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 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
As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered(LPSO)phase and density of lamellar γ' phase were prepared,and the microstructure,mechanical,and degradation properties w...As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered(LPSO)phase and density of lamellar γ' phase were prepared,and the microstructure,mechanical,and degradation properties were investigated.Coupling the bulk LPSO phase and the lamellar γ' phase,and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ' phase,a synergistic increase in strength and degradation rate can be achieved.On the one hand,the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ' phase,which provide more galvanic corrosion.Moreover,high densities of the lamellar γ' phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized(DRXed)grains during the hot extrusion.On the other hand,the ultimate tensile strength(UTS)and tensile yield strength(TYS)of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa,respectively,which was mainly attributed to grain boundary and texture strengthening,bulk LPSO phase and lamellar γ' phase strengthening.Overall,Mg^(-1)4Er-4Ni alloy,which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ' phase,re-alized a synergistic enhancement of strength and degradation rate.The UTS,TYS,and degradation rate of Mg^(-1)4Er-4Ni were 514 MPa,358 MPa,and 142.5 mg cm^(-2)h^(-1)(3 wt%KCl solution at 93◦C),respectively.This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments.展开更多
The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered(LPSO)phase during tension and compression was investigated by in-situ synchrotron diffraction.T...The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered(LPSO)phase during tension and compression was investigated by in-situ synchrotron diffraction.The micro-yielding,macro-yielding,tension-compression asymmetry and strain hardening behavior of the alloys were explored by combining with deformation mechanisms.The micro-yielding is dominated by basal slip of dynamic recrystallized(DRXed)grains in tension,while it is dominated by extension twinning of non-dynamic recrystallized(non-DRXed)grains in compression.At macro-yielding,the non-DRXed grains are still elastic deformed in tension and the basal slip of DRXed grains in compression are activated.Meanwhile,the LPSO phase still retains elastic deformation,but can bear more load,so the higher the volume fraction of hard LPSO phase,the higher the tensile/compressive macro-yield strength of the alloys.Benefiting from the low volume fraction of the non-DRXed grains and the delay effect of LPSO andγphases on extension twinning,the as-extruded alloys exhibit excellent tension-compression symmetry.When the volume fraction of LPSO phase reaches∼50%,tension-compression asymmetry is reversed,which is due to the fact that the LPSO phase is stronger in compression than in tension.The tensile strain hardening behavior is dominated by dislocation slip,while the dominate mechanism for compressive strain hardening changes from twinning in theα-Mg grains to kinking of the LPSO phase with increasing volume fraction of LPSO phase.The activation of kinking leads to the constant compressive strain hardening rate of∼2500 MPa,which is significantly higher than the tensile strain hardening rate.展开更多
This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period ...This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.展开更多
A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long peri...A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long period stacking ordered(LPSO)phase were characterized,and the mechanical properties uniformity was investigated.Moreover,a quantitative relationship between the microstructure and tensile yield strength was established.The results showed that the grains in the processed zone(PZ)and interfacial zone(IZ)were refined from 50μm to 3μm and 4μm,respectively,and numerous original LPSO phases were broken.In IZ,some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms.The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly,greatly increasing the transformation rate of LPSO phase.After MFSP,the ultimate tensile strength,yield strength and elongation to failure of the large-scale plate were 367 MPa,305 MPa and 18.0% respectively.Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample.In particularly,the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ.This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.展开更多
In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LP...In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LPSO and polygonal Mg24Y5 phases,leading to the formation of a high-dense network of needle-like oxides at the oxidation front.These oxides grew laterally along the oxide/matrix interfaces,forming a thicker,continuous scale that effectively blocked elemental diffusion.Hence,the preferential oxidation along the needle-like LPSO is believed to accelerate the formation of a thicker and continuous oxide scale,further improving the oxidation resistance of the Mg-11Y-1Al alloy.展开更多
Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys,achieving a balance between strength and toughness has proven challenging.This paper introduces a method for...Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys,achieving a balance between strength and toughness has proven challenging.This paper introduces a method for regulating the overlapping structure of the lamellar long-period stacking ordered(LPSO)phase andβ′phase to achieve a balance between strength and toughness in the alloy.By focusing on the extruded VW93A alloy cabin component,the study delves into the mechanism of the alloy's strength and toughness through a comparative analysis of the microstructure characteristics and room-temperature mechanical properties of the alloys in various states.Additionally,the molecular dynamics simulation is employed to clarify the mechanism of the alloy's strength and toughness balance induced by the overlapping structure.The findings reveal that when theβ′phase precipitates in the alloy alone,a significant increase in strength is achieved by pinning dislocations,albeit at the expense of reduced plasticity.Conversely,the presence of the lamellar LPSO phase disperses dislocations between the LPSO phase lamellae,thereby enhancing plasticity by avoiding stress concentration resulting from dislocation stacking.When both phases coexist in the alloy and form an overlapping structure,the dispersion of dislocations due to the lamellar LPSO phase weakens the pinning effect of theβ′phase,further reducing dislocation stacking and resulting in a balance of strength and toughness in the alloy.Ultimately,the alloy with the overlapping structure exhibits an ultimate tensile strength and elongation of 421 MPa and 20.1%,respectively.展开更多
In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusti...In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530℃for 16 h and 24 h,with values of 13.56%and 3.93%respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150℃,200℃,250℃,and 300℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250℃.However,at a temperature 300℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.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
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 c...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
Effects of solid solution treatment and cooling on the morphology of long period stacking order(LPSO)phase and precipitation hardening behavior of Mg?2Dy?0.5Ni(molar fraction,%)alloy were investigated.Microstructures ...Effects of solid solution treatment and cooling on the morphology of long period stacking order(LPSO)phase and precipitation hardening behavior of Mg?2Dy?0.5Ni(molar fraction,%)alloy were investigated.Microstructures of the as-cast alloy mainly consisted ofα-Mg phase,bamboo-like Mg12DyNi phase with LPSO structure distributed between dendrites and small amounts of cubic Dy phases.During solid solution treatment at565oC for12h and subsequent different cooling conditions,dot-shaped,block,fine lamellar and rod-shaped LPSO phases precipitate in Mg matrix,respectively.For continuous cooling conditions(furnace and air cooling),the fine lamellar LPSO phase generally forms in grain interior and its volume fraction increases and block LPSO phase coarsens with increasing cooling time.For discontinuous cooling conditions(air cooling after furnace cooling to415and265°C),the dot-shaped LPSO grows into the rod-shaped phase,which results in an decrease of cooling hardening behavior of alloy.展开更多
The compressive deformation behavior of the extruded WZ42(Mg98.5Y1Zn0.5 in at.%)magnesium alloy containing a low amount of long-period stacking ordered(LPSO)phase was studied by in-situ synchrotron radiation diffracti...The compressive deformation behavior of the extruded WZ42(Mg98.5Y1Zn0.5 in at.%)magnesium alloy containing a low amount of long-period stacking ordered(LPSO)phase was studied by in-situ synchrotron radiation diffraction technique.Tests were conducted at temperatures between room temperature and 350℃.Detailed microstructure investigation was provided by scanning electron microscopy,particularly the backscattered electron imaging and electron backscatter diffraction technique.The results show that twinning lost its dominance and kinking of the LPSO phase became more pronounced with increasing deformation temperature.No cracks of the LPSO phase and no debonding r at the interface between the LPSO phase and the Mg matrix were observed at temperatures above 200℃.At 350℃,the LPSO phase lost its strengthening effect and the deformation of the alloy was mainly realized by the dynamic recrystallization of the Mg matrix.展开更多
The Mg-1Gd-0.75Er-0.5Zn-0.18Zr(at.%)alloy with long-period stacking ordered(LPSO)phase was prepared by metal mold casting and hot extrusion.The extruded samples had a typical bimodal microstructure.The different fract...The Mg-1Gd-0.75Er-0.5Zn-0.18Zr(at.%)alloy with long-period stacking ordered(LPSO)phase was prepared by metal mold casting and hot extrusion.The extruded samples had a typical bimodal microstructure.The different fractions of equiaxed grains were observed in annealed samples.The percentage of fine grains decreased in the extruded Mg alloys with and without annealing treatment when the extrusion temperature was increased.The LPSO phases promote recrystal-lization behavior in the samples through particle-stimulated nucleation(PSN)mechanism.The Mg alloys extruded at 300℃ with or without annealing treatment obtained the best tensile properties.At the low extrusion temperature,more finely equiaxed grains with random texture are formed through PSN,and more LPSO phase kink bands are formed,which could improve the mechanical properties of the extruded Mg alloys.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 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
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 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
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 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support from the National Key Research and Development Program of China(No.2021YFB3701100)the Natural Science Foundation Commission of China(Grant Nos.U20A20234 and 51874062)+1 种基金the Fundamental Re-search Funds for Central Universities(No.2022CDJKYJH004C)the Science and Technology Major Project of Shanxi Province(No.20191102008).
文摘As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered(LPSO)phase and density of lamellar γ' phase were prepared,and the microstructure,mechanical,and degradation properties were investigated.Coupling the bulk LPSO phase and the lamellar γ' phase,and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ' phase,a synergistic increase in strength and degradation rate can be achieved.On the one hand,the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ' phase,which provide more galvanic corrosion.Moreover,high densities of the lamellar γ' phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized(DRXed)grains during the hot extrusion.On the other hand,the ultimate tensile strength(UTS)and tensile yield strength(TYS)of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa,respectively,which was mainly attributed to grain boundary and texture strengthening,bulk LPSO phase and lamellar γ' phase strengthening.Overall,Mg^(-1)4Er-4Ni alloy,which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ' phase,re-alized a synergistic enhancement of strength and degradation rate.The UTS,TYS,and degradation rate of Mg^(-1)4Er-4Ni were 514 MPa,358 MPa,and 142.5 mg cm^(-2)h^(-1)(3 wt%KCl solution at 93◦C),respectively.This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments.
基金supported by National Natural Science Foundation of China(no.U21A2047,no.51971076 and no.52001069).
文摘The deformation behavior of the as-extruded Mg-Y-Ni alloys with different volume fraction of long period stacking ordered(LPSO)phase during tension and compression was investigated by in-situ synchrotron diffraction.The micro-yielding,macro-yielding,tension-compression asymmetry and strain hardening behavior of the alloys were explored by combining with deformation mechanisms.The micro-yielding is dominated by basal slip of dynamic recrystallized(DRXed)grains in tension,while it is dominated by extension twinning of non-dynamic recrystallized(non-DRXed)grains in compression.At macro-yielding,the non-DRXed grains are still elastic deformed in tension and the basal slip of DRXed grains in compression are activated.Meanwhile,the LPSO phase still retains elastic deformation,but can bear more load,so the higher the volume fraction of hard LPSO phase,the higher the tensile/compressive macro-yield strength of the alloys.Benefiting from the low volume fraction of the non-DRXed grains and the delay effect of LPSO andγphases on extension twinning,the as-extruded alloys exhibit excellent tension-compression symmetry.When the volume fraction of LPSO phase reaches∼50%,tension-compression asymmetry is reversed,which is due to the fact that the LPSO phase is stronger in compression than in tension.The tensile strain hardening behavior is dominated by dislocation slip,while the dominate mechanism for compressive strain hardening changes from twinning in theα-Mg grains to kinking of the LPSO phase with increasing volume fraction of LPSO phase.The activation of kinking leads to the constant compressive strain hardening rate of∼2500 MPa,which is significantly higher than the tensile strain hardening rate.
基金funded by the National Natural Science Foundation of China(Nos.51801189)The Central Guidance on Local Science and Technology Development Fund of Shanxi Province(Nos.YDZJTSX2021A027)+2 种基金The National Natural Science Foundation of China(Nos.51801189)The Science and Technology Major Project of Shanxi Province(No.20191102008,20191102007)The North University of China Youth Academic Leader Project(No.11045505).
文摘This work studied the microstructure,mechanical properties and damping properties of Mg_(95.34)Ni_(2)Y_(2.66) and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys systematically.The difference in the evolution of the long-period stacked ordered(LPSO)phase in the two alloys during heat treatment was the focus.The morphology of the as-cast Mg_(95.34)Ni_(2)Y_(2.66)presented a disordered network.After heat treatment at 773 K for 2 hours,the eutectic phase was integrated into the matrix,and the LPSO phase maintained the 18R structure.As Zn partially replaced Ni,the crystal grains became rounded in the cast alloy,and lamellar LPSO phases and more solid solution atoms were contained in the matrix after heat treatment of the Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloy.Both Zn and the heat treatment had a significant effect on damping.Obvious dislocation internal friction peaks and grain boundary internal friction peaks were found after temperature-dependent damping of the Mg_(95.34)Ni_(2)Y_(2.66)and Mg_(95.34)Zn_(1)Ni_(1)Y_(2.66)alloys.After heat treatment,the dislocation peak was significantly increased,especially in the alloy Mg_(95.34)Ni_(2)Y_(2).66.The annealed Mg_(95.34)Ni_(2)Y_(2.66)alloy with a rod-shaped LPSO phase exhibited a good damping performance of 0.14 atε=10^(−3),which was due to the difference between the second phase and solid solution atom content.These factors also affected the dynamic modulus of the alloy.The results of this study will help in further development of high-damping magnesium alloys.
基金supported by the National Key Research and Development Program of China(2021YFB3501002)State Key Program of National Natural Science Foundation of China(5203405)+3 种基金National Natural Science Foundation of China(51974220,52104383)National Key Research and Development Program of China(2021YFB3700902)Key Research and Development Program of Shaanxi Province(2020ZDLGY13-06,2017ZDXM-GY-037)Shaanxi Province National Science Fund for Distinguished Young Scholars(2022JC-24)。
文摘A large-scale fine-grained Mg-Gd-Y-Zn-Zr alloy plate with high strength and ductility was successfully prepared by multi-pass friction stir processing(MFSP)technology in this work.The structure of grains and long period stacking ordered(LPSO)phase were characterized,and the mechanical properties uniformity was investigated.Moreover,a quantitative relationship between the microstructure and tensile yield strength was established.The results showed that the grains in the processed zone(PZ)and interfacial zone(IZ)were refined from 50μm to 3μm and 4μm,respectively,and numerous original LPSO phases were broken.In IZ,some block-shaped 18R LPSO phases were transformed into needle-like 14H LPSO phases due to stacking faults and the short-range diffusion of solute atoms.The severe shear deformation in the form of kinetic energy caused profuse stacking fault to be generated and move rapidly,greatly increasing the transformation rate of LPSO phase.After MFSP,the ultimate tensile strength,yield strength and elongation to failure of the large-scale plate were 367 MPa,305 MPa and 18.0% respectively.Grain refinement and LPSO phase strengthening were the major strengthening mechanisms for the MFSP sample.In particularly,the strength of IZ was comparable to that of PZ because the strength contribution of the 14H LPSO phase offsets the lack of grain refinement strengthening in IZ.This result opposes the widely accepted notion that IZ is a weak region in MFSP-prepared large-scale fine-grained plate.
基金the financial support from the National Key Research and Development Program of China(No.2022YFB3708400)the National Science and Technology Major Project(J2019-VIII-0003-0165)the Space Utilization System of China Manned Space Engineering(No.KJZ-YY-WCL04).
文摘In this study,we investigated the oxidation of the Mg-11Y-1Al alloy at 500℃in an Ar-20%O2environment.Multiscale analysis showed the network-like long-period stacking ordered(LPSO)phase transformed into needle-like LPSO and polygonal Mg24Y5 phases,leading to the formation of a high-dense network of needle-like oxides at the oxidation front.These oxides grew laterally along the oxide/matrix interfaces,forming a thicker,continuous scale that effectively blocked elemental diffusion.Hence,the preferential oxidation along the needle-like LPSO is believed to accelerate the formation of a thicker and continuous oxide scale,further improving the oxidation resistance of the Mg-11Y-1Al alloy.
基金financially supported by the Special Project of Science and Technology Cooperation and Exchange of Shanxi Province(No.202104041101033)the special fund for Science and Technology Innovation Teams of Shanxi Province.
文摘Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys,achieving a balance between strength and toughness has proven challenging.This paper introduces a method for regulating the overlapping structure of the lamellar long-period stacking ordered(LPSO)phase andβ′phase to achieve a balance between strength and toughness in the alloy.By focusing on the extruded VW93A alloy cabin component,the study delves into the mechanism of the alloy's strength and toughness through a comparative analysis of the microstructure characteristics and room-temperature mechanical properties of the alloys in various states.Additionally,the molecular dynamics simulation is employed to clarify the mechanism of the alloy's strength and toughness balance induced by the overlapping structure.The findings reveal that when theβ′phase precipitates in the alloy alone,a significant increase in strength is achieved by pinning dislocations,albeit at the expense of reduced plasticity.Conversely,the presence of the lamellar LPSO phase disperses dislocations between the LPSO phase lamellae,thereby enhancing plasticity by avoiding stress concentration resulting from dislocation stacking.When both phases coexist in the alloy and form an overlapping structure,the dispersion of dislocations due to the lamellar LPSO phase weakens the pinning effect of theβ′phase,further reducing dislocation stacking and resulting in a balance of strength and toughness in the alloy.Ultimately,the alloy with the overlapping structure exhibits an ultimate tensile strength and elongation of 421 MPa and 20.1%,respectively.
基金supported by the Qinghai Provincial Science and Technology Department Basic Research Program(No.2023-ZJ-913M).
文摘In this study,the high-temperature stability and the generation mechanism of the Portevin-Le Chatelier(PLC)effect in solid-solution Mg-1Al-12Y alloy with different heat treatment processes were investigated by adjusting the content of long-period stacking ordered(LPSO)phases.It was found that the content of LPSO phases in the alloys differed the most after heat treatment at 530℃for 16 h and 24 h,with values of 13.56%and 3.93%respectively.Subsequently,high-temperature tensile experiments were conducted on these two alloys at temperatures of 150℃,200℃,250℃,and 300℃.The results showed that both alloys exhibited the PLC effect at temperatures ranging from 150 to 250℃.However,at a temperature 300℃,only the alloy with a greater concentration of LPSO phases exhibited the PLC effect,whereas the alloy with a lower proportion of LPSO phases did not exhibit this phenomenon.Additionally,both alloys exhibited remarkable high-temperature stability,with the alloy containing a greater percentage of LPSO phases also demonstrating superior strength.The underlying mechanism for this phenomenon lies in the exceptional high-temperature stability exhibited by the second phase within the alloy.Furthermore,the LPSO phase effectively obstructs the movement of dislocations,and it also undergoing kinking to facilitate plastic deformation of the alloy.The results indicate that the PLC effect can be suppressed by reducing dislocation pile-up at grain boundaries,which leads to a decrease in alloy plasticity but an increase in strength.The presence of the PLC effect in the WA121 alloy is attributed to the abundant dispersed second phase within the alloy,which initially hinders the movement of dislocations,leading to an increase in stress,and subsequently releases the dislocations,allowing them to continue their movement and thereby reducing in stress.
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.
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Projects(51301082,51464031) supported by the National Natural Science Foundation of ChinaProject(2015011038) supported by the Natural Science Foundation of Shanxi Province,China
文摘Effects of solid solution treatment and cooling on the morphology of long period stacking order(LPSO)phase and precipitation hardening behavior of Mg?2Dy?0.5Ni(molar fraction,%)alloy were investigated.Microstructures of the as-cast alloy mainly consisted ofα-Mg phase,bamboo-like Mg12DyNi phase with LPSO structure distributed between dendrites and small amounts of cubic Dy phases.During solid solution treatment at565oC for12h and subsequent different cooling conditions,dot-shaped,block,fine lamellar and rod-shaped LPSO phases precipitate in Mg matrix,respectively.For continuous cooling conditions(furnace and air cooling),the fine lamellar LPSO phase generally forms in grain interior and its volume fraction increases and block LPSO phase coarsens with increasing cooling time.For discontinuous cooling conditions(air cooling after furnace cooling to415and265°C),the dot-shaped LPSO grows into the rod-shaped phase,which results in an decrease of cooling hardening behavior of alloy.
基金The authors acknowledge the Deutsches Elektronen-Synchrotron for the provision of facilities within the framework of the proposal I-20170459 ECThe authors are also grateful for support from the Grant Agency of the Charles University,grant number 1262217+3 种基金the grant SVV-2019-260442the Czech Science Foundation under grant 17-21855Sthe Operational Programme Research,Development and Education,The Ministry of Education,Youth and Sports(OP RDE,MEYS),grant number CZ.02.1.01/0.0/0.0/16_013/0001794GG thanks the support of the Spanish Ministry of Economy and Competitiveness,grant number MAT2016-78850-R.
文摘The compressive deformation behavior of the extruded WZ42(Mg98.5Y1Zn0.5 in at.%)magnesium alloy containing a low amount of long-period stacking ordered(LPSO)phase was studied by in-situ synchrotron radiation diffraction technique.Tests were conducted at temperatures between room temperature and 350℃.Detailed microstructure investigation was provided by scanning electron microscopy,particularly the backscattered electron imaging and electron backscatter diffraction technique.The results show that twinning lost its dominance and kinking of the LPSO phase became more pronounced with increasing deformation temperature.No cracks of the LPSO phase and no debonding r at the interface between the LPSO phase and the Mg matrix were observed at temperatures above 200℃.At 350℃,the LPSO phase lost its strengthening effect and the deformation of the alloy was mainly realized by the dynamic recrystallization of the Mg matrix.
基金support from Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX21_1764)Department Education of Jiangsu Province(No.22KJB430003)Guangdong Basic and Applied Basic Research Foundation(No.2020A1515110394).
文摘The Mg-1Gd-0.75Er-0.5Zn-0.18Zr(at.%)alloy with long-period stacking ordered(LPSO)phase was prepared by metal mold casting and hot extrusion.The extruded samples had a typical bimodal microstructure.The different fractions of equiaxed grains were observed in annealed samples.The percentage of fine grains decreased in the extruded Mg alloys with and without annealing treatment when the extrusion temperature was increased.The LPSO phases promote recrystal-lization behavior in the samples through particle-stimulated nucleation(PSN)mechanism.The Mg alloys extruded at 300℃ with or without annealing treatment obtained the best tensile properties.At the low extrusion temperature,more finely equiaxed grains with random texture are formed through PSN,and more LPSO phase kink bands are formed,which could improve the mechanical properties of the extruded Mg alloys.
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.
