To address the zero-sample challenge in preparation parameter design for newly developed alloys,a novel machine learning strategy that integrates basic dataset construction with Bayesian optimization,was proposed.The ...To address the zero-sample challenge in preparation parameter design for newly developed alloys,a novel machine learning strategy that integrates basic dataset construction with Bayesian optimization,was proposed.The impact of basic sample dataset construction methods,optimization benchmarks and multi-objective utility functions on Bayesian optimization was investigated.It was found that the combination of orthogonal design,linear benchmark,and shifted multiplicative utility function exhibits the best optimization performance.The strategy was then applied to a new Cu-Ni-Co-Si alloy with ultra-low Co content(0.7 wt.%Co),previously designed by our research team.Rapid optimization of six preparation parameters in the two-stage deformation and aging process of the zero-sample alloy was achieved through only 23 experiments.The measured ultimate tensile strength and electrical conductivity of the new alloy were 878 MPa and 44.0%(IACS),respectively,reaching the comprehensive performance level of the Cu-Ni-Co-Si alloy(C70350 alloy)containing 1.0-2.0 wt.%Co.展开更多
Machine learning-assisted methods for rapid and accurate prediction of temperature field,mushy zone,and grain size were proposed for the heating−cooling combined mold(HCCM)horizontal continuous casting of C70250 alloy...Machine learning-assisted methods for rapid and accurate prediction of temperature field,mushy zone,and grain size were proposed for the heating−cooling combined mold(HCCM)horizontal continuous casting of C70250 alloy plates.First,finite element simulations of casting processes were carried out with various parameters to build a dataset.Subsequently,different machine learning algorithms were employed to achieve high precision in predicting temperature fields,mushy zone locations,mushy zone inclination angle,and billet grain size.Finally,the process parameters were quickly optimized using a strategy consisting of random generation,prediction,and screening,allowing the mushy zone to be controlled to the desired target.The optimized parameters are 1234℃for heating mold temperature,47 mm/min for casting speed,and 10 L/min for cooling water flow rate.The optimized mushy zone is located in the middle of the second heat insulation section and has an inclination angle of roughly 7°.展开更多
Magnesium matrix nanocomposite reinforced with carbon nanotubes(CNTs/AZ91D) was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing.The microstructures and mechanical properties of th...Magnesium matrix nanocomposite reinforced with carbon nanotubes(CNTs/AZ91D) was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing.The microstructures and mechanical properties of the nanocomposite were investigated.The results show that CNTs are well dispersed in the matrix and combined with the matrix very well.As compared with AZ91D magnesium alloy matrix,the tensile strength,yield strength and elongation of the 1.5%CNTs/AZ91D nanocomposite are improved by 22%,21%and 42%respectively in permanent mold casting.The strength and ductility of the nanocomposite are improved simultaneously.The tensile fracture analysis shows that the damage mechanism of nanocomposite is still brittle fracture.But the CNTs can prevent the local crack propagation to some extent.展开更多
This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulicturbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the...This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulicturbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the rapidgrowth of the national economy in recent years and the expected high growth in the coming 10 to 20 years. Someheavy and large castings such as mill housing and hydraulic turbine runner crown, blade and band for Three GorgesProject have been successfully made. However, the domestic production capability is still far from meeting the giganticrequirements. The domestic capability still lags behind the world class level, and a lot of heavy castings still dependon import. The paper also gives a particular introduction of the key technologies in the manufacturing of heavy steelcastings like metal melting, foundry technology, heat treatment technology and numerical simulation technique, etc.In addition, several case studies on the application of numerical simulation in the production of heavy steel castingsare presented.展开更多
Tin bronze wires were produced by dieless drawing. The effects of heating power, the distance between cooler and heater as well as feeding speed on the diameter, the temperature field, and the deformation region profi...Tin bronze wires were produced by dieless drawing. The effects of heating power, the distance between cooler and heater as well as feeding speed on the diameter, the temperature field, and the deformation region profile of the wires were investigated. The results indi-cated that each processing parameter exhibited both lower and upper limits of stable deformation based on the criterion of stable deformation with the diameter fluctuation of ±0.05 mm. Both the temperature and its gradient of the deformation region increased with increasing heating power under stable deformation, but decreased with an increase in feeding speed. As the distance between cooler and heater increased, the temperature of the deformation region increased and the slope of the deformation region profile decreased. The processing limit map of sta-ble deformation exhibited a closed curve and the unstable deformation consisted of wire breakage and diameter fluctuations.展开更多
Numerical simulation is the most powerful computational and analysis tool for a large variety of engineering and physical problems.For a complex problem relating to multi-field,multi-process and multi-scale,different ...Numerical simulation is the most powerful computational and analysis tool for a large variety of engineering and physical problems.For a complex problem relating to multi-field,multi-process and multi-scale,different computing tools have to be developed so as to solve particular fields at different scales and for different processes.Therefore,the integration of different types of software is inevitable.However,it is difficult to perform the transfer of the meshes and simulated results among software packages because of the lack of shared data formats or encrypted data formats.An image processing based method for three-dimensional model reconstruction for numerical simulation was proposed,which presents a solution to the integration problem by a series of slice or projection images obtained by the post-processing modules of the numerical simulation software.By means of mapping image pixels to meshes of either finite difference or finite element models,the geometry contour can be extracted to export the stereolithography model.The values of results,represented by color,can be deduced and assigned to the meshes.All the models with data can be directly or indirectly integrated into other software as a continued or new numerical simulation.The three-dimensional reconstruction method has been validated in numerical simulation of castings and case studies were provided in this study.展开更多
Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study...Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study,a machine-learning-assisted method for di-gital modeling of the forging force and autonomous control in response to forging parameter disturbances was proposed.First,finite ele-ment simulations of the forging processes were conducted under varying friction factors,die temperatures,billet temperatures,and for-ging velocities,and the sample data,including process parameters and forging force under different forging strokes,were gathered.Pre-diction models for the forging force were established using the support vector regression algorithm.The prediction error of F_(f),that is,the forging force required to fill the die cavity fully,was as low as 4.1%.To further improve the prediction accuracy of the model for the ac-tual F_(f),two rounds of iterative forging experiments were conducted using the Bayesian optimization algorithm,and the prediction error of F_(f) in the forging experiments was reduced from 6.0%to 1.5%.Finally,the prediction model of F_(f) combined with a genetic algorithm was used to establish an autonomous optimization strategy for the forging velocity at each stage of the forging stroke,when the billet and die temperatures were disturbed,which realized the autonomous control in response to disturbances.In cases of−20 or−40℃ reductions in the die and billet temperatures,forging experiments conducted with the autonomous optimization strategy maintained the measured F_(f) around the target value of 180 t,with the relative error ranging from−1.3%to+3.1%.This work provides a reference for the study of di-gital modeling and autonomous optimization control of quality factors in the forging process.展开更多
Recent studies have shown that synergistic precipitation of continuous precipitates(CPs)and discontinuous precipitates(DPs)is a promising method to simultaneously improve the strength and electrical conductivity of Cu...Recent studies have shown that synergistic precipitation of continuous precipitates(CPs)and discontinuous precipitates(DPs)is a promising method to simultaneously improve the strength and electrical conductivity of Cu-Ni-Si alloy.However,the complex relationship between precipitates and two-stage aging process presents a significant challenge for the optimization of process parameters.In this study,machine learning models were established based on orthogonal experiment to mine the relationship between two-stage aging parameters and properties of Cu-5.3Ni-1.3Si-0.12Nb alloy with preferred formation of DPs.Two-stage aging parameters of 400℃/75 min+400℃/30 min were then obtained by multi-objective optimization combined with an experimental iteration strategy,resulting in a tensile strength of 875 MPa and a conductivity of 41.43%IACS,respectively.Such an excellent comprehensive performance of the alloy is attributed to the combined precipitation of DPs and CPs(with a total volume fraction of 5.4%and a volume ratio of CPs to DPs of 6.7).This study could provide a new approach and insight for improving the comprehensive properties of the Cu-Ni-Si alloys.展开更多
Solute atoms and precipitates significantly influence the mechanical properties of Mg alloys.Previous studies have mainly focused on the segregation behaviors of Mg alloys after annealing.In this study,we investigated...Solute atoms and precipitates significantly influence the mechanical properties of Mg alloys.Previous studies have mainly focused on the segregation behaviors of Mg alloys after annealing.In this study,we investigated the segregation behaviors of an Mg-RE alloy under deformation.We found that the enrichment of solute atoms occurred in{101^(-)1}compressive twin boundaries under compression at 298 K without any annealing in an Mg-RE alloy by scanning transmission electron microscopy and energy-dispersive X-ray analysis.The segregated solutes and precipitates impeded the twin growth,partially contributing to the formation of small-sized{101^(-)1}compressive twins.This research indicates the twin boundaries can be strengthened by segregated solutes and precipitates formed under deformation at room temperature.展开更多
Deep learning has achieved great progress in image recognition,segmentation,semantic recognition and game theory.In this study,a latest deep learning model,a conditional diffusion model was adopted as a surrogate mode...Deep learning has achieved great progress in image recognition,segmentation,semantic recognition and game theory.In this study,a latest deep learning model,a conditional diffusion model was adopted as a surrogate model to predict the heat transfer during the casting process instead of numerical simulation.The conditional diffusion model was established and trained with the geometry shapes,initial temperature fields and temperature fields at t_(i) as the condition and random noise sampled from standard normal distribution as the input.The output was the temperature field at t_(i+1).Therefore,the temperature field at t_(i+1)can be predicted as the temperature field at t_(i) is known,and the continuous temperature fields of all the time steps can be predicted based on the initial temperature field of an arbitrary 2D geometry.A training set with 3022D shapes and their simulated temperature fields at different time steps was established.The accuracy for the temperature field for a single time step reaches 97.7%,and that for continuous time steps reaches 69.1%with the main error actually existing in the sand mold.The effect of geometry shape and initial temperature field on the prediction accuracy was investigated,the former achieves better result than the latter because the former can identify casting,mold and chill by different colors in the input images.The diffusion model has proved the potential as a surrogate model for numerical simulation of the casting process.展开更多
This work managed the extrusion strain path by designing various extrusion die cavities,successfully realizing the texture modification for the ZK60 magnesium alloy.The mechanisms involving the texture dependence on t...This work managed the extrusion strain path by designing various extrusion die cavities,successfully realizing the texture modification for the ZK60 magnesium alloy.The mechanisms involving the texture dependence on the extrusion die cavity as well as their effects on the mechanical properties were emphatically investigated.Results showed that dynamic recrystallization refined the grain size and improved the microstructure homogeneity in the three extrusion specimens,but did not produce too large microstructure differences.By comparison,significant texture differences developed owing to the various extrusion die cavities,which here were mainly reflected in the strong or weak texture components for the c-axes//TD and the c-axes//ND.Such texture differences started from the deformation texture instead of the recrystallization texture whose roles only consisted in dispersing the texture component and reducing the texture intensity.The results from the finite element analysis and the visco-plastic self-consistent model indicated that,in order to accommodate the different strain components induced by the extrusion die cavities,slip systems or tension twinning were activated differently,and this was the critical reason causing the above texture differences.One modified Hall-Petch relationship was adopted to analyze the conjoint effects of grain refinement and texture variation on the yield stress.Additionally,the quantitative results about deformation mechanism activation fractions demonstrated that the texture variations influenced the competition relationships between the twinning induced deformation and the slip dominant deformation,and the former generally produced the lower yield stress and the increasing stage of strain hardening rate,while the latter produced the higher yield stress and the continuous decline of strain hardening rate.展开更多
In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occur...In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occurs due to the intrusion of gases generated during the resin burning of the sand core into castings during the casting process.Therefore,a gas generation and flow constitution model was established,in which the gas generation rate is a function of temperature and time,and the flow of gas is controlled by the gas release,conservation,and Darcy's law.The heat transfer and gas flow during casting process was numerically simulated.The dangerous point of cores is firstly identified by a virtual heat transfer method based on the similarity between heat transfer and gas flow in the sand core.The gas pores in castings are predicted by the gas pressure,the viscosity and state of the melt for these dangerous points.Three distinct sand core structures were designed and used for the production of iron castings,and the simulated gas pore results were validated by the obtained castings.展开更多
Designing low-density,high-strength Mg-Li alloys is a major challenge in achieving extreme lightweighting of high-end equipment.This study proposes an interpretable machine learning strategy to simultaneously enhance ...Designing low-density,high-strength Mg-Li alloys is a major challenge in achieving extreme lightweighting of high-end equipment.This study proposes an interpretable machine learning strategy to simultaneously enhance the mechanical properties and corrosion resistance of Mg-Li alloy.Key alloy factors(KAFs)influencing ultimate tensile strength(UTS),elongation(EL),and corrosion rate(CR)were identified through alloy factor construction and screening.Using KAFs and processing parameters as inputs,gradient boosting regression models for UTS,EL,and CR were established,achieving the coefficients of determination of test-set above 0.85.Then,SHapley Additive exPlanations(SHAP)analysis quantified the impact of KAFs,and an element evaluation method was established to identify Al,Si,Ca,and Zn as candidates for alloy design.Finally,three new alloys were designed via multi-objective optimization.In the hot-extruded state,they exhibited UTS of 253∼273 MPa,EL of 18.4%∼27.9%,CR of 0.55∼1.61 mg/(cm^(2)·day),and ρ of 1.49∼1.54 g/cm^(3).Compared to LAZ103,the new alloys show 34%∼44%higher UTS,35%∼79%lower CR,and comparable ρ.Microstructural analysis revealed increasedα-Mg,decreasedβ-Li,reduced coarse secondary phases,and fine Ca-/Si-rich precipitates which are conducive to grain refinement and dislocation density increasing,synergistically enhancing comprehensive property.展开更多
The excellent strength-ductility combination of hetero-grained Mg alloys has been reported to stem from pronounced hetero-deformation induced(HDI)stress.This stress alters the internal stress state of various slip sys...The excellent strength-ductility combination of hetero-grained Mg alloys has been reported to stem from pronounced hetero-deformation induced(HDI)stress.This stress alters the internal stress state of various slip systems and triggers significant activity of non-basal slips.However,the HDI stress state of different slip systems,and the mechanisms underlying the selective activation between basal and non-basal slips remain unclear to date.This study develops a novel HDI stress partitioning framework that in-situ calculates the crystallographic parameters and geometrical information of each datapoint within grains,aiming to reveal the correlation between HDI stress partitioning on individual slip systems and localized deformation model in the case of bimodal-grained ZK60 alloy.The framework demonstrates that HDI stress shows a strong dependence on the density of geometrically necessary dislocations(GNDs)and slip-system-level grain size,while exhibiting a relatively weaker correlation with equivalent-circle size of the hetero-grains.Given the close relation between the stress partitioning and the physical parameters,the framework can accurately predict the single and multiple slip activity fields obtained from highresolution digital image correlation(HR-DIC).This holds even for slip systems with low Schmid factors,which are theoretically difficult to activate.Using this framework,it is found that HDI stress plays a more prominent role in diminishing the effective resolved shear stress(RSS)of basaland prismatic(i.e.,component)dislocations,while having a negligible effect on pyramidal<c+a>slips.Benefiting from the increased ratio of RSS_(<c+a>)/RSS_(),pyramidal<c+a>dislocations are extensively activated,leading to excellent strength-ductility combination in the bimodal-grained ZK60 alloy.展开更多
A comparative investigation was conducted to evaluate the microstructure,mechanical properties,and corrosion resistance of hot-stamped steels fabricated via the compact strip production(CSP)and conventional cold-rolli...A comparative investigation was conducted to evaluate the microstructure,mechanical properties,and corrosion resistance of hot-stamped steels fabricated via the compact strip production(CSP)and conventional cold-rolling methods.CSP steel exhibited an initial microstructure comprising ferrite,pearlite,and minor bainite,which retained a characteristic hot-rolled banded structure with refined ferrite grains(5.7μm).In contrast,conventionally processed steel displayed coarser equiaxed ferrite(9.8μm).In terms of mechanical properties,CSP parts demonstrated superior tensile strength(>1433 MPa)and elongation(>6.48%)compared to conventional counterparts(average elongation of 5.27%).However,CSP samples showed a 23 HV lower hardness,attributed to a deeper decarburization layer.Enhanced strength in CSP steel was linked to finer prior austenite grains and dislocation density inherited from the initial microstructure,despite potential undissolved cementite at lower austenitizing temperatures.Corrosion testing revealed improved resistance in CSP-processed steel,likely due to finer grains acting as barriers to corrosion propagation.The trade-offs in CSP are highlighted:while achieving higher strength-ductility synergy and corrosion resistance,decarburization effects necessitate optimization to mitigate hardness reduction.The potential of CSP for high-performance automotive applications requiring balanced mechanical and anti-corrosion properties is underscored.展开更多
Simultaneously achieving high strength and high electrical conductivity in Cu–Ni–Si alloys pose a significant challenge, which greatly constrains its applications in the electronics industry. This paper offers a new...Simultaneously achieving high strength and high electrical conductivity in Cu–Ni–Si alloys pose a significant challenge, which greatly constrains its applications in the electronics industry. This paper offers a new pathway to improve properties, by preparation of nanometer lamellar discontinuous precipitates(DPs) arranged with the approximate same direction through a combination of deformationaging and cold rolling process. The strengthening effect is primarily attributed to nanometer-lamellar DPs strengthening and dislocation strengthening mechanism. The accumulation of dislocations at the interface between nanometer lamellar DPs and matrix during cold deformation process can results in the decrease of dislocation density inside the matrix grains, leading to the acceptably slight reduction of electrical conductivity during cold rolling. The alloy exhibits an electrical conductivity of 45.32%IACS(international annealed copper standard, IACS), a tensile strength of 882.67 MPa, and a yield strength of 811.33 MPa by this method. This study can provide a guidance for the composition and microstructure design of a Cu–Ni–Si alloy in the future, by controlling the morphology and distribution of DPs.展开更多
Pyroelectric materials, known for their ability to convert thermal energy into electrical signals, have garnered significant attention due to their wide-ranging applications. In this work, we report the fabrication of...Pyroelectric materials, known for their ability to convert thermal energy into electrical signals, have garnered significant attention due to their wide-ranging applications. In this work, we report the fabrication of high-performance pyroelectric photodetectors utilizing a heterostructure of carbon nanotube film(CNTF) and silver nanostructure film(Ag NSF)on a lead zirconate titanate(PZT) substrate. The resulting device exhibits an impressive broad-spectrum photoelectric response, covering wavelengths from ultraviolet to near-infrared, with a responsivity range of 0.49 V·W^(-1)–1.01 V·W^(-1) and a fast response time of 8 ms–40 ms. The enhanced photoelectric properties of the CNTF/Ag NSF/PZT composite suggest its strong potential for applications in advanced broadband photodetectors, positioning this material system as a promising candidate for next-generation optoelectronic devices.展开更多
To explore atomic-level phenomena in the Cu-Ni-Sn alloy,a second nearest-neighbor modified embedded-atom method(2NN MEAM)potential has been developed for the Cu-Ni-Sn system,building upon the work of other researchers...To explore atomic-level phenomena in the Cu-Ni-Sn alloy,a second nearest-neighbor modified embedded-atom method(2NN MEAM)potential has been developed for the Cu-Ni-Sn system,building upon the work of other researchers.This potential demonstrates remarkable accuracy in predicting the lattice constant,with a relative error of less than 0.5%when compared to density functional theory(DFT)results,and it achieves a 10%relative error in the enthalpy of formation compared to experimental data,marking substantial advancements over prior models.The bulk modulus is predicted with a relative error of 8%compared to DFT.Notably,the potential effectively simulates the processes of melting and solidification of Cu-15Ni-8Sn,with a simulated melting point that closely aligns with the experimental value,within a 7.5%margin.This serves as a foundation for establishing a 2NN MEAM potential for a flawless Cu-Ni-Sn system and its microalloying systems.展开更多
A multistage solution treatment process was applied for nickel-based single crystal superalloys,complemented by various aging durations and cooling rates.The microstructure was characterized by scanning electron micro...A multistage solution treatment process was applied for nickel-based single crystal superalloys,complemented by various aging durations and cooling rates.The microstructure was characterized by scanning electron microscopy(SEM)to observe the γ'phase.Additionally,phase field simulations were conducted to model the growth ofγ'precipitates during aging and analyze their morphological evolution.The experimental results demonstrated that the multistage solution treatment effectively eliminated eutectic phases and carbides.Moreover,samples aged for 10 min exhibited larger and more rectangularγ'precipitates compared with those aged for 5 min.Notably,secondary γ'precipitates were observed in samples subjected to water cooling.Two indices for quantifying rectangularization were proposed and successfully applied.Based on the simulation results,lattice mismatch induced coherency stresses and elevated stress triaxiality along the <111> direction contributed to the rectangularization of theγ'phase.展开更多
The transformation of the dissimilar metals in the welding area into a single metal is an important method for achieving high-quality welded connection in the dissimilar metal laminated composite plate.In this study,a...The transformation of the dissimilar metals in the welding area into a single metal is an important method for achieving high-quality welded connection in the dissimilar metal laminated composite plate.In this study,a high-performance titanium/steel composite plate(TSCP)with pure titaniumization in the welding area was prepared by cold spraying,hot rolling and heat treatment processes.The results indicate that cold spraying achieves effective pre-composite deposition of titanium particles while inhibiting interfacial oxidation and Fe-Ti alloying reactions,producing a relatively dense pure titanium coating with a low porosity of only 1.2%.Hot rolling eliminates internal defects and promotes strong metallurgical bonding of the composite interface.The heat treatment promotes the recrystallization and reduces the dislocation density within the coating.The interfacial bonding strength of the welding area with pure titaniumization of TSCP is 257 MPa,and the tensile strength of that is 414 MPa,reaching 95.6%of the TSCP’s base material.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52404387,52090041,52374379,52425409)Xiaomi Young Scholars Program China,the National Postdoctoral Program for Innovative Talents,China(No.BX20230042)China Postdoctoral Science Foundation(No.2024M750174)。
文摘To address the zero-sample challenge in preparation parameter design for newly developed alloys,a novel machine learning strategy that integrates basic dataset construction with Bayesian optimization,was proposed.The impact of basic sample dataset construction methods,optimization benchmarks and multi-objective utility functions on Bayesian optimization was investigated.It was found that the combination of orthogonal design,linear benchmark,and shifted multiplicative utility function exhibits the best optimization performance.The strategy was then applied to a new Cu-Ni-Co-Si alloy with ultra-low Co content(0.7 wt.%Co),previously designed by our research team.Rapid optimization of six preparation parameters in the two-stage deformation and aging process of the zero-sample alloy was achieved through only 23 experiments.The measured ultimate tensile strength and electrical conductivity of the new alloy were 878 MPa and 44.0%(IACS),respectively,reaching the comprehensive performance level of the Cu-Ni-Co-Si alloy(C70350 alloy)containing 1.0-2.0 wt.%Co.
基金financially supported by the National Key Research and Development Program of China (No. 2023YFB3812601)the National Natural Science Foundation of China (No. 51925401)the Young Elite Scientists Sponsorship Program by CAST, China (No. 2022QNRC001)。
文摘Machine learning-assisted methods for rapid and accurate prediction of temperature field,mushy zone,and grain size were proposed for the heating−cooling combined mold(HCCM)horizontal continuous casting of C70250 alloy plates.First,finite element simulations of casting processes were carried out with various parameters to build a dataset.Subsequently,different machine learning algorithms were employed to achieve high precision in predicting temperature fields,mushy zone locations,mushy zone inclination angle,and billet grain size.Finally,the process parameters were quickly optimized using a strategy consisting of random generation,prediction,and screening,allowing the mushy zone to be controlled to the desired target.The optimized parameters are 1234℃for heating mold temperature,47 mm/min for casting speed,and 10 L/min for cooling water flow rate.The optimized mushy zone is located in the middle of the second heat insulation section and has an inclination angle of roughly 7°.
文摘Magnesium matrix nanocomposite reinforced with carbon nanotubes(CNTs/AZ91D) was fabricated by mechanical stirring and high intensity ultrasonic dispersion processing.The microstructures and mechanical properties of the nanocomposite were investigated.The results show that CNTs are well dispersed in the matrix and combined with the matrix very well.As compared with AZ91D magnesium alloy matrix,the tensile strength,yield strength and elongation of the 1.5%CNTs/AZ91D nanocomposite are improved by 22%,21%and 42%respectively in permanent mold casting.The strength and ductility of the nanocomposite are improved simultaneously.The tensile fracture analysis shows that the damage mechanism of nanocomposite is still brittle fracture.But the CNTs can prevent the local crack propagation to some extent.
文摘This paper expatiates on domestic status of heavy steel casting production, with a special focus on hydraulicturbine castings for Three Gorges Project. In China, there is magnificent demand for heavy castings with the rapidgrowth of the national economy in recent years and the expected high growth in the coming 10 to 20 years. Someheavy and large castings such as mill housing and hydraulic turbine runner crown, blade and band for Three GorgesProject have been successfully made. However, the domestic production capability is still far from meeting the giganticrequirements. The domestic capability still lags behind the world class level, and a lot of heavy castings still dependon import. The paper also gives a particular introduction of the key technologies in the manufacturing of heavy steelcastings like metal melting, foundry technology, heat treatment technology and numerical simulation technique, etc.In addition, several case studies on the application of numerical simulation in the production of heavy steel castingsare presented.
基金supported by the National Basic Research Priorities Program of China (No.2006CB605200)the National Natural Science Foundation of China (No.50634010, 50674008)+1 种基金the Program for New Century Excellent Talents in Chinese Universities (No.NCET-06-0083)the Universities Fundamental Research Foundation of MOE (No FRF-TP-10-002B)
文摘Tin bronze wires were produced by dieless drawing. The effects of heating power, the distance between cooler and heater as well as feeding speed on the diameter, the temperature field, and the deformation region profile of the wires were investigated. The results indi-cated that each processing parameter exhibited both lower and upper limits of stable deformation based on the criterion of stable deformation with the diameter fluctuation of ±0.05 mm. Both the temperature and its gradient of the deformation region increased with increasing heating power under stable deformation, but decreased with an increase in feeding speed. As the distance between cooler and heater increased, the temperature of the deformation region increased and the slope of the deformation region profile decreased. The processing limit map of sta-ble deformation exhibited a closed curve and the unstable deformation consisted of wire breakage and diameter fluctuations.
基金funded by National Key R&D Program of China(No.2021YFB3401200)the National Natural Science Foundation of China(No.51875308)the Beijing Nature Sciences Fund-Haidian Originality Cooperation Project(L212002).
文摘Numerical simulation is the most powerful computational and analysis tool for a large variety of engineering and physical problems.For a complex problem relating to multi-field,multi-process and multi-scale,different computing tools have to be developed so as to solve particular fields at different scales and for different processes.Therefore,the integration of different types of software is inevitable.However,it is difficult to perform the transfer of the meshes and simulated results among software packages because of the lack of shared data formats or encrypted data formats.An image processing based method for three-dimensional model reconstruction for numerical simulation was proposed,which presents a solution to the integration problem by a series of slice or projection images obtained by the post-processing modules of the numerical simulation software.By means of mapping image pixels to meshes of either finite difference or finite element models,the geometry contour can be extracted to export the stereolithography model.The values of results,represented by color,can be deduced and assigned to the meshes.All the models with data can be directly or indirectly integrated into other software as a continued or new numerical simulation.The three-dimensional reconstruction method has been validated in numerical simulation of castings and case studies were provided in this study.
基金financially supported by the National Key Research and Development Program of China(No.2022YFB3706901)the National Natural Science Foundation of China(No.52090041)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC 001).
文摘Digital modeling and autonomous control of the die forging process are significant challenges in realizing high-quality intelli-gent forging of components.Using the die forging of AA2014 aluminum alloy as a case study,a machine-learning-assisted method for di-gital modeling of the forging force and autonomous control in response to forging parameter disturbances was proposed.First,finite ele-ment simulations of the forging processes were conducted under varying friction factors,die temperatures,billet temperatures,and for-ging velocities,and the sample data,including process parameters and forging force under different forging strokes,were gathered.Pre-diction models for the forging force were established using the support vector regression algorithm.The prediction error of F_(f),that is,the forging force required to fill the die cavity fully,was as low as 4.1%.To further improve the prediction accuracy of the model for the ac-tual F_(f),two rounds of iterative forging experiments were conducted using the Bayesian optimization algorithm,and the prediction error of F_(f) in the forging experiments was reduced from 6.0%to 1.5%.Finally,the prediction model of F_(f) combined with a genetic algorithm was used to establish an autonomous optimization strategy for the forging velocity at each stage of the forging stroke,when the billet and die temperatures were disturbed,which realized the autonomous control in response to disturbances.In cases of−20 or−40℃ reductions in the die and billet temperatures,forging experiments conducted with the autonomous optimization strategy maintained the measured F_(f) around the target value of 180 t,with the relative error ranging from−1.3%to+3.1%.This work provides a reference for the study of di-gital modeling and autonomous optimization control of quality factors in the forging process.
基金financially supported by the National Key Research and Development Program of China(No.2023YFB3812601)the National Natural Science Foundation of China(Nos.51925401,92066205 and 92266301)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001).
文摘Recent studies have shown that synergistic precipitation of continuous precipitates(CPs)and discontinuous precipitates(DPs)is a promising method to simultaneously improve the strength and electrical conductivity of Cu-Ni-Si alloy.However,the complex relationship between precipitates and two-stage aging process presents a significant challenge for the optimization of process parameters.In this study,machine learning models were established based on orthogonal experiment to mine the relationship between two-stage aging parameters and properties of Cu-5.3Ni-1.3Si-0.12Nb alloy with preferred formation of DPs.Two-stage aging parameters of 400℃/75 min+400℃/30 min were then obtained by multi-objective optimization combined with an experimental iteration strategy,resulting in a tensile strength of 875 MPa and a conductivity of 41.43%IACS,respectively.Such an excellent comprehensive performance of the alloy is attributed to the combined precipitation of DPs and CPs(with a total volume fraction of 5.4%and a volume ratio of CPs to DPs of 6.7).This study could provide a new approach and insight for improving the comprehensive properties of the Cu-Ni-Si alloys.
基金support from Interdisciplinary Research Project for Young Teachers of USTB Fundamental Research Funds for the Central Universities(Grant no.FRF-IDRY-23-030).
文摘Solute atoms and precipitates significantly influence the mechanical properties of Mg alloys.Previous studies have mainly focused on the segregation behaviors of Mg alloys after annealing.In this study,we investigated the segregation behaviors of an Mg-RE alloy under deformation.We found that the enrichment of solute atoms occurred in{101^(-)1}compressive twin boundaries under compression at 298 K without any annealing in an Mg-RE alloy by scanning transmission electron microscopy and energy-dispersive X-ray analysis.The segregated solutes and precipitates impeded the twin growth,partially contributing to the formation of small-sized{101^(-)1}compressive twins.This research indicates the twin boundaries can be strengthened by segregated solutes and precipitates formed under deformation at room temperature.
基金sponsored by Tsinghua-Toyota Joint Research Fund
文摘Deep learning has achieved great progress in image recognition,segmentation,semantic recognition and game theory.In this study,a latest deep learning model,a conditional diffusion model was adopted as a surrogate model to predict the heat transfer during the casting process instead of numerical simulation.The conditional diffusion model was established and trained with the geometry shapes,initial temperature fields and temperature fields at t_(i) as the condition and random noise sampled from standard normal distribution as the input.The output was the temperature field at t_(i+1).Therefore,the temperature field at t_(i+1)can be predicted as the temperature field at t_(i) is known,and the continuous temperature fields of all the time steps can be predicted based on the initial temperature field of an arbitrary 2D geometry.A training set with 3022D shapes and their simulated temperature fields at different time steps was established.The accuracy for the temperature field for a single time step reaches 97.7%,and that for continuous time steps reaches 69.1%with the main error actually existing in the sand mold.The effect of geometry shape and initial temperature field on the prediction accuracy was investigated,the former achieves better result than the latter because the former can identify casting,mold and chill by different colors in the input images.The diffusion model has proved the potential as a surrogate model for numerical simulation of the casting process.
基金supported by National Natural Science Foundation of China(Grant No.52205344,51925401)Postdoctoral Research Foundation of China(Grant No.2023M732398)+1 种基金National Key Laboratory Foundation of Science and Technology on Materials under Shock and Impact(Grant No.WDZC2023-1)Key Research and Development Program of Shandong Province(Grant No.2023CXPT066).
文摘This work managed the extrusion strain path by designing various extrusion die cavities,successfully realizing the texture modification for the ZK60 magnesium alloy.The mechanisms involving the texture dependence on the extrusion die cavity as well as their effects on the mechanical properties were emphatically investigated.Results showed that dynamic recrystallization refined the grain size and improved the microstructure homogeneity in the three extrusion specimens,but did not produce too large microstructure differences.By comparison,significant texture differences developed owing to the various extrusion die cavities,which here were mainly reflected in the strong or weak texture components for the c-axes//TD and the c-axes//ND.Such texture differences started from the deformation texture instead of the recrystallization texture whose roles only consisted in dispersing the texture component and reducing the texture intensity.The results from the finite element analysis and the visco-plastic self-consistent model indicated that,in order to accommodate the different strain components induced by the extrusion die cavities,slip systems or tension twinning were activated differently,and this was the critical reason causing the above texture differences.One modified Hall-Petch relationship was adopted to analyze the conjoint effects of grain refinement and texture variation on the yield stress.Additionally,the quantitative results about deformation mechanism activation fractions demonstrated that the texture variations influenced the competition relationships between the twinning induced deformation and the slip dominant deformation,and the former generally produced the lower yield stress and the increasing stage of strain hardening rate,while the latter produced the higher yield stress and the continuous decline of strain hardening rate.
基金funded by the Beijing Nature Sciences Fund Haidian Originality Cooperation Project (Grant No. L212002)。
文摘In the production of castings,intrusive gas pore represents a kind of common defects which can lead to leakage in high gas-tightness requirement castings,such as cylinder blocks and cylinder heads for engines.It occurs due to the intrusion of gases generated during the resin burning of the sand core into castings during the casting process.Therefore,a gas generation and flow constitution model was established,in which the gas generation rate is a function of temperature and time,and the flow of gas is controlled by the gas release,conservation,and Darcy's law.The heat transfer and gas flow during casting process was numerically simulated.The dangerous point of cores is firstly identified by a virtual heat transfer method based on the similarity between heat transfer and gas flow in the sand core.The gas pores in castings are predicted by the gas pressure,the viscosity and state of the melt for these dangerous points.Three distinct sand core structures were designed and used for the production of iron castings,and the simulated gas pore results were validated by the obtained castings.
基金supported by the Advanced Materials-National Science and Technology Major Project(No.2025ZD0619700)National Natural Science Foundation of China(No.52401002,92570301)+1 种基金China Postdoctoral Science Foundation funded project(No.2024M760200)Fundamental Research Funds for the Central Universities(No.FRF-BD-25-007).
文摘Designing low-density,high-strength Mg-Li alloys is a major challenge in achieving extreme lightweighting of high-end equipment.This study proposes an interpretable machine learning strategy to simultaneously enhance the mechanical properties and corrosion resistance of Mg-Li alloy.Key alloy factors(KAFs)influencing ultimate tensile strength(UTS),elongation(EL),and corrosion rate(CR)were identified through alloy factor construction and screening.Using KAFs and processing parameters as inputs,gradient boosting regression models for UTS,EL,and CR were established,achieving the coefficients of determination of test-set above 0.85.Then,SHapley Additive exPlanations(SHAP)analysis quantified the impact of KAFs,and an element evaluation method was established to identify Al,Si,Ca,and Zn as candidates for alloy design.Finally,three new alloys were designed via multi-objective optimization.In the hot-extruded state,they exhibited UTS of 253∼273 MPa,EL of 18.4%∼27.9%,CR of 0.55∼1.61 mg/(cm^(2)·day),and ρ of 1.49∼1.54 g/cm^(3).Compared to LAZ103,the new alloys show 34%∼44%higher UTS,35%∼79%lower CR,and comparable ρ.Microstructural analysis revealed increasedα-Mg,decreasedβ-Li,reduced coarse secondary phases,and fine Ca-/Si-rich precipitates which are conducive to grain refinement and dislocation density increasing,synergistically enhancing comprehensive property.
基金the National Natural Science Foundation of China(No.52305385,U23A20541,52471131,52201057)the University Natural Science Research Project of Anhui Province(No.2022AH050316).
文摘The excellent strength-ductility combination of hetero-grained Mg alloys has been reported to stem from pronounced hetero-deformation induced(HDI)stress.This stress alters the internal stress state of various slip systems and triggers significant activity of non-basal slips.However,the HDI stress state of different slip systems,and the mechanisms underlying the selective activation between basal and non-basal slips remain unclear to date.This study develops a novel HDI stress partitioning framework that in-situ calculates the crystallographic parameters and geometrical information of each datapoint within grains,aiming to reveal the correlation between HDI stress partitioning on individual slip systems and localized deformation model in the case of bimodal-grained ZK60 alloy.The framework demonstrates that HDI stress shows a strong dependence on the density of geometrically necessary dislocations(GNDs)and slip-system-level grain size,while exhibiting a relatively weaker correlation with equivalent-circle size of the hetero-grains.Given the close relation between the stress partitioning and the physical parameters,the framework can accurately predict the single and multiple slip activity fields obtained from highresolution digital image correlation(HR-DIC).This holds even for slip systems with low Schmid factors,which are theoretically difficult to activate.Using this framework,it is found that HDI stress plays a more prominent role in diminishing the effective resolved shear stress(RSS)of basaland prismatic(i.e.,component)dislocations,while having a negligible effect on pyramidal<c+a>slips.Benefiting from the increased ratio of RSS_(<c+a>)/RSS_(),pyramidal<c+a>dislocations are extensively activated,leading to excellent strength-ductility combination in the bimodal-grained ZK60 alloy.
基金National Key Research and Development Program of China(Grant No.2021YFB3702405)the National Natural Science Foundation of China(Grant No.52471036)the Basic and Applied Basic Research Foundation of Guangdong Province(Grant No.2023A1515012363).
文摘A comparative investigation was conducted to evaluate the microstructure,mechanical properties,and corrosion resistance of hot-stamped steels fabricated via the compact strip production(CSP)and conventional cold-rolling methods.CSP steel exhibited an initial microstructure comprising ferrite,pearlite,and minor bainite,which retained a characteristic hot-rolled banded structure with refined ferrite grains(5.7μm).In contrast,conventionally processed steel displayed coarser equiaxed ferrite(9.8μm).In terms of mechanical properties,CSP parts demonstrated superior tensile strength(>1433 MPa)and elongation(>6.48%)compared to conventional counterparts(average elongation of 5.27%).However,CSP samples showed a 23 HV lower hardness,attributed to a deeper decarburization layer.Enhanced strength in CSP steel was linked to finer prior austenite grains and dislocation density inherited from the initial microstructure,despite potential undissolved cementite at lower austenitizing temperatures.Corrosion testing revealed improved resistance in CSP-processed steel,likely due to finer grains acting as barriers to corrosion propagation.The trade-offs in CSP are highlighted:while achieving higher strength-ductility synergy and corrosion resistance,decarburization effects necessitate optimization to mitigate hardness reduction.The potential of CSP for high-performance automotive applications requiring balanced mechanical and anti-corrosion properties is underscored.
基金supported by the National Key Research and Development Program of China (No. 2023YFB3812601)the National Natural Science Founda tion of China (Nos. 51925401, 92066205, and 92266301)。
文摘Simultaneously achieving high strength and high electrical conductivity in Cu–Ni–Si alloys pose a significant challenge, which greatly constrains its applications in the electronics industry. This paper offers a new pathway to improve properties, by preparation of nanometer lamellar discontinuous precipitates(DPs) arranged with the approximate same direction through a combination of deformationaging and cold rolling process. The strengthening effect is primarily attributed to nanometer-lamellar DPs strengthening and dislocation strengthening mechanism. The accumulation of dislocations at the interface between nanometer lamellar DPs and matrix during cold deformation process can results in the decrease of dislocation density inside the matrix grains, leading to the acceptably slight reduction of electrical conductivity during cold rolling. The alloy exhibits an electrical conductivity of 45.32%IACS(international annealed copper standard, IACS), a tensile strength of 882.67 MPa, and a yield strength of 811.33 MPa by this method. This study can provide a guidance for the composition and microstructure design of a Cu–Ni–Si alloy in the future, by controlling the morphology and distribution of DPs.
基金Project supported in part by the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics (Grant No. KF202007)the NSAF (Grant No. U1730246)。
文摘Pyroelectric materials, known for their ability to convert thermal energy into electrical signals, have garnered significant attention due to their wide-ranging applications. In this work, we report the fabrication of high-performance pyroelectric photodetectors utilizing a heterostructure of carbon nanotube film(CNTF) and silver nanostructure film(Ag NSF)on a lead zirconate titanate(PZT) substrate. The resulting device exhibits an impressive broad-spectrum photoelectric response, covering wavelengths from ultraviolet to near-infrared, with a responsivity range of 0.49 V·W^(-1)–1.01 V·W^(-1) and a fast response time of 8 ms–40 ms. The enhanced photoelectric properties of the CNTF/Ag NSF/PZT composite suggest its strong potential for applications in advanced broadband photodetectors, positioning this material system as a promising candidate for next-generation optoelectronic devices.
基金sponsored by the Science and Technology Foundation of Guizhou Provincial Education Department(No.QJJ[2024]60)Guizhou Provincial Basic Research Program(Natural Science)(No.QKHJC[2024]Youth 214)+1 种基金Science and Technology Foundation of Guizhou Minzu University(No.GZMUZK[2024]QD21)Research Projects of Anshun University(No.asxybsjj202413).
文摘To explore atomic-level phenomena in the Cu-Ni-Sn alloy,a second nearest-neighbor modified embedded-atom method(2NN MEAM)potential has been developed for the Cu-Ni-Sn system,building upon the work of other researchers.This potential demonstrates remarkable accuracy in predicting the lattice constant,with a relative error of less than 0.5%when compared to density functional theory(DFT)results,and it achieves a 10%relative error in the enthalpy of formation compared to experimental data,marking substantial advancements over prior models.The bulk modulus is predicted with a relative error of 8%compared to DFT.Notably,the potential effectively simulates the processes of melting and solidification of Cu-15Ni-8Sn,with a simulated melting point that closely aligns with the experimental value,within a 7.5%margin.This serves as a foundation for establishing a 2NN MEAM potential for a flawless Cu-Ni-Sn system and its microalloying systems.
基金supported by the Stable Support Project and the Major National Science and Technology Project,China(Nos.2017-Ⅶ-0008-0101,2017-Ⅵ-0003-0073)。
文摘A multistage solution treatment process was applied for nickel-based single crystal superalloys,complemented by various aging durations and cooling rates.The microstructure was characterized by scanning electron microscopy(SEM)to observe the γ'phase.Additionally,phase field simulations were conducted to model the growth ofγ'precipitates during aging and analyze their morphological evolution.The experimental results demonstrated that the multistage solution treatment effectively eliminated eutectic phases and carbides.Moreover,samples aged for 10 min exhibited larger and more rectangularγ'precipitates compared with those aged for 5 min.Notably,secondary γ'precipitates were observed in samples subjected to water cooling.Two indices for quantifying rectangularization were proposed and successfully applied.Based on the simulation results,lattice mismatch induced coherency stresses and elevated stress triaxiality along the <111> direction contributed to the rectangularization of theγ'phase.
基金financially supported by the National Key R&D Program of China(No.2018YFA0707300)the National Natural Science Foundation of China(No.52374376)。
文摘The transformation of the dissimilar metals in the welding area into a single metal is an important method for achieving high-quality welded connection in the dissimilar metal laminated composite plate.In this study,a high-performance titanium/steel composite plate(TSCP)with pure titaniumization in the welding area was prepared by cold spraying,hot rolling and heat treatment processes.The results indicate that cold spraying achieves effective pre-composite deposition of titanium particles while inhibiting interfacial oxidation and Fe-Ti alloying reactions,producing a relatively dense pure titanium coating with a low porosity of only 1.2%.Hot rolling eliminates internal defects and promotes strong metallurgical bonding of the composite interface.The heat treatment promotes the recrystallization and reduces the dislocation density within the coating.The interfacial bonding strength of the welding area with pure titaniumization of TSCP is 257 MPa,and the tensile strength of that is 414 MPa,reaching 95.6%of the TSCP’s base material.
