For the purpose of investigating the microstructure evolution and deformation behavior of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)apparatus was used under high strain rates from 755 s^(...For the purpose of investigating the microstructure evolution and deformation behavior of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)apparatus was used under high strain rates from 755 s^(-1) to 2826 s^(-1) in the present work at room temperature.The microstructures of extruded Mg-Gd-Y Magnesium alloy under different strain rates and along different compression directions were observed by metallographic microscope.The results show that,microstructures of extruded Mg-Gd-Y Magnesium alloy along ED,TD and ND compression directions are sensitive to strain rates.The amount of twins firstly increases and then decreases with strain rates being increased,and the recrystal grains increase and grow up.When the strain rate reaches 2500 s^(-1),the adiabatic shear band(ASB)begins to form.The formation process of the adiabatic shear band can be divided into three stages.In the first stage,under the impact load a great deal of twins form and the deformation mechanism is twinning.In the second stage,discontinuous ASB forms due to twins adjusting the directions of located grains and the deformation mechanisms are twinning and non-basal slip.In the last stage,non-basal slip turns to basal slip and continuous ASB forms.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation.展开更多
The application of some semi-solid forming magnesium alloys is restricted due to their weak mechanical properties. To improve the mechanical properties, it is necessary to research the regularity and theory of semi-so...The application of some semi-solid forming magnesium alloys is restricted due to their weak mechanical properties. To improve the mechanical properties, it is necessary to research the regularity and theory of semi-solid microstructure evolution of the alloy. In this study, microstructure evolution of ZA72 alloy during the partial remelting, and the effect of holding temperature and holding time on the semi-solid microstructure evolution of ZA72 magnesium alloy were investigated by means of OM, SEM and EDS analysis. The results indicate that the microstructure with small and spheroidal semi-solid particles which are available for thixo-forming can be obtained using proper heating parameters. After being isothermally treated at between 580 and 610 ℃ for 30 min, the equivalent size and shape factor of primary solid phase of ZA72 alloy decrease gradually, while the liquid volume fraction increases. When isothermally treated at 600 ℃ and held for different times from 15 to 60 min, with the increase of holding time, the equivalent size of primary particles decreases at first and then increases gradually; while the shape factor decreases gradually. The best heat treatment parameters in this experiment are to hold at 610 ℃ for 30 min. Compared with as-cast ZA72 alloy, the sizes of the eutectic phase and second α-Mg phase obtained in semi-solid state are smaller due to the higher solidification rate and the higher under-cooling degree than as-cast state. These decrease the fracture probability during tensile stress and improve the properties of the ZA72 alloy by semi-solid forming.展开更多
Al-Si metal matrix composites (MMCs) reinforced with 20 vol.% alumina-silicate shot fibers (Al2O3-SiO2(sf)) were fabricated by an infiltration squeeze method. Pure Pr metal was added into these composites. The effect ...Al-Si metal matrix composites (MMCs) reinforced with 20 vol.% alumina-silicate shot fibers (Al2O3-SiO2(sf)) were fabricated by an infiltration squeeze method. Pure Pr metal was added into these composites. The effect of Pr addition on the microstructure evolution of Al-Si MMCs was investigated by SEM,TEM,and EDS. Pr addition is favorable to make uniform microstructures with the modified eutectic Si crystal. PrAlSi phase with high contents of Pr and Si is observed on the interface between the fiber and the matrix. The addition of Pr promotes interface SiO2 reduction,and SiO2 comes from the crystallization of Al2O3-SiO2 short fibers.展开更多
The formability of magnesium alloys at ambient temperature can be enhanced by alloying additions such as Ca and RE elements,which is ascribed to the weakened basal texture.To produce magnesium alloy sheets with excell...The formability of magnesium alloys at ambient temperature can be enhanced by alloying additions such as Ca and RE elements,which is ascribed to the weakened basal texture.To produce magnesium alloy sheets with excellent comprehensive performance,the evolution of texture characterization during fabrication process and subsequent effect of texture on mechanical properties are vital controlling factors.In this investigation,three experimental Mg-3Al series alloys were hot rolled and annealed to sheets with 1 mm thickness.The microstructure evolution during rolling and annealing process was investigated.Furthermore,the influence of texture on tensile properties along different tensile directions was also studied.The results show that weakened basal texture and refined grains were achieved with the co-addition of Ca and RE element.However,strengthening of mechanical properties wasn't obtained.During hot rolling process,microstructure was refined,second phase particles broken,and basal texture was increased.While basal texture was weakened during annealing process.Recrystallization behavior influenced by formation of second phase was dominated to attenuate basal texture.Tensile deformation behavior was controlled by basal slip and followed Schmid factor criterion.Moreover,the weakened basal texture and activation of non-basal slips during hot rolling process can contribute to diminish the anisotropy of tensile properties.展开更多
In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the in...In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the interactive effects of material hardening, recovery and dynamic recrystallization(DRX) on the characteristic deformation behavior were considered by incorporating the evolution laws of viscoplastic flow, dislocation activities, DRX nucleation and boundary migration in a coupled manner. The model parameters were calibrated based on the experimental data analysis and genetic algorithm(GA) based objective optimization. The predicted flow stress, DRX fraction and average grain size match well with experimental results. The proposed model was embedded in the finite element(FE) software DEFORM-3 D via user defined subroutine to simulate the hot compression and equal channel angular extrusion(ECAE) processes. The heterogeneous microstructure distributions at different deformation zones and the dislocation density evolution with competitive deformation mechanisms were captured.This study can provide a theoretical solution for the hot working problems of magnesium alloy.展开更多
High strength steel products with good ductility can be produced via Q&P hot stamping process,while the phase transformation of the process is more complicated than common hot stamping since two-step quenching and...High strength steel products with good ductility can be produced via Q&P hot stamping process,while the phase transformation of the process is more complicated than common hot stamping since two-step quenching and one-step carbon partitioning processes are involved.In this study,an integrated model of microstructure evolution relating to Q&P hot stamping was presented with a persuasively predicted results of mechanical properties.The transformation of diffusional phase and non-diffusional phase,including original austenite grain size individually,were considered,as well as the carbon partitioning process which affects the secondary martensite transformation temperature and the subsequent phase transformations.Afterwards,the mechanical properties including hardness,strength,and elongation were calculated through a series of theoretical and empirical models in accordance with phase contents.Especially,a modified elongation prediction model was generated ultimately with higher accuracy than the existed Mileiko’s model.In the end,the unified model was applied to simulate the Q&P hot stamping process of a U-cup part based on the finite element software LS-DYNA,where the calculated outputs were coincident with the measured consequences.展开更多
The effect of self-reactivation on the CO_(2) capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM...The effect of self-reactivation on the CO_(2) capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM and N_2 adsorption analysis to explain the self-reactivation mechanism.The results show that the CaO in the spent sorbent discharged from the calciner absorbs the vapor in the air to form Ca(OH)_(2) and further Ca(OH)_(2)·2 H_(2) O under environmental conditions,during which process the CO_(2) capture capacity of the spent sorbent can be self-reactivated.The microstructure of the spent sorbent is improved by the self-reactivation process,resulting in more porous microstructure,higher BET surface area and pore volume.Compared with the calcined spent sorbent that has experienced 20 cycles,the pore volume and BET surface area are increased by 6.69 times and 56.3% after self-reactivation when φ=170%.The improved microstructure makes it easier for the CO_(2) diffusion and carbonation reaction in the sorbent.Therefore,the CO_(2) capture capacity of the spent sorbent is enhanced by self-reactivation process.A self-reactivation process coupled with calcium looping process was proposed to reuse the discharged spent calcium based sorbent from the calciner.Higher average carbonation conversion and CO_(2) capture efficiency can be achieved when self-reactivated spent sorbent is used as supplementary sorbent in the calciner rather than fresh CaCO_(3) under the same conditions.展开更多
Metal additive manufacturing technology has been widely used in prototyping,parts manufacturing and repairing.Metal additive manufacturing is a multi-scale and multi-physical coupling process with complex physical phe...Metal additive manufacturing technology has been widely used in prototyping,parts manufacturing and repairing.Metal additive manufacturing is a multi-scale and multi-physical coupling process with complex physical phenomena of heat and mass transfer and microstructure evolution.It is hard to directly observe the dynamic behavior and microstructure evolution of molten pool during additive manufacturing.Therefore,numerical simulation of additive manufacturing process is significant since it can efficiently and pertinently predict and analyze the physical phenomena in the process of metal additive manufacturing,and provide a reference for technological parameters selection.In this review,the research progress of numerical simulation of metal additive manufacturing is discussed.Various aspects of numerical simulation models are reviewed,including:(1)Introduction of basic control method and physical description of numerical simulation models;(2)Comparison of various heat and mass transfer models based on different physical assumptions(heat conduction model;heat flux coupling model;discrete powder particle heat flux coupling model);(3)Applications of various microstructure evolution models[phase field(PF),cellular automata(CA),and Monte Carlo(MC)].Finally,the development trend of numerical simulation of metal additive manufacturing,including the thermal-flow-solid coupling model and deep learning for numerical model,is analyzed.展开更多
Mechanical properties and microstructure evolution of Mg-8.4 wt pct Li alloy have been investi- gated. The superplastic elongation-to-failure 920% at 573 K and initial strain rate of 5 × 10-4 s-1 at low nominal s...Mechanical properties and microstructure evolution of Mg-8.4 wt pct Li alloy have been investi- gated. The superplastic elongation-to-failure 920% at 573 K and initial strain rate of 5 × 10-4 s-1 at low nominal stress 2 MPa has been demonstrated. It was shown through optical microstructure that the average grain sizes at gauge length section before and after superplastic tension and at grip section were 7.5 μm, 31.7 μm and 20 μm respectively, indicating significant deformation induced grain growth and static grain growth. Comparison of experiment data with published data for superplastic Mg-Li alloys shows that fine grain size and about 50 to 50 phase ratio contribute to achieving the largest superplasticity. Some related research works in other alloys are compiled and further evidences to such theoretic argument are provided.展开更多
Regarding the as-cast Mg-9.5Gd-4Y-2.2Zn-0.5Zr alloy,the effect of heat treatment on its properties at room temperature(RT),as well as the mechanical properties and microstructure evolution of various peak-aging sample...Regarding the as-cast Mg-9.5Gd-4Y-2.2Zn-0.5Zr alloy,the effect of heat treatment on its properties at room temperature(RT),as well as the mechanical properties and microstructure evolution of various peak-aging samples at different tensile temperatures were discussed in this article.The results indicated that the optimal heat treatment process of the alloy was:520℃×24 h+200℃×112 h.Under this condition,the yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)at RT were:238 MPa,327 MPa and 2.5%,respectively.As the tensile temperature increases,the strength increases firstly and then decreases,but the ductility increases monotonously.The microstructures evolution of 200℃ peak-aging(200PA)and 250℃ peak-aging(250PA)samples were different with the increasing tensile tenperature.When tensile test processed at 150℃,the denseβ’phase and rod-shaped basalγ’phase will be formed in the 200PA sample.However,at 300℃,theβ’phases disappeared.Theβ’and LPSO phases in the 250PA sample coarsened gradually as the tensile temperature increased,and 14H-LPSO phases were formed during tensile at 300℃.The 200PA sample reached the highest strength when tensile at 150℃,which was attributed to the hindrance of the basal dislocation and non-basal dislocation slip by the prismaticβ’phases and the newly formed basalγ’precipitates.展开更多
Hot forming with synchronous cooling(HFSC)is a novel technique for heat-treatable,high-strength aluminum alloys,which allows the alloys to acquire good formability,negligible springback,rapid processing and better mec...Hot forming with synchronous cooling(HFSC)is a novel technique for heat-treatable,high-strength aluminum alloys,which allows the alloys to acquire good formability,negligible springback,rapid processing and better mechanical properties.However,the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature and strain rate effects.Uniaxial tensile tests in a temperature range of 250—450℃and a strain rate range of 0.01—1 s-1 for AA2024-H18 aluminum alloy sheet are conducted with a Gleeble-3500 Thermal-Mechanical Simulation Tester.And based on metallography observation and analysis,AA2024-H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250—450 ℃.Strain rate shows different effects on ductility at different temperatures.Compared with traditional warm/hot forming methods,AA2024-H18 aluminum alloy achieves a better work-hardening result through HFSC operations,which promises an improved formability at elevated temperature and thus good mechanical properties of final part.After HSFC operations,the microstructure of the specimens is composed of elongated static recrystallization grain.展开更多
The Cu_(65)Ni_(35) alloy liquid was undercooled by the fluxing method,and the rapid solidification structure was obtained by natural cooling.The solidification interface migration information of Cu_(65)Ni_(35) alloy l...The Cu_(65)Ni_(35) alloy liquid was undercooled by the fluxing method,and the rapid solidification structure was obtained by natural cooling.The solidification interface migration information of Cu_(65)Ni_(35) alloy liquid in rapid solidification stage was photographed with the help of high-speed camera,and the recalescence velocity was calculated.The microstructure evolution of the alloy was systematically studied by observing the microstructure morphology and taking photos on the metallographic microscope.By analyzing the evolution of dendrite grain size and microstructure microhardness with undercoolingand relying on electron backscatter diffraction(EBSD)technology,the grain refinement mechanism of microstructure under high undercooling and low undercooling is finally confirmed.展开更多
The microstructure evolution and age-hardening response for different Sm/Sn ratios(0-2.55,in wt.%)of Mg-Sn-Sm alloys were investigated.The second phase formation in as-cast alloys and the Mg_(3)Sm precipitates formed ...The microstructure evolution and age-hardening response for different Sm/Sn ratios(0-2.55,in wt.%)of Mg-Sn-Sm alloys were investigated.The second phase formation in as-cast alloys and the Mg_(3)Sm precipitates formed in aged alloys were characterized using XRD,FESEM and HAADF-STEM with EDS techniques.Results indicate that the Sm/Sn ratio has a great influence on the phase constitution,α-Mg grain size and age-hardening response.With the increment of Sm/Sn ratio,Mg_(41)Sm_(5) and thermally stable MgSnSm phases precipitate.When the Sm/Sn ratio is about 1.19,the secondary dendrite arm spacing ofα-Mg grains significantly decreases.Furthermore,the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response,the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition(ageing at 220 ℃ for a short time of 4 h).This is attributed to the large volume fraction of needle-like Mg_(3)Sm precipitates formed in theα-Mg matrix during ageing treatment,which results in a significant precipitation strengthening effect.展开更多
This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and trans...This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.展开更多
Zirconium tritiated(ZrTx)is an alternative target material for deuteron-triton(D-T)reaction neutron generator.The isotopic replacement and microstructure evolution induced by hydrogen isotope implantation could signif...Zirconium tritiated(ZrTx)is an alternative target material for deuteron-triton(D-T)reaction neutron generator.The isotopic replacement and microstructure evolution induced by hydrogen isotope implantation could significantly affect the performance of the target film.In this work,the zirconium deuteride film deposited on Mo/Si substrate was implanted by 150 keV protons with fluence from 1×10^(16 ) to 1×10^(18 )protons/cm^(2).After implantation,the depth profiles of retained hydrogen(H)and deuterium(D)in these target films were analyzed by elastic recoil detection analysis(ERDA),and time of flight-secondary ion mass spectrometry(ToF-SIMS).Additionally,the microstructure evolution was also observed by x-ray diffraction(XRD)and scanning electron microscope(SEM).The D concentration in the ZrDx film decreased versus the proton implantation fluence.An analytical model was proposed to describe the hydrogen isotopic trapping and exchange as functions of incident protons fluence.Additionally,the XRD analysis revealed that no new phase was formed after proton implantation.Furthermore,circular flakings were observed on the ZrDx surface from SEM images at fluence up to 1×10^(18) protons/cm^(2),and this surface morphology was considered to associate with the hydrogen atoms congregation in Mo/Si boundary.展开更多
Direct laser deposition(DLD),as a popular metal additive manufacturing process,shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component.However,during the processi...Direct laser deposition(DLD),as a popular metal additive manufacturing process,shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component.However,during the processing of DLD,the deposited steel layer is affected by the subsequent layer depositing.The DLD block shows different microstructure and mechanical properties at the bottom,middle and top of the deposited parts.To date,there are few research works about the effects of inter-layer interval time and laser power on the microstructure evolution and mechanical properties of the deposited layers.In this study,the idle time and laser power layer by layer during DLD of 12CrNi2 steel were controlled to cause the deposited layers to maintain a high cooling rate,while the bottom deposited layer was subjected to a weak tempering effect.Results show that a high proportion of martensite is produced,which improves the strength of the deposited layer.Under the laser scanning strategy of laser power 2,500 W,scanning velocity 5 mm·s^(-1),powder feeding rate 11 g·min^(-1),overlap rate 50%,and a laser power difference of 50 W and a 2 min interval,the tensile strength of the deposited layer of 12CrNi2 steel is in the range of 873-1,022 MPa,and the elongation is in the range of 16.2%-18.9%.This study provides a method to reduce the tempering effect of the subsequent deposition layers on the bottom layers,which can increase the proportion of martensite in the low-alloy high-strength steel,so as to improve the yield strength of the alloy steel.展开更多
The hot-plate rolling(HPR)process is adopted to achieve the optimal strength-ductility for the in-situ nano-TiC_(P)/Al-Mg-Si composites.There was no crack in the sheet by single pass of hot-plate rolling with a thickn...The hot-plate rolling(HPR)process is adopted to achieve the optimal strength-ductility for the in-situ nano-TiC_(P)/Al-Mg-Si composites.There was no crack in the sheet by single pass of hot-plate rolling with a thickness reduction of 80%,while there were numerous cracks in the sheet by two passes of conventional hot rolling to achieve a total reduction of 50%.The microstructure and mechanical properties of the composites subjected to 80%thickness reduction of hot rolling at 540℃were investigated by tensile tests,scanning electron microscopy,and electron backscatter diffraction.The yield strength and ultimate tensile strength of in-situ nano-TiC_(P)/Al-Mg-Si composites after the hot-plate rolling process and T6 heat treatment increased significantly due to the dislocation strengthening and precipitation strengthening.展开更多
Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment.The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated....Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment.The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated.Meanwhile,the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied.Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure.During the semi-solid thermal transformation,the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time.The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605℃ for 30 min is the optimal.The average size of solid particles,shape factor,and solid fraction are 42μm,1.45 and 61.8%,respectively.At the same time,a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.展开更多
The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si,Al-2.5Li-1Cu-1.6Mg-0.8Si,and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated.The results show that t...The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si,Al-2.5Li-1Cu-1.6Mg-0.8Si,and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated.The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio.The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg_(2)Si primary phase at the expense of the AlLiSi primary phase.Moreover,a tiny amount of T_(B)-Al_(7.5)Cu_(4)Li phase transforms into S-Al_(2)CuMg phase with the increase of Mg content.In addition,the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase.After ageing treatment,the precipitation sequence as a function of Mg/Si ratio is as follows:δ/δ'+AlLiSi(Mg/Si is~1)→δ/δ'+β'-Mg_(2)Si+AlLiSi(Mg/Si is~2)→δ/δ'+β'-Mg_(2)Si(Mg/Si is~3).A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing.The rod-likeβ'-Mg_(2)Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.展开更多
The influence of different Si contents on the microstructure evolution and mechanical properties of Al⁃Mg⁃Si⁃Cu⁃Zn alloys was systematically studied using tensile testing,OM,SEM,EDS,and EBSD.The results indicate that ...The influence of different Si contents on the microstructure evolution and mechanical properties of Al⁃Mg⁃Si⁃Cu⁃Zn alloys was systematically studied using tensile testing,OM,SEM,EDS,and EBSD.The results indicate that the grain size of as⁃cast alloys was gradually reduced with the increase of the Si content,which mainly resulted from the formation of many iron⁃rich phases and precipitates during the casting process.During homogenization treatment,the plate⁃likeβ⁃AlFeSi phases in the alloy with a higher Si content easily transformed to the sphericalα⁃Al(FeMn)Si phases,which is helpful for improving the formability of alloys.The microstructure evolution of the alloys was also greatly dependent on the content of Si that the number density and homogeneous distribution level of precipitates in the final cold rolled alloys both increased with the increase of the Si content,which further provided a positive effect on the formation of fine recrystallization grains during the subsequent solution treatment.As a result,the yield strength,ultimate tensile strength,and elongation of the pre⁃aged alloys in the direction of 45°with respect to the rolling direction were all increased with increasing Si content.展开更多
基金the financial support from the Ministry of Science and Technology of People’s Republic of China(National Basic Research Program of China,No:2011BAE22B05Research and evaluation of magnesium alloy protection,connectivity and reliability)+1 种基金a Science and Technology Plan of Liaoning Province,China,No:201202160Research of the mechanism of ASB in AZ31 Magnesium alloy under high speed impact.
文摘For the purpose of investigating the microstructure evolution and deformation behavior of magnesium under high strain rates,the Split Hopkinson Pressure Bar(SHPB)apparatus was used under high strain rates from 755 s^(-1) to 2826 s^(-1) in the present work at room temperature.The microstructures of extruded Mg-Gd-Y Magnesium alloy under different strain rates and along different compression directions were observed by metallographic microscope.The results show that,microstructures of extruded Mg-Gd-Y Magnesium alloy along ED,TD and ND compression directions are sensitive to strain rates.The amount of twins firstly increases and then decreases with strain rates being increased,and the recrystal grains increase and grow up.When the strain rate reaches 2500 s^(-1),the adiabatic shear band(ASB)begins to form.The formation process of the adiabatic shear band can be divided into three stages.In the first stage,under the impact load a great deal of twins form and the deformation mechanism is twinning.In the second stage,discontinuous ASB forms due to twins adjusting the directions of located grains and the deformation mechanisms are twinning and non-basal slip.In the last stage,non-basal slip turns to basal slip and continuous ASB forms.The dynamic compression fracture mechanism of extruded Mg-Gd-Y Magnesium alloy is multi-crack propagation.
基金supported by the National Basic Research Program of China (grant No. 2010CB635106)the High School Basic Scientific Research Program of Gansu Province
文摘The application of some semi-solid forming magnesium alloys is restricted due to their weak mechanical properties. To improve the mechanical properties, it is necessary to research the regularity and theory of semi-solid microstructure evolution of the alloy. In this study, microstructure evolution of ZA72 alloy during the partial remelting, and the effect of holding temperature and holding time on the semi-solid microstructure evolution of ZA72 magnesium alloy were investigated by means of OM, SEM and EDS analysis. The results indicate that the microstructure with small and spheroidal semi-solid particles which are available for thixo-forming can be obtained using proper heating parameters. After being isothermally treated at between 580 and 610 ℃ for 30 min, the equivalent size and shape factor of primary solid phase of ZA72 alloy decrease gradually, while the liquid volume fraction increases. When isothermally treated at 600 ℃ and held for different times from 15 to 60 min, with the increase of holding time, the equivalent size of primary particles decreases at first and then increases gradually; while the shape factor decreases gradually. The best heat treatment parameters in this experiment are to hold at 610 ℃ for 30 min. Compared with as-cast ZA72 alloy, the sizes of the eutectic phase and second α-Mg phase obtained in semi-solid state are smaller due to the higher solidification rate and the higher under-cooling degree than as-cast state. These decrease the fracture probability during tensile stress and improve the properties of the ZA72 alloy by semi-solid forming.
文摘Al-Si metal matrix composites (MMCs) reinforced with 20 vol.% alumina-silicate shot fibers (Al2O3-SiO2(sf)) were fabricated by an infiltration squeeze method. Pure Pr metal was added into these composites. The effect of Pr addition on the microstructure evolution of Al-Si MMCs was investigated by SEM,TEM,and EDS. Pr addition is favorable to make uniform microstructures with the modified eutectic Si crystal. PrAlSi phase with high contents of Pr and Si is observed on the interface between the fiber and the matrix. The addition of Pr promotes interface SiO2 reduction,and SiO2 comes from the crystallization of Al2O3-SiO2 short fibers.
基金The authors would like to thank the financial support of Fundamental Research Funds for the Central Universities(No.2302019FRF-IC-19-018)Aviation Science Foundation Project(No.20181174001).
文摘The formability of magnesium alloys at ambient temperature can be enhanced by alloying additions such as Ca and RE elements,which is ascribed to the weakened basal texture.To produce magnesium alloy sheets with excellent comprehensive performance,the evolution of texture characterization during fabrication process and subsequent effect of texture on mechanical properties are vital controlling factors.In this investigation,three experimental Mg-3Al series alloys were hot rolled and annealed to sheets with 1 mm thickness.The microstructure evolution during rolling and annealing process was investigated.Furthermore,the influence of texture on tensile properties along different tensile directions was also studied.The results show that weakened basal texture and refined grains were achieved with the co-addition of Ca and RE element.However,strengthening of mechanical properties wasn't obtained.During hot rolling process,microstructure was refined,second phase particles broken,and basal texture was increased.While basal texture was weakened during annealing process.Recrystallization behavior influenced by formation of second phase was dominated to attenuate basal texture.Tensile deformation behavior was controlled by basal slip and followed Schmid factor criterion.Moreover,the weakened basal texture and activation of non-basal slips during hot rolling process can contribute to diminish the anisotropy of tensile properties.
基金funding supported by National Natural Science Foundation of China(No.52175285)Beijing Municipal Natural Science Foundation(No.3182025)+1 种基金National Defense Science and Technology Rapid support Project(No.61409230113)Scientific and Technological Innovation Foundation of Shunde Graduate School,USTB and Fundamental Research Funds for the Central Universities(No.FRFBD-20-08A,FRF-TP-20-009A2)。
文摘In this paper, a unified internal state variable(ISV) model for predicting microstructure evolution during hot working process of AZ80 magnesium alloy was developed. A novel aspect of the proposed model is that the interactive effects of material hardening, recovery and dynamic recrystallization(DRX) on the characteristic deformation behavior were considered by incorporating the evolution laws of viscoplastic flow, dislocation activities, DRX nucleation and boundary migration in a coupled manner. The model parameters were calibrated based on the experimental data analysis and genetic algorithm(GA) based objective optimization. The predicted flow stress, DRX fraction and average grain size match well with experimental results. The proposed model was embedded in the finite element(FE) software DEFORM-3 D via user defined subroutine to simulate the hot compression and equal channel angular extrusion(ECAE) processes. The heterogeneous microstructure distributions at different deformation zones and the dislocation density evolution with competitive deformation mechanisms were captured.This study can provide a theoretical solution for the hot working problems of magnesium alloy.
基金Supported by National Natural Science Foundation of China (Grant Nos. 51775336,U1564203)Program of Shanghai Academic Research Leadership (Grant No. 19XD1401900)
文摘High strength steel products with good ductility can be produced via Q&P hot stamping process,while the phase transformation of the process is more complicated than common hot stamping since two-step quenching and one-step carbon partitioning processes are involved.In this study,an integrated model of microstructure evolution relating to Q&P hot stamping was presented with a persuasively predicted results of mechanical properties.The transformation of diffusional phase and non-diffusional phase,including original austenite grain size individually,were considered,as well as the carbon partitioning process which affects the secondary martensite transformation temperature and the subsequent phase transformations.Afterwards,the mechanical properties including hardness,strength,and elongation were calculated through a series of theoretical and empirical models in accordance with phase contents.Especially,a modified elongation prediction model was generated ultimately with higher accuracy than the existed Mileiko’s model.In the end,the unified model was applied to simulate the Q&P hot stamping process of a U-cup part based on the finite element software LS-DYNA,where the calculated outputs were coincident with the measured consequences.
基金supported by the National Natural Science Foundation of China (51706094)。
文摘The effect of self-reactivation on the CO_(2) capture capacity of the spent calcium based sorbent was investigated in a dual-fixed bed reactor.The sampled sorbents from the dual-fixed bed reactor were sent for XRD,SEM and N_2 adsorption analysis to explain the self-reactivation mechanism.The results show that the CaO in the spent sorbent discharged from the calciner absorbs the vapor in the air to form Ca(OH)_(2) and further Ca(OH)_(2)·2 H_(2) O under environmental conditions,during which process the CO_(2) capture capacity of the spent sorbent can be self-reactivated.The microstructure of the spent sorbent is improved by the self-reactivation process,resulting in more porous microstructure,higher BET surface area and pore volume.Compared with the calcined spent sorbent that has experienced 20 cycles,the pore volume and BET surface area are increased by 6.69 times and 56.3% after self-reactivation when φ=170%.The improved microstructure makes it easier for the CO_(2) diffusion and carbonation reaction in the sorbent.Therefore,the CO_(2) capture capacity of the spent sorbent is enhanced by self-reactivation process.A self-reactivation process coupled with calcium looping process was proposed to reuse the discharged spent calcium based sorbent from the calciner.Higher average carbonation conversion and CO_(2) capture efficiency can be achieved when self-reactivated spent sorbent is used as supplementary sorbent in the calciner rather than fresh CaCO_(3) under the same conditions.
基金the National Key R&D Program of China(No.2017YFE0123500 and No.2017YFB1103701)。
文摘Metal additive manufacturing technology has been widely used in prototyping,parts manufacturing and repairing.Metal additive manufacturing is a multi-scale and multi-physical coupling process with complex physical phenomena of heat and mass transfer and microstructure evolution.It is hard to directly observe the dynamic behavior and microstructure evolution of molten pool during additive manufacturing.Therefore,numerical simulation of additive manufacturing process is significant since it can efficiently and pertinently predict and analyze the physical phenomena in the process of metal additive manufacturing,and provide a reference for technological parameters selection.In this review,the research progress of numerical simulation of metal additive manufacturing is discussed.Various aspects of numerical simulation models are reviewed,including:(1)Introduction of basic control method and physical description of numerical simulation models;(2)Comparison of various heat and mass transfer models based on different physical assumptions(heat conduction model;heat flux coupling model;discrete powder particle heat flux coupling model);(3)Applications of various microstructure evolution models[phase field(PF),cellular automata(CA),and Monte Carlo(MC)].Finally,the development trend of numerical simulation of metal additive manufacturing,including the thermal-flow-solid coupling model and deep learning for numerical model,is analyzed.
基金Ph.D fund of China National Education Commission !project number9314515
文摘Mechanical properties and microstructure evolution of Mg-8.4 wt pct Li alloy have been investi- gated. The superplastic elongation-to-failure 920% at 573 K and initial strain rate of 5 × 10-4 s-1 at low nominal stress 2 MPa has been demonstrated. It was shown through optical microstructure that the average grain sizes at gauge length section before and after superplastic tension and at grip section were 7.5 μm, 31.7 μm and 20 μm respectively, indicating significant deformation induced grain growth and static grain growth. Comparison of experiment data with published data for superplastic Mg-Li alloys shows that fine grain size and about 50 to 50 phase ratio contribute to achieving the largest superplasticity. Some related research works in other alloys are compiled and further evidences to such theoretic argument are provided.
基金supported by the National Natu-ral Science Foundation of China(Grant No.52075501).
文摘Regarding the as-cast Mg-9.5Gd-4Y-2.2Zn-0.5Zr alloy,the effect of heat treatment on its properties at room temperature(RT),as well as the mechanical properties and microstructure evolution of various peak-aging samples at different tensile temperatures were discussed in this article.The results indicated that the optimal heat treatment process of the alloy was:520℃×24 h+200℃×112 h.Under this condition,the yield strength(YS),ultimate tensile strength(UTS)and elongation(EL)at RT were:238 MPa,327 MPa and 2.5%,respectively.As the tensile temperature increases,the strength increases firstly and then decreases,but the ductility increases monotonously.The microstructures evolution of 200℃ peak-aging(200PA)and 250℃ peak-aging(250PA)samples were different with the increasing tensile tenperature.When tensile test processed at 150℃,the denseβ’phase and rod-shaped basalγ’phase will be formed in the 200PA sample.However,at 300℃,theβ’phases disappeared.Theβ’and LPSO phases in the 250PA sample coarsened gradually as the tensile temperature increased,and 14H-LPSO phases were formed during tensile at 300℃.The 200PA sample reached the highest strength when tensile at 150℃,which was attributed to the hindrance of the basal dislocation and non-basal dislocation slip by the prismaticβ’phases and the newly formed basalγ’precipitates.
基金supported by the National Natural Science Foundation of China(No.51175252)
文摘Hot forming with synchronous cooling(HFSC)is a novel technique for heat-treatable,high-strength aluminum alloys,which allows the alloys to acquire good formability,negligible springback,rapid processing and better mechanical properties.However,the deformation behavior and microstructure evolution of the alloys during HFSC are complex and need to be studied due to the temperature and strain rate effects.Uniaxial tensile tests in a temperature range of 250—450℃and a strain rate range of 0.01—1 s-1 for AA2024-H18 aluminum alloy sheet are conducted with a Gleeble-3500 Thermal-Mechanical Simulation Tester.And based on metallography observation and analysis,AA2024-H18 aluminum alloy sheet in HSFC process exhibits hardening and dynamic recovery behaviors within the temperature range of 250—450 ℃.Strain rate shows different effects on ductility at different temperatures.Compared with traditional warm/hot forming methods,AA2024-H18 aluminum alloy achieves a better work-hardening result through HFSC operations,which promises an improved formability at elevated temperature and thus good mechanical properties of final part.After HSFC operations,the microstructure of the specimens is composed of elongated static recrystallization grain.
基金Funded by the National Natural Science Foundation of China(No.51701187)the Basic Applied Research Projects in Shanxi Province(201801D221151)。
文摘The Cu_(65)Ni_(35) alloy liquid was undercooled by the fluxing method,and the rapid solidification structure was obtained by natural cooling.The solidification interface migration information of Cu_(65)Ni_(35) alloy liquid in rapid solidification stage was photographed with the help of high-speed camera,and the recalescence velocity was calculated.The microstructure evolution of the alloy was systematically studied by observing the microstructure morphology and taking photos on the metallographic microscope.By analyzing the evolution of dendrite grain size and microstructure microhardness with undercoolingand relying on electron backscatter diffraction(EBSD)technology,the grain refinement mechanism of microstructure under high undercooling and low undercooling is finally confirmed.
基金the Natural Science Foundation of Inner Mongolia under Grant No.2020MS05014the Science and Technology Planning of Inner Mongolia under Grant No.2020GG0318.
文摘The microstructure evolution and age-hardening response for different Sm/Sn ratios(0-2.55,in wt.%)of Mg-Sn-Sm alloys were investigated.The second phase formation in as-cast alloys and the Mg_(3)Sm precipitates formed in aged alloys were characterized using XRD,FESEM and HAADF-STEM with EDS techniques.Results indicate that the Sm/Sn ratio has a great influence on the phase constitution,α-Mg grain size and age-hardening response.With the increment of Sm/Sn ratio,Mg_(41)Sm_(5) and thermally stable MgSnSm phases precipitate.When the Sm/Sn ratio is about 1.19,the secondary dendrite arm spacing ofα-Mg grains significantly decreases.Furthermore,the alloy with Sm/Sn ratio up to 2.55 exhibits the highest age-hardening response,the hardness value increases from 52 HB at solution-treated condition to 74 HB at peak-aged condition(ageing at 220 ℃ for a short time of 4 h).This is attributed to the large volume fraction of needle-like Mg_(3)Sm precipitates formed in theα-Mg matrix during ageing treatment,which results in a significant precipitation strengthening effect.
基金supported by the National Natural Science Foundation of China (Nos. 51805358 and 51775366)Key Research and Development Program of Jinzhong (No. Y201023)College Students’ Innovative Entrepreneurial Training Plan Program (No. 202010112011)
文摘This study fabricates an AZ31 magnesium alloy tube by spinning technology-power stagger forward spinning.The microstructure evolution of the tube is investigated by combining electron backscatter diffraction and transmission electron microscopy analysis,and the corrosion resistance is measured by an electrochemical corrosion test.Results show that the grains are obviously more uniform and finer along the wall thickness’s direction of the AZ31 alloy tube after the third spinning pass.The number of twins ascends first and then descends,while the varying trend of low-angle grain boundaries(LAGBs)is opposite to that of the twins as the spinning pass increases.With the increase of the total spinning deformation,the deformation texture initially increases and the c-axis of the{0001}crystal plane gradually rotates to the axial direction of the tube;the deformation texture then decreases and the orientation of grains becomes more random.The main mechanism of grain refinement is dynamic recrystallization by the twin-induced way and bowing out of the nucleation at grain boundaries during the first and second pass.However,the dominant mechanism of the refined grain is the high-temperature dynamic recovery in the third pass,and the microstructure mainly consists of substructured grains.After the spinning deformation,the corrosion resistance of the AZ31 alloy tube decreases due to the combined effect of twins and high density-dislocations.
基金supported by the National Natural Science Foundation of China(Grant Nos.11905206 and 11975217).
文摘Zirconium tritiated(ZrTx)is an alternative target material for deuteron-triton(D-T)reaction neutron generator.The isotopic replacement and microstructure evolution induced by hydrogen isotope implantation could significantly affect the performance of the target film.In this work,the zirconium deuteride film deposited on Mo/Si substrate was implanted by 150 keV protons with fluence from 1×10^(16 ) to 1×10^(18 )protons/cm^(2).After implantation,the depth profiles of retained hydrogen(H)and deuterium(D)in these target films were analyzed by elastic recoil detection analysis(ERDA),and time of flight-secondary ion mass spectrometry(ToF-SIMS).Additionally,the microstructure evolution was also observed by x-ray diffraction(XRD)and scanning electron microscope(SEM).The D concentration in the ZrDx film decreased versus the proton implantation fluence.An analytical model was proposed to describe the hydrogen isotopic trapping and exchange as functions of incident protons fluence.Additionally,the XRD analysis revealed that no new phase was formed after proton implantation.Furthermore,circular flakings were observed on the ZrDx surface from SEM images at fluence up to 1×10^(18) protons/cm^(2),and this surface morphology was considered to associate with the hydrogen atoms congregation in Mo/Si boundary.
基金the National Key Technologies Research and Development Program of China(Grant No.2016YFB1100200)。
文摘Direct laser deposition(DLD),as a popular metal additive manufacturing process,shows advantages of technical flexibility and high efficiency to gain a high-performance alloy steel component.However,during the processing of DLD,the deposited steel layer is affected by the subsequent layer depositing.The DLD block shows different microstructure and mechanical properties at the bottom,middle and top of the deposited parts.To date,there are few research works about the effects of inter-layer interval time and laser power on the microstructure evolution and mechanical properties of the deposited layers.In this study,the idle time and laser power layer by layer during DLD of 12CrNi2 steel were controlled to cause the deposited layers to maintain a high cooling rate,while the bottom deposited layer was subjected to a weak tempering effect.Results show that a high proportion of martensite is produced,which improves the strength of the deposited layer.Under the laser scanning strategy of laser power 2,500 W,scanning velocity 5 mm·s^(-1),powder feeding rate 11 g·min^(-1),overlap rate 50%,and a laser power difference of 50 W and a 2 min interval,the tensile strength of the deposited layer of 12CrNi2 steel is in the range of 873-1,022 MPa,and the elongation is in the range of 16.2%-18.9%.This study provides a method to reduce the tempering effect of the subsequent deposition layers on the bottom layers,which can increase the proportion of martensite in the low-alloy high-strength steel,so as to improve the yield strength of the alloy steel.
基金the National Natural Science Foundation of China(No.51790483)。
文摘The hot-plate rolling(HPR)process is adopted to achieve the optimal strength-ductility for the in-situ nano-TiC_(P)/Al-Mg-Si composites.There was no crack in the sheet by single pass of hot-plate rolling with a thickness reduction of 80%,while there were numerous cracks in the sheet by two passes of conventional hot rolling to achieve a total reduction of 50%.The microstructure and mechanical properties of the composites subjected to 80%thickness reduction of hot rolling at 540℃were investigated by tensile tests,scanning electron microscopy,and electron backscatter diffraction.The yield strength and ultimate tensile strength of in-situ nano-TiC_(P)/Al-Mg-Si composites after the hot-plate rolling process and T6 heat treatment increased significantly due to the dislocation strengthening and precipitation strengthening.
基金financially supported by the National Natural Science Foundation of China (Grant No. 51464032)
文摘Semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys were prepared by semi-solid isothermal heat treatment.The effects of the La element on the as-cast and semi-solid microstructures of Mg-7Zn alloy were investigated.Meanwhile,the effects of isothermal temperature and holding time on the evolution of the semi-solid microstructure of Mg-7Zn-0.3La alloy were also studied.Results indicate that the addition of a small amount of La can significantly refine the as-cast and semi-solid microstructure.During the semi-solid thermal transformation,the size and shape factor of solid particles decrease at first and then increase with the increase of isothermal temperature and holding time.The semi-solid microstructure of Mg-7Zn-0.3La alloy obtained by holding at 605℃ for 30 min is the optimal.The average size of solid particles,shape factor,and solid fraction are 42μm,1.45 and 61.8%,respectively.At the same time,a comparative study on the coarsening process of particles in the semi-solid billets of Mg-7Zn and Mg-7Zn-0.3La alloys reveals that the addition of La effectively decreases the coarsening rate of solid particles and restricts the growth of solid particles.
基金financially supported by the National Natural Science Foundation of China(51774105)Touyan Innovation Team Program(XNAUEA5640208420)。
文摘The effect of the Mg/Si ratio of Al-2.5Li-1Cu-0.8Mg-0.8Si,Al-2.5Li-1Cu-1.6Mg-0.8Si,and Al-2.5Li-1Cu-2.4Mg-0.8Si alloys on the microstructure evolution and mechanical properties was investigated.The results show that the primary phases and their morphologies in the as-cast alloys are found to vary with the Mg/Si ratio.The improvement of Mg/Si ratio of as-cast alloys promotes the formation of Mg_(2)Si primary phase at the expense of the AlLiSi primary phase.Moreover,a tiny amount of T_(B)-Al_(7.5)Cu_(4)Li phase transforms into S-Al_(2)CuMg phase with the increase of Mg content.In addition,the increase of Mg/Si ratio also causes the Cu-rich intergranular phase distributed along crystal boundary to Si-rich intergranular phase.After ageing treatment,the precipitation sequence as a function of Mg/Si ratio is as follows:δ/δ'+AlLiSi(Mg/Si is~1)→δ/δ'+β'-Mg_(2)Si+AlLiSi(Mg/Si is~2)→δ/δ'+β'-Mg_(2)Si(Mg/Si is~3).A good combination of strength and ductility can be obtained in Al-2.5Li-1Cu-2.4Mg-0.8Si alloy after solution and ageing.The rod-likeβ'-Mg_(2)Si precipitate has a positive influence on the comprehensive mechanical properties of the alloy.
基金Supported by the National Key Research and Development Program of China(Grant No.2016YFB0300801)the National Natural Science Foundation of China(Grant Nos.51871029,51571023 and 51301016)+1 种基金the Beijing Natural Science Foundation(Grant No.2172038)the Government Guided Program Intergovernmental Bilateral Innovation Cooperation Project(Grant No.BZ2019019)
文摘The influence of different Si contents on the microstructure evolution and mechanical properties of Al⁃Mg⁃Si⁃Cu⁃Zn alloys was systematically studied using tensile testing,OM,SEM,EDS,and EBSD.The results indicate that the grain size of as⁃cast alloys was gradually reduced with the increase of the Si content,which mainly resulted from the formation of many iron⁃rich phases and precipitates during the casting process.During homogenization treatment,the plate⁃likeβ⁃AlFeSi phases in the alloy with a higher Si content easily transformed to the sphericalα⁃Al(FeMn)Si phases,which is helpful for improving the formability of alloys.The microstructure evolution of the alloys was also greatly dependent on the content of Si that the number density and homogeneous distribution level of precipitates in the final cold rolled alloys both increased with the increase of the Si content,which further provided a positive effect on the formation of fine recrystallization grains during the subsequent solution treatment.As a result,the yield strength,ultimate tensile strength,and elongation of the pre⁃aged alloys in the direction of 45°with respect to the rolling direction were all increased with increasing Si content.
