In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and proper...In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.展开更多
Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic s...Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.展开更多
With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are desi...With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are designed to meet the requirements of high strength and high toughness of spring flat steel,through the test,the product surface quality and internal quality all meet the national standards,the performance indicators to meet user requirements.展开更多
Two new low-alloyed Mg-2RE-0.8Mn-0.6Ca-0.5Zn(wt%,RE=Sm or Y)alloys are developed,which can be produced on an in-dustrial scale via relatively high-speed extrusion.These two alloys are not only comparable to commercial...Two new low-alloyed Mg-2RE-0.8Mn-0.6Ca-0.5Zn(wt%,RE=Sm or Y)alloys are developed,which can be produced on an in-dustrial scale via relatively high-speed extrusion.These two alloys are not only comparable to commercial AZ31 alloy in extrudability,but also have superior mechanical properties,especially in terms of yield strength(YS).The excellent extrudability is related to less coarse second-phase particles and high initial melting point of the two as-cast alloys.The high strength-ductility mainly comes from the formation of fine grains,nano-spaced submicron/nano precipitates,and weak texture.Moreover,it is worth noting that the YS of the two alloys can maintain above 160 MPa at elevated temperature of 250°C,significantly higher than that of AZ31 alloy(YS:45 MPa).The Zn/Ca solute segregation at grain boundaries,the improved heat resistance of matrix due to addition of RE,and the high melting points of strengthening particles(Mn,MgZn_(2),and Mg-Zn-RE/Mg-Zn-RE-Ca)are mainly responsible for the excellent high-temperature strength.展开更多
The present work investigates copper slag as a substitute for river sand in high-strength concrete.The concrete mixtures were manufactured with 10%,30%,50%,70%,and 100%of copper slag to evaluate the mechanical and dur...The present work investigates copper slag as a substitute for river sand in high-strength concrete.The concrete mixtures were manufactured with 10%,30%,50%,70%,and 100%of copper slag to evaluate the mechanical and durability properties.The experimental results indicate that replacing copper slag above 50%affects the performance characteristics of the concrete due to its high angularity and lower water absorption characteristics.The strength of concrete with 50%copper slag is improved by 5.6%,whereas the strength of concrete with 100%copper slag is reduced by 2.75%at 28 days.However,increased curing to 90days improves the strength of the former by 7.16%and reduces the latter by only 0.23%.The water absorption,porosity,and rapid chloride penetration of the concrete mixtures with 100%copper slag are increased by 10.44%,13.20%,and 19.56%compared to control concrete.Micro-structural investigations through SEM infer higher replacement of copper results in higher void formation due to its reduced water absorption.展开更多
The ongoing effort to create methods for detecting and quantifying fatigue damage is motivated by the high levels of uncertainty in present fatigue-life prediction approaches and the frequently catastrophic nature of ...The ongoing effort to create methods for detecting and quantifying fatigue damage is motivated by the high levels of uncertainty in present fatigue-life prediction approaches and the frequently catastrophic nature of fatigue failure.The fatigue life of high strength aluminum alloy 2090-T83 is predicted in this study using a variety of artificial intelligence and machine learning techniques for constant amplitude and negative stress ratios(R?1).Artificial neural networks(ANN),adaptive neuro-fuzzy inference systems(ANFIS),support-vector machines(SVM),a random forest model(RF),and an extreme-gradient tree-boosting model(XGB)are trained using numerical and experimental input data obtained from fatigue tests based on a relatively low number of stress measurements.In particular,the coefficients of the traditional force law formula are found using relevant numerical methods.It is shown that,in comparison to traditional approaches,the neural network and neuro-fuzzy models produce better results,with the neural network models trained using the boosting iterations technique providing the best performances.Building strong models from weak models,XGB helps to predict fatigue life by reducing model partiality and variation in supervised learning.Fuzzy neural models can be used to predict the fatigue life of alloys more accurately than neural networks and traditional methods.展开更多
To systematically investigate the kinetics and formation mechanisms of intragranular ferrite(IGF), isothermal heat treatment in the temperature range of 450℃to 600℃ with holding for 30 s to 300 s, analysis of the ...To systematically investigate the kinetics and formation mechanisms of intragranular ferrite(IGF), isothermal heat treatment in the temperature range of 450℃to 600℃ with holding for 30 s to 300 s, analysis of the corresponding microstructures, and observation of the precipitated particles were conducted in V-N microalloyed 600 MPa high strength rebar steel. The potency of V(C,N) for IGF nucleation was also analyzed statistically. The results show that the dominant microstructure transforms from bainite(B) and acicular ferrite(AF) to grain boundary ferrite(GBF), intragranular polygonal ferrite(IPF), and pearlite(P) as the isothermal temperature increases from 450℃ to 600℃. When the holding time at 600℃ is extended from 30 s to 60 s, 120 s, and 300 s, the GBF content ranges from 6.0vol% to 6.5vol% and the IPF content increases from 0.5vol% to 2.8vol%, 13.1vol%, and 13.5vol%, respectively, because the ferrite transformation preferentially occurs at the grain boundaries and then occurs at the austenite grains. Notably, V(C,N) particles are the most effective nucleation site for the formation of IPF, accounting for 51% of the said formation.展开更多
Corrosion is a primary cause of the slippage of friction⁃type high⁃strength bolted(FHSB)T⁃stub connections.This paper attempts to quantify the residual capacity of FHSB T⁃stub connections with corroded nuts.Firstly,co...Corrosion is a primary cause of the slippage of friction⁃type high⁃strength bolted(FHSB)T⁃stub connections.This paper attempts to quantify the residual capacity of FHSB T⁃stub connections with corroded nuts.Firstly,corrosion simulation tests were conducted on 48 manually cut nuts to find out the relationship between the damage degree of nut section and the residual clamping force(RCF)of bolt.Then,static load tests were carried out on 24 FHSB T⁃stub connections with nuts of different degrees of damage to obtain the failure modes.By finite⁃element(FE)models,a comparative analysis was performed on the initial friction load(IFL)and ultimate strength(US)of each connection with corroded nuts.Finally,the parameters of 96 FE models for FHSB T⁃stub connections were analyzed and used to derive the calculation formulas for the degree of damage for each nut and the IFL and US of each connection.The results show that the RCF decay of a bolt is a quadratic function of the equivalent radius loss ratio and the shear failure after nut corrosion;the IFL of each connection had a clear linear correlation with the RCF of the corresponding bolts,and the correlation depends on the applied load and static friction on connecting plate interface induced by the clamping force;the static friction had little impact on the US of the connection;the proposed IFL and US formulas can effectively derive the residual anti⁃slip capacity of FHSB T⁃stub connections from the degree of damage of the corroded nut section.The research results provide a scientific basis for the replacement and maintenance of corroded bolts of FHSB T⁃stub connections.展开更多
The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated....The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated.It is found that steel with combined addition of Mo and V appears to be the most promising one than those containing V and Nb or containing V alone under the same pro- cessing conditions.From CCT curve of the steel and the cooling curve of the bar determined by sim- ulating the cooling rate in mill practice,the reason why 40Si2MnMoV bar has excellent combination of strength and ductility is clarified.展开更多
As the main seismic component of a bridge,seismic damage to the bridge pier has a greater effect on its subsequent service.In the offshore chloride environment,the issues(e.g.,reinforcement bar corrosion and attenuati...As the main seismic component of a bridge,seismic damage to the bridge pier has a greater effect on its subsequent service.In the offshore chloride environment,the issues(e.g.,reinforcement bar corrosion and attenuation of concrete strength)of piers caused by chloride ion seriously curtail the normal service life and deteriorate the anti-seismic property of bridge structures.The engineered cementitious composite(ECC)-reinforced concrete(RC)composite pier with high strength reinforcement bars(HSRB)is expected to solve the above problems.This study aims to clarify the time-varying seismic vulnerability(SV)of the HSRBECC-RC composite pier during its full life cycle(FLC).Based on OpenSees,the refined finite element analysis models of RC pier,ECC-RC composite pier,and HSRBECC-RC composite pier have been established.Moreover,using the nonlinear time-path dynamic analysis method,the influence of chloride ion erosion on the time-dependent seismic vulnerability(SV)of these different piers in different service life and different peak ground acceleration(PGA)were analyzed from a dynamic point of view.The research shows that the exceeding probability(EP)of the same damage level increases with the enhancement of service time and PGA and with the increase of destruction,the exceeding probability(EP)of slight damage(DL-1),moderate damage(DL-2),serious damage(DL-3),and complete collapse(DL-4)decreases in turn;the corrosion degree of chloride ion to piers is small during the early service period,the time-varying vulnerability curve of the bridge piers is almost the same as that of a new bridge,and during later service,as the extent of chloride ion corrosion deepens,exceeding probability(EP)under severe damage(DL-3)and complete collapse(DL-4)is increased,and the seismic performance is significantly enhanced.展开更多
Higher strength is always the goal pursued by researchers for the structural materials,especially for the lightweight magnesium(Mg)alloys which generally have relatively low strength at present.From this aspect,the pr...Higher strength is always the goal pursued by researchers for the structural materials,especially for the lightweight magnesium(Mg)alloys which generally have relatively low strength at present.From this aspect,the present paper reviews the recent reports of a kind of Mg alloys,i.e.Mg-RE(RE:rare earths,mainly Gd or Y)casting and wrought alloys,which have been able to achieve high strength compared with common or commercial Mg alloys,from the viewpoint and content of the alloy system,alloying constitution,preparation process,tensile strength and each of the main strengthening mechanisms.This review of recent research and developments in high-strength Mg-RE alloys is beneficial for the further design of Mg alloys with higher strength as well as excellent comprehensive performance.展开更多
China is quite poor in argent resource. Roughly 80% of this industrial argent is imported every year. In order to improve the situation, we took advantage of rare earth (RE) mineral resource and successfully developed...China is quite poor in argent resource. Roughly 80% of this industrial argent is imported every year. In order to improve the situation, we took advantage of rare earth (RE) mineral resource and successfully developed the non-argent Lanthanum-tellurium-copper alloy as a substitute for industry argent-copper. In our research, we were able to successfully apply rare earth lanthanum to copper alloy. The defects as porosity, inclusion, etc. originating from nonvacuum melting processing were controlled. Fine grain was obtained. Meanwhile, the comprehensive properties of the copper alloy, such as strength, conductivity and thermal conductivity were improved. The research results in increasing conductivity and thermal conductivity by 5% and 15%, respectively, while the tensile strength is increased by 6% higher than Ag-Cu alloy. The anti-electric corrosion property is good, and there is no argent-cadmium steam population originating from the electric arc effect. The addition of lanthanum further reduces the content of oxygen and hydrogen. The optimum quantity of the addition of RE lanthanum in the copper alloy is 0.010% - 0.020% .展开更多
Lightweight structure is an important method to increase vehicle fuel efficiency. High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight. Howeve...Lightweight structure is an important method to increase vehicle fuel efficiency. High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight. However, the lightweight structures must show the improved capability for structural rigidity and crash energy absorption. Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles. Currently, many research works focus on component level axial crash testing and simulation of high strength steels. However, the effects of high strength steel parts to the impact of auto body are not considered. The goal of this research is to study the application of hot forming high strength steel(HFHSS) in order to evaluate the potential using in vehicle design for lightweight and passive safety. The performance of HFHSS is investigated by using both experimental and analytical techniques. In particular, the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body. Automotive components made of HFHSS and general high strength steel(GHSS) are considered in this study. The material characterization of HFHSS is carried out through material experiments. The finite element method, in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme(C-NCAP) crash test. The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated. The results from the simulation analyses of HFHSS are compared with those of GHSS. The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact. Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts. Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts. The experiments and simulation are conducted to the HFHSS parts on auto body. The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.展开更多
As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys....As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.展开更多
The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steel...The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.展开更多
Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The eff...Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite (MA) constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.展开更多
In the current study,a homogenous ultra-fine grained microstructure with average grain size of 1.0μm is achieved in the Mg-Zn-Ca-Mn alloy through the reduplicative equal channel angular pressing(ECAP)at 300℃,and the...In the current study,a homogenous ultra-fine grained microstructure with average grain size of 1.0μm is achieved in the Mg-Zn-Ca-Mn alloy through the reduplicative equal channel angular pressing(ECAP)at 300℃,and the mechanical properties are remarkably improved,with room-temperature yield strength of 269.6 MPa and elongation of 22.7%.The twinning deformation results in a discontinuous recrystallization behavior in the initial stage of ECAP.With further deformation,the continuously dynamic recrystallization contributes to an obvious grain refinement effect.The activation of non-basal slip system leads to the formation of a unique basal texture,which is related to the elevated ECAP temperature and the decreased grain size.Both grain refinement and texture modification derived from ECAP process result in the increase of yield strength,while the cracked secondary phase particles are beneficial to the enhanced ductility,through reducing the stress concentration and hindering premature failure.展开更多
As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In ...As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In present, retrogression and re-ageing (RRA)treatment, which can improve both strength and SCCR of 7XXX series alloy, is a best method to solvethis problem. The effect of RRA treatment on the microstructure evolution of a new type lowfrequency electric-magnetic casting Al-9.OZn-2.45Mg-2.2Cu-0.15Zr alloy was investigated using DSCand TEM technologies. The results show that the typical microstructure of the alloy at T6 conditionis characterized by both fine eta' and GP zone homogeneously distributed in the matrix andcontinuous r) particles occurred on the grain-boundary. After RRA treatment, the matrixprecipitations are mainly fine and dispersed eta' and eta phases, being coarser and more stable thanthat from T6 temper. While, the grain-boundary microstructure is very close to that resulting fromT73 temper. High retrogression temperature and long retrogression time leads to a more stablemicrostructure after re-ageing.展开更多
The high strength martensite steels are widely used in aerospace,ocean engineering,etc.,due to their high strength,good ductility and acceptable corrosion resistance.This paper provides a review for the influence of m...The high strength martensite steels are widely used in aerospace,ocean engineering,etc.,due to their high strength,good ductility and acceptable corrosion resistance.This paper provides a review for the influence of microstructure on corrosion behavior of high strength martensite steels.Pitting is the most common corrosion type of high strength stainless steels,which always occurs at weak area of passive film such as inclusions,carbide/intermetallic interfaces.Meanwhile,the chromium carbide precipitations in the martensitic lath/prior austenite boundaries always result in intergranular corrosion.The precipitation,dislocation and grain/lath boundary are also used as crack nucleation and hydrogen traps,leading to hydrogen embrittlement and stress corrosion cracking for high strength martensite steels.Yet,the retained/reversed austenite has beneficial effects on the corrosion resistance and could reduce the sensitivity of stress corrosion cracking for high strength martensite steels.Finally,the corrosion mechanisms of additive manufacturing high strength steels and the ideas for designing new high strength martensite steel are explored.展开更多
To develop a high strength low alloy (HSLA) steel with high strength and high toughness, a series of martensitic steels were studied through alloying with various elements and thermodynamic simulation. The microstru...To develop a high strength low alloy (HSLA) steel with high strength and high toughness, a series of martensitic steels were studied through alloying with various elements and thermodynamic simulation. The microstructure and mechanical properties of the designed steel were investigated by optical microscopy, scanning electron microscopy, tensile testing and Charpy impact test. The results show that cementite exists between 500℃ and 700℃, M7C3 exits below 720℃, and they are much lower than the austenitizing temperature of the designed steel. Furthermore, the Ti(C,N) precipitate exists until 1280℃, which refines the microstructure and increases the strength and toughness. The optimal alloying components are 0.19% C, 1.19% Si, 2.83% Mn, 1.24% Ni, and 0.049% Ti; the tensile strength and the V notch impact toughness of the designed steel are more than 1500 MPa and 100 J, respectively.展开更多
基金Project(U2202255)supported by the National Natural Science Foundation of ChinaProject(2024JJ2076)supported by the Hunan Provincial Natural Science Foundation of ChinaProject(2023Z092)supported by the Key Technology Research Program of Ningbo,China。
文摘In this paper,equal channel angular pressing and thermomechanical treatment was employed to improve the strength and electrical conductivity of an aging strengthened Cu-Ti-Cr-Mg alloy,and the microstructure and properties of the alloy were investigated in detail.The results showed that the samples deformed by the combination of cryogenic equal channel angular pressing(ECAP)and rolling had good comprehensive properties after aging at 400℃.The tensile strength of the peak-aged and over-aged samples was 1120 MPa and 940 MPa,with their corresponding electrical conductivity of 14.7%IACS and 22.1%IACS,respectively.ECAP and cryogenic rolling introduced high density dislocations,leading to the inhibition of the softening effects and refinement of the grains.After a long time aging at 400℃,the alloy exhibited ultra-high strength with obvious increasing electrical conductivity.The high strength was attributed to the synergistic effect of work hardening,grain refinement strengthening and precipitation strengthening.The precipitation of a large amount of Ti atoms from the matrix led to the high electrical conductivity of the over-aged sample.
文摘Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.
文摘With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are designed to meet the requirements of high strength and high toughness of spring flat steel,through the test,the product surface quality and internal quality all meet the national standards,the performance indicators to meet user requirements.
基金supported by the National Natural Science Foundation of China(Nos.52071093 and 51871069)the Key Laboratory of Micro-Systems and Micro-Structures Manufacturing(HIT)+2 种基金Ministry of Education(No.2020 KM009)the Student Research and Innovation Fund of the Fundamental Research Funds for the Central Universities(No.3072022GIP1004)the Science and Technology Innovation Major Project of Ningbo City,China(No.2019B10103).
文摘Two new low-alloyed Mg-2RE-0.8Mn-0.6Ca-0.5Zn(wt%,RE=Sm or Y)alloys are developed,which can be produced on an in-dustrial scale via relatively high-speed extrusion.These two alloys are not only comparable to commercial AZ31 alloy in extrudability,but also have superior mechanical properties,especially in terms of yield strength(YS).The excellent extrudability is related to less coarse second-phase particles and high initial melting point of the two as-cast alloys.The high strength-ductility mainly comes from the formation of fine grains,nano-spaced submicron/nano precipitates,and weak texture.Moreover,it is worth noting that the YS of the two alloys can maintain above 160 MPa at elevated temperature of 250°C,significantly higher than that of AZ31 alloy(YS:45 MPa).The Zn/Ca solute segregation at grain boundaries,the improved heat resistance of matrix due to addition of RE,and the high melting points of strengthening particles(Mn,MgZn_(2),and Mg-Zn-RE/Mg-Zn-RE-Ca)are mainly responsible for the excellent high-temperature strength.
基金Part by a Grant from Sona College of TechnologySalem。
文摘The present work investigates copper slag as a substitute for river sand in high-strength concrete.The concrete mixtures were manufactured with 10%,30%,50%,70%,and 100%of copper slag to evaluate the mechanical and durability properties.The experimental results indicate that replacing copper slag above 50%affects the performance characteristics of the concrete due to its high angularity and lower water absorption characteristics.The strength of concrete with 50%copper slag is improved by 5.6%,whereas the strength of concrete with 100%copper slag is reduced by 2.75%at 28 days.However,increased curing to 90days improves the strength of the former by 7.16%and reduces the latter by only 0.23%.The water absorption,porosity,and rapid chloride penetration of the concrete mixtures with 100%copper slag are increased by 10.44%,13.20%,and 19.56%compared to control concrete.Micro-structural investigations through SEM infer higher replacement of copper results in higher void formation due to its reduced water absorption.
文摘The ongoing effort to create methods for detecting and quantifying fatigue damage is motivated by the high levels of uncertainty in present fatigue-life prediction approaches and the frequently catastrophic nature of fatigue failure.The fatigue life of high strength aluminum alloy 2090-T83 is predicted in this study using a variety of artificial intelligence and machine learning techniques for constant amplitude and negative stress ratios(R?1).Artificial neural networks(ANN),adaptive neuro-fuzzy inference systems(ANFIS),support-vector machines(SVM),a random forest model(RF),and an extreme-gradient tree-boosting model(XGB)are trained using numerical and experimental input data obtained from fatigue tests based on a relatively low number of stress measurements.In particular,the coefficients of the traditional force law formula are found using relevant numerical methods.It is shown that,in comparison to traditional approaches,the neural network and neuro-fuzzy models produce better results,with the neural network models trained using the boosting iterations technique providing the best performances.Building strong models from weak models,XGB helps to predict fatigue life by reducing model partiality and variation in supervised learning.Fuzzy neural models can be used to predict the fatigue life of alloys more accurately than neural networks and traditional methods.
基金the finacial support by National Natural Science Foundation of China (Nos. 51374018 and 51174020)
文摘To systematically investigate the kinetics and formation mechanisms of intragranular ferrite(IGF), isothermal heat treatment in the temperature range of 450℃to 600℃ with holding for 30 s to 300 s, analysis of the corresponding microstructures, and observation of the precipitated particles were conducted in V-N microalloyed 600 MPa high strength rebar steel. The potency of V(C,N) for IGF nucleation was also analyzed statistically. The results show that the dominant microstructure transforms from bainite(B) and acicular ferrite(AF) to grain boundary ferrite(GBF), intragranular polygonal ferrite(IPF), and pearlite(P) as the isothermal temperature increases from 450℃ to 600℃. When the holding time at 600℃ is extended from 30 s to 60 s, 120 s, and 300 s, the GBF content ranges from 6.0vol% to 6.5vol% and the IPF content increases from 0.5vol% to 2.8vol%, 13.1vol%, and 13.5vol%, respectively, because the ferrite transformation preferentially occurs at the grain boundaries and then occurs at the austenite grains. Notably, V(C,N) particles are the most effective nucleation site for the formation of IPF, accounting for 51% of the said formation.
文摘Corrosion is a primary cause of the slippage of friction⁃type high⁃strength bolted(FHSB)T⁃stub connections.This paper attempts to quantify the residual capacity of FHSB T⁃stub connections with corroded nuts.Firstly,corrosion simulation tests were conducted on 48 manually cut nuts to find out the relationship between the damage degree of nut section and the residual clamping force(RCF)of bolt.Then,static load tests were carried out on 24 FHSB T⁃stub connections with nuts of different degrees of damage to obtain the failure modes.By finite⁃element(FE)models,a comparative analysis was performed on the initial friction load(IFL)and ultimate strength(US)of each connection with corroded nuts.Finally,the parameters of 96 FE models for FHSB T⁃stub connections were analyzed and used to derive the calculation formulas for the degree of damage for each nut and the IFL and US of each connection.The results show that the RCF decay of a bolt is a quadratic function of the equivalent radius loss ratio and the shear failure after nut corrosion;the IFL of each connection had a clear linear correlation with the RCF of the corresponding bolts,and the correlation depends on the applied load and static friction on connecting plate interface induced by the clamping force;the static friction had little impact on the US of the connection;the proposed IFL and US formulas can effectively derive the residual anti⁃slip capacity of FHSB T⁃stub connections from the degree of damage of the corroded nut section.The research results provide a scientific basis for the replacement and maintenance of corroded bolts of FHSB T⁃stub connections.
文摘The influence of alloying elements and cooling conditions after rolling on the microstructures and mechanical properties of a series of medium carbon Si-Mn-Mo-V high-strength precision-formed rebars were investigated.It is found that steel with combined addition of Mo and V appears to be the most promising one than those containing V and Nb or containing V alone under the same pro- cessing conditions.From CCT curve of the steel and the cooling curve of the bar determined by sim- ulating the cooling rate in mill practice,the reason why 40Si2MnMoV bar has excellent combination of strength and ductility is clarified.
基金National Natural Science Foundation of China under Grant No.51608488China Postdoctoral Science Foundation under Grant No.2020M672277Scientific and Technological Project of Henan province,China under Grant No.192102210185。
文摘As the main seismic component of a bridge,seismic damage to the bridge pier has a greater effect on its subsequent service.In the offshore chloride environment,the issues(e.g.,reinforcement bar corrosion and attenuation of concrete strength)of piers caused by chloride ion seriously curtail the normal service life and deteriorate the anti-seismic property of bridge structures.The engineered cementitious composite(ECC)-reinforced concrete(RC)composite pier with high strength reinforcement bars(HSRB)is expected to solve the above problems.This study aims to clarify the time-varying seismic vulnerability(SV)of the HSRBECC-RC composite pier during its full life cycle(FLC).Based on OpenSees,the refined finite element analysis models of RC pier,ECC-RC composite pier,and HSRBECC-RC composite pier have been established.Moreover,using the nonlinear time-path dynamic analysis method,the influence of chloride ion erosion on the time-dependent seismic vulnerability(SV)of these different piers in different service life and different peak ground acceleration(PGA)were analyzed from a dynamic point of view.The research shows that the exceeding probability(EP)of the same damage level increases with the enhancement of service time and PGA and with the increase of destruction,the exceeding probability(EP)of slight damage(DL-1),moderate damage(DL-2),serious damage(DL-3),and complete collapse(DL-4)decreases in turn;the corrosion degree of chloride ion to piers is small during the early service period,the time-varying vulnerability curve of the bridge piers is almost the same as that of a new bridge,and during later service,as the extent of chloride ion corrosion deepens,exceeding probability(EP)under severe damage(DL-3)and complete collapse(DL-4)is increased,and the seismic performance is significantly enhanced.
基金supported by Natural Science Foundation of Heilongjiang Province of China(E2017030,ZD2017010)National Natural Science Foundation of China(51671063,51771060,51871069)+1 种基金Fundamental Research Funds for the Central Universities(HEUCFM181002)Foundation of State Key Laboratory of Rare Earth Resources Utilization(RERU2018017).
文摘Higher strength is always the goal pursued by researchers for the structural materials,especially for the lightweight magnesium(Mg)alloys which generally have relatively low strength at present.From this aspect,the present paper reviews the recent reports of a kind of Mg alloys,i.e.Mg-RE(RE:rare earths,mainly Gd or Y)casting and wrought alloys,which have been able to achieve high strength compared with common or commercial Mg alloys,from the viewpoint and content of the alloy system,alloying constitution,preparation process,tensile strength and each of the main strengthening mechanisms.This review of recent research and developments in high-strength Mg-RE alloys is beneficial for the further design of Mg alloys with higher strength as well as excellent comprehensive performance.
基金Project supported by the National Scientific and Technological Achievements Spread Project (2004EC00299)Science and Technology Type Middle and Small Business Technique Invention Fund (04C26225121390)
文摘China is quite poor in argent resource. Roughly 80% of this industrial argent is imported every year. In order to improve the situation, we took advantage of rare earth (RE) mineral resource and successfully developed the non-argent Lanthanum-tellurium-copper alloy as a substitute for industry argent-copper. In our research, we were able to successfully apply rare earth lanthanum to copper alloy. The defects as porosity, inclusion, etc. originating from nonvacuum melting processing were controlled. Fine grain was obtained. Meanwhile, the comprehensive properties of the copper alloy, such as strength, conductivity and thermal conductivity were improved. The research results in increasing conductivity and thermal conductivity by 5% and 15%, respectively, while the tensile strength is increased by 6% higher than Ag-Cu alloy. The anti-electric corrosion property is good, and there is no argent-cadmium steam population originating from the electric arc effect. The addition of lanthanum further reduces the content of oxygen and hydrogen. The optimum quantity of the addition of RE lanthanum in the copper alloy is 0.010% - 0.020% .
基金supported by National Natural Science Foundation of China(Grant No.19832020)National Science Fund of Outstanding Youths of China (Grant No.10125208)+1 种基金Chongqing Municipal Programs for Science and Technology Development of China(Grant No.CSTC, 2007AA4008)National Key Technology R&D Program of China(Grant No.2006BA104B04-2)
文摘Lightweight structure is an important method to increase vehicle fuel efficiency. High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight. However, the lightweight structures must show the improved capability for structural rigidity and crash energy absorption. Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles. Currently, many research works focus on component level axial crash testing and simulation of high strength steels. However, the effects of high strength steel parts to the impact of auto body are not considered. The goal of this research is to study the application of hot forming high strength steel(HFHSS) in order to evaluate the potential using in vehicle design for lightweight and passive safety. The performance of HFHSS is investigated by using both experimental and analytical techniques. In particular, the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body. Automotive components made of HFHSS and general high strength steel(GHSS) are considered in this study. The material characterization of HFHSS is carried out through material experiments. The finite element method, in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme(C-NCAP) crash test. The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated. The results from the simulation analyses of HFHSS are compared with those of GHSS. The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact. Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts. Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts. The experiments and simulation are conducted to the HFHSS parts on auto body. The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.
基金supported by the National Natural Science Foundation of China(51201103&51304135)the Specialized Research Fund for the Doctoral Program of Higher Education(20110073120008)+2 种基金the New Century Excellent Talents in University of Ministry of Education of China(NCET-11-0329)the Program of Shanghai Subject Chief of Engineering(14XD1425000)the Assembly Pre-research Project(51312030706)
文摘As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.
基金supported by the National Science and Technology Infrastructure Platforms Construction Projects of China (Grant No2005DKA10400)the National Science Foundation of China (No50871021)
文摘The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.
文摘Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite (MA) constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.
基金financial aid from the National Natural Science Foundation(Grant nos.51771178,51671152,51874225)the Key Research and Development Program of Shanxi Province(Grant no.2018ZDXMGY-149)+1 种基金the Youth Innovation Team of Shanxi Universitiesthe Natural Science Foundation of Jilin Province(Grant no.20180414016GH)。
文摘In the current study,a homogenous ultra-fine grained microstructure with average grain size of 1.0μm is achieved in the Mg-Zn-Ca-Mn alloy through the reduplicative equal channel angular pressing(ECAP)at 300℃,and the mechanical properties are remarkably improved,with room-temperature yield strength of 269.6 MPa and elongation of 22.7%.The twinning deformation results in a discontinuous recrystallization behavior in the initial stage of ECAP.With further deformation,the continuously dynamic recrystallization contributes to an obvious grain refinement effect.The activation of non-basal slip system leads to the formation of a unique basal texture,which is related to the elevated ECAP temperature and the decreased grain size.Both grain refinement and texture modification derived from ECAP process result in the increase of yield strength,while the cracked secondary phase particles are beneficial to the enhanced ductility,through reducing the stress concentration and hindering premature failure.
文摘As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In present, retrogression and re-ageing (RRA)treatment, which can improve both strength and SCCR of 7XXX series alloy, is a best method to solvethis problem. The effect of RRA treatment on the microstructure evolution of a new type lowfrequency electric-magnetic casting Al-9.OZn-2.45Mg-2.2Cu-0.15Zr alloy was investigated using DSCand TEM technologies. The results show that the typical microstructure of the alloy at T6 conditionis characterized by both fine eta' and GP zone homogeneously distributed in the matrix andcontinuous r) particles occurred on the grain-boundary. After RRA treatment, the matrixprecipitations are mainly fine and dispersed eta' and eta phases, being coarser and more stable thanthat from T6 temper. While, the grain-boundary microstructure is very close to that resulting fromT73 temper. High retrogression temperature and long retrogression time leads to a more stablemicrostructure after re-ageing.
文摘The high strength martensite steels are widely used in aerospace,ocean engineering,etc.,due to their high strength,good ductility and acceptable corrosion resistance.This paper provides a review for the influence of microstructure on corrosion behavior of high strength martensite steels.Pitting is the most common corrosion type of high strength stainless steels,which always occurs at weak area of passive film such as inclusions,carbide/intermetallic interfaces.Meanwhile,the chromium carbide precipitations in the martensitic lath/prior austenite boundaries always result in intergranular corrosion.The precipitation,dislocation and grain/lath boundary are also used as crack nucleation and hydrogen traps,leading to hydrogen embrittlement and stress corrosion cracking for high strength martensite steels.Yet,the retained/reversed austenite has beneficial effects on the corrosion resistance and could reduce the sensitivity of stress corrosion cracking for high strength martensite steels.Finally,the corrosion mechanisms of additive manufacturing high strength steels and the ideas for designing new high strength martensite steel are explored.
基金financially supported by the Scientific Research Foundation of Guangxi University (No.XBZ110407)
文摘To develop a high strength low alloy (HSLA) steel with high strength and high toughness, a series of martensitic steels were studied through alloying with various elements and thermodynamic simulation. The microstructure and mechanical properties of the designed steel were investigated by optical microscopy, scanning electron microscopy, tensile testing and Charpy impact test. The results show that cementite exists between 500℃ and 700℃, M7C3 exits below 720℃, and they are much lower than the austenitizing temperature of the designed steel. Furthermore, the Ti(C,N) precipitate exists until 1280℃, which refines the microstructure and increases the strength and toughness. The optimal alloying components are 0.19% C, 1.19% Si, 2.83% Mn, 1.24% Ni, and 0.049% Ti; the tensile strength and the V notch impact toughness of the designed steel are more than 1500 MPa and 100 J, respectively.