innovation and Entrepreneurship Training Program(xj2023118450625)。
文摘Effects of different volume fraction of long-period stacking ordered(LPSO)phase on the microstructure,mechanical property and anisotropy of the as-extruded Mg-xZn-yY-0.1Mn(x=1 wt%,2 wt%,4 wt%and y=2 wt%,4 wt%,8 wt%)alloys were studied by an optical microscope,a scanning electron microscope,texture analysis,a transmission electron microscope and tensile testing.The results reveal that the volume fraction of LPSO phase increases from ZW12 to ZW24 to ZW48 alloys with the elevating Zn and Y content but constant Y/Zn value,and the mechanical strength of the LPSO-containing Mg-Zn-Y-Mn system is gradually improved when increasing LPSO phases.With the highest volume fraction of LPSO phase,ZW48 alloy presents the highest ultimate tensile strength(UTS)of 427 MPa along the extrusion direction(ED)when compared with those of ZW12 alloy with the UTS of 307 MPa and ZW24 alloy with the UTS of 347 MPa.Moreover,the elongation ratio of ZW48 alloy is maintained to moderate 9.9%,which is also the highest among three studied alloys.On the other hand,texture analysis demonstrates that the basal texture of the a-Mg phase in the ZW48 alloy is significantly weakened by the generation of more LPSO phases.On the contrary,a high texture intensity of a-Mg phase and obvious mechanical anisotropy can be observed for the ZW12 alloy.However,mechanical anisotropy still exists in the ZW48 alloy containing massive LPSO phases,which is attributed primarily to the zonal distribution of large LPSO along the ED.
基金supported by the Qinghai Provincial Science and Technology Department Basic Research Program(No.2025ZY029).
文摘The LPSO phase can effectively enhance the mechanical properties of Mg alloys.To investigate the impact of different LPSO phase contents and morphologies on the mechanical properties and strengthening mechanisms of Mg-Y-Al alloys under room temperature deformation,this study prepared Mg-12Y-1Al(WA121)alloys containing Bulk-LPSO(B-LPSO),Lattice-LPSO(L-LPSO),and Needle-like LPSO(N-LPSO)with different contents through different heat-treatment processes.The results indicate that with the increase in heat treatment time,the contents of B-LPSO phases remain essentially unchanged,and the contents of L-LPSO and N-LPSO phases gradually increase.The increase in N-LPSO phase content is the most pronounced,with the highest content(7.29%)observed in the alloy treated for 4.5 h.Moreover,the alloy treated for 4.5 h exhibits the best mechanical properties,with ultimate tensile strength(UTS),tensile yield strength(TYS),and elongation(EL)values of 177 MPa,139 MPa,and 4.27%,respectively.Compared to the as-cast alloy,UTS,TYS,and EL increased by 9.94%,11.2%,and 27.1%,respectively.The study reveals that all three LPSO phases exhibit excellent dislocation hindering effects,effectively enhancing strength of the alloy.Additionally,the N-LPSO phase,due to its dense distribution,forms numerous dislocation channels within the grains,dispersing stress concentration within the grains to improve plasticity of the alloy.Furthermore,the interaction between the N-LPSO phase and the other phases in the alloy can also enhance plasticity of the alloy.Therefore,the alloy treated for 4.5 h demonstrates a synergistic improvement in strength and plasticity.Research has revealed that the precipitation mechanism of the N-LPSO phase in the as-cast WA121 alloy involves the formation of an Al-rich region adjacent to the needle-like Mg_(24)Y_(5) phase.Subsequently,the Y element provided by the dissolving Mg_(24)Y_(5) phase reacts with this region,ultimately leading to the formation of the needle-like LPSO phase.
基金the National Natural Science Foundation of China(Grant no.52475342,51975175 and 52375329).
文摘The heterostructure preparation in Mg-rare earth(RE)alloy has attracted much attention due to the excellent enhancement of strength and ductility.However,the effect of heterostructure composition on mechanical properties in Mg-RE alloy is still not clear.In this work,three types of heterostructures with different composition induced by lamellar 14H long period stacking ordered(LPSO)phase were achieved in the Mg-Gd-Y-Zn-Zr alloys after cyclic extrusion and compression(CEC).The heterostructure was mainly composed of dynamic recrystallization(DRX)grains,deformed coarse grains,multiscale LPSO phase(blocky,granular,lamellar LPSO phase).The strength and ductility of Mg-Gd-Y-Zn-Zr alloy with heterostructure were simultaneously improved.The DRX behavior during CEC process was largely affected by the lamellar LPSO phase.The lamellar LPSO with large spacing(∼92 nm)and low thickness(∼13.46 nm)is easy to occur kinking behavior and the zigzag kinking area can serve as nucleation sites to promote DRX behavior.While the lamellar LPSO phase with high thickness(∼23.41 nm)and similar spacing(∼82 nm)was ruptured into granular LPSO phase and thus increase the volume fraction of granular LPSO phase,which made a great contribution to DRX behavior by particle stimulated nucleation.The main deformation mechanism of solution treatment+furnace cooling(SF)sample during CEC process is dominated by the multiple slips composed of basal slips,prismatic slips and pyramidal slips.For the solution treatment+air cooling(SA)sample and solution treatment+ageing treatment(ST)sample,the activation of basal slips is the critical deformation mechanism.The main contribution to yield strength is from the grain boundary,dislocation and hetero-deformation induced(HDI)strengthening.Moreover,the HDI strengthening in the SF and SA sample after CEC deformation is much larger than that of ST sample due to the distinct heterostructure composition.
基金the financial supports from the Key Research and Development Program of Hunan Province,China(No.2023GK2020)。
文摘The homogenized Mg−5.6Gd−0.8Zn(wt.%)alloys were treated with water cooling and furnace cooling to obtain specimens without and with the 14H long-period stacking ordered(LPSO)phase.Subsequently,multi-directional forging(MDF)experiments were carried out.The microstructure and mechanical properties of different regions(the center,middle and edge regions)in the MDFed alloys were systematically investigated,and the effect of LPSO phase on them was discussed.The results show that the alloys in different regions undergo significant grain refinement during the MDF process.Inhomogeneous microstructures with different degrees of dynamic recrystallization(DRX)are formed,resulting in microhardness heterogeneity.The alloy with the LPSO phase has higher microstructure homogeneity,a higher degree of recrystallization,and better comprehensive mechanical properties than the alloy without the LPSO phase.The furnace-cooled alloy after 18 passes of MDF has the best comprehensive mechanical properties,with an ultimate compressive strength of 488 MPa,yield strength of 258 MPa,and fracture strain of 21.2%.DRX behavior is closely related to the LPSO phase and deformation temperature.The kinked LPSO phase can act as a potential nucleation site for DRX grains,while the fragmented LPSO phase promotes DRX nucleation through the particle-stimulated nucleation mechanism.
基金financially supported by the National Key Research and Development Program of China(No.2021YFB3701100)the National Natural Science Foundation of China(Nos.U20A20234,51874062)+1 种基金the Postdoctoral Science Foundation of China(Nos.2023M730390,2022M710563)the Natural Science Foundation Commission,China(Nos.CSTB2023NSCQ-BHX0164,CSTB2022NSCQ-BHX0029)。
文摘Suitable heat treatment processes were adopted to regulate the precipitation of the lamellar LPSO phase andβ′phase in Mg−Gd−Y−Zn−Zr−Nd alloy.The effects of lamellar LPSO phase andβ′phase on the mechanical properties and damping capacity of the alloy were studied systematically.Experimental results demonstrate that the lamellar LPSO phase is more conducive to dynamic recrystallization processes,leading to a high degree of recrystallization and a weak texture intensity,resulting in a higher plasticity and damping capacity.After aging treatment,theβ′precipitates exhibit pronounced aging strengthening and increase the number of mobile interfaces,thus enhancing the strength and damping capacity at the same time.Through regulating lamellar LPSO and agedβ′phase,the alloy achieves high strength and high damping capacity:ultimate tensile strength of 498 MPa,yield strength of 371 MPa and damping capacity of 0.02 at strain amplitude of 1×10^(−3).
基金Project(BK20160869)supported by the Natural Science Foundation of Jiangsu Province,ChinaProject(GY12015009)supported by the Nantong Science and Technology Program,China+1 种基金Project(2015B01314)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(51501039)supported by the National Natural Science Foundation of China
文摘The microstructural evolution of a 18R single phase （S 18） alloy during annealing at 773 K for 100 h was investigated in order to reveal the formation mechanism of 14H phase. The results showed that the as-cast S 18 alloy was composed of 18R phase （its volume fraction exceeds 93%）, W particles and α-Mg phase. The 18R phase in S18 alloy was thermally stable and was not transformed into 14H long period stacking ordered （LPSO） phase during annealing. However, 14H lamellas formed within tiny α-Mg slices, and their average size and volume fraction increased with prolonging annealing time. Moreover, the 14H phase is nucleated within α-Mg independently on the basis of basal stacking faults （SFs）. The broadening growth of 14H lamellas is an interface-controlled process which involves ledges on basal planes, while the lengthening growth is a diffusion-controlled process and is associated with diffusion of solute atoms. The formation mechanism of 14H phase in this alloy could be explained as α-Mg＇→α-Mg＋14H.
基金the Natural Sciences and Engineering Research Council of Canada (NSERC)Ontario Trillium Scholarships (OTS) program for providing financial support+8 种基金financial support by the Premier’s Research Excellence Award (PREA)Canada Foundation for Innovation (CFI)Ryerson Research Chair (RRC) programthe Ministry of Science and Technology of China (2014DFG52810)National Great Theoretic Research Project of China (2013CB632200)National Natural Science Foundation of China (Project 51474043)Ministry of Education of China (SRFDR 20130191110018)Chongqing Municipal Government(CSTC2013JCYJC60001)Chongqing Science and Technology Commission (CSTC2011gjhz50001)
文摘This study was aimed at identifying underlying strengthening mechanisms and predicting the yield strength of as-extruded Mg-Zn-Y alloys with varying amounts of yttrium （Y） element. The addition of Y resulted in the formation of ternary 1 （Mg3YZn6）, W （Mg3Y2Zn3） and LPSO （Mg12YZn） phases which subse- quently reinforced alloys ZM31 ＋ 0.3Y, ZM31 ＋ 3.2Y and ZM31 ＋ 6Y, where the value denoted the amount of Y element （in wt%）. Yield strength of the alloys was determined via uniaxial compression testing, and grain size and second-phase particles were characterized using OM and SEM. In-situ high-temperature XRD was performed to determine the coefficient of thermal expansion （CTE）, which was derived to be 1.38 x 10^-5 K^-1 and 2.35 x 10^-5 K^-1 for W and LPSO phases, respectively. The individual strengthening effects in each material were quantified for the first time, including grain refinement, Orowan looping, thermal mismatch, dislocation density, load-bearing, and particle shearing contributions. Grain refinement was one of the major strengthening mechanisms and it was present in all the alloys studied, irrespective of the second-phase particles. Orowan looping and crE mismatch were the predominant strengthening mechanisms in the ZM31＋0.3Y and ZM31 ＋ 3.2Y alloys containing I and W phases, respectively, while load-bearing and second-phase shearing were the salient mechanisms contributing largely to the superior yield strength of the LPSO-reinforced ZM31 ＋ 6Y alloy.2017 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science ＆ Technology.
文摘The mechanical properties of two main precipitating phases(LPSO and MgRE)and matrix in Mg-Gd-Y-Nd-Zn bioalloy were examined using nanoindentation method.A new is suggested for characterizing the elastic-plastic behavior,fracture toughness and strain rate sensitivity(SRS)of materials within micro/nanoscale.Firstly,a nanomechanical model was developed for extracting hardness(H),young’s modulus(E)and yield stress(σY)from the characteristic load points which were subsequently analyzed by atomic force microscope(AFM)images.The elasticity data and AFM data were then utilized for determination of plastic deformation in constituent phases.The displacement of the indentation gets the highest value for Mg matrix and between precipitates,depth is more in LPSO rather than that of MgRE.The serrated flow or the behavior of shear bands may originate from the side effect of the interface region in Mg alloys with precipitates.It can be deduced that the KIC produced by both L method and energy-based calculation are both reliable for KIC approximation.The maximum load in simulation withμ=0.2 friction is marginally lesser than that of the frictionless(μ=0)one while elastic recovery of indentation withμ=0.2 is higher to some extent.
基金supports of the Natural Science Foundation of Jiangsu Province of China (No. BK20160869)the Fundamental Research Funds for the Central Universities (No. 2018B16614)the National Natural Science Foundation of China (No. 51774109)
文摘Casting magnesium alloys hold the greatest share of magnesium application products due to their short processing period, low cost and near net shape forming. Compared with conventional commercial magnesium alloys or other Mg–RE-based alloys, the novel Mg–RE–TM cast alloys with long period stacking ordered(LPSO) phases usually possess a higher strength and are promising candidates for aluminum alloy applications. Up to now, two ways: alloying design and casting process control(including subsequent heat treatments), have been predominantly employed to further improve the mechanical properties of these alloys. Alloying with other elements or ceramic particles could alter the solidifi cation pattern of alloys, change the morphology of LPSO phases and refi ne the microstructures. Diff erent casting techniques(conventional casting, rapidly solidifi cation, directional solidifi cation, etc.) introduce various microstructure characteristics, such as dendritic structure, nanocrystalline, metastable phase, anisotropy. Further heat treatments could activate the transformation of various LPSO structures and precipitation of diverse precipitates. All these evolutions exert great impacts on the mechanical properties of the LPSO-containing alloys. However, the underlying mechanisms still remain a subject of debate. Therefore, this review mainly provides the state of the art of the casting magnesium alloys research and the accompanying challenges and summarizes some topics that merit future investigation for developing high-performance Mg–RE–TM cast alloys.
基金National Natural Science Foundation of China(Nos.U1610123,51674226,51574207,51574206,51274175)International Cooperation project of the Ministry of Science and Technology of China(No.2014DFA50320)+4 种基金The Science and Technology Major Project of Shanxi Province(No.MC2016-06)International Science and Technology Cooperation Project of Shanxi Province(No.2015081041)Research Project Supported by Shanxi Scholarship Council of China(No.2016-Key 2)Transformation of Scientific and Technological Achievements Special Guide Project of Shanxi Province(No.201604D131029)Shanxi Province Science Foundation for Youths(No.201601D021062)
文摘The microstructure and damping capacities of MgZnxYi.33x(x=l-4at.%)alloys were discussed and researched.The main phase composition of the alloys consists of a_Mg and long-period stacking ordered(LPSO)phase.Due to increasedLPSO phase,grain size was refined.LPSO phase was advantageous to the damping properties of the Mg-Zn-Y alloys.Mg-7%Zn-12.8%Y has the highest damping capacity up to0.04.Due to stacking fault probability,the LPSO phase in the Mg-Zn-Yalloys could be new damping source to dissipate energy so as to contribute to the improvement of damping capacities.
基金supported by the National Natural Science Foundation of China(Nos.51574175 and 51474153)the Ph.D.Programs Foundation of Ministry of Education of China(No. 20111402110004)the Natural Science Foundation of Shanxi Province(Nos.2009011028-3 and 2012011022-1)
文摘The microstructure of the precipitated phases of Mg95.sGd3Zn1Zro.2 alloys with long-period stacking ordered structure before and after heat treatment is discussed. The corrosion properties of the as-cast （F）, solid-solution （T4） and aging-treated （T6） alloys in 1% NaC1 solution are studied. The hydrogen evolution and electrochemical measurements display that the as-cast Mg95.sGd3Zn1Zro.2 alloy with the continuous network eutectic phase exhibits the greatest corrosion resistance, while T6 sample with some needle-like phases and the particle phases is the worst among the three alloys. It is proposed to be mainly related to the amount, composition, microstructure and distribution of the precipitated phases.
基金Project supported by the National Natural Science Foundation of China (5150101551871195)。
文摘The microstructures and strengthening mechanisms of the Mg-8.2 Gd-4.6 Y-1.5 Zn-0.4 Zr(wt%) alloy with long-period stacking ordered(LPSO),β’ and γ type phases were systematically studied.The results show that the LPSO with lamellar and block structures forms near the grain boundaries.The grains are clearly refined,and the 18 R LPSO phase is oriented along the extrusion direction after extrusion.Some particles also precipitate from the Mg matrix dynamically.The extruded alloy exhibits a remarkable agehardening response,and mechanical properties,with a tensile strength(TS) of 449 MPa,yield strength(YS) of 362 MPa,and elongation of 7.9% obtained in the peak-aged alloy.The strengthening mechanisms of the alloy in different states are discussed.Grain boundary and precipitation strengthening are the main strengthening mechanisms for the peak-aged alloy.
基金This work is financially supported by the National Key Research and Development Program of China(Grant No.2016YFB0301100)the Chongqing Foundation and Advanced Research Project(Grant No.cstc2019jcyj-zdxmX0010)+1 种基金the Natural Science Foundation Commission of China(Grant No.51571044 and 51874062)Fundamental Research Funds for the Central Universities(Grant No.2018CDGFCL0005 and 2019CDXYCL0031).
文摘In this work,as-cast Mg-Ni-Y alloys were proposed to develop a feasible material for fracturing balls,and their mechanical performance and corrosion behavior were systematically investigated.Long period stacking order(LPSO)phase was firstly introduced to improve both the mechanical properties and degradation rate of magnesium alloys.With the increase of LPSO phase,the compressive strength was improved significantly,while the elongation of the alloys decreased owing to the relatively brittle nature of LPSO phase.Due to the higher corrosion potential of LPSO phase,the LPSO phase can accelerate the corrosion process by providing more micro-couples.However,the LPSO phase would serve as the corrosion barrier between the corrosion medium and the matrix when the contents of LPSO phase are too high in Mg92.5Ni3Y4.5 and Mg87.5Ni5Y7.5 alloys.As-cast Mg97.5Ni1Y1.5 alloy with satisfactory mechanical properties and rapid degradation rate was successfully developed,exhibiting a high degradation rate of 6675 mm/a(93℃)in 3 wt.%KCl solution and a favorable ultimate compressive strength of 410 MPa.The degradation rate of Mg97.5Ni1Y1.5 alloy is 2-5 times of the current commercial magnesium alloy fracturing materials.
基金supported by the National Key Research and Development Program of China (No.2021YFB3701100)the National Key Research and Development Program of China (Grant No.2018YFE0115800)the National Natural Science Foundation of China (Grant No.52105412)。
文摘Featured initial microstructures of Mg-11Gd-4Y-2Zn-0.5Zr alloy(wt%) were obtained by adjusting temperatures of solid solution and cooling methods, including island intergranular 18R and 14H LPSO phases with low-density stacking faults, differentially spaced lamellar intragranular 14H-LPSO phases, and network intergranular 18R-LPSO phases with high-density intragranular stacking faults. Effects of these featured LPSO phases and stacking faults on dynamic recrystallization(DRX) behavior were investigated via hot compression. Promoted DRX behavior via particle stimulated nucleation(PSN) is introduced by coexisting intergranular island 18R and 14H LPSO phases and intragranular wide spacing lamellar 14H-LPSO phases, contributing the highest DRX fraction of 42.6%. Conversely, it is found that DRX behavior with network intergranular 18R-LPSO phases and dense intragranular stacking fault is considerably inhibited with the lowest fraction of 22.8%. That is, the restricted DRX due to dislocations pinning by stacking faults overwhelms the enhanced DRX behavior via PSN of island intergranular 18R and 14H LPSO phases. Specially, compared with dense intragranular lamellar 14H-LPSO phases, high-density stacking faults exert a larger inhibition effect on DRX behavior.
基金the National Natural Science Foundation of China(51361010,51665012)supported by China Scholarship Council.
文摘The influence of solid solution treatment on the microstructure and corrosion resistance of as-cast Mg_(95.5)Zn_(1.5)Y_(3)alloy is characterized.The microstructure of the as-cast Mg_(95.5)Zn_(1.5)Y_(3)alloy mainly consisted ofα-Mg,W(Mg_(3)Zn_(3)Y_(2))phase,and the long period stacking ordered(LPSO)(Mg_(12)ZnY)phase.After solid solution treatment,most of the W phase disappears gradually with increasing solution treatment time,with only a small amount of W phase distributed as particle.The LPSO phase slightly dissolved into substrate,and its morphology transitions from blocky shape to rod shape.Solid solution treatment of Mg_(95.5)Zn_(1.5)Y_(3)exhibits excellent corrosion resistance,because the Y and Zn atoms became enriched in the matrix and the changed morphologies of the LPSO and W phases were modified through heat treatment.The alloy created with solid solution treatment at 520℃for 10 hours exhibits corrosion potential of−1.419 V,suggesting a significant improvement in corrosion performance.
基金financially supported by the National Natural Foundation China (51671118 and 51871143)the Science and Technology Committee of Shanghai Municipality(19010500400)the “Chenguang” Program from the Shanghai Municipal Education Commission (17CG42)。
文摘The long-period stacking ordered phases(LPSOs) in Mg-Ni-Y system have been attracting great interest as effective strengthening components because of their unique structural characteristics and deformation mechanism.However,the phase relationships in LPSOs are complicated and unclear,which restricts the design of advanced magnesium-based alloys.The aim of the present work is to experimentally determine the phase equilibria relationships focusing on LPSOs and establish the thermodynamic description for Mg-Ni-Y system.Four types of LPSOs,that is,14H,12R,18R and 10H,are confirmed through equilibrated alloys and high-resolution transmission electron microscopy(HR-TEM).The formation enthalpies of LPSOs(14H,12R,18R and 10H) are calculated based on density functional theories(DFT) calculations.A new ternary compound,termed as τ phase,is observed for the first time which is likely to be the distorted structure of 12R as determined from the TEM image which shows a 12-layer closed packing plane distance of 3.252nm and a shear angle of 83.2°between(0002) and(10■0) planes.Based on the determined phase equilibria relationship,the Mg-Ni-Y system is assessed and a selfconsistent description is obtained where the LPSOs are modeled as the stoichiometric compounds.The comparison between the calculation result and experimental data suggests the accuracy of the present thermodynamic database in the Mg-rich corner.
基金supported by the National Natural Science Foundation of China(Nos.51871069,52071093,and 52201137)the Opening Project of Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology(No.ASMA202205)+1 种基金the Student Research and Innovation Fund of the Fundamental Research Funds for the Central Universities(No.3072022GIP1004)the Beijing Municipal Natural Science Foundation(No.2202004).
文摘It is a long-term challenge to further improve the corrosion resistance while ensuring the strength of magnesium(Mg)alloys.Revealing the effect of potential fluctuation on the micro-galvanic corrosion and the subsequent film formation is important for understanding the corrosion mechanism of Mg alloys with multiple strengthening phases/structures.Here,we prepared the high-strength Mg-14.4Er-1.44Zn-0.3Zr(wt.%)alloys containing hybrid structures,i.e.,elongated long-period stacking ordered(LPSO)blocks+intragranular stacking faults(SFs)/LPSO lamellae.The Mg alloy with elongated LPSO blocks and intragranular LPSO lamellae(EZ-500 alloy)obtains good corrosion resistance(2.2 mm y^(–1)),while the Mg alloy containing elongated LPSO blocks and intragranular SFs(EZ-400 alloy)shows a significantly higher corrosion rate(6.9 mm y^(–1)).The results of scanning Kelvin probe force microscopy(SKPFM)show the elongated LPSO blocks act as cathode phase(87 mV in EZ-400 alloy),and the SFs serve as the weak anode(30 mV in EZ-400 alloy),resulting in high potential fluctuation in EZ-400 alloy.On the contrary,both elongated blocks and intragranular lamellae are cathodic LPSO phase(67–69 mV)in EZ-500 alloy,leading to a lower potential fluctuation.Quasi in-situ atomic force microscope(AFM)observation indicates that high potential fluctuation would cause strong micro-galvanic corrosion,and subsequently leads to the failure in rapid formation of corrosion film,finally forming a loose and porous film,while relatively low potential fluctuation could result in more uniform corrosion mode and facilitate the rapid formation of protective film.Therefore,we propose that it is an effective way to develop high-strength corrosionresistant Mg alloys by controlling the potential fluctuation to form a“uniform potential”strengthening microstructure。
基金the Ministry of Science and Higher Education of the Russian Federation in the framework of Increase Competitiveness Program of NUST«MISiS»(No.К2-2020-025),implemented by a governmental decree dated 16th of March 2013,N 211.
文摘The Mg–Zn–Y–Zr alloys with long-period stacking-ordered(LPSO)and W eutectic phases were investigated to develop new magnesium casting alloys.The temperatures for T6 heat treatment were selected based on the hardness and electrical conductivity measurements.The hot tearing susceptibility of the alloys with LPSO phase is lower than that of the alloys with W phase,which is associated with the freezing range of the alloys.However,the investigated alloys displayed the same fluidity.Under T6 conditions,increasing the Y content in the alloys resulted in increased yield strength,whereas other tensile properties were similar for the alloys.The corrosion resistance was higher for the alloys with LPSO phase compared to that of the alloys with W phase.Mg−2.5Zn−3.7Y−0.3Zr(mass fraction,%)alloy with LPSO phase possessed high castability and mechanical properties,with a corrosion rate of 2 mm/year.
基金supported by the National Key Research and Development Project (2018YFE0115800, 2020YFE0202600)Youth Talent Project of China National Nuclear Corporation (CNNC2019YTEP-HEU01, CNNC2021YTEP-HEU01)+4 种基金the NSFC Funding (51701051, 52001083, 52171111, U2141207)China Postdoctoral Science Foundation Funded Project (2019T120255)Natural Science Foundation of Heilongjiang (LH2019E030)Heilongjiang Touyan Innovation Team Programthe supports from the U.S. National Science Foundation [DMR-1611180 and 1809640] with the program directors, Drs. Judith Yang, Gary Shiflet, and Diana Farkas.
文摘Achieving high strength in Mg alloys is usually accompanied by ductility loss.Here,a novel Mg97Y1Zn1Ho1 at.%alloy with a yield strength of 403 MPa and an elongation of 10%is developed.The strength-ductility synergy is obtained by a comprehensive strategy,including a lamella bimodal microstructure design and the introduction of nano-spaced solute-segregated 14H long-period stacking-ordered phase(14H LPSO phase)through rare-earth Ho alloying.The lamella bimodal microstructure consists of elongated un-recrystallized(un-DRXed)coarse grains and fine dynamically-recrystallized grains(DRXed regions).The nano-spaced solute-segregated 14H LPSO phase is distributed in DRXed regions.The outstanding yield strength is mainly contributed by grain-boundary strengthening,18R LPSO strengthening,and fiberlike reinforcement strengthening from the nano-spaced 14H LPSO phase.The high elongation is due primarily to the combined effects of the bimodal and lamellar microstructures through enhancing the work-hardening capability.
基金Project supported by the National Natural Science Foundation of China(51961021,52001152 and 51901174)China Postdoctoral Science Foundation(2020M673383)。
文摘A yield phenomenon was firstly reported in an extruded Mg-6.8Y-2.5Cu alloy and the corresponding microstructure was also investigated in this work,The cast alloy is mainly composed ofα-Mg,18R long period stacking order(LPSO)phase,eutectic phase(Mg_(20)Cu_(4)Y_(1)),and Mg_(2)Cu phase.The 18R LPSO phase at the dendritic grain boundary transforms into the 14H LPSO phase in the grain interior during homogenization.After extrusion,the grain size of the homogenized alloy is remarkably refined to-3.69μm and the second phase is significantly broken and distributed in the extrusion direction.Tensile testing curves of the extrude alloy at room temperature indicate that the yield strength and ultimate tensile strength increase while the elongation of the alloy decreases with increasing strain rate.Interestingly,a yield plateau fo rms and gradually decreases with increasing strain rate.The yield phenomenon is related to the dislocation multiplication and the interaction between the movable dislocations and solute atoms.
