The microstructural evolution of AA7055 aluminum alloy under dynamic impact loading with the strain rate of 1.3 × 10^4 s^-1 controlled by a split Hopkinson pressure bar was investigated, and compared with that un...The microstructural evolution of AA7055 aluminum alloy under dynamic impact loading with the strain rate of 1.3 × 10^4 s^-1 controlled by a split Hopkinson pressure bar was investigated, and compared with that under quasi-static mechanical loading in compression with strain rate of 1.0 × 10^-3 s^-1. The quasi-static-compressed sample exhibited equiaxed dislocation cells, which were different from the elongated and incomplete dislocation cells for the alloy undergoing dynamic compression. The high strain-rate compression also induced the formation of localized shear bands in which the recrystallizations characterized as fine equiaxed grains were observed. The microstructural evolutions under both quasi-static and dynamic compressions are rationalized in terms of the dislocation cell model combined with the dislocation kinetics, in addition to the adiabatic temperature rise in shear bands at high strain rate.展开更多
The microstructural evolutions of 5Mn steel during various heat treatments have been investiga- ted by in-situ transmission electron microscopy （TEM）. The specimen of 5Mn steel was pre- pared using focused ion beam ...The microstructural evolutions of 5Mn steel during various heat treatments have been investiga- ted by in-situ transmission electron microscopy （TEM）. The specimen of 5Mn steel was pre- pared using focused ion beam （FIB） milling, which allowed the selection of specific morphology of interest prior to the in-situ observation, The complete austenization at 800 ℃ was verified at the atomic scale by minimizing thermal expansion and sample drift in a heating holder based on micro-electro-mechanical-systems. During annealing at 650 ℃, the formation of reverted austen- ite was dynamically observed, while the morphologies of austenite laths of 5Mn steel after in-situ heating were quite similar to that after ex-situ intereritical annealing. During annealing at 500 ℃, the morphological evolution of cementite and associated Mn diffusion were investigated. It was demonstrated that a combination of FIB sampling and high temperature in-situ TEM enables us to probe the morphological evolution and elemental diffusion of specific areas of interest in steel at high spatial resolution.展开更多
High manganese steels(HMS),known for their exceptional strength-ductility balance,are increasingly utilized in dynamic loading applications.This review examines the effects of strain rate on their mechanical propertie...High manganese steels(HMS),known for their exceptional strength-ductility balance,are increasingly utilized in dynamic loading applications.This review examines the effects of strain rate on their mechanical properties and microstructural evolution,focusing on strain rate hardening,adiabatic heating softening,and dynamic strain aging(DSA).The influence of strain rate on yield strength,ultimate tensile strength,strain hardening,and ductility is discussed,highlighting both positive and negative sensitivities across different alloy compositions and strain rate regimes.The strain rate response of various deformation mechanisms,including deformation twinning,dislocation slip,and phase transformation,is examined alongside their influence on microstructural evolution,alloy design,and industrial applications.The intricate role of DSA is also analyzed,emphasizing its contribution to strain rate sensitivity.To optimize HMS for dynamic environments,future research should focus on advanced modeling and processing techniques,in-situ characterization methods,and a deeper understanding of thermally activated processes and stacking fault energy-controlled mechanisms.This review provides insights into strain rate effects,guiding alloy design,and technological advancements of the new HMS.展开更多
This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined wi...This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.展开更多
High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material...High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.展开更多
The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and micr...The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and microstructural evolution of 304 stainless steel after HPT were investigated by X-ray diffraction(XRD)analysis,electron backscatter diffraction(EBSD)analysis,transmission electron microscopy(TEM),nanoindentation test and differential scanning calorimetry(DSC)analysis.The experimental results show that HPT causes elongated nanocrystalline grains of 25 nm width along the torsion direction.After 10 turns of HPT,the deformation-induced martensitic transformation is completed and the hardness increases from 3 GPa to 8.5 GPa at the edge of the disc.However,a local reverse phase transformation from martensite to austenite is observed in the peripheral regions of the sample after 30 turns of HPT,leading to a higher volume fraction of austenite,and the hardness of the sample also decreases accordingly.展开更多
To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced materi...To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.展开更多
Ag-Cu alloys are extensively used in sliding electric contacts due to their superior electrical conductivity,but their limited wear resistance reduces component longevity.Surface severe plastic deformation(SSPD)has em...Ag-Cu alloys are extensively used in sliding electric contacts due to their superior electrical conductivity,but their limited wear resistance reduces component longevity.Surface severe plastic deformation(SSPD)has emerged as a promising method to enhance wear resistance and reduce friction of metals without altering the matrix composition.In this study,an Ag-20 wt.%Cu alloy was subjected to SSPD for various durations,with the aim of improving tribological performance.The microstructure,hardness,and current-carrying tribological performance under different currents were systematically investigated,along with an exploration of the underlying mechanisms.The results show that in addition to introducing a high density of dislocations on the surface,SSPD also encourages the formation of(111)texture,and particularly disperses the initially long strips of Curich phase into short strips and fine particles.It promotes a tribo-film composed primarily of a mixture of Cu_(2)O and CuO that forms on the worn surface of the surface-treated sample under the 1 A current,thus significantly reducing the friction coefficient and electrical noise.Under the 10 A current,the sample treated for 60 min possesses the optimal friction coefficient(0.429),wear rate(0.791×10^(−6)mm^(3)/(N m)),and electrical noise(0.240 V).In contrast to the Ag/Cu layered structure observed on the worn subsurface of the untreated sample,a single-phase Ag(Cu)solid solution forms on the worn subsurface of the 60-min treated sample,which improves the current-carrying tribological performance.This work provides valuable insights for the development and application of electrical contact alloys with excellent performance.展开更多
The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al all...The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.展开更多
In order to develop a marine engineering material with excellent mechanical properties and corrosion resistance,a novel non-equiatomic Co_(1.5)CrFeNi_(1.5)Ti_(0.6)high-entropy alloy(HEA)was fabricated through mechanic...In order to develop a marine engineering material with excellent mechanical properties and corrosion resistance,a novel non-equiatomic Co_(1.5)CrFeNi_(1.5)Ti_(0.6)high-entropy alloy(HEA)was fabricated through mechanical alloying and spark plasma sintering.The results revealed that the sintering temperature significantly affected the microstructure and phase composition of the HEA owing to the diffusion rate,homogenization,and sluggish diffusion effect of metal atoms.At sintering temperatures below 1050℃,HEA mainly consisted of face-centered cubic(FCC),Ni_(3)Ti(ε),Ni_(2.67)Ti_(1.33)(R),and Fe-Cr(σ)phases.The microstructure of alloy comprised coarse dendritic crystals,whose content and size gradually decreased with increasing sintering temperature.However,the HEA sintered above 1100℃contained only fine equiaxed crystals.HEA sintered at 1100℃featured only the FCC solid solution,while theε-phase precipitated at temperatures above 1150℃.At a sintering temperature of 1050℃,the alloy microstructure consisted of short rod-like dendrites and fine equiaxed crystals.This alloy achieved the highest yield strength of 1198.71 MPa owing to the effects of precipitation strengthening and grain boundary strengthening.Meanwhile,HEA sintered above 1050℃exhibited significantly improved corrosion resistance.Considering the microstructure,mechanical,and corrosion properties,1050℃was identified as the optimal sintering temperature for Co_(1.5)CrFeNi_(1.5)Ti_(0.6)HEA.展开更多
Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformat...Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 ℃). When deformed near the γ′ solvus temperature (1110 ℃), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 ℃), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 ℃), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 ℃, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.展开更多
The microstructural evolution,mechanical properties,and corrosion behavior of Ti-12Ni(wt.%)specimens produced by laser powder bed fusion(LPBF)using various volume energy density(VED)processing parameter values were in...The microstructural evolution,mechanical properties,and corrosion behavior of Ti-12Ni(wt.%)specimens produced by laser powder bed fusion(LPBF)using various volume energy density(VED)processing parameter values were investigated.The results showed that the alloy prepared at a low VED of 67 J/mm^(3)consisted of near-βgrains.At a VED of 133 J/mm^(3),the alloy exhibited coarse primary Ti2Ni and fine eutectoid structure.This eutectoid structure consisted ofαlaths and two types of nanoscale Ti2Ni,one in the form of short rods and the other with a spherical morphology.Further increase of the VED to 267 J/mm^(3)led to coarsening of the eutectoid structure.The dispersed Ti2Ni nanoparticles exhibited a significant strengthening effect.The alloy produced at a VED of 133 J/mm^(3)showed the greatest strength with a nanohardness of(7.8±0.1)GPa and a compressive strength of(1777±27)MPa.However,the presence of Ni segregation and holes produced by the LPBF processing adversely affected the corrosion resistance of the alloy.展开更多
Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructur...Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified.It is found that ferrite side plates form preceding to acicular ferrites,although the starting temperature of respective component decreases as the cooling rate is raised.In particular,the growth rate of acicular ferrite is measured to increase significantly,rising from 30.4μm/s at a cooling rate of 3 K/s to 109.0μm/s at 15 K/s,driven primarily by an ever-increasing degree of undercooling.These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations,which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.展开更多
The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning cal...The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, includingTB(Al7Cu4Li),θ(Al2Cu),R(Al5CuLi3) andS(Al2CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, theTB,θ,R,S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al7Cu2Fe and AlCuMn phases, and the size of Al7Cu2Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.展开更多
The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive spectr...The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive spectrometry（EDS）,X-ray diffraction（XRD） and differential scanning calorimetry（DSC）.The results show that severe dendritic segregation exists in Al-Zn-Cu-Mg-Sc-Zr alloy ingot.There are a lot of eutectic phases at grain boundary and the distribution of the main elements varies periodically along interdendritic region.The main eutectic phases at grain boundary are Al7Cu2Fe phase and T（Al2Mg3Zn3）.The residual phases are dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time,which can be described by a constitutive equation in exponential function.The overburnt temperature of the alloy is 473.9 ℃.The optimum parameters of homogenization are 470 ℃ and 24 h,which is consistent with the result of homogenization kinetic analysis.展开更多
As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K...As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K and 873 K, respectively. The influence of solution treatment and aging on microstructural evolution and mechanical behavior of NiTi alloy was systematically investigated by transmission electron microscopy （TEM）, high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM） and compression test. Solution treatment contributes to eliminating the Ti2Ni phase in the as-received NiTi sample, in which the TiC phase is unable to be removed. Solution treatment leads to ordered domain of atomic arrangement in NiTi alloy. In all the aged NiTi samples, the Ni4Ti3 precipitates, the R phase and the B2 austenite coexist in the NiTi matrix at room temperature, while the martensitic twins can be observed in the NiTi samples aged at 873 K. In the NiTi samples aged at 573 and 723 K, the fine and dense Ni4Ti3 precipitates distribute uniformly in the NiTi matrix, and thus they are coherent with the B2 matrix. However, in the NiTi sample aged at 873 K, the Ni4Ti3 precipitates exhibit the very inhomogeneous size, and they are coherent, semi-coherent and incoherent with the B2 matrix. In the case of aging at 723 K, the NiTi sample exhibits the maximum yield strength, where the fine and homogeneous Ni4Ti3 precipitates act as the effective obstacles against the dislocation motion, which results in the maximum critical resolved shear stress for dislocation slip.展开更多
The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion（ECAE） during semisolid isothermal treatment（SSIT） was investigated by means of optical metalloscopy and image an...The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion（ECAE） during semisolid isothermal treatment（SSIT） was investigated by means of optical metalloscopy and image analysis equipment.The process involved application of ECAE to as-cast alloy at 310 ℃ to induce strain prior to heating in the semisolid region for different time lengths.The results show that extrusion pass,isothermal temperature and processing route have an influence on microstructural evolution of predeformed AZ61 magnesium alloy during SSIT.With the increase of extrusion pass,the solid particle size is reduced gradually.When isothermal temperature increases from 530 ℃ to 560 ℃,the average particle size increases from 22 μm to 35 μm.When isothermal temperature is 575 ℃,the average particle size decreases.The particle size of microstructure of AZ61 magnesium alloy predeformed by ECAE at BC during SSIT is the finest.展开更多
Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg...Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg17Al12 and the precipitated β-Mg17Al12 phases appeared in the as-cast alloy. The β-Mg17Al12 phase dissolved into α-Mg matrix mostly and the structure kept fine after the optimized homogenization treatment at 380 °C for 15 h. Dynamic recrystallization and consequent grain refinement occurred during extrusion. The banded β-Mg17Al12 precipitates paralleled to the extrusion direction were observed after ageing treatment. The banded precipitation should be attributed to the solidification segregation which was elongated during the subsequent extrusion. Furthermore, the effects of temperature, holding time of homogenization and ageing treatment, and extrusion processing parameters on the microstructural evolution of AZ91 alloy were also discussed in details according to the experimental results.展开更多
The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray...The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） and differential scanning calorimetry （DSC）. The results show that serious dendritic segregation exists in studied alloy ingot. There are many eutectic phases with low melting-point at grain boundary and the distribution of main elements along interdendritic region varies periodically. Elements Zn, Mg and Cu distribute unevenly from grain boundary to the inside of alloy. With increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into matrix α（Al） gradually during homogenization treatment, all elements become more homogenized. The overburnt temperature of studied alloy is 476.7 °C. When homogenization temperature increases to 480 °C, some spherical phases and redissolved triangular constituents at grain boundaries can be easily observed. Combined with microstructural evolution and differential scanning calorimeter, the optimum homogenization parameter is at 470 °C for 24 h.展开更多
The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ran...The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ranging from 0.001 to 10 s -1 .The steady flow stress increased with increasing the strain rate or decreasing the deformation temperature,which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of 150.25 kJ/mol.The tendency of dynamic recrystallization enhanced at high deforming temperatures and low strain rates,which corresponded to low Z values.With decreasing Z value,the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly,the subgrain size increased and the dislocation density decreased.展开更多
基金financially supported by the National Basic Research Program of China (No.G2011CB012806)
文摘The microstructural evolution of AA7055 aluminum alloy under dynamic impact loading with the strain rate of 1.3 × 10^4 s^-1 controlled by a split Hopkinson pressure bar was investigated, and compared with that under quasi-static mechanical loading in compression with strain rate of 1.0 × 10^-3 s^-1. The quasi-static-compressed sample exhibited equiaxed dislocation cells, which were different from the elongated and incomplete dislocation cells for the alloy undergoing dynamic compression. The high strain-rate compression also induced the formation of localized shear bands in which the recrystallizations characterized as fine equiaxed grains were observed. The microstructural evolutions under both quasi-static and dynamic compressions are rationalized in terms of the dislocation cell model combined with the dislocation kinetics, in addition to the adiabatic temperature rise in shear bands at high strain rate.
基金funded by National Basic Research Program of China(2010CB630800,2015CB921700)National Natural Science Foundation of China(51671112,51471096,51390471,11374174)+2 种基金National Key Research and Development Program(2016YFB0700402)National Key Scientific Instruments and Equipment Development Project(2013YQ120353)Tsinghua University(20141081200)
文摘The microstructural evolutions of 5Mn steel during various heat treatments have been investiga- ted by in-situ transmission electron microscopy （TEM）. The specimen of 5Mn steel was pre- pared using focused ion beam （FIB） milling, which allowed the selection of specific morphology of interest prior to the in-situ observation, The complete austenization at 800 ℃ was verified at the atomic scale by minimizing thermal expansion and sample drift in a heating holder based on micro-electro-mechanical-systems. During annealing at 650 ℃, the formation of reverted austen- ite was dynamically observed, while the morphologies of austenite laths of 5Mn steel after in-situ heating were quite similar to that after ex-situ intereritical annealing. During annealing at 500 ℃, the morphological evolution of cementite and associated Mn diffusion were investigated. It was demonstrated that a combination of FIB sampling and high temperature in-situ TEM enables us to probe the morphological evolution and elemental diffusion of specific areas of interest in steel at high spatial resolution.
基金supported by the National Natural Science Foundation(No.52101128)the Jiangsu Provincial Key Research and Development Program(No.BE023059)+1 种基金Postdoctoral Science Foundation(No.2022M710021)and the Northeastern University Postdoctoral Research Fund(No.20220202)of China。
文摘High manganese steels(HMS),known for their exceptional strength-ductility balance,are increasingly utilized in dynamic loading applications.This review examines the effects of strain rate on their mechanical properties and microstructural evolution,focusing on strain rate hardening,adiabatic heating softening,and dynamic strain aging(DSA).The influence of strain rate on yield strength,ultimate tensile strength,strain hardening,and ductility is discussed,highlighting both positive and negative sensitivities across different alloy compositions and strain rate regimes.The strain rate response of various deformation mechanisms,including deformation twinning,dislocation slip,and phase transformation,is examined alongside their influence on microstructural evolution,alloy design,and industrial applications.The intricate role of DSA is also analyzed,emphasizing its contribution to strain rate sensitivity.To optimize HMS for dynamic environments,future research should focus on advanced modeling and processing techniques,in-situ characterization methods,and a deeper understanding of thermally activated processes and stacking fault energy-controlled mechanisms.This review provides insights into strain rate effects,guiding alloy design,and technological advancements of the new HMS.
基金Funded by the Central Government-Guided Local Development Fund Project(No.YDZJSX2025D042)the Key R&D Program of Shanxi Province(No.202202150401018)+1 种基金the Basic Research Program of Shanxi Province(No.20210302124220)the State Key Laboratory of CAD/CG of Zhejiang University(No.A2325)。
文摘This study systematically investigated the microstructural evolution of binary Ni-Cu alloys(Cu55Ni45,Cu60Ni40,and Ni65Cu35)under deep undercooling conditions.The controlled rapid solidification experiments combined with optical microscopy and electron backscatter diffraction(EBSD)analysis demonstrate that increasing undercooling(ΔT)can induce a consistent sequence of microstructural transitions:coarse dendrites,fine equiaxed grains(first refinement),oriented fine dendrites,and fine equiaxed grains(second refinement).Two distinct grain refinement events are identified,with critical undercooling thresholds(ΔT)dependent on composition:increasing Cu content increases the critical undercoolingΔT*required for the second refinement(Cu55Ni45:227 K;Cu60Ni40:217 K;Ni65Cu35:200 K).The BCT(Bridgman Crystal Growth)model quantitatively elucidates this behavior,revealing a shift from solute-diffusion-dominated growth at low undercooling to thermally dominated diffusion at high undercooling(ΔT).Crucially,refined grains at high undercooling exhibit smaller sizes(10μm)and higher uniformity than those at low undercooling(20μm).These findings provide fundamental insights into non-equilibrium solidification mechanisms and establish a foundation for designing high-performance Ni-Cu alloys via deep undercooling processing.
基金Project(52274369)supported by the National Natural Science Foundation of China。
文摘High-purity silver(Ag)is extensively utilized in electronics,aerospace,and other advanced industries due to its excellent thermal conductivity,electrical conductivity,and machinability.However,the prohibitive material cost poses substantial challenges for optimizing thermal processing parameters through repetitive experimental trials.In this work,hot compression experiments on high-purity silver were conducted using a Gleeble-3800 thermal simulator.The high temperature deformation behaviors,dynamic recovery(DRV)and dynamic recrystallization(DRX)of high-purity silver were studied by constructing an Arrhenius constitutive equation and developing thermal processing maps.The results show that plastic instability of high-purity silver occurs at high strain rates and the optimized hot processing parameters are the strain rate below 0.001 s^(−1) and the temperature of 340−400℃.Microstructural observations exhibit that DRV prefers to occur at lower deformation temperatures(e.g.,250℃).This is attributed to the low stacking fault energy of high-purity silver,which facilitates the decomposition of dislocations into partial dislocations and promotes high-density dislocation accumulation.Furthermore,DRX in high-purity silver becomes increasingly pronounced with increasing deformation temperature and reaches saturation at 350℃.
基金Funded by the National Natural Science Foundation of China(No.51905215)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.SJCX231233)。
文摘The 304 austenitic stainless steel was processed by high-pressure torsion(HPT)at room temperature with 10,20,and 30 rotations under a pressure of 3 GPa and a rotation speed of 1 r/min.The phase transformation and microstructural evolution of 304 stainless steel after HPT were investigated by X-ray diffraction(XRD)analysis,electron backscatter diffraction(EBSD)analysis,transmission electron microscopy(TEM),nanoindentation test and differential scanning calorimetry(DSC)analysis.The experimental results show that HPT causes elongated nanocrystalline grains of 25 nm width along the torsion direction.After 10 turns of HPT,the deformation-induced martensitic transformation is completed and the hardness increases from 3 GPa to 8.5 GPa at the edge of the disc.However,a local reverse phase transformation from martensite to austenite is observed in the peripheral regions of the sample after 30 turns of HPT,leading to a higher volume fraction of austenite,and the hardness of the sample also decreases accordingly.
基金supported by the National Key Research and Development Program of China(No.2022YFC2406000)the Guangdong Basic and Applied Basic Research Foundation(2024A1515011024)+5 种基金the Guangzhou Science and Technology Project(2024A04J4943)the Guangdong Academy of Sciences Development Special Fund Project(2022GDASZH-2022010107)the Guangdong province Science and Technology Plan Projects(2023B1212120008,2023B1212060045)the GDAS Projects of International cooperation platform of Science and Technology(2022GDASZH-2022010203-003)Special Support Foundation of Guangdong Province(2023TQ07Z559)Shenzhen Basic Research Project(JCYJ20210324120001003 and JCYJ20220531091802006)。
文摘To clarify the densification behavior,deformation response and strengthening mechanisms of selective laser melted(SLM)Mg-RE alloys,this study systematically investigates a representative WE43 alloy via advanced material characterization techniques.A suitable laser output mode fell into the transition mode,allowing for the fabrication of nearly full-density samples(porosity=0.85±0.021%)with favorable mechanical properties(yield strength=351 MPa,ultimate tensile strength=417 MPa,the elongation at break=6.5%and microhardness=137.9±6.15 HV_(0.1))using optimal processing parameters(P=80 W,v=250 mm/s and d=50μm).Viscoplastic self-consistent analysis and transmission electron microscopy observations reveal that the plastic deformation response of the SLM Mg-RE alloys is primarily driven by basal and prismatic slips.Starting from a random texture before deformation(maximum multiple of ultimate density,Max.MUD=3.95),plastic stretching led the grains to align with the Z-axis,finally resulting in a{0001}<1010>texture orientation after fracture(Max.MUD=8.755).Main phases of the SLM state are mainly composed ofα-Mg,Mg_(24)Y_(5) andβ'-Mg_(41)Nd_(5),with an average grain size of only 4.27μm(about a quarter of that in the extruded state),resulting in a favorable strength-toughness ratio.Except for the nano-β'phase and semi-coherent Mg_(24)Y_(5) phase(mismatch=16.12%)around the grain boundaries,a small amount of nano-ZrO_(2) and Y_(2)O_(3) particles also play a role in dispersion strengthening.The high mechanical properties of the SLM state are chiefly attributed to precipitation hardening(44.41%),solid solution strengthening(34.06%)and grain boundary strengthening(21.53%),with precipitation hardening being predominantly driven by dislocation strengthening(67.77%).High-performance SLM Mg-RE alloy components were manufactured and showcased at TCT Asia 2024,receiving favorable attention.This work underscores the significant application potential of SLM Mg-RE alloys and establishes a strong foundation for advancing their use in the biomedical fields.
文摘Ag-Cu alloys are extensively used in sliding electric contacts due to their superior electrical conductivity,but their limited wear resistance reduces component longevity.Surface severe plastic deformation(SSPD)has emerged as a promising method to enhance wear resistance and reduce friction of metals without altering the matrix composition.In this study,an Ag-20 wt.%Cu alloy was subjected to SSPD for various durations,with the aim of improving tribological performance.The microstructure,hardness,and current-carrying tribological performance under different currents were systematically investigated,along with an exploration of the underlying mechanisms.The results show that in addition to introducing a high density of dislocations on the surface,SSPD also encourages the formation of(111)texture,and particularly disperses the initially long strips of Curich phase into short strips and fine particles.It promotes a tribo-film composed primarily of a mixture of Cu_(2)O and CuO that forms on the worn surface of the surface-treated sample under the 1 A current,thus significantly reducing the friction coefficient and electrical noise.Under the 10 A current,the sample treated for 60 min possesses the optimal friction coefficient(0.429),wear rate(0.791×10^(−6)mm^(3)/(N m)),and electrical noise(0.240 V).In contrast to the Ag/Cu layered structure observed on the worn subsurface of the untreated sample,a single-phase Ag(Cu)solid solution forms on the worn subsurface of the 60-min treated sample,which improves the current-carrying tribological performance.This work provides valuable insights for the development and application of electrical contact alloys with excellent performance.
基金supported by the National Natural Science Foundation of China(Grant Nos.52074229,52371035)the Key R&D Plan of Sichuan Province(Grant No.SC2022A1C01J)the State Key Lab of Advanced Metals and Materials(Grant No.2020-ZD05).
文摘The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.
基金supported by Special Fund for the Development of 1500-Meter Subsea Christmas Trees and Control Systems.
文摘In order to develop a marine engineering material with excellent mechanical properties and corrosion resistance,a novel non-equiatomic Co_(1.5)CrFeNi_(1.5)Ti_(0.6)high-entropy alloy(HEA)was fabricated through mechanical alloying and spark plasma sintering.The results revealed that the sintering temperature significantly affected the microstructure and phase composition of the HEA owing to the diffusion rate,homogenization,and sluggish diffusion effect of metal atoms.At sintering temperatures below 1050℃,HEA mainly consisted of face-centered cubic(FCC),Ni_(3)Ti(ε),Ni_(2.67)Ti_(1.33)(R),and Fe-Cr(σ)phases.The microstructure of alloy comprised coarse dendritic crystals,whose content and size gradually decreased with increasing sintering temperature.However,the HEA sintered above 1100℃contained only fine equiaxed crystals.HEA sintered at 1100℃featured only the FCC solid solution,while theε-phase precipitated at temperatures above 1150℃.At a sintering temperature of 1050℃,the alloy microstructure consisted of short rod-like dendrites and fine equiaxed crystals.This alloy achieved the highest yield strength of 1198.71 MPa owing to the effects of precipitation strengthening and grain boundary strengthening.Meanwhile,HEA sintered above 1050℃exhibited significantly improved corrosion resistance.Considering the microstructure,mechanical,and corrosion properties,1050℃was identified as the optimal sintering temperature for Co_(1.5)CrFeNi_(1.5)Ti_(0.6)HEA.
基金supported by the National Science and Technology Major Project of China(2017-VI-0018-0090).
文摘Isothermal compression tests were used to establish constitutive models of the hot deformation of GH4742 superalloy. The microstructural evolution of double cone samples with large strain gradients during hot deformation and subsequent solvus treatment was studied. The results showed that the grain size during dynamic recrystallization (DRX) did not exceed 6 μm, and the volume fraction during DRX did not exceed 45% at all reduction rates when it deformed below the γ′ solvus temperature (1080 ℃). When deformed near the γ′ solvus temperature (1110 ℃), the volume fraction and grain size increase significantly during DRX due to the dissolution and coarsening of some γ′ precipitates. When deformed above the γ′ solvus temperature (1140 ℃), even at a high reduction rate of 20 mm/s, the volume fraction during DRX reached 75%, and the grain size during DRX increased to 25 μm. At a reduction rate of 0.5 mm/s, the grain size during DRX reached 65 μm. When the sample is deformed below the γ′ solvus temperature (1080 ℃), stored strain energy accumulates in the sample, which is beneficial for the development of post dynamic recrystallization during subsequent subsolvus heat treatment, resulting in a noticeable increase in the recrystallization volume fraction. The recrystallization volume fraction of predeformed samples deformed at 1110 and 1140 ℃, followed by subsolvus heat treatment, was almost unchanged. The microstructure of the predeformed sample following supersolvus heat treatment consists of coarse equiaxed grains.
基金supported by the National Natural Science Foundation of China(Nos.12374022,U23A20540)the Technological Base Project,China(No.JSHS2022206A001)+2 种基金the Natural Science Foundation of Hunan Province for Distinguished Young Scholars,China(No.2023JJ10075)the Scientific and Technological Project of Yunnan Precious Metals Laboratory,China(No.YPML-202305247)the Central South University Research Program of Advanced Interdisciplinary Studies,China(No.2023QYJC038).
文摘The microstructural evolution,mechanical properties,and corrosion behavior of Ti-12Ni(wt.%)specimens produced by laser powder bed fusion(LPBF)using various volume energy density(VED)processing parameter values were investigated.The results showed that the alloy prepared at a low VED of 67 J/mm^(3)consisted of near-βgrains.At a VED of 133 J/mm^(3),the alloy exhibited coarse primary Ti2Ni and fine eutectoid structure.This eutectoid structure consisted ofαlaths and two types of nanoscale Ti2Ni,one in the form of short rods and the other with a spherical morphology.Further increase of the VED to 267 J/mm^(3)led to coarsening of the eutectoid structure.The dispersed Ti2Ni nanoparticles exhibited a significant strengthening effect.The alloy produced at a VED of 133 J/mm^(3)showed the greatest strength with a nanohardness of(7.8±0.1)GPa and a compressive strength of(1777±27)MPa.However,the presence of Ni segregation and holes produced by the LPBF processing adversely affected the corrosion resistance of the alloy.
基金support from the National Natural Science Foundation of China(Grant Nos.U20A20277 and 52350610226)National Key Research and Development Plan of China(Grant No.2022YFE0123300).
文摘Microstructural evolution features have been systematically investigated for the weld metal of EH36 shipbuilding steel under an in situ confocal scanning laser microscope.The influence of cooling rate on microstructural changes during the transformation from austenite to ferrite has been clarified.It is found that ferrite side plates form preceding to acicular ferrites,although the starting temperature of respective component decreases as the cooling rate is raised.In particular,the growth rate of acicular ferrite is measured to increase significantly,rising from 30.4μm/s at a cooling rate of 3 K/s to 109.0μm/s at 15 K/s,driven primarily by an ever-increasing degree of undercooling.These findings highlight the critical role of cooling rate in dictating the sequence and growth rate of microstructural transformations,which is crucial for optimizing welding processes to obtain desired microstructures while avoiding the formation of deleterious components.
基金Project(2013JSJJ0001)supported by Teachers’Research Found,ChinaProject(2013AA032401)supported by the National High Technology Research and Development Program of ChinaProject supported by the Nonferrous Metal Oriented Advanced Structural Materials and Manufacturing Cooperative Innovation Center,China
文摘The microstructural evolution of a Mg, Ag and Zn micro-alloyed Al?3.8Cu?1.28Li (mass fraction, %) alloy ingot during two-step homogenization was examined in detail by optical microscopy (OM), differential scanning calorimetry (DSC), electron probe micro-analysis (EPMA) and X-ray diffraction (XRD) methods. The results show that severe dendritic segregation exists in the as-cast ingot. There are many secondary phases, includingTB(Al7Cu4Li),θ(Al2Cu),R(Al5CuLi3) andS(Al2CuMg) phases, and a small amount of (Mg+Ag+Zn)-containing and AlCuFeMn phases. The fractions of intermetallic phases decrease sharply after 2 h of second-step homogenization. By prolonging the second-step homogenization time, theTB,θ,R,S and (Mg+Ag+Zn)-containing phases completely dissolve into the matrix. The dendritic segregation is eliminated, and the homogenization kinetics can be described by a constitutive equation in exponential function. However, it seems that the AlCuFeMn phase is separated into Al7Cu2Fe and AlCuMn phases, and the size of Al7Cu2Fe phase exhibits nearly no change when the second-step homogenization time is longer than 2 h.
基金Project (2006AA03Z523) supported by the National High-tech Research and Development Program of China
文摘The microstructural evolution and composition distribution of an Al-Zn-Cu-Mg-Sc-Zr alloy during homogenization were investigated by optical microscopy（OM）,scanning electron microscopy（SEM）,energy dispersive spectrometry（EDS）,X-ray diffraction（XRD） and differential scanning calorimetry（DSC）.The results show that severe dendritic segregation exists in Al-Zn-Cu-Mg-Sc-Zr alloy ingot.There are a lot of eutectic phases at grain boundary and the distribution of the main elements varies periodically along interdendritic region.The main eutectic phases at grain boundary are Al7Cu2Fe phase and T（Al2Mg3Zn3）.The residual phases are dissolved into the matrix gradually during homogenization with increasing temperature and prolonging holding time,which can be described by a constitutive equation in exponential function.The overburnt temperature of the alloy is 473.9 ℃.The optimum parameters of homogenization are 470 ℃ and 24 h,which is consistent with the result of homogenization kinetic analysis.
基金Project (51071056) supported by the National Natural Science Foundation of ChinaProjects (HEUCF121712,HEUCF201317002) supported by the Fundamental Research Funds for the Central Universities of China
文摘As-received nickel-titanium （NiTi） shape memory alloy with a nominal composition of Ni50.9Ti49.1 （mole fraction,%） was subjected to solution treatment at 1123 K for 2 h and subsequent aging for 2 h at 573 K, 723 K and 873 K, respectively. The influence of solution treatment and aging on microstructural evolution and mechanical behavior of NiTi alloy was systematically investigated by transmission electron microscopy （TEM）, high resolution transmission electron microscopy （HRTEM）, scanning electron microscopy （SEM） and compression test. Solution treatment contributes to eliminating the Ti2Ni phase in the as-received NiTi sample, in which the TiC phase is unable to be removed. Solution treatment leads to ordered domain of atomic arrangement in NiTi alloy. In all the aged NiTi samples, the Ni4Ti3 precipitates, the R phase and the B2 austenite coexist in the NiTi matrix at room temperature, while the martensitic twins can be observed in the NiTi samples aged at 873 K. In the NiTi samples aged at 573 and 723 K, the fine and dense Ni4Ti3 precipitates distribute uniformly in the NiTi matrix, and thus they are coherent with the B2 matrix. However, in the NiTi sample aged at 873 K, the Ni4Ti3 precipitates exhibit the very inhomogeneous size, and they are coherent, semi-coherent and incoherent with the B2 matrix. In the case of aging at 723 K, the NiTi sample exhibits the maximum yield strength, where the fine and homogeneous Ni4Ti3 precipitates act as the effective obstacles against the dislocation motion, which results in the maximum critical resolved shear stress for dislocation slip.
基金Project(51075099) supported by the National Natural Science Foundation of ChinaProject(E201038) supported by Natural Science Foundation of the Heilongjiang Province,China+3 种基金Project(20090460884) supported by the China Postdoctoral Science Foundation Project(SKLSP201121) supported by the Fund of the State Key Laboratory of Solidification Processing in NWPU,ChinaProject (2011RFQXG010) supported by the Harbin City Young Scientists Foundation,ChinaProject(LBH-T1102) supported by the Specially Postdoctoral Science Foundation of Heilongjiang Province,China
文摘The microstructural evolution of AZ61 magnesium alloy predeformed by equal channel angular extrusion（ECAE） during semisolid isothermal treatment（SSIT） was investigated by means of optical metalloscopy and image analysis equipment.The process involved application of ECAE to as-cast alloy at 310 ℃ to induce strain prior to heating in the semisolid region for different time lengths.The results show that extrusion pass,isothermal temperature and processing route have an influence on microstructural evolution of predeformed AZ61 magnesium alloy during SSIT.With the increase of extrusion pass,the solid particle size is reduced gradually.When isothermal temperature increases from 530 ℃ to 560 ℃,the average particle size increases from 22 μm to 35 μm.When isothermal temperature is 575 ℃,the average particle size decreases.The particle size of microstructure of AZ61 magnesium alloy predeformed by ECAE at BC during SSIT is the finest.
基金Project (2011A090200104) supported by Guangdong Science and Technology Special Projects, China
文摘Microstructural evolution of AZ91 magnesium alloy was investigated during homogenizing annealing treatment, hot extrusion and ageing treatment, respectively. The results exhibited that both the divorced eutectic β-Mg17Al12 and the precipitated β-Mg17Al12 phases appeared in the as-cast alloy. The β-Mg17Al12 phase dissolved into α-Mg matrix mostly and the structure kept fine after the optimized homogenization treatment at 380 °C for 15 h. Dynamic recrystallization and consequent grain refinement occurred during extrusion. The banded β-Mg17Al12 precipitates paralleled to the extrusion direction were observed after ageing treatment. The banded precipitation should be attributed to the solidification segregation which was elongated during the subsequent extrusion. Furthermore, the effects of temperature, holding time of homogenization and ageing treatment, and extrusion processing parameters on the microstructural evolution of AZ91 alloy were also discussed in details according to the experimental results.
基金Project (2012CB619503) supported by the National Basic Research Program of China
文摘The microstructural evolution of Al-Zn-Mg-Zr alloy with trace amount of Sc during homogenization treatment was studied by means of metallographic analysis, scanning electron microscopy （SEM）, energy dispersive X-ray （EDX） and differential scanning calorimetry （DSC）. The results show that serious dendritic segregation exists in studied alloy ingot. There are many eutectic phases with low melting-point at grain boundary and the distribution of main elements along interdendritic region varies periodically. Elements Zn, Mg and Cu distribute unevenly from grain boundary to the inside of alloy. With increasing the homogenization temperature or prolonging the holding time, the residual phases are dissolved into matrix α（Al） gradually during homogenization treatment, all elements become more homogenized. The overburnt temperature of studied alloy is 476.7 °C. When homogenization temperature increases to 480 °C, some spherical phases and redissolved triangular constituents at grain boundaries can be easily observed. Combined with microstructural evolution and differential scanning calorimeter, the optimum homogenization parameter is at 470 °C for 24 h.
基金Project(2012CB619503)supported by the High-tech Research and Development Program of China
文摘The hot deformation behavior of Al-Zn-Mg-0.25Sc-Zr alloy and its microstructural evolution were investigated by isothermal axisymmetric hot compression tests at temperatures from 340 to 500°C and strain rates ranging from 0.001 to 10 s -1 .The steady flow stress increased with increasing the strain rate or decreasing the deformation temperature,which can be described by a hyperbolic-sine constitutive equation with the deformation activation energy of 150.25 kJ/mol.The tendency of dynamic recrystallization enhanced at high deforming temperatures and low strain rates,which corresponded to low Z values.With decreasing Z value,the main softening mechanism of the alloy transformed from dynamic recovery to dynamic recrystallization, correspondingly,the subgrain size increased and the dislocation density decreased.
